Lighthouse

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A HDR image of a traditional lighthouse
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 are used to mark dangerous coastlines, hazardous shoals away from the coast, and safe entries to harbors and can also assist in aerial navigation. Because of modern navigational aids, the number of operational lighthouses has declined to less than 1,500 worldwide.

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:Albanian (far), French (phare), Italian and Spanish (faro), Portuguese (farol), Romanian (far), Swedish (fyr), Bulgarian and Russian (фар), and Greek (φάρος). The word "pharology" (study of the lighthouses) is also derived from the island's name.

History

A modern automated lighthouse on St. Paul Island
The Roman lighthouse at Dover Castle.

Ancient

The Lighthouse of Alexandria was a tower built in the 3rd century BC (between 285 and 247 BC) on the island of Pharos in Alexandria, Egypt to serve as that port's landmark, and later, its lighthouse. With a height variously estimated at between 115 and 135 metres (383 - 440 ft) it was among the tallest man-made structures on Earth for many centuries, and was identified as one of the Seven Wonders of the World by classical writers. Two lighthouses, each called the Pharos, were built at Dover soon after the Norman conquest of England. They were sited on the two heights (Eastern Heights and Western Heights) and modelled on the one built for Caligula's aborted invasion at Boulogne.

In the Islamic world, lighthouses were also known. The Tang Dynasty Chinese writer Jia Dan once wrote in his book (written between 785 - 805) that in the sea route forming the opening mouth of the Persian Gulf, the medieval Iranians had erected large minaret towers that served as lighthouses. Confirming the Chinese reports, a century later, the Arab writers al-Mas'udi and al-Muqaddasi wrote of the same lighthouses.

In China, the medieval mosque at Canton had a minaret that served as a lighthouse. The later Song Dynasty Chinese pagoda tower built in medieval Hangzhou, known as the Liuhe Pagoda (erected in 1165), also served as a lighthouse for sailers along the Qiantang River.

Modern

The first lighthouse in America was at Boston on Little Brewster Island (1716). The first keeper was George Worthylake who was drowned, along with his wife and daughter, when returning to the island in 1718. The original tower was destroyed by the British and eventually reconstructed in 1784. The oldest existing lighthouse in America is Sandy Hook, NJ (1764), which is still in operation.

The US Lighthouse Service was created in 1789 by the 9th Act of the first Congress. Over the years, lighthouses were placed under the direction of Department of Revenue (this department was disbanded in 1820), Treasury (until 1903), the Commerce and Transportation. The Lighthouse Board (of the U. S. Lighthouse Establishment) held sway from 1852 to July 1, 1910 when Commerce created the Bureau of Lighthouses. The Coast Guard took over on July 7, 1939.

After 1852 the country was divided into Districts; originally eight, they eventually numbered 19. Today the Coast Guard only has ten districts. The USLHE had a District Inspector (Naval Officer) as operational control. He ran the district in tandem with an Army Corps of Engineer who was in charge of engineering projects. In 1910 civilians started replacing the military officers.

Lighthouse keepers were needed to trim the wicks, replenish fuel, wind clockworks and perform maintenance tasks such as cleaning lenes and windows. In 1907 Nils Gustaf Dalén produced the sun valve which turned the beacon on and off using daylight. The first one was erected on Furuholmen’s lighthouse between Stockholm and Vaxholm[1]. In 1912 Dalén was awarded the Nobel Prize in Physics for his invention of 'automatic valves designed to be used in combination with gas accumulators in lighthouses'[2]

Dalén's inventions 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.

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.

Light Technology

The lighthouses in Finland as of the year 1909, showing differing architecture.

In a modern lighthouse, the source of light is called the "lamp" (be it electric or fueled by oil) and the magnification of the light is caused by the "lens" or "optic".

Lamp Technology

Whale oil was used with solid wicks as the source of light until a parabolic reflector system was introduced around 1810. Although the Fresnel lens was invented in 1822, it wasn’t used in the US until the 1850s. Colza oil (pressed from wild cabbages) replaced whale oil in the early 1850s, but our farmers' lack of interest in growing this caused the service to switch to lard oil in the mid 1850s. Kerosene started replacing lard oil in the 1870s and the service was finally totally converted by the late 1880s. Electricity started to replace kerosene around the turn of the century. All U. S. lighthouses had Fresnel lenses by 1860.

Lens Technology

Prior to modern strobe lights, lens were used to concentrate the light from a continuous source. Two tasks were involved:

  • 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.

To assist in distinguishing between lighthouses, the time interval of the light 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.

Building

Building Design

In order to be effective, the lamp needs to be placed at an appropriate height so as to be seen over the horizon before the danger is reached by a mariner. The necessary height can be determined by taking the square root of the height of a light in feet and multiplying it by 1.414 to get the distance to the horizon in nautical miles.

Where dangerous shoals are located far off a flat sandy beach, the prototypical tall masonary coastal beach lighthouse is constucted. Often these are cylindrical to reduce the effect of wind on a tall structure on less stable soil. An example of this style is Cape May Lighthouse

Where a tall cliff exists, a smaller structure may be placed atop it as the location is already high above the water, such as at Horton Point Lighouse. Sometimes, such a location can actually be too high as along the west coast of the United States. In these cases, the lights are often placed below the top of the cliff to ensure that they can still be seen at the surface during periods of fog. An example of this is Point Reyes Lighthouse.

As technology advanced, prefabricated skeletal iron or steel light houses tended to be used for lighthouses constructed in the twentieth century. These often have a narrow cylindrical core surounded by an open lattice work bracing, such as Finns Point Range Light.

Some times a lighthouse needs to be constructed in the water itself. Wavewashed lights are masonary stuctures so constructed to withstand water impact, such as Fastnet Lighthouse. In shallower bays, screwpile ironwork structures are screwed into the seabed and a low wooden structure is placed above the open framework, such as Thomas Point Shoal Light. As screwpiles can be disrupted by ice, in northern climates steel caison lighthouses such as Orient Point Light are used instead. Orient Long Beach Bar (Bug Light) is an interesting blend of a screwpile light that was later converted to a caison light because of the threat of ice damage.

Finally, in waters too deep for a conventional structure, a lightship might be used instead of a lighthouse. Most of these have now been replaced by light platforms (such as Ambrose Light) similar to those used for offshore oil exploration.

Building Components

While the buildings differ depending on the lights location and purpose, they tend to share the following components.

A Light Station consists of the Lighthouse tower and all of the outbuildings, i.e. the keeper¹s living quarters, fuelhouse, boathouse, fog-signaling building, etc. The Lighthouse itself consists of a tower structure supporting the lantern room were the light operates. The Lantern Room is the glassed-in housing at the top of a lighthouse tower containing the lamp and lens. Its glass "storm panes" are supported by metal Astragal bars (running vertically or diagonally). At the top of the lantern room is a stormproof ventilator designed to remove the smoke of the lamps and the daytime heat that builds up in such a glass enclosure. A grounding system is usually connected to the metal roof to provide a safe conduit for any lighning strikes.

Immediately beneath the lantern room is usually a Watch Room or Service Room where fuel and other supplies were kept and where the keeper prepared the lanterns for the night and often stood watch. The clockworks (for rotating the lenses) were also located there. On a lighthouse tower, an open platform called Gallery is often located outside the Watchroom (called the Main Gallery) and/or Lantern Room (Lantern Gallery.) This was mainly used for cleaning the outside of the windows of the Lantern Room.

Lights near to each other that are similar in shape are often painted in a unique pattern so they can easily be recognized during the daylight. This marking is called a day mark.

Maintenance

Outcrops of rocks along coastlines can prove treacherous to ships.

In the United States, lighthouses are maintained by the United States Coast Guard. In the UK 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.

Preservation

As lighthouses have become less essential to navigation, many of their historic structures have faced demolition or neglect. Many groups have been formed to restore and save lighthouses around the world. They include the World Lighthouse Society and the United States Lighthouse Society. In Canada, the Nova Scotia Lighthouse Preservation Society won heritage status for Sambro Island Lighthouse and has sponsored heritage legislation for lighthouses. Another international group is the Amateur Radio Lighthouse Society, or ARLHS which sends ham radio operators to remote lighthouses throughout the world.

Notable lighthouses

Split Point Lighthouse, as seen in the television series Round the Twist.
See List of lighthouses and lightvessels

In some locations, lighthouses have become popular travel destinations and the buildings are being maintained as tourist attractions. See, for example, the Cape Hatteras lighthouse, the Portland Head Light and Peggys Cove lighthouse.

Another example is the Split Point Lighthouse in Aireys Inlet, Victoria, Australia. The 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.

Cabo Branco lighthouse in South America.

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.

Sambro Island Lighthouse, near Halifax, Nova Scotia, is the oldest surviving lighthouse in the Western Hemisphere. Built by the British in 1758, it has survived the many wars that destroyed earlier lighthouses in North and South America.

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.

Symbolism

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.

Range Lights

Range Lights in Nantucket, MA. This view indicates that the observer is to the left of the desired channel.

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. 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).

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.

Gallery

See also

References

  • Against Darkness and Storm: Lighthouses of the Northeast Harry Thurston, Halifax: Nimbus, 1993.
  1. ^ http://www.aga.com/web/web2000/com/WPPcom.nsf/pages/History_SunValve
  2. ^ http://nobelprize.org/nobel_prizes/physics/laureates/1912/dalen-bio.html

External links

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