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 non-SI name also used for this unit (1 nt = 1 cd/m2).[1] The term nit is believed to come from the Latin word nitere, to shine.[2]

As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a display device. The sRGB spec for monitors targets 80 cd/m2.[3] Typically, calibrated monitors should have a brightness of 120 cd/m2. Most consumer desktop liquid crystal displays have luminances of 200 to 300 cd/m2.[4] High-definition televisions range from 450 to about 1500 cd/m2.

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 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
  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. ↑ Buser, Pierre; Imbert, Michel (1992). Vision. MIT Press. p. 53. ISBN 978-0-262-02336-8.
  2. ↑ Boyd, RLF, ed. (1992). Astronomical Photometry. Springer. p. 9. ISBN 978-0-7923-1653-4.
  3. ↑ "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.
  4. ↑ "PC Perspective".
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