A rare-gas arc lamp includes a pair of coil filaments disposed at the opposite ends of an elongated bulb for increasing an area of a positive column produced between the coil filament pair in a direction perpendicular to the elongated axis of the bulb, and a rare-gas mainly including xenon gas and having substantially no mercury therein sealed in the bulb at a prescribed pressure selected from the range between 20 Torr and 200 Torr. The combination of the coil filament pair and the xenon gas sealed in the bulb at a prescribed pressure in the range of 20 Torr to 200 Torr may reduce visible changes in a luminance distribution of the lamp when the positive column fluctuates during the operation of the lamp.