HIGH PRESSURE DISCHARGE LAMP

Abstract

A high pressure discharge lamp, in which an anode and a cathode are disposed opposite each other in a bulb, achieves a long service life due to thorium (Th) being stably supplied to the cathode tip for a long time after lamp operation has been commence since the formation of the flicker phenomenon is suppressed over a long time due to the cathode being made of tungsten which contains thorium oxide on a surface space from the cathode tip, a carbide layer of tungsten carbide is formed and the cathode being bordered by an emitter containing body of tungsten which contains thorium dioxide, and a carbide layer of tungsten carbide being formed at least in a region bordering the cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a high pressure discharge lamp in accordance with the invention;

FIG. 2 is a schematic depiction of the cathode of a high pressure discharge lamp in accordance with the invention;

FIG. 3 is a schematic perspective view of the support body for emissive material which is held fast by the cathode in a high pressure discharge lamp in accordance with the invention;

FIG. 4 is a schematic cross-sectional view of the cathode of a high pressure discharge lamp in accordance with the invention which retains the emitter containing body;

FIG. 5 illustrates the motion of the thorium (Th) in the cathode in a high pressure discharge lamp in accordance with the invention;

FIG. 6 is a schematic cross-sectional view of the cathode of a high pressure discharge lamp in accordance with the invention which retains another emitter containing body;

FIG. 7 is a plot of the data of test results in which the situation of flicker formation was studied;

FIG. 8 is a schematic cross-sectional view of a conventional high pressure discharge lamp;

FIG. 9 is an enlarged view of the cathode of a conventional high pressure discharge lamp; and

FIG. 10 is an enlarged view of cathode of another conventional high pressure discharge lamp.

Claims

1. High pressure discharge lamp, comprising: a bulb in which an anode and a cathode are disposed opposite each other, the cathode being formed of tungsten which contains thorium oxide, and a carbide layer of tungsten carbide being formed on an outer surface of the cathode away from a tip end of the cathode,an emitter containing body of tungsten which contains thorium dioxide bordering with at least a partial region the outer surface of the cathode, anda carbide layer of tungsten carbide formed in said partial region bordering the cathode.

2. High pressure discharge lamp in accordance with claim 1, wherein the emitter containing body is a solid body provided with a through opening, and wherein the cathode forms a fit within said through opening by which the emitter containing body is held fast on the cathode.

3. High pressure discharge lamp in accordance with claim 1, wherein the emitter containing body is a linear body with which the cathode is wound at least in regions.

4. High pressure discharge lamp in accordance with claim 1, wherein the cathode has a tip region, a first body part and a second body part, the second body part being located between the first body part and the tip region and having a smaller diameter than the first body part.

5. High pressure discharge lamp in accordance with claim 4, wherein the emitter containing body is located on the outer surface of the second body part.