Patent ID: 8188663

Claim:
A high intensity discharge lamp comprising a discharge vessel having a wall enclosing a discharge space, an ionizable material contained in said space, and at least two electrodes each having an embedded portion and an electrode shaft extending from the wall of the discharge vessel and ending with a tip of the electrode, the electrodes being arranged in said space for establishment of an electric arc between said tips, wherein each of the electrode shafts of the electrodes comprises a thickened portion arranged between the embedded portion and the tip of the electrode, a first shaft section extending between the embedded portion and the thickened portion, the first shaft section having a first length and a first shaft diameter having substantially the same diameter as the embedded portion, and a second shaft section extending between the thickened portion and the tip of the electrode, the second shaft section having a second length and a second shaft diameter, and wherein the thickened portion has a greater overall diameter than any of the first and second shaft diameters thereby having a specific surface higher than the specific surface of the first shaft section and the specific surface of the second shaft section, respectively, and being arranged to limit the temperature of the electrode shaft at the inner wall by heat dissipation, and the thickened portion has a minimum distance from the inner wall of at least 50% of the first shaft diameter, the length of the second shaft section is at least 100% of the second shaft diameter, and the first length is at most equal to the second length.