Patent ID: 7808180
Filing Date: 2010-10-05
Classification: H01J

Abstract:
1. An electrode for a high pressure discharge lamp comprising: an electrode rod having an electrode tip, wherein the electrode rod includes thorium; and a coil of material which is free of thorium and thorium oxide; wherein the electrode rod has a first part covered with the material, the first part having a first diameter which is smaller than a tip diameter of the electrode tip, and wherein the electrode rod has a second part not covered with the material, the second part having a second diameter which is smaller than the first diameter, the second part being located away from the electrode tip, and the first part being located near the electrode tip between the second part and the electrode tip, wherein the coil has individual windings located around the electrode tip, the individual windings being melted to remove the thorium from the electrode tip and to form a continuous coating over the electrode tip so that the individual windings are melted split-free to each other to form a continuous surface with no visible internal cavities remaining between the electrode rod and the coil; and wherein the lamp has a color shift of ΔX (difference colour point to 15 hours) at 500 hours of ≦|15|, and at 1000 hours of ≦|15|, a color shift of ΔY (difference colour point to 15 hours) at 750 hours of ≦|15|, the color shift of ΔX at 1750 hours being ≦|15|, the color shift of ΔY at 2000 hours being ≦|15|, and the color shift of ΔX at 2250 hours being ≦|15|.