- May 10, 2008
- Reaction score
- Dallas, TX
My understanding is that it is per wavelength: insofar as a body failsto be a perfect absorber it fails to be a perfect blackbody radiator, and at the same wavelengths. I was first made aware of this in a discussion on the vulnerability of spacecraft radiators in combat: you can't protect them from laser fire by making them reflective or transparent, because they'll fail to emit in the affected wavelengths to the exact same degree as they'll fail to absorb. I remember that the discussion specifically covered wavelength specific effects on blackbody radiation.In the total energy balance yes, but not per wavelength. What you say is true for line emission, but that's not the mechanism we're dealing with here - we have line absorption but broad blackbody emission.
After doing a bit of research,
gives the equation
\[ \alpha_\lambda = \epsilon_\lambda \]
which, given the lambda subscript, and if I read the article correctly, I believe bears out that absorbtivity and emissivity are equal per wavelength.