spectral luminous efficacy, <for a specified photometric condition>

K(λ), <for photopic vision>; K′(λ), <for scotopic vision>; K_mes;m(λ), <for mesopic vision>; K₁₀(λ), <for the CIE 10° photopic photometric observer>; K_M(λ), <for the CIE 1988 modified 2° spectral luminous efficiency function for photopic vision>

product of spectral luminous efficiency and maximum 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(λ) is used. For other photometric conditions the respective symbol for identification shall be used.

Note 2 to entry: Spectral luminous efficacy for photopic vision is expressed by
K(λ) = K_m V(λ)
where K_m is maximum luminous efficacy, V(λ) is spectral luminous efficiency and λ is wavelength.

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