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{{Short description|Visual signaling device for optical communication}}
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[[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.
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.
== History ==
[[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" />
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
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 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.
▲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.
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 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,
== See also ==
* [[Colt Acetylene Flash Lantern]]
* [[Flag semaphore]]
* [[Heliograph]]
* [[VS-17]]
== References ==
{{Reflist}}
== External links ==
{{Commons category|Signalling lamps}}
* [http://www.airwaysmuseum.com/Aldis%20lamp%20&%20Very%20pistol.htm An Aldis lamp in operation]
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[[Category:Optical communications]]
[[Category:Semaphore]]
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