Irradiance

Information about Irradiance

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 interchangeably for radiation emerging from a surface. The SI units for all of these quantities are watts per square metre (WÂ·m^-2), while the cgs units are ergs per square centimeter per second (ergÂ·cm^-2Â·s^-1, often used in astronomy). These quantities are sometimes called intensity, but this usage leads to confusion with radiant intensity, which has different units.

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 WÂ·m^-3, or commonly WÂ·m^-2Â·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.

SI radiometry units
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Quantity	Symbol	SI unit	Abbr.	Notes
Radiant energy	Q	joule	J	energy
Radiant flux	F	watt	W	radiant energy per unit time, also called radiant power
Radiant intensity	I	watt per steradian	Wsr⁻¹	power per unit solid angle
Radiance	L	watt per steradian per square metre	Wsr⁻¹m⁻²	power per unit solid angle per unit projected source area. Sometimes confusingly called "intensity".
Irradiance	E	watt per square metre	Wm⁻²	power incident on a surface. Sometimes confusingly called "intensity".
Radiant exitance / Radiant emittance	M	watt per square metre	Wm⁻²	power emitted from a surface.
Radiosity	J or J_λ	watt per square metre	Wm⁻²	emitted plus reflected power leaving a surface
Spectral radiance	L_λ or L_ν	watt per steradian per metre³ or watt per steradian per square metre per hertz	Wsr⁻¹m⁻³ or Wsr⁻¹m⁻²Hz⁻¹	commonly measured in Wsr⁻¹m⁻²nm⁻¹
Spectral irradiance	E_λ or E_ν	watt per metre³ or watt per square metre per hertz	Wm⁻³ or Wm⁻²Hz⁻¹	commonly measured in Wm⁻²nm⁻¹

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.
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Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other.
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Area is a physical quantity expressing the size of a part of a surface. The term Surface area is the summation of the areas of the exposed sides of an object.

Units

Units for measuring surface area include:

square metre = SI derived unit

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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:

One of two Italian words:
sÃ¬ (accented) for "yes"
si

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Branding NewsTalk 1240
First air date 1945
Frequency 1240 kHz
Format News-Talk-Sports
Power 1,000 watts
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Owner MacDonald Garber Broadcasting
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square metre (also spelled meter, see spelling differences) is the SI derived unit of area, with symbol mÂ². It is defined as the area of a square whose sides measure exactly one metre.
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centimetre-gram-second system (CGS) is a system of physical units. It is always the same for mechanical units, but there are several variants of electric additions. It was replaced by the MKS, or metre-kilogram-second system, which in turn was replaced by the International
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ERGS is an abbreviation of:

Electronic Route Guidance System In the United States, 1970s era government sponsored in-vehicle navigation and route guidance systems.
The plural of erg

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second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time.

SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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Astronomy is the scientific study of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation).
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In physics, intensity is a measure of the time-averaged energy flux. To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area (i.e.
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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 (WÂ·sr^-1).
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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:

One of two Italian words:
sÃ¬ (accented) for "yes"
si

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Radiant energy is the energy of electromagnetic waves.^[1] The quantity of radiant energy may be calculated by integrating radiant flux (or power) with respect to time and, like all forms of energy, its SI unit is the joule.
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The joule (IPA: [dʒuːl] or [dʒaʊl]) (symbol: J) is the SI unit of energy.
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energy (from the Greek ενεργός, energos, "active, working")^[1] is a scalar physical quantity that is a property of objects and systems of objects which is conserved by nature.
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In radiometry, radiant flux or radiant power is the measure of the total power of electromagnetic radiation (including visible light). The power may be the total emitted from a source, or the total landing on a particular surface.
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The steradian (symbol: sr) is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane.
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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.
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Radiosity is the total of emitted and reflected radiation leaving a surface, in the fields of Optics and Heat Transfer. Hemispherical radiosity is the integral of the spectral intensity of reflected plus emitted radiation over the hemispherical solid angle^[1].
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Irradiance

Information about Irradiance

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