Lighthouse (redirected from Lighthouses)

lighthouse, towerlike structure erected to give guidance and warning to ships and aircraft by either visible or radioelectrical means. Lighthouses were long built to conform in structure to their geographical location. Until the beginning of the 19th cent. tallow candles, coal fires, and oil lamps were used as illuminating agents; coal gas followed, to be succeeded by acetylene. Electricity was used for the first time at South Foreland Light, England, in 1858. Other 19th-century innovations were rapidly revolving lights, the incandescent oil-vapor light, fog bells, whistles, sirens, diaphones (fog signals similar to sirens), and the Fresnel lens (used to focus the beam).

In modern lighthouses there are three kinds of lighting systems: the catoptric system, in which rays of light are reflected from silvered mirrors to form a parallel beam visible at a distance; the dioptric, or refractive, system, in which the rays pass through optical glass and are refracted as they enter and emerge from it; and the catadioptric system, in which rays are both refracted and reflected. Increased use of radio beams and radar has made the conventional lighthouse obsolete.

History

Lighthouses date back to ancient Egypt, where priests maintained the beacon fires. For about 1,500 years the lighthouse of Pharos, built in the 3d cent. B.C., guided ships into the Nile; it was lighted by a wood fire and showed smoke by day and a glow by night. The Romans built famous lighthouses in Ostia, Ravenna, and Messina and on both sides of the English Channel.

In the United States the tower for the Boston Light on Little Brewster Island was built in 1716; the first structure of the Brant Point Light, Nantucket, was built in 1746; and Beavertail Light on Conanicut Island, Narragansett Bay, was erected in 1749. In 1789 the U.S. government took over the care of lighthouses from their former private owners. The government set up (1852) the Lighthouse Board, which was eventually superseded by the Lighthouse Service, established (1910) to supervise lighthouses and lightships (see lightship). In 1939 this service was transferred from the Dept. of Commerce to the U.S. Coast Guard.

Bibliography

See H. C. Adamson, Keepers of the Lights (1955); D. A. Stevenson, The World's Lighthouses before 1820 (1960); F. R. Holland, America's Lighthouses: Their Illustrated History Since 1716 (1972).

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lighthouse

Structure, usually with a tower, built onshore or on the seabed to signal danger or provide aid to seafarers. The first known lighthouse was the Pharos of Alexandria. The modern lighthouse dates only from the early 18th century. Initially made of wood, these towers were often washed away in severe storms. The first lighthouse made of interlocking masonry blocks was built on the treacherous Eddystone Rocks reef, off Plymouth, England (1759). Interlocking masonry blocks remained the principal material of lighthouse construction until they were replaced by concrete and steel in the 20th century. Modern construction methods have facilitated the building of offshore lighthouses. The most common illuminant is the electric-filament lamp. Refinements in lenses (e.g., the Fresnel lens) and reflectors made it possible to substantially increase the light's intensity. Radio and satellite-based navigation systems have greatly reduced the need for large lighthouses in sighting land.

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lighthouse [′līt‚hau̇s]

(navigation)

A structure equipped with a powerful light to aid in navigation.

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lighthouse

A tall structure, such as a tower, with a powerful source of light on top; located on a sea-coast or other water channel to provide guidance for mariners at sea. Lighthouses were important facilities in establishing seafaring commerce and continued to be influential until the latter part of the 20th century, when they were largely replaced by electronic guidance systems.

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Lighthouse 

a tower that serves as an orientation point in identifying shore and vessel locations and in warning of navigational hazards.

Lighthouses are equipped with optical lighting systems and with technical means for producing signals: acoustic atmospheric devices (nautophone, diaphone, siren), underwater devices (underwater bells, oscillators), radio engineering devices (radio beacon), or combined radio and acoustic devices (a radio beacon receiver-transmitter operating synchronously with a nautophone or oscillator).

Lighthouses are usually built on promontories at the entrances to ports, bays, and estuaries and sometimes on cliffs, reefs, or sandbars. Floating beacons are used to warn of hazards far from shore or to provide receivers at port entrances. These are anchored ships specially constructed to carry signaling equipment.

For purposes of positive identification, each lighthouse is assigned a particular set of light, acoustic, or radio signals. The basic characteristics of a lighthouse include the distinctive architecture of its tower, its sector of illumination, the height of the light above sea level, and the color and character of the light (continuous uniform light, single flashes or groups of flashes at uniform time intervals, occulting light, and continuous light intensifying at uniform intervals). The characteristic features of radio beacons include their operating frequency, operating schedule, and code signal. Acoustic signals are usually operated only when visibility is poor. Like radio beacons, they are characterized by their schedule and code.

The operating ranges are 20-50 km for light signals, 30-500 km or more for radio beacons, 5-15 km for acoustic signals transmitted through air, and up to 25 km for hydroacoustic signals.

Lighthouses have been used since antiquity and are associated with the development of navigation itself. At first, bonfires on high shore points were used; later, artificial structures were built. The lighthouse at Alexandria on the Island of Pharos was 143 m high and was one of the seven wonders of the ancient world. Built of white marble in 283 B.Cl, it remained standing for about 1,500 years. In Russia, the first lighthouses were built in 1702 at the mouth of the Don River and in 1704 above the Peter and Paul Fortress in St. Petersburg.

The optical light system of a lighthouse consists of light sources, optical apparatus, and a lanternlike structure protecting the optical equipment from atmospheric effects. The light sources in use include incandescent electric lamps, fluorescent tubes, flashers, acetylene lamps, and, less often, kerosene lamps. The optical apparatus includes a system of reflecting or refracting lenses that concentrates the light stream emitted by the source into a beam with a small scattering angle.

Data on lighthouses are provided in special books, sailing directions, and marine navigation maps.

REFERENCE

Martynov, K. B. Navigatsionnoe oborudovanie morskikh putei. Moscow, 1962.

V. L. ONDZUL’