High-pressure discharge lamp, particularly low-rated power discharge lamp, with enhanced quality of light output

Abstract

To improve the arc stability of high-pressure discharge lamps, particularly f power ratings of up to about only 250 W, the cathode (4) is formed as an elongated, essentially cylindrical base body (8) having a tapering, conical region (9) terminating in a tip (10). The base body (8), only, is covered with a carbide coating along its length, except for an end portion for electrical connection; the carbide coating starts at the junction or transition between the cylindrical base body portion and the conical end portion. This cathode construction is easier and cheaper to make than prior art cathodes, by coating an essentially cylindrical cathode and then etching or grinding and polishing the tapering end region (9). The electrode is preferably made essentially of tungsten, doped with thorium oxide present up to about 0.6%, optionally also potassium, aluminum and silicon in tiny amounts. The electrode spacing is between 0.4 to 0.8 mm, and when used as a mercury high-pressure discharge lamp, filled with 70 to 130 mg per cubic centimeter mercury; when used as a xenon lamp, the xenon fill is preferably present at a cold fill pressure of between about 2 and 15 bar.

Dependencies are inferred from the claim text.