Radiant Flux - Units

Units

The SI unit of radiant flux is the watt (W), which has dimensions of energy/time or, in SI units joules/second.

SI radiometry units
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Quantity Unit Dimension Notes
Radiant energy Qe joule J M⋅L2⋅T−2 energy
Radiant flux Φe watt W M⋅L2⋅T−3 radiant energy per unit time, also called radiant power.
Spectral power Φeλ 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 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.
Spectral radiance Leλ
or
Leν		 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		 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.
Irradiance Ee 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.
Spectral irradiance Eeλ
or
Eeν		 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.
Radiant exitance /
Radiant emittance		 Me watt per square metre W⋅m−2 M⋅T−3 power emitted from a surface.
Spectral radiant exitance /
Spectral radiant emittance		 Meλ
or
Meν		 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		 power emitted from a surface per wavelength or frequency.
Radiosity Je or Jeλ 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

Read more about this topic:  Radiant Flux

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