The illuminance (abbreviation: (E) specifies the luminous flux in the lux (lx) unit of measurement, of a light source that hits a certain area. It is 1 lux, when the luminous flux of 1 lumen evenly illuminates a 1 square metre surface. The illuminance is measured with a luxmeter on horizontal and vertical surfaces. With the same illuminance a white room appears brighter than a darker one (see reflectance).

See also:

Luminous Flux