Patent ID: 7868553

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, optionally mercury, and a halide component comprising a rare earth halide selected from the group consisting of lanthanum halides, praseodymium halides, neodymium halides, samarium halides, cerium halides, and combinations thereof; and wherein the fill is free of all rare earth halides other than halides of lanthanum, praseodymium, neodymium, samarium, and cerium; a source of available oxygen in the discharge vessel, the rare earth being 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.