View source for Candela per square metre

{{Short description|SI derived unit of luminance}}
{{redirect|Nit (unit)|the unit of information entropy|Nat (unit)}}
{{Infobox Unit
| name = Candela per square metre
| standard = [[SI]]
| quantity = [[luminance]]
| symbol = cd/m<sup>2</sup>
| extralabel = In [[SI base unit]]s:
| extradata = [[candela|cd]]·[[metre|m]]<sup>−2</sup>
}}
The '''candela per square metre''' (symbol: '''cd/m<sup>2</sup>''') 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]]. 

The '''nit''' (symbol: '''nt''') is a deprecated non-SI name also used for this unit (1 nt = 1&nbsp;cd/m<sup>2</sup>).<ref>{{cite book | title = Vision | first1 = Pierre | last1 = Buser | first2 = Michel | last2 = Imbert | publisher = MIT Press | year = 1992 | isbn = 978-0-262-02336-8 | page = [https://archive.org/details/vision0000buse/page/53 53] | url = https://archive.org/details/vision0000buse| url-access = registration | quote = nit luminance. }}</ref> The term ''nit'' is believed to come from the Latin word {{wikt-lang|la|niteo|nitēre}}, "to shine".<ref>{{cite book | title = Astronomical Photometry | editor-first = RLF | editor-last = Boyd | publisher = Springer | year = 1992 | isbn = 978-0-7923-1653-4 | page = 9 | url = https://books.google.com/books?id=ojzepXhy9DIC&q=nitere+nit+luminance&pg=PA9}}</ref>

As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a [[Electronic visual display|display device]]. The [[sRGB]] spec for [[Computer monitor|monitors]] targets {{val|80|u=cd|up=m2}}.<ref>{{cite web | id = IEC 61966-2-1 | year = 1999 | title = Multimedia systems and equipment – Colour measurement and management – Part 2-1: Colour management – Default RGB colour space – sRGB | publisher = [[International Electrotechnical Commission]] | url = https://webstore.iec.ch/publication/6169 }}</ref> Typically, monitors calibrated for [[Standard-dynamic-range video|SDR]] broadcast or studio [[color grading]] should have a brightness of {{val|100|u=cd|up=m2}}.<ref>{{Cite web |date=2013-08-13 |title=ITU-R BT.2035-7 |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2035-0-201307-I!!PDF-E.pdf |url-status=live |archive-url=https://web.archive.org/web/20221220125027/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2035-0-201307-I!!PDF-E.pdf |archive-date=2022-12-20 |access-date=2022-12-20 |website=A reference viewing environment for evaluation of HDTV program material or completed programmes}}</ref> Most consumer desktop [[liquid crystal display]]s have luminances of 200 to 300&nbsp;cd/m<sup>2</sup>.<ref>{{cite web |title=Acer Ferrari One 200 Review – More than a Netbook |first=Jonathan  |last=Hung |date=May 3, 2010 |work= PC Perspective | url=https://www.pcper.com/reviews/Mobile/Acer-Ferrari-One-200-Review-More-Netbook/Video-Quality |access-date=2018-01-21}}</ref> [[High-dynamic-range video|HDR]] displays range from around 400 to 2500&nbsp;cd/m<sup>2</sup>.<ref>{{Cite web |last=Cohen |first=Steven |title=What is HDR? High dynamic range TVs and formats, explained |url=https://www.businessinsider.com/guides/tech/what-is-hdr-tv |access-date=2024-05-08 |website=Business Insider |language=en-US}}</ref>

==Comparison with other units of luminance==
One candela per square metre is equal to:
*10<sup>−4</sup> [[stilb (unit)|stilbs]] (the [[CGS]] unit of luminance)
*π×10<sup>−4</sup> [[lambert (unit)|lambert]]s
*π [[apostilb]]s
*0.292 [[foot-lambert]]s
*π×10<sup>3</sup> [[skot (unit)|skot]]s
*π×10<sup>7</sup> [[bril (unit)|bril]]s
*1 nit
{{luminance conversions}}

==See also==
* [[Orders of magnitude (luminance)]]
* [[Photometry (optics)]]

{{SI light units}}

==References==
{{reflist |64em}}

==External links==
* [https://webstore.iec.ch/publication/6169 IEC 61966-2-1:1999 Multimedia systems and equipment – Colour measurement and management – Part 2-1: Colour management – Default RGB colour space – sRGB]
* [http://www.iec.ch/si/ IEC International System of Units zone]

[[Category:Units of luminance]]
[[Category:SI derived units]]
[[Category:Area-specific quantities]]