A male firefly attracts mates by emanating bioluminescent light from a lantern on its abdomen. The lantern is comprised of three layers: a luminous layer, a nanostructured cuticle, and a dorsal layer. Typically, a material like the cuticle would block the bioluminescent light emitted from the luminous layer; it would be reflected back internally and never seen from the outside. This is because the wavelengths of light emitted from the luminous layer would not match up evenly with the surface of the cuticle, so it would hit it and bounce back.
But the firefly’s design addresses this challenge. The surface of its cuticle is covered in a series of precise nanostructures arranged in an orderly fashion. These “nanobumps” perfectly match the wavelength of light being emitted, ensuring that it passes right through the cuticle so a female can see it. Approximately 41% of the light produced is efficiently transmitted outside the firefly’s cuticle.Edit Summary
“This work reports an engineering inspiration of the cuticular nanostructures found in a fire?y lantern. The light organs exist on the abdominal segments of a fire?y (Luciola lateralis Motschulsky) in males, as shown in Fig. 1B. Unlike the normal (N), the lantern (L) cuticle has longitudinal nanostructures with a highly ordered arrangement along the sagittal plane of a fire?y body (Fig. 1 C–E). The physical dimensions were statistically extracted from the SEM images. The period, height, and width roughly range near 250 nm, 110 nm, and 150 nm, respectively. For further investigation, the bioluminescent spectra were measured with a microscopic spectrometer and the result shows a center wavelength of 563 nm in males (68 nm in bandwidth). The transmittance of bioluminescent light (λ= 560 nm) through the lantern cuticle was calculated by using a finite difference time domain (FDTD) method (Fig. 1F). The refractive index of chitin as cuticle medium (reported value: 1.56) (20) was chosen for this FDTD calculation. The maximum transmission are clearly shown at 250 nm in period, 150 nm in width, and 110 nm in height, very similar to what is observed in nature. The nanostructured surface serves as a single layer with the calculated effective refractive index of roughly 1.24 (21), the thickness of which matches well with a quarter wavelength over the square root of refractive index in cuticular medium (i.e., the antireflection condition). This result indicates that the highly ordered cuticular nanostructures surrounding the ventral photogenic layer play an important role for reducing the index mismatch between air and the cuticle surface for high light extraction of bioluminescent light. For an anatomical perspective, a fire?y lantern consists of a dorsal layer, a photogenic layer, and a cuticle (Fig. 1G). The photogenic layer emits bioluminescent light in all directions. The light passes through the cuticle either directly or after reflecting off the dorsal layer, which is located under the photogenic layer and also known as a dielectric mirror (17, 18, 22). The natural design can inspire the configuration of high-power LED packages” (Kim et al. 2012:1-2).