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November 30

Little experiment to determine whether it's worth having blinds/curtains open in the day in winter

I'm interested in whether the heat from the sun on cold, overcast days in northern England is worth having the blinds open for during the winter. I reckon it is but my mother reckons it isn't. My plan to determine this experimentally is to use an Arduino or similar to record the temperature on the windowsill every five minutes and store it on an SD card. I thought it could also be interesting to record the light intensity (I would probably measure that every 15-30 seconds and store an average alongside the temperature). My question is what should I use to measure the light intensity? I know that LEDs will generate a small voltage but I also have some photodiodes (if I can find them) or maybe just a CdS light-dependent resistor, assuming that it doesn't max out too easily. Or would something else entirely be much better? The heating would not be on for the duration of the experiment. --05:58, 30 November 2023 (UTC) 92.7.46.126 (talk) 05:58, 30 November 2023 (UTC)[reply]

The outcome will be dependent on the insulation value of the windows. Undoubtably direct sunlight coming in will contribute some heat (this is a commonplace observation I often make at my partially glazed front door), but this may or may not be negated by more heat radiating or conducting out (I will charitably assume no actual draughts). Any light-intensity measuring instruments you use need to be able to capture infrared as well as visible light – specifically photographic instruments may not. {The poster formerly known as 87.81.230.195} 51.194.245.32 (talk) 08:21, 30 November 2023 (UTC)[reply]

I'm pretty sure that on a typical Western European overcast winter day (I'm in the Netherlands), the thermal radiation from the clouds exceeds the sunlight by a comfortable margin, but the outgoing thermal radiation is even more. When sitting at a north facing window, clear days feel a lot colder than overcast days at the same temperature. Of course, good, modern windows are supposed to be fairly reflective in the infrared, but taking infrared into account may be useful. It will vary with the height (and therefore temperature) of the cloud base, but not by a huge amount. Semiconductor-based light sensors have some cut-off; above the wavelength corresponding to the band gap of the semiconductor they can't detect light.

FYI: I would take two rooms, one with the blinds/curtains open, the other closed, and record temperature during the day. Next day with identical weather, swap the roles of the rooms to compensate for differences in window size and room heat capacity. PiusImpavidus (talk) 10:16, 30 November 2023 (UTC)[reply]

To obtain data that can be properly used to draw a conclusion, the experiment should also be repeated on several days, preferably under varying weather conditions (outside temperature, precipitation, wind factor, sky coverage). There should be some effect; see also Greenhouse § Theory of operation. Before you engage in performing this non-trivial experiment, you should decide for which size of the effect you will consider it "worth" having the blinds/curtains open. --Lambiam 12:20, 30 November 2023 (UTC)[reply]