Structural colours is a term used to describe objects that do not have any pigment yet get their colours from the light that is being reflected in microstructures and by this manipulating our brain’s way to see colours (like in a rainbow). In nature, tremendous numbers of orders and patterns are generated spontaneously, which enliven our surroundings. One of the most remarkable consequences of these processes reveals itself as so-called structural colour, which exhibits striking brilliance owing to elaborate structures furnished with living creatures. They sometimes reflect surprisingly intense light in a wide angular range, while in other cases prohibit any reflection of light. These functions are natural consequences of complicated interactions between light and the structures through purely physical properties of light. The scientific definition of structural colour has not yet been settled and its characteristics are often referred to in contrast to pigmentary colour. When a substance is illuminated with white light, we see a specific colour if the reflected light of only a particular wavelength range is visible to our eyes.
Wavelength of light
There are two ways to eliminate the other wavelengths of light: one is the case where the light is absorbed in a material, which is usually the case for ordinary coloration mechanisms in colour materials such as in pigments, dyes, and metals. In these materials, the illuminating light interacts with electrons and excites them to higher excited states by virtue of the energy consumption of light. The colour, in this case, is any way caused by the exchange of energies between light and the electrons. The other is the case where light is reflected and/or deflected from reaching the eyes owing to the presence of the structure. The coloration, in this case, is based on a purely physical operation of light that interacts with various types of spatial inhomogeneity. Thus, it does not essentially involve loss of light energy. In this sense, fundamental optical processes such as reflection, refraction, interference, diffraction, and scattering can become sources of structural colours. In fact, even a simple prism should be categorized into this type of structural colour, because the light waves with different wavelengths are deflected differently by virtue of its wavelength-dependent refractive index. In general, the mechanisms of structural colours are categorized into several optical phenomena such as thin-film interference, multilayer interference, diffraction grating and photonic crystals. See also biomimicry, biomimicking in the eco fashion dictionary
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