![]() ![]() The sensitivity of the eye peaks at 555 nm and falls off to approximately 10-4 at 380 and 750 nm. It is a weighted average because the human eye does not respond equally to all visible wavelengths. Thus, luminous flux is a weighted average of the Radiant Flux in the visible spectrum. More specifically, it is energy radiated over wavelengths sensitive to the human eye, from about 330 nm to 780 nm. Luminous Flux (Φv) is energy per unit time (dQ/dt) that is radiated from a source over visible wavelengths. Luminous flux is not used to compare brightness, as this is a subjective perception which varies according to the distance from the light source and the angular spread of the light from the source. Consumers commonly compare the luminous flux of different light bulbs since it provides an estimate of the apparent amount of light the bulb will produce, and a lightbulb with a higher ratio of luminous flux to consumed power is more efficient. Luminous flux is often used as an objective measure of the useful light emitted by a light source, and is typically reported on the packaging for light bulbs, although it is not always prominent. It differs from radiant flux, the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light), in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. In photometry, luminous flux or luminous power is the measure of the perceived power of light.
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