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/m² | extralabel = In SI base units: | extradata = cd·m⁻² }} The '''candela per square metre''' (symbol: '''cd/m²'''; alternatively titled '''candela per square meter''') 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/m²).<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 display device. The sRGB spec for 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 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 displays have luminances of 200 to 300&nbsp;cd/m².<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> HDR displays range from around 400 to 2500&nbsp;cd/m².<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: * 10⁻⁴ stilbs (the CGS unit of luminance) * {{math|''π''}} × 10⁻⁴ lamberts * {{math|''π''}} apostilbs * 0.292 foot-lamberts * {{math|''π''}} × 10³ skots * {{math|''π''}} × 10⁷ brils * 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