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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 (W.m^{-2}), or cgs units of ergs per square centimeter per second (erg.cm^{-2}.s^{-1}, often used in astronomy).
Equations
surface area of star:
4\pi R^2
total power radiated (Luminosity):
L\ =\ 4\pi R^2\sigma T^4
power per area at distance d (Irradiance):
I\ =\ \frac{L}{4\pi d^2}\ =\ \frac{R^2}{d^2}\sigma T^4
(\sigma is the Stefan-Boltzmann constant, 5.67×10^{-8} \, W\cdot m^{-2}\cdot K^{-4})
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!
Irradiance is the power per area of the radiation received by a surface.
It is measured in SI units of watts per square meter (W.m^{-2}), or cgs units of ergs per square centimeter per second (erg.cm^{-2}.s^{-1}, often used in astronomy).
Equations
surface area of star:
4\pi R^2
total power radiated (Luminosity):
L\ =\ 4\pi R^2\sigma T^4
power per area at distance d (Irradiance):
I\ =\ \frac{L}{4\pi d^2}\ =\ \frac{R^2}{d^2}\sigma T^4
(\sigma is the Stefan-Boltzmann constant, 5.67×10^{-8} \, W\cdot m^{-2}\cdot K^{-4})
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!