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Radiant intensity



In radiometry, radiant intensity is a measure of the intensity of electromagnetic radiation. It is defined as power per unit solid angle. The SI unit of radiant intensity is watts per steradian (W·sr-1). It is distinct from intensity defined by irradiance or radiant exitance which measure radiation directed at or emitted from a given surface area.

Additional recommended knowledge

See also

  • Candela
  • Luminous intensity
  • Intensity

SI radiometry units

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Quantity Symbol SI unit Abbr. Notes
Radiant energy Q joule J energy
Radiant flux Φ watt W radiant energy per unit time, also called radiant power
Radiant intensity I watt per steradian W·sr−1 power per unit solid angle
Radiance L watt per steradian per square metre W·sr−1·m−2 power per unit solid angle per unit projected source area.

Sometimes confusingly called "intensity".

Irradiance E watt per square metre W·m−2 power incident on a surface.

Sometimes confusingly called "intensity".

Radiant exitance / Radiant emittance M watt per square metre W·m−2 power emitted from a surface.
Radiosity J or Jλ watt per square metre W·m−2 emitted plus reflected power leaving a surface
Spectral radiance Lλ
or
Lν
watt per steradian per metre3 or

watt per steradian per square metre per hertz

W·sr−1·m−3
or

W·sr−1·m−2·Hz−1

commonly measured in W·sr−1·m−2·nm−1
Spectral irradiance Eλ
or
Eν
watt per metre3 or
watt per square metre per hertz
W·m−3
or
W·m−2·Hz−1
commonly measured in W·m−2·nm−1
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radiant_intensity". A list of authors is available in Wikipedia.
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