World Library  
Flag as Inappropriate
Email this Article

Signal lamp

Article Id: WHEBN0002121650
Reproduction Date:

Title: Signal lamp  
Author: World Heritage Encyclopedia
Language: English
Subject: Morse code, Shutter (photography), Signalman (rank), Optical chopper, Baltimore-Washington telegraph line
Publisher: World Heritage Encyclopedia

Signal lamp

Signal lamp training during World War II.

A signal lamp (sometimes called an Aldis lamp, named after Arthur Cyril Webb Aldis who invented a widely used design) is a visual signaling device for optical communication (typically using Morse code). Modern signal lamps are a focused lamp which can produce a 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 naval vessels and in airport control towers (using color signals for stop or clearance).

Naval usage

US Navy sailor sending Morse code using a signal lamp.

Aldis lamps were pioneered by the British Royal Navy in the late 19th century, and continue to be used through the present day on naval vessels. They provide handy, secure communications during periods of radio silence as well as other times and were particularly useful for convoys operating during the Battle of the Atlantic. There were several types. Some signal lamps were mounted on the mastheads of ships, some small hand-held versions were also used ('The Aldis lamp') and other more powerful ones were mounted on pedestals. These larger ones used a carbon arc lamp as their light source with a diameter of 20 inches (50 cm). These could be used to signal to the horizon, even in conditions of bright sunlight. Although it was originally thought that it was only possible to communicate by line-of-sight, in practice it was possible to illuminate cloud bases both during the night and day which allowed for communication beyond the horizon. A maximum transmission rate possible by using flashing lights is no more than 14 wpm. They have a secondary function as simple spotlights.

Early history

Begbie signalling oil lamp, 1918

The idea of flashing dots and dashes from a lantern was first put into practice by Captain, later Vice Admiral, Philip Colomb, of the British Royal Navy, 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.

Another signalling lamp was the Begbie lamp, a kerosene lamp with a lens to focus the light over a long distance.[1]

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.

During the trench warfare of World War I when wire communications were often cut, German signals used three types of optical Morse transmitters called Blinkgerät, the intermediate type for distances of up to 4 km (2.5 miles) at daylight and of up to 8 km (5 miles) at night, using red filters for undetected communications.

Modern use

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.

Air traffic control usage

In 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 landing lights.[2]

See also


  1. ^ Neal McEwen, K5RW. "Victorian Era Visual Signalling Instruments -Black Watch, 42nd Royal Highland Regiment Signalling Unit, c. 1898". Retrieved 2012-06-13. 
  2. ^ FAA Aeronautical Information Manual, section 4-3-13. Traffic Control Light Signals

External links

  • An Aldis lamp in operation
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.