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Longstreet Highroad Guide to the Georgia Coast & Okefenokee

By Richard J. Lenz

Design by Lenz, Inc. Decatur, Georgia.



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Fresnel Lenses

Fresnel lenses were used in orders or strengths depending on the intensity needed for a particular location. First order lights are for primary landfall coastal lighthouses and second order lights are considered seacoast or landfall lights. Third and fourth order lights (such as St. Simons Lighthouse) mark harbor entrances, and fifth to sixth order lights, like the one used by Cockspur Island Beacon, are used for rivers and channels. Tybee Lighthouse’s first order lens, valued at $3 million, is 9 feet tall and can shine a light that can be seen 18 miles away. The Fresnel lens was invented by French physicist Augustin Fresnel in 1827, who used prisms to capture and concentrate 90 percent of a lamp’s light and focalizing it into an intense horizontal beam. The precise manufacturing needed produce the lens—hand-ground from perfectly molded lead crystal—required the skill of an artisan. His invention improved lighthouses’ range from a few miles to almost 20. Some other first order lighthouses include the ones in St. Augustine and Pensacola, Florida, and Block Island Southeast.


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Published (print): 1999, Published (Web): March 2000, Revised (Web): November 2002, ISBN: 1-56352-542-9
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