In the visible wavelength range the luminous efficacy is identified as the ratio of the emitted luminous flux in lumens (lm) to usually electrical power consumed (in watt). The dimension is lm/w. It is a measure of how efficiently a light source converts the electric power applied into visible light and establishes a connection between the physical quantity (electric) power and the physiological parameter luminous flux which depends on the spectral sensitivity of the human eye.
Wherein invisible light, such as in the infrared or ultraviolet wavelength range, the declaration of lm/W is not possible. Here the ratio of emitted power to power consumed is used and called the energy conversion efficiency. This ratio is a measure of how efficiently a light source operates as well.
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