colour light

Noun

colour light signal (plural colour light signals)

1. (UK) An electric railway signal with colour aspects, showing either red or green in a 2-aspect signal, with the addition of a yellow or double yellow aspect (meaning caution) in 3- and 4-aspect signals.
   • Colour-light signals, for both day and night work, came into use at a much later date, and their first use on any scale in this country was on the London underground railways, where the principle adopted was largely American in origin. But although light signalling is credited to America, one of...1955 April, R. H. Warring, “Some Early Railway Signals”, in Railway Magazine, pages 231-232

   Synonyms:

   colour light