Lighting a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m). The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m. The amount of useful light emitted from a source or the luminous flux is measured in lumen (lm). The SI unit of illuminance and luminous emittance, being the luminous power per area, is measured in Lux. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes
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",