Candela of a single point light source of intensity "I", at a distance "r" and normally incident, this reduces to Candela The candela ( or ; symbol: cd) is the base unit of luminous intensity in the International System of Units (SI); that is, luminous power per unit solid angle emitted by a point light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the standard luminosity function (a model of the sensitivity
Content (measure theory) by This is an outer measure, in other words it has the following properties: The function μ above is an outer measure on the family of all subsets. Therefore it becomes a measure when restricted to the measurable subsets for the outer measure, which are the subsets "E" such that μ("X") = μ("X"∩"E") + μ("X"\"E") for all subsets "X". If the space is locally compact then every open set is measurable for this measure. The measure μ does not necessarily coincide with the content λ on compact sets, However it does if λ is regular in the sense that for