Search Light
an electric arc light the rays of which are collected in a parallel beam that may be projected to a great distance and turned in any direction. Search lights are used on naval vessels to show at night the approach of hostile vessels, and to detect floating mines or torpedo boats; also for illuminating signal flags and for signaling by long and short flashes. This system of signaling is used in the army also. Messages may be sent 20 miles or more. Search lights are, broadly speaking, of two kinds: concentrated beams and dispersed beams. The latter were extensively used in the World War to illuminate large areas of water that had been laid with mines. The light is also used in the commercial marine, by liners, etc.