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
Borel measure for every half-open interval formula_14 is sometimes called "the" Borel measure on formula_10. This measure turns out to be the restriction on the Borel σ-algebra of the Lebesgue measure formula_16, which is a complete measure and is defined on the Lebesgue σ-algebra. The Lebesgue σ-algebra is actually the "completion" of the Borel σ-algebra, which means that it is the smallest σ-algebra which contains all the Borel sets and has a complete measure on it. Also, the Borel measure and the Lebesgue measure coincide on the Borel sets (i.e., formula_17 for every Borel measurable set, where formula_4 is the Borel measure