The density of luminous flux incident upon a surface. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux.
Photometric measure of amount of light radiated onto a surface. Radiometric equivalent is irradiance. Standard measurement unit lm ft^-2 .
luminous flux incident upon a surface of unit area. Measured in lux or lumen per square metre. See also cosine correction