An Aldis lamp is a handheld, focused signal lamp with a trigger mechanism that opens and closes a shutter, producing the short and long flashes of Morse code.
Where the Name Comes From
The lamp is named after its inventor, Arthur C.W. Aldis, a British engineer who developed the design in the early 20th century — the name has stuck as the generic term for this type of directional signal lamp, similar to how “Thermos” became a generic term for vacuum flasks.
How It’s Used
The operator aims the lamp directly at the receiving vessel and squeezes the trigger to produce flashes — short presses for Morse dots, longer presses for dashes — spelling out a message that a trained observer on the receiving end reads back letter by letter, typically using binoculars at distance.
Why a Focused Beam Matters
Unlike a general signal light, the Aldis lamp’s focused, directional beam means the message is genuinely intended for and mainly visible to the specific vessel being signaled, rather than broadcasting to everyone nearby — useful for directed communication rather than general alerts.
Current Role Aboard Ship
Aldis lamps remain standard equipment on merchant vessels as a recognized backup communication method — genuinely useful when radio isn’t practical or available, though day-to-day communication has shifted almost entirely to voice radio. The skill of both sending and reading Morse code via lamp is maintained through training specifically because it’s a competency you can’t develop in the moment you actually need it.
Exam Relevance
Aldis lamp operation and its role as a visual signaling backup are covered within GMDSS and Ship Knowledge topics in deck officer competency exams, typically alongside basic Morse code proficiency.