a measure of the visible electromagnetic radiation

a luminance unit equal to 1 candle per square meter measured perpendicular to the rays from the source

a former luminance unit equal to one lumen per square foot

an old unit of luminance, withdrawn from use in 1978, the SI unit of luminance is the candela per square metre.

the CGS unit of luminance for objects that are not self-luminous, equal to one candela per square centimeter.