Luminous Flux

The time rate of flow of radiant energy, evaluated in terms of a standardized visual response. Unless otherwise indicated, the luminous flux is defined for photopic vision. For scotopic vision, the corresponding spectral luminous efficiency function, V'(λ), and the corresponding maximum spectral luminous efficacy, K’m, are substituted in the above equation. Km and K’m are derived from the basic SI definition of luminous intensity and have the values 683 lm/W and 1,700 lm/W, respectively.