Ushio Denki Kabushiki Kaisha

Kazuo Nakamura

Tatsushi Igarashi

Osamu Mizuno

Shoichi Mayama

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.

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Kakogawa, Japan

Kazuo Nakamura