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Question:

    How is the light of a lighthouse magnified so that it can be seen many miles out at sea?

Answer:    

    A lighthouse light is a concentrated beam, focused by special lenses. Because of its highly increased intensity, this beam of light can travel a very long distance.

The design of the lighthouse light as we know it today, originated at the beginning of the 18th Century. The French inventor Augustin Fresnel had correctly deduced that light was pure energy that traveled in waves, and he then spent his life developing lenses and reflectors that could capture and concentrate light. The first lighthouse optics that he designed combined highly polished prisms with an array of lenses that captured light and concentrated it back into a main beam. The design was concentric in arrangement, funneling the light into a beam that was many times brighter than its source. This light could be seen for more than 20 miles. Fresnel’s design of concentric glass rings to concentrate light is still used today in the production of automobile headlights, traffic signals and projectors. Many of today’s lighthouses have a system of rotating lenses, and the newer ones flash off and on as a way of conserving energy.

Standard DisclaimerRelated Web Sites
  • The Fresnel Lens - A look at the Fresnel lens, from the Cape Hatteras National Seashore website.
  • Lighthouses and the Fresnel Lens - This Web site gives a brief description of the Fresnel lens, along with additional Web links where you can find more information about the Fresnel lens.
  • National Lighthouse Museum - Located on the former site of the United States Lighthouse Service’s (USLHS) General Depot in St. George, Staten Island, the National Lighthouse Museum educates visitors about the history and technology of the nation’s lighthouses.
  • Science, Optics and You: How Does it Work? Lighthouses - How lighthouses work is described along with a list of lighthouse activities for students.
  • Smithsonian National Museum of American History: Lighthouse postcards - “This online collection showcases the lighthouse postcards in the Engineering Collections at the Smithsonian's National Museum of American History. It includes digitized images of 272 postcards, general information on the U.S. and Canadian lighthouses represented in the collection, and customized nautical charts provided by the National Oceanographic and Atmospheric Administration.”
  • US Lighthouse Society - “The United States Lighthouse Society is a non-profit historical and educational organization incorporated to educate, inform, and entertain those who are interested in America's lighthouses, past and present.”

Library of Congress Web SiteFurther Reading
  • Crompton, Samuel Willard. The ultimate book of lighthouses: history, legend, lore, design, technology, romance. San Diego, CA, Thunder Bay Press, c2000. 256 p.
  • Fleming, Candace. Women of the lights. Morton Grove, IL, A. Whitman, 1996. 71 p. (Juvenile).
  • Jones, Ray. The lighthouse encyclopedia: the definitive reference. Guilford, Conn., Globe Pequot Press, c2004. 274 p.
  • Lighthouses of the world. Compiled by the International Association of Marine Aids to Navigation and Lighthouse Authorities. Old Saybrook, CT, Globe Pequot Press, c1998. 164 p.
  • Lighthouses and the age of engineering: The nineteenth century. (In) Naish, John Michael. Seamarks: their history and development. London, Stanford Maritime, 1985. 192 p.

SearchFor more print resources...
Search on "beacons", "lenses," "lighthouses. The term, "lighthouses," may be subdivided by geographical area, e.g.,"lighthouses--Chesapeake Bay," "lighthouses--Florida," and "lighthouses--Italy."
in the Library of Congress Online Catalog.

Photo:  young boy skipping away from lighthouse.
Fire Island lighthouse and keeper's
5 year old son. Prints & Photographs
Division, Library of Congress.

Colorized postcard of river, lighthouse and cathedral  in the distance,
The lighthouse and cathedral, Marseilles, France. Prints & Photographs, Library of Congress

Photos of lighthouse among palm trees.
St. Augustine Lighthouse, Anastasia Island, Florida. Prints and Photographs Division, Library of Congress.

Two diagram of lighthouse exterior and  cross-cut of interior.
Light House for South West Ledge, L.I. Sound. Prints and Photographs Division, Library of Congress.

Photo of three men in a boar in foreground, with lighthouse , surrounded by water, in distance.
Leaving Stepping Stones Lighthouse.
Prints and Photographs Division, Library of Congress.

Photo of a lighthouse on  small rocky island.
Light House for South West Ledge, L.I. Sound. Prints & Photographs, Library of Congress

Color poster of men in a lighthouse, with one man in the water fleeing open  mouthed whale.
Happy Hooligan Theatrical Poster.
Prints & Photographs, Library of Congress.

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 October 2, 2018
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