End-of-life lamp starter disabling circuit

摘要

A disabling circuit for deactivating a high pressure sodium lamp starting and operating circuit when the lamp exhibits end-of-life cycling includes a normally closed thermal switch connected to the starting and operating circuit is inoperative, the switch having contacts which open in response to an elevated temperature. A heating element is connected in parallel with the lamp so that the voltage across the lamp is applied to the heating element. The heating element is supported in a selected heat conducting relationship with the thermal switch so that a predetermined elevated temperature is reached and the contacts are opened only after the dissipation of an amount of energy resulting from repeatedly high lamp open-circuit voltage accompanying end-of-life cycling.