Who glows there? Different mechanisms elicit various types of natural glow, from recycling the sun’s rays to complex chemical reactions
Creating light from darkness
The term bioluminescence is used to describe light that is produced by a chemical reaction inside an organism. The vital substance in this reaction is luciferin, an unremarkable molecule in itself, but which can react with oxygen to produce photons of light. The process is aided by the enzyme luciferase, but doesn’t need an external source of light, which is why deep-sea creatures like anglerfish can use it to lure and trap unsuspecting prey.
There are at least four different types of luciferin found across the animal kingdom, each with a corresponding luciferase. Some bioluminescent species rely on a supply of these molecules within their diet, as they are unable to create them within their bodies.
Simple light exchange
Unlike bioluminescence, this process relies on energy from an external light source. The light is absorbed by the animal and re-emitted again almost instantaneously. If the light source disappears, so does the fluorescent glow.
Not only do fluorescent animals reflect light, but they also change it. The particles of light become unstable and lose energy, causing the colour of the resultant glow to be altered. This means that the reflected light can be a completely different colour from the source. Butterfly wings contain fluorescent pigments that intensify their colouration, either to attract mates or repel predators.
Laundry detergents use fluorescence get our clothes ‘whiter than white’; they absorb ultraviolet light that isn’t visible to the human eye and fluoresce it into the visible spectrum.
The light that lingers
Like a glow-in-the-dark sticker, phosphorescent animals absorb light energy from the Sun and then use it to give off an eerie glow. It’s a similar process to fluorescence, but the difference is that phosphorescent animals can ‘save up’ light from an external source and release it over time.
Like fluorescence, phosphorescence depends on the presence of a light source, such as the Sun. However, the electrons become excited to a higher degree than in fluorescence and they release light slowly and at a lower intensity.
Animals like jellyfish use this glow after absorbing light from the sun-filled surface waters of the open ocean. This makes them more vulnerable to predators, but more attractive to prey.
Image from www.flickr.com/photos/stuutje