Lumen

The lumen is the SI unit of luminous flux, which quantifies the perceived power of visible light emitted by a source. Luminous flux differs from power, which encompasses all electromagnetic waves emitted, including non-visible ones such as thermal radiation (infrared). By contrast, luminous flux is weighted according to a model of the human eye's sensitivity to various wavelengths; this weighting is standardized by the CIE and ISO.

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LUMINOSIT

The science of light, made practical — photometry in plain English, plus the lumen, lux, candela, and energy calculators every lighting decision needs.

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