Spectral Luminous Efficacy

For radiation in the range of wavelengths λ or frequencies v perceived by the human eye, that is, in the visible range, the spectral luminous efficacy of radiant power is the ratio of the luminous flux at a given wavelength of light (monochromatic light) to the corresponding radiant power, or radiant flux. Spectral luminous efficacy is denoted by K(\\) and assumes its maximum value K_m ≃ 680 lumens/watt at λ = 555 nanometers.

A related quantity of some importance is the spectral luminous efficiency V(λ) = K(λ)/K_m. It has also been called the relative spectral luminous efficacy and the relative luminosity (the term “luminosity” was formerly applied to the spectral luminous effi cacy). The system of photometric quantities is based on the two quantities K(λ) and V(λ). (See alsoLUMINOUS EFFICACY OF RADIANT POWER and .)