Iridescence (also known as goniochromism) is generally known as the property of certain surfaces that appear to change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and sea shells.
Iridescence is often caused by multiple reflections from two or more semi-transparent surfaces in which phase shift and interference of the reflections modulates the incidental light (by amplifying or attenuating some frequencies more than others). This process, termed thin-film interference, is the functional analog of selective wavelength attenuation as seen with the Fabry–Pérot interferometer.
In biological (and biomimetic) uses, colours are traditionally produced with pigments, so colours produced other than by pigment are called structural coloration. The use of often multilayered microstructures usually also produces iridescence, as quite elaborate arrangements are needed to avoid reflecting different colours in different directions. Structural coloration has been understood in general terms since Robert Hooke's 1665 book Micrographia.
The word iridescence is derived in part from the Greek word ἶρις îris (gen. ἴριδος íridos), meaning rainbow, which in turn derives from the goddess Iris of Greek mythology, who is the personification of the rainbow and acted as a messenger of the gods. Goniochromism is derived from the Greek words gonia, meaning angle, and chroma, meaning color.
Arthropods and mollusks
The feathers of some birds, such as kingfishers, hummingbirds, parrots, crows, ravens, starlings, grackles, ducks, and peacocks are often iridescent. A single iridescent species of gecko, Cnemaspis kolhapurensis, was identified in India in 2009. The tapetum lucidum, present in the eyes of many vertebrates, may also be iridescent.
Minerals and compounds
Iridescence in an engine oil spill.
- Bioluminescence, irrespective of angle
- Cloud iridescence
- Dichroic filter
- Labradorescence (Adularescence)
- Structural color
- Thin-film optics
- "Iridescence in Lepidoptera". Photonics in Nature (originally in Physics Review). University of Exeter. September 1998. Retrieved April 27, 2012.
- Hooke, Robert. Micrographia. Chapter 36 ('Observ. XXXVI. Of Peacoks, Ducks, and Other Feathers of Changeable Colours.')
- Ball, Philip (May 2012). "Scientific American". Nature's Color Tricks 306 (5): 74–79. doi:10.1038/scientificamerican0512-74. PMID 22550931. Retrieved April 23, 2012.
|Wikimedia Commons has media related to Iridescence.|