luminance factor (at a surface of a non-self-radiating medium in a given direction, under specified conditions of illumination) [βv]

ratio of the luminance of the surface element, in the given direction, to that of the perfect reflecting or transmitting diffuser identically illuminated and viewed

Unit: 1

NOTE For photoluminescent media, the luminance factor consists of 2 components: the reflected luminance factor, βv,R, and the luminescent luminance factor, βv,L. The sum of the reflected and luminescent luminance factors is the total luminance factor, βv,T: βv,T = βv,R + βv,L.
The subscript R is used here for the reflected luminance factor because it is more intuitive than the traditional S and avoids confusion with the use of S to denote a state of polarization.

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