Abstract: A pulsed light source includes a sealed, ultraviolet-transmissive lamp tube defining a discharge region containing a rare gas or a mixture of rare gases, anode and cathode electrodes sealed into the lamp tube at opposite ends, leads for connecting the electrodes to a pulsed source of electrical energy and a phosphor material located on a surface external to the discharge region. The lamp tube contains mercury in sufficient quantity to cover the cathode electrode when the lamp tube is oriented with the cathode electrode at the bottom. The cathode electrode is protected by the mercury from sputtering that results from ion bombardment. The mercury emits pulsed ultraviolet radiation which stimulates emission of visible light by the phosphor material. Lamp tube pressure is below 200 torr. The light source is operable over a range of pulse widths and duty cycles. The color of light emission is determined by the phosphor.