Lumen

Lumen is the unit of measure of the total visible light emitted by a source. Lumen (symbol; lm) is the >SI derived unit of >Luminous Flux. >Luminous Flux differs from power (watt or radiant flux) by taking into account the sensitivities of the human eye to different wavelengths, while radiant flux indicate the total power of all the light emitted - independent of the eyes ability to perceive it.