maximum luminous efficacy, <for a specified photometric condition>

K_m, <for photopic vision>;  , <for scotopic vision>; K_m,mes;m , <for mesopic vision>; K_m,10 , <for the CIE 10° photopic photometric observer>; K_m,M , <for the CIE 1988 modified 2° spectral luminous efficiency function for photopic vision>

maximum value of spectral luminous efficacy for a specified photometric condition

Note 1 to entry: The photometric condition should be specified (e.g. photopic, scotopic, mesopic). If it is not specified, photopic vision is assumed and the symbol K_m is used. For other photometric conditions the respective symbol for identification shall be used.

Note 2 to entry: The value of maximum luminous efficacy for photopic vision is calculated by

where V(λ) is the spectral luminous efficiency for photopic vision and λ_cd is the wavelength in air corresponding to the frequency 540 × 10¹² Hz specified in the definition of the SI unit candela.

Note 3 to entry: The maximum luminous efficacy is expressed in lumen per watt (lm⋅W⁻¹).