Radiometry

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In optics, radiometry is the field that studies the measurement of electromagnetic radiation, including visible light. Note that light is also measured using the techniques of photometry, which deal with brightness as perceived by the human eye, rather than absolute power.

Radiometry is important in astronomy, especially radio astronomy, and is important for Earth remote sensing. The measurement techniques categorized as radiometry in optics are called photometry in some astronomical applications, contrary to the optics usage of the term.

Spectroradiometry is the measurement of absolute radiometric quantities in narrow bands of wavelength.^[1]

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SI radiometry units

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, I	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

[edit] See also

• Reflectivity

[edit] References

1. ^ Leslie D. Stroebel and Richard D. Zakia (1993). Focal Encyclopedia of Photography, 3rd ed., Focal Press, p. 115. ISBN 0240514173. 

[edit] External links

• Radiometry and photometry FAQ Professor Jim Palmer's Radiometry FAQ page (University of Arizona).