The Morpho butterfly (Morpho peleides) is famous for its stunning blue color, which results from the nanostructure of its wings instead of pigments. This phenomenon has inspired experts to develop a novel, bright, balanced lighting technology.
Morpho Butterfly's Brilliant Blue Color
Pigments and dyes produce specific colors by absorbing and reflecting wavelengths of light. This behavior is exhibited by some insects like the cochineal insect from which the natural dye carmine is obtained.
However, there are species of butterflies that use light-interacting structures on their wing scales to create color. The cuticle on the scales of their wings is made of nano- and microscale, transparent, chitin-and-air layered structures.
In the case of Morpho butterflies, their wings contain tiny scales with microscopic ridges, cross ribs, and other structures. In other words, the color is created by structures that play with light waves to make brilliant blues and speckles.
As light hits the surface of butterfly wings, it diffracts and interferes due to multiscale structures. The incoming light waves are diffracted by cross ribs, which protrude from the sides of ridges in the wing scale. The diffracted light waves interfere with each other to make certain color wavelengths cancel out while others get intensified and reflected.
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Designing an Enhanced Optical Diffuser
At Osaka University, researchers developed a water-repelling nanostructured optical diffuser that surpasses the functionality of other conventional diffusers. This work has the potential to solve typical lighting problems in modern technologies.
Standard lighting can be tiring because it does not illuminate evenly. To address this problem, most display technologies use optical diffusers to make the light output more uniform. However, conventional optical diffusers have disadvantages, such as reduced light output, incompatibility in some emitted colors, and the demand for special cleaning efforts.
In designing an improved light diffuser, the researchers took their inspiration from Morpho butterflies. These insects have randomly arranged multilayer architecture, which enables structural color, a selective reflection of blue light over ≥±40° angle from the illumination direction.
The research uses this inspiration to design a simplified light diffuser with high transmittance and wide angular spread while working for a range of colors without dispersion. They also wanted the diffuser to be easily cleaned by simple water rinse and shaped with standard nanofabrication tools.
The research team created two-dimensional nanopatterns in common transparent polydimethylsiloxane elastomers. According to study lead author Kazuma Yamashita, the nanopatterns are of binary height but random width, while the two surfaces have different structural scales. His team reports an effective light diffuser for short- and long-wavelength light.
Yamashita and his team customized the patterns of the diffuser surfaces to enhance the performance for blue and red light, as well as their self-cleaning properties. The experimentally measured optical transmittance was more than 93% over the visible light spectrum. Meanwhile, the light diffusion was substantial and could be controlled into an anisotropic shape.
When protective cover glass layers are applied on either side of the light diffuser, the optical properties are maintained mainly while protecting it against scratching. As the glass minimizes the need for careful handling, it indicates the technology's utility to daylight-harvesting windows.
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