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Asignal lamp (sometimes called anAldis lamp or aMorse lamp[1]) is a visual signaling device foroptical communication by flashes of a lamp, typically usingMorse code. The idea of flashing dots and dashes from a lantern was first put into practice by CaptainPhilip Howard Colomb, of the Royal Navy, in 1867. Colomb's design usedlimelight for illumination, and his original code was not the same asMorse code. DuringWorld War I, German signalers used optical Morse transmitters calledBlinkgerät, 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 foraviation light signals inair traffic control towers, as a backup device in case of a complete failure of an aircraft's radio.
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Signal lamps were pioneered by theRoyal Navy in the late 19th century. They were the second generation of signalling in the Royal Navy, after theflag signals most famously used to spread Nelson's rallying-cry, "England expects that every man will do his duty", before theBattle of Trafalgar.[2]
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 usedlimelight for illumination.[3] His original code was not identical toMorse code, but the latter was subsequently adopted.[2]
Another signalling lamp was the Begbie lamp, akerosene lamp with a lens to focus the light over a long distance.[4]
During thetrench warfare ofWorld War I when wire communications were often cut, German signals used three types of optical Morse transmitters, calledBlinkgerät, the intermediate type for distances of up to 4 km (2.5 mi) in daylight and of up to 8 km (5 mi) at night, using red filters for undetected communications.[5]
TheLight, Signal, Gun Type, Navy, US orBlinker Tube was a signaling device used by landing parties to contact ships without being seen by the enemy.[6]
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In 1944, British inventorArthur Cyril Webb Aldis[7] patented a small hand-held design,[8] which featured an improved shutter.[9]
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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 ofoptical sight, and were most commonly used onnaval vessels and inair 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 inMorse code. On the recipient ship, a signalman would observe the blinking light, often withbinoculars, and translate the code into text. The maximum transmission rate possible via such flashing light apparatus is no more than 14words per minute.[citation needed]
Some signal lamps are mounted on themastheads of ships while some small hand-held versions are also used. Other more powerful versions are mounted on pedestals. These larger ones use acarbon arc lamp as their light source, with a diameter of 20 inches (510 mm). These can be used to signal to the horizon, even in conditions of bright sunlight.
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 ofradio silence, such as forconvoys operating during theBattle of the Atlantic.
The Commonwealth navies andNATO 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 theinfrared (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.[10]
Signal lamps are still used today foraviation light signals inair 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 inMorse code. Aircraft can acknowledge signals by rocking their wings or flashing theirlanding lights.[11]
