METAL VAPOR DISCHARGE LAMP

PURPOSE:To enable prevention of over-heat damage of a balast by melting off certainly the coil filament of a thermo-acting switch type starter contained in an outer tube in case of a luminous tube being in leakage. CONSTITUTION:When a voltage is applied to a lamp in a state of a luminous tube being in leakage and Xenon gas leaks out in an outer tube 1, the lamp is lighted under a certain condition unless a coil filament 9 should be melted off before the thermo-acting switch 8 operates and the balast 12 is damaged by burning. Accordingly, by melting off the coil filament 9, over-heat damage of the balast 12 can be prevented. A condition to melt off the coil filament 9 is as 0.1