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
Pre-measure Σ includes "R"). The infimum of the empty set is taken to be formula_6. Pre-measure In mathematics, a pre-measure is a function that is, in some sense, a precursor to a "bona fide" measure on a given space. Indeed, one of the fundamental theorems in measure theory states that a pre-measure can be extended to a measure. Let "R" be a ring of subsets (closed under union and relative complement) of a fixed set "X" and let "μ": "R" → [0, +∞] be a set function. "μ" is called a pre-measure if and, for every countable (or finite) sequence {"A"}