A unit of measurement of the light intensity on a surface area. Lux differs from "lumens." The lux rating will decrease the farther away it is measured from the light source, but the lumen rating will remain the same.
One lux is equal to the illumination of a surface one meter away from a single candle; technically, one lumen per square meter. Whereas a "lumen" measures light intensity in all directions from a light source, "lux" measures the intensity in a specific location from the source. See lumen