Lighthouse
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An 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 fire. More primitive navigational aids were once used such as a fire on top of a hill or cliff (see beacon).
Because of modern navigational aids, the number of operational lighthouses has declined to less than 1,500 worldwide. Lighthouses are used to mark dangerous coastlines, hazardous shoals away from the coast, and safe entries to harbors.
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 and Spanish (faro), Portuguese (farol), Romanian (far) and Greek (φάρος). The word "pharology" (study of the lighthouses), is also derived from the island's name.
Design
In order to conserve power, the light is concentrated.
In old lighthouses:
- vertically the light is bundled into horizontal directions
- horizontally the light is bundled into one or a few directions at a time, with the light beam sweeping around; as a result, in addition to seeing the light beam from the side, from every horizontal direction there are instants that one sees the light directly, hence from a larger distance.
Efficiently concentrating the light from an omnidirectional source of the type used in lighthouses requires a lens of very large diameter. This would lead to a very thick and heavy lens if naively implemented. A Fresnel lens is a type of lens developed for lighthouses. Its design enables the construction of lenses of large size and short focal length without the weight and volume of material which would be required in a lens of conventional design. Some lighthouses, such as those at Cape Race, Newfoundland, and Makapu'u Point, Hawaii, used a special hyperradiant lens manufactured by the firm of Chance Bros.
In modern, automated lighthouses, this system of rotating lenses is often replaced by a very bright light that emits brief omnidirectional flashes (concentrating the light in time rather than space). These lights are similar to the aerodrome beacons used to warn aircraft away from tall structures.
In any of these designs an observer, rather than seeing a continuous weak light, sees a brighter light during short time intervals. These instants of bright light are arranged to create a characteristic light pattern specific to the particular lighthouse. For example, for the lighthouse of Scheveningen the time intervals between these instants are alternately 2.5 and 7.5 seconds.
Maintenance
In the United States, lighthouses are maintained by the United States Coast Guard. In the United Kingdom, those in England and Wales are looked after by Trinity House, those in Scotland by the Northern Lighthouse Board, and those in all of Ireland by the Commissioners of Irish Lights. In Canada, they are managed by the Canadian Coast Guard. In Australia, lighthouses are looked after by the Australian Maritime Safety Authority.
Automation
In the beginning of the 20th century Swedish inventor Gustav Dahlén invented the AGA Lighthouse which effectively made lighthouse keepers obsolete. However, for many years lighthouses still had keepers, partly because lighthouse keepers could serve as a rescue service if necessary. Improvements in maritime navigation and safety such as GPS have led to the phasing out of non-automated lighthouses, with the last keepers removed in the 1990s.
Today there are a few keeper-run lighthouses left in existence; the vast majority, however, have been fully automated. The greatest lighthouse mystery was the unexplained disappearance of three keepers from Eilean Mor off the Isle of Lewis in December 1900 (see Flannan Isles for the details.)
In inaccessible locations, modern lighthouses are being installed. These are much more functional and less picturesque buildings; usually they are solar-powered and have a single flashing light which does not rotate sitting on a steel skeleton tower.
Notable Lighthouses
In some locations, lighthouses have become popular tourist destinations and the buildings are being maintained as tourist attractions. See, for example, Cape Hatteras lighthouse
Such an example is the Split Point Lighthouse in Aireys Inlet, Victoria, Australia. The popular children's series Round the Twist followed the adventures encountered by a family living in a mysterious lighthouse; and used the area around the Split Point Lighthouse for many exterior scenes. Since summer 2005, half-hour tours are available to those wishing to climb this lighthouse.
Bengtskär lighthouse is the highest (52 meters) in the Nordic countries. It is situated to the south of Hanko, Finland. It was built in 1906 and it is the first lighthouse museum in Finland.
The Soviet Union built a number of automated lighthouses powered by radioisotope thermoelectric generators in remote locations. They operated for very long periods of time without external support with great reliablility [link]. However numerous installations have been found deteriorated, stolen and/or vandalized ([Bellona's report]). Some of these lighthouses cannot be found due to poor record keeping.
Gallery
External links
- [Maritime Heritage Network], an online directory of maritime history resources in the Pacific Northwest region of the United States, including a list of all lighthouses.
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