An illuminometer (or lux meter) is an
instrument that specifically measures luminosity and brightness. That
is, the measurement of the illumination intensity (illuminance) is the
degree to which the object is illuminated, that is, the ratio of the
luminous flux obtained by the surface of the object to the illuminated
area. The illuminometer usually consists of a selenium photocell or a
silicon photocell and a microampere meter.
