The
lux (symbol:
lx) is the
SI unit of
illuminance and
luminous emittance, measuring
luminous flux per unit area. It is equal to one
lumen per square metre. In
photometry, this is used as a measure of the intensity, as perceived by the human eye, of
light that hits or passes through a surface. It is analogous to the
radiometric unit watts per square metre, but with the power at each
wavelength weighted according to the
luminosity function, a standardized model of
human visual brightness perception. In English, "lux" is used in both singular and plural.