Abstract: Structural color, which is generated along with particular optical phenomena such as reflection, scattering, interfe-rence of light caused by the specific surface microstructures of materials, has aroused wide attention in the fields of materials science, biology and physics in recent years. Nature’s millions of years of evolution has produced a rich variety of creatures owning structural colors, such as colorful insects and birds. Based on the studies of biological structural colors, several different mechanisms of the structural coloration in nature have been proposed. The complete insights on essence of biological structural coloration are the prerequisite of the practical applications of structural colors. In contrast to the other brilliant colors, white is often ignored, and scant studies have been conducted to investigate the optics of white structural coloration. Structural whiteness relies heavily on sophisticated surface microstructure which can result in broadband reflection of light, i.e. the wavelength-independent reflection of incident light with a step-like reflectance spectrum. In the past few years, biological white structural coloration has captured gradually increased research interest, and our perceptions of how the broadband reflection happens have become more and more profound. Structural whiteness are common in nature, such as white color on the surface of butterflies, beetles and marine organisms. Generating mechanisms of natural structural whiteness by light broadband reflection are different. The structural whiteness on skin of some fishes may be resulted from constructive interference of layer-by-layer microstructure. Whiteness on beetle cuticles and butterfly wing scales can be ascribed to the multiple scattering of incident light on their surface disordered microstructures. White structural coloration of giant clams is the outgrowth of color mixing effect of the colorful plots on its epidermis microstructure. And white structural coloration of the Saharan silver ants is caused by the light total internal reflection by its hair. Therefore, summarizing the optical principles of light broadband reflection is of particular significance to the practical utilization of white structural coloration. This review aims to elucidate the principles and fundamentals of natural structural whiteness from the perspectives of Bragg reflector, disordered structure, color mixing effect and special structures found in natural creatures such as marine animals, plants, beetles, butterflies, etc. The studies on understanding of natural broadband reflection principle are crucial to the manufacture of artificial optical regulatory functional materials, which will in consequence promote the development and innovation in the fields of accurate optical instruments, display screens, light-emitting devices, cooling coatings, etc.
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2018, Vol. 32 
