Candela per square metre

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

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.

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

The nit (symbol: nt) is a deprecated 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 ≈ 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

• Orders of magnitude (luminance)
• Photometry (optics)

SI photometry quantities

• v
• t
• e

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: SI Photometry Radiometry

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. Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ for luminous efficacy of a source.