2 ms·

You can have dielectric coatings on a mirror that increase the reflectivity to >99.9% (and over a wide range of wavelengths). You can of course get a lot more

• adrian_b 4y ago
  99.9% for visible light does not mean 99.9% for all the solar light. Most dielectric coatings absorb ultraviolet light so they reflect much less of the total solar light, most likely less than 90%. Such a mirror with dielectric coatings would not be able to cool the object on which it is applied, unlike the paints which are discussed in the article, which are based on boron nitride, barium sulfate, calcium carbonate or fluorinated polymers, all of which do not absorb ultraviolet light. The common white paints based on titanium white or zinc white also absorb ultraviolet light, so they cannot be used for cooling an object illuminated by the Sun.