Electric discharge lamps

Abstract

In a tubular high pressure electric discharge lamp, for example a high pressure sodium lamp, the conformation of the interior and/or exterior longitudinal surface of the tubular discharge envelope wall is such as to produce a non-circular cross-section of the interior and/or exterior of the envelope, the configuration of the envelope being such as to give an asymmetric polar distribution of the light emitted from the lamp as a whole. The envelope may be of uniform wall thickness, both the exterior and the interior being of similar non-circular cross-section, for example elliptical, ovate or substantially rectangular. Alternatively, the wall may be of varying thickness around the circumference, such that one or more optical elements, for example lenses, prisms or multiple prisms, are incorporated in the wall structure, the internal and external cross-sections of the tube thus being of different shape, and possibly one or the other being circular. The preferred material for the fabrication of the envelope is transparent crystalline corundum.