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About LighthousesAn aid for navigation and pilotage at sea, a lighthouse is a tower building or framework sending out light from a system of lamps and lenses or, in older times, from a burning fire. More primitive navigational aids were once used such as a beacon fire on top of a hill or cliff.
Perhaps the most famous lighthouse in history is the Lighthouse of Alexandria, built on the island of Pharos in ancient Egypt. The name of the island is still used as the noun for "lighthouse" in some languages, for example French (phare), Italian (faro), Spanish (faro) and Portuguese (farol). In the beginning of the 20th century Swedish inventor Gustav Dahlén invented the AGA Lighthouse which made manned lighthouses obsolete. Today there are no manned lighthouses left in existence. Because of modern navigational aids, the number of active lighthouses has declined to fewer than 1,500 worldwide. Lighthouses are used to mark dangerous coastlines, hazardous shoals away from the coast and safe entries to harbors. The light is used efficiently:
Thus an observer, rather than seeing a continuous weak light, sees a brighter light during short time intervals. These instants of bright light a arranged to create a characteristic light pattern specific to the particular lighthouse, e.g. for that of Scheveningen the time intervals between these instants are alternately 2.5 and 7.5 seconds. Lighthouses have become popular tourist destinations. In the United States, lighthouses are maintained by the United States Coast Guard. In the United Kingdom, they are looked after by Trinity House.
also see:
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lighthouse" and from http://www.white-on.com
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