# Phot

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{{short description|Measure of illuminance}}{{For|the 9th-century theologian and scholar|Patriarch Photius I of Constantinople}}
{{Infobox unit
| name         = Phot
| image        = 
| caption      = 
| standard     = [CGS](/source/Centimetre%E2%80%93gram%E2%80%93second_system_of_units) units
| quantity     = [Illuminance](/source/Illuminance)
| symbol       = ph
| symbol2      = 
| namedafter   = 
| extralabel   = 
| extradata    = 
| units1       = [SI derived unit](/source/SI_derived_unit)
| inunits1     = {{val|10000|u=[lx](/source/lux)}}
| units2       = [SAE](/source/United_States_customary_units) units
| inunits2     = 929 [fc](/source/Foot-candle)
}}
A '''phot''' ('''ph''') is a [photometric](/source/photometry_(optics)) unit of [illuminance](/source/illuminance), or [luminous flux](/source/luminous_flux) through an area. It is not an [SI](/source/SI) unit but rather is associated with the older [centimetre–gram–second system of units](/source/centimetre%E2%80%93gram%E2%80%93second_system_of_units). The name was coined by [André Blondel](/source/Andr%C3%A9_Blondel) in 1921.<ref>Parry Moon. "System of photometer concepts", in the ''Journal of the Optical Society of America'', volume 32, number 6 (June 1942), [doi:10.1364/JOSA.32.000348](/source/doi%3A10.1364%2FJOSA.32.000348). – Page 355: "The lumen was proposed by Blondel in 1894 and is now universally accepted. The names, phot and stilb were likewise coined by Blondel (1921) and are in general use on the Continent."</ref>

Metric equivalence:

:<math>1\ \mathrm{phot} = 1\ \frac{\mathrm{lumen}}{\mathrm{centimetre}^2} = 10,000\ \frac{\mathrm{lumens}}{\mathrm{metre}^2} = 10,000\ \mathrm{lux} = 10\ \mathrm{kilolux}</math>

Metric dimensions:

:Illuminance = [luminous intensity](/source/luminous_intensity) × [solid angle](/source/solid_angle) / length<sup>2</sup>

== See also ==

* [Illuminance](/source/Illuminance)
* [Lumen (unit)](/source/Lumen_(unit))
* [Lux](/source/Lux)
* [Photometry (optics)](/source/Photometry_(optics))
* [Light](/source/Light)

== References ==
<references/>

== External links ==
* Knowledgedoor, LLC (2005). [http://www.knowledgedoor.com/1/Library_of_Units_and_Constants/Quantity_Index/illuminance.htm Library of Units and Constants: Illuminance Quantity]. Retrieved 2006-07-21.
* [http://www.convertthis.com/converters/illuminance.aspx Illuminance Converter]. Retrieved 2006-07-21.

{{CGS units}}

Category:Units of illuminance
Category:Centimetre–gram–second system of units

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Adapted from the Wikipedia article [Phot](https://en.wikipedia.org/wiki/Phot) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Phot?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.