It's a fairly recent development[0], a few years before that the principle was demonstrated as a special surface coating on smooth surfaces rather than paint. A

It's a fairly recent development[0], a few years before that the principle was demonstrated as a special surface coating on smooth surfaces rather than paint. And it's about the IR window[1], which is smaller than the whole IR spectrum. And sunlight delivers most of its energy in visible light and near IR, so there isn't a problem with reflecting the incoming light while radiating away into cold space in the IR window[2]. [0] https://ceramics.org/ceramic-tech-today/materials-innovations/new-reflecting-paint-achieves-full-daytime-sub-ambient-radiative-cooling https://ceramics.org/ceramic-tech-today/materials-innovation... [1] https://en.wikipedia.org/wiki/Infrared_window https://en.wikipedia.org/wiki/Infrared_window [2] https://www.researchgate.net/figure/Illustration-showing-desired-low-absorptivity-over-Solar-Spectrum-relative-to-desired_fig10_326902771 https://www.researchgate.net/figure/Illustration-showing-des...