# e-ILV

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# 17-21-029

spectral distribution

spectral concentration

Xλ

density of a radiant or luminous or photon quantity, X(λ), with respect to wavelength, λ, at the wavelength λ

Note 1 to entry: The term "spectral distribution" is to be preferred to the equivalent term "spectral concentration" when dealing with the function Xλ(λ) over a range of wavelengths, not at a particular wavelength.

Note 2 to entry: Usually Xλ is also a function of λ and in this case, in order to stress this, can be written Xλ(λ) without any change of meaning.

Note 3 to entry: The spectral distribution of radiant flux is expressed in watt per nanometre (W⋅nm−1), the spectral distribution of luminous flux is expressed in lumen per nanometre (lm·nm−1), the spectral distribution of photon flux is expressed in nanometre to the power minus one (nm−1). The units of spectral distributions of other quantities are expressed accordingly.

Note 4 to entry: The quantity X can also be expressed as a function of frequency, ν, wavenumber, σ, etc.; the corresponding symbols are X(ν), X(σ), etc. and the corresponding densities with respect to frequency, ν, wavenumber, σ, etc. are Xν, Xσ, etc., in which case the expression of units will also change accordingly.

Note 5 to entry: This entry was numbered 845-01-17 in IEC 60050-845:1987.

Note 6 to entry: This entry was numbered 17-1213 and 17-1212 in CIE S 017:2011.

Publication date: 2020-12