Radiative cooling (RC) is passive cooling strategy that cools without any electricity input could therefore have a significant impact on global energy consumption.

Recently, Sandeep Chamoli and LI Wei from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS), Mahommad Elkabash from Massachusetts Institute of Technology, and GUO Chunlei from University of Rochester, assessesed the advantages and disadvantages of introducing angular selectivity in RC under various conditions and highlighted the conditions where angularly selective thermal emission could be advantageous. This study was published in Nanophotonics.

Spectrally selective thermal emitters, under some conditions, can cool down an object to deep sub-freezing temperatures. However, this work investigated another degree of freedom, angular selectivity, and showed that under ideal conditions, angularly selective thermal emitters can cool an object down by 80 degrees. Additionally, angularly thermal emitters can reach subfreezing temperatures even in humid environments while spectrally selective thermal emitters have negligible cooling performance.

Besides, a spectrally and angularly selective thermal emitter based on a novel thin film architecture was developed.

In this way, medications and superconductors can be passively cooled to to deep subfreezing temperatures.