Luminance denotes the signal determining the contrast values of an image, from the darkest of dark to the whitest of whites. The other part of the signal is colour, called chrominance. This fundamental photometric quantity is characteristic of the intrinsic emission from a source,independently of its geometry. Luminance is the flux emitted per unit surface area and per unit solid angle.
Unit: Cd/m², W/m²/sr, photons/s/m²/sr
It can be shown that the illumination of the plane image produced by an imaging system is proportional to the luminance of the source. The visual impression is proportional to the luminance of the objects because the illumination of the retina of theeye is proportional to the luminance.
The illumination of the retina of the eye is proportional to the luminance. © DR