Phot

For the 9th-century theologian and scholar, see Patriarch Photius I of Constantinople.

A phot (ph) is a photometric unit of illuminance, 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 name was coined by André Blondel in 1921.^[1]

Phot
Unit system	CGS units
Unit of	Illuminance
Symbol	ph
Conversions
1 ph in ...	... is equal to ...
SI derived unit	10000 lx
SAE units	929 fc

Metric equivalence:

${\displaystyle 1\ \mathrm {phot} =1\ {\frac {\mathrm {lumen} }{\mathrm {centimetre} ^{2}}}=10,000\ {\frac {\mathrm {lumens} }{\mathrm {metre} ^{2}}}=10,000\ \mathrm {lux} =10\ \mathrm {kilolux} }$

Metric dimensions:

Illuminance = luminous intensity × solid angle / length²

See also

• Illuminance
• Lumen (unit)
• Lux
• Photometry (optics)
• Light