Phot

Phot

Phot is a unit of illuminance in the centimetre-gram-second system of units (CGS). It is defined as one lumen per square centimetre. The phot is not commonly used in modern scientific contexts, where the lux (one lumen per square metre) is the preferred unit of illuminance in the International System of Units (SI).

Definition

The phot is defined as:

1 phot = 1 lumen/cm²

This means that if a surface receives one lumen of luminous flux per square centimetre, it has an illuminance of one phot.

History

The phot was introduced as part of the CGS system, which was widely used in the 19th and early 20th centuries. However, with the adoption of the SI system, the use of the phot has declined in favor of the lux.

Conversion

To convert between phots and lux:

1 phot = 10,000 lux

1 lux = 0.0001 phot

This conversion is based on the fact that there are 10,000 square centimetres in a square metre.

Applications

While the phot is largely obsolete, it may still be encountered in historical scientific literature and in certain specialized fields. Modern applications typically use the lux for measuring illuminance.

See also

• Lumen (unit)
• Lux
• Illuminance
• Centimetre-gram-second system of units
• International System of Units

Related pages

• Luminous flux
• Luminous intensity
• Candela
• Radiometry
• Photometry (optics)

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