The candela per square metre (symbol: cd/m
2) is the unit of
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, is emitted from, or is reflected from a particular area, and falls with ...
in the
International System of Units
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
(SI). The unit is based on the
candela
The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to ...
, the SI unit of
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, the SI unit of
area. The nit (symbol: nt) is a non-SI name also used for this unit (1 nt = 1 cd/m
2). The term ''nit'' is believed to come from the Latin word , "to shine".
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 . Typically, monitors calibrated for
SDR broadcast or studio color grading should have a brightness of . Most consumer desktop
liquid crystal display
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...
s have luminances of 200 to 300 cd/m
2.
HDR displays range from 450 to above 1600 cd/m
2.
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
apostilb The apostilb is an obsolete unit of luminance. The SI unit of luminance is the candela per square metre (cd/m2). In 1942 Parry Moon proposed to rename the apostilb the blondel, after the French physicist André Blondel. The symbol for the apostilb ...
s
*0.292
foot-lambert
A foot-lambert or footlambert (fL, sometimes fl or ft-L) is a unit of luminance in United States customary units and some other unit systems. A foot-lambert equals 1/π or 0.3183 candela per square foot, or 3.426 candela per square meter (the corr ...
s
*π×10
3 skots
*π×10
7 brils
*1 nit
See also
*
Orders of magnitude (luminance)
*
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power. ...
References
{{reflist , 64em
External links
IEC 61966-2-1:1999 Multimedia systems and equipment – Colour measurement and management – Part 2-1: Colour management – Default RGB colour space – sRGBIEC International System of Units zone
Units of luminance
SI derived units