quotient of the radiance of a surface element in a specified direction,
Note 1 to entry: The definition holds for a surface element of a non-self-radiating medium, in a specified direction and under specified conditions of irradiation.
Note 2 to entry: Radiance factor is equivalent to reflectance factor or luminance factor when the cone angle is infinitely small, and is equivalent to reflectance when the cone angle is 2π sr. These quantities are also defined spectrally and called spectral radiance factor,
Note 3 to entry: The ideal isotropic (Lambertian) diffuser with reflectance or transmittance equal to 1 is called a perfect diffuser.
Note 4 to entry: For photoluminescent media, the radiance factor contains two components, the reflected radiance factor,
The subscript R is used here for the reflected radiance 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 5 to entry: The radiance factor has unit one.
Note 6 to entry: This entry was numbered 845-04-68 in IEC 60050-845:1987.
Note 7 to entry: This entry was numbered 17-1015 in CIE S 017:2011.