Constructive vs. destructive interference: light waves 1 and 2 produce constructive reinforcement if they are in phase (A). Crests align with crests and troughs align with troughs, reinforcing one another. Destructive cancellation is observed when they are out of phase (B).
http://www.webexhibits.org/causesofcolor/15.html
NOTE: 1  The gorget is the brilliantly colored area on the throat of a male hummingbird. 2  Distal means outward part and proximal means inward part. 3  A feather consists of many tiny sub-feathers, called barbs. 4  The barbs consist of many tiny sub-feathers called barbules. 5  Back to article.
http://www.hummingbirdworld.com/h/iridescent.htm
...The colors do not directly depend on selective pigment absorption and reflection, as do brown and blacks produced by the melanin pigments of non-iridescent feathers. Rather, they depend on interference coloration, such as that resulting from the colors seen in an oil film or soap-bubble.
http://www.hummingbirdworld.com/h/iridescent.htm
Sample, lighting,observation, and cutting angle Iridescence is difficult to quantify because its intensity issignificantly affected by sample, lighting, and observation angle(Wang, 1991). For example, intensity of iridescence increased asboth lighting and observation angle decreased (Wang 1991).
http://www.beefresearch.org/CMDocs/BeefResearch/Beef%20Iridescence.pdf
For a visualof this effect, see Figures 1 and 2. Mechanism of iridescence Food product appearance is based on three factors: a light source, an object that absorbs and reflects light,and an observer.
http://www.beefresearch.org/CMDocs/BeefResearch/Beef%20Iridescence.pdf
Interference of light beams reflected from the front and back surfaces of a thin parallel film. This effect can be seen in soap bubbles. As either the angle, the thickness of the film, or the wavelength changes, the wavelength and the color of light produced by constructive interference changes.
http://www.webexhibits.org/causesofcolor/15.html
NOTE: The gorget is the brilliantly colored area on the throat of a male hummingbird. Distal means outward part and proximal means inward part. A feather consists of many tiny sub-feathers, called barbs. The barbs consist of many tiny sub-feathers called barbules. Barbicels are tiny hooks that hold the barbules together.
http://www.hummingbirdworld.com/h/iridescent.htm
In particular, A-and I-band striations combined with lightparallel to muscle bundles likely produces iridescence. Wang (1991) further concludedthat iridescence is primarily associated with the microstructure of intact meat products asground products did not produce iridescence. Iridescence: A rainbow of colors,causes, and concerns Prepared by: Richard A. Mancini, Ph.D.
http://www.beefresearch.org/CMDocs/BeefResearch/Beef%20Iridescence.pdf
Iridescence is aphysical phenomenon that results in shiny, rainbow-like colors seen not only in raw and cooked meatproducts, but also in peacock feathers, fish scales, and soap bubbles. The most common colors associatedwith iridescence on the surface of cooked meat products are green, red, orange, and yellow.
http://www.beefresearch.org/CMDocs/BeefResearch/Beef%20Iridescence.pdf
Thus, the optimum refractive index for red feathers is about 1.85; for blue feathers it is about 1.5. Hummingbird feathers may attain any refractive index within this range because the iridescence portions of the barbules are densely packed with tiny, tightly packed layers of platlets.
http://www.hummingbirdworld.com/h/iridescent.htm
what produces iridescence?
A and I band striations combined with light parallel to muscle bundles likely produces iridescence. A and I band striations combined with lightparallel to muscle bundles likely produces iridescence.