Candela per square metre
The candela per square metre (cd/m2) is the derived SI unit of luminance. The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area. Nit (nt) is a deprecated non-SI name also used for this unit (1 nit = 1 cd/m2).
As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a display device. Most consumer desktop liquid crystal displays have luminances of 200 to 300 cd/m2; the sRGB spec for monitors targets 80 cd/m2. HDTVs range from 450 to about 1000 cd/m2. Typically, calibrated monitors should have a brightness of 120 cd/m2.
Nit is believed to come from the Latin word nitere, to shine.
Comparison to other units of luminance 
One candela per square metre is equal to:
- 10−4 stilbs (the CGS unit of luminance)
- π×10−4 lamberts
- π apostilbs
- 0.292 foot-lamberts
- π×103 skots
- π×107 brils
See also 
|Luminous energy||Qv [nb 2]||lumen second||lm⋅s||T⋅J [nb 3]||units are sometimes called talbots|
|Luminous flux||Φv [nb 2]||lumen (= cd⋅sr)||lm||J [nb 3]||also called luminous power|
|Luminous intensity||Iv||candela (= lm/sr)||cd||J [nb 3]||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 [nb 2]||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|
- Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities.
- 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.
- Pierre Buser and Michel Imbert (1992). Vision. MIT Press. p. 53. ISBN 978-0-262-02336-8.
- "PC Perspective".
- "IEC 61966-2-1:1999 Multimedia systems and equipment - Colour measurement and management - Part 2-1: Colour management - Default RGB colour space - sRGB". International Electrotechnical Commission.
- R. L. F. Boyd (ed.) (1992). Astronomical Photometry. Springer. p. 9. ISBN 978-0-7923-1653-4.