A luxmeter (also called luxmeter or light meter) is a measuring instrument that allows you to simply and quickly measure the real and non-subjective illuminance of an environment. The unit of measurement is lux (lx). It contains a photoelectric cell that captures light and converts it into electrical impulses), which are interpreted and represented on a display or needle with the corresponding lux scale.

The modern lux meter works on the principle of a C.C.D. cell. or photovoltaic; An integrated circuit receives a certain amount of light (photons that constitute the "signal", a brightness energy) and transforms it into an electrical (analog) signal. This signal is visible by the movement of a needle, the lighting of a diode or the setting of a figure. A photoresistor associated with an ohmmeter would play the same role.

A spectrum correction filter prevents spectrum differences from distorting the measurement (yellow light is more efficient than blue, for example, in producing an electron from the energy of a packet of photons).

Lux meters can have several scales to adapt to weak or strong luminosities (up to several tens of thousands of lux).

They have first been used by photographers and filmmakers. It is increasingly used by energy producers to optimize indoor lighting (20 to 60% of electricity is consumed by lighting) or outdoor lighting (which often wastes a lot of energy). They are also used, more rarely, to measure the luminosity of the sky in meteorology, to measure the light received on the ground in forests or in greenhouses.

In recent years it has also begun to be used by ecologists, astronomers and architects to develop quantitative indices of light pollution or light intrusion to reduce them or adapt engineering strategies. Also in museums and exhibition halls to control the appropriate illuminance parameters for proper conservation of the exhibited objects.

Another use is that given by hygiene and safety professionals, in order to determine the possibility of the occurrence of an occupational disease due to lighting deficiencies, since this is established by labor legislation in many countries (law 19587 on occupational safety and hygiene in Argentina or NOM-025-STPS-2008 in Mexico, which talks about lighting conditions in workplaces, to name a few examples).

They are also used by technicians in occupational risk prevention in the workplace.