Iridescence is a physical phenomenon of interference which occurs when light penetrates two thin structures with different reflective properties. The platelets located on the bird's barbules are only about 2.5 microns in length and 0.2 microns thick, and are filled with air. The thickness of the platelets and volume of air each contains influences the path of light creating different colours ranging from red, at one end of the spectrum, to blue at the opposite end. Also, depending on the viewing angle, the hummingbird's throat may appear golden-coloured to one bird-watcher and black to another who is just a few feet away.
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