A lamp includes a discharge vessel. Tungsten electrodes extend into the discharge vessel. An ionizable fill is sealed within the vessel. The fill includes a buffer gas, optionally free mercury, a halide component which includes a rare earth halide selected from the group consisting of lanthanum halides, praseodymium halides, neodymium halides, samarium halides, cerium halides, and combinations thereof. A source of available oxygen is present in the discharge vessel. The rare earth halide is present in an amount such that, during lamp operation, in combination with the source of available oxygen, it maintains a difference in vapor phase solubility for tungsten species between a wall of the discharge vessel and at least a portion of at least one of the electrodes.