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73-527: Old Hunstanton Lighthouse is a former lighthouse located in Old Hunstanton in the English county of Norfolk , generally called Hunstanton Lighthouse (or, less formally, 'Hunston Lighthouse') during its operational life. It was built at the highest point available on this part of the coast, on top of Hunstanton Cliffs , and served to help guide vessels into the safe water of Lynn Deeps . Although

146-475: A group occulting light (the lamp being eclipsed twice for two seconds apiece, every thirty seconds). In 1897 the tower was repainted red, with a broad white stripe. The present lighthouse ceased operations in 1921, and the lantern storey was removed from the top of the tower the following year. To compensate for its closure, improvements were made to the light of the Inner Dowsing lightvessel . In 1922

219-402: A rescue service , if necessary. Improvements in maritime navigation and safety, such Global Positioning System (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

292-640: A Diesel generator for backup. Many Fresnel lens installations have been replaced by rotating aerobeacons , which require less maintenance.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 (LED) panels. LED lights, which use less energy and are easier to maintain, had come into widespread use by 2020. In

365-399: A cost of over £200. The front light of the pair was candle-lit; the rear had a coal-fired brazier . They were found to be 'of great benefit'. In 1710 it was reported that the lighthouses were 'decayed and want repairing and will admit of great alterations and improvements'. That same year Knight's niece Rebecca and her husband James Everard were granted the right to receive the light dues for

438-607: A distance of seven leagues ', (though this latter claim has been called 'extravagant'). In 1788 Everard sold his patent rights to Samuel Lane, Collector of Customs for the Port of Lynn. Forty years later, Hunstanton was one of just five lighthouses in England still in private hands, and in 1836 legislation was enacted which empowered the Corporation of Trinity House to purchase the leases of these last remaining private concessions;

511-436: A filament source. Experimental installations of laser 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 , was replaced by a conventional light after four years, because

584-457: A form of concrete that will set under water used by the Romans, and developed a technique of securing the granite blocks together using dovetail joints and marble dowels . 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

657-414: A horizontal plane, and horizontally the light is focused into one or a few directions at a time, with the light beam 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 . This concentration of light is accomplished with a rotating lens assembly. In early lighthouses, the light source

730-427: A more powerful hyperradiant Fresnel lens manufactured by the firm of Chance Brothers . 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

803-602: A navigator with a line of position called a range in North America and a transit 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 in the United Kingdom. The closer light

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876-521: 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 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 . Colonel Orlando M. Poe , engineer to General William Tecumseh Sherman in

949-402: 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. Before modern strobe lights , lenses were used to concentrate the light from a continuous source. Vertical light rays of the lamp are redirected into

1022-411: A reservoir mounted above the burner. The lamp was first produced by Matthew Boulton , 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 lamps were powered by a steam-driven magneto . John Richardson Wigham was the first to develop

1095-415: 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. John Smeaton is noteworthy for having designed

1168-477: 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 fuel was vaporized at high pressure and burned to heat the mantle, giving an output of over six times

1241-469: A way through sands and shoals off the Lincolnshire coast. Writing some fifty years after they were installed, Walker described them as follows: 'Each of the reflectors at Hunstanton contains 700 small mirrors of looking-glass, every one of which reflects part of the light of the small lamp placed in its focus'. The light was described in 1781 as 'constant and certain' and 'clearly distinguished at sea at

1314-613: Is a unit of length . It was common in Europe and Latin America , but is no longer an official unit in any nation. Derived from an ancient Celtic unit and adopted by the Romans as the leuga , the league became a common unit of measurement throughout western Europe. Since the Middle Ages, many values have been specified in several countries, ranging from 2.2 km (1.4 mi) to 7.9 km (4.9 mi). It may have originally represented, roughly,

1387-419: Is one example. Race Rocks Light in western Canada is painted in horizontal black and white bands to stand out against the horizon. 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 H {\displaystyle D=1.22{\sqrt {H}}} , where H

1460-484: 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. There are two types of lighthouses: ones that are located on land, and ones that are offshore. League (unit) A league

1533-510: 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

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1606-484: The pie (Spanish foot ) and on the precision of measurement, but was officially equivalent to 4,180 metres (2.6 miles ) before the legua was abolished by Philip II in 1568. It remains in use in parts of Latin America , where its exact meaning varies. In the early Hispanic settlements of New Mexico , Texas , California , and Colorado , a league was also a unit of area, defined as 25 million square varas or about 4,428.4 acres . This usage of league

1679-622: 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 . Aligning two fixed points on land provides

1752-497: The Northern Lighthouse Board on installing parabolic reflectors in their towers around the coast of Scotland. As described in 1812, the light was provided by eighteen lamps set within 18-inch (460 mm) diameter reflectors 'fixed upon two shelves, one placed over the other'; the lamps were arranged so as to direct the greatest concentration of light in a north by east direction, indicating to far-off vessels

1825-513: 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 in Britain and the St. George Reef Light of California. In shallower bays, Screw-pile lighthouse ironwork structures are screwed into

1898-466: 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 suspended over the flame, creating a bright, steady light. The Argand lamp used whale oil , colza , olive oil or other vegetable oil as fuel, supplied by a gravity feed from

1971-405: 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

2044-495: 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

2117-491: The beam was too narrow to be seen easily. 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 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

2190-406: The choice of light sources, mountings, reflector design, the use of Fresnel lenses , 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

2263-533: 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 panels , with batteries instead of

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2336-488: The construction of lenses of large aperture and short focal length , 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

2409-625: The development of the lighthouse. In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs and promontories , unlike many modern lighthouses. The most famous lighthouse structure from antiquity was the Pharos of Alexandria , Egypt , which collapsed following a series of earthquakes between 956 and 1323. The intact Tower of Hercules at A Coruña , Spain gives insight into ancient lighthouse construction; other evidence about lighthouses exists in depictions on coins and mosaics, of which many represent

2482-473: The distance a person could walk in an hour . The league was used in Ancient Rome , defined as 1½ Roman miles (7,500 Roman feet , modern 2.2 km or 1.4 miles). The origin is the leuga Gallica (also: leu c a Callica ) , the league of Gaul . The Argentine league ( legua ) is 5.572 km (3.462 mi) or 6,666 varas : 1 vara is 0.83 m (33 in). On land,

2555-473: 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 developed the multi-part Fresnel lens for use in lighthouses. His design allowed for

2628-475: The entrance into a harbor, such as New London Harbor Light . 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

2701-527: The establishment of a lighthouse in the vicinity, it appears that sailors used the lights burning in St Edmund's Chapel to guide them into The Wash by night. The pair of lighthouses that later stood on the site were known as the 'Chapel Lights'; and in 1838 their successor was still referred to, by John Purdy , as 'the Chapel Light, on Hunstanton Point'. In 1663 permission was sought by a consortium of

2774-535: The following year, Hunstanton and the other lights were vested in Trinity House. Trinity House promptly began work on replacing the wooden tower and its light, technology having advanced significantly in the sixty years since it was built. Work began in 1838 on a new lighthouse: designed by James Walker and built by William Candler of Lynn, it was first lit on 3 September 1840. It was a white-painted cylindrical brick tower, 63 feet (19 m) high, which placed

2847-455: 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 and grounding system connected to

2920-409: The league (Spanish legua ) is still used in the original sense of the distance that can be covered on foot in an hour, so that a league along a good road on level ground is a greater distance than a league on a difficult path over rough terrain. In Portugal , Brazil and other parts of the former Portuguese Empire , there were several units called league (Portuguese: légua ): The names of

2993-611: The league is most commonly defined as three miles (4.83 km), although the length of a mile could vary from place to place as well as depending on the era. At sea, a league is three  nmi (3.452 mi; 5.556 km). English usage also included many of the other leagues mentioned below (for example, in discussing the Treaty of Tordesillas ). The French lieue  — at different times — existed in several variants, namely 10,000, 12,000, 13,200 and 14,400 French feet , about 3.25 to 4.68 km (2.02 to 2.91 miles). It

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3066-417: The light at an elevation of 109 feet (33 m) above sea level; In place of the multiple lamps and reflectors, a single three-wick oil lamp was installed, set within a sizeable ( second-order ) fixed catadioptric optic , designed by J. Cookson & co. of Newcastle-upon-Tyne . The lighthouse initially displayed a fixed white light as before; but from 1844 a red sector was added to the light, indicating

3139-535: The light is concentrated, if needed, by the "lens" or "optic". Power sources for lighthouses in the 20th–21st centuries vary. Originally lit by open fires and later candles, the Argand hollow wick lamp and parabolic reflector were introduced in the late 18th century. Whale oil was also used with wicks as the source of light. Kerosene became popular in the 1870s and electricity and acetylene gas derived on-site from calcium carbide began replacing kerosene around

3212-509: The lighthouse at Ostia . Coins from Alexandria, Ostia, and Laodicea in Syria also exist. 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

3285-469: 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 (pronounced / f r eɪ ˈ n ɛ l / ) 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

3358-478: The lighthouse was sold at auction for £1,300; the tower was left unused, but the adjacent cottages were converted into tearooms. Between 1934 and 1957 the tower was used as an observation post by the Royal Observer Corps (it was at this time that an additional storey was added to the top of the tower where the lantern had formerly stood). Acquired subsequently by Hunstanton Urban District Council ,

3431-470: The luminosity of traditional oil lights. The use of gas as illuminant became widely available with the invention of the Dalén light by Swedish engineer Gustaf Dalén . He used Agamassan (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

3504-535: The merchants and ship-owners of Boston and Lynn to erect one or more lights near St Edmund's Point, to help guide their vessels into The Wash . That November, a warrant was issued by Charles II to John Knight, permitting him to build a light or lights 'upon the Hunston-cliffe or chappel lands', and to maintain them by levying dues on passing ships. The first lights, a pair of stone towers which functioned as leading lights , were built by him in 1665, at

3577-421: 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

3650-418: 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 for nearly fifty years during which time he designed and oversaw the construction and later improvement of numerous lighthouses. He innovated in

3723-402: 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. Before the development of clearly defined ports , 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

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3796-406: The period of the next fifty years. Substantial repairs were undertaken. By 1750 the front lighthouse, the smaller of the two, seems to have been taken out of commission. It seems that the structure remained standing for a time: but while two lighthouses are shown on John Cary 's county map of 1787, there is only one on his map of 1794. In around 1776 the rear lighthouse was destroyed by a fire. It

3869-478: The position of the Roaring Middle shoal . The light had a range of 16 nautical miles (30 km; 18 mi). The new lighthouse was flanked by a pair of two-storey gabled houses for the keepers , which were connected by castellated wings to the lighthouse itself. The cost of building the tower and the dwellings together came to £2,696 13 s 3 d . In 1883 Hunstanton Lighthouse was altered to display

3942-464: The present lighthouse was built in 1840, there had been a lighthouse on the site since the 17th century (prior to which a light to aid navigation may have been displayed from St Edmund's Chapel , the ruins of which stand nearby). Prior to the establishment of the Lynn Well light vessel in 1828, Hunstanton Lighthouse provided the only visible guide to ships seeking to enter The Wash at night. Before

4015-440: The property was sold by them in 1965, to become a private residence and later a holiday let . The two keepers' houses remained in place until at least the early 1960s, since when one has been demolished, and a modern annexe has been added to the other. Lighthouse Lighthouses mark dangerous coastlines, hazardous shoals , reefs , rocks, and safe entries to harbors; they also assist in aerial navigation . Once widely used,

4088-465: 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 were a major shipwreck hazard for mariners sailing through the English Channel . The first lighthouse built there was an octagonal wooden structure, anchored by 12 iron stanchions secured in the rock, and

4161-451: 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

4234-516: The several léguas referred to the number of units that made the length corresponding to an angle degree of a meridian arc . For compatibility after Portugal adopted the metric system, the metric légua of 5.0 km was used. In Brazil, the léguas is still used occasionally, where it has been described as about 6.6 km. The legua or Spanish league was originally understood as equivalent to 3 millas (Spanish miles ). This varied depending on local standards for

4307-554: The siege of Atlanta, designed and built some of the most exotic lighthouses in the most difficult locations on the U.S. Great Lakes . French merchant navy officer Marius Michel Pasha built almost a hundred lighthouses along the coasts of the Ottoman Empire in a period of twenty years after the Crimean War (1853–1856). In a lighthouse, the source of light is called the "lamp" (whether electric or fuelled by oil) and

4380-528: The surface during periods of fog or low clouds, as at Point Reyes Lighthouse . Another example is in San Diego , California : 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

4453-599: The third and most famous Eddystone Lighthouse , but some builders are well known for their work in building multiple lighthouses. The Stevenson family ( Robert , Alan , David , Thomas , David Alan , and Charles ) made lighthouse building a three-generation profession in Scotland. Richard Henry Brunton designed and built 26 Japanese lighthouses in Meiji Era Japan, which became known as Brunton's "children". Blind Irishman Alexander Mitchell invented and built

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4526-486: 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 € 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

4599-480: The turn of the 20th century. Carbide was promoted by the Dalén light , 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 (then Soviet Union ) were powered by radioisotope thermoelectric generators (RTGs). These had the advantage of providing power day or night and did not need refuelling or maintenance. However, after

4672-535: 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 . The black and white barber pole spiral pattern of Cape Hatteras Lighthouse

4745-643: 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 , Newfoundland, and Makapuu Point , Hawaii, used

4818-437: 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

4891-459: Was built by Henry Winstanley 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 John Smeaton rebuilt the lighthouse from 1756 to 1759; 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 , using granite blocks. He rediscovered and used " hydraulic lime ",

4964-683: Was built on piles that were screwed into the sandy or muddy seabed. Construction of his design began in 1838 at the mouth of the Thames 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). Until 1782 the source of illumination had generally been wood pyres or burning coal. The Argand lamp , invented in 1782 by

5037-518: Was equipped with parabolic reflectors and oil lamps in place of a coal fire. Thus Hunstanton is said to have been the first 'major coast light' in Britain to employ an illuminant other than coal, and the first lighthouse in the world to be fitted with a parabolic reflector (though similar claims are made for Hutchinson 's lighthouses in Liverpool ). The lighting apparatus was devised and installed by Ezekiel Walker of Lynn, who later went on to advise

5110-494: Was replaced by a new wooden structure, commissioned by Edward Everard of Lynn (grandson of the above-mentioned Rebecca and John), who had inherited the patent rights: a circular tower 33 feet (10 m) high, tapering from 11 ft (3.4 m) to 8 ft (2.4 m) in diameter from bottom to top. It placed the light at 85 feet (26 m) above sea level. Atop the tower was a simple square lantern room, glazed to seaward, which contained an innovative lighting array. The lantern

5183-506: Was the predominant light source in lighthouses from the 1900s to the 1960s, when electric lighting had become dominant. 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

5256-506: Was used along with the metric system for a while, but is long discontinued. A metric lieue was used in France from 1812 to 1840, with 1 metric lieue being exactly 4,000 m, or 4 km (about 2.5 mi). It is this unit that is referenced in both the title and the body text of Jules Verne 's novel Twenty Thousand Leagues Under the Seas (1870). In some rural parts of Mexico,

5329-598: Was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary ; its light could be seen from more than 20 miles (32 km) out. Fresnel's invention increased the luminosity of the lighthouse lamp by a factor of four and his system is still in common use. 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

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