Poster: What the white orchid can teach us about radiative cooling

Sub-ambient radiative cooling has great promise for non-electric heat mitigation. Passive, direct-sunlight, sub-ambient cooling requires ultra-high reflectivity in the solar spectrum and high emissivity in the long wave infrared between 8 and 13 microns. Here, we explored the remarkable properties of white Phalaenopsis Orchid petal whose average reflectivity exceeds even Barium Sulfate and Zinc Oxide when tested in an integrating sphere and exceeded the whiteness of the whitest commercial paint. Using 3D optical profilometry, we found a rich 3D multi-scale substructure which included epidermal cells, walls, grating-like features and transparent sub-micron spheres. We will discuss both the full-spectrum properties of the Orchid and its potential for biomimicry in radiative cooling.