Starting arrangement for high-intensity-discharge sodium lamp

Claim 1

In combination with a high-intensity-discharge sodium lamp comprising an arc tube formed as an elongated hollow alumina body member of predetermined dimensions having alumina end-closure members hermetically sealed to the end portions of the hollow body member and enclosing a discharge-sustaining filling comprising sodium and inert ionizable starting gas, electrodes operatively positioned within said arc tube proximate the ends thereof, electrical lead-in means sealed to and extending through said alumina end-closure members and connecting to said electrodes to form composite electrode-lead-in structures, a light-transmitting protective outer envelope surrounding said arc tube, frame means positioned within said outer envelope for supporting said arc tube in predetermined position within said outer envelope, electrical adaptor means affixed to said outer envelope for connection to a source of power, a pair of electrical connection means connecting said electrical adaptor means to said electrical lead-in means, and one of said electrical connection means including said frame means to electrically connect one of said electrodes to said electrical adaptor means, the improvement which comprises: (a) electrically conducting ceramic means hermetically sealed to and extending through said arc tube at least at one end thereof to form electrically conducting path means through said arc tube, a portion of said conducting ceramic means positioned interiorly of said arc tube and electrically insulated from the proximate electrical lead-in means, said conducting ceramic means comprising refractory-oxide-based ceramic matrix which is non-reactive with respect to high-temperature sodium vapor and which possesses the predetermined thermal-physical-chemical properties required to form a high-temperature seal, with alumina, and said refractory-oxide-based conducting ceramic means having embedded therein a predetermined amount of finely divided refractory metal which is inert with respect to said discharge-sustaining filling to provide said conducting ceramic means with a predetermined electrical conductivity; (b) electrically insulating barrier means positioned intermediate said arc-tube-interior portion of said conducting ceramic means and portions of said electrical lead-in conductor means which project interiorly of said arc tube and are proximate said conducting ceramic means, and said barrier means being dimensioned to intercept any condensed discharge-sustaining filling and prevent same from forming a conducting path between said conducting ceramic means and the proximate lead-in conductor means; and (c) during starting of said lamp said conducting ceramic means electrically connect, exteriorly of said arc tube, to the said electrode which is positioned proximate the opposite end of said arc tube from the connected conducting ceramic means, and during starting of said lamp the total electrical resistance between said arc-tube-interior portion of said conducting ceramic means and the connected opposite electrode permitting the maintenance of a glow-type discharge within said arc tube between said arc tube interior portion of said conducting ceramic means and the said composite electrode-lead-in structure which is proximate thereto to ionize the atmosphere within said arc tube.