Absorption spectra and emission spectra are identical for thermodynamic reasons. But emissions happen in the infrared and absorption from sunlight happens at vi

Absorption spectra and emission spectra are identical for thermodynamic reasons. But emissions happen in the infrared and absorption from sunlight happens at visible frequencies. So if you reflect visible light and absorb infrared light, you can stay cool in the Sun. Conversely, applying ultra-thin metal coatings to carbon-black objects can make them reflect infrared and absorb visible light, which is ideal for solar-thermal collectors.