/looh"meuh neuhns/ , n.
1. the state or quality of being luminous.
2. Also called luminosity . the quality or condition of radiating or reflecting light: the blinding luminance of the sun.
3. Optics. the quantitative measure of brightness of a light source or an illuminated surface, equal to luminous flux per unit solid angle emitted per unit projected area of the source or surface.
[ 1875-80; lumin- (s. of lumen ) light + -ANCE ]