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Radiant exposure

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In radiometry, radiant exposure or fluence is the radiant energy received by a surface per unit area, or equivalently the irradiance of a surface, integrated over time of irradiation, and spectral exposure is the radiant exposure per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of radiant exposure is the joule per square metre (J/m2), while that of spectral exposure in frequency is the joule per square metre per hertz (J⋅m−2⋅Hz−1) and that of spectral exposure in wavelength is the joule per square metre per metre (J/m3)—commonly the joule per square metre per nanometre (J⋅m−2⋅nm−1).

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Mathematical definitions

Radiant exposure

Radiant exposure of a surface, denoted He ("e" for "energetic", to avoid confusion with photometric quantities), is defined as[1] where

  • ∂ is the partial derivative symbol;
  • Qe is the radiant energy;
  • A is the area;
  • T is the duration of irradiation;
  • Ee is the irradiance.

Spectral exposure

Spectral exposure in frequency of a surface, denoted He,ν, is defined as[1] where ν is the frequency.

Spectral exposure in wavelength of a surface, denoted He,λ, is defined as[1] where λ is the wavelength.

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SI radiometry units

More information Quantity, Unit ...
  1. Standards organizations recommend that radiometric quantities should be denoted with suffix "e" (for "energetic") to avoid confusion with photometric or photon quantities.
  2. Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.
  3. Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.)
  4. Spectral quantities given per unit wavelength are denoted with suffix "λ".
  5. Directional quantities are denoted with suffix "Ω".
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See also

References

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