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A shutter over a light.
Also known as: Aldis lamp, Signalling lamp, Shuttered lamp
The lamp signalling in coded flashes by opening and closing a shutter over a light source.
Signals in coded flashes by shuttering a directed light source.
Contexts: Navigation
Works at night and in radio silence, which is why it survived the arrival of radio in naval use and is still carried — a channel kept precisely because it is not radio.
Contexts: Navigation
Directional like the heliograph but independent of the sun, so it trades the heliograph's range for the ability to work at any hour.
Contexts: Navigation
A lamp behind a circular concave mirror with a hinged shutter worked by a trigger, sighted through a small aperture at the receiving station.
Both send coded flashes to a station whose position must already be known, one using the sun and one a lamp.