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
Measure (mathematics) if is a finite real number (rather than ∞). Nonzero finite measures are analogous to probability measures in the sense that any finite measure is proportional to the probability measure formula_15. A measure is called "σ-finite" if can be decomposed into a countable union of measurable sets of finite measure. Analogously, a set in a measure space is said to have a "σ-finite measure" if it is a countable union of sets with finite measure. For example, the real numbers with the standard Lebesgue measure are σ-finite but not finite. Consider the closed intervals for all integers ; there are