LIGHTHOUSE

structure, usually with a tower, built onshore or on the seabed to serve as an aid to maritime coastal navigation, warning the mariner of hazards, establishing his position, and guiding him to his destination. From the sea a lighthouse may be identified by the distinctive shape or colour of its structure, by the colour or flash pattern of its light, or by the coded pattern of its radio signal. The development of electronic navigation systems has had a great effect on the role of lighthouses. Powerful lights are becoming superfluous, especially for landfall, but there has been a significant increase in minor lights and lighted buoys, which are still necessary to guide the navigator through busy and often tortuous coastal waters and harbour approaches. Among mariners there is still a natural preference for the reassurance of visual navigation, and lighted marks also have the advantages of simplicity, reliability, and low cost. In addition, they can be used by vessels with no special equipment on board, providing the ultimate backup against the failure of more sophisticated systems. structure, usually with a tower, built onshore or on the seabed to serve as an aid to maritime coastal navigation. From the sea a lighthouse may be identified by the distinctive shape or colour of its structure, by the colour or flash pattern of its light, or by the coded pattern of its radio signal. The first known lighthouse was the Pharos of Alexandria, which stood some 350 feet (110 m) high. During the first few centuries AD the Phoenicians and Romans also built lighthouses at numerous sites, ranging from the Black Sea, along the Mediterranean and Atlantic coasts, to Britain. After the fall of the Roman Empire in the 5th century, there was little maritime trade or travel, and no lighthouses were built in Europe until the revival of commerce in the 12th century. The French and Italians built the earliest of these lighthouses, followed by the Hanseatic League, which constructed a number of such structures along the Scandinavian and German coasts. The modern lighthouse dates from the early 18th century. Initially these towers were made of wood, but wooden towers were often washed away in severe storms. The first lighthouse made of interlocking masonry blocks was built on the treacherous Eddystone Rocks reef in England in 1759. This structure, designed by the engineer John Smeaton, was also the first to employ the classic curved hyperbolic design. Following the success of Smeaton's innovations, a large number of lighthouses were built on the open sea. Interlocking masonry blocks remained the principal material of lighthouse construction until they were replaced by concrete and steel in the 20th century. There are now three major kinds of offshore lighthouse structures. The first rests on a hollow, steel cylinder (caisson) that is partly sunk into the seabed and then filled with concrete. The second utilizes a concrete base that sinks to the bottom of the water, thus anchoring the lighthouse tower that rises from this base. The third, resembling an offshore oil rig, consists of a large deck supported by tubular steel piles driven into the seabed; the tower rises from the deck. Most lighthouses also have landing pads for helicopters. The standard illuminant of modern lighthouses (as well as lightships and buoys) is the electric lamp. The most common type is the electric-filament lamp, which requires as much as 1.5 kilowatts to as little as 5 watts in small buoys. Refinements in lenses and reflectors have made it possible for a 250-watt bulb to be boosted to several hundred thousand candlepower, or candelas. The maximum intensity now sought in lighthouse beams is in the range of 100,000 candelas; this gives a beam that can be seen from 20 nautical miles (37 km) in clear weather. Sirens and horns are commonly used to provide audible warnings when a lighthouse and its beacon are obscured by bad weather. But because the range of their sound is also highly dependent on weather conditions, many lighthouses are also fitted with radio and radar beacons, which either amplify a ship's radar or emit signals of their own that can be detected by navigators. Radio and satellite-based navigation systems have greatly reduced the need for large lighthouses in sighting land, although smaller structures are still important aids to navigating crowded coastal waters and shipping lanes. Almost all lighthouses are now completely automated, eliminating the expense of maintenance by resident crews. Modern computerized lighthouses analyze the weather, activate foghorns and other equipment, and transmit signals to remote control stations ashore. Additional reading Kenneth Sutton Jones, Pharos: The Lighthouse Yesterday, Today, and Tomorrow (1985), a comprehensive and detailed treatment, includes a discussion of future trends. David Stevenson, The World's Lighthouses before 1820 (1959), is a classic work by a member of the famous family of Scottish lighthouse engineers. Patrick Beaver, A History of Lighthouses (1971), provides historical descriptions of the construction of important lighthouses in various parts of the world, as well as the people involved.douglas B. Hague and Rosemary Christie, Lighthouses: Their Architecture, History, and Archaeology (1975), offers a history of lighthouse building, construction, engineering, and architecture from earliest times throughout the world. Robert Stevenson, English Lighthouse Tours, ed. by David Stevenson (1946), is an edited version of a detailed journal kept during a tour of English lighthouses. Hilary Poland Mead, Trinity House (1947), discusses the origins and history of the lighthouse authority for England and Wales. George R. Putnam, Lighthouses and Lightships of the United States, new and rev. ed. (1933), provides a historical survey of most of the major lighthouses and lightships of the United States through the early 20th century; it may be supplemented by Francis Ross Holland, Jr., America's Lighthouses: Their Illustrated History Since 1716 (1972, reissued 1988). United States, Coast Guard, Historically Famous Lighthouses (1950), and Coast Guard History, new ed. (1982), provide brief insights into the work of the U.S. Coast Guard and some of its more famous lighthouses. Ian C. Clingan