Arc tube having particular volume and gas pressure for luminous flux

Abstract

An arc tube for a discharge lamp unit which emits light which is suitable in luminous flux, color temperature, and chromaticity. The arc tube is composed of a closed glass ball in which electrodes confront one another and which is sealingly charged with light emitting materials, namely, mercury and a metal iodide of NaI and ScI.sub.3 groups together with Xe inert gas. In accordance with the invention, the closed glass ball has a volume of 20 to 50 .mu.l, the density of the mercury in the closed glass ball is in a range of 2.times.10.sup.-2 to 4.times.10.sup.-2 mg/.mu.l, the density of the metal iodide is in a range of 6.times.10.sup.-3 to 12.times.10.sup.-3 mg/.mu.l, and the charged Xe gas pressure is 3 to 6 atm. These ranges make it possible to readily manufacture on a large scale arc tubes which are substantially equal in performance, being substantially uniform in tube voltage, luminous flux, color temperature and chromaticity.

Dependencies are inferred from the claim text.