# 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]

Metric equivalence:

$1\ \mathrm{phot} = 1\ \frac{\mathrm{lumen}}{\mathrm{centimeter}^2} = 10,000\ \frac{\mathrm{lumens}}{\mathrm{meter}^2} = 10,000\ \mathrm{lux} = 10\ \mathrm{kilolux}$

Metric dimensions:

illuminance = luminous intensity × solid angle / length2