# Candela per square metre

(Redirected from Cd/m2)

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 deprecated non-SI name also used for this unit (1 nit = 1 cd/m2).[1]

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;[2] the sRGB spec for monitors targets 80 cd/m2.[3] HDTVs range from 450 to about 1000 cd/m2. Typically, calibrated monitors should have a brightness of 120 cd/m2.

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:

SI photometry units
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
Luminous energy Qv [nb 2] lumen second lm⋅s TJ [nb 3] units are sometimes called talbots
Luminous flux Φv [nb 2] lumen (= cd⋅sr) lm J [nb 3] also called luminous power
Luminous intensity Iv candela (= lm/sr) cd J [nb 3] an SI base unit, luminous flux per unit solid angle
Luminance Lv candela per square metre cd/m2 L−2J units are sometimes called nits
Illuminance Ev lux (= lm/m2) lx L−2J used for light incident on a surface
Luminous emittance Mv lux (= lm/m2) lx L−2J used for light emitted from a surface
Luminous exposure Hv lux second lx⋅s L−2TJ
Luminous energy density ωv lumen second per metre3 lm⋅sm−3 L−3TJ
Luminous efficacy η [nb 2] lumen per watt lm/W M−1L−2T3J ratio of luminous flux to radiant flux
Luminous efficiency V 1 also called luminous coefficient