Книга: Luminous efficacy: Figure of merit, Luminous flux, Lumen (unit), Power (physics), Watt, Electromagnetic spectrum, Human eye, Wavelength, Emission spectrum, ... radiation, Luminous coefficient

Luminous efficacy is a figure of merit for light sources. It is the ratio of luminous flux (in lumens) to power (usually measured in watts). Depending on context, the power can be either the radiant flux of the source's output, or it can be the total electric power consumed by the source. Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation (LER), and the latter luminous efficacy of a source (LES). The LES describes how well the source provides visible light from a given amount of electricity. The LER is a characteristic of a given spectrum that describes how sensitive the human eye is to the mix of wavelengths involved. The luminous efficacy of a source is the LER of its emission spectrum times the conversion efficiency from electrical energy to electromagnetic radiation.