Irradiation (physical quantity)

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Physical size
Surname Irradiation
Formula symbol ,
Size and
unit system
unit dimension
SI J · m -2 M · T −2

The irradiation or irradiation is a physical quantity , mainly in the radiometry is used. It is the time-integrated irradiance and indicates the incident radiation energy of electromagnetic radiation per area. The symbol for irradiation is , the SI unit is joules per square meter (J / m 2 ). In the case of accumulating receivers (e.g. a photo plate ), the irradiation is a measure of the area-related potential of the radiation.

Irradiation should not be confused with fluence ; the latter is a particle-related quantity (unit of measurement m −2 ).


For a given location, the irradiation can be expressed as the radiation energy Q per area or, equivalent, as the integral of the irradiance E over the given period of time .

The photometric equivalent of the radiation, that is, weighted with the sensitivity of the human eye, is the exposure H v .


This size is also used in technical, scientific, but also medical areas:

The duration of the irradiation depends on the application and may be specified separately. The time interval to which the measurement relates can range from a few attoseconds (ultrashort pulse laser) to hours ( sunburn ) to years (fading of car paintwork). A reference variable for the time interval often emerges from the application.

Relationship with other radiometric quantities

radiometric quantity Symbol a) SI unit description photometric equivalent b) symbol SI unit
Radiant flux
radiant power, radiant flux, radiant power
( watt )
Radiant energy through time Luminous flux
luminous flux, luminous power
( lumens )
Radiant intensity
irradiance, radiant intensity
W / sr Radiation flux through solid angles Luminous intensity
luminous intensity
cd = lm / sr
( candela )
W / m 2 Radiation flux through the receiver surface 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
W / m 2 sr Radiant intensity through effective transmitter area Luminance luminance
cd / m 2
Radiant energy
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 Exposure
luminous exposure
lx s
Radiation yield
radiant efficiency
1 Radiation flux through absorbed (mostly electrical) power Luminous efficiency
(overall) luminous efficacy
lm / W
a)The index "e" is used to distinguish it from the photometric quantities. It can be omitted.
b)The photometric quantities are the radiometric quantities, weighted with the photometric radiation equivalent K , which indicates the sensitivity of the human eye.


  • Ludwig Bergmann , Clemens Schaefer : Optics . 9th edition. Walter de Gruyter, Berlin 1993, ISBN 3-11-012973-6 (textbook on experimental physics; 3).
  • Commission Électrotechnique Internationale (CEI): Vocabulaire international de l'éclairage . Publication CIE No. 17.4. Central Bureau of the CEI. 1987. (Vocabulaire électrotechnique international 50 (845))

References and comments

  1. Although in English the “radiant exposure” is sometimes inconsistently referred to as “radiometric fluence” (fluence)