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Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area. "Irradiance" is used when the electromagnetic radiation is incident on the surface. The other two terms are used interchangably for radiation emerging from a surface. The SI units for all of these quantities are watts per square metre (W/m2). These quantities are sometimes called intensity, but this usage leads to confusion with radiant intensity, which has different units. In telecommunication and physics, radiometry is the science of radiation measurement. ...
Electromagnetic radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ...
The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...
The watt (symbol: W) is the SI derived unit of power. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
In physics, intensity is a measure of the time-averaged energy flux. ...
In physics, intensity is a measure of the time-averaged energy flux. ...
All of these quantities characterize the total amount of radiation present, at all frequencies. It is also common to consider each frequency in the spectrum separately. When this is done for radiation incident on a surface, it is called spectral irradiance, and has SI units W/m3, or commonly W·m-2·nm-1.
If a point source radiates light uniformly in all directions and there is no absorption, then the irradiance drops off in proportion to the distance from the object squared, since the total power is constant and it is spread over an area that increases with the square of the distance from the source.
See also | SI radiometry units edit Illuminance is the total luminous flux incident per unit area. ...
The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...
| | 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". Radiant energy is the energy transported by electromagnetic waves. ...
The joule (symbol: J) is the SI unit of energy, or work. ...
The joule (symbol: J) is the SI unit of energy, or work. ...
Luminous flux or luminous power is the measure of the perceived power of light. ...
The watt (symbol: W) is the SI derived unit of power. ...
The watt (symbol: W) is the SI derived unit of power. ...
In physics, intensity is a measure of the time-averaged energy flux. ...
The watt (symbol: W) is the SI derived unit of power. ...
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ...
Radiance is a physical quantity used in the sphere of radiometry to measure the intensity of a light beam, defined as power per unit solid angle per unit projected area of the source. ...
The watt (symbol: W) is the SI derived unit of power. ...
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
| | Irradiance | E | watt per square metre | W·m−2 | power incident on a surface.
Sometimes confusingly called "intensity". The watt (symbol: W) is the SI derived unit of power. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
In physics, intensity is a measure of the time-averaged energy flux. ...
| | Radiant emittance / Radiant exitance | M | watt per square metre | W·m−2 | power emitted from a surface.
Sometimes confusingly called "intensity". Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area. ...
The watt (symbol: W) is the SI derived unit of power. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
In physics, intensity is a measure of the time-averaged energy flux. ...
| | Spectral radiance | Lλ
or
Lν | watt per steradian per metre3 or
watt per steradian per square metre per Hertz Radiance and spectral radiance are radiometric measures that describe the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. ...
The watt (symbol: W) is the SI derived unit of power. ...
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ...
The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ...
The watt (symbol: W) is the SI derived unit of power. ...
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
The hertz (symbol: Hz) is the SI unit of frequency. ...
| 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 | kkkk Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area. ...
The watt (symbol: W) is the SI derived unit of power. ...
The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. ...
The watt (symbol: W) is the SI derived unit of power. ...
A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...
The hertz (symbol: Hz) is the SI unit of frequency. ...
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