High pressure discharge lamp with a starting circuit contained therein

A high pressure discharge lamp connected to a power supply by an inductive reactance element, comprising a hermetically sealed light emitting tube provided with a pair of opposed electrodes, the interior of the light emitting tube being filled with at least a luminous metal and gas, a series starting circuit including a normally closed thermoresponsive switch and a resistor in series shunted across said electrodes, and an evacuated outer envelope containing therein said series starting circuit and said light emitting tube, the resistance value of said resistor being set such that:

• (1) a current flows through said series starting circuit sufficient to open said thermoresponsive switch in response to heating of said resistor before a discharge is started between said electrodes and sufficient to induce across said reactance element a pulse of voltage higher than the starting voltage of said lamp when said thermoresponsive switch opens, thereby to start a discharge between the electrodes, and (2) the current flowing through said series starting circuit is substantially equal to or less than the lamp current during the stable state of the lamp, whereby the pulse energy is insufficient to damage the reactance element, and the current through the switch is insufficient to damage the switch when it opens.