Signal lamp training during World War II A signal lamp (sometimes called an Aldis lamp or a Morse lamp) is a

semaphore Semaphore (; ) is the use of an apparatus to create a visual signal transmitted over distance. A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms. Semaphores can be used for telegraphy when arr ...

system using a visual signaling device for

optical communication Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date ...

, typically using

Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...

. 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 Limelight (also known as Drummond light or calcium light)James R. Smith (2004). ''San Francisco's Lost Landmarks'', Quill Driver Books. is a type of stage lighting once used in theatres and music halls. An intense illumination is created whe ...

for illumination, and his original code was not the same as

. During

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...

, German signalers used optical Morse transmitters called ', 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 the case of a radio failure or aircraft not equipped with a radio, or in the case of a deaf pilot, air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the gro ...

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

towers, as a backup device in case of a complete failure of an aircraft's radio.

History

upBegbie signalling oil lamp, 1918 Signal lamps were pioneered by the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against Fr ...

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 The Battle of Trafalgar (21 October 1805) was a naval engagement between the British Royal Navy and the combined fleets of the French and Spanish Navies during the War of the Third Coalition (August–December 1805) of the Napoleonic Wars (1 ...

. 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

for illumination. His original code was not identical to

, but the latter was subsequently adopted. Another signalling lamp was the Begbie lamp, a

kerosene lamp A kerosene lamp (also known as a paraffin lamp in some countries) is a type of lighting device that uses kerosene as a fuel. Kerosene lamps have a wick or mantle as light source, protected by a glass chimney or globe; lamps may be used on a ta ...

with a lens to focus the light over a long distance. During the

trench warfare Trench warfare is a type of land warfare using occupied lines largely comprising Trench#Military engineering, military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artille ...

when wire communications were often cut, German signals used three types of optical Morse transmitters, called ', 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. In 1944 Arthur Cyril Webb Aldis patented a small hand-held design, which featured an improved shutter.

Design

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 A sight is an aiming device used to assist in visually aligning ranged weapons, surveying instruments or optical illumination equipments with the intended target. Sights can be a simple set or system of physical markers that have to be aligne ...

, and were most commonly used on naval vessels and in

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

. On the recipient ship, a signalman would observe the blinking light, often with

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

, and translate the code into text. The maximum transmission rate possible via such flashing light apparatus is no more than 14

words per minute Words per minute, commonly abbreviated wpm (sometimes uppercased WPM), is a measure of words processed in a minute, often used as a measurement of the speed of typing, reading or Morse code sending and receiving. Alphanumeric entry Since words ...

. Some signal lamps are mounted on the mastheads 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 An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s ...

as their light source, with a diameter of . 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 A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support and can help maintain cohesion within a unit. It may also be used ...

s operating during the

Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...

. The Commonwealth navies and

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two N ...

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 Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

(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. Signal lamps are still used today for

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

. Aircraft can acknowledge signals by rocking their wings or flashing their landing lights.

References

External links

An Aldis lamp in operation
{{Telecommunications History of telecommunications Types of lamp Military communications Morse code Optical communications Semaphore

History

Design

Modern use

See also

References

External links