A phot (ph) is a
photometric unit of
illuminance
In photometry (optics), photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate ...
, or
luminous flux through an area. It is not an
SI unit but rather is associated with the older
centimetre–gram–second system of units
The centimetre–gram–second system of units (CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unamb ...
. The name was coined by
André Blondel
André-Eugène Blondel (28 August 1863 – 15 November 1938) was a French engineer and physicist. He is the inventor of the electromechanical oscillograph and a system of photometric units of measurement.
Life
Blondel was born in Chaumont, Ha ...
in 1921.
[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. – 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."]
Metric equivalence:
:
Metric dimensions:
:Illuminance =
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 huma ...
×
solid angle / length
2
See also
*
Illuminance
In photometry (optics), photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate ...
*
Lumen (unit)
*
Lux
*
Photometry (optics)
Photometry is a branch of optics that deals with measuring light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectr ...
*
Light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
References
External links
* Knowledgedoor, LLC (2005)
Library of Units and Constants: Illuminance Quantity Retrieved 2006-07-21.
Illuminance Converter Retrieved 2006-07-21.
{{CGS units
Units of illuminance
Centimetre–gram–second system of units