Lighthouse

From Wikipedia, the free encyclopedia

(Redirected from Lighthouses)

For other uses, see Lighthouse (disambiguation).

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. Lighthouses also provide coordinate location for small aircrafts travelling at night. 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), Swedish, Danish and Norwegian (fyr), Romanian (far) and Greek (φάρος). The word "pharology" (study of the lighthouses), is also derived from the island's name.

1 History
2 Design
3 Maintenance
4 Automation
5 Notable Lighthouses
6 Symbology
7 Range Lights
8 Gallery
9 See also
10 External links
11 References

[edit] History

A modern automated lighthouse on St. Paul Island

Lighthouses originally contained an open fire. Later, they were gas-powered and electric.

[edit] Design

Image:Finnish Lighthouses 1909.JPG

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.

This concentration of light is accomplished with a rotating lens assembly. In very old lighthouses, the light source was a kerosene lamp, and the lenses were rotated by a clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly usually floated in mercury to reduce friction. In more modern lighthouses, electric lights and clock drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers.

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.

Other design techniques are used to aid the navigator. Lights near to each other are painted in a unique style so they can easily be recognized during the daylight (thus, this marking is called a day mark.) Likewise the time interval of the light (see above) or the color pattern of the lens is varied. Sector lights have particular obstructions in one or more sectors, and a portion of the lantern house may have a red or green filter applied so the navigator gets additional input on which side the ship is approaching from. Modern lighthouses have unique metal attachments so the radar signature of the light is also unique.

[edit] Maintenance

Image:RockyCoast.jpg

In the United States, lighthouses are maintained by the United States Coast Guard. In Britain and Ireland, 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.

[edit] 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 have been fully automated.

Often in inaccessible locations, modern lighthouses 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.

[edit] Notable Lighthouses

Image:SplitPointLighthouse.jpg

See List of lighthouses and lightvessels

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.

Image:Joao Pessoa Paraiba Farol do Cabo Branco.jpg

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 [1]. 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.

In Brazil, (South America), "Cabo Branco lighthouse" is strategically located in Joao Pessoa at the easternmost point of the Americas at 34º 47' 38" west longitude and 7º 9' 28" south latitude. Due to its location this lighthouse has become an important touristic attraction.

In December 1900 there was an unexplained disappearance of three keepers from Eilean Mor off the Isle of Lewis in the Flannan Isles.

[edit] Symbology

Lighthouses are used as symbols by certain organizations. Marriage Encounter uses the lighthouse as their symbol.

Lighthouses are often interpreted in dreams as beacons of truth or as male fertility and influence. One commonly seen has a spiral red stripe said by Milton William Cooper and others to be symbolic of the snake of Lucifer.

[edit] Range Lights

Image:NantucketRangeLites.jpg

A problem with a single lighthouse is that it is only a point at night. For many navigation problems, this is insufficient.

If the navigator is trying to find the path into a river, he needs a better way, such as the Range light. Two lights are used in this scheme, one is named the front range, the other is called the rear range. The rear range light is always taller than the front range light. When you are on the path into the river, the two lights line up one on top of the other.

This provides better aid for the navigator. When the vessel is on the correct course, the two lights line up. But when on the wrong course, the difference in height makes it very obvious whether to travel left or right to correct the problem.

This technology was first developed in Europe in 1837 where they are referred to as Leading Lights. <ref> Terry Pepper, eMail communication, Sept. 19, 2006. </ref> The first usage in the US is not well defined, but there are some listed in the 1854 Light list (Cherry Hill, NJ, North Point, MD, Beacon Island). <ref> Terry Pepper, op. cit. </ref>

This technology works not only for finding the way into a river, it can be used to navigate the entire river. For instance, it is possible to sail on the Elbe river in Germany at night, and each time it is necessary to make a turn, the navigator lines up the next range lights. This takes you all the way from Hamburg out to the sea, using one pair of range lights after another.

[edit] Gallery

The Peggys Point lighthouse in Nova Scotia, Canada.	Fairport Harbor West Breakwater Lighthouse, Fairport Harbor, Ohio viewed from the Headlands Dunes State Nature Preserve	Fairport Harbor West Breakwater Lighthouse, Fairport Harbor, Ohio viewed from the Headlands Dunes State Nature Preserve	Cape Willoughby Lighthouse, Kangaroo Island, South Australia
Portland Bill lighthouse, Isle of Portland, Dorset	Scarborough Harbour Lighthouse, Scarborough, North Yorkshire, England	A 1999 photo of the Navassa Island lighthouse. The lightkeepers quarters appear in the backgound.	McClain's State Park Lighthouse, Upper Peninsula, Michigan
Point Reyes Lighthouse	Nauset Light and lightkeeper's house, Eastham, Massachusetts	Spurn Point Lighthouse, East Yorkshire, England.	Admiralty Head Lighthouse Inactive, used as interpretive center by a local environmental group
Strumble Head Lighthouse, Wales	Neuwerk Lighthouse, Hamburg, Germany, completed 1369	The Eddystone Lighthouse, situated off the coast of Cornwall, England.	Hunting Island Light House, South Carolina
Byron Bay Lighthouse, New South Wales, Australia	Cape Disappointment Lighthouse	The tall Bengtskär lighthouse also functions as a museum.	Cabo Branco Lighthouse, Joao Pessoa, Brazil

[edit] See also

List of lighthouses and lightvessels
Jean Guichard - Lighthouses photographer
Lens lantern

[edit] External links

Image:Commons-logo.svg	Wikimedia Commons has media related to: Lighthouses

LighthouseFans A user-contributed database of lighthouses around the world with community forums and current lighthouse news.
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.
Lighthouses in the Netherlands Written in Dutch and partly in English, with recent pictures.
South African Lighthouses English website with photo's and detailed info about all the lighthouses in South Africa.
Photos of lighthoses in Galiza
Top 25 Lighthouse Web Sites List International list of top web sites about lighthouses displaying latest rank, monthly vote count, ratings and more.
Gallery of Lighthouses zh-min-nan:Teng-thah