Patent ID: 6366020
Filing Date: 2002-04-02
Classification: H01J

Abstract:
A discharge lamp adapted to operate on DC current, said lamp comprising a ceramic arc tube having a fill of mercury, rare gas, and metal halides, said arc tube being sealed with an anode and a cathode in capillaries and forming an envelope, said envelope having a metal heat shield and a metal foil tube, said shield being in the form of a cup which is placed on an end of cathode side of the DC metal halide arc tube, the height of the heat shield cup being adjusted in accordance with the cathode arrangement and metal halide fill composition within the arc tube said metal foil tube surrounding the top of the capillary on the anode side said foil cup and foil tube serving as heat shields for the discharge lamp to preserve the heat for the cathode end to boost the cold spot temperature to an operable region when the lamp is not operated with anode at bottom, said heat shield arrangement providing a cold spot temperature variation of the DC ceramic metal halide lamp equivalent to a AC ceramic metal halide lamp for different operating positions to achieve operation of said lamp with universal orientation.