Moths have unique sub-wavelength structures coating their eyes which dramatically minimize light reflection over a much broader range of wavelengths than conventional anti-reflective coatings. The outer surfaces of moth corneal lenses are covered with a regular pattern of conical protuberances, generally 200-300 nm in height and spacing. These protuberances reduce light reflection by creating a refractive index gradient between the air-lens interface, more gradually transitioning the change in light speed between the air and eye and hence minimizing reflection. These unique structures help moths evade detection by predators in moonlight and maximize light capture for seeing in the dark. Moth-eye inspired antireflective coatings that demonstrate high-performance over large band widths at low fabrication cost have recently been developed for solar panels, with many other potential products applications.
“The eyes of moths have two characteristic optical structures that probably function to increase the light sensitivity: the tapetal mirror and the corneal nipple array (Miller, 1979). The tapetum is composed of tracheoles at the proximal portion of the rhabdom and reflects unabsorbed light back into the rhabdom, thus providing a second chance for light to be absorbed. The corneal nipple array, known as the ‘moth-eye’ structure, is a set of protuberances of height about 200•nm, acting as a thin-film antireflection coating. These structures are basically retained in the apposition eyes of true butterflies, but all species in the family Papilionidae lack both (Bernhard et al., 1970; Stavenga et al., 2006).” (Takemura et al. 2007)