The Science of Iridescence
The fantastical dancing light that an iridescent butterfly wing reflects has forever enamored our affections. Beyond the romantic lure what are the components that create these striking aerial devices? While most living organisms produce colors using pigments (also known as biochromes) where light is absorbed to produce a particular color – animals that use iridescence produce colors without pigments. This mechanism is called Coherent scattering of light and also known as structural color. Light goes in an organized structure and bounces out in a very predictable fashion. To achieve this coherent scattering there are microscopic nano-structures on each individual scale that covers their wings. There are three main types of configurations used for iridescence are generously called 1, 2 and 3.
Type 1 is constructed of multi layered reflectors in which light can only enter in one direction and exit out at the same angle. This method specifically used by the famous Blue Morpho butterflies as well as being used in our LED lights.
Type 2 is also another multi layered reflector, but is in the form similar to a tiny satellite dish. In the case of the Blue Mountain Swallowtail (Papilio Ulysses) the dishes are very shallow and therefore only reflect a vibrant blue. Whereas in the case of the Sea Green Swallowtail (Papilio lorquinanus) these dishes are deeper and therefore give a dual effect of blue from one angle and green from another. As you further change the shape and depth of these dishes, the results produce an array of different colors. For example the Madagascan Sunset moth (Urania ripheus) and it’s varying diversification of hues.
Type 3 is in the form of a gyroid structure in which polarized iridescence is also reflected. It’s format could perhaps be compared to that of a crystal. It‘s pattern is very regular and repeats often. When light enters this structure it then shines out in all directions reflecting a green to a bluish green color along with polarized light in which our eyes can not detect. This example may be seen in the small Green Hairstreak butterflies.
Next time you are admiring the simple pleasure of gazing into the shine of these glossy hypnotists, perhaps you might also be in awe of the fascinating complexity of nature’s
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