A glow discharge starter is usually connected across or in parallel with an arc discharge lamp and contains a pair of electrodes. At least one of the electrodes comprises a bimetallic element which, when heated as a result of the glow discharge, bends towards the other electrode. When contact is made, the glow discharge ceases causing the bimetallic element to cool and withdraw from the contacted electrode. When contact is broken, a voltage pulse induced by the induction of the ballast, appears across the opposed electrodes of the lamp thereby initiating an arc discharge within the lamp. If the lamp ignition does not occur after the first voltage pulse, the glow discharge starter sequence is repeated until lamp ignition occurs.
A glow discharge starter of the aforementioned type is described, for example, in the book "Light Sources" by Elenbaas, Philips Technical Library, pages 102-103. Other examples of glow discharge starters are shown in U.S. Pat. Nos. 2,324,907; 2,332,809; 2,376,669; 2,740,861; 2,930,872 and 2,930,873 and German Pat. No. DE3320933A1. Examples of commercially available glow discharge starters are the GB-5A manufactured by GTE Sylvania S.A., Costa Rica, San Jose and the PL13 manufactured by Osram, a division of Siemans A.G., Munich, W. Germany.
The normal glass used for the glow discharge starter envelope has a wall thickness in the range of about 0.025 inch (0.635 millimeter) to about 0.035 inch (0.887 millimeter). Prior glow discharge starters generally displace a volume greater than 0.75 cubic centimeter. By using the teachings of the present invention, it is possible to reduce the size of the glow discharge starter to about one-third the size of prior starters. It has been found that an excessive amount of heat is required to seal glass with the above mentioned wall thickness range. The excessive heat creates several problems in the manufacture of the glow discharge starter.
First, as a result of this heat, the electrical conductors and bimetallic element associated with the heat sensitive bimetallic element tend to undesirably oxidize. Also, a relatively large sealing capacity is required and an excessive amount of flushing gas must be employed in an effort to reduce the oxide formation on the electrical leads and bimetallic element, when glass having a relatively thick wall thickness is utilized.
Second, the increased heat requires the use or more expensive segmented electrical conductors. Generally, a short section of stiff nickel coated steel is butt welded to a small diameter soft wire having a nickel-iron alloy core sheathed in a copper shell. The steel internal portion of the electrical conductors which form the electrodes, are needed to maintain proper spacing between the free end of the bimetallic element and the other electrode. The heat generated during manufacture when the electrical conductors are sealed into the envelope causes the bimetallic element to put a spreading force on the electrical conductors.
Third, a standard press seal alone cannot be used in these prior glow discharge starters to hold the electrodes in their spaced relationship because the sealing heat would overstress the bimetallic element, causing misalignment of the electrodes. As a result, the prior glow discharge starters use various approaches. One approach involves sealing a glass bead or base on the electrical conductors to act as a heat sink during the subsequent press sealing operation. An alternate approach comprises first sealing the electrical conductors in a flare tube with an exhaust stem to form a mount. The mount is then sealed into the envelope.