W
hen living organisms give off light as a result of internal
chemical reactions, scientists refer to the phenomenon as
bioluminescence. If it is dark enough outside, we can see this light
with our human eyes. Biofluorescence, on the other hand, is only
visible to fish and some other marine animals. More than 180
biofluorescent fish species are known to exist. They range from
sharks to soles to sand stargazers and scorpion fishes.
In biofluorescence, a molecule absorbs high-energy
light (typically blue light) and immediately returns it to the
surroundings as lower-energy light (typically green and red
light). The molecule immediately emits this lower-energy light, a
phenomenon that scientists refer to as fluorescence.
Fish can see fluorescent colors because their eyes have a filter
that removes blue light from their field of vision. The high-energy
blues that excite the fluorescent molecules overwhelm the eyes’
BiOFLuOrESCENCE VErSuS
PHOSPHOrESCENCE
Bioluminescent and fluorescent organisms give off light in very
different ways. However, fluorescence and phosphorescence are very
similar processes. in fluorescence, a molecule is excited (absorbs
light energy) and immediately returns it to the surroundings as lower-
energy light. in phosphorescence, a molecule absorbs light energy
but returns it slowly. A phosphorescent glow continues even after
the high-energy exciting light is removed. A fluorescent glow stops
immediately if the high-energy light is removed.
B i o f l u o r e s c e n c e • 3 9
