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John Doty wrote:
>> The reason why it's called a black-body radiation is not because 
>> it radiates better when black.  No, they call it that because a black
>> body does not reflect anything *extra* besides the radiation it already
>> emanetes.

>Not true. Emission and absorption are determined by the same function of wavelength,
> commonly called ???emissivity???. The higher the emissivity, the darker the material
> will appear at the given wavelength. If you had a material for which this was not
> true, you could construct a machine that would violate the second law of thermodynamics.

It's not entirely clear to me here if we disagree here.
I'll reparse your words later when I have more time.

>> But, to summarise, it will only help reflecting incoming radiation,
>> it will not matter one iota for primary heat radiation.

>Not true. Polymers generally have higher emissivity in the infrared than shiny metal.
> We exploit this in spacecraft design by covering surfaces we want to keep cold with
> ???silver teflon??? tape. The outer teflon layer is highly emissive in the thermal
> infrared, but transparent to most of the incoming solar radiation. The silver
> backing has very low emissivity, so it reflects the incoming radiation.

>In space engineering, we sometimes capture this effect by defining an average emissivity, 
>??, over thermal infrared wavelengths, and and average emissivity, ??, over the
> solar spectrum. We call ?? ???absorptivity??? to distinguish it from ??,
> but the real distinction is just the wavelength range, not the physics.

>When you???re not operating in a vacuum, coating the bare metal with a polymer will
> very likely improve radiative cooling. It is, however, an additional thermal
> resistance between the metal and the air, so it will impair conductive and convective
> cooling. Detailed calculation and measurement is the only way to resolve this.

I concede here, I guess my textbook knowledge here falls short with respect
to modern material knowledge.
-- 
Stephen.