Talk:Luminous efficacy/Archive 1

Archive 1

Example: Electroluminescent devices

Another example I would find interesting is electroluminescent devices. Night light panels often draw on the order of 0.05W or less but that appears to be due to very low output rather than good efficiency. The web browsing I have done so far suggests 3lm/W or less for panels; I have been unable to find a source for EL "wire".

—The preceding unsigned comment was added by 63.193.211.225 (talk) 16:05, 15 December 2006 (UTC).

Spelling

Is 'Luminous efficacy' correctly spelled, or is 'efficacy' some word with special meaning? Electron9 09:13, 11 January 2007 (UTC)

See definitions. Dicklyon 20:57, 11 January 2007 (UTC)

Merge Lighting efficiency?

Since nobody supported this idea, I'm removing the merge tag. Dicklyon 04:10, 10 July 2006 (UTC)

The merge seems like an obvious good idea to me. On the whole, Luminous efficacy is a better article (gives sources, has more details). Kingdon 20:39, 14 September 2006 (UTC)

As a reminder, the old (June 06) proposal was to merge Lighting efficiency into here; I just noticed that that the other article still has its mergeto tag. It seems like a very distinct topic to me, focusing on practical light sources as opposed to the concept. But they could be integrated if someone was motivated to work on that. Dicklyon 22:14, 14 September 2006 (UTC)

Oppose. The more I look at it the more separate the concepts seem. We should explain that. The efficacies and efficiencies in this article are purely photometry/radiometry relationships on spectra. The lighting efficiency of the other article is with respect to power consumed, not power radiated, and includes effects of energy loss via conduction and convection, if I understand correctly. Dicklyon 22:33, 14 September 2006 (UTC)

This article covers that too. The section on Overall luminous efficacy explicitly deals with efficacy and efficiency of light emission as a function of input electrical power, i.e. including the effect of losses due to conduction, convection, heat, etc.--Srleffler 00:06, 15 September 2006 (UTC)

The overlap is quite strong, and each has tabulated information that the other is lacking. The main difference between the two is mere emphasis. This article focuses on the technical definition of luminous efficacy/efficiency, and compares the standard and "overall" types in one article. The other article focuses more on the practical issue of how efficient a given lighting technology is. Both foci seem useful--one for those interested in photometry, and one for those who want to know more about light bulbs. If anything, I think we should probably split and merge the other way: move the overall efficacy/efficiency information into the other article, keeping the practical layman's terms approach in the introduction and providing a more technical explanation with links between the two articles. This article could be limited to the "true" luminous efficacy/efficiency, with some explanation of the distinction between this and the overall value and links to the other article.--Srleffler 00:20, 15 September 2006 (UTC)

That kind of split makes sense to me. The key thing would be having the two articles link to each other cleanly, and cutting down on the material which is duplicated. Kingdon 14:20, 15 September 2006 (UTC)

I don't see the need for two articles here. This article needs at lease some examples to make sense and there is is no reason to have the information in two places. I support the original merge.--agr 14:07, 21 September 2006 (UTC)

There doesn't seem to be a consensus one way or another here, so I've tried merging the pages, and we'll see if the result is acceptable. This article is not really much changed, and I think the changes are largely ones we would want to keep even in the absence of a merge. The major change is that lighting efficiency now redirects here. I think this is best, since "lighting efficiency" as defined there was really just the overall luminous efficacy, as defined here. It seems better to have one article that explains it all in context, rather than two. I'm certainly open to splitting off the "Lighting efficiency" section of the merged article, and moving that back to "lighting efficiency" with appropriate links, if that seems better to most people.--Srleffler 06:02, 25 September 2006 (UTC)

Xenon Lamp efficiency?

Am yet to see any xenon lamp rated at 150lm/W. Osram XBO line for example has a maximum of 500000lm per 10000W, that's 50lm/W. I would like to see a model rated above 60lm/W in any catalog. Most such lamps are below that, at about 40lm/W. Unless I see any new data I'll correct the article in the next few days. --Rnbc 02:38, 22 February 2007 (UTC)

Read the reference.[1] The lamp with 150 lm/W is clearly a specialty item, with 20 kW total power consumption. The largest XBO bulb is only 12 kW. The efficiencies given in the reference agree with the XBO datasheet for the 1 kW and 5 kW models. --Srleffler 03:47, 22 February 2007 (UTC)

Where can I buy that 3000000lm/20kW widget? I would like to see the catalog and technical specifications... Perhaps it's a model with the same chemistry as car's xenon headlamps, witch are not exactly "xenon", but only use xenon for a quick start effect. And they don't have the nice and continuous xenon spectra also. --Rnbc 01:51, 24 February 2007 (UTC)

No idea. I hunted online but couldn't find anything. IMAX bulbs consume 15 kW, but they are no more efficient than the 12 kW XBO bulbs.--Srleffler 02:00, 24 February 2007 (UTC)

Well, just consider this: the solar spectra itself has an efficiency of about 100lm/W (a little less), and that's as high as you can get with a blackbody-like spectra. Xenon spectra exibits some UV lines, and some very strong lines in the IR, being otherwise rather flat in the visible, even more flat than a blackbody, so it has more blue and red, lowering efficiency greatly from an ideal blackbody due to all these factors combined. I find it really amazing they can get as high as 50lm/W, let alone 150lm/W: I still think that number is bogus.

I changed the wording to de-emphasize the high value and give a more typical range. I agree with you that the 150 lm/W number is suspicious, but this is original research. The 150 lm/W number is supported by a reference. Before we change it, we should try to find a reference that explicitly gives the range of efficiencies that can be obtained with Xenon (or quotes a value for the highest obtained, etc.). The XBO catalog doesn't do it, since that only tells us what their range is; they don't assert that there aren't more efficient Xenon lamps in existence.--Srleffler 04:12, 25 February 2007 (UTC)

Ok, but let me tell you that the reference mentioning 150lm/W contains no part numbers, no model references, nothing: It's just a number. I wouldn't consider that "reliable". Also, I've looked at a few catalogs (from philips, osram, ushio, hanovia) and found nothing above 50lm/W. I found a few references for 60lm/W when in the context os Xenon-long-arc lamps, but nothing solid with part numbers and model specificaations.

Yes, it's probably just a typo—they probably meant 50 lm/W.--Srleffler 02:52, 26 February 2007 (UTC)

Tungsten lamp curve

This curve does not accurately reflect the emission of a tungsten lamp for reasons explained in the talk page for Blackbody radiation.[2] Furthermore, it contradicts the text of the article, viz., "...most of its emission is in the infrared." This graph should be removed and replaced by a more accurate one. Drphysics 18:54, 15 March 2007 (UTC)

Link to discussion--Srleffler 20:31, 15 March 2007 (UTC)

add clarifying details

This is a very important, difficult, and confusing subject. Many lighting-related articles are involved, and share tables as templates. The "Lighting efficiency" table needs more columns, so that those of us trying to make sense of this have some hope. The various sources listed should be characterized with deg-K range etc. The text says that "True luminous efficacy is a property of the radiation emitted by a source" and then leaves us hanging. Please add a column to the table that gives this actual "true luminous efficacy" for each source. Please add the total W radiated by each source, and how much (% or W) of that is in the visible spectrum.

Electric power goes into an incandescent bulb. Some of the energy is radiated. Some of that is in the visible spectrum. Some of that the human eye sees well, some barely at all. That is three levels of nested loss. A fairly simple and important concept. But not clear in the WP lighting articles, and the relevant numbers are not given, only some sorts of "final" numbers that confuse because it is not clear what/which factors they are including how.

The table should probably also list a few monochromatic color sources to help with understanding the color-weighting aspects.

Without an extremely clear exposition of these matters, we cannot understand the "efficiency" aspects of incandescent lighting, nor understand comparisons with other types of lighting.

Also for the fluorescent tubes, we need a note clarifying whether these numbers are for the tubes themselves, or for the whole tube and ballast system as a whole. (And I assume these numbers are not for typical lighting devices installed in typical luminares, which should also be at least mentioned in a footnote, mentioning typical additional losses - these "overall" numbers are not truly "overall" from an applications perspective.) -69.87.201.16 11:01, 25 May 2007 (UTC)

Add theoretical maximum efficacy for white light?

I notice the theoretical maximum efficiency for lumens per watt is 683. However, this is only for a single monochromatic wavelength of green. Would it not be feasible to add another entry to give the theoretical maximum of white light to around 227.67 (which is basically 683/3)? --Skytopia 06:36, 4 October 2007 (UTC)

Where do you get that number from? It's not clear to me that there even is a theoretical maximum of white light, since it would depend on what your definition of "white" is. In any event, a citation supporting the new information would be required.--Srleffler 17:26, 4 October 2007 (UTC)

Note also that, as mentioned in the article, an "ideal" white light source with a perfectly flat spectrum has a luminous efficacy of 242.5 lm/W, which is higher than your supposed maximum.--Srleffler 13:19, 7 October 2007 (UTC)

Is there any actual WP:RS for this number, or for this concept of an ideal white light source? Does it mean equal energy per wavelength from 400 to 700 nm? Or what? I can find no source that says. Also, what about the maximum luminous efficiency of an ideal blackbody? There must be some temperature at which efficiency is maximized, and the efficiency at that point is well defined and probably well known. Do you know? Looks like maybe near 14.5% at 7000K, but do we have an actual source and actual numbers? Here is a book that says it peaks at 6500K, but doesn't give the efficiency number. Is it possible that the "ideal white light" being discussed is in fact a blockbody, not a flat spectrum? Dicklyon (talk) 01:27, 6 January 2008 (UTC)

I suspect it's equal power per unit frequency in that range, actually. In audio and electronics "white" noise is noise with equal power per unit frequency. Note that the article already gives 95 lm/W at 6300°C as the maximum efficacy for a blackbody, and it cites a source.--Srleffler (talk) 18:23, 6 January 2008 (UTC)

Ah, I see it now. It says 6300 C or 6600 K, which agrees with my calculation. Why does it say "[sic]" in the quote? I don't think you're right on the equal energy per frequency; I've never seen such a thing in talk of optical spectra, but equal per wavelength is common and gives very nearly the answer quoted; still need a source and a better number for that one, though. Dicklyon (talk) 20:53, 6 January 2008 (UTC)

I added the [sic] because he uses "efficiency" to describe what should, in the context of this article, be "efficacy".--Srleffler (talk) 01:28, 7 January 2008 (UTC)

Seems like it implies he said something wrong, when it's really just an alternative usage of a correct term. OK if I take it out? Dicklyon (talk) 01:49, 7 January 2008 (UTC)

No. Given the definitions in this article, his usage is wrong. It would potentially be confusing to have "efficiency" used to mean lm/W without marking it. An alternative might be to do an editorial correction in the quote: "...and the theoretical luminous [efficacy] is 95 lumens per watt."--Srleffler (talk) 05:04, 7 January 2008 (UTC)

I understand it's wrong [sic] per the definitions in the article. But that's not his fault; what he said was correct and consistent, and the "sic" makes it look like we think he said something wrong. It's pretty common to use it that way. Dicklyon (talk) 05:10, 7 January 2008 (UTC)

I just calculated the blackbody max. Based on 1 nm data and simple sums, using 1931 y(lambda) and a matlab blackbody code snippet that I found online, the max luminous efficiency is 13.97% (95.4 lm/W), attained for temps from 6500 to 6700 K (that is, it varies less than 0.01% across that temp range, with a peak near 6630). And I get 243.13 for the mean y(lambda) from 400 to 700 nm, so you're right that the 242.5 number probably does come from a flat spectrum over that range. It would sure be nice to have a source for these things, and maybe better numerics for more definitive numbers. Dicklyon (talk) 03:40, 6 January 2008 (UTC)

Here is a source that says 93 is max, at 6300 K. And here is one that shows the peak at 6600K but doesn't give the exact value, just a plot. And this one says about 6800 K. Dicklyon (talk) 04:08, 6 January 2008 (UTC)

You're right, 242.5 is mentioned higher up the article. I hadn't seen that previously. Do you think it would be a good idea to list it in the lower table as well? I know it's a slight duplicate of information, but it's nice to compare the theoretical maximum against the other white-ish lights in that table. Also, the information 683 lm/W is duplicated as well.

Also in regards to the point that a more efficient white light source can be made more efficient with say... 3 wavelengths, instead of a multitude of wavelengths, I'm not sure that's the case. If it's true, then they've got to be very close in efficiency anyway (do you know the 3 wavelength stat by any chance?)

Finally, I thought the link to Luminosity_function link was appropriate along with the other three. In this kind of article, confusion can stem from the finer points of what lumens actually are, so it's good to include it in there.--Skytopia (talk) 18:06, 29 March 2008 (UTC)

I took it out not just because it's a duplicate, but also because it is misleading. It's not really correct to talk about a "theoretical maximum" efficacy for white light, since "white" is not a well-defined thing. The value we are tossing around (242.5 lm/W) is the luminous efficacy of a perfectly flat spectrum through the visible, with no light outside the visible spectrum. This is "ideal" in the mathematical sense: an idealized or optimally simple form of "white" light. It's not necessarily the best white light source possible. One could make a lamp that produces a nice smooth continuous spectrum that is humped in the middle; something like the luminosity function, but perhaps with not as big a ratio of green to red or blue. Such a source could have an efficacy greater than 242.5 lm/W, and would appear nice and white to an observer.

I removed the extra link to luminosity function, since it already appears in the article. The "see also" section is for linking to relevant pages that are not already linked.--Srleffler (talk) 18:21, 29 March 2008 (UTC)

I think the main reason I would still like the (admittedly somewhat engineered) value for maximum white light efficiency in the main table as well is so that one can see how much more technology can progress before 'white light' efficiency maxes out. You're right that a slight hump towards green will still be considered by the average observer to be more or less 'whitish', but let's assume that 'pure white' (whatever that is) is actually a goal. For that goal, I think the definition of a flat line throughout the visible spectrum fulfils that quite well.

If a light is tinted slightly red, green or blue, it can be difficult for people to see that. But that doesn't make it any less tinted; it's just that the eye has temporarily 'adapted' to that new level as white. However, the illusion is lost more and more as you keep adding more saturation to the light, which is why the best value for perceptive white light would be in the 'middle' of the illusion area (around 6000-6500K). Therefore, this makes perceptive white somewhat an absolute value, as well as just a mere relative one. --Skytopia (talk) 12:53, 16 April 2008 (UTC)

There is nothing special about the flat spectrum. It is neither the maximum in efficiency nor a good definition of "white". It is completely unnatural. Remember that our eyes are designed to see primarily with a ~6500 K blackbody illumination. That strongly-humped spectrum is probably the best definition of what "white" is. A blackbody spectrum truncated to cover only the visible range would probably have a higher luminous efficacy than the flat spectrum, too. The flat spectrum is by no means an indicator of the maximum luminous efficacy that can be achieved by a "white" source.

I think you seriously underestimate the human brain's ability to adapt to different ambient lighting. Our vision system is quite adept at "retuning" to perceive ambient illumination as white, even when the same light would be perceived as quite strongly coloured when compared to more typical illumination. This is not a trick or an illusion—it is an essential feature of how the human vision system works. White is relative.--Srleffler (talk) 04:39, 17 April 2008 (UTC)

I agree with Srleffler, that white is not any particular color. However, once you pick a chromaticity for white, say D50 or D65, or whatever you want, then you have a well-defined optimization problem to find the maximum lumens per watt. It would be interesting to work out. I wonder if that's been done. If not, such original research has no place in the article. Dicklyon (talk) 05:07, 17 April 2008 (UTC)

I study and create optical illusions, so I am well aware of how colours (including white) can fool the visual system. However, if the sensation of '100% white' was relative only, then why is it easy for anyone to tell the difference between illumination of a ~6500K light bulb compared to that of the more orangey 2700K illumination provided by incandescent bulbs? I can be in a room with either illumination for hours, and while my eyes can adapt to each, it only takes a moment's thought to tell which illumination is closer to actual white (whatever that is). Therefore, closer values to the 6000-6500K ballpark would also be distinguishable from 6500K to lesser degrees, even after acclimatization. --Skytopia (talk) 08:07, 17 April 2008 (UTC)

Should the "ideal white light" entry on the first table be changed to something like "flat spectrum 400nm-700nm" or "constant power 400nm-700nm" then? I found the entry confusing without a definition of what "ideal white" is.Totsugeki (talk) 21:01, 16 October 2008 (UTC)

I agree, but we need a source that is clearer about how this "ideal" light is defined. The source cited in the article doesn't say. Looking around for this number on the net, I find lots of people who have obtained it from Wikipedia, many of whom are confused about what it means (e.g. assuming that it is a theoretical maximum for "white" light, which it is not.) I'm going to delete it from the article until a better source can be found.--Srleffler (talk) 23:03, 16 October 2008 (UTC)

Type	Luminous efficacy (lm/W)	Luminous efficiency
ideal white light source	242.5	35.5%

Lumens are a cheap, dirty, convenient and very useful tool for the lighting industry, but that is all. Indeed, without qualification, the word itself has no meaning. Lumens are imaginary units - in the case of the human eye, a lumen is a power figure (mW for instance), with a correction applied to allow for human eye sensitivity - that corrected figure is a lumen figure. That correction is a long-standing figure determined from average experimentally determined figures. However, life is not even that simple as photopic and scotopic sensitivity, and hence the correction figures, are subtly but significantly different - very important when comparing ofice and stret lighting for instance. If you happen to be a farmer using artificial lighting during winter, neither of these figures are of use - but plant/photosynthesis lumens are - and they are a million miles from human eye lumens. I very much doubt figures exist beyond photopic and scotopic human, and plant lumens, but correction figures will be unique for each and all forms of life. —Preceding unsigned comment added by Pperdix (talk • contribs) 16:34, 30 November 2009 (UTC)

The word has the meaning it is defined to have, like any other unit of measure. Unqualified, lumens are a measure based on the photopic sensitivity curve. Measures based on other sensitivity curves are not properly called "lumens".--Srleffler (talk) 02:46, 2 December 2009 (UTC)

Luminous efficacy of display screens

I would find it interesting to see figures on luminous efficacy and efficiency of different display technologies. As I understand some of the screens produce light pretty effectively. --Khokkanen 11:14, 7 October 2007 (UTC)

I just added a cathodoluminescence section to the table (prompted by the release of the Vu1 ESL lightbulb, so if someone does find a good number for CRTs, that's the category for it. DMPalmer (talk) 21:18, 6 January 2011 (UTC)

Comparison of tungsten lamps needed

100Watt tungsten lamps are more efficient than 60Watt lamps. Ordinary "pear shaped" bulbs are more efficient than "candle" bulbs. Quartz is better than glass. 110V lamps are better than 240Volt. Presumably, 12Volt-halogen are better than mains powered halogen. Is this simply to do with the filament temperature, and that a higher-resistance filament must be thinner, therefore must run cooler lest it burn out rapidly? —Preceding unsigned comment added by 81.187.40.226 (talk) 05:31, 14 November 2007 (UTC)

Some extra data points (information from the packaging of the light bulbs), all referring to 220/240V bulbs:

• A 60 Watt "16x life" (Greenstock) bulb emits 320 lumens, whereas a regular 60 Watt bulb emits 700 lumens, and a HalogenA bulb emits 840 lumens.
• A 100 Watt GLS "triple-life plus" bulb emits 1120 lumens, whereas a regular "single life" (1000 hour) bulb emits 1330 lumens.
• A 25 Watt Greenstock 8x candle bulb emits 160 lumens, whereas a 28 Watt Osram "Halogen Energy Saver" candle bulb emits 340 lumens. —Preceding unsigned comment added by 87.194.171.29 (talk) 00:26, 6 January 2008 (UTC)

Filament lamp efficacies are determined by design and legislation. For any given basic design, the lumens, mutiplied by the rated life will be constant - you can have a 50 lumen per watt lamp that lasts 2000 hours or a 100 lumen per watt lamp that lasts 1000 hours, but not a 100 lumen per watt lamp that lasts 2000 hours, unless you use a different technology (move from a standard gas-filled glass lamp to halogen-doped quartz, for instance). The volts applied to the lamp are irrelevant (so long as they are correct for the particular design) - within the limits of design set by some very simple physics and chemistry, you can design what you like for any voltage. For details of design limitations, see "The Science of Incandescence" by Dr Milan R Vukcevich - the incandescent lamp designers' bible.. —Preceding unsigned comment added by Pperdix (talk • contribs) 16:46, 30 November 2009 (UTC)

My impression is that for any given incandescent lamp technology, if you design for higher voltage operation, you have to accept either shorter lifetime or lower efficacy.--Srleffler (talk) 02:54, 2 December 2009 (UTC)

The efficiency and life of a filament lamp is a compromise. As noted above, you can increase the efficiency (by raising the filament temperature) but at the expense of lamp life. Generally, standard service filament bulbs are operated such that the average life if the bulb is 1000 hours. This gives a good compromise between efficiency, colour temperature and life. Broadly, the actual amount of light output is a function of the filament temperature and its volume. The life, on the other hand is a function of its surface area (that is the area from which the filament evaporates).

A 240 volt, 100 watt GLS lamp has a luminous efficiency of 13 lm/W (in round numbers) for a 1000 hour life. To construct a 120 version of the same lamp, the filament has to have one quarter of the resistance and be capable of carying twice the current. Thus the cylinder that is the filament in the 120 volt lamp is twice the cross sectional area and only half as long as that of the 240 volt lamp. Although the volume is the same, the surface area is reduced. Thus the lamp can be operated at a higher temperature (and hence efficiency) for the same life. A 120 volt 100 watt lamp thus has a luminous efficiency of 17 lm/W (again, in round numbers).

Extending the argument to a 12 volt 100 watt lamp unfortunately, does not provide a comparable efficiency gain and for a 1000 hour life only 19 lm/W can be achieved. However, other techniques can be used to provide an efficiency and life gain, the most notable of which is to produce a halogen version of the lamp where 22 lm/W becomes easily achievable with a 4000 hour life. It is perhaps odd that the lamp manufacturers do not mark the packaging of low voltage halogen lamps with efficiency information or the lumen output (have a look next time you are in a lamp store!). They also understate the life.

It is worth noting here that the stated efficiency of comact fluorescent lamps of 60 lm/W only applies to the versions of the lamp with the somewhat cold bluish 6500K (equivalent) phosphor. The prefered domestic version with the 'Incandescent White' phosphor (intended to mimick the 2700K filament temperature of a (120 volt) 100 watt bulb, only has an efficiency of 24 lm/W due to the pink component of the phosphor being much less efficient than the blue. 86.176.70.246 (talk) 15:07, 25 November 2010 (UTC)

Yes, lower color temperature lamps have lower efficacy than high CCT lamps but surely UK lamps are not as bad as all that! For North American products with an Energy Star label, (here's the standard, [3], page 6 has the table) a white lamp must make at least 50 lumens per watt (bare lamps) and have at least an 80 CRI. What do the EU standards say? --Wtshymanski (talk) 15:59, 25 November 2010 (UTC)

Reference no longer exists!

http://www.ts-audio.biz/tsshop/WGS/411/PRD/LFH0324408/Osram_6406330_500mA_52V_E10_BLK1_MINIWATT-Halogen-Gluehlampe_f.Taschenl..htm points to a page which no longer exists. This is currently reference #12 (#11, in German, is dead, too). That is all.65.183.135.231 (talk) 16:47, 2 June 2008 (UTC)

Thanks. I have marked the links as dead.--Srleffler (talk) 17:32, 2 June 2008 (UTC)

some numbers for non-white LED's

non-white LED's work in a different way from white ones (they don't have the coating on top of the LED), and all the figures for efficacy are available on the net. It would be good if someone could source some numbers and add them to this article. I may if I have some spare time. 192.102.214.6 (talk) 10:25, 19 June 2008 (UTC)

Sounds like a good idea, but please limit it to just a few entries—perhaps red, green, and blue.--Srleffler (talk) 11:29, 19 June 2008 (UTC)

I'd love to know the "wall-plug efficiency" of monochromatic light sources such as LEDs and lasers (especially green ones at ~555nm).Totsugeki (talk) 20:11, 16 October 2008 (UTC)

Me too, but I think we should just limit the article to a couple types of LED that are intended for use for illumination or indicator lights.--Srleffler (talk) 22:36, 16 October 2008 (UTC)

I stumbled upon this: [4]. Apparently laser diodes can reach 60% wall-plug efficiency. If the site mentioned the wavelength, the lm/W figure could be calculated. Totsugeki (talk) 18:08, 27 December 2009 (UTC)

Values in examples table

Regarding the table listed in the Examples section

I just added a spiral bulb to the Fluorescent section of the examples table: Spiral tube with electronic ballast (9320lm/75W or 124.3lm/W). It is a relatively new type of bulb from Panasonic that is selling well in Japan (I bought one too), but I can't find it on English websites. I included a link to a press release about them from June 2010. It's NOT a compact fluorescent, but a long tube curled into a flat spiral. -- PTS, 27 Sept 2010

I disagree with a lot of the information in the table. I'm not deleting it since someone put a lot of time intor creating it and some of the info may be useful to others. Efficacy would be calculated based on lamp lumens (either initial or average) / wattage of ballast when paired with the lamp * ballast factor. Example for a 32W T8 fluorescent lamp with a 2-lamp electronic instant start ballast. 2714 lumens (mean) per lamp, 2 lamps, 59W for ballast, 0.90 ballast factor. 2714 lum * 2 lamps / 59W * .9 BF = 82.8 lumens/Watt. Initial lumen efficacy would be about 90 lumens/Watt. While the table above claims 60 lumens/Watt) —Preceding unsigned comment added by 204.177.188.65 (talk • contribs)

This may need to be looked into. I assume the "ballast factor" you're referring to is a power factor. The efficacy is the flux in lumens divided by the actual power consumed, in watts. It's possible some of our sources have reported volt-ampere values incorrectly as "watts" (failing to allow for the power factor of the ballast), but the error is in using watts for something that is not actual power. Do ballast manufacturers report volt-amp ratings for ballasts in "watts"?--Srleffler (talk) 18:17, 2 July 2008 (UTC)

I notice that, using your example above, if a 32 W lamp emits 2714 lm, the efficacy is 2714 lm / 32 W = 85 lm/W, which is not far from the value you give. This may neglect losses in the ballast however.--Srleffler (talk) 18:24, 2 July 2008 (UTC)

I removed the following entries from the table, as uncited:

Category	Type	Overall luminous efficacy (lm/W)	Overall luminous efficiency
	34 W fluorescent tube (T12)	50	7%
	32 W fluorescent tube (T8)	60	9%
	36 W fluorescent tube (T8)	up to 93	up to 14%
	28 W fluorescent tube (T5)	104	15.2%

Looking around, I found a US government publication that gives some recommended efficiency specs for lighting. From their examples, it appears that not only is there some electrical loss in the ballast, but the actual light output of the lamps as driven is lower than their rated values. Crunching their numbers gives "real" values of 58 lm/W for "base" 34 W T12 lighting with magnetic ballasts, 81 lm/W for a "recommended" 32 W T8 system with electronic ballasts, and 92 lm/W for a "best available" 32 W T8 system. I updated the article with this info. I left it generic regarding the length and rated power of the tubes, just giving a range for T8 tubes with electronic ballasts.--Srleffler (talk) 04:59, 4 July 2008 (UTC)

I disagree with the examples in the lighting efficiency table also because they contradict the definition presented earlier, namely that "overall luminous efficacy is the ratio between the total luminous flux emitted by a device and the total amount of input power (electrical, etc.) it consumes. It is also sometimes referred to as the wall-plug luminous efficacy or simply wall-plug efficacy. When expressed in dimensionless form (for example, as a fraction of the maximum possible luminous efficacy), this value may be called overall luminous efficiency, wall-plug luminous efficiency, or simply the lighting efficiency." The numbers in the table for overall luminous efficiency are simply the overall luminous efficacy of the source divided by 683. This contradicts the stated definition as 683 lumens per watt is only relevant if the light source is 555 nm monochromatic light. If the spectrum consists of any other wavelengths, then the maximum possible luminous efficacy of the source will be less than 683. In short, you need to know the luminous efficacy of the emitted spectrum in order to calculate the overall luminous efficiency, or the number obtained is meaningless. Simply dividing the overall luminous efficacy by 683 doesn't tell you what percentage of input power is converted to visible light, which is how overall luminous efficiency, also known as the wall-plug luminous efficiency, is defined according to the article. As it stands now all the last column of the table really tells you how well the source does compared to the theoretical maximum any source can have. While easy to calculate, it tells little about what percentage of electrical input power is being converted to visible light. The table really needs to be revised. —Preceding unsigned comment added by 72.229.177.183 (talk) 11:59, 13 December 2009 (UTC)

You are misinterpreting the article. The value 683 lm/W is not merely relevant for 555 nm light; rather, this value is the maximum possible luminous efficacy for any light source. It turns out that there is only one way to make a light source with the maximum possible overall luminous efficacy: the source must convert all the electrical energy into light with wavelength 555 nm. Any other spectrum of light will result in a lower luminous efficacy.

So, as the article explains, the overall efficacy values given are the ratio between the luminous flux emitted and the electrical power consumed, and the overall efficiency values given are the ratio of the efficacies to the maximum possible luminous efficacy, which is 683 lm/W.

It is almost never useful to ask "what percentage of electrical input power is being converted to visible light", and that is not what luminous efficacy and efficiency are. They are measures of the utility of the source for illumination. A source that converts 100% of the energy to light just on the edge of the visible spectrum isn't very useful because your eye isn't very sensitive there. A source that converts 10% of the energy to light near the middle of the spectrum will appear much brighter. Luminous efficacy and efficiency reflect this.

Luminous efficiency is not actually very useful. Luminous efficacy is the real, physically relevant, measure. People are used to seeing efficiencies as percentages, however, so they convert the efficacy into a more familiar form. The efficiency doesn't convey anything different than the efficacy; it is just the same quantity in a different set of units.--Srleffler (talk) 15:53, 13 December 2009 (UTC)

I think where we disagree here is in the definition of efficiency. Sure, efficiency is merely efficacy in a unitless form. But generally in engineering efficiency is somehow related to how well a system is doing relative to some theoretical maximum. In nearly all cases efficiency is defined such that a 100% is reached in a system where 100% of the input is converted to the desired output. In the case here, the input is electrical power in watts, and the desired output is visible radiant energy, also in watts. Lumens are used to weight this visible radiant energy by the eye's response function of course, and you obviously want the bulk of your emitted visible radiation in the area where the eye's response is greatest. The problem with the table as it exists now should be obvious. It is impossible for any light source, except 555 nm monochromatic light, to reach 100%, even if that light source converts 100% of the input power to visible light in whatever spectrum it is emitting. This flies in the face of every other definition of efficiency I have seen.

It is quite true what you say about where in the visible spectrum the light is emitted mattering. No arguments there, although obviously most common light sources do in fact tend to emit heavily in the areas where the eye response is greatest.. However, I take issue when you say it is almost never useful to ask what percentage of electrical input power is being converted to visible light. In fact, this is a very useful measure as it allows you to determine how much waste heat you must deal with. This is particularly relevant with solid-state light sources such as LEDs where nearly 100% of the heat must be dealt with via a heat sink. It is even relevant with fluorescent technology where the heat is removed via a combination of conduction and convection, plus a very small amount of radiation. In all cases this is real heat which must be somehow dealt with. Therefore, knowing the percentage of electrical power converted to visible light not only allows you to calculate the waste heat, but it also gives you some idea of how much potential room for improvement exists. For example, right now the best linear flourescents convert about 30% of the input power to visible light. The best commercially available white LEDs convert about 45%. The best blue LEDs convert around 55% ( despite this their efficacy numbers are still low due to the eye's poor response at 450 to 470 nm ). You might find this interesting: http://lighting.sandia.gov/lightingdocs/OIDA_SSL_LED_Roadmap_Full.pdf

See pages 9 and 10 in particular which deal with maximizing the luminous efficacy of the emitted spectrum while still maintaining light which appears white, and has decent color rendering. As you might gather from reading the paper, the solid state lighting industry is all about maximizing the luminous efficacy by both maximizing the efficacy of the emitted spectrum, and maximizing the percentage of electrical power converted to visible light. Of course, 683 lumens per watt will remain the maximum possible efficacy any light source can have, but for real-world light sources which are mostly varying degrees of "white" it's not a terribly useful basis of comparison.

Finally, I'll grant that if we wanted revise the table as I say then there remains the practical problem of finding the luminous efficacies of the various emitted spectra of all those light sources. Such information isn't generally commonly available outside of the LED industry. So perhaps for now simply put a disclaimer that a light source can be 100% efficient at converting electrical power to visible light, and still have an efficiency well under 100% if you define efficiency as efficacy divided by 683. And perhaps give some of the real world numbers I mentioned above as examples. —Preceding unsigned comment added by 72.229.177.183 (talk) 00:15, 14 December 2009 (UTC)

The efficiencies given are doing precisely what you ask for in your first sentence: they give the measure of how well the system is doing relative to a theoretical maximum—the maximum possible luminous efficacy. This is the correct measure if you want to know how efficient a source is at illumination. If you wanted a hypothetical source that would let you see as well as possible for the least amount of energy, you would want the source with a luminous efficacy of 683 lm/W. This is by definition the 100% for luminous efficiency. You go wrong when you write "the input is electrical power in watts, and the desired output is visible radiant energy, also in watts". The desired output is luminous flux, which is measured in lumens, not watts. The question here is not "how much visible light can I get for a given amount of power", but "how well can I see using a given amount of power". These are significantly different questions, and they should not be confused. The fact that nothing but a 555 nm source can reach 100% is correct: nothing will let you see as well as a 555 nm source, for a given amount of power.

If you want to know about waste heat, luminous efficacy and efficiency are the wrong measures to consider. You want radiant efficiency: how many watts of visible light are emitted for each watt consumed. Different quantity. It has its own article: Wall-plug efficiency. Note, though, that if you want to know about heat load, the percent of the input power that is converted into visible light is not the right measure to consider. All of the power that is consumed ultimately becomes heat. The only question is whether the heat is dissipated inside the light fixture, or radiated out of it. If you want to know about heating of the fixture, you need to know what fraction of the power consumed is radiated as electromagnetic radiation of any wavelength, not just visible light. With many sources, infrared carries a lot of energy out of the fixture. Conversely, when considering heating of things outside the fixture, visible light heats things just as well as infrared does, so you would not want to exclude visible light in analyzing radiant heating of things exposed to the source. The fraction of input power that is emitted as visible light is not generally of much use.

LED researchers seem to use some different terminology and concepts, compared to optics. Fundamentally, the parameters they should optimize are the overall luminous efficacy (LES) and the CRI. There is a tradeoff between the two: one cannot have both perfect efficacy and perfect CRI. One must choose a compromise. They like to split the problem of obtaining high overall luminous efficacy into two separate problems: optimizing the conversion of power into visible radiation, and optimizing the spectrum of the visible radiation to achieve a desired LER and CRI. The cutoff at the edges of the visible spectrum is arbitrary, and would be nonsensical for anything but an LED, where the emission spectrum can be tailored so that there is little emission outside the visible. --Srleffler (talk) 03:51, 14 December 2009 (UTC)

From the sense of adhering to a definition what you say here makes sense. To me it would just make more sense to define 100% efficiency as "the maximum possible luminous efficacy of a source with same spectrum" as it allows any source to potentially be 100% efficient. Or better yet define luminous efficiency as the luminous efficacy of the emitted spectrum divided by 683. At least that makes some physical sense in that you're seeing how efficient at lighting the emitted spectrum is relative to the theoretical maximum of 683. Yes, there will always be a trade off of CRI and lighting efficiency as you say. This new definition allows you to see how much of a trade off is made independent of how well the light source actually converts electrical power into visible light. And in some papers I've even seen it defined that way-as you say LED researchers seem to use different terminology and concepts. But if the usual definition of luminous efficiency is efficacy divided by 683, then so be it. Unfortunately this causes even more confusion with a subject many already are confused by. The confusion stems from people equating the figures in the last column to wall-plug efficiency, insisting that the figures there tell you how much of the input power is converted to visible light, when in fact they don't. Perhaps this article and the one on wall-plug efficiency should be merged, and another column-"wall-plug efficiency", added to the table, in order to eliminate this source of confusion. While I don't have wall-plug efficiencies for ALL of the light sources in the table, I know enough of them to make adding another column worthwhile should the authors of the article choose to.

Also, for the sources likely to be of most interest in the future, namely solid-state lighting of all kinds, wall-plug efficiency in fact allows you to obtain a good estimate of the fixture's waste heat. LEDs don't emit a significant percentage of their input power as infrared. Neither do fluorescents for that matter, although they do emit several percent as non-visible UV. Incandescent on the other hand actually radiates far more infrared than visible light.

72.229.177.183 (talk) 07:40, 14 December 2009 (UTC)

Those are both useful "efficiencies", as is the one defined in the article. The first defines the degree to which a particular light source approaches its ideal realization. It does not allow comparison between sources that produce different spectra, however. The second one is "LER", as used by LED researchers, expressed as a percentage; it is purely a measure of the utility of the spectrum without regard for the efficiency with which it is produced. Which metric is best depends on what question one wants to answer.

These issues aren't unique to luminous efficiency. Radiometry and photometry are confusing fields because there are many different measures used. To the uninitiated, the distinctions between them are unintuitive. They exist because different circumstances require different metrics to provide the required information.--Srleffler (talk) 07:00, 15 December 2009 (UTC)

No definition of Lumen or lm is provided

It would help if this article included a definition of Lumen and that lm is its abbreviation. A link to the detailed article about them would be good, too. http://en.wikipedia.org/wiki/Lumen_%28unit%29 —Preceding unsigned comment added by Seldenball (talk • contribs) 12:01, 6 August 2008 (UTC)

Lumen is linked the first time the term is used. Same with Luminous flux. The "Explanation" section explains the concepts involved, and defines lm/W as an abbreviation for lumens per watt.--Srleffler (talk) 04:48, 7 August 2008 (UTC)

Image from German Wikipedia

The German page has this image which I think would make a useful addition to the article. It shows the luminous efficiency of a blackbody radiator as a function of its temperature (I think). Unfortunately the captions on the image are in German and there is no source data for the image so that I could recreate it. I replaced the captions with English equivalents, but I won't add it to the article in case I misunderstood the German version.

Totsugeki (talk) 20:40, 16 October 2008 (UTC)

This is great. The axes need units, however: % for the y-axis and kelvins (K) for the x-axis. --Srleffler (talk) 22:58, 16 October 2008 (UTC)

Updated it. Totsugeki (talk) 00:32, 17 October 2008 (UTC)

This is a great addition...but are we sure the units are % on the vertical, and is that defined the same as in the article, that is relative to a green line? —Preceding unsigned comment added by Ccrrccrr (talk • contribs) 07:30, 14 November 2008 (UTC)

Definitions: overall and per radiant watt

There are two definitions of luminous efficacy that are commonly applied: lumens per radiant watt, and lumens per input power to the light source (overall luminous efficacy). This article treats the first as being the primary, correct usage of the term, and denigrates the other as being confusing and implies that it might be incorrect to call it "luminous efficacy".

I think that this is a biased point of view. The term "luminous efficacy" without any qualifiers is widely used to mean what the article calls "overall luminous efficacy". Regardless of what we as editors think should be the correct usage, we don't get to decide what is correct.

I agree with the article that the conflict between the two usages is a problem. However, I have more often seen people confused in the other direction--for example, people from the lighting field reading a lm/W value on an LED datasheet and thinking it means overall luminous efficacy when in fact it is being used for lm(radiant watt), which we might call spectral luminous efficacy. Making up our own rule about what is correct and what is not will not help the situation, and it's against WP policy. Unless there are authoritative sources that back up one as being correct and the other being incorrect (and there aren't authoritative sources with the opposite POV), we need to represent the real state of the world here, not how we wish it to be.

I propose that the article should be re-written to mention both definitions in the lead, to put them on equal footing, and to warn against the potential confusion. I think that it is easy to find authoritative sources that use the terms both ways.Ccrrccrr (talk) 20:45, 14 December 2008 (UTC)

ps: two more minor notes. First, "overall" isn't necessarily the right term. In ligthing, people distinguish between lamp efficacy (lamp lumen output/lamp electric power input) and system efficacy (fixture lumen output/ballast electrical input); "overall" might imply the latter. Also, I think that using "lighting efficiency" for any kind of lumens/watt is a worse choice of words--efficiency should be unitless. For example, radiant watts per input watt, or lumens out of of fixture per lumens out of a lamp for fixture efficiency.Ccrrccrr (talk) 20:45, 14 December 2008 (UTC)

I'm fine with the rewrite you propose. Your post reminded me of the LED issue, of which I had become aware only recently. Someone needs to review the LED entries in the "overall efficacy" table, and review whether the citations support inclusion of the cited numbers in the "overall efficacy" table. I suspect that the efficacies for the "prototype" LEDs listed are actually lumens per radiant watt rather than "overall" efficacy, as defined here.--Srleffler (talk) 04:30, 16 December 2008 (UTC)

I'm OK with the proposed change, provided that reliable sources are cited in support of both definitions. Alternatively, if had reliable sources with sufficient weight showing that one use is preferred, we could go with that. I agree it's basically not up to us, but up to sources. Dicklyon (talk) 05:11, 16 December 2008 (UTC)

I found a good source that even provides that official international standard terminology, so I edited the whole article to explain and use that terminology. Additional editing might be called for in light of the information in that article (no pun intended). If nothing else, it has a great table of some values of luminous efficacy of radiation that we could use to expand our table of those.Ccrrccrr (talk) 16:09, 26 December 2008 (UTC)

Srleffler, thanks for your copy edits. They are quite helpful. Two minior changes that I have doubts about: First, shouldn't we include the information about the international standard terminology? Maybe that goes in the section with that table of units? But I thought it was a nice fit with the discussion of possible confusion. I don't like the way you rephrased that discussion. Second, the heading on the table for luminous efficacy of a source: I know it sounds a little funny there, but I thought it was best to stick with standard terminology, given that the potential for confusion is strongly in evidence.Ccrrccrr (talk) 18:21, 26 December 2008 (UTC)

CFL efficacy and efficiency

I have just added a paragraph to the CFL article based on some of the data in this article. The bit that worries me is this use of that figure of 683 lm/W, the 'efficacy of an ideal light source'. You guys seem to reference that to the Luminosity function article, which in turn cites it to the Commission Internationale de l'Éclairage... At that point, what I remember of A-Level and University physics is getting spread too thin... Without being too picky, we only need a bottom line or a headline figure and this article is referenced as the main source of details, is what I wrote for CFLs acceptably accurate for a lay readership? (This link may be useful if what I wrote is already hacked away) --Nigelj (talk) 16:40, 24 December 2008 (UTC)

Seems generally OK. I tweaked the wording a bit. One sometimes sees a different "efficiency" figure used, which is the fraction of the energy that is emitted as photons within the visible spectrum. Your wording suggested that this was the definition being used. The efficiency numbers, defined that way, are higher. The definition used here takes into account the fact that the eye is not equally sensitive to all wavelengths of visible light. Red light is less useful for illumination than green light, because the eye is much less sensitive to red. A source with more green will illuminate a room more efficiently than a source with less green and more red and blue. The 683 lm/W is the physical upper limit. No source can produce a higher efficacy than that. The number corresponds to the efficacy you get when all of the light is emitted at exactly the wavelength to which the eye is most sensitive, and no energy is lost or wasted.--Srleffler (talk) 04:15, 25 December 2008 (UTC)

Thanks for that, Srleffler. You're right, I think what the average, technically literate, but non-specialist, reader would like to see - both here in the tables and in places like the CFL article - are some figures for "the fraction of the energy that is emitted as photons within the visible spectrum". Should we use a lower constant - there are a few quoted in the 250 lm/W range in places?

I think it is not actually possible to get to the holy grail figure: to say, "this lamp converts x% of incoming electrical energy into photons of visible light" regardless of whether they are red, green, blue etc. A lot of energy may be put out as almost-invisible near-UV by some lamps. So, we would need a curve representing the average human eye's response to each part of the spectrum (i.e. not necessarily a black-body curve). But then, CFL and LED lamp manufacturers at best give us an overall efficacy figure with no spectral curve to work from. So we can't proceed that way.

If we can pick a constant figure, either 683 or something lower, I think it should be used consistently in several articles including for the tables in this one. As it says above, other sources on the web are now starting to pick up such headline 'facts' from Wikipedia now, so it really is worth putting some effort in to get to the bottom of this, along with the right descriptive words to make it clear what we are saying and what we're not in every case. --Nigelj (talk) 10:01, 26 December 2008 (UTC)

We can't just pick a number out of the air. It has to be correct, and supported by some source. In fact, there is no such number. There is no way to convert an efficacy in lumens per watt into a "percentage of energy emitted in the visible spectrum". You have to know the actual emission spectrum of the light source to get the latter. I would be fine with quoting figures for efficiency defined the latter way, but the figure for each type of lamp has to be supported by an outside source.--Srleffler (talk) 14:10, 26 December 2008 (UTC)

Srleffler is quite correct. We don't get to pick a number and use it consistently. That's original research. So I did the necessary unoriginal research, and put in correct numbers with an authoritative reference. Which also turns out the to be an excellent ref. for this article... Hopefully what I wrote is understandable--if not please edit and/or complain here.Ccrrccrr (talk) 15:21, 26 December 2008 (UTC)

There's still a problem. The two factors Ohno talks about are the LER, and the conversion efficiency from electricity to EM radiation. Not all EM radiation is in the visible spectrum. A figure for efficiency of conversion from electricity to visible photons would still be useful, but you have not provided that. I don't think the conversion efficiency to all EM radiation is sufficiently useful to mention in the CFL article. I have rephrased to give efficiencies as defined here (% of 683 lm/W).--Srleffler (talk) 17:25, 26 December 2008 (UTC)

Thanks for the prompt attention to this. Actually, the numbers I provided are based on considering only the visible spectrum, not total radiation (see the "illuminant A" entry in the table in the reference--it says 400 nm to 700 nm only, and the 248 lm/W is consistent with that). So changing the description of the numbers without changing the numbers themselves doesn't work. So I changed some of the description back but left your other editing in place (thanks for your attention to the details).

I'm not really comfortable with including "overall efficiency" numbers there without a discussion of what they mean. Problems: 1) They are OR: both the numbers and the whole concept--we'd need a source for the concept. 2) They are relative to ideal monochromatic green light. I don't think that's a relevant comparison for considering residential illumination; and I don't think it's fair to reader to shift the comparison to green light without any mention of that. I didn't delete that yet, but might unless it gets more support here.Ccrrccrr (talk) 18:09, 26 December 2008 (UTC)

Perhaps we can remove the overall efficiency numbers or do something different, but your last edit there introduced what seem to me to be factually incorrect definitions. I believe you are misinterpreting the reference. In splitting up the luminous efficacy into radiant efficiency and luminous efficacy of radiation, Ohno makes the radiant efficiency the conversion efficiency to all EM radiation. It cannot be otherwise, because the luminous efficacy of radiation is defined by integrating over the whole EM spectrum. This is also the standard definition of radiant efficiency. I don't see anything in the paper that contradicts this interpretation or implies that he is using nonstandard definitions. The distinction is important because most light sources emit some radiation outside the visible spectrum. Incandescent lights emit lots of infrared, and possibly some ultraviolet. CFL's emit some UV. The radiant efficiency is the efficiency of conversion of electrical energy into radiation. The LER then determines how efficiently that radiation is detected by our eyes, taking into account both the variation in sensitivity of the eyes over the visible spectrum, and the falloff of sensitivity outside the visible range. Note that the variation in sensitivity over the visible range is not distinct from the falloff outside; there is no sharp cutoff.--Srleffler (talk) 21:10, 26 December 2008 (UTC)

I absolutely agree with all of your statements about the reasons this is messy. I think that is why Ohno chose to truncate. If you read p. 95, you will surely agree that the LERs in there are for truncated spectra. Although Ohno does not include limits on the integration, I agree with your interpretation that from an idealized physicist point of view, they should be 0 to infinity. However, for reasons explained below (next section), I don't think there's any way to take that 100% seriously and get to two separate numbers for radiant efficiency and luminous efficacy of radiation. I think that what people are interested in in practice generally corresponds to integrating from 400 to 700, as Ohno actually did. If you have a proposal for a way to do it with integrating from zero to infinity (or at least 20 um to 300 nm), that could be more elegant, but I don't think it's of any engineering importance; nor do I think it's easy to do.Ccrrccrr (talk) 23:42, 26 December 2008 (UTC)

Measuring from 300 nm to 20 µm and perhaps much beyond is a pain, but it isn't impossible. Such measurements are done through calorimetry: the light is absorbed by a surface with uniform (ideally high) absorption over a broad spectral range, and you measure the temperature change in the absorber. One doesn't need to do this, of course, to get the luminous efficiency of a source, which is the figure most commonly quoted. You only need to do it to get the denominator for a LER measurement (since the numerator is not affected by radiation much outside the visible range). In measuring LER, one would certainly not truncate the spectrum to the visible range. This would be terribly inaccurate, and it would be misleading the call the result "luminous efficacy". Doing so would not comply with international standards. It's not clear how Ohno's LER values for incandescent and fluorescent sources are obtained. He was working with tabulated PSD data for some example sources. He may well have simply integrated over the available data to get an "LER". Without information on what range his data happened to cover, though, it seems inappropriate to presume that it only covered the visible range. It wouldn't be unusual to have data extending into the IR and UV for these sources, especially if one plans to calculate LER.

I've taken another look at pages 94–5 in Ohno's paper. He is not truncating a spectrum for purposes of analysis, as you propose. Rather, he is modeling a source (an idealized LED), where one can in principle engineer the output spectrum to be anything one desires. Obviously, designing the device such that its spectrum includes no emission outside the visible band is desirable, since this increases the efficiency. Since the idealized design doesn't include any power outside the visible band, there is no need to consider radiation outside the visible band in the analysis.--Srleffler (talk) 07:14, 27 December 2008 (UTC)

I agree about what Ohno says and does, and I agree about how one could make the measurement. So rather than continuing to have expend effort explaining on the talk page explaining to me stuff I already know, let's figure out how to work together to make the two pages, CFL and this one, explain this stuff to people who don't yet know about it. The issue we want to get at here is what can we say in the CFL article that is helpful to people understanding the efficiency of CFLs and comparing them to incandescents. The fact that one could measure true LER doesn't get us very far if we don't have that data. So here are our choices: 1) include the information there now, with explanations somewhere about LER with integration over limited bands... 2)Provide luminous efficacy of a source, and don't discuss efficiency at all, 3) Find data on broadband LER or efficiency to provide the data in the form that you prefer. Or perhaps there are some other options or compromises between those? Perhaps only discuss CFLs where the "optical" and "thermal" bands are well separated, such that an "optical" LER is more clear cut, and doesn't involve an arbitrary cutoff (e.g. 700 nm) upon which the results are highly sensitive? What do you think we should do?

In terms of making the CFL article useful to people for understanding the technology, it would be great to have a breakdown of 100 units of energy, going in the ballast, 90 units going into the lamp, 40 coming out of the arc as UV photons, and then 20 coming out of the phosphor as visible photons. Those are made-up numbers so we can't but that in, but to me, that means that the engineered system is 20% efficient--20% of the energy going in comes out as the final product that we want. Then the next issue is the LER of the spectrum emitted by the phosphor. Inserting thermal radiation back into the equation at that point doesn't really help understanding the CFL technology is a systematic way.Ccrrccrr (talk) 15:17, 27 December 2008 (UTC)

Another option would be to drop LER and talk only about the overall luminous efficacy (l.e. of the source), since that is the quantity for which lots of data is available and the interpretation is clear. LER data are much more limited, and we have this question of interpretation, regarding how the values were obtained. I think we should remove the radiant efficiency values from the article, since their interpretation is unclear. The current explanation (unless it's changed since yesterday) is misleading, since it implies that this is the efficiency of production of visible radiation. It would be good to separate ballast loss from lamp loss and have data for both. I agree that if we use the luminous efficiency we should explain it.--Srleffler (talk) 17:51, 27 December 2008 (UTC)

I don't think the "overall efficiency" used here is OR. I'm pretty sure we can find sources that use this definition of efficiency. I don't know of another way to obtain an efficiency figure from the luminous efficacy of a source. Your objection to referencing the efficiency to monochromatic green light is strange. The efficiency is referenced to the maximum efficiency possible. If you want to know how well you can see by any given source (independent of colour rendering), what you want to know is how many lumens of light that source produces. The luminous efficacy is the efficacy with which the source produces lumens of light. No source can be more efficaceous than an ideal monochromatic 555 nm source. You might not want to illuminate your house with it, but that isn't because it's not efficient, it's because we also care about colour rendering. As Ohno notes, there is a tradeoff between efficiency and colour rendering.--Srleffler (talk) 21:10, 26 December 2008 (UTC)

Great, it would be useful to have those sources referenced. Again, I agree with all of your facts. I would be OK with including it with an explanation of what it is, and a reference documenting that it is not OR.Ccrrccrr (talk) 23:42, 26 December 2008 (UTC)

I'll look into it when I have a chance.--Srleffler (talk) 07:14, 27 December 2008 (UTC)

Stuff to do

Notes for myself or for anyone else who cares to work in this on things to improve:

• Explain the possibility of quoting LER with total radiation in the denominator, or only based on the visible range. This is the root of confusion that just arose in the CFL article, so it probably needs discussion here. e.g., 248 lm/W for "illuminant A" in the visible range, vs. about 17 lm/W for a 3000 K blackbody including all radiation.
• Explain the different between lamp and system efficacies (in particular, including the ballast losses or only the lamp).

Ccrrccrr (talk) 18:27, 26 December 2008 (UTC)

Your first point above makes no sense. You can't simply cut the spectrum off at the edges of the "visible range". There is not really any sharp edge. The eye's response falls off gradually with wavelength, following the luminosity function. We obtain efficacies and efficiencies by integrating the spectrum the source emits (all of it, visible or not) times the luminosity function, over wavelength. Someone who cuts off radiation outside the visible range before calculating LER is simply making an error.--Srleffler (talk) 21:15, 26 December 2008 (UTC)

If that is the case, then my reference, which is a proper peer reviewed reference "makes no sense" and "is simply making an error". It includes an LER number for illuminant A (see standard illuminant) truncated to 400 to 700 nm. You are right that truncation to 400 to 700 nm is arbitrary because the eye doesn't in fact cut off abruptly--there's a very long but very small tail. However, you'll have a hard time finding data on how much thermal radiation a CFL emits in the 7-14 micron range. Without that, there would be no way to find a value for the "proper" taking a purist physicist approach that you must include the whole spectrum. (I'm not going to insist that the EMI radiated at 10 kHz to several MHz be included, but the thermal radiation could easily larger than the radiation in the 400-700 nm band.) Likewise, although it's possible to calculate the LER of a blackbody at 2850 K, it would be very hard to find it for an actual incandescent lamp--it's affected by the IR transmission curve of the glass, and the thermal radiation from the glass itself, which is warmed both by convection from the fill gas and by radiation at wavelengths it absorbs....

For an idealized theoretical construct, it makes sense to include all radiation in LER. For a source like an LED, it can make sense to include all the radiation in the peak of the LED emission, whether all within 400 nm to 700 nm or not, and to neglect the thermal radiation. For a fluorescent, one would neglect thermal radiation; for the 365 nm and shorter wavelengths, I could see arguing that either way depending on context, although I think my reference neglects them. But I don't know how to do anything sensible with an incandescent lamp other than picking an arbitrary cutoff for what's visible if you want to talk about the efficiency rather than the efficacy. (Unless you just want to report efficacy in other units.)Ccrrccrr (talk) 23:24, 26 December 2008 (UTC)

Remember, you don't need a spectrally-resolved measurement over the whole spectrum. All you need is the total power emitted as EM radiation, and a spectrally-resolved measurement over the band where the luminosity function is non-zero. You can get the total radiated power over a pretty large band just by absorbing the emission and measuring temperature change. Things like absorption and thermal emission from the glass envelope of a bulb are not a problem either. They are just part of the performance of the bulb itself. There does have to be an arbitrary cutoff (you're not likely going to include RF emission, for example), but the cutoff one would use when doing this right would extend far beyond the visible band.

Ohno's truncated illuminant A is an interesting case. It would be wrong to say that the value given is an LER for the illuminant A spectrum. LER has a particular definition, and this does not comply. It's fine, however, to propose an idealized source that has the illuminant A spectrum in the visible band and no emission outside, and to calculate the LER of such a source. It makes sense for Ohno to do this, because he is modeling LED sources where the emission spectrum can be engineered. So, it's not an "LER" of an illuminant A source with the spectrum truncated in the calculation of LER. Rather, it's the standard LER of a source that is like the illuminant A source in the visible, but which has no emission outside. --Srleffler (talk) 07:37, 27 December 2008 (UTC)

You are right that Ohno calculates LER of a truncated spectrum, rather than calculating a "limited bandwidth LER" of illuminant A. Thus, it is not an example of the "limited bandwidth LER" that I am proposing to discuss here. And you are right that he's not specific about the band over which he models LED spectra, although if you look at the plots, they all pretty much go to zero by the edges of the 400 to 700 range plotted, so whether or not there is some tiny tail of energy modeled at 390 nm for a blue LED makes no significant difference to value of LER calculated. What would, however, make a large difference would be whether or not the far IR (~7 to 14 micron) was included. For an LED with 30% efficiency at producing radiation in or near the visible range, 70% of the input power is "lost as heat". Most of the leaves the LED chip via conduction; then it goes to a heat sink that delivers it to the ambient via some mixture of radiation and convection. It might be half and half convection and radiation, but even if it were only 10% radiation, that would make a 20% difference in the LER value, so it can't be neglected. As you explain above, it is possible to make appropriate measurements to find out the "true" LER, but I don't think anybody would do that for an LED, because 1) It doesn't help advance the engineering--from an engineering point of view, that IR is not part of the radiation you were producing with the engineered light production system--it's part of the waste heat that you are trying to get rid of, and 2) The results would depend on the particular heatsink configuration used. A manufacturer reporting an LER number on a datasheet would need all kinds of detail about the setup; Ohno would need models of heatsinks in the paper, and would need to specify what I'd call the efficiency of the LED, to determine how much exits as heat that might become thermal radiation. It's true that formally, the proper definition of LER includes all radiation, but maintaining that stance gets silly when the optical radiation is so clearly separated from the thermal radiation. And it's not just Ohno that quotes LER for LEDs based only on the optical radiation. As a random example, here's an LED datasheet. On p. 6, the 500 and 155 lm/W use the integral of the optical range data, shown on p. 7, and would be substantially smaller if they included thermal radiation as well. Ccrrccrr (talk) 14:43, 27 December 2008 (UTC)

What you've written makes sense. I think this is why LED manufacturers use LER and nobody else does. Since the emission spectrum of LEDs can be engineered to not extend much beyond the visible band, they are amenable to treatment using this truncated LER that considers only that direct emission. --Srleffler (talk) 18:01, 27 December 2008 (UTC)

new record for LED efficiency

As referred to in LED, Cree Achieves 161 Lumens per Watt from a High-Power LED. We should probably be consistent and edit Luminous efficacy accordingly.

We removed that from this article recently. The luminous efficacies LED manufacturers cite are not the values we tabulate here for light sources. The table in this article is the ratio of visible light output to total electrical power consumed. The values the LED manufacturers give are the luminous efficacy of the radiation emitted, i.e. the ratio of visible light output to all light emitted. One might consider this an inflated value, since it neglects any energy lost as heat, etc. Note also that manufacturer's press releases are not reliable sources. They can be used as sources for Wikipedia articles only when they meet certain conditions, including that the information not be self-serving. Inflated luminous efficacy figures probably count as self-serving.

For these reasons, we removed all of the "prototype" LEDs from the table. It's easier to verify the luminous efficacy claims of devices in actual production, especially since the datasheets usually give the light output, voltage, and current.--Srleffler (talk) 04:58, 13 January 2009 (UTC)

Correction: The manufacturer's press releases are most definitely NOT luminous efficacy of the radiation emitted as some here have mistakingly thought. They are instead the output of the source in lumens divided by the input power to the LED in watts. This is quite clear simply by reading them. The luminous efficacy of radiation emitted for a typical phosphor white LED is typically around 330 lumens per watt, while the efficacy numbers claimed by manufacturers are well below that, with 186 lumens per watt being the current record as of December 2009. —Preceding unsigned comment added by 72.229.177.183 (talk) 11:36, 13 December 2009 (UTC)

Fine. We still require a reliable source for any information to be included in the article. For all we know, Cree could simply be lying about what they have achieved in their laboratory. We have only their word for it that they have made a 186 lm/W LED. We have no evidence that anyone else has tested it and published the results, and you can't order one of these diodes from Cree and test it yourself. The article reports values that have either been published by independent, unbiased sources, or data for production units that are readily available and can be tested by anyone. The Wikipedia policies on this are Wikipedia:Verifiability and Wikipedia:Reliable sources.--Srleffler (talk) 16:03, 13 December 2009 (UTC)

No arguments from me about not considering manufacturer's press releases to be reliable sources of information. The exception might be if they allowed their laboratory prototypes to be independently tested by NIST or some other standards organization. As far as I know, the maximum efficacy of production LEDs is 150 lumens per watt, and the article agrees with me. —Preceding unsigned comment added by 72.229.177.183 (talk) 00:20, 14 December 2009 (UTC)

Absolutely, if an independent body tested the devices and published the results we could cite that publication and use the results here. In fact, Cree's own researchers could publish their results in a peer-reviewed scientific journal and that would also be acceptable. We trust the journal's editors and publishers to ensure accuracy and unbiased measurement.--Srleffler (talk) 05:39, 14 December 2009 (UTC)

Neon?

How do neon lamps and neon signs compare? -- Beland (talk) 17:39, 18 February 2009 (UTC)

Search the neon lamp article for the word "lumen". There's a paragraph there on efficiency.--Srleffler (talk) 03:57, 19 February 2009 (UTC)

Definitions again

People from the lighting field and people from the optics field use the term luminous efficacy for different things. When they see others using it differently they assume that the others are wrong. Citing an optics book to prove one vs. the other doesn't help--that only verifies that it's used that way in one field. We could have two articles--one called Luminous efficacy (optics) and one called Luminous efficacy (lighting) but that would be dumb. Or we could decide that everyone in the lighting field should change their terminology (Just kidding). But really, the best thing is to have the lead of the article explain that there are two different meanings, so that someone who ran across the term in some context can better figure out what was meant.

This has been discussed extensively--see the section on definitions above.

One thing that was left hanging in that discussion was that I thought we should note in the lead that the terminology, "luminous efficacy of a source" and "luminous efficacy of radiation" is actually recommended by an international standard. Someone took that out, and I'm not sure why. It said, at one point:

Luminous efficacy of radiation (LER) is a characteristic of a given spectrum that describes how sensitive the human eye is to the mix of wavelengths involved. The proper full names of these two different types of luminous efficacy, as recommended by international standards, are luminous efficacy of a source for the ratio of luminous flux to input power and luminous efficacy of radiation, for the ratio of luminous flux to radiant power. [1] However, these are both commonly shortened to luminous efficacy so it is often necessary to figure out which is being discussed from the context.

The recent edit referred to those terms as being used in the non-refereed literature. It's true that the paper cited is a conference paper, but it's from NIST, and it cites the international standards. And the author is project leader for photometry at NIST. If want more, here's an invited conference paper on the topic at hand: [5]

The situation is this: the generic term LE is used for both LES and LER. That's sad but true and the WP article needs to recognize that. We can also state the international standard terms, LES and LER. The fact that reputable sources use LE for one, or use it for the other, doesn't prove anything new. Ccrrccrr (talk) 00:25, 4 November 2009 (UTC)

You beat me to the revert. Yes, the article needs to explain the differences in usage between fields, not merely choose one and present it as preferred. The edit seemed rather POV-ish, in that it arbitrarily chose one source's definition over others'. The other editor's version also left the lede broken, with text that depended on ideas introduced in the part that was removed. I also think it was an outright error for it to assert that luminous efficicacy is the ratio of luminous flux to radiant power, and it should not have tied these quantities to specific units (lumens and watts). Physical quantities can be measured in various units.--Srleffler (talk) 07:12, 4 November 2009 (UTC)

Yes, thanks for picking up on a few of the more subtle problems with the edit.Ccrrccrr (talk) 12:37, 4 November 2009 (UTC)

I'm the guy with the edit. I teach radiometry at a local university and we define (and teach) efficacy based on the definitions developed by classical authors in the field such as Boyd, Grum, Nicodemus, Stimson etc. I have about 8 or 9 radiometry/photometry books and none of them use the definition related to input power consumption. However, in two of my 'optics' books, that also cover radiometry/photometry, one book uses the definition based on input power while the other uses a definition based on output radiant power, both unfortunately, termed luminous efficacy. But again, these are optics books. As for efficacy itself, the definition that relates radiant power to useful (human observed/perceived) power seems to make the most sense. Perhaps there needs to be two definitions, as you have mentioned. However, to redefine luminous efficacy LE in terms of input electrical power would mean that all the classic texts are wrong. I would leave LE in terms of radiant output power and come up with a new definition for source consumption, i.e., like what has been suggested. Just my 2 cents. Sorry for the abrupt change on my part. Let's get to the bottom of this for I am in the process of writing a manuscript for my soon-to-be published radiometry text. BTW, I know some people at NIST and will make a phone call or two to see if I can get some additional information on the state of things. Please advise. Thanks.--ejipci —Preceding undated comment added 17:22, 4 November 2009 (UTC).

I rephrased the intro to put the two uses of the term on a more equal footing. See what you think. Note that our role, as an encyclopedia, is to document actual usage, not to prescribe it. The fact that different authors use the same term for two different things is unfortunate, but it is not our place to fix that, only to explain it to the reader. As Ccrrccrr notes, we could have two separate articles, but the two concepts are so closely related that it makes more sense to cover them together, so we can compare and contrast them.--Srleffler (talk) 18:01, 4 November 2009 (UTC)

I think Srleffler's re-write is perfect. I agree with putting them on equal footing in the lead--I'm not sure how it ended up with LES being described as "most commonly". In reply to ejipci, it's not an issue of the classic texts being "wrong". It's just that when you are working within one field, you can use a term without any further qualifiers and be perfectly correct, while in another field, you can again use a term without any further qualifiers and again be perfectly correct. To give an example, if you talk to computer professionals and they say "mouse" it means something different than when biologists say "mouse". We don't need to insist that computer professionals say "computer mouse" every time, or write indignant letters to computer textbook publishers saying that they are "wrong". However, if we are writing in a context where either could be meant, it is very helpful to specify which is meant.

Both usages are very well established in some areas. What I've observed is that the lighting community and the physics community are interacting more in the solid-state lighting area, and that's where the two different usages collide. So I think there is a newly emerging need to specify more carefully -- a need that didn't exist in the classic texts. My reading of Ohno is that the CIE has deemed it useful to use LES and LER to distinguish, and that those are now official terms. My sense is that LER is a moderately widely used or at least understood term, whereas LES is really only used to make the distinction when necessary.

Ejipci, I think that if you are writing a text on this, you would want get your hands on the CIE standards and make sure you know what are the current official terms, not just what the classic terms are. Presumably you have access to good interlibrary loan through your University. Perhaps Ohno can help you identify the right sources. Standards do change--for example the curie has been replaced by the becquerel.

I quote: "I would leave LE in terms of radiant output power and come up with a new definition for source consumption, i.e., like what has been suggested." Unfortunately wikipedia editors don't get to do that. But standards bodies do. So we need to go with what they come up with.

Ccrrccrr (talk) 19:42, 4 November 2009 (UTC)

"Up to"

In the lighting efficiency examples table, discharge lamps have ranges of values (e.g. "80-100" for T8 with electronic control gear). LEDs used to have "10-150", but it's been replaced with "up to 150", which, I think, should be reverted back to a range of values. The efficacy depends on such factors as temperature, phosphor composition and phosphor aging. Totsugeki (talk) 23:15, 20 December 2009 (UTC)

I changed it because it wasn't clear to me that the low end number was still accurate. Are such inefficient white LEDs still on the market? What is the least efficient white LED now available? Feel free to add the low end back to the range, but look around for sources and update it if you can. --Srleffler (talk) 05:33, 22 December 2009 (UTC)

I had sources in the past, believe me, 10 is very high for the low number. And production changes slowly. Electronic parts can be delivered for decades. Wispanow (talk) 07:00, 22 December 2009 (UTC)

I've tested quite a few white LEDs ( see this link: http://www.candlepowerforums.com/vb/showthread.php?t=89607 ), including ones made as long ago as 2001. The worst efficacy numbers I've gotten have been in the low 20s, and none of those are still in production. If it is necessary to have a range of values in the table, then 25 to 30 would probably be a good minimum number to go with. Even extremely inexpensive, mass-produced white LEDs are matching or greatly exceeding that number these days. While true that electronic parts can be delivered for decades, in the white LED world where efficacies rise by double digit percentages each year, a manufacturer would have a hard time selling parts with the same specs as those from even a few years ago. It's pretty safe to say white LEDs with efficacies of 10 lm/W are no longer being made or sold.

72.229.177.183 (talk) 17:57, 25 December 2009 (UTC)

LED efficacy is exaggerated

The LED efficacy numbers given in the table seem to be for the emitter only, but those for CF include the circuitry to drive the fluorescent tube. This doesn't seem like a fair comparison to me. There are very few drop-in replacement LED lights that can be used in a standard mains fixture like a CF can. One of the best I know of is the GE 73716, which runs 28 lm/W. Others, particularly night lights, have very poor efficacy, almost as bad as incandescent. Rees11 (talk) 13:21, 22 December 2009 (UTC)

It wouldn't make sense to quote LED efficacy any other way because of the numerous ways they can be incorporated into a device. A CF tube by definition can only be used in its intended application with a ballast which drives it using mains voltage. There really is no other common way to use CF tubes. Therefore, it makes sense to quote the efficacy of the total system. Same thing with linear flourescent tubes. LEDs on the other hand can be driven directly from a small battery, or can use any one of many types of ballasts, depending upon the application. Some of these ballasts can have efficiencies as high as 97%-98%. This is particularly true for automotive ballasts driving series strings of 3 or more LEDs. Ballasts for use with mains voltage generally have lower efficiencies, but even here 85% to 90% is possible, although I've seen some which were worse than 50%. Given the wide range of ballast efficiencies, and multitude of applications, it makes much more sense to continue quoting the efficiencies of the LED emitters only. Another good reason for continuing to do it this way is because LED efficacy varies greatly with drive current. Usually you quote efficacy at the manufacturer's rated drive current. At higher currents efficacy degrades quite a bit, and at lower currents it is actually higher than at rated current. This makes LED efficacy highly application dependent, depending upon both ballast type and drive current. By instead quoting efficacy at standard industry drive currents ( usually 20 mA for small indicator LEDs and 350 mA for power LEDs ), you can directly compare emitters of the same type.

72.229.177.183 (talk) 18:18, 25 December 2009 (UTC)

I disagree. LED is exactly analogous to fluorescent. Both need a constant current source of some kind. This can be a passive device (magnetic ballast for fluorescent, dropping resistor for LED) or an active circuit. You can't compare just the emitter of one device to the entire system of the other device. Rees11 (talk) 01:08, 26 December 2009 (UTC)

The problem is finding some sort of standard to use if you were to do it the way you suggest. Given the wide array of LED applications, that can only result in confusion. Also, as far as I'm aware, right now the only light source where the efficacy of the ballast is a factor are CF bulbs. Even linear tubes are tested, and the ratings given, for the tube itself. Same thing for sodium vapor, HID, etc. In all cases the manufacturer rates the output of the light emitter on some sort of standardized ballast which gives the tube a known amount of power. For example, a 32 watt T8 tube is rated on a magnetic ballast which drives the tube at exactly 32 watts. The manufacturer will say the tube puts out x lumens when driven at 32 watts. The efficiency of the ballast doesn't enter into the equation except for lamp designers making a lighting fixture ( and then you also need to deal with the fixture efficiency ). So why should LEDs be any different? If anything, CF bulbs are the oddity here, but by definition it wouldn't be possible for a standards lab to rate them without their integral ballast. Now if we were to rate screw-in LED bulbs only, then I would agree with you as there would be no way to test them without their ballast. But if we're talking about LED emitters, then the ratings are given at industry standard drive currents, same as is currently done with linear fluorescent tubes. Besides that, in many LED applications the ballast will only absorb a small percentage of the input power.

A lot of the poor ratings of today's screw-in LED bulbs are due to overdriving the emitters so that you use fewer of them, and also optical losses. You can take a 100 lumen per watt LED to start. Now if you drive it at 3 times rated current you'll probably be down to 65 lumens per watt or less. Add in 20% optical losses if the light is focused, and perhaps another 15% ballast losses, and now you're around 45 lumens per watt, less than half of what the bare emitter is rated at. On the other hand, suppose you underdrive the emitters, don't need optics, and use a very efficient ballast. You could potentially end up with a bulb exceeding 120 lumens per watt. The point is that unless you're quoting the efficacy of screw-in LED bulbs, or some other type of complete LED plug-and-play fixture, it makes little sense to take the ballast into account. The line in the article is for bare LED emitters only. If someone wants to add another line for LED screw-in bulbs, then that's fine. I've actually tested a wide range of those. Efficacies range from around 15 lumens per watt to about 60 lumens per watt, and those figures include ballast and optical losses.

72.229.177.183 (talk) 04:53, 26 December 2009 (UTC)

I'm not suggesting that system efficacy is somehow a superior metric, just that all the values should be either system efficacy or emitter efficacy. If you mix the two then the table is useless.

As far as I can tell, the numbers for CF, linear fluorescent (T8 and T12), and sulfer lamp are all for system efficacy (including ballast or other electronics). The number for metal halide seems to be for the lamp only. Rees11 (talk) 21:46, 27 December 2009 (UTC)

The numbers for incandescent lamps are also for the emitter only. Same thing with the metal halide and sodium vapor lamps. Regarding the linear fluorescents, it is noted in the table that the figures include the ballast. Truth is with electronic ballasts especially the losses aren't very high. Driving a T8 tube on an electronic ballast, instead of the magnetic ballast which it is rated on, increases output by about 10% at the same power level. And incidentally the ballast losses are roughly 10% to 15%. In effect, the efficiency increase driving the tube electronically more or less makes up for the ballast losses. As for LEDs, it's fine to include ballast losses if you're talking about a complete system such as an LED screw-in lamp, and you actually added a line for that. However, on any well-designed line voltage ballast losses are only going to be around 10% to 15%. This doesn't change the overall efficacy numbers by all that much. And for DC applications, such as automotive, ballast efficiencies can exceed 96%, making the system efficacy mostly dependent upon the chosen drive current and optical losses, rather than ballast losses. Like I said, if you choose to start using system efficacy only, especially for LEDs, it quickly gets very messy and complex. There are just too many variables and ways to use LEDs. LED screw-in bulbs are only a tiny fraction of the market. Linear tubes and CF bulbs are generally only used one way-in line voltage ballast-driven applications. Ballast losses are well-known and don't differ all that much between manufacturers, so it is fairly easy to account for them.

And by the way, if you look at this link, there do exist some LED srew-in bulbs with efficacies of 75 lumens per watt or greater: http://techon.nikkeibp.co.jp/article/HONSHI/20091126/178024/ The problem right now is the huge range in values I've seen. Some are as low as 15, while others can exceed 80.

72.229.177.183 (talk) 06:51, 28 December 2009 (UTC)

Efficacy table again

I see someone has been removing the Toshiba bulb, presumably on wp:rs grounds. That's fine by me, but if we do that I think we should remove all the lights that are sourced from press releases or product catalogs. Which would be most of them.

A possible compromise might be to include them, but with a note that says the numbers come from the manufacturer. Rees11 (talk) 17:23, 3 January 2010 (UTC)

I'm not sure if that is the grounds intended. Hopefully whoever is removing it will explain their objection. Please do not remove lights just because the sources are not adequate, unless you have reason to be skeptical of the claimed efficiencies. While any editor can remove anything that is unsourced, blanket removal of unsourced material that isn't really in any doubt is disruptive.

Note that press releases are a little different from product catalogs. Neither is a reliable source, but under certain conditions we accept information that individuals or companies publish about themselves. I have argued in the past here that product catalogs and datasheets are satisfactory references for the specifications of commercially-available products, unless there is some reason to suppose that the manufacturer is being dishonest. I am more skeptical about press releases—especially when they report R&D results that are not yet ready for market. Press releases are more likely to contain inflated or misleading claims. --Srleffler (talk) 19:53, 3 January 2010 (UTC)

I agree. The edit log says "No believable lm/W given" but I don't think we can reject well-sourced material just because we don't believe it. I think the Toshiba bulb should go back in, particularly because it's the only example of a modern high efficiency LED system (not just emitter) (but see discussion on system vs. emitter above). Of course I'd like to see independent confirmation, but I don't think 93 is unbelievable, or so obviously wrong that we should reject it. Rees11 (talk) 21:03, 3 January 2010 (UTC)

I agree too, the manufacturer's data (from a suitably large and established manufacturer) should be good enough for WP: they have higher powers than us to contend with if they publish duff data on their latest products. It would be different if Toshiba were an unheard-of start-up and this their only product.

On a slightly unrelated tack, Srleffler said, "While any editor can remove anything that is unsourced, blanket removal of unsourced material that isn't really in any doubt is disruptive." I have in the past had this problem on technical articles where non-technical people just remove things they don't like even though it is obvious and indisputable to anyone who understand the topic, but technically unsourced. Is there a policy that you know of anywhere that supports such an eminently sensible guideline? --Nigelj (talk) 21:23, 3 January 2010 (UTC)

Would that there were such a policy. I've had more than one run-in with Wikipedia:Sword-skeleton theory and Randy from Boise. --Wtshymanski (talk) 21:51, 3 January 2010 (UTC)

I'm going to put the Toshiba bulb back in. Please keep a watch on this article, and if it gets removed again, try to get the editor to discuss his reasons here. Rees11 (talk) 23:31, 3 January 2010 (UTC)

According to the first reference (according to press info by Toshiba) [6] the 93 lm/W is the efficacy of the LED-chip, not the lamp. Give a detailed reference, which states the lm/W at 120V or stop reverting! I think, you will have no chance, because Toshiba likes to advertise with the lm/W of the chip.

At anybody:

• Semiconductors are usually measured at 25 °C CHIP-temperature. This is often a lot different from the chip-temperature at 25°C ambient temperature. If you look at the specifications, you will see that the efficiency STRONGLY decreases with increasing temperature.

• The chips are always covered: losses.

• Losses from the supply are not included.

• Reality and the pressure for reducing cost has additional negative effects.

As a experienced engineer, i see a need for stopping a unreal hype about LEDs or emotional fans of them. Give a detailed reference with lm/W @ 120V or stop reverting. Wispanow (talk) 09:07, 4 January 2010 (UTC)

It would help a lot if you could stop being confrontational and discuss this before reverting. Many of us, myself included, would agree to remove this if we thought the number was wrong. Rees11 (talk) 12:25, 4 January 2010 (UTC)

Here's an LED lighting fixture which manages 89 lumens per watt as tested by an independent lab: http://ledsreview.com/news/418/

It's not a screw-in bulb, but it nevertheless proves the point that LED fixtures are capable of matching or exceeding conventional light sources. Maybe we should add it to the examples?

As for the Toshiba bulb, usually when a manufacturer releases a new product, they state the lumens as verified by an independent testing agency. They don't pull these numbers out of a hat. What makes you ( Wispanow ) think the flux is for the chip only, and at a chip temperature of 25°C? Frankly, if that's the case, then Toshiba shouldn't be bragging as 93 lm/W in cool white was state of the art about 3 years ago. Look at this article: http://ledsreview.com/news/367/ There's a chart which states the input power, flux, CRI, lifetime, and price. The price applies to the complete bulb, as I'm sure the other figures do also. Toshiba could get into a lot more trouble than violating Wikipedia policy by overstating the efficacy, as could anyone selling the lamp. Also, as one who has tested over two dozen of these screw-in LED lamps, I find the 93 lm/W figure entirely believeable, especially with the huge heat sink they're using. The best lamp I tested so far managed close to 60 lm/W. That's under real world conditions, after I let it warm up for an hour, and includes ballast and optical losses. And my testing methods are conservative as my tests of a standard 40 watt incandescent actually gave me lower numbers than what the package said. Given all that, 93 lm/W using state of the art LEDs isn't much of a stretch. I'm already talking with the person I did the testing for about making a 100+ lm/W LED bulb using CREE XP-Gs. Based on my test numbers for the bare LED, and estimation of ballast/optical losses, it seems quite feasible.

Finally, I'll grant your point about the hype regarding LEDs and the need to test manufacturers claims. On the flip side of that, there is a growing contingent who insist LED lighting will never be able to compete with conventional sources. I'm an engineer also, and work with LEDs on a daily basis. I know exactly what they're capable and not capable of doing. For example, if someone released an LED screw-in lamp claiming 150 lm/W, I would be very skeptical. Such performance just isn't possible using today's LEDs, even if you underdrive them, once you include ballast and optical losses. What I'm really a lot more skeptical of than flux claims are lifetime claims. I've tested some LED lamps which faded to under 70% of initial output after 2 weeks. Those are usually the ones using small indicator-type LEDs, as opposed to a few larger power LEDs. The latter actually can last 50,000+ hours under real-world conditions. So yes, healthy skepticism is in order here, but we also need to be open-minded. LEDs are advancing quite rapidly. Claims made today for new products might on the surface seem ridiculous if you don't follow developments regularly.

72.229.177.183 (talk) 13:09, 4 January 2010 (UTC)

I found product literature for Toshiba LED lighting: http://www.toshiba.co.jp/lighting/products/pdf/english/TOSHIBA_LED_LightingLiterature.PDF ( see page 2 ). While this literature doesn't have the lamp in question, they have a 4.3 watt, 84 lm/W lamp. This should hopefully settle the argument regarding the validity of the 93 lm/W claim for Toshiba's newest LED lamp. I also found a picture of the box the 8.7 W lamp is being sold in: http://www.akaricenter.com/hakunetu/toshiba/lel-aw8n.htm Again, I hope this finally settles the argument. Note the 810 lumens and 8.7 watts stated right on the box.

72.229.177.183 (talk) 13:27, 4 January 2010 (UTC)

Reference error and misunderstanding: I spoke from the 8.7 Volt LED-package, which was described in the first reference. The second ref weren't better. Finally it turned to be a 8.7 Watt bulb, which is now believable. Wispanow (talk) 15:25, 4 January 2010 (UTC)

@72.229.177.183: "As for the Toshiba bulb, usually when a manufacturer releases a new product, they state the lumens as verified by an independent testing agency.": Do you have experience, a reference or just having a nice dream? I never heard from such a company. I would be thankful for info; this would change everything. Wispanow (talk) 15:36, 4 January 2010 (UTC)

It's my understanding that the lumens numbers on light bulb packages are obtained from independent photometric testing. See here for the applicable standards in Canada ( USA has something similar but I couldn't find a source ): http://oee.nrcan.gc.ca/regulations/bulletin/lighting-products-dec08.cfm?attr=4 Note however that this independent verification usually only applies if lumens is stated on the package. There are many LED bulbs out there with claims on the package such as "As much light as a 60 watt bulb with only 5 watts". Legislation is being drafted to address this problem, and require honestly in labeling for LED bulbs. In my opinion, the sooner this happens, the better. 72.229.177.183 (talk) 16:21, 4 January 2010 (UTC)

Do we really need to extend LED efficacy below that of incandescent lamps? No-one is going to sell a general lighting product with lower efficacy than an incandescent bulb. --Wtshymanski (talk) 17:15, 4 January 2010 (UTC)

Efficacy table again #2

Thank you. Lucky Canada. In Germany (and Europe) testing of consumer products COULD be made, and COULD be made according to rules (DIN), but is nearly ever made by the manufacturer. But even in Canada: The testing agency is not really independent? Paid from a big company? And: What is the punishment if the figures are only achievable in very rare conditions, like -20°C or only with one percent of specially selected products?

"No-one is going to sell a general lighting product with lower efficacy than an incandescent bulb.": Sold [7] Wispanow (talk) 17:41, 4 January 2010 (UTC)

Note that the link you provided says "available until stock exhausted", and with a very low quantity in stock. I think it's pretty obvious that this LED is no longer being manufactured, probably hasn't been for a long time, and therefore shouldn't be included in the table as an example. Given the extensive testing I've done on white LEDs, including ones made as early as 2001, I think the minimum number in the table should be 20 or 25. I've yet to test a white LED which didn't manage at least that. Nowadays even the extremely inexpensive ones manage 30s or even 40s.

And regarding the testing agencies, yes, they're independent. If they were found to fake results for payment, they would likely cease to be accredited testing agencies. They also have to use procedures and equipment which is NIST traceable. And there are certain conditions they must test under, so that can't game the results by testing under ideal conditions. 72.229.177.183 (talk) 17:56, 4 January 2010 (UTC)

Three reasons:

1. It is manufactured.Toshiba TLWA1100
2. This page lists not only current and future products, but also past products. It is not described as "current examples" but examples.
3. For the same reason 150 lm/W is listed, be happy as a fan of high figures. Otherwise i take the efficacy at 100°C, which is 2.3 lm/W see datasheet Wispanow (talk) 13:09, 5 January 2010 (UTC)

Every time I follow one of these links I wind up at loose diodes , not a screw-in lighting product; and I don't even see "lumens" tabulated, just "candelas". Are these not pilot light products, not aimed at replacement of general service incandescent and fluorescent lamps? --Wtshymanski (talk) 14:30, 5 January 2010 (UTC)

There is nearly NO product aimed at replacement of general service incandescent and fluorescent lamps ! The high power, temperature and radiation are causing problems today. And candelas are a lot better for the manufacturer: If the efficacy is too low, he just bundels the light. The above discussed Toshiba with the very high 93 lm/W (and this is manufacturers data) is one of the few i know. Wispanow (talk) 15:19, 5 January 2010 (UTC)

Yes, those are pilot light products, not general illumination LEDs. Also, they are UV LED/RGB phosphor, which is atypical, and far less efficient than the much more common blue plus yellow phosphor whites. The existence of a data sheet doesn't prove they're still being manufactured. I can dig up data sheets for parts which ceased production decades ago. Given the high price and very poor specs, they would have a tough time selling these when you can buy much brighter LEDs in the same type of package for 1/20th as much from just about any electronics distributor. If we're going to have examples, then let's have examples typical of what is actually being mass produced on both the low end and high end, not cherry pick the worst and best possible examples, or in the best and worst possible operating environments, or examples made in tiny quantities for niche uses ( which is most likely the case for the TLWA1100 LED ). If that's the case, then I'm actually aware of Nichia having a 250 lm/W prototype which the author of this article confirmed despite my skepticism: http://spectrum.ieee.org/semiconductors/optoelectronics/the-leds-dark-secret/2 Maybe we should add this to the examples as a counterpoint to the very poor example chosen to represent the lower end of the LED efficacy range? As I've said, I work with white LEDs on a daily basis, and have yet to see any which are that inefficient, either in the past or the present. And no, I'm not a fan of high figures, only realistic ones. If someone stuck 300 lm/W in the examples, I can assure you I would remove it as soon as I saw it. 72.229.177.183 (talk) 15:28, 5 January 2010 (UTC)

"Testing in something like real-world general lighting conditions, not on a helium-cooled solid-silver heatsink pulsed for 0.1 ms?" If they have such high efficacy in REAL WORLD EXAMPLES, everywhere are independent testers, give me a source which measured this. Wispanow (talk) 16:27, 5 January 2010 (UTC)

http://www.compoundsemiconductor.net/csc/news-details.php?cat=news&id=37614 72.229.177.183 (talk) 16:51, 5 January 2010 (UTC)

Citable Data for LED Retrofits

The US Department of Energy has a program ("CALiPER") that evaluates solid-state lighting products on the market: [8]. Their reports have nice, independent, citable measurements. Benchmark reports: [9] [10] [11]. For example, LED lamps designed to replace linear fluorescents had measured efficacies from 19 to 42 lm/W. Omnidirectional screw-in LED lamps had efficacies from 13(!) to 62 lm/W. Totsugeki (talk) 04:46, 5 January 2010 (UTC)

This is wonderful. Thank you. As i thought: most data, especially for LEDs, are too high. I think these ranges should be listed as a example. Especially T8 / T12 (T5 should be the same) buyers of LED replacements are betrayed. Wispanow (talk) 14:46, 5 January 2010 (UTC)

More data here Wispanow (talk) 14:49, 5 January 2010 (UTC)

A great reference...testing in something like real-world general lighting conditions, not on a helium-cooled solid-silver heatsink pulsed for 0.1 ms. (YEAH ! Wispanow (talk) 15:21, 5 January 2010 (UTC))

We should maybe have two lines for efficacy of bare LED diodes and another for solid-state lighting products quoting the Department of Energy "Caliper" results. Of course then we will get someone tagging the article as not reflecting a world-wide view, to which I say "Dig up comparable results from some other country". SOmetimes the American taxpayers get good value for their money. --Wtshymanski (talk) 14:55, 5 January 2010 (UTC)

Absolutely right. But not two tables: just adding the span of the results. And: This are NO special american results! Don't think Europe/China/Japan has any different manufacturer. I even added a comment to the white led example.Wispanow (talk) 15:25, 5 January 2010 (UTC)

Regarding changing the data for T8s/T12s, remember that the CALiPER source includes fixture efficiency in their efficacy calculations, whereas the examples table has data for a bare tube running on a ballast. If we're simply directly comparing light sources, which seems to be the point of the examples table, then it makes no sense to include fixture efficiency for any light source, especially given how widely fixture efficiencies vary. I'm not even sure it makes sense to include ballast losses, but in some cases, such as CF bulbs and LED bulbs, there just isn't a viable alternative, and it is noted that ballast losses are included. 72.229.177.183 (talk) 15:42, 5 January 2010 (UTC)

Ballast losses should be included NORMALLY, because some don't need any ballast, some need costly and probably lossy ones. Wispanow (talk) 16:22, 5 January 2010 (UTC)

If so, then we need to include them for all of the discharge lamps. Most of those figures in the examples are for the lamps only. 72.229.177.183 (talk) 16:52, 5 January 2010 (UTC)

Multiple entries for white LEDs sounds like a good idea. E.g. white lED diode only, screw-in omnidirectional retrofit, linear fluorescent retrofit, halogen spot retrofit. Cite CALiPER measurements for the retrofit values. White LED diode only results could be cited from datasheets. Totsugeki (talk) 18:40, 5 January 2010 (UTC)

So with all this discussion of citing the Caliper results and not mfrs' datasheets and press releases (which caliper shows aren't reliable), why is the table dominated by the latter? Are people editing the page who are not participating in the discussion here? Ccrrccrr (talk) 23:32, 21 February 2010 (UTC)

What system of units?

The "Efficacy and efficiency" section begins

In some other systems of units, luminous flux has the same units as radiant flux.

without referring to a specific system of units which have the same flux units (i.e. what other is relative to), or specifying which systems that don't. I don't know the answer to either, but this ought to be be specified. Mumiemonstret (talk) 15:40, 6 September 2010 (UTC)

Radiation vs source

If I have a hypothetical 100 watt (input) light source that gives off 10 watts of 555 nm light, 10 watts of infrared, 10 watts of ultraviolet, and 70 watts of heat, its efficacy as a source (LES) is 10*683/100 = 68.3 lumens/ watt. However, the mix of EM radiation it produces has an LER of 10*683/30 = 227.7 lumens/watt. The numbers are significantly different and that's why it's very important to say which one you mean, especially in a press release from Binford Labs claiming their new white LED produced "300 lumnes/watt" efficacy. --Wtshymanski (talk) 19:05, 27 October 2010 (UTC)

Luminous efficacy over time

It'd be nice to graph the state of the art in luminous efficacy over time (as technology has advanced, not as product has aged). It'll be a gag to look back at data like this (Archive) over time. --Elvey (talk) 00:23, 29 December 2010 (UTC)

Measure of visibility

I'd like to say something in the lead like "Luminious efficacy is a measure of the visibility of the energy emitted by a source." Or something like that. We're measuring how well we can see the energy (well, power) coming out. Hotwire bulb, we can see 17 lumens coming out of every 100 watts we put in. Wonder LED, we might see 200 lumens for every watt we putt in. Radio transmitter or far UV LED or hot stove, we see 0 lumens no matter how many watts we put in. Comments? --Wtshymanski (talk) 20:54, 7 April 2011 (UTC)

I like the spirit of that, but I think that the wording you chose works for LER, but not LES. LES combines the efficiency of the apparatus with the visibility of the spectrum, whereas LER could be said to only capture the visibility of the spectrum (trying to use similarly somewhat non-technical language). I encourage you and others keep working on that idea.Ccrrccrr (talk) 03:02, 8 April 2011 (UTC)

Yeah, just once I'd like to write a fully general true statement on Wikipedia without getting lost in our usual forest of subordinate clauses. I think we can qualify this later on; by saying it this way we get rid of the wickedly abstract "lumens" and focus on the point of the discussion, which is "how well can we see given thus-and-so power input". The research continues.

How about "Luminous efficacy is a measure of how well a light source produces visible light." Oh, I like that. And we don't need blue links to explain the first sentence of the article! (and it's fully general...you can interpres "light source" as the radiation, or as the light bulb!) I'm going for it. --Wtshymanski (talk) 16:30, 8 April 2011 (UTC)

I like too. Bravo!Ccrrccrr (talk) 21:36, 8 April 2011 (UTC)

Rephrasing things in active voice often makes them sound much better. If Einstein thought physics should be clear to a barmaid, we've got a long way to go for most articles. --Wtshymanski (talk) 21:54, 8 April 2011 (UTC)

Need table references and comments for OLED (Organic Light-Emitting Diode) lighting

A request to add data for OLEDs was made by 192.131.85.207 / 192.131.85.210. Request removed from article content, and added here. Does anyone have any decent sources? Rwessel (talk) 21:48, 19 July 2011 (UTC)

I added a request at Talk:Organic_light-emitting_diode.Imgaril (talk) 15:48, 12 September 2011 (UTC)

Source of the efficacy graph

The citation for the Cathodoluminescence light pointed to a commercial website. A real citation is needed, at the very least from a known manufacturer. — Preceding unsigned comment added by 129.132.133.141 (talk) 15:47, 19 December 2012 (UTC)

I cannot find any source of description of data generation to the graph File:Blackbody efficiency.png. The description page does not say anything about the method. Background for the question is a simular calculation I did using the CIE data and equations, which suggest a peak at 6600 K, not 7000 K. Even switching to the CIE 1978 curve rather than the standard reference CIE 1931 does not shift the peak noticably. However, my calculations actually do fit the 251 lm/W for the truncated 5800 K blackbody (see Luminous efficacy#cite_note-ideal-white-7) as well as other values from the literature, so that I tend to trust them more than the graph in question.--SiriusB (talk) 14:49, 13 December 2011 (UTC)

Update: I have uploaded my results as SVG image, scaled for efficacy rather than efficiency, but with an auxiliary scale for the latter, and ranging up to 16000 K:

— Preceding unsigned comment added by SiriusB (talk • contribs) 15:05, 14 December 2011 (UTC)

The source "TJ KEEFE nature of light" has ceased to exist. I have been googling for an hour or so now, and all I can find is links to same place wiki links to, or links to wiki. The original has been taken down and the author's homepage has been last updated 2005. — Preceding unsigned comment added by 194.251.142.28 (talk) 14:12, 7 January 2013 (UTC)

A more useful measure of lighting efficiency

I'd like to quote the efficiency of an artificial light source as a percentage, but I don't want "100%" to mean "Green light at 555 nm" as nobody would want to illuminate their kitchen or living room with that kind of radiation. I'd like "100%" to mean the theoretical maximum that could be achieved with the same visible colour as the source I am evaluating. Of course, I'm not quite sure how "visible colour" should be defined here. Is the same "colour temperature" good enough, or do should we insist on an identical spectrum over the range of wavelengths that might be visible for a human? In any case, is there a standard term for what I want? — Preceding unsigned comment added by 217.140.96.21 (talk) 15:59, 7 January 2013 (UTC)

One thought that occured to me would be to include "%age of input power emitted as heat/UV", where cursory searching lets me get something like {blackbody emitter at 2000K=incandescent: 97.5%, at 3000K=halogen: 85%, at 6600K=star: 40% (wolfram alpha); LED: 87-90% and T5 fluorescent: 73% (http://lumiversal.net/upload/T5%20v.%20LED.pdf); Low pressure sodium: 60% (calculated by me)}—Lidnariq (talk) 19:05, 22 January 2013 (UTC)

About "promotional" content

Cree has announced a new led with a luminous efficiency of 276lm/W. Since the quoted phisorg link is quite outdated, I had updated the link wich speaks about the theoretical limit to point to cree press release http://www.cree.com/news-and-events/cree-news/press-releases/2013/february/276-lpw

The post has been removed as it had been marked ad "link to promotional press release". While I agree this information is not verified, nonetheless it deserves to be mentioned as the result is close to the theoretical limit. — Preceding unsigned comment added by 193.203.232.5 (talk) 15:35, 6 March 2013 (UTC)

Colouring of graph "spectral radiance of a black body"

The colours of the lines in the graph "spectral radiance of a black body" is confusing. The grading should go from red to blue for increasing temperature of the radiating body. In the graph the reverse is used. −Woodstone (talk) 11:18, 26 April 2013 (UTC)

I don’t think the graph uses the colors that way at all. The light blue and black lines would make no sense in that context. I think it’s just five colors intended to be visually distinctive. Rwessel (talk) 09:50, 27 April 2013 (UTC)

Of course, that's what I gathered. Nevertheless the random choice turns out most unfortunately. It is distracting when looking at the graph. Even no colouring would be better, since the lines do not intersect. −Woodstone (talk) 10:17, 27 April 2013 (UTC)

Since the colors were meaningless, I changed it to a uniform color. Dicklyon (talk) 06:17, 30 July 2013 (UTC)

Should be "Artificial source"

While the term Luminous efficacy could also refer to natural light sources, the article is only concerning artificial light sources. It's well documented that the firefly approaches 100% efficiency through its bio-luminescence. Perhaps this should be added to the article, as well as references to the 2013 publications which used processes derived from natural light sources to improve luminous efficacy? 99.157.75.6 (talk) 04:46, 14 May 2015 (UTC) Jonathan W

The lighting efficiency section already constrains itself to artificial sources, while much of the preceding section (all the black body stuff) really applies to anything. While Luciferase is, in isolation, quite efficient, you need a source for ATP and luciferin, neither of which can be generated without energy input. OTOH, the article could use some reference to biochemical processes (artificial or not). Rwessel (talk) 06:34, 14 May 2015 (UTC)

Commercial Bias?

The chart on this table has citations which link to product pages, most of which are moved. The chart also represents LED bulbs as more efficient than CFLs on the consumer level, but the opposite more often true. I don't know where these figures came from, but they seems designed to sell new LED bulbs which in most cases are less efficient than CFLs. Maybe i'm just cynical. — Preceding unsigned comment added by 24.10.125.31 (talk) 19:44, 6 December 2013 (UTC)

I agree. in particular:

4.1 W LED screw base lamp (120 V) 	58.5–82.9[25] 	8.6–12%
5.4 W LED screw base lamp (100 V 50/60 Hz) 	101.9[26] 	14.9%
6.9 W LED screw base lamp (120 V) 	55.1–81.9[25] 	8.1–12%
7 W LED PAR20 (120 V) 	28.6[27] 	4.2%
7 W LED PAR30 (110-230 V) 	60[28] 	8.8%
8.7 W LED screw base lamp (120 V) 	69–93.1[25][29] 	10.1–13.6%

All this information is superfluous as an LED light source is scalable in power without impacting efficiency. The variation of efficiency in these light sources is simply due to the design decisions the engineers made when building these specific products and in no way is applicable to LEDs, light sources, or luminous efficacy in general.Nick Hill (talk) 23:33, 29 July 2015 (UTC)

Lighting-efficiency Examples does not seem to cover cold-cathode fluorescent lamps

as cold-cathode fluorescent lamps widely used in LCD monitor/TV backlights. - Rod57 (talk) 19:10, 28 September 2015 (UTC)

Maximum efficacy of a white light source

"Ideal 5800 K black-body, truncated to 400–700 nm (ideal "white" source) = 251 lm/W" and "Theoretical limit (white LED with phosphorescence color mixing) = 260-300 lm/W"

If I get that right, only one of them can be true, right? Kinaro7 (talk) 19:45, 29 July 2013 (UTC)

I don't think they obviously conflict - the black body number is from filtering a black body, which (by definition) produces radiation over a broad spectrum, so that only the "white" light is visible, thus throwing away nearly two thirds of the emitted photons. Phosphors, OTOH, emit photons in vary narrow ranges of energies, so a well chosen mix of phosphors could, theoretically, not emit any light outside the nominal 400-700nm spectrum that is "white light", and the efficiency numbers would be that of the underlying LED (that's stimulating the phosphors), the efficiency of doing that stimulation, and the efficiency of the photon re-emission by the phosphors, but would not include an inefficiencies due to emitting non-useful photons (as does a black body). OTOH, I don't understand the physic well enough to comment on what the actual numbers are, although both seem reasonably cited. Rwessel (talk) 05:17, 30 July 2013 (UTC)

I agree. The point is that with more flexibility of spectrum you can be more efficient than the most efficient blackbody. What's less clear is what the actual theoretical limit is. It could be calculated, but only if the chromaticity of acceptable "white" was bounded first. Dicklyon (talk) 06:05, 30 July 2013 (UTC)

Ah, I get it. An LED isn't even a thermal emitter. How would you calculate the theoretical limit (lm/W) for a white (380 nm - 780 nm) light source, that doesn't emit any other wavelengths? Kinaro7 (talk) 13:49, 2 August 2013 (UTC)

The most efficient thing one could build would be two monospectral light sources that just so happen to be perceived by the eye as white. Of course, the color rendering index will be awful. To calculate this limit, pick two points on the outside of the CIExy curve that connect through the white center, look up their efficiencies, then divide by the total power of both sources.—Lidnariq (talk) 20:56, 24 November 2013 (UTC)

I think for the casual reader (that is, somebody with limited background in lighting topics), it might be clearer to show the human eye response curve and then describe several monochromatic light sources at different frequencies, where each monochromatic light source is theoretically ideal and converts 100% of the input energy to photons. Each is 100% "efficient" at converting electrons to photons, but only the 555 nm source has 100% luminous efficiency and 100% luminous efficacy. This could then be a stepping-stone to the discussion about white light -- as noted above, white light can be produced with various perceived color temperatures, and a given perceived color temperature may be made of varying combinations of light colors; using a wide range of source light colors is desirable for improved CRI but may require production of wavelengths with low luminous efficiency/efficacy; and in the end the overall efficiency/efficacy will be reduced as the fraction of high-efficacy wavelengths is reduced and the fraction of low-efficacy wavelengths is increased. — Preceding unsigned comment added by 50.0.151.165 (talk) 22:25, 16 January 2016 (UTC)

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Maximum efficacy for CRI=95

Regarding this edit: I did look at the reference. It does not support the claims in the article. The reference does say "For instance, we can demand a CRI of 95 and seek the highest $\eta _{S}$ that can result from a blackbody function truncated by...", but then it goes on to say "...The Planckian offset exceeds 5.4 × 10⁻³ for CRI values below ~94, at which point the spectral luminous efficacy is $\eta _{S}\approx 310\ {\text{lm/W}}$." [emphasis mine] This does not support the claim in the Wikipedia article that the maximum efficacy at CRI=95 is 310 lm/W, because the cited reference explicitly says that this is the efficacy at CRI=93.9 (per the text in figure 5).

Similarly, figure six in the reference explicitly contradicts the claim in the article that the maximum efficacy for CRI 95 at 2800 K is 370 lm/W. From the figure, the efficacy is 370 lm/W for CRI = 87.4. The efficacy at CRI = 95 is only about 330 lm/W.--Srleffler (talk) 16:35, 22 December 2018 (UTC)

Furthermore, I'm not convinced that it comes close to showing that that's the maximum possible with any spectrum. Rather it's just the best they could to within the family of truncated blackbody spectra. And they didn't even try the CRI limited experiment at the ~4000 blackbody temperature that would give the best results.Ccrrccrr (talk) 03:21, 11 February 2019 (UTC)

And here's a reference with, perhaps, the real answer, perahps Hung, Po-Chieh, and Jeffrey Y. Tsao. "Maximum white luminous efficacy of radiation versus color rendering index and color temperature: Exact results and a useful analytic expression." Journal of Display Technology 9.6 (2013): 405-412.

Didn't have access to that one but this one is useful: Spectral optimization simulation of white light based on the photopic eye-sensitivity curve, J. Appl. Phys. 119, 053103 (2016); https://doi.org/10.1063/1.4941396, Qi Dai, Luoxi Hao, Yi Lin, and Zhe Cui. They optimize a three-peak source with a constraint of CRI = 90 and obtain LER of 390.4 at CCT 2800, 371.4 at 4000K, and 330.5 at 6500. Ccrrccrr (talk) 03:57, 11 February 2019 (UTC)

I removed the asymmetrically truncated entries again. As I state above, the 2800 K one was not supported by the reference, and this was not fixed by Ccrrccrr's edit. Ccrrccrr did fix the asymmetrically truncated 5800 K entry, but It's such an arbitrary set of conditions that I don't see it as worth including in this table. A value that is a proven optimum efficiency for a given CRI might be worth mentioning, but this is not that.--Srleffler (talk) 05:53, 11 February 2019 (UTC)

I agree that the truncated blackbody spectra are just weird hacks. Maybe their relatively high efficiency at high CRI is interesting for a three-parameter spectrum, but it should be easy to beat with an optimized spectrum. Looks like that Hung & Tsao paper would have the answer. Dicklyon (talk) 06:58, 11 February 2019 (UTC)

That paper is available as PDF on Google Scholar. It shows that the optimum spectra are "spiky", no doubt an artifact of the CRI being defined by a small set of discrete spectra. I would be good to also see how close a smooth spectrum can come to being as efficient, and whether it looks like a truncated blackbody in that case. Anyway, interesting but not very encyclopedic primary-source stuff so far. Dicklyon (talk) 07:09, 11 February 2019 (UTC)