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{{Short description|Visual signaling device for optical communication}}
[[Image:Signal lamp training.jpg|thumb|250px|Signal lamp training during World War II.]]'''Signal lamp''', also called '''Aldis lamp''', is a visual signaling device for [[optical communication]] (typically using [[Morse code]]) – essentially a focused lamp which can produce a pulse of light. It is named after its inventor [[ACW Aldis]]. This pulse is achieved by opening and closing ''shutters'' mounted in front of the lamp, either via a manually-operated pressure switch or, in later versions, automatically. The lamps were usually equipped with some form of [[optical sight]], and were most commonly used on [[warship|naval vessels]] and in [[airport]] [[Air traffic control|control tower]]s (using color signals for stop or clearance).
{{citations|date=November 2020}}
[[file:Signal lamp training.jpg|thumb|Signal lamp training during World War II]]
 
A '''signal lamp''' (sometimes called an '''Aldis lamp''' or a '''Morse lamp'''<ref>{{cite book|author=Walter Lord|author-link=Walter Lord|title=[[The Night Lives On]]}}</ref>) is a visual signaling device for [[optical communication]] by flashes of a lamp, typically using [[Morse code]]. The idea of flashing dots and dashes from a lantern was first put into practice by Captain [[Philip Howard Colomb]], of the Royal Navy, in 1867. Colomb's design used [[limelight]] for illumination, and his original code was not the same as [[Morse code]]. During [[World War I]], German signalers used optical Morse transmitters called ''{{lang|de|Blinkgerät}}'', with a range of up to 8&nbsp;km (5&nbsp;miles) at night, using red filters for undetected communications.
Aldis lamps were pioneered by the British [[Royal Navy]] in the late [[19th Century]], and were used until the end of the [[20th Century]] on naval vessels. They provided handy, secure communications during periods of [[radio silence]] as well as other times and were particularly useful for [[convoy]]s operating during the [[Battle of the Atlantic]]. There were several types. Some signal lamps were mounted on the mastheads of ships, some small handheld versions were also used ('The Aldis lamp') and other more powerful ones were mounted on pedestals These larger ones used a
[[Arc_lamp#Carbon_arc_lamp|carbon arc lamp]] as their light source with a diameter of 20 inches (50 cm). These could be used to signal to the horizon in optimum conditions. They had a secondary function as simple [[searchlight|spotlights]].
 
Modern signal lamps produce a focused pulse of light, either by opening and closing shutters mounted in front of the lamp, or by tilting a concave mirror. They continue to be used to the present day on naval vessels and for [[aviation light signals]] in [[air traffic control]] towers, as a backup device in case of a complete failure of an aircraft's radio.
The idea of flashing dots and dashes from a lantern was first put in to practice by Captain, later Vice Admiral, Philip Colomb in 1867. His original code, which the Navy used for seven years, was not identical with Morse, but [[Morse code]] was eventually adopted with the addition of several special signals. Flashing lights were the second generation of signalling in the Royal Navy, after the flag signals most famously used to spread Nelson's rallying-cry before the [[Battle of Trafalgar]].
 
== TriviaHistory ==▼
The Royal Navy phased out the use of Aldis lamps in [[1997]], although by that time they were largely ceremonial. Other modern forces have followed suit as technological advances in digital communications have made the device obsolete.
[[File:Turkish heliograph at Huj2.jpg|thumb|left|An Ottoman heliograph crew using a A Blinkgerät (left)]]
▲== Trivia ==
[[file:Begbie signalling oil lamp (Signalling, 1918).jpg|thumb|upright|Begbie signalling oil lamp, 1918]]
*[[1970]]: ''[[Monty Python's Flying Circus]]'' Season 2 episode # 15 featured a sketch "JULIUS CAESAR ON AN ALDIS LAMP''".
Signal lamps were pioneered by the [[Royal Navy]] in the late 19th century. They were the second generation of signalling in the Royal Navy, after the [[flag signals]] most famously used to spread Nelson's rallying-cry, "''[[England expects that every man will do his duty]]''", before the [[Battle of Trafalgar]].<ref name="Telegraph">{{Cite web|url=http://www.deadmedia.org/notes/24/241.html|title=The Dead media Project:Working Notes:24.1|website=www.deadmedia.org}}</ref>
 
The idea of flashing dots and dashes from a lantern was first put into practice by Captain, later Vice Admiral, [[Philip Howard Colomb]], of the Royal Navy, in 1867. Colomb's design used [[limelight]] for illumination.<ref>{{cite book | editor-first = Christopher H. | editor-last = Sterling | title = Military Communications: From Ancient Times to the 21st Century | year = 2008 | location = Santa Barbara, California | publisher = ABC-CLIO, Inc. | isbn = 978-1-85109-732-6| page = 209 | url = https://books.google.com/books?id=RBC2nY1rp5MC&pg=PA209}}</ref> His original code was not identical to [[Morse code]], but the latter was subsequently adopted.<ref name="Telegraph" />
 
Another signalling lamp was the Begbie lamp, a [[kerosene lamp]] with a lens to focus the light over a long distance.<ref>{{cite web|author=Neal McEwen, K5RW |url=http://www.telegraph-office.com/pages/Black-Watch-Signal-Unit.html |title=Victorian Era Visual Signalling Instruments -Black Watch, 42nd Royal Highland Regiment Signalling Unit, c. 1898 |publisher=Telegraph-office.com |access-date=2012-06-13}}</ref>
 
During the [[trench warfare]] of [[World War I]] when wire communications were often cut, German signals used three types of optical Morse transmitters, called ''{{lang|de|Blinkgerät}}'', the intermediate type for distances of up to 4&nbsp;km (2.5&nbsp;miles) in daylight and of up to 8&nbsp;km (5&nbsp;miles) at night, using red filters for undetected communications.<ref>{{Cite web|url=https://www.sto.nato.int/publications/STO%20Educational%20Notes/STO-EN-MSG-141/EN-MSG-141-01.pdf|title=Battle Management Language|last=Galvin|date=May 29, 2002|access-date=April 7, 2019}}</ref>
 
In 1944, British inventor [[Arthur Cyril Webb Aldis]]<ref>[https://www.commsmuseum.co.uk/Visual%20Signalling/vissig.htm "VISUAL SIGNALLING", Royal Navy Communications Branch Museum/Library website] </ref> patented a small hand-held design,<ref>{{ cite web | title = Visual Signalling | url = http://www.rnmuseumradarandcommunications2006.org.uk/CommsColRight/Visual%20Signalling/vissig.htm | work = HMS Collingwood Heritage Collection }}</ref> which featured an improved shutter.<ref>{{Cite web|url=https://www.freepatentsonline.com/2363566.html|title=Signaling lamp}}</ref>
 
== Design ==
{{unreferenced section|date=March 2016}}
Modern signal lamps can produce a focused pulse of light. In large versions, this pulse is achieved by opening and closing shutters mounted in front of the lamp, either via a manually operated pressure switch, or, in later versions, automatically. With hand-held lamps, a concave mirror is tilted by a trigger to focus the light into pulses. The lamps were usually equipped with some form of [[optical sight]], and were most commonly used on [[warship|naval vessels]] and in [[air traffic control]] towers, using colour signals for stop or clearance. In manual signalling, a signalman would aim the light at the recipient ship and turn a lever, opening and closing the shutter over the lamp, to emit flashes of light to spell out text messages in [[Morse code]]. On the recipient ship, a signalman would observe the blinking light, often with [[binoculars]], and translate the code into text. The maximum transmission rate possible via such flashing light apparatus is no more than 14 [[words per minute]].{{citation needed|date=November 2020}}
 
Some signal lamps are mounted on the [[mast (sailing)|masthead]]s of ships while some small hand-held versions are also used. Other more powerful versions are mounted on pedestals. These larger ones use a [[carbon arc lamp]] as their light source, with a diameter of {{convert|20|in}}. These can be used to signal to the horizon, even in conditions of bright sunlight.
 
== Modern use ==
[[File:Seaman send Morse code signals.jpg|thumb|upright|A United States Navy sailor sending Morse code using a signal lamp]]
Signal lamps continue to be used to the present day on naval vessels. They provide handy, relatively secure communications, which are especially useful during periods of [[radio silence]], such as for [[convoy]]s operating during the [[Battle of the Atlantic]].
 
The Commonwealth navies and [[NATO]] forces use signal lamps when radio communications need to be silent or electronic "[[spoofing attack|spoofing]]" is likely. Also, given the prevalence of night vision equipment in today's armed forces, signaling at night is usually done with lights that operate in the [[infrared]] (IR) portion of the electromagnetic spectrum, making them less likely to be detected. All modern forces have followed suit due to technological advances in digital communications.<ref>{{ cite web|url=http://www.jproc.ca/rrp/rrp2/visual_lights.html|work = Visual Signalling in the RCN | title = Directional and Non-Directional Light Signalling | author = Jerry Proc | access-date = 2016-08-05 }}</ref>
 
Signal lamps are still used today for [[aviation light signals]] in [[air traffic control]] towers as a backup device in case of a complete failure of an aircraft's radio. Light signals can be green, red, or white, and steady or flashing. Messages are limited to a handful of basic instructions, ''e.g.'', "land", "stop", etc.; they are not intended to be used for transmitting messages in [[Morse code]]. Aircraft can acknowledge signals by rocking their wings or flashing their [[aircraft landing lights|landing lights]].<ref>{{Cite web | url=http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim0403.html#N2Ab4ROBE|archive-url=https://web.archive.org/web/20121104154734/http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim0403.html | url-status=dead | title=FAA Aeronautical Information Manual, section 4-3-13. Traffic Control Light Signals | archive-date=November 4, 2012 }}</ref>
 
== See also ==
* [[Colt Acetylene Flash Lantern]]
* [[Flag semaphore]]
* [[Heliograph]]
* [[VS-17]]
 
==External linksReferences ==
{{Reflist}}
*[http://www.airwaysmuseum.com/Aldis%20lamp%20&%20Very%20pistol.htm An Aldis lamp in operation]▼
 
*[http://home.no.net/fenja256/superaldis Superaldis, an Aldis lamp simulator]
== External links ==
{{Commons category|Signalling lamps}}
▲* [http://www.airwaysmuseum.com/Aldis%20lamp%20&%20Very%20pistol.htm An Aldis lamp in operation]
 
{{Morse code}}
{{Telecommunications}}
 
[[Category:History of telecommunications]]
[[Category:Types of lamp]]
[[Category:Military communications]]
[[Category:EarlyMorse telecommunicationscode]]
[[Category:LampsOptical communications]]
[[Category:Semaphore]]
 
[[de:Signallampe]]
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