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A luxmeter is a sensor that can be used to simply and quickly measure the illumination in the visual spectrum at a given point (interior architecture, night environment, etc.). The measurement is absolute and not relative. The unit of measurement is lux.

Modern luxmeters operate on the principle of a cell C.C.D or photovoltaic cell: an integrated circuit receives a certain amount of light (photons constituting the "signal" which is a radiation energy) and transforms it into an electrical signal (analog signal). This signal is visualized by the displacement of a needle, the lighting of a diode, the display of a digit ... A spectrum correction filter makes it possible to prevent spectrum differences from distorting the measurement ( for example, yellow light is more effective than blue for producing an electron from the energy of a photon packet)

Luxmeters can have multiple scales to adapt to low or high brightness (up to several tens of thousands of lux). The traditional unit of measurement is lux, which corresponds to the light carried by a candle flame at 1 meter distance from the light actually received at a given point (interior architecture, night environment)

The luxmeter was first used by photographers or filmmakers, by lighting designers. It is increasingly used by energy companies to optimize indoor lighting (20 to 60% of electricity is consumed by lighting) or outdoor (which often wastes a lot of energy). They are also used more rarely to measure the brightness of the sky in meteorology, to measure the light received on the ground in the forest or in a greenhouse.

In recent years, it has been used by ecologists, astronomers or architects "HQE" (High environmental quality) to establish quantitative indices of light pollution or light intrusion in order to reduce them by adapted lighting equipment and strategies. This device is also used by biomedical engineers in the medical field at the operating theater level to measure the lighting power of surgical lights. It is also used in industry to determine if workers have the lighting they need to do their jobs.