ISO 31-6

ISO 31-6 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to light and related electromagnetic radiations. It is superseded by ISO 80000-7.

ISO 31-6 was initially published in 1980, and amended in 1985. It received a revision in 1992, which was amended in 1998. The standard was ultimately withdrawn in 2008, when it was replaced by ISO 80000-7.

Definitions

The definitions of ISO 31-6, as defined in 1980, included:

Quantity		Unit			Remarks
Name	Symbol	Name	Symbol	Definition
frequency	f, v	hertz	Hz	1 Hz = 1 s−1
circular frequency	ω	reciprocal second, second to the power of minus one	s−1
		radian per second	rad/s
wavelength	λ	metre	m
		ångström	Å	1 Å = 10−10 m	1 Å = 10 nm
wavenumber, repetency	σ	reciprocal metre, metre to the power of minus one	m−1		The multiple cm−1 is often used.
circular wavenumber, circular repetency	k
velocity (speed) of propagation of electromagnetic waves in vacuo	c, c0	metre per second	m/s		c = (2.99792458 ± 0.000000012) × 108 m/s. Sometimes c is used for the phase velocity in a medium, in which case c0 is used for the velocity in vacuo.
radiant energy	Q, W, (U, Qe)	joule	J	1 J = 1 kg·m2/s2
radiant energy density	w, (u)	joule per cubic metre	J/m3
spectral concentration of radiant energy density (in terms of wavelength), spectral radiant energy density (in terms of wavelength)	wλ	joule per metre to the fourth power	J/m4
radiant power, radiant energy flux	P, Φ, (Φe)	watt	W	1 W = 1 J/s
radiant energy fluence rate	φ, ψ	watt per square metre	W/m2
radiant intensity	I, (Ie)	watt per steradian	W/sr