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A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and
lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
and to serve as a
beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
for
navigational aid A navigational aid (NAVAID), also known as aid to navigation (ATON), is any sort of signal, markers or guidance equipment which aids the traveler in navigation, usually nautical or aviation travel. Common types of such aids include lighthouses, ...
for
maritime pilot A maritime pilot, marine pilot, harbor pilot, port pilot, ship pilot, or simply pilot, is a mariner who has specific knowledge of an often dangerous or congested waterway, such as harbors or river mouths. Maritime pilots know local details s ...
s at sea or on inland waterways. Lighthouses mark dangerous coastlines, hazardous
shoal In oceanography, geomorphology, and Earth science, geoscience, a shoal is a natural submerged ridge, bank (geography), bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body ...
s,
reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
s, rocks, and safe entries to harbors; they also assist in
aerial navigation The basic principles of air navigation are identical to general navigation, which includes the process of planning, recording, and controlling the movement of a craft from one place to another. Successful air navigation involves piloting an airc ...
. Once widely used, the number of operational lighthouses has declined due to the expense of maintenance and the advent of much cheaper, more sophisticated, and more effective electronic navigational systems.


History


Ancient lighthouses

Before the development of clearly defined
port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manch ...
s, mariners were guided by fires built on hilltops. Since elevating the fire would improve visibility, placing the fire on a platform became a practice that led to the development of the lighthouse. In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for
reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
s and
promontories A promontory is a raised mass of landform, land that projects into a Upland and lowland, lowland or a body of water (in which case it is a peninsula). Most promontories either are formed from a hard ridge of rock that has resisted the erosion, e ...
, unlike many modern lighthouses. The most famous lighthouse structure from antiquity was the Pharos of
Alexandria Alexandria ( ; ) is the List of cities and towns in Egypt#Largest cities, second largest city in Egypt and the List of coastal settlements of the Mediterranean Sea, largest city on the Mediterranean coast. It lies at the western edge of the Nile ...
,
Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...
, which collapsed following a series of earthquakes between 956 and 1323. The intact
Tower of Hercules The Tower of Hercules (, ) is the oldest known extant Roman lighthouse. Built in the 1st century, the tower is located on a peninsula about from the center of A Coruña, Galicia, in northwestern Spain. Until the 20th century, it was known as the ...
at
A Coruña A Coruña (; ; also informally called just Coruña; historical English: Corunna or The Groyne) is a city and municipality in Galicia, Spain. It is Galicia's second largest city, behind Vigo. The city is the provincial capital of the province ...
, Spain gives insight into ancient lighthouse construction; other evidence about lighthouses exists in depictions on coins and mosaics, of which many represent the lighthouse at Ostia. Coins from Alexandria, Ostia, and Laodicea in Syria also exist.


Modern construction

The modern era of lighthouses began at the turn of the 18th century, as the number of lighthouses being constructed increased significantly due to much higher levels of transatlantic commerce. Advances in structural engineering and new and efficient lighting equipment allowed for the creation of larger and more powerful lighthouses, including ones exposed to the sea. The function of lighthouses was gradually changed from indicating ports to the providing of a visible warning against shipping hazards, such as rocks or reefs. The
Eddystone Rocks The Eddystone or Eddystone Rocks are a seaswept and eroded group of rocks ranging southwest of Rame Head in Cornwall, England, United Kingdom. Although the nearest point on the mainland to the Eddystone is in Cornwall, the rocks fall within the ...
were a major shipwreck hazard for mariners sailing through the
English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...
. The first lighthouse built there was an octagonal wooden structure, anchored by 12 iron stanchions secured in the rock, and was built by
Henry Winstanley Henry Winstanley (31 March 1644 – 27 November 1703) was an English painter, engineer, and merchant who constructed the first Eddystone Lighthouse after losing two of his ships on the Eddystone rocks. He died while working on the project dur ...
from 1696 to 1698. His lighthouse was the first tower in the world to have been fully exposed to the open sea. The
civil engineer A civil engineer is a person who practices civil engineering – the application of planning, designing, constructing, maintaining, and operating infrastructure while protecting the public and environmental health, as well as improving existing i ...
John Smeaton John Smeaton (8 June 1724 – 28 October 1792) was an English civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminent scholar, who introduced various ...
rebuilt the
lighthouse A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lens (optics), lenses and to serve as a beacon for navigational aid for maritime pilots at sea or on inland waterways. Ligh ...
from 1756 to 1759;Majdalany, Fred: ''The Eddystone Light''. 1960 his tower marked a major step forward in the design of lighthouses and remained in use until 1877. He modeled the shape of his lighthouse on that of an
oak tree An oak is a hardwood tree or shrub in the genus ''Quercus'' of the Fagaceae, beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northe ...
, using
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
blocks. He rediscovered and used "
hydraulic lime Hydraulic lime (HL) is a general term for a variety of lime different from calcium oxide (quicklime), that sets by hydration and consists of calcium silicate and calcium aluminate, compounds that can harden in contact with water. This contras ...
", a form of
concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
that will set under water used by the Romans, and developed a technique of securing the granite blocks together using
dovetail joint A dovetail joint or simply dovetail is a joinery technique most commonly used in woodworking joinery (carpentry), including furniture, cabinets, log buildings, and traditional timber framing. Noted for its resistance to being pulled apart, a ...
s and marble
dowels The dowel is a cylindrical shape made of wood, plastic, or metal. In its original manufactured form, a dowel is long and called a ''dowel rod'', which are often cut into shorter ''dowel pins''. Dowels are commonly used as structural reinforceme ...
. The dovetailing feature served to improve the structural stability, although Smeaton also had to taper the thickness of the tower towards the top, for which he curved the tower inwards on a gentle gradient. This profile had the added advantage of allowing some of the energy of the waves to dissipate on impact with the walls. His lighthouse was the prototype for the modern lighthouse and influenced all subsequent engineers. One such influence was Robert Stevenson, himself a seminal figure in the development of lighthouse design and construction. His greatest achievement was the construction of the Bell Rock Lighthouse in 1810, one of the most impressive feats of engineering of the age. This structure was based upon Smeaton's design, but with several improved features, such as the incorporation of rotating lights, alternating between red and white. Stevenson worked for the
Northern Lighthouse Board The Northern Lighthouse Board (NLB) is the general lighthouse authority for Scotland and the Isle of Man. It is a non-departmental public body responsible for ocean, marine navigation aids around coastal areas. History The NLB was formed by ...
for nearly fifty years during which time he designed and oversaw the construction and later improvement of numerous lighthouses. He innovated in the choice of light sources, mountings, reflector design, the use of
Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens (optics), lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. The simpler Dioptrics, d ...
es, and in rotation and shuttering systems providing lighthouses with individual signatures allowing them to be identified by seafarers. He also invented the movable jib and the balance-crane as a necessary part for lighthouse construction. Alexander Mitchell designed the first screw-pile lighthouse – his lighthouse was built on piles that were
screw A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the screw head, head. The most common uses of screws are to hold objects together and there are many forms for a variety ...
ed into the sandy or muddy seabed. Construction of his design began in 1838 at the mouth of the
Thames The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after th ...
and was known as the Maplin Sands lighthouse, and first lit in 1841. Although its construction began later, the Wyre Light in Fleetwood, Lancashire, was the first to be lit (in 1840).


Lighting improvements

Until 1782 the source of illumination had generally been wood pyres or burning coal. The
Argand lamp The Argand lamp is a type of oil lamp invented in 1780 by Aimé Argand. Its output is 6 to 10 candelas, brighter than that of earlier lamps. Its more complete combustion of the candle wick and oil than in other lamps required much less frequen ...
, invented in 1782 by the Swiss scientist Aimé Argand revolutionized lighthouse illumination with its steady smokeless flame. Early models used ground glass which was sometimes tinted around the wick. Later models used a mantle of
thorium dioxide Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is mainly a by-product of lanthanide and uranium production. Thorianite is the name of the mineralogical for ...
suspended over the flame, creating a bright, steady light. The Argand lamp used
whale oil Whale oil is oil obtained from the blubber of whales. Oil from the bowhead whale was sometimes known as train-oil, which comes from the Dutch word ''traan'' ("tear drop"). Sperm oil, a special kind of oil used in the cavities of sperm whales, ...
, colza,
olive oil Olive oil is a vegetable oil obtained by pressing whole olives (the fruit of ''Olea europaea'', a traditional Tree fruit, tree crop of the Mediterranean Basin) and extracting the oil. It is commonly used in cooking for frying foods, as a cond ...
or other
vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed ...
as fuel, supplied by a
gravity feed Gravity feed is the use of earth's gravity to move something (usually a liquid) from one place to another. It is a simple means of moving a liquid without the use of a pump. A common application is the supply of fuel to an internal combustion e ...
from a reservoir mounted above the burner. The lamp was first produced by
Matthew Boulton Matthew Boulton ( ; 3 September 172817 August 1809) was an English businessman, inventor, mechanical engineer, and silversmith. He was a business partner of the Scottish engineer James Watt. In the final quarter of the 18th century, the par ...
, in partnership with Argand, in 1784, and became the standard for lighthouses for over a century. South Foreland Lighthouse was the first tower to successfully use an electric light in 1875. The lighthouse's carbon
arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...
s were powered by a steam-driven
magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
. John Richardson Wigham was the first to develop a system for gas illumination of lighthouses. His improved gas 'crocus' burner at the Baily Lighthouse near Dublin was 13 times more powerful than the most brilliant light then known. The vaporized oil burner was invented in 1901 by Arthur Kitson, and improved by David Hood at
Trinity House The Corporation of Trinity House of Deptford Strond, also known as Trinity House (and formally as The Master, Wardens and Assistants of the Guild Fraternity or Brotherhood of the most glorious and undivided Trinity and of St Clement in the ...
. The fuel was vaporized at high pressure and burned to heat the mantle, giving an output of over six times the luminosity of traditional oil lights. The use of gas as illuminant became widely available with the invention of the
Dalén light A Dalén light is a flashing light produced from burning of carbide gas (acetylene), combined with a solar sensor which automatically operates the light only during darkness. Overview In the last quarter of the 19th century navigation buoys bega ...
by Swedish engineer
Gustaf Dalén Nils Gustaf Dalén (; 30 November 1869 – 9 December 1937) was a Swedish engineer and inventor who received the Nobel Prize in Physics in 1912 "for his invention of Sun valve, automatic regulators for use in conjunction with gas accumulators fo ...
. He used
Agamassan Agamassan is a porous substrate used to safely absorb acetylene and thus allow the transport, storage and commercial use of the otherwise unstable gas. It was developed and patented by the Swedish Nobel Laureate and industrialist Gustaf Dalén. ...
(Aga), a substrate, to absorb the gas, allowing the gas to be stored, and hence used, safely. Dalén also invented the ' sun valve', which automatically regulated the light and turned it off during the daytime. The technology was the predominant light source in lighthouses from the 1900s to the 1960s, when electric lighting had become dominant.


Optical systems

With the development of the steady illumination of the Argand lamp, the application of optical lenses to increase and focus the light intensity became a practical possibility. William Hutchinson developed the first practical optical system in 1777, known as a catoptric system. This rudimentary system effectively collimated the emitted light into a concentrated beam, thereby greatly increasing the light's visibility. The ability to focus the light led to the first revolving lighthouse beams, where the light would appear to the mariners as a series of intermittent flashes. It also became possible to transmit complex signals using the light flashes. French physicist and engineer
Augustin-Jean Fresnel Augustin-Jean Fresnel (10 May 1788 – 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Isaac Newton, Newton's c ...
developed the multi-part
Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens (optics), lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. The simpler Dioptrics, d ...
for use in lighthouses. His design allowed for the construction of lenses of large
aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
and short
focal length The focal length of an Optics, optical system is a measure of how strongly the system converges or diverges light; it is the Multiplicative inverse, inverse of the system's optical power. A positive focal length indicates that a system Converge ...
, without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can also capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances. The first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the
Gironde estuary The Gironde estuary ( , US usually ; , ; , ) is a navigable estuary (though often referred to as a river) in southwest France and is formed from the meeting of the rivers Dordogne and Garonne just downstream of the centre of Bordeaux. Coverin ...
; its light could be seen from more than out. Fresnel's invention increased the
luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
of the lighthouse lamp by a factor of four and his system is still in common use.


Modern lighthouses

The introduction of electrification and automatic lamp changers began to make lighthouse keepers obsolete. 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
Global Positioning System The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...
(GPS), led to the phasing out of non-automated lighthouses across the world. Although several closed due to safety concerns, Canada still maintains 49 staffed lighthouses, split roughly evenly across east and west coasts. The remaining modern lighthouses are usually illuminated by a single stationary flashing light powered by solar-charged batteries and mounted on a steel skeleton tower. Where the power requirement is too great for solar power alone, ''cycle charging'' of the battery by a Diesel generator is provided. The generator only comes into use when the battery needs charging, saving fuel and increasing periods between maintenance.


Famous lighthouse builders

John Smeaton John Smeaton (8 June 1724 – 28 October 1792) was an English civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminent scholar, who introduced various ...
is noteworthy for having designed the third and most famous
Eddystone Lighthouse The Eddystone Lighthouse is a lighthouse on the Eddystone Rocks, south of Rame Head in Cornwall, England. The rocks are submerged below the surface of the sea and are composed of Precambrian gneiss. View at 1:50000 scale The current structu ...
, but some builders are well known for their work in building multiple lighthouses. The Stevenson family (
Robert The name Robert is an ancient Germanic given name, from Proto-Germanic "fame" and "bright" (''Hrōþiberhtaz''). Compare Old Dutch ''Robrecht'' and Old High German ''Hrodebert'' (a compound of ''Hrōþ, Hruod'' () "fame, glory, honour, prais ...
,
Alan Alan may refer to: People *Alan (surname), an English and Kurdish surname * Alan (given name), an English given name ** List of people with given name Alan ''Following are people commonly referred to solely by "Alan" or by a homonymous name.'' * ...
,
David David (; , "beloved one") was a king of ancient Israel and Judah and the third king of the United Monarchy, according to the Hebrew Bible and Old Testament. The Tel Dan stele, an Aramaic-inscribed stone erected by a king of Aram-Dam ...
,
Thomas Thomas may refer to: People * List of people with given name Thomas * Thomas (name) * Thomas (surname) * Saint Thomas (disambiguation) * Thomas Aquinas (1225–1274) Italian Dominican friar, philosopher, and Doctor of the Church * Thomas the A ...
, David Alan, and
Charles Charles is a masculine given name predominantly found in English language, English and French language, French speaking countries. It is from the French form ''Charles'' of the Proto-Germanic, Proto-Germanic name (in runic alphabet) or ''* ...
) made lighthouse building a three-generation profession in Scotland. Richard Henry Brunton designed and built 26 Japanese lighthouses in
Meiji Era The was an Japanese era name, era of History of Japan, Japanese history that extended from October 23, 1868, to July 30, 1912. The Meiji era was the first half of the Empire of Japan, when the Japanese people moved from being an isolated feu ...
Japan, which became known as Brunton's "children". Blind Irishman Alexander Mitchell invented and built a number of screw-pile lighthouses. Englishman James Douglass was knighted for his work on the fourth Eddystone Lighthouse.
United States Army Corps of Engineers The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil wo ...
Lieutenant George Meade built numerous lighthouses along the Atlantic and Gulf coasts before gaining wider fame as the winning general at the
Battle of Gettysburg The Battle of Gettysburg () was a three-day battle in the American Civil War, which was fought between the Union and Confederate armies between July 1 and July 3, 1863, in and around Gettysburg, Pennsylvania. The battle, won by the Union, ...
. Colonel Orlando M. Poe, engineer to General William Tecumseh Sherman in the siege of Atlanta, designed and built some of the most exotic lighthouses in the most difficult locations on the U.S.
Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...
. French merchant navy officer Marius Michel Pasha built almost a hundred lighthouses along the coasts of the
Ottoman Empire The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...
in a period of twenty years after the
Crimean War The Crimean War was fought between the Russian Empire and an alliance of the Ottoman Empire, the Second French Empire, the United Kingdom of Great Britain and Ireland, and the Kingdom of Sardinia (1720–1861), Kingdom of Sardinia-Piedmont fro ...
(1853–1856).


Technology

In a lighthouse, the source of light is called the "lamp" (whether electric or fuelled by oil) and the light is concentrated, if needed, by the "lens" or "optic". Power sources for lighthouses in the 20th–21st centuries vary.


Power

Originally lit by open fires and later candles, the Argand hollow wick lamp and
parabolic reflector A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a Mirror, reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface ge ...
were introduced in the late 18th century.
Whale oil Whale oil is oil obtained from the blubber of whales. Oil from the bowhead whale was sometimes known as train-oil, which comes from the Dutch word ''traan'' ("tear drop"). Sperm oil, a special kind of oil used in the cavities of sperm whales, ...
was also used with wicks as the source of light.
Kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...
became popular in the 1870s and electricity and
acetylene Acetylene (Chemical nomenclature, systematic name: ethyne) is a chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is u ...
gas derived on-site from
calcium carbide Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of . Its main use industrially is in the production of acetylene and calcium cyanamide. The pure material is colorless, while pieces of technica ...
began replacing kerosene around the turn of the 20th century. Carbide was promoted by the
Dalén light A Dalén light is a flashing light produced from burning of carbide gas (acetylene), combined with a solar sensor which automatically operates the light only during darkness. Overview In the last quarter of the 19th century navigation buoys bega ...
, which automatically lit the lamp at nightfall and extinguished it at dawn. In the second half of the 20th century, many remote lighthouses in
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
(then
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
) were powered by
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...
s (RTGs). These had the advantage of providing power day or night and did not need refuelling or maintenance. However, after the collapse of the Soviet government in 1990s, most of the official records on the locations, and condition, of these lighthouses were reportedly lost. Over time, the condition of RTGs in Russia degraded; many of them fell victim to vandalism and scrap metal thieves, who may not have been aware of the dangerous radioactive contents. Energy-efficient LED lights can be powered by
solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...
s, with batteries instead of a Diesel generator for backup.


Light source

Many Fresnel lens installations have been replaced by rotating
aerobeacon An aerobeacon is a light assembly used to create a fixed or flashing signal visible over long distances. It consists of a high intensity electric lamp mounted with a focusing device in a cylindrical housing, which usually is rotated on a vertical ...
s, which require less maintenance. In modern automated lighthouses, the system of rotating lenses is often replaced by a high intensity light that emits brief omnidirectional flashes, concentrating the light in time rather than direction. These lights are similar to obstruction lights used to warn aircraft of tall structures. Later innovations were "Vega Lights", and experiments with
light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...
(LED) panels. LED lights, which use less energy and are easier to maintain, had come into widespread use by 2020. In the United Kingdom and Ireland about a third of lighthouses had been converted from filament light sources to use LEDs, and conversion continued with about three per year. The light sources are designed to replicate the colour and character of the traditional light as closely as possible. The change is often not noticed by people in the region, but sometimes a proposed change leads to calls to preserve the traditional light, including in some cases a rotating beam. A typical LED system designed to fit into the traditional 19th century Fresnel lens enclosure was developed by Trinity House and two other lighthouse authorities and costs about
The euro sign () is the currency sign used for the euro, the official currency of the eurozone. The design was presented to the public by the European Commission on 12 December 1996. It consists of a stylized letter E (or epsilon), crossed by t ...
20,000, depending on configuration, according to a supplier; it has large fins to dissipate heat. Lifetime of the LED light source is 50,000 to 100,000 hours, compared to about 1,000 hours for a filament source.


Laser light

Experimental installations of
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
lights, either at high power to provide a "line of light" in the sky or, utilising low power, aimed towards mariners have identified problems of increased complexity in installation and maintenance, and high power requirements. The first practical installation, in 1971 at Point Danger lighthouse,
Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
, was replaced by a conventional light after four years, because the beam was too narrow to be seen easily.


Light characteristics

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
light characteristic A light characteristic is all of the properties that make a particular somewhat navigational light identifiable. Graphical and textual descriptions of navigational light sequences and colours are displayed on nautical charts and in Light Lists ...
or pattern specific to a lighthouse. For example, the Scheveningen Lighthouse flashes are alternately 2.5 and 7.5 seconds. Some lights have sectors of a particular color (usually formed by colored panes in the lantern) to distinguish safe water areas from dangerous shoals. Modern lighthouses often have unique reflectors or racon transponders so the radar signature of the light is also unique.


Lens

Before modern
strobe light A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Ancient Greek ('), meaning ...
s,
lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
were used to concentrate the light from a continuous source. Vertical light rays of the lamp are redirected into a horizontal plane, and horizontally the light is focused into one or a few directions at a time, with the
light beam A light beam or beam of light is a directional projection of light energy radiating from a light source. Sunlight forms a light beam (a sunbeam) when filtered through media such as clouds, foliage, or windows. To artificially produce a li ...
swept around. As a result, in addition to seeing the side of the light beam, the light is directly visible from greater distances, and with an identifying
light characteristic A light characteristic is all of the properties that make a particular somewhat navigational light identifiable. Graphical and textual descriptions of navigational light sequences and colours are displayed on nautical charts and in Light Lists ...
. This concentration of light is accomplished with a rotating lens assembly. In early lighthouses, the light source was a kerosene lamp or, earlier, an animal or vegetable oil Argand lamp, and the lenses rotated by a weight driven clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly sometimes floated in liquid mercury to reduce friction. In more modern lighthouses, electric lights and motor drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers. Efficiently concentrating the light from a large omnidirectional light source requires a very large diameter lens. This would require a very thick and heavy lens if a conventional lens were used. The
Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens (optics), lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. The simpler Dioptrics, d ...
(pronounced ) focused 85% of a lamp's light versus the 20% focused with the parabolic reflectors of the time. Its design enabled construction of lenses of large size and short focal length without the weight and volume of material in conventional lens designs. Fresnel lighthouse lenses are ranked by ''order'', a measure of refracting power, with a first order lens being the largest, most powerful and expensive; and a sixth order lens being the smallest. The order is based on the focal length of the lens. A first order lens has the longest focal length, with the sixth being the shortest. Coastal lighthouses generally use first, second, or third order lenses, while harbor lights and beacons use fourth, fifth, or sixth order lenses. Some lighthouses, such as those at
Cape Race Cape Race is a point of land located at the southeastern tip of the Avalon Peninsula on the island of Newfoundland, in Newfoundland and Labrador, Canada. Its name is thought to come from the original Portuguese name for this cape, "Raso", mean ...
, Newfoundland, and Makapuu Point, Hawaii, used a more powerful hyperradiant Fresnel lens manufactured by the firm of
Chance Brothers Chance Brothers and Company was an English glassworks originally based in Spon Lane, Smethwick, West Midlands (county), West Midlands (formerly in Staffordshire), in England. It was a leading glass manufacturer and a pioneer of British glassma ...
.


Building


Components

While lighthouse buildings differ depending on the location and purpose, they tend to have common components. A light station comprises the lighthouse tower and all outbuildings, such as the keeper's living quarters, fuel house, boathouse, and fog-signaling building. The Lighthouse itself consists of a tower structure supporting the lantern room where 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 muntins (glazing 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 heat that builds in the glass enclosure. A
lightning rod A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it is most likely to strike the rod and be conducted ...
and grounding system connected to the metal cupola roof provides a safe conduit for any lightning 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 the gallery is often located outside the watch room (called the Main Gallery) or Lantern Room (Lantern Gallery). This was mainly used for cleaning the outside of the windows of the Lantern Room. Lighthouses near to each other that are similar in shape are often painted in a unique pattern so they can easily be recognized during daylight, a marking known as a
daymark A daymark is a navigational aid for sailors and maritime pilot, pilots, distinctively marked to maximize its visibility in daylight. The word is also used in a more specific, technical sense to refer to a signboard or daytime identifier that ...
. The black and white barber pole spiral pattern of Cape Hatteras Lighthouse is one example. Race Rocks Light in western Canada is painted in horizontal black and white bands to stand out against the horizon.


Design

For effectiveness, the lamp must be high enough to be seen before the danger is reached by a mariner. The minimum height is calculated by trigonometry (see Distance to the horizon) as D = 1.22 \sqrt , where ''H'' is the height above water in feet, and ''D'' is the distance from the lighthouse to the horizon in nautical miles, the lighthouse range. Where dangerous shoals are located far off a flat sandy beach, the prototypical tall masonry coastal lighthouse is constructed to assist the navigator making a landfall after an ocean crossing. Often these are cylindrical to reduce the effect of wind on a tall structure, such as Cape May Light. Smaller versions of this design are often used as harbor lights to mark the entrance into a harbor, such as
New London Harbor Light New London Harbor Light is a lighthouse in Connecticut on the west side of the New London harbor entrance. It is the nation's fifth oldest light station and the seventh oldest U.S. lighthouse. It is both the oldest and the tallest lighthouse in ...
. Where a tall cliff exists, a smaller structure may be placed on top such as at Horton Point Light. Sometimes, such a location can be too high, for example along the west coast of the United States, where frequent low clouds can obscure the light. In these cases, lighthouses are placed below the clifftop to ensure that they can still be seen at the surface during periods of fog or low clouds, as at Point Reyes Lighthouse. Another example is in
San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...
,
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
: the Old Point Loma lighthouse was too high up and often obscured by fog, so it was replaced in 1891 with a lower lighthouse, New Point Loma lighthouse. As technology advanced, prefabricated skeletal iron or steel structures tended to be used for lighthouses constructed in the 20th century. These often have a narrow cylindrical core surrounded by an open lattice work bracing, such as Finns Point Range Light. Sometimes a lighthouse needs to be constructed in the water itself. Wave-washed lighthouses are masonry structures constructed to withstand water impact, such as
Eddystone Lighthouse The Eddystone Lighthouse is a lighthouse on the Eddystone Rocks, south of Rame Head in Cornwall, England. The rocks are submerged below the surface of the sea and are composed of Precambrian gneiss. View at 1:50000 scale The current structu ...
in Britain and the St. George Reef Light of California. In shallower bays, Screw-pile lighthouse ironwork structures are screwed into the seabed and a low wooden structure is placed above the open framework, such as Thomas Point Shoal Lighthouse. As screw piles can be disrupted by ice, steel caisson lighthouses such as Orient Point Light are used in cold climates. Orient Long Beach Bar Light (Bug Light) is a blend of a screw pile light that was converted to a caisson light because of the threat of ice damage. Skeletal iron towers with screw-pile foundations were built on the Florida Reef along the Florida Keys, beginning with the Carysfort Reef Light in 1852. In waters too deep for a conventional structure, a lightship might be used instead of a lighthouse, such as the former lightship ''Columbia''. Most of these have now been replaced by fixed light platforms (such as Ambrose Light) similar to those used for offshore oil exploration.


Range lights

Aligning two fixed points on land provides a navigator with a line of position called a range in North America and a
transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1980 film), a 1980 Israeli film * ''Transit'' (1986 film), a Canadian short film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countrie ...
in Britain. Ranges can be used to precisely align a vessel within a narrow channel such as a river. With landmarks of a range illuminated with a set of fixed lighthouses, nighttime navigation is possible. Such paired lighthouses are called range lights in North America and
leading lights Leading lights, also known as range lights in the United States, are a pair of light beacons used in navigation to indicate a safe passage for vessels entering a shallow or dangerous channel; they may also be used for position fixing. At nigh ...
in the United Kingdom. The closer light is referred to as the beacon or front range; the further light is called the rear range. The rear range light is almost always taller than the front. When a vessel is on the correct course, the two lights align vertically, but when the observer is out of position, the difference in alignment indicates the direction of travel to correct the course.


Location

There are two types of lighthouses: ones that are located on land, and ones that are offshore. ''Offshore Lighthouses'' are lighthouses that are not close to land. There can be a number of reasons for these lighthouses to be built. There can be a
shoal In oceanography, geomorphology, and Earth science, geoscience, a shoal is a natural submerged ridge, bank (geography), bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body ...
,
reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
or submerged
island An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...
several miles from land. The current Cordouan Lighthouse was completed in 1611, from the shore on a small islet, but was built on a previous lighthouse that can be traced back to the 880s and is the oldest surviving lighthouse in
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
. It is connected to the mainland by a causeway. The oldest surviving oceanic offshore lighthouse is Bell Rock Lighthouse in the
North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...
, off the coast of
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
.


Maintenance


Asia and Oceania

In
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, lighthouses are conducted by the
Australian Maritime Safety Authority Australian Maritime Safety Authority (AMSA) is an Australian statutory authority responsible for the regulation and safety oversight of Australia's shipping fleet and management of Australia's International Maritime Organization, international ...
. In
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
, lighthouses are maintained by the Directorate General of Lighthouses and Lightships, an office of the
Ministry of Ports, Shipping and Waterways The Ministry of Ports, Shipping and Waterways is the Indian ministry responsible for formulation and administration of the rules, regulations and laws relating to ports, shipping and waterways. The minister is Sarbananda Sonowal. History In ...
.


Europe

The former Soviet government built a number of automated lighthouses powered by
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...
s in remote locations in northern Russia. They operated for long periods without external support with great reliability. However, numerous installations deteriorated, were stolen, or vandalized. Some cannot be found due to poor record-keeping. The
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
and the
Republic of Ireland Ireland ( ), also known as the Republic of Ireland (), is a country in Northwestern Europe, north-western Europe consisting of 26 of the 32 Counties of Ireland, counties of the island of Ireland, with a population of about 5.4 million. ...
together have three bodies: lighthouses around the coasts of England and Wales are looked after by
Trinity House The Corporation of Trinity House of Deptford Strond, also known as Trinity House (and formally as The Master, Wardens and Assistants of the Guild Fraternity or Brotherhood of the most glorious and undivided Trinity and of St Clement in the ...
, those around Scotland and the Isle of Man by the
Northern Lighthouse Board The Northern Lighthouse Board (NLB) is the general lighthouse authority for Scotland and the Isle of Man. It is a non-departmental public body responsible for ocean, marine navigation aids around coastal areas. History The NLB was formed by ...
and those around Ireland by the Commissioners of Irish Lights.


North America

In Canada, lighthouses are managed by the Canadian Coast Guard. In the United States, lighthouses are maintained by the
United States Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...
, into which the United States Lighthouse Service was merged in 1939.


Preservation

As lighthouses became less essential to navigation, many of their historic structures faced demolition or neglect. In the United States, the National Historic Lighthouse Preservation Act of 2000 provides for the transfer of lighthouse structures to local governments and private non-profit groups, while the USCG continues to maintain the lamps and lenses. In Canada, the Nova Scotia Lighthouse Preservation Society won heritage status for Sambro Island Lighthouse, and sponsored the Heritage Lighthouse Protection Act to change Canadian federal laws to protect lighthouses. Many groups formed to restore and save lighthouses around the world, including the World Lighthouse Society and the United States Lighthouse Society, as well as the Amateur Radio Lighthouse Society, which sends amateur radio operators to publicize the preservation of remote lighthouses throughout the world.


See also

* Aviation obstruction lighting * Crib lighthouse * Day beacon *
Foghorn A foghorn or fog signal is a device that uses sound to warn vehicles of navigational hazards such as rocky coastlines, or boats of the presence of other vessels, in foggy conditions. The term is most often used in relation to marine transport. ...
* Fresnel lens sizes (orders) * Lens lantern * Lighthouse keeper * Lists of lighthouses *
Lists of lightvessels This article lists lightvessels around the world. Most surviving light vessels reside in the United Kingdom and the United States. Some of the lightvessels mentioned in the lists have been renamed more than once, while others have been re-stationed ...
* Pharology * Pintsch gas * Sea mark


References

;Notes ;Bibliography * Bathurst, Bella. ''The lighthouse Stevensons''. New York: Perennial, 2000. * Beaver, Patrick. ''A History of Lighthouses''. London: Peter Davies Ltd, 1971. . * Crompton, Samuel, W; Rhein, Michael, J. ''The Ultimate Book of Lighthouses''. San Diego, CA: Thunder Bay Press, 2002. . * Jones, Ray; Roberts, Bruce. ''American Lighthouses''. Globe Pequot, 1998. 1st ed. . * Stevenson, D. Alan. ''The world's lighthouses before 1820''. London:
Oxford University Press Oxford University Press (OUP) is the publishing house of the University of Oxford. It is the largest university press in the world. Its first book was printed in Oxford in 1478, with the Press officially granted the legal right to print books ...
, 1959.


Further reading

* Noble, Dennis. ''Lighthouses & Keepers: U. S. Lighthouse Service and Its Legacy''. Annapolis: U.S. Naval Institute Press, 1997. . * Putnam, George R. ''Lighthouses and Lightships of the United States''. Boston: Houghton Mifflin Co., 1933. * Rawlings, William. 2021. ''Lighthouses of the Georgia Coast.'' Macon, GA: Mercer University Press. * Weiss, George. ''The Lighthouse Service, Its History, Activities and Organization''. Baltimore: Johns Hopkins Press, 1926.


External links


United States Lighthouses"Lighthouses Of Strange Designs, December 1930, Popular Science
* Research tool with details of over 14,700 lighthouses and navigation lights around the world with photos and links. *Pharology Website
Pharology: The Study of Lighthouses
. Reference source for the history and development of lighthouses of the world. * Includes 54 diagrams and photographs. {{Authority control Heraldic charges Articles containing video clips Ancient Greek technology Egyptian inventions Greek inventions Maritime safety