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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
- Standards organizations recommend that radiometric quantities should be denoted with suffix "e" (for "energetic") to avoid confusion with photometric or photon quantities.
- Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.
- Spectral quantities given per unit wavelength are denoted with suffix "λ".
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See also
References
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