# 17-24-077

luminance factor

βv; β

quotient of the luminance of a surface element in a specified direction, Lv,n, and the luminance of the perfect reflecting diffuser or perfect transmitting diffuser identically illuminated and viewed, Lv,d

Note 1 to entry: The definition holds for a surface element of a non-luminous medium, in a given direction and under specified conditions of irradiation.

Note 2 to entry: This quantity is also defined spectrally and is called "spectral luminance factor".

Note 3 to entry: For photoluminescent media, the luminance factor consists of two components: the reflected luminance factor, βv,R, and the luminescent luminance factor, βv,L. The sum of the reflected and luminescent luminance factors is called "total luminance factor" and can be expressed by 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.

Note 4 to entry: The luminance factor has unit one.

Note 5 to entry: This entry was numbered 845-04-69 in IEC 60050-845:1987.

Note 6 to entry: This entry was numbered 17-717 in CIE S 017:2011.

Publication date: 2020-12