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 It is superseded by ISO 80000-7.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 The standard was ultimately withdrawn in 2008, when it was replaced by ISO 80000-7.[1]
The definitions of ISO 31-6, as defined in 1980, included:[2]
| 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.[a] 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 | |||
