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

$K_{\text{m}}=\frac{\text{683}}{V\text{(}{\lambda }_{\text{cd}}\text{)}}\text{cd}\cdot \text{sr}\cdot {\text{W}}^{-\text{1}}\approx 683\text{ lm}\cdot {\text{W}}^{-1}$

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).