Ushio Denki Kabushiki Kaisha

Shoichi Mayama

Tatsushi Igarashi

Kyosuke Fujina

Katsuoki Miyasu

Osamu Mizuno

Kazuo Nakamura

A discharge lamp in which ultraviolet radiation of short wavelengths can be advantageously cut and in which the amount of emitted light (i-line) of 365 nm wavelength can be increased is achieved according to the invention by providing a quartz glass arc tube that is coated with a plurality of coating layers which include a layer which has Ta.sub.2 O.sub.5 as the main component, and at least one additional coating layer which has a refraction coefficient which differs from the refraction coefficient of the coating layer having the Ta.sub.2 O.sub.5 main component. These layers act to prevent the reflection of light with a wavelength of 365 nm which is incident on the coatings on the arc tube and to cut at least 50% of the ultraviolet radiation having wavelengths of 230 nm or less. According to the invention, the coating layers can be provided on the outer side of the arc tube, on the inner side of the arc tube, or on both on the inner and outer sides of the arc tube.

Discharge lamp having a plurality of coating layers

A discharge lamp provided with an anode of the water cooled type achieves advantageous cooling directly connected a tungsten tip piece to a tip of a body element of the anode that is formed of copper has a water cooling arrangement therein, by having a maximum outer diameter of the tungsten tip piece about equal to an outer diameter D (mm) of the body element, and by maintaining the relationship between the outer diameter D and the thickness of the tungsten tip piece L of: 0.2.ltoreq.L/D.ltoreq.0.5. In accordance with a preferred embodiment, the tungsten tip piece is directly connected to a tip of a cylindrical body element inside of which a cooling water feed tube is arranged extending coaxially to the body element, and in which cooling water is fed from a base of this cooling water feed tube, along the cooling water feed tube, strikes an inner side of the tip end of the body element and finally is conveyed through a gap between an inner side of the body element and an outer side of the cooling water feed tube which serves as a cooling water drainage duct. Preferably, the tungsten tip piece has the shape of a truncated cone whose maximum outer diameter is about equal to the outer diameter D (mm) of the body element and a thickness in a lengthwise direction of the body element.

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Himeji, Japan

Shoichi Mayama