Radiant intensity
Encyclopedia : R : RA : RAD : Radiant intensity
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). It is distinct from intensity defined by irradiance or radiant exitance which measure radiation directed at or emitted from a given surface area.
See also
| 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 | watt per square metre | W·m−2 | power incident on a surface. Sometimes confusingly called "intensity". |
| Radiant emittance / Radiant exitance | M | watt per square metre | W·m−2 | power emitted from a surface. Sometimes confusingly called "intensity". |
| 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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