Luminance
From The Glossary of Digital Photography
Luminance is the light reflected from a surface or emitted by an object. It is also known as lightness and it is similar to the brightness of an image, Lightness is one of the three properties of light (the others are hue and saturation). Luminance is the brightness as perceived by the eye. The unit for measuring luminance is candela per square meter or cd/m'2. See also lightness
