(adsbygoogle = window.adsbygoogle || []).push({}); Definition/Summary

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).

Equations

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 radiationon(received by) a surface, while radiance, and radiant intensity emittance excitance or flux, relate to radiationfroma 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!

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# What is irradiance

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

Loading...

Similar Threads - irradiance | Date |
---|---|

I Calculated solar irradiation not matching up with measured | Mar 24, 2016 |

Confirmation on the Effect of Solar Irradiance | May 14, 2015 |

Extrasolar Planet Irradiance | Apr 27, 2011 |

Solar spectral irradiance at earth's TOA | Jul 11, 2010 |

**Physics Forums - The Fusion of Science and Community**