Fresnel Lens .......  History & Facts

This is a first-order Fresnel lens, made in France and shipped to the United States in the mid-19th century.  It consists of concentric rings of glass prisms that bend the light coming front a lamp inside the lens into a narrow beam.  This lens has 1,176 prisms and 24 bullseyes.  At the center, the bullseyes work like a magnilying glass so that the light beam is even more powerful.  The lens sections are held together by brass frames weighing five to six tons.  The entire lens weighs in at approximately six to eight tons.

This type of lens can throw its beam to a distance of 26 miles.                  Tests showed that an open flame lost nearly 97% of its light, and a flame with reflectors behind it still lost 83% of its light.  The Fresnel lens was able to capture all but 17% of its light. 

At first, an oil lamp with five wicks provided the light source.  Kerosene was the preferred fuel. With the advent of electricity,  lamps came into use. 

Augustin Fresnel.

As a child, he was a slow learner who showed little interest in language studies or in tests of memory. By the age of 8, he could barely read. Yet his boyhood friends, for whom he studiously determined how to increase the power of popguns and bows, called him "the genius." When applied to optics, his genius proved to be real and considerable. Where others had improved existing lighthouse technology, Fresnel leapt forward by studying the behavior of light itself. His studies both advanced the understanding of the nature of light and produced the most important breakthrough in lighthouse lights in 2,000 years.

Fresnel worked out a number of formulas to calculate the way light changes direction, or refracts, while passing through glass prisms. Working with some of the most advanced glassmakers of the day, he produced a combination of prism shapes that together made up a lens. The Fresnel lighthouse lens used a large lamp at the focal plane as its light source. It also contained a central panel of magnifying glasses surrounded above and below by concentric rings of prisms and mirrors, all angled to gather light, intensify it and project it outward.

The various reflector systems installed in lighthouses during the 40 years preceding the introduction of the Fresnel lens certainly had been improvements over the open fires or candles in lantern rooms. Still, they could trap only a small percentage of the light. All prior systems paled by comparison with the Fresnel lens.

The first Fresnel lens, installed in the elegant Cardovan Tower lighthouse on France's Gironde River in 1822, was visible to the horizon, more than 20 miles away. Sailors had long romanticized lighthouses. Now scientists could rhapsodize, too. "Nothing can be more beautiful than an entire apparatus for a fixed light," one engineer said of Fresnel's device. "I know of no work of art more beautifully creditable to the boldness, ardor, intelligence, and zeal of the artist."

Fresnel lenses soon shone along the ragged coastlines of Europe, but surprisingly, America was slower to see the light. As mariners came to depend on Europe's powerful new lights, they complained bitterly about the puny lamps lighting America's coasts.

 Despite the clear superiority of Fresnel lenses, the parsimonious bureaucrat in charge of federal lighthouses, Stephen Pleasanton, considered the cost prohibitive. Finally, the uproar became so great that in 1838 Congress launched an investigation. It was not until then that Congress coughed up the cash to import a few Fresnel lenses. The first were installed in 1841 inside the two towers at Navesink Lighthouse, overlooking the approach to New York Harbor.

Only after 1852, when the United States created a Lighthouse Board made up of eminent scientists and mariners, including Joseph Henry of the Smithsonian and Alexander Bache of the U.S. Coast Survey, did the great lenses really begin to light America's coastline. By the Civil War, nearly all lighthouses in the United States had Fresnel lenses.