An installation of semi-cut-off street-lighting lanterns, erected on a semi-rural main road and mounted at a height of 30 ft, has been compared with an adjacent installation of cut-off lanterns mounted at 35 ft. Both used 400-watt mercury lamps with a spacing of 120 ft. A group of 107 drivers including private car, bus, and lorry drivers, rated the installations approximately equal with regard to the intensity of illumination, the venues of illumination and the standard of visibility provided. However, they rated the semi cut-off installation. Most driver-the ratio was 1.75:1- preferred the cut-off installation to the semi-cut-off one. Revealing powers (with a correction applied for disability glare) were much the same for the brighter parts of the road in the even darker vertical backgrounds beyond the footways the revealing power was higher in the cut-off than in the semi-cut-off installation. The results of this investigation indicate a slight advantage for the cut-off over the semi-cut-off installation on this type of road.
Abstract