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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.
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The field of spectroradiometry concerns itself with the measurement of absolute radiometric quantities in narrow wavelength intervals. [1] It is useful to sample the spectrum with narrow bandwidth and wavelength increments because many sources have line structures [2] Most often in spectroradiometry, spectral irradiance is the desired measurement.
I (x, t ; r 1, ν) is defined to be such that a virtual source area, dA 1, containing the point P 1, is an apparent emitter of a small but finite amount of energy dE transported by radiation of frequencies (ν, ν + dν) in a small time duration dt, where = (,;,) (), and where θ 1 is the angle between the line of propagation r and the normal P 1 N 1 to dA 1; the effective destination of ...
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).
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 ...
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Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include jansky ( 1 Jy = 10 −26 W⋅m −2 ⋅Hz −1 ) and solar flux unit ( 1 sfu = 10 −22 W⋅m −2 ⋅Hz −1 = 10 ...