Ignition device for high pressure discharge lamps

Claim 1

An igniting device for a lighting circuit including a high pressure vapor lamp having first and second terminals comprising: a self-induction type ballast having first and second output terminals; a thermal switch enclosed in a hermetically sealed vacuum enclosure separate from said lamp and said ballast so that said lamp is extractable from said circuit when malfunctioning without removing said switch from said circuit, said thermal switch having first and second arms coupled to said first and second ballast terminals and to said first and second lamp terminals respectively, said first arm being stationary and said second arm having one fixed end and one movable end, said movable end being in contact with said first arm when said switch is closed and out of contact with said first arm when said switch is opened, said switch providing a short circuit across said lamp when closed to generate heat within said enclosure; said second arm being a bimetallic strip movable to open said switch upon heat being stored in said hermetically sealed enclosure upon current flowing through said switch when said switch is closed; and over-voltage protecting means connected in parallel with said lamp and to said movable end, said protecting means having a higher breakdown voltage than the igniting voltage of said lamp.