  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.
