What is luminous intensity?
In physics, radiant intensity and radiance are integrated across a wide range of wavelengths. In color science, we are interested in power only in the visible band. Radiant intensity, weighted by the spectral sensitivity associated with the brightness sensation of vision, is luminous intensity. It is expressed in units of candelas (cd). The weighting curve is defined numerically and standardized by the CIE; it is called the luminous efficiency of the Standard Observer. It is all-positive, and peaks at about 555 nm.
