Photonic thermal management of coloured objects

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.