emissivity

• For sufficiently small optical thickness, absorptivity and emissivity are about equal to their emission cross sections per unit area facing the direction being considered; thus absorptivity and emissivity increase over geometric distance in proportion to cross section per unit volume. —  RealClimate
• After the first reflection or scattering, the intensity I1 = I0* (1-absorptivity) + Ibb*emissivity. —  RealClimate
• As I understand it, sometimes we refer to this as grey body radiation, indicating that the spectral emissivity is constant at all wavelengths, in which case one may simply speak of "the emissivity." —  RealClimate
• However, when the spectral emissivity is not constant, one can still apply Planck's law to describe it by calculating its intensity at a given frequency as a function of temperature, but one multiplies that intensity by the spectral emissivity, where the spectral emissivity is the emissivity at the corresponding wavelength. —  RealClimate
• Boost efficiency with weather-stripping or replace with energy efficient models with a U­-factor of .30 or lower and with low-emissivity (low-E) coatings.

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