Candela per square metre
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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:
- 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
See also
| Quantity | Unit | Dimension | Notes | |||||
|---|---|---|---|---|---|---|---|---|
| Name | Symbol[nb 1]r | 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 | ||||||||
- ↑ 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
- ↑ 2.0 2.1 2.2 Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
- ↑ 3.0 3.1 3.2 "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.
References
External links
- IEC 61966-2-1:1999 Multimedia systems and equipment - Colour measurement and management - Part 2-1: Colour management - Default RGB colour space - sRGB
- IEC International System of Units zone
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