Patent ID: 8358070

Claim:
A lamp comprising: a discharge vessel; tungsten electrodes extending into the discharge vessel; an ionizable fill sealed within the vessel, the fill comprising: a buffer gas, a lanthanide halide component consisting of a rare earth halide selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and combinations thereof; and a source of oxygen within the discharge vessel, wherein the source of oxygen consists of an oxide of a lanthanide selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and combinations thereof, which has an oxidation state greater than 3 and forms an unstable oxide, and is present in an amount such that the solubility of tungsten species in the fill during lamp operation is lower adjacent at least a portion of one of the electrodes than at a wall of the discharge vessel, such that tungsten from the electrode that would otherwise be deposited on the wall during lamp operation is transported back to the electrode to improve lumen maintenance.