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candela per square metre
Unit system	SI
Unit of	luminance
Symbol	cd/m²
In SI base units:	cd·m⁻²

The candela per square metre (symbol: cd/m²; alternatively titled candela per square meter) 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 around 400 to 2500 cd/m².^[6]

Comparison with 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
1 nit

Units of luminance
v t e		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 ≈ 2,919
1 asb	=	1 ⁄ π ≈ 0.3183	10⁻⁴ ⁄ π ≈ 3.183×10⁻⁵	1	10⁷	10³	10⁻⁴	0.3048² ≈ 0.0929
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 ≈ 9.29×10⁻⁹
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 ≈ 9.29×10⁻⁵
1 L	=	10⁴ ⁄ π ≈ 3,183	1 ⁄ π ≈ 0.3183	10⁴	10¹¹	10⁷	1	0.3048²×10⁴ ≈ 929
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

SI photometry quantities
v
t
e
Quantity		Unit		Dimension ^{[nb 1]}	Notes
Name	Symbol^{[nb 2]}	Name	Symbol	Dimension ^{[nb 1]}	Notes
Luminous energy	Q_v^{[nb 3]}	lumen second	lm⋅s	T⋅J	The lumen second is sometimes called the talbot.
Luminous flux, luminous power	Φ_v^{[nb 3]}	lumen (= candela steradian)	lm (= cd⋅sr)	J	Luminous energy per unit time
Luminous intensity	I_v	candela (= lumen per steradian)	cd (= lm/sr)	J	Luminous flux per unit solid angle
Luminance	L_v	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	E_v	lux (= lumen per square metre)	lx (= lm/m²)	L⁻²⋅J	Luminous flux incident on a surface
Luminous exitance, luminous emittance	M_v	lumen per square metre	lm/m²	L⁻²⋅J	Luminous flux emitted from a surface
Luminous exposure	H_v	lux second	lx⋅s	L⁻²⋅T⋅J	Time-integrated illuminance
Luminous energy density	ω_v	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: SI Photometry Radiometry

↑ 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.
↑ 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
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

↑ Buser, Pierre; Imbert, Michel (1992). Vision. MIT Press. p. 53. ISBN 978-0-262-02336-8. nit luminance.
↑ Boyd, RLF, ed. (1992). Astronomical Photometry. Springer. p. 9. ISBN 978-0-7923-1653-4.
↑ "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.
↑ "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.
↑ Hung, Jonathan (May 3, 2010). "Acer Ferrari One 200 Review – More than a Netbook". PC Perspective. Retrieved 2018-01-21.
↑ Cohen, Steven. "What is HDR? High dynamic range TVs and formats, explained". Business Insider. Retrieved 2024-05-08.

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Comparison with other units of luminance

See also

References

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