GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
Photoelastic stress in lenses, Photo 1 of 2. Photoelastic stress in spectacles' plastic lenses is observed by placing it between co-aligned (Photo 1) and crossed (Photo 2) linear polarizers. Built-in stress causes optical birefringence which is revealed as colored bands when illuminated by white light. Photo 1 of 2.
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