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But for teflon to passively cool, it would have to be strongly absorbent in the IR.

The way it works is this: the sun’s rays are at 5500 K. So you pick the set of materials that reflect light in the visible gap (the atmosphere takes care of the rest).

This keeps the material from getting heat.

Then, from this set, you pick a material that is strongly absorbent in IR.

If it absorbs in IR, itll emit there too, there y cooling itself

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Specifically, it needs to absorb/emit in a frequency range called the “sky window”, where the atmosphere is transparent. In this range, the object is basically seeing the cold of space at a few Kelvin, so that almost no energy is absorbed and a lot is emitted.

The trick is to design a system where the total power absorbed across the solar irradiance spectrum is less than the power that is emitted in the sky window, so that the system is a net power sink (in this case to the tune of 100W per sq. meter or so).

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