colour light signal

colour light signal (plural colour light signals)

1. (rail transport, British spelling) 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.
   • 1955 April, R. H. Warring, “Some Early Railway Signals”, in Railway Magazine, pages 231-232:

     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 the first instances of its use was an experimental installation at Herne Hill, although it did not find favour in this country for overground working until some fifty years later.

• colour-light signal, color light signal, color-light signal

• “colour light signal”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.