Luminous energy is the perceived energy of light. This is also called the quality of light.
Luminous flux (lm)
Luminous flux or luminous power is the measure of the perceived power of light. The SI unit of luminous flux is the lumen(lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian.
Luminous Intensity (cd)
Luminous intensity is a measure of the wavelength-weighted power emitted by a light sources in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd).
Luminance (cd/m2)
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square meter cd/m2.
Luminous Efficacy (lm/W)
Luminous efficacy is a figure of merit for light sources. It is the ratio of luminous flux (in lumens) to power(usually measured in watts). As most commonly used, it is the ratio of luminous flux emitted from a light sources to the electric power consumed by the source, and thus describes how well the source provides visible light from a given amount of electricity. This is also referred to as luminous efficacy of a source. In SI, luminous efficacy has units of lumens per watt(lm/W).
Luminance (lx)
Luminance is used in photometry as a measure of the apparent intensity of light hitting or passing throught a surface. It is analogous to the radiometric unit watts per square meter, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human brightness protection. The SI unit of Luminance is lux(lx). Lux is derived unit based on lumen, and lumen is based on candela.
SI photometry units
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Quantity
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Symbol
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SI Unit
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Abbr.
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Remarks
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Luminous Energy
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Qv
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lumen second
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lm·s
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units are sometimes called "talbots"
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Luminous Flux
|
F
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lumen (= cd·sr
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lm
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also called "luminous power"
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Luminous Intensity
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Iv
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candela(=lm/sr)
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cd
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an SI base unit
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Luminance
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Lv
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candela per square meter
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cd/m2
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units are sometimes called "nits"
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Illuminance
|
Ev
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lux (= lm/m2)
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lx
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used for light incident on a surface
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Luminous Emittance
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Mv
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lux (= lm/m2)
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lx
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used for light emitted from a surface
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Luminous Efficacy
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lumen per watt
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lm/W
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ratio of luminous flux to radiant flux
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