a measure of the visible electromagnetic radiation

a unit of illuminance on a surface that is everywhere 1 foot from a point source of 1 candle

a cgs unit of illumination equal to the brightness of a perfectly diffusing surface that emits or reflects one lumen per square centimeter

a unit of illumination equal to 1 lumen per square meter; 0.0929 foot candle

a unit of illumination equal to 1 lumen per square centimeter; 10,000 phots equal 1 lux

a unit of illumination equal to one thousandth of a lux.