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). Radiant intensity is distinct from irradiance and radiant exitance, which are often called intensity in branches of physics other than radiometry.
SI radiometry units- v
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| Quantity | Symbol | SI unit | Symbol | 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. |
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| Spectral radiance | Leλ or Leν |
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 | 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 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. |
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| 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 |
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 | 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 | ||||||||
Famous quotes containing the words radiant and/or intensity:
“Prayer is the fair and radiant daughter of all the human virtues, the arch connecting heaven and earth, the sweet companion that is alike the lion and the dove; and prayer will give you the key of heaven. As pure and as bold as innocence, as strong as all things are that are entire and single, this fair and invincible queen rests on the material world; she has taken possession of it; for, like the sun, she casts about it a sphere of light.”
—Honoré De Balzac (1799–1850)
“Murder is born of love, and love attains the greatest intensity in murder.”
—Octave Mirbeau (1850–1917)