Phot
Encyclopedia
A phot 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.
Metric equivalence:
Metric dimensions:
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...
unit of illuminance
Illuminance
In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...
, or luminous flux
Luminous flux
In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of...
through an area. It is not an SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
unit, but rather is associated with the older centimetre gram second system of units
Centimetre gram second system of units
The centimetre–gram–second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time...
. The name was coined by André Blondel
André Blondel
André-Eugène Blondel was a French engineer and physicist. He is the inventor of the electromechanical oscillograph and a system of photometric units of measurement.-Life:...
in 1921.
Metric equivalence:
Metric dimensions:
- illuminance = luminous intensityLuminous intensityIn 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 human eye...
× solid angleSolid angleThe solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
/ length2