quotient of the luminance at a surface element of a medium in a given direction and the illuminance on the medium
Note 1 to entry: The bi-directional reflectance distribution function (BRDF) is similar to the luminance coefficient except that it is defined for directional incident radiation.
Note 2 to entry: The luminance coefficient is expressed in steradian to the power minus one (sr−1).
Note 3 to entry: This entry was numbered 845-04-71 in IEC 60050-845:1987.
Note 4 to entry: This entry was numbered 17-712 in CIE S 017:2011.