maximum luminous efficacy, <for a specified photometric condition>
Km, <for photopic vision>; , <for scotopic vision>; Km,mes;m , <for mesopic vision>; Km,10 , <for the CIE 10° photopic photometric observer>; Km,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 Km 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 λcd 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).