In radiometry, radiant flux or radiant power is the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light). The power may be the total emitted from a source, or the total landing on a particular surface.
The SI unit of radiant flux is the watt (W), which has dimensions of energy/time or, in SI units joules/second.
Quantity | Symbol[nb 1] | SI unit | Symbol | Dimension | Notes | |||
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Radiant energy | Qe[nb 2] | joule | J | M⋅L2⋅T−2 | energy | |||
Radiant flux | Φe[nb 2] | watt | W | M⋅L2⋅T−3 | radiant energy per unit time, also called radiant power. | |||
Spectral power | Φeλ[nb 2][nb 3] | watt per metre | W⋅m−1 | M⋅L⋅T−3 | radiant power per wavelength. | |||
Radiant intensity | Ie | watt per steradian | W⋅sr−1 | M⋅L2⋅T−3 | power per unit solid angle. | |||
Spectral intensity | Ieλ[nb 3] | watt per steradian per metre | W⋅sr−1⋅m−1 | M⋅L⋅T−3 | radiant intensity per wavelength. | |||
Radiance | Le | watt per steradian per square metre | W⋅sr−1⋅m−2 | M⋅T−3 | power per unit solid angle per unit projected source area. confusingly called "intensity" in some other fields of study. |
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Spectral radiance | Leλ[nb 3] or Leν[nb 4] |
watt per steradian per metre3 or watt per steradian per square |
W⋅sr−1⋅m−3 or W⋅sr−1⋅m−2⋅Hz−1 |
M⋅L−1⋅T−3 or M⋅T−2 |
commonly measured in W⋅sr−1⋅m−2⋅nm−1 with surface area and either wavelength or frequency. |
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Irradiance | Ee[nb 2] | watt per square metre | W⋅m−2 | M⋅T−3 | power incident on a surface, also called radiant flux density. sometimes confusingly called "intensity" as well. |
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Spectral irradiance | Eeλ[nb 3] or Eeν[nb 4] |
watt per metre3 or watt per square metre per hertz |
W⋅m−3 or W⋅m−2⋅Hz−1 |
M⋅L−1⋅T−3 or M⋅T−2 |
commonly measured in W⋅m−2⋅nm−1 or 10−22W⋅m−2⋅Hz−1, known as solar flux unit.[nb 5] |
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Radiant exitance / Radiant emittance |
Me[nb 2] | watt per square metre | W⋅m−2 | M⋅T−3 | power emitted from a surface. | |||
Spectral radiant exitance / Spectral radiant emittance |
Meλ[nb 3] or Meν[nb 4] |
watt per metre3 or watt per square |
W⋅m−3 or W⋅m−2⋅Hz−1 |
M⋅L−1⋅T−3 or M⋅T−2 |
power emitted from a surface per wavelength or frequency. |
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Radiosity | Je or Jeλ[nb 3] | watt per square metre | W⋅m−2 | M⋅T−3 | emitted plus reflected power leaving a surface. | |||
Radiant exposure | He | joule per square metre | J⋅m−2 | M⋅T−2 | ||||
Radiant energy density | ωe | joule per metre3 | J⋅m−3 | M⋅L−1⋅T−2 | ||||
See also: SI · Radiometry · Photometry |
Boyd, Robert (1983). Radiometry and the Detection of Optical Radiation (Pure & Applied Optics Series). Wiley-Interscience. ISBN 978-0471861881. http://www.amazon.com/Radiometry-Detection-Optical-Radiation-Applied/dp/047186188X/ref=sr_1_1?s=books&ie=UTF8&qid=1313084491&sr=1-1.