photometry Photometry can refer to:
* Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision
* Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electro ...
, the lumen second (lm⋅s) is the unit of
luminous energy
In photometry, luminous energy is the perceived energy of light. This is sometimes called the quantity of light.International System of Units (SI). It is based on the lumen, the SI unit of luminous flux, and the second, the
SI base unit
The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all ...
of time.
The lumen second is sometimes called the talbot (symbol T). This name was coined in 1937 by the Committee on Colorimetry,
Optical Society of America
Optica (formerly known as The Optical Society (OSA) and before that as the Optical Society of America) is a professional society of individuals and companies with an interest in optics and photonics. It publishes journals and organizes conference ...
William Fox Talbot
William Henry Fox Talbot Fellow of the Royal Society, FRS FRSE Royal Astronomical Society, FRAS (; 11 February 180017 September 1877) was an English scientist, inventor, and photography pioneer who invented the Salt print, salted paper and calo ...
. The talbot is exactly equal to the lumen second:
:1 T = 1 lm⋅s
The use of the symbol T for talbots conflicts with T as the symbol for the tesla, the SI unit of magnetic flux density.
The photometric unit lumerg or lumberg, proposed by the Committee on Colorimetry in 1937, correlates with the old CGS unit
erg
The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...
in the same way that the lumen second correlates with the
radiometric
Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ...
unit joule, so that .Loyd Ancile Jones. ''Colorimetry: Preliminary draft of a report on nomenclature and definitions''. Journal of the
Optical Society of America
Optica (formerly known as The Optical Society (OSA) and before that as the Optical Society of America) is a professional society of individuals and companies with an interest in optics and photonics. It publishes journals and organizes conference ...
, Volume 27, page 211 (June 1937): “Referring again to Table I, terms (21) and (22) represent names for units which the committee has voted to adopt. The decision was almost unanimous in the case of recommending talbot as a psychophysical correlate of joule. The vote on lumerg as the psychophysical correlate of the
erg
The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...