The brightness portion of the video signal, seen as gradations of black and white.
brightness, usually of a surface, i.e. luminous intensity per unit area. unit: candelas per square meter, usually expressed in millicandelas per square meter.
A unit of lighting measurement identical to radiance except that it is based on the visual (photopic) brightness of a light source rather than the total brightness. It is expressed in lumens (rather than watts) per steradian per surface unit. A commonly used alternative unit is the footlambert (fL). See Radiance below.