The need to cool people in a warming world has led to renewed interest in radiative cooling in recent years. Most recent research has focused on the development of spectrum-selective materials designed to radiate in the atmospheric window while suppressing absorption of radiation outside of this window. However the alternative approach of using angular selectivity, via the inclusion of nonimaging optical components to restrict the cooling element’s field of view, has been neglected. Here we argue for the value of nonimaging optics in the design of practical radiative cooling systems.

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Harry Apostoleris and Matteo Chiesa, "Spectral selectivity or nonimaging optics: Which to use for radiative cooling?," Proc. SPIE 10758, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration XV, 107580I (Presented at SPIE Optical Engineering + Applications: August 20, 2018; Published: 14 September 2018); https://doi.org/10.1117/12.2321040.