Candela per square metre
Unit systemSI
Unit ofluminance
Symbolcd/m2
In SI base units:cd·m−2

The candela per square metre (symbol: cd/m2) is the unit of luminance in the International System of Units (SI). The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area.

The nit (symbol: 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 nitēre, "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, monitors calibrated for SDR broadcast or studio color grading should have a brightness of 100 cd/m2.[4] Most consumer desktop liquid crystal displays have luminances of 200 to 300 cd/m2.[5] HDR displays range from 450 to above 1600 cd/m2.[6]

Comparison with other units of luminance

One candela per square metre is equal to:

Units of luminance
cd/m2 (SI unit)
≡ nit ≡ lm/m2/sr		 stilb (sb) (CGS unit)
≡ cd/cm2		 apostilb (asb)
≡ blondel		 bril skot (sk) lambert (L) foot-lambert (fL)
= 1 ⁄ π cd/ft2
1 cd/m2 = 1 10−4 π
≈ 3.142		 107 π
≈ 3.142×107		 103 π
≈ 3.142×103		 10−4 π
≈ 3.142×10−4		 0.30482 π
≈ 0.2919
1 sb = 104 1 104 π
≈ 3.142×104		 1011 π
≈ 3.142×1011		 107 π
≈ 3.142×107		 π
≈ 3.142		 30.482 π
≈ 2919
1 asb = 1 ⁄ π
≈ 0.3183		 10−4 ⁄ π
≈ 3.183×10−5		 1 107 103 10−4 0.30482
≈ 0.09290
1 bril = 10−7 ⁄ π
≈ 3.183×10−8		 10−11 ⁄ π
≈ 3.183×10−12		 10−7 1 10−4 10−11 0.30482×10−7
≈ 9.290×10−9
1 sk = 10−3 ⁄ π
≈ 3.183×10−4		 10−7 ⁄ π
≈ 3.183×10−8		 10−3 104 1 10−7 0.30482×10−3
≈ 9.290×10−5
1 L = 104 ⁄ π
≈ 3183		 1 ⁄ π
≈ 0.3183		 104 1011 107 1 0.30482×104
≈ 929.0
1 fL = 1 ⁄ 0.30482 ⁄ π
≈ 3.426		 1 ⁄ 30.482 ⁄ π
≈ 3.426×10−4		 1 ⁄ 0.30482
≈ 10.76		 107 ⁄ 0.30482
≈ 1.076×108		 103 ⁄ 0.30482
≈ 1.076×104		 10−4 ⁄ 0.30482
≈ 1.076×10−3		 1

See also

SI photometry quantities
Quantity Unit Dimension
[nb 1]		 Notes
Name Symbol[nb 2] Name Symbol
Luminous energy Qv[nb 3] lumen second lm⋅s T⋅J The lumen second is sometimes called the talbot.
Luminous flux, luminous power Φv[nb 3] lumen (= candela steradian) lm (= cd⋅sr) J Luminous energy per unit time
Luminous intensity Iv candela (= lumen per steradian) cd (= lm/sr) J Luminous flux per unit solid angle
Luminance Lv candela per square metre cd/m2 (= lm/(sr⋅m2)) L−2⋅J Luminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit.
Illuminance Ev lux (= lumen per square metre) lx (= lm/m2) L−2⋅J Luminous flux incident on a surface
Luminous exitance, luminous emittance Mv lumen per square metre lm/m2 L−2⋅J Luminous flux emitted from a surface
Luminous exposure Hv lux second lx⋅s L−2⋅T⋅J Time-integrated illuminance
Luminous energy density ωv lumen second per cubic metre lm⋅s/m3 L−3⋅T⋅J
Luminous efficacy (of radiation) K lumen per watt lm/W M−1⋅L−2⋅T3⋅J Ratio of luminous flux to radiant flux
Luminous efficacy (of a source) η[nb 3] lumen per watt lm/W M−1⋅L−2⋅T3⋅J Ratio of luminous flux to power consumption
Luminous efficiency, luminous coefficient V 1 Luminous efficacy normalized by the maximum possible efficacy
See also:
  1. ↑ The symbols in this column denote dimensions; "L", "T" and "J" are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule.
  2. ↑ Standards organizations recommend that photometric quantities be denoted with a subscript "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
  3. 1 2 3 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.

References

  1. ↑ Buser, Pierre; Imbert, Michel (1992). Vision. MIT Press. p. 53. ISBN 978-0-262-02336-8. nit luminance.
  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. ↑ "ITU-R BT.2035-7" (PDF). A reference viewing environment for evaluation of HDTV program material or completed programmes. 2013-08-13. Archived (PDF) from the original on 2022-12-20. Retrieved 2022-12-20.
  5. ↑ Hung, Jonathan (May 3, 2010). "Acer Ferrari One 200 Review – More than a Netbook". PC Perspective. Retrieved 2018-01-21.
  6. ↑ "Pro Display Tech Specs". Apple.
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