Photometry is the science of measurement of light, in terms of its apparent brightness to the human eye. It is distinct from radiometry, which is the science of measurement of light in terms of absolute power. Note that this term is used differently in astronomy. For information on the astronomical method, see Photometry (astronomy).
|Luminous energy||Qv [nb 2]||lumen second||lm⋅s||T⋅J [nb 3]||Units are sometimes called talbots.|
|Luminous flux / luminous power||Φv [nb 2]||lumen (= cd⋅sr)||lm||J [nb 3]||Luminous energy per unit time.|
|Luminous intensity||Iv||candela (= lm/sr)||cd||J [nb 3]||Luminous flux per unit solid angle.|
|Luminance||Lv||candela per square metre||cd/m2||L−2⋅J||Luminous flux per unit solid angle per unit projected source area. Units are sometimes called nits.|
|Illuminance||Ev||lux (= lm/m2)||lx||L−2⋅J||Luminous flux incident on a surface.|
|Luminous exitance / luminous emittance||Mv||lux||lx||L−2⋅J||Luminous flux emitted from a surface.|
|Luminous exposure||Hv||lux second||lx⋅s||L−2⋅T⋅J|
|Luminous energy density||ωv||lumen second per cubic metre||lm⋅s⋅m−3||L−3⋅T⋅J|
|Luminous efficacy||η [nb 2]||lumen per watt||lm/W||M−1⋅L−2⋅T3⋅J||Ratio of luminous flux to radiant flux or power consumption, depending on context.|
|Luminous efficiency / luminous coefficient||V||1|
|See also: SI · Photometry · Radiometry|
- Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967
- Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
- "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.
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Pages in category "Photometry"
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