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The reference spectrum in ASTM G177 is limited to the global irradiance in the ultraviolet (280–400 nm), and corresponds to "high-UV" conditions frequently encountered in arid and elevated sites, such as in the southwest USA. This spectrum is to be used as a reference for testing the degradation and durability of materials.
Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: =where M(λ) is the spectral irradiance (or exitance) of the light (SI units: W/m 2 = kg·m −1 ·s −3); Φ is the radiant flux of the source (SI unit: watt, W); A is the area over which the radiant flux is integrated (SI unit: square meter, m 2); and λ is the wavelength (SI unit: meter, m).
The two forms have different dimensions and units: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W⋅m −2 ⋅Hz −1), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W⋅m −3), or more commonly watts per square metre per nanometre (W⋅m −2 ...
Radiant intensity is used to characterize the emission of radiation by an antenna: [2], = (), where E e is the irradiance of the antenna;; r is the distance from the antenna.; Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is ...
In radiometry, radiant exposure or fluence is the radiant energy received by a surface per unit area, or equivalently the irradiance of a surface, integrated over time of irradiation, and spectral exposure is the radiant exposure per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.
The plot for vapor is a transformation of data Synthetic spectrum for gas mixture ' Pure H 2 O ' (296K, 1 atm) retrieved from Hitran on the Web Information System. [6] Liquid water absorption spectrum across a wide wavelength range [missing source] The absorption of electromagnetic radiation by water depends on the state of the water.
Photosynthetically active radiation (PAR) spans the visible light portion of the electromagnetic spectrum from 400 to 700 nanometers. Photosynthetically active radiation (PAR) designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.
Brightness temperature or radiance temperature is a measure of the intensity of electromagnetic energy coming from a source. [1] In particular, it is the temperature at which a black body would have to be in order to duplicate the observed intensity of a grey body object at a frequency . [2]