Thorium-free electrode with improved color stability

Abstract

The present invention relates to an electrode comprising thorium as a minor component for a high-pressure discharge lamp, a high-pressure discharge lamp, and a method of manufacturing therefore. The electrode of the present invention can be used for a high pressure discharge lamp, whereby—the electrode rod is free of thorium, preferably thorium oxide, or comprises thorium, preferably thorium oxide, as a minor constituent,—a covering member made of refractory metal, free of thorium, preferably thorium oxide, is circumference coated on said electrode rod in a vicinity of the discharge side tip, whereby the entire surface of the electrode rod is completely coated over the range the covering member extends,—the electrode rod tip of said electrode rod is not or at least partly coated with said covering member,—at least the part of the electrode tip of said electrode rod which is not coated by said covering member being free of thorium, preferably thorium oxide,—optional the electrode tip is formed into a ball like shape or semi-sphere electrode tip, whereby the covering member is circumference split free joint with said formed electrode tip.

Dependencies are inferred from the claim text.