The New Zealand Railways Magazine, Volume 2, Issue 4 (August 1, 1927)
Railway signalling has made tremendous progress since the day when a lighted candle placed in the window of a stationmaster's house served as primitive warning to the drivers of approaching trains on the Stockton and Darlington lines. To-day automatic colour light signalling represents the high-water mark of signalling practice, and in a recent installation on its York and Darlington tracks, the London & North Eastern Railway has advanced even further than usual, by combining with the automatic equipment a novel form of approach lighting of signals.
No suitable power supply being available for this installation, operation by primary batteries is provided for, with approach lighting as a means of reducing current consumption. Normally the signals are not illuminated. When a train approaches to within 1,200 or 1,800 yards, the colour light signal is illuminated through track circuit control, and the red, yellow or green light is displayed, according to the length of clear headway in advance of the signal. On passing a signal, the train causes a red light to be exhibited in the rear, until it has proceeded a distance of from 1,600 to 2,000 yards. Although largely experimental in character, the York-Darlington installation promises to pave the way for the general utilisation of approach lighting on suitable sections of track.