Phot (ph)
The phot is the CGS unit of illuminance, one lumen per square centimetre, or 10,000 lux.
Symbol: ph
Quantity: illuminance (light falling on a surface)
SI relation: 1 ph = 10000 lx (exact)
Derivation: 1 ph = 1 lm/cm² = 10⁴ lx.
Exact: yes, by definition
Typical uses
- Older optics literature
Convert phots to other units
| Conversion | 1 ph equals | Reverse |
|---|---|---|
| phot to lux | 10000 lx | lux to phot |
| phot to foot-candle | 929.0304 fc | foot-candle to phot |
| phot to kilolux | 10 klx | kilolux to phot |
| phot to millilux | 10000000 mlx | millilux to phot |
Open the Illuminance Converter (Lux, Foot-candle) to convert any value between all units.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "phot".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Phot (ph). Retrieved October 25, 2026, from https://scientificconverters.com/units/phot/
IEEE
Scientific Converters, "Phot (ph)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/units/phot/