Photometric Unit

a unit of measurement of a photometric quantity. Examples of photometric quantities are luminous intensity, illuminance, luminance, and luminous flux. The unit of luminous intensity is the candela (cd), formerly known as the candle. It can be reproduced from photometric standards and is a base unit in the International System of Units.

Besides the units in the International System, other units of illuminance and luminance are also used; for example, 1 phot = 10⁴ lux, 1 footcandle (or 1 lumen per square foot) = 10.764 lux, 1 stilb = 10⁴ cd/m²,1 lambert = (1/π) x 10⁴ cd/m², and 1 footlambert X 3.426 cd/m².