The candela per square metre (cd/m²) is the derived SI unit of luminance

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

. The unit is based on the candela

Candela

The candela is the SI base unit of luminous intensity; that is, power emitted by a light source in a particular direction, weighted by the luminosity function . A common candle emits light with a luminous intensity of roughly one candela...

, the SI unit of luminous intensity

Luminous intensity

In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye...

, and the square metre

Square metre

The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...

, the SI unit of area

Area

Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...

. Nit (nt) is a deprecated non-SI name also used for this unit (1 nit = 1 cd/m²).

Most consumer desktop liquid crystal display

Liquid crystal display

A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

s have luminances of 200 to 300 cd/m²; the sRGB spec for monitors targets 80 cd/m². HDTVs range from 450 to about 1000 cd/m².

Nit is believed to come from the Latin nitere, to shine.

Comparison to other units of luminance

One candela per square metre is equal to:

• 10⁻⁴ stilbs
  Stilb (unit)
  The stilb is the CGS unit of luminance for objects that are not self-luminous. It is equal to one candela per square centimeter or 104 nits . The name was coined by the French physicist André Blondel around 1920. It comes from the Greek word stilbein meaning "to glitter".It was in common use in...
  
   (the CGS unit of luminance)
• π×10⁻⁴ lambert
  Lambert (unit)
  The lambert is a non-SI unit of luminance named for Johann Heinrich Lambert , a Swiss mathematician, physicist and astronomer. A related unit of luminance, the foot-lambert, is used in the lighting, cinema and flight simulation industries...
  
  s
• π apostilb
  Apostilb
  The apostilb is an old unit of luminance, which was withdrawn from use in 1978. The SI unit of luminance is the candela per square metre . In 1942 it was proposed to rename the apostilb the blondel, after the French physicist André Blondel...
  
  s
• 0.292 foot-lamberts
• π×10³ skots
• π×10⁷ brils

External links

• Radiometry vs. Photometry FAQ