Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae)

TL;DR

This study investigates how the lantern structure of Photuris fireflies enhances light extraction by analyzing morphological features and optical properties, revealing adaptations that mitigate total internal reflection.

Contribution

It provides a detailed analysis of the lantern's morphology and models its optical properties, identifying structural features that improve bioluminescent light emission.

Findings

External scale roughness improves light escape

Lower refractive index at photocyte cluster enhances emission

Structural adaptations partially overcome internal reflection

Abstract

A common problem of light sources emitting from an homogeneous high-refractive index medium into air is the loss of photons by total internal reflection. Bioluminescent organisms, as well as artificial devices, have to face this problem. It is expected that life, with its mechanisms for evolution, would have selected appropriate optical structures to get around this problem, at least partially. The morphology of the lantern of a specific firefly in the genus Photuris has been examined. The optical properties of the different parts of this lantern have been modeled, in order to determine their positive or adverse effect with regard to the global light extraction. We conclude that the most efficient pieces of the lantern structure are the misfit of the external scales (which produce abrupt roughness in air) and the lowering of the refractive index at the level of the cluster of photocytes, where the bioluminescent production takes place.