In radiometry, radiant flux or radiant power is the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light). In Optics, radiometry is the field that studies the Measurement of Electromagnetic radiation, including Visible light. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The power may be the total emitted from a source, or the total landing on a particular surface.

Units

The SI unit of radiant flux is the watt (W), which has dimensions of energy/time or, in SI units joules/second. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

See also

• Luminous flux
• Power (physics)
• Radiosity (heat transfer)

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SI radiometry units

Quantity	Symbol	SI unit	Abbr. In photometry, luminous flux or luminous power is the measure of the perceived power of Light. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for In the fields of Optics and Heat transfer, radiosity is the total emitted and reflected radiation leaving a surface	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. Radiant energy is the Energy of Electromagnetic waves The quantity of radiant energy may be calculated by integrating Radiant flux (or power The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. In Radiometry, radiant intensity is a measure of the The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The steradian (symbol sr) is the SI unit of Solid angle. It is used to describe two-dimensional angular spans in three- Dimensional space 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 M^2 redirects here For other uses see M². CM2 redirects here Sometimes confusingly called "intensity".
Irradiance	E, I	watt per square metre	W·m−2	power incident on a surface. Irradiance, radiant emittance, and radiant exitance are Radiometry terms for the power of Electromagnetic radiation at a surface per unit Sometimes confusingly called "intensity". In Physics, intensity is a measure of the time-averaged Energy Flux.
Radiant exitance / Radiant emittance	M	watt per square metre	W·m−2	power emitted from a surface. Irradiance, radiant emittance, and radiant exitance are Radiometry terms for the power of Electromagnetic radiation at a surface per unit
Radiosity	J or Jλ	watt per square metre	W·m−2	emitted plus reflected power leaving a surface
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

In the fields of Optics and Heat transfer, radiosity is the total emitted and reflected radiation leaving a surface 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 The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Irradiance, radiant emittance, and radiant exitance are Radiometry terms for the power of Electromagnetic radiation at a surface per unit

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