Luminance Luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted or reflected from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m). A non-SI term for the same unit is the nit. The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m. Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance
Spherical measure "r" > 0, where "A" denotes the “inflation” of "A" by "r", i.e. In particular, if "σ"("A") ≥ ½ and "n" ≥ 2, then Spherical measure In mathematics — specifically, in geometric measure theory — spherical measure "σ" is the “natural” Borel measure on the "n"-sphere S. Spherical measure is often normalized so that it is a probability measure on the sphere, i.e. so that "σ"(S) = 1. There are several ways to define spherical measure. One way is to use the usual “round” or “arclength” metric "ρ" on S; that is, for points "x" and "y" in S, "ρ"("x",