Category:Photometry

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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).

The main article for this category is Photometry (optics).

SI photometry units
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
Luminous energy Qv [nb 2] lumen second lm⋅s TJ [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 power per unit solid angle.
Luminance Lv candela per square metre cd/m2 L−2J Luminous power per unit solid angle per unit projected source area. Units are sometimes called nits.
Illuminance Ev lux (= lm/m2) lx L−2J Luminous power incident on a surface.
Luminous exitance / Luminous emittance Mv lux lx L−2J Luminous power emitted from a surface.
Luminous exposure Hv lux second lx⋅s L−2TJ
Luminous energy density ωv lumen second per cubic metre lm⋅s⋅m−3 L−3TJ
Luminous efficacy η [nb 2] lumen per watt lm/W M−1L−2T3J Ratio of luminous flux to radiant flux.
Luminous efficiency / Luminous coefficient V 1
See also: SI · Photometry · Radiometry
  1. ^ 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
  2. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
  3. ^ a b c "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.

Subcategories

This category has the following 8 subcategories, out of 8 total.

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