In
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 ...
, luminous energy is the perceived
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
of
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
. This is sometimes called the quantity of light.
[electropedia](_blank)
International Electrotechnical Vocabulary
The International Electrotechnical Vocabulary (IEV) serves to promote the global unification of terminology in the field of electrotechnology, electronics and telecommunications. It is developed by IEC Technical Committee 1 (Terminology), and pub ...
(IEV) of the International Electrotechnical Commission: entry # 845-21-037 Luminous energy is not the same as
radiant energy
Radiant may refer to:
Computers, software, and video games
* Radiant (software), a content management system
* GtkRadiant, a level editor created by id Software for their games
* Radiant AI, a technology developed by Bethesda Softworks for '' ...
, the corresponding objective
physical quantity. This is because the
human eye can only see light in the
visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wa ...
and has different sensitivities to
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
of different
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s within the spectrum. When adapted for bright conditions (
photopic vision
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visu ...
), the eye is most sensitive to light at a wavelength of 555
nm. Light with a given amount of radiant energy will have more luminous energy if the wavelength is 555 nm than if the wavelength is longer or shorter. Light whose wavelength is well outside the
visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wa ...
has a luminous energy of zero, regardless of the amount of radiant energy present.
The
SI unit of luminous energy is the
lumen second, which is unofficially known as the
talbot in honor of
William Henry Fox Talbot
William Henry Fox Talbot 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 calotype processes, precursors t ...
. In other
systems of units, luminous energy may be expressed in basic units of energy.
Explanation
Luminous energy
is related to radiant energy
by the expression
Here
is the wavelength of light, and
is the
luminosity function
A luminous efficiency function or luminosity function represents the average spectral sensitivity of human visual perception of light. It is based on subjective judgements of which of a pair of different-colored lights is brighter, to descri ...
, which represents the eye's sensitivity to different wavelengths of light.
Luminous energy is the integrated
luminous flux in a given period of time:
See also
*
Coefficient of utilization
A coefficient of utilization (CU) is a measure of the efficiency of a luminaire in transferring luminous energy to the working plane in a particular area. The CU is the ratio of luminous flux from a luminaire incident upon a work plane to that emit ...
*
Radiant energy
Radiant may refer to:
Computers, software, and video games
* Radiant (software), a content management system
* GtkRadiant, a level editor created by id Software for their games
* Radiant AI, a technology developed by Bethesda Softworks for '' ...
References
Physical quantities
Photometry
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