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
- t
- e
| 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. |
|||
| 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. |
|||
| 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 |
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 | ||||||||
Famous quotes containing the words radiant and/or intensity:
“The base emotions Plato banned
have left a radio-active and not radiant land.”
—Libby Houston (b. 1941)
“The bourgeois treasures nothing more highly than the self.... And so at the cost of intensity he achieves his own preservation and security. His harvest is a quiet mind which he prefers to being possessed by God, as he prefers comfort to pleasure, convenience to liberty, and a pleasant temperature to that deathly inner consuming fire.”
—Hermann Hesse (1877–1962)