Beacon

For other uses, seeBeacon (disambiguation).

Abeaconis an intentionally conspicuous device designed to attract attention to aspecific location.A common example is thelighthouse,which draws attention to a fixed point that can be used to navigate around obstacles or into port. More modern examples include a variety ofradio beaconsthat can be read onradio direction findersin all weather, andradar transpondersthat appear onradardisplays.

Beacons can also be combined with semaphoric or other indicators to provide importantinformation,such as the status of an airport, by the colour and rotational pattern of itsairport beacon,or of pending weather as indicated on aweather beaconmounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form ofoptical telegraphy.

For navigation

A navigational beacon denoting the presence of Orontes Bank offPort Vincent, South Australia.

Beacons help guidenavigatorsto their destinations. Types of navigational beacons includeradarreflectors,radio beacons,sonic and visual signals. Visual beacons range from small, single-pile structures to largelighthousesor light stations and can be located on land or on water. Lighted beacons are calledlights;unlighted beacons are calleddaybeacons.Aerodrome beaconsare used to indicate locations of airports and helipads.

Handheld beacons are also employed inaircraft 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)

16th-century beacon hut inCulmstock,Devon, England

Historically, beacons were fires lit at well-known locations on hills or high places, used either aslighthousesfornavigation at sea,or for signalling over land that enemy troops were approaching, in order to alert defenses. As signals, beacons are an ancient form ofoptical telegraphand were part of arelay league.

Systems of this kind have existed for centuries over much of the world. The ancient Greeks called themphryctoriae,while beacons figure on several occasions on thecolumn of Trajan.

In imperial China, sentinels on and near theGreat Wall of Chinaused a sophisticated system of daytime smoke and nighttime flame to send signals along long chains of beacon towers.

Legend has it thatKing You of Zhouplayed a trick multiple times in order to amuse his often melancholy concubine, ordering beacon towers lit to fool his vassals and soldiers. But when enemies, led by theMarquess of Shenreally arrived at the wall, although the towers were lit, no defenders came, leading to King Yōu's death and the collapse of the Western Zhou dynasty.China's system of beacon towers was not extant prior to theHan dynasty.

Thucydideswrote that during thePeloponnesian War,thePeloponnesianswho were inCorcyrawere informed by night-time beacon signals of the approach of sixty Athenian vessels fromLefkada.

In the 10th century, during theArab–Byzantine wars,theByzantine Empireused abeacon systemto transmit messages from the border with theAbbasid Caliphate,acrossAnatoliato theimperial palacein the Byzantine capital,Constantinople.It was devised byLeo the Mathematicianfor EmperorTheophilos,but either abolished or radically curtailed by Theophilos' son and successor,Michael III.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 EmperorManuel I Komnenos.

In Scandinavia manyhill fortswere part of beacon networks to warn against invading pillagers. In Finland, these beacons were calledvainovalkeat,"persecution fires", orvartiotulet,"guard fires", and were used to warn Finn settlements of imminent raids by the Vikings.

InWales,theBrecon Beaconswere named for beacons used to warn of approaching English raiders. In England, the most famous examples are the beacons used inElizabethan Englandto warn of the approachingSpanish Armada.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 theLord High Admiral.The money due for the maintenance of beacons was calledBeaconagiumand was levied by the sheriff of each county.In theScottish borderscountry, a system of beacon fires was at one time established to warn of incursions by the English.Humeand Eggerstone castles and Soltra Edge were part of this network.

In Spain, the border ofGranadain the territory of theCrown of Castilehad 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

A CORE Survival HEL-STAR 6 IR strobe mounted atop this marine's helmet

Infraredstrobes and other infrared beacons have increasingly been used in modern combat when operating at night as they can only be seen throughnight vision goggles.As a result, they are often used to mark friendly positions as a form ofIFFto prevent friendly fire and improve coordination. Soldiers will typically affix them to theirhelmetsor 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, andchemlights.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

Main article:Emergency vehicle lighting

Beacon positions on police car

Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians.Emergency vehiclessuch 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 withhalogen bulbssimilar to those used in vehicleheadlamps,xenonflashtubes,orLEDs.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 andbonfiresare also used to mark occasions and celebrate events.

Beacons have also allegedly been abused byshipwreckers.An illicit fire at a wrong position would be used to direct a ship againstshoalsorbeaches,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, abeaconis a type offramewhich 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 byindoor navigation and positioningapplications.

Beaconingis 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

InAeschylus' tragedyAgamemnon,a chain of eight beacons staffed by so-calledlampadóphoroiinformClytemnestrainArgos,within a single night's time, thatTroyhas just fallen under her husband king Agamemnon's control, after a famousten years siege.

InJ. R. R. Tolkien'shigh fantasynovel,The Lord of the Rings,aseries of beaconsalerts the entire realm ofGondorwhen the kingdom is under attack. These beacon posts were staffed by messengers who would carry word of their lighting to eitherRohanorBelfalas.InPeter Jackson'sfilm 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 publishing

The Beaconwas an influential Caribbean magazine published in Trinidad in the 1930s.New Beacon Bookswas the first Caribbean publishing house in England, founded in London in 1966, was named after theBeaconjournal.

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 inroboticsand inCombat 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.

See also

• Aerodrome beacon
• Beacon mode service
• Beacon School
• Belisha beacon
• Emergency locator beacon
• Emergency position-indicating radiobeacon station(ELTs, PLBs & EPIRBs)
• iBeacon
• Lantern
• Leading lights
• Lighthouse of Alexandria
• Milestone/Kilometric point
• Polaris
• Strobe beacon
• Time ball
• Trail blazing
• Warning light (disambiguation)
• Weather beacon
• Web beacon