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"The side lamps were carried on part or un- fitted freight trains and shone a white light forward so that the loco crew could check that the train was complete at night. They were carried on both sides of the van at once, normally on the rear balcony brackets where the guard was afforded some protection from the wind when running at speed, but this was not a hard and fast rule and on 25mph maximum class K or 9 trains they might well be on the front balcony's brackets, especially where trains changed direction. The 'normal' display while the train was running was thus of 3 red lights to the rear in an upside down triangle formation, but not always, as follows.
They shone a red to the rear as stated, but this was in the form of a removable slide-in shade that the guard removed from the side adjacent to a running line if his train was in a loop, refuge siding, or reception/departure road, or on a slow or goods line adjacent to a fast running line that traffic might overtake on. This was to re-assure the drivers of such trains that they were not about to collide with the rear of a freight train travelling perhaps 60mph slower than them, especially on curves where perspective can play nasty tricks with you at night! Thus the display would be of 2 red lights, the main tail lamp and the side lamp on the side of the train away from the faster line, and a white on the side closest to it. There was a slide-in on one side of the lamp to store the shade in, but when you were in a loop or siding you just left it sticking out the top of the main slide-in!
On the GWR/BR (W), the white light was similarly displayed to the rear on 'relief' lines even when they were separated from the faster running line by another running line in the opposite direction.
They were painted black or white, and about the same dimensions as the normal head and tall lamps, and used the same paraffin reservoirs and burners. They fitted differently to the brackets, though, a slot being provided either side of the lamp. The handle was oriented the other way around as well. In an emergency in which the guard wishes to draw the attention of the loco crew to have the train stopped, he can reverse the lamps so that they show a red light forward; if the loco crew don't notice, the next signal box or passing train will! If the emergency is more serious than this, you have plenty else to worry about...
There seems to have been no rhyme or reason to black or white painting in BR days, but I have a general impression that there were more black painted ones towards the end of the brake van period. I believe GW ones may have been red painted. Fully fitted freight trains carried a single tail lamp without the side lamps, as did all other traffic above Class C or 6, and of course still do!"
