Photonic thermal management of coloured objects

TLDR

The colours of outdoor structures are chosen for functional or aesthetic reasons, yet each colour requires careful control of its radiative thermal load for heating or cooling. The authors aim to calculate the full tunable range of radiative thermal load for every colour. They perform a comprehensive photonic calculation to determine this range across the visible spectrum. The results show a radiative load range exceeding 680 W m⁻² for all colours, peaking at 866 W m⁻², and experimentally demonstrate that two pink photonic structures can differ by 47.6 °C under sunlight, with one being over 20 °C hotter or cooler than a comparable commercial paint and 10 °C hotter than a commercial black paint, underscoring the potential of photonic thermal management.

Abstract

The colours of outdoor structures, such as automobiles, buildings and clothing, are typically chosen for functional or aesthetic reasons. With a chosen colour, however, one must control the radiative thermal load for heating or cooling purposes. Here we provide a comprehensive calculation of the tunable range of radiative thermal load for all colours. The range exceeds 680 Wm-2 for all colours, and can be as high as 866 Wm-2, resulting from effects of metamerism, infrared solar absorption and radiative cooling. We experimentally demonstrate that two photonic structures with the same pink colour can have their temperatures differ by 47.6 °C under sunlight. These structures are over 20 °C either cooler or hotter than a commercial paint with a comparable colour. Furthermore, the hotter pink structure is 10 °C hotter than a commercial black paint. These results elucidate the fundamental potentials of photonic thermal management for coloured objects.