Radiant energy
The radiation energy is a physical quantity in radiometry . It is the energy that is transported by electromagnetic waves , for example light , or the energy of electromagnetic waves that is contained in a given area of space and at a defined point in time . The SI unit of radiant energy is the joule .
description
If you consider electromagnetic radiation as a stream of photons , the radiant energy is the energy transported in this stream.
The energy of a photon only depends on the frequency:
with Planck's quantum of action and the frequency of the wave .
In the macroscopic area (very many photons) one often uses the symbols or for the radiation energy instead of . For monochromatic electromagnetic radiation, for example for monochromatic (single-colored) light , the radiation energy is the product of the number of photons in the spatial area and the energy of a photon:
As a rule, however, electromagnetic radiation consists of photons of different energies. In the case of light, one speaks of polychromatic (multicolored) light . For a general description of the radiation energy one must therefore consider the spectral distribution, which indicates how many photons are in a frequency range from to :
The following results for the radiation energy:
- ,
Connection with other quantities
Radiated power
Looking at the time when a certain amount of radiation energy is transported, there is the radiation power (also called radiant flux) .
Photometry
In photometry , the sensitivity of the human eye is also taken into account, which depends on the frequency or wavelength. The quantity weighted in this way is the amount of light . The indices e and v stand for energetic and visual .
Overview
radiometric quantity | Symbol a) | SI unit | description | photometric equivalent b) | symbol | SI unit |
Radiant flux radiant power, radiant flux, radiant power |
W ( watt ) |
Radiant energy through time |
Luminous flux luminous flux, luminous power |
lm ( lumens ) |
||
Radiant intensity irradiance, radiant intensity |
W / sr | Radiation flux through solid angles |
Luminous intensity luminous intensity |
cd = lm / sr ( candela ) |
||
Irradiance irradiance |
W / m 2 | Radiation flux through the receiver surface |
Illuminance illuminance |
lx = lm / m 2 ( lux ) |
||
Specific radiation emission current density, radiant exitance |
W / m 2 | Radiation flux through the transmitter surface |
Specific light emission luminous exitance |
lm / m 2 | ||
Radiance radiance, radiance, radiance |
W / m 2 sr | Radiant intensity through effective transmitter area |
Luminance luminance |
cd / m 2 | ||
Radiant energy amount of radiation, radiant energy |
J ( joules ) |
by radiation transmitted energy |
Amount of light luminous energy, quantity of light |
lm · s | ||
Irradiation irradiation, radiant exposure |
J / m 2 | Radiant energy through the receiver surface |
Exposure luminous exposure |
lx s | ||
Radiation yield radiant efficiency |
1 | Radiation flux through absorbed (mostly electrical) power |
Luminous efficiency (overall) luminous efficacy |
lm / W |
Individual evidence
- ↑ Horst Stöcker (editor): Pocket book of physics: formulas, tables, overviews . 6., corr. German edition, Frankfurt am Main 2010, ISBN 978-3-8171-1861-8 , pp. 369 (XXIV, 1079).
- ↑ Horst Stöcker (editor), ibid, p. 734.