spectral luminous efficacy of radiant flux

[3.10] K(\lambda )=\Phi _{v\lambda }/\Phi _{e\lambda }

The quotient of the luminous flux at a given wavelength by the radiant flux at that wavelength. It is expressed in lumens per watt.

Note: This term was formerly called luminosity factor. The reciprocal of the maximum luminous efficacy of radiant flux is sometimes called “mechanical equivalent of light”; that is, the ratio between radiant and luminous flux at the wavelength of maximum luminous efficacy. The most probable value is 0.00146 W/lm, corresponding to 683 lm/W as the maximum possible luminous efficacy. For scotopic vision values (see Table A.7), the maximum luminous efficacy is 1,700 “scotopic lumens” per watt.

(See also radiant flux (radiant power) and radiant efficiency.)

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