<P> The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source . Luminous flux differs from power (radiant flux) in that radiant flux includes all electromagnetic waves emitted, while luminous flux is weighted according to a model (a "luminosity function") of the human eye's sensitivity to various wavelengths . Lumens are related to lux in that one lux is one lumen per square meter . </P> <P> The lumen is defined in relation to the candela as </P>

What is the difference between lux and lumens in a flashlight
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