Radiant flux



In visible light). The power may be the total emitted from a source, or the total landing on a particular surface.

Units

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

See also

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 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
 
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