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{{Short description|Visual signaling device for optical communication}}
{{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 km (5 miles) at night, using red filters for undetected communications.
== Navy usage ==▼
[[Image:Seaman send Morse code signals.jpg|thumb|250px|US Navy sailor sending Morse code using a signal lamp.]]▼
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.
[[File:Turkish heliograph at Huj2.jpg|thumb|left|An Ottoman heliograph crew using a A Blinkgerät (left)]]
[[file:Begbie signalling oil lamp (Signalling, 1918).jpg|thumb|upright|Begbie signalling oil lamp, 1918]]
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" />
The Commonwealth Navies and NATO forces use signal lamps when radio communications need to be silent or electronic "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) spectrum making them less likely to be detected. All modern forces have followed suit due to technological advances in digital communications.▼
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 km (2.5 miles) in daylight and of up to 8 km (5 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 [[Air traffic control|air traffic control towers]], signal lamps are still used today, as a backup device in case of a complete failure of an aircraft's radio. Light signals can be red, green 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>[http://www.faa.gov/air_traffic/publications/atpubs/aim/Chap4/aim0403.html FAA Aeronautical Information Manual, section 4-3-13. Traffic Control Light Signals]</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>
▲== See also ==
== 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 ==
▲[[
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
▲
* [[Colt Acetylene Flash Lantern]]
* [[Flag semaphore]]
* [[Heliograph]]
* [[
== References ==
{{
== External links ==
{{
* [http://www.airwaysmuseum.com/Aldis%20lamp%20&%20Very%20pistol.htm An Aldis lamp in operation]
{{Morse code}}
{{Telecommunications}}
[[Category:
[[Category:
[[Category:Military communications]]
[[Category:Morse code]]
[[Category:Optical communications]]
[[Category:Semaphore]]
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