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What is irradiance

  1. Jul 23, 2014 #1

    Irradiance is the power per area of the radiation received by a surface.

    It is measured in SI units of watts per square meter ([itex]W.m^{-2}[/itex]), or cgs units of ergs per square centimeter per second ([itex]erg.cm^{-2}.s^{-1}[/itex], often used in astronomy).


    surface area of star:
    [tex]4\pi R^2[/tex]
    total power radiated (Luminosity):
    [tex]L\ =\ 4\pi R^2\sigma T^4[/tex]
    power per area at distance d (Irradiance):
    [tex]I\ =\ \frac{L}{4\pi d^2}\ =\ \frac{R^2}{d^2}\sigma T^4[/tex]
    ([itex]\sigma[/itex] is the Stefan-Boltzmann constant, [itex]5.67×10^{-8} \, W\cdot m^{-2}\cdot K^{-4}[/itex])

    Extended explanation

    Other similar units:

    "Ir-" means "on", so irradiance relates to radiation on (received by) a surface, while radiance, and radiant intensity emittance excitance or flux, relate to radiation from a surface.

    * This entry is from our old Library feature. If you know who wrote it, please let us know so we can attribute a writer. Thanks!
  2. jcsd
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