Note 1 to entry: Most photometers are designed to simulate the spectral luminous efficiency for photopic vision, V(λ), and are calibrated using a source corresponding to CIE standard illuminant A. For such a photometer, the spectral mismatch correction factor can be calculated using the equation:

${\displaystyle F^{*}=\frac{{\displaystyle \underset{\lambda }{\int }S(\lambda )V(\lambda )\text{d}\lambda }}{{\displaystyle \underset{\lambda }{\int }S(\lambda )s_{\text{rel}}(\lambda )\text{d}\lambda }}\frac{{\displaystyle \underset{\lambda }{\int }{S}_{\text{A}}(\lambda )s_{\text{rel}}(\lambda )\text{d}\lambda }}{{\displaystyle \underset{\lambda }{\int }{S}_{\text{A}}(\lambda )V(\lambda )\text{d}\lambda }}}$

where s_rel(λ) is the relative spectral responsivity of the photometer and S(λ) and S_A(λ) are the respective relative spectral power distributions of the source to be measured and CIE standard illuminant A.

Note 2 to entry: The term "colour correction factor" is no longer used.

Note 3 to entry: The term spectral mismatch correction factor can also be applied to other detectors whose response is intended to simulate a particular observer function, such as actinic radiometers.

Note 4 to entry: The spectral mismatch correction factor has unit one.