Light illumination is the amount of light illuminating a point on a surface.
Illuminating sources can be natural (daylight) or from lamps, lighter, etc.
In SI, derived unit of illuminance is lux (lx) and equals to meter candle. It means,
illuminance on a surface is one candela source per meter. Foot candle (lumen
per square foot) is a non-SI unit of illumination. 1 foot candle (fc) equals to
10.76 lux.
Other units to measure the illumination are meter candle, flame, lumen per
square meter, nox, phot, watts per square centimeter.