Abstract: An extra-high pressure mercury lamp includes an arc tube made of quartz glass. The lamp includes an arc tube portion and sealing portions connected to the arc tube portion, and encloses 0.15 mg/mm3 or more of mercury. A pair of electrodes are disposed face to face in the arc tube. Each electrode has a rod portion and a base end portion. The base end portion of each electrode is embedded in one of the sealing portions. One of the pair of electrodes serves as a cathode and includes a head portion, which has a larger diameter than the rod portion. A cylinder portion is connected to a rear end portion of the head portion. The cylinder portion extends in the axis direction of the electrode and surrounds the rod portion. The cylinder portion has an inner surface separated from the rod portion.

Abstract: An extra-high pressure mercury lamp includes an arc tube made of quartz glass. The lamp includes an arc tube portion and sealing portions connected to the arc tube portion, and encloses 0.15 mg/mm3 or more of mercury. A pair of electrodes are disposed face to face in the arc tube. Each electrode has a rod portion and a base end portion. The base end portion of each electrode is embedded in one of the sealing portions. One of the pair of electrodes serves as a cathode and includes a head portion, which has a larger diameter than the rod portion. A cylinder portion is connected to a rear end portion of the head portion. The cylinder portion extends in the axis direction of the electrode and surrounds the rod portion. The cylinder portion has an inner surface separated from the rod portion.

Abstract: In a light source unit which has a discharge lamp which is located in a differential pressure passage system, an arrangement in which the discharge lamp and a concave reflector can be cooled with high efficiency is achieved by a discharge lamp being attached in the neck of a concave reflector which is located essentially horizontally, and at the same time, in the differential pressure passage system. Furthermore, at least one cooling air discharge opening is located in the neck area of the concave reflector; translucent glass covers the front opening of the concave reflector; and at least one cooling air injection opening is located in the area of the front opening of the concave reflector and has directional accuracy with reference to the inside of the concave reflector.

Abstract: A method for producing a fused silica envelope for use in a discharge lamp in which the inner surface of a fused silica tube is coated with a formulation containing titanium alcoholate and the coating treated by the steps including baking at a temperature of at least 1720.degree. C. to cause TiO.sub.2 to diffuse into the tube. The method results in a Ti concentration in a range of 1 .mu.m-10 .mu.m from the inner surface of the wall of the envelope is 0.5%-7% in terms of TiO.sub.2 and the product of the overall average Ti concentration and the thickness of the wall of the envelope ranges from 3.7% .mu.m to 42% .mu.m. During the baking step, the tube is shaped to include a bulb-like portion by inflating the silica tube.