Illumination, or the amount of light in a given area, is measured in several units. The most common unit is the phot, which is equal to one lumen per square centimeter. A lumen is the total amount of visible light emitted by a source, and is equal to the amount of light produced by one CANDLE. The unit of luminous intensity, or the amount of light emitted in a particular direction, is the candela. This is equal to the amount of light produced by one CANDLE at a distance of one meter.