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radiance, L

Radiant power, P, leaving or passing through a small transparent element of surface in a given direction from the source about the solid angleΩ, divided by the solid angle and by the orthogonally projected area of the element in a plane normal to the given beam direction, d S ⊥ = d S cos ⁡ θ
Notes:
  1. Mathematical definition:
    L = d 2 P d Ω d S ⊥ = d 2 P d Ω d S cos ⁡ θ
    for a divergent beam propagating in an elementary cone of the solid angleΩ containing the direction θ. SI unit is W m −2 sr −1.
  2. For a parallel beam it is the radiant power, P, of all wavelengths leaving or passing through a small element of surface in a given direction from the source divided by the orthogonally projected area of the element in a plane normal to the given direction of the beam, θ. Mathematical definition in this case: d P / ( d S cos ⁡ θ ) If the radiant power is constant over the surface area considered, P / S cos ⁡ θ. SI unit is W m −2.
  3. Equivalent to L = ∫ λ L λ ⁢ d λ, where L λ is the spectral radiance at wavelengthλ.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 408
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IUPAC > Gold Book > math/physics > quantities
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.R05037.
Original PDF version: http://www.iupac.org/goldbook/R05037.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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