JPS57191954A - Metal vapor electric-discharge lamp - Google Patents

Abstract

PURPOSE:To enable prevention of any functional variation of a near-by conductor, which is installed outside the emission tube of a metal vapor electric-discarge lamp in order to increase its starting performance, and enable the starting voltage of the lamp to be stably reduced. CONSTITUTION:During the starting of a metal vapor electric-discharge lamp, a bimetal switch 24 of a starting unit 20 is closed, and a near-by conductor 16 is in contact with the outer surface of an emission bulb 12. When the bimetal switch 24 is opened as a tungsten filament 22 generates heat, its kick voltage is added to the secondary voltage of a ballast, and high-voltage pulses are generated. Thus generated high-voltage pulses are applied to electrodes 15a and 15b as well as to the near-by conductor 16, weak glow discharge is initiated across the electrode 15b and the inner wall of the emission bulb 12, and the above glow discharge is switched into are discharge carried out across electrodes 15a and 15b. Here, when the conductor 16 is made to have a plate-like shape and the width (S) of the conductor is restricted to above 20x, the glow discharge carried out during the starting grows and shifts securely to the electrode having the same electric potential as the near-by conductor 16. Consequently, stable starting performance of the lamp can be realized, and the starting voltage of the lamp can be reduced.