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Glare-Reducing Sunglasses, Inspired at Summer Camp

We learned how to build a proper campfire, roast marshmallows, and tell ghost stories.  We learned how to canoe, fish, and for the unfortunate few, treat a bad case of poison ivy.  When our kids go to summer camp, should we expect more?  In 1922, 13-year-old Edwin H. Land learned something so inspiring it changed his life forever:

• "...Land observed the camp director use a piece of Iceland spar to extinguish glare from a table top to illustrate the excitement of physics.  Land attributed the whole direction of his career to this demonstration."¹

Less than a decade later, Land filed a U.S. patent application for his invention of a synthetic sheet polarizer.²  Similar to the Iceland spar he observed at summer camp, also known as calcite crystal (CAS Registry Number 13397-26-7), Land's synthetic sheet polarizer reduced reflective glare from sunlight by filtering out, or absorbing, certain light waves.  However, instead of a single crystal, it was made of billions of needle-shaped, sub-microscopic crystals aligned in parallel and suspended in plastic.

In subsequent years, Land filed several U.S. patent applications that improved upon his original invention.  Most notably, his U.S. patent application filed in 1939 described a synthetic sheet polarizer that replaced the billions of sub-microscopic crystals with molecules of polyvinyl alcohol (CAS Registry Number 9002-89-5) dyed with iodine (CAS Registry Number 7553-56-2):

• "I have found that sheets or films of certain transparent plastic materials having elongated or chain-like molecules may be employed to produce excellent light-polarizers when the sheets have been softened, as for example by heating, stretched to orient their molecules, and then dyed or tinted, preferably with a polarizing polyiodide."³

While many will not recognize his name or the synthetic sheet polarizer he invented, most are familiar with the company founded by Land - the Polaroid Corporation - and the instant photography products he introduced in 1948.  As the age of instant photography appears to be near its end,⁴ Land's summer camp-inspired invention of a synthetic sheet polarizer continues to live on, most notably as a popular glare-reducing feature in sunglass lenses.

Contributed by
Peter S. Carlton, Ph.D.
CAS Communications

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Additional Resources

You can use SciFinder or STN to search the CAS databases for additional information about Edwin H. Land, calcite crystals, and synthetic sheet polarizers.  If your organization is enabled to use the web version of SciFinder, you can click the links in this article to directly access details of the substances and references.

For more information on calcite, polyvinyl alcohol, and iodine, visit Common Chemistry, a free web resource that contains CAS Registry Numbers for approximately 7800 chemicals of widespread general public interest.

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References

1. McElheny, V.K. Biographical Memoirs - Edwin Herbert Land. Proc. Am. Philos. Soc. 2002, 146, 112-122.
2. Land, E.H.; Friedman, J.S. Polarizing Refracting Bodies. U.S. Patent 1,918,848, July 18, 1933.
3. Land, E.H. Light Polarizer Suitable for Use Between Sheets of Glass. U.S. Patent 2,237,567, April 8, 1941.
4. Jarvis, L.M. What's That Stuff? - Instant Film. Chemical & Engineering News, March 23, 2009, p 42.

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