Abstract: A voltage regulator tube for an ignition system of an internal combustion engine, comprising: a cylindrical enclosure made of electrical insulating material and formed with a hollow extending therethrough; a first metallic sealing member for sealing one opening of the hollow, which is electrically connected to a secondary winding of an ignition coil; a first main electrode mounted on the first metallic sealing member in the hollow; a second metallic sealing member for sealing the other opening of the hollow, which is electrically connected to a spark plug; and a second main electrode which is mounted on the second metallic sealing member in the hollow such that the first and second main electrodes confront each other; wherein inert gas is hermetically filled in the hollow; wherein the following equation is satisfied:-1.5.ltoreq.0.8L-0.72R+3.11H-5.81.ltoreq.1.

Abstract: A discharge tube for an ignition apparatus is composed of a tube-shaped casing made of electrical insulating material which is closed at both end parts with end members, the end members have openings which are smaller in diameter than the inner diameter of the casing, both the openings are sealed by metallic sealing members, respectively, and a thickness of the wall of the casing, an inner diameter and an outer diameter of the casing and a distance between both the end members are restricted within predetermined ranges.