This article will be permanently flagged as inappropriate and made unaccessible to everyone. Are you certain this article is inappropriate? Excessive Violence Sexual Content Political / Social
Email Address:
Article Id: WHEBN0000556970 Reproduction Date:
In radiometry (measurement of electromagnetic radiation), irradiance is the radiant flux (power) received by a surface per unit area, and spectral irradiance is the irradiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of irradiance is the watt per square metre (W/m2), while that of spectral irradiance is the watt per square metre per hertz (W·m−2·Hz−1) or the watt per square metre per metre (W·m−3)—commonly the watt per square metre per nanometre (W·m−2·nm−1). The CGS unit erg per square centimetre per second (erg·cm−2·s−1) is often used in astronomy. Irradiance is often called "intensity" in branches of physics other than radiometry, but in radiometry this usage leads to confusion with radiant intensity.
Irradiance of a surface, denoted Ee ("e" for "energetic", to avoid confusion with photometric quantities), is defined as[1]
where
If we want to talk about the radiant flux emitted by a surface, we speak of radiant exitance.
Spectral irradiance in frequency of a surface, denoted Ee,ν, is defined as[1]
where ν is the frequency.
Spectral irradiance in wavelength of a surface, denoted Ee,λ, is defined as[1]
where λ is the wavelength.
Irradiance of a surface is also, according to the definition of radiant flux, equal to the time-average of the component of the Poynting vector perpendicular to the surface:
For a propagating sinusoidal linearly polarized electromagnetic plane wave, the Poynting vector always points to the direction of propagation while oscillating in magnitude. The irradiance of a surface is then given by[2]
This formula assumes that the magnetic susceptibility is negligible, i.e. that μr ≈ 1 where μr is the magnetic permeability of the propagation medium. This assumption is typically valid in transparent media in the optical frequency range.
The global irradiance on a horizontal surface on Earth consists of the direct irradiance Ee,dir and diffuse irradiance Ee,diff. On a tilted plane, there is another irradiance component, Ee,refl, which is the component that is reflected from the ground. The average ground reflection is about 20% of the global irradiance. Hence, the irradiance Ee on a tilted plane consists of three components:[3]
The integral of solar irradiance over a time period is called "solar exposure" or "insolation".[3][4]
Talk radio, Sports radio, Cadillac, Michigan, Wkad, Wlxv
Watt, Metre, Frequency, Power (physics), Astronomy
Watt, Radiometry, Frequency, Emissivity, Absorptance
Sound, Second, Wave, Radio, South America
Solar System, Physical cosmology, Star, Dark matter, Mars
Photography, Lux, Watt, Si, Exposure value
Watt, Emissivity, Radiometry, Radiant flux, Frequency
Image, Photonics, Irradiance, International System of Units, Ampere
Watt, Radiometry, Frequency, Astronomy, Physics
Irradiance, Fortran, Solar panel, Modtran, Air mass (solar energy)