Candela per square metre

"Nit (unit)" redirects here. For the unit of information entropy, see Nat (unit).

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.

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;[1] the sRGB spec for monitors targets 80 cd/m2.[2] High-definition televisions range from 450 to about 1000 cd/m2. Typically, calibrated monitors should have a brightness of 120 cd/m2.

Nit (nt) is a non-SI name also used for this unit (1 nt = 1 cd/m2).[3] The term nit is believed to come from the Latin word nitere, to shine.[4]

Comparison to other units of luminance

One candela per square metre is equal to:

See also

SI photometry quantities
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
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 power per unit solid angle.
Luminance Lv candela per square metre cd/m2 L−2⋅J Luminous power per unit solid angle per unit projected source area. Units are sometimes called nits.
Illuminance Ev lux (= lm/m2) lx L−2⋅J Luminous power incident on a surface.
Luminous exitance / luminous emittance Mv lux lx L−2⋅J Luminous power 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
  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. 1 2 3 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
  3. 1 2 3 "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.

References

  1. ↑ "PC Perspective".
  2. ↑ "Multimedia systems and equipment – Colour measurement and management – Part 2-1: Colour management – Default RGB colour space – sRGB". International Electrotechnical Commission. 1999. IEC 61966-2-1.
  3. ↑ Buser, Pierre; Imbert, Michel (1992). Vision. MIT Press. p. 53. ISBN 978-0-262-02336-8.
  4. ↑ Boyd, RLF, ed. (1992). Astronomical Photometry. Springer. p. 9. ISBN 978-0-7923-1653-4.

External links

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