Luminous Flux - Contexts

Contexts

Luminous flux is often used as an objective measure of the useful power emitted by a light source, and is typically reported on the packaging for light bulbs, although it is not always prominent. Energy conscious 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 is useful when comparing the luminous efficacy of incandescent and compact fluorescent bulbs.

Luminous flux is not used to compare brightness, as this is a subjective perception which varies according to the distance from the light source.

SI photometry units
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Quantity Symbol SI unit Symbol Dimension Notes
Luminous energy Qv lumen second lm⋅s T⋅J units are sometimes called talbots
Luminous flux Φv lumen (= cd⋅sr) lm J also called luminous power
Luminous intensity Iv candela (= lm/sr) cd J an SI base unit, luminous flux per unit solid angle
Luminance Lv candela per square metre cd/m2 L−2⋅J units are sometimes called nits
Illuminance Ev lux (= lm/m2) lx L−2⋅J used for light incident on a surface
Luminous emittance Mv lux (= lm/m2) lx L−2⋅J used for light emitted from a surface
Luminous exposure Hv lux second lx⋅s L−2⋅T⋅J
Luminous energy density ωv lumen second per metre3 lm⋅s⋅m−3 L−3⋅T⋅J
Luminous efficacy η lumen per watt lm/W M−1⋅L−2⋅T3⋅J ratio of luminous flux to radiant flux
Luminous efficiency V 1 also called luminous coefficient
See also: SI · Photometry · Radiometry

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