A ceramic arctube preferably for a high pressure discharge lamp. The ceramic arctube can have an anti-reflection interference coating on the outside or inside surface of the bulb section of the arctube. The outside and/or inside surface of the outer wall of the bulb section of the arctube can be substantially spherical to increase efficiency. The wall thickness of the outer wall of the bulb section can be shaped to lens rays from the arc toward a preselected region of a retlector optically coupled to the arctube to increase efficiency.