Your unit is W ( watt ).
For electromagnetic radiation with a frequency of 540 THz (green light with a wavelength of 555 nm), a photon current of 2 corresponds .79e18 s −1 of a radiation power of 1 W.
Basic photometric law
In order to determine the dependence of the radiant power on a surface element of a radiator surface of the luminance of a Lambert radiator (constant surface brightness) on a surface element located at a distance , the so-called fundamental photometric law can be used, which combines Lambert's law of cosines and the law of photometric distance .
This depends, among other things, on the mutual position of the two surfaces in space, which is taken into account by the angle and between the beam direction and the surface normals.
Relation to other sizes
If the radiation output is related to the size of the irradiated area, the irradiance is obtained (unit: W / m²):
If, on the other hand, it is related to the solid angle into which a light beam emanating from a light source falls, then the radiation intensity is obtained
with the unit W / sr.
In photometry (lighting technology) the corresponding measurand is the luminous flux , measured in the unit lumen . While the radiant power (mostly written in this context ) is an energetic , i.e. objective, measured variable, the spectral sensitivity of the human eye is included in the luminous flux ( V-lambda curve ). The link between the two quantities is the photometric radiation equivalent of the light source
which depends on their wavelength spectrum.
The following table gives an overview of quantities and units in radiometry and photometry:
|radiometric quantity||Symbol a)||SI unit||description||photometric equivalent b)||symbol||SI unit|
radiant power, radiant flux, radiant power
( watt )
|Radiant energy through time||
luminous flux, luminous power
( lumens )
irradiance, radiant intensity
|W / sr||Radiation flux through solid angles||
|cd = lm / sr
( candela )
|W / m 2||Radiation flux through the receiver surface||
|lx = lm / m 2
( lux )
emission current density, radiant exitance
|W / m 2||Radiation flux through the transmitter surface||
Specific light emission
|lm / m 2|
radiance, radiance, radiance
|W / m 2 sr||Radiant intensity through effective transmitter area||
||cd / m 2|
amount of radiation, radiant energy
( joules )
|by radiation transmitted energy||
Amount of light
luminous energy, quantity of light
|lm · s|
irradiation, radiant exposure
|J / m 2||Radiant energy through the receiver surface||
|1||Radiation flux through absorbed (mostly electrical) power||
(overall) luminous efficacy
|lm / W|
- F. Pedrotti, L. Pedrotti, W. Bausch, H. Schmidt: Optics for engineers: Fundamentals . 2nd Edition. Springer, Berlin 2001, ISBN 3-540-67379-2 .