Luminance – is the quantitative expression for the amount of light reflected by a surface in a specific direction. A more familiar word is brightness, although this term must, strictly speaking, be reserved to describe the subjective impression of luminance on the eye. The luminance of a surface is determined by the illuminance on the surface in question and its reflective properties. Luminance is expressed in candelas per square metre (cd/m²), also referred to as the nit. Other units are lambert, stilb, apostilb, blondel, and skot. In Imperial units the unit is candelas per square foot (cd/ft²) or the foot-lambert.
