The British "Aldis portable daylight signalling lamp", or "Aldis Lamp" has been a staple of aerial and marine visual signalling from 1916 to the present day. Fig. 1, 2 and 3 are respectively side, top and front cross-section views from Aldis's filing for a French patent. The top right is an illustration of the view from the exterior ,and the bottom right figure is a side-cross section from a 1918 Royal Navy signalling manual.
I created this figure as a collage of cleaned-up historical figures from 1918[1], 1920[2] and 1926[3]. The 1926 figure appears to be the reproduction of another 1918 figure[1a].The boxed figure at lower right is from a British Navy signalling manual issued Nov 21, 1918. The 1918 configuration differs from the 1920/1926 configuration in that the grip power switch (5) is on the back of the grip in 1918, and in the front (h) in the 1920 and 1926 references, and the power cord input to the handle is on the base in 1918 and on the side of the base (u) in 1920 and 1926.
Otherwise, the 1918, 1920 and 1926 configurations seem identical to me - while the details of the top sight (2) in 1918 figure seem simpler than that of the top sight (O) in 1920 1926, the text accompanying the 1918 figure ([1] pp 107-110) make it clear that all three top sight features shown in 1920 and 1926 were present in 1918: (1) a "telescopic" sight, (2) an "open" sight, adjacent to the telescope, and (3) A "V" sight above the telescope.
Arthur Cyril Webb Aldis was developing his Aldis portable daylight signalling lamp in early 1915 for signalling between aeroplanes and the ground[4], filed for a British patent on it on April 11, 1916[5], and it was in use by the Royal Flying Corps in the Battle of the Somme in July of 1916[6].
The Aldis portable daylight signalling lamp was used by the British Royal Flying Corps, Royal Navy, US Navy and the French in WWI on planes, on the ground, on tanks, on submarines, and on ships, and saw extensive use during the interwar period and WWII, especially in the air and at sea. Aldis lamps looking remarkably like the 1918 model are on sale for marine use in the current day (April 2025)[7].
Aldis chose to use a rocking mirror to create flashes with crisp onset and offset, rather than the shutters used on many contemporary light-flashing signal devices. Aldis did mention the possibility of flashing by the application/removal of electrical power, which was the method used by his contemporary Oliver Lucas in his Lucas Daylight Signalling lamp introduced at almost exactly the same time (just in time for the Battle of the Somme) for ground use. The Lucas lamp was used extensively thereafter by the British and American armies, as the Aldis lamp reigned for Royal Navy and Royal Air Force use.
Both Aldis and Lucas chose to use a "Mangin mirror"[8], sometimes called a "lens mirror" rather than a parabolic reflector. Aldis described his reasons for doing so (and other subtleties of his design) in his extense 1920 14-page paper: "The Optical Theory of Portable Daylight Signalling Lamps" [9]
I've appended the text description from the 1918 signalling manual after the reference list.
You may view a gallery of photographs of Aldis lamps here:
www.flickr.com/photos/signalmirror/galleries/721577207863...
You may also view an excellent short video about Aldis lamps by Giles Messier on YouTube here:
youtu.be/x1QKGvRxbXY?si=96ffZ8TEajhfmzWw
A modern video demonstration of a 1940 Aldis lamp (still with the rocking Mangin mirror) can be seen on YouTube here:
youtu.be/BGKJiAcjZrw?si=nHlWR5e4KjTAWpBe
Over 100 historical images showing Aldis Lamps (most dating from WW2) may be viewed at the Imperial War Museum Website, here:
www.iwm.org.uk/collections/search?query=aldis&page=0
Nearly 50 historical images showing Aldis Lamps (most dating from WW2) may be viewed at the Australian War Memorial website, here:
www.awm.gov.au/advanced-search?query=%22aldis%20lamp%22&a...
I donate any intellectual property rights I may have earned by my processing (cleanup, combination, rearrangement, annotation, etc.) of the input elements to the public domain under a CC0 license.
I believe the input elements to my work are in the public domain in the USA (and many other locations) as items published prior to 1930, but copyright laws vary with location and time, so it is your responsibility to determine how you can use it in your situation.
The preview you see here is not full resolution - if you wish to reuse this, you may choose from the various sizes available for you ( up to 3549 x 261 pixels) to freely download here:
www.flickr.com/photos/signalmirror/54431412506/sizes/l
[1] "Aldis Signalling Lantern. Patt. No. 5110", in "Handbook of Signalling, 1918", Naval Staff. Signal Division, 21st Nov 1918, page 93 (Aldis signalling also mentioned on pages 12, 90, 107-110)
books.google.com/books?id=1MZc-NSE0SYC&dq=aldis&p...
[1a] Figure 16. Aldis Signal Lamp. Source: Air Dept Pamphlet No. 41, AIR 1/699/27/3/417.
from page 59 of:
Department of War Studies King’s College, London
British Naval Aviation and the Anti-Submarine Campaign, 1917-18
John J. Abbatiello Thesis submitted for the Degree of Doctor of Philosophy 2004
Publication date 2004-07-22
Approved for public release, distribution unlimited
archive.org/details/DTIC_ADA425512/page/59/mode/1up?q=aldis
[2] "Perfectionnements aux lampes de signaux"
FR510071A • 1920-11-26 • ARTHUR CYRIL WEBB ALDIS
Earliest priority: 1920-02-16 • Earliest publication: 1920-11-26
worldwide.espacenet.com/patent/search/family/008911510/pu...
[3] "Aldis portable daylight signalling lamp", in "Catalogue of Optical and General Scientific Instrument",
Optical Convention, 1926, pages 244-245
books.google.com/books?id=uevqAAAAMAAJ&pg=PA244&d...
[4] "My First War-time Flying Experience" by A. C. W. Aldis,
in The Amateur Photographer and Photography, April 16, 1919, page 342
books.google.com/books?id=_xZLAQAAMAAJ&pg=PA342&d...
[5]1916-04-11: British Patent filing by Aldis for "Improvements relating to signalling lamps"
GB141077A • 1920-05-06 • ARTHUR CYRIL WEBB ALDIS
Earliest priority: 1916-04-11 • Earliest publication: 1920-05-06
worldwide.espacenet.com/patent/search/family/009793885/pu...
[6] Use on aircraft in Battle of Somme in July 1916, per
this quote from from Major General Trenchard, Headquarters, RFC from
IWM DOCS: Typescript Report, Advanced Headquarters, RFC, July 30, 1916
(contained in Quinell Papers 83/17/1) cited as reference [2] in Chapter 4 of:
"Somme Success: The Royal Flying Corps and the Battle of The Somme 1916"
by Peter Hart, Casemate Publishers, 2012, ISBN1781598029, 9781781598023
books.google.com/books?id=ObXNDwAAQBAJ&q=Aldis
"Lamps have been used with success both by day and night, especially by No. 9
Squadron working with XIII Corps. The Aldis pattern with the pistol grip is the
best ..."
[7]The Francis FSP127(MK V) Aldis Lamp sold by Francis Searchlights looks externally like the 1918 Aldis lamp shown here, though there are internal differences (including using a tubular shutter for modulation rather than the rocking mirror, and a parabolic aluminum reflector rather than the 1918 glass Mangin mirror)
www.alphatronmarine.com/en/product/fsp127mk-v-341/
[8] "Mangin Mirror" at Wikipedia:
en.wikipedia.org/wiki/Mangin_mirror
[9] "The Optical Theory of Portable Daylight Signalling Lamps"
by A.C.W. Aldis, M.A., Lecture delivered, 11th March, 1920
Transactions of the Optical Society, V21N4, 1919-1920, pp 113-126
=== text from [1] pp 107-110 ====
Aldis Signalling Lantern.
116. The Aldis Signalling Lantern is supplied to vessels primarily to replace the Cruiser Arc Lantern. It is particularly suitable for signalling to aircraft and is always to be used for this purpose when range and circumstances permit.
2. The lamp is supplied with a short length of twin cable and plug piece. One terminal of the bulb is in metallic connection with the lamp case. The lamp is, therefore, only suitable for use on an earth circuit.
Arrangements are being made to provide a combined plug and resistance, so that power may be taken from any of the 3 or 5 way gun circuit boxes in ships fitted with low-power gun circuits. Vessels not fitted for dynamo firing can use the secondary batteries already supplied. Pattern 3361 cells have been found suitable. The cells must be arranged to give a terminal voltage of 11 to 11.3 volts at the lamp bulb. The lamp should take about 3 amperes. Six cells of pattern, 3361 will normally provide the correct power supply, depending on the state of the contacts and condition of the cells.
3. The lantern consists of
(a) Barrel fitted with a pistol grip.
(b) Hinged mirror.
(c) Detachable glass front.
(d) Cowl.
(e) Sighting arrangement fitted on top of the barrel.
(f) Lamp bulb.
The pistol grip is fitted with two keys-the lower key is the contact key and must always be kept pressed while the lantern is being used. The upper key is the signalling key and actuates the movement of the mirror.
4. When signalling, the lamp is always burning, but no rays are visible to the observer until the signalling key is pressed, which alters the angle of the mirror and deflects the rays down to the observer.
5. For day signalling the glass front may be kept on, but in these circumstances the lamp has a wide divergence. If it is desired to limit this divergence by day, and in all cases by night, the glass front should be detached, and the cowl shipped in its place.
6. The sight fitted on top of the barrel is a combination of 3 sights, any one of which may be used according to circumstances :
(1) A "telescopic" sight. This must always be used for testing the sighting adjustment. (See para. 8.)
(2) An "open" sight, fitted to the left of the telescope.
(3) A "V" sight fitted above the telescope.
7. The lantern as supplied to vessels is fitted with an 11-volt bulb which is at present difficult to produce in sufficient quantities; it is, therefore, important not to overburn the lamp (see para. 2), nor is there any need to do so. The bulb is shipped horizontally, the stem of the cup which holds the bulb being fitted with a key which fits into a featherway in the socket. A screw collar keeps the whole in place. The socket in the stem piece of the bulb must never be tampered with.
8. These lanterns should be periodically tested for "sighting adjustment." At a distance of between 30 to 50 feet a fixed object should be viewed through the centre of the telescopic sight; this centre is marked by a square formed by hair lines drawn across the front of the lens. At the same time the trigger which operates the mirror should be pulled. If it is found that the beam of light is projected directly on to the object viewed through the telescopic sight, then the sighting adjustment is correct. If the beam should fall short of or beyond the object in view, then the lantern is out of adjustment.
9. The re-adjustment is made by means of the setscrew at the back of the lamp which varies the movement of the mirror controlling the travel of the beam. This set screw must never be used for altering the length of the beat of the signalling key, as this would at once throw out the sighting adjustment.
10. Adjustments should not be attempted by altering the position of the sight which is pinned to the body of the lantern.
11. All Aldis signalling lanterns are carefully adjusted before issue, and the mirror set screw held in position by a locking nut. Under normal usage these lanterns should not require re-adjustment.
