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.
Highlights
The colours of outdoor structures, such as automobiles, buildings and clothing, are typically chosen for functional or aesthetic reasons
We show that for every given colour, there is a very significant tunable range in its thermal load, due to the physical effects of infrared solar absorption and radiative cooling, as well as the physiological effect of metamerism, since colour arises from the human perception of the visible spectrum
We characterize the thermal performance of the ‘cold’ and the ‘hot’ photonic structures, as well as the two paint samples in an outdoor environment (Methods)
Summary
The colours of outdoor structures, such as automobiles, buildings and clothing, are typically chosen for functional or aesthetic reasons. There has been a large body of work on colour objects seeking to achieve thermal loads that are different from conventional paints For this purpose, significant efforts have been made to control the absorption of the near infrared part of the solar radiation that contributes to the thermal load but not the colour of an object[21,22,23]. We show that for every given colour, there is a very significant tunable range in its thermal load, due to the physical effects of infrared solar absorption and radiative cooling, as well as the physiological effect of metamerism, since colour arises from the human perception of the visible spectrum
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