A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the

lighthouse A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways. Lighthouses mar ...

, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More modern examples include a variety of

radio beacon In navigation, a radio beacon or radiobeacon is a kind of beacon, a device that marks a fixed location and allows direction-finding equipment to find relative bearing. But instead of employing visible light, radio beacons transmit electromagnet ...

s that can be read on

radio direction finder Direction finding (DF), or radio direction finding (RDF), isin accordance with International Telecommunication Union (ITU)defined as radio location that uses the reception of radio waves to determine the direction in which a radio station ...

s in all weather, and radar transponders that appear on radar displays. Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its

airport beacon An aerodrome beacon or rotating beacon or aeronautical beacon is a beacon installed at an airport or aerodrome to indicate its location to aircraft pilots at night. An aerodrome beacon is mounted on top of a towering structure, often a contro ...

, or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form of optical telegraphy.

For navigation

Beacons help guide navigators to their destinations. Types of navigational beacons include radar reflectors, radio beacons, sonic and visual signals. Visual beacons range from small, single-pile structures to large

s or light stations and can be located on land or on water. Lighted beacons are called ''lights''; unlighted beacons are called ''

daybeacon A day beacon (sometimes "daybeacon") is an unlighted nautical sea mark. A signboard identifying it is called a day mark. Day beacons typically mark channels whose key points are marked by lighted buoys. They may also mark smaller navigable rout ...

s''.

Aerodrome beacon An aerodrome beacon or rotating beacon or aeronautical beacon is a beacon installed at an airport or aerodrome to indicate its location to aircraft pilots at night. An aerodrome beacon is mounted on top of a towering structure, often a control ...

s are used to indicate locations of airports and helipads. Handheld beacons are also employed in aircraft marshalling, and are used by the marshal to deliver instructions to the crew of aircraft as they move around an active airport, heliport or aircraft carrier.

For defensive communications (historical)

Historically, beacons were fires lit at well-known locations on hills or high places, used either as

s for navigation at sea, or for signalling over land that enemy troops were approaching, in order to alert defenses. As signals, beacons are an ancient form of

optical telegraph An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals. There are two main types of such systems; the semaphore telegraph which uses pivoted indicator arms and ...

and were part of a relay league. Systems of this kind have existed for centuries over much of the world. The ancient Greeks called them '' phryctoriae'', while beacons figure on several occasions on the column of Trajan. In ancient China, sentinels on and near the Great Wall of China used a sophisticated system of daytime smoke and nighttime flame to send signals along long chains of beacon towers. Legend has it that Zhōu Yōu Wáng, king of the Western Zhou dynasty, played a trick multiple times in order to amuse his often melancholy concubine, ordering beacon towers lit to fool his Marquess and soldiers. But when enemies, led by Marquess of Shen really arrived at the wall, although the towers were lit, no defenders came, leading to Yōu's death and the collapse of the Western Zhou dynasty. Thucydides wrote that during the

Peloponnesian War The Peloponnesian War (431–404 BC) was an ancient Greek war fought between Athens and Sparta and their respective allies for the hegemony of the Greek world. The war remained undecided for a long time until the decisive intervention of th ...

, the Peloponnesians who were in Corcyra were informed by night-time beacon signals of the approach of sixty Athenian vessels from Lefkada. In the 10th century, during the

Arab–Byzantine wars The Arab–Byzantine wars were a series of wars between a number of Muslim Arab dynasties and the Byzantine Empire between the 7th and 11th centuries AD. Conflict started during the initial Muslim conquests, under the expansionist Rashidun an ...

, the Byzantine Empire used a beacon system to transmit messages from the border with the Abbasid Caliphate, across Anatolia to the imperial palace in the Byzantine capital, Constantinople. It was devised by Leo the Mathematician for Emperor Theophilos, but either abolished or radically curtailed by Theophilos' son and successor,

Michael III Michael III ( grc-gre, Μιχαήλ; 9 January 840 – 24 September 867), also known as Michael the Drunkard, was Byzantine Emperor from 842 to 867. Michael III was the third and traditionally last member of the Amorian (or Phrygian) dynasty. ...

. Beacons were later used in Greece as well, while the surviving parts of the beacon system in Anatolia seem to have been reactivated in the 12th century by Emperor

Manuel I Komnenos Manuel I Komnenos ( el, Μανουήλ Κομνηνός, translit=Manouíl Komnenos, translit-std=ISO; 28 November 1118 – 24 September 1180), Romanization of Greek, Latinized Comnenus, also called Porphyrogennetos (; "born in the purple"), w ...

. In Scandinavia many hill forts were part of beacon networks to warn against invading pillagers. In Finland, these beacons were called ''vainovalkeat'', "persecution fires", or ''vartiotulet'', "guard fires", and were used to warn Finn settlements of imminent raids by the Vikings. In Wales, the

Brecon Beacons The Brecon Beacons ( cy, Bannau Brycheiniog, ) are a mountain range in South Wales. In a narrow sense, the name refers to the range of Old Red Sandstone peaks which lie to the south of Brecon. Sometimes referred to as "the central Beacons" t ...

were named for beacons used to warn of approaching English raiders. In England, the most famous examples are the beacons used in Elizabethan England to warn of the approaching

Spanish Armada The Spanish Armada (a.k.a. the Enterprise of England, es, Grande y Felicísima Armada, links=no, lit=Great and Most Fortunate Navy) was a Spanish fleet that sailed from Lisbon in late May 1588, commanded by the Duke of Medina Sidonia, an aris ...

. Many hills in England were named Beacon Hill after such beacons. In England the authority to erect beacons originally lay with the King and later was delegated to the Lord High Admiral. The money due for the maintenance of beacons was called ''Beaconagium'' and was levied by the sheriff of each county. In the

Scottish border The Anglo-Scottish border () is a border separating Scotland and England which runs for between Marshall Meadows Bay on the east coast and the Solway Firth in the west. The surrounding area is sometimes referred to as "the Borderlands". The ...

s country, a system of beacon fires was at one time established to warn of incursions by the English.

Hume Hume most commonly refers to: * David Hume (1711–1776), Scottish philosopher Hume may also refer to: People * Hume (surname) * Hume (given name) * James Hume Nisbet (1849–1923), Scottish-born novelist and artist In fiction * Hume, the ...

and Eggerstone castles and Soltra Edge were part of this network. In Spain, the border of

Granada Granada (,, DIN 31635, DIN: ; grc, Ἐλιβύργη, Elibýrgē; la, Illiberis or . ) is the capital city of the province of Granada, in the autonomous communities of Spain, autonomous community of Andalusia, Spain. Granada is located at the fo ...

in the territory of the

Crown of Castile The Crown of Castile was a medieval polity in the Iberian Peninsula that formed in 1230 as a result of the third and definitive union of the crowns and, some decades later, the parliaments of the kingdoms of Castile and León upon the accessi ...

had a complex beacon network to warn against Moorish raiders and military campaigns. Due to the progressive advance of the borders throughout the process of the Reconquista, the entire Spanish geography is full of defensive lines of castles, towers and fortifications, visually connected to each other, which served as fortified beacons. Some examples are the Route of the Vinalopó castles or the distribution of the castles in Jaén.

Military use (20th-21st century)

Infrared marker

Infrared strobes and other infrared beacons have increasingly been used in modern combat when operating at night as they can only be seen through night vision goggles. As a result, they are often used to mark friendly positions as a form of

IFF In logic and related fields such as mathematics and philosophy, "if and only if" (shortened as "iff") is a biconditional logical connective between statements, where either both statements are true or both are false. The connective is bicondi ...

to prevent friendly fire and improve coordination. Soldiers will typically affix them to their helmets or other gear so they are easily visible to others using night vision including other infantry, ground vehicles, and aerial platforms (drones, helicopters, planes, etc). Passive markers include IR patches, which reflect infrared light, and

chemlight A glow stick, also known as a light stick, chem light, light wand, light rod, and rave light, is a self-contained, short-term light-source. It consists of a translucent plastic tube containing isolated substances that, when combined, make light ...

s. The earliest such beacons were often IR chemlights taped to helmets. As time went on, more sophisticated options began to emerge with electronically powered infrared strobes with specific mounting solutions for attaching to helmets or load bearing equipment. These strobes may have settings which allow constant on or strobes of IR light, hence the name. Advancements in near-peer technology, however, present risk since if friendly units can see the strobe with night vision so could enemies with night vision capabilities. As a result, some in the American military have stressed that efforts should be made to improve training regarding light discipline (IR and visible) and other means of reducing a unit's visible signature.

On vehicles

Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians. Emergency vehicles such as fire engines, ambulances, police cars, tow trucks, construction vehicles, and snow-removal vehicles carry beacon lights. The color of the lamps varies by jurisdiction; typical colors are blue and/or red for police, fire, and medical-emergency vehicles; amber for hazards (slow-moving vehicles, wide loads, tow trucks, security personnel, construction vehicles, etc.); green for volunteer firefighters or for medical personnel, and violet for funerary vehicles. Beacons may be constructed with

halogen bulbs A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small ...

similar to those used in vehicle headlamps, xenon flashtubes, or LEDs. Incandescent and xenon light sources require the vehicle's engine to continue running to ensure that the battery is not depleted when the lights are used for a prolonged period. The low power consumption of LEDs allows the vehicle's engine to remain turned off while the lights operate.

Other uses

Beacons and

bonfire A bonfire is a large and controlled outdoor fire, used either for informal disposal of burnable waste material or as part of a celebration. Etymology The earliest recorded uses of the word date back to the late 15th century, with the Catho ...

s are also used to mark occasions and celebrate events. Beacons have also allegedly been abused by shipwreckers. An illicit fire at a wrong position would be used to direct a ship against

shoal In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material and rises from the bed of a body of water to near the surface. It ...

s or beaches, so that its cargo could be looted after the ship sank or ran aground. There are, however, no historically substantiated occurrences of such intentional shipwrecking. In wireless networks, a beacon is a type of frame which is sent by the access point (or WiFi router) to indicate that it is on. Bluetooth based beacons periodically send out a data packet and this could be used by software to identify the beacon location. This is typically used by indoor navigation and positioning applications. ''Beaconing'' is the process that allows a network to self-repair network problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.

In fiction

In Aeschylus' tragedy '' Agamemnon'', a chain of eight beacons staffed by so-called ''lampadóphoroi'' inform Clytemnestra in Argos, within a single night's time, that Troy has just fallen under her husband king Agamemnon's control, after a famous ten years siege. In J. R. R. Tolkien's high fantasy novel, '' The Lord of the Rings'', a series of beacons alerts the entire realm of Gondor when the kingdom is under attack. These beacon posts were staffed by messengers who would carry word of their lighting to either Rohan or Belfalas. In

Peter Jackson Sir Peter Robert Jackson (born 31 October 1961) is a New Zealand film director, screenwriter and producer. He is best known as the director, writer and producer of the ''Lord of the Rings'' trilogy (2001–2003) and the ''Hobbit'' trilogy ( ...

's film adaptation of the novel, the beacons serve as a connection between the two realms of Rohan and Gondor, alerting one another directly when they require military aid, as opposed to relying on messengers as in the novel.

In retail

Beacons are sometimes used in retail to send digital coupons or invitations to customers passing by.

Types

Infrared beacon

An infrared beacon (IR beacon) transmits a modulated light beam in the infrared spectrum, which can be identified easily and positively. A line of sight clear of obstacles between the transmitter and the receiver is essential. IR beacons have a number of applications in robotics and in Combat Identification (CID). Infrared beacons are the key infrastructure for the Universal Traffic Management System (UTMS) in Japan. They perform two-way communication with travelling vehicles based on highly directional infrared communication technology and have a vehicle detecting capability to provide more accurate traffic information.

Sonar beacon

A sonar beacon is an underwater device which transmits sonic or ultrasonic signals for the purpose of providing bearing information. The most common type is that of a rugged watertight sonar transmitter attached to a submarine and capable of operating independently of the electrical system of the boat. It can be used in cases of emergencies to guide salvage vessels to the location of a disabled submarine.

References

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