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One lamp showing different colours in turn.
Also known as: Single lamp signal, Colour changing signal head
A North American signal in which a single lamp changes colour by moving a coloured filter in front of it.
Shows different aspects from one lamp by moving a coloured filter across it.
Contexts: Public information
Reduces a multi-lamp head to a single lens, which was economical when lamps were expensive and became a maintenance liability when the moving part outlived the electronics around it.
Contexts: Public information
A single large round lens on the head, showing one colour at a time as an internal filter moves across the light.