PURPOSE: To prevent a heat damage to a stabilizer due to leakage of a high pressure sodium (Na) lamp light emitting tube so as to enhance safety by extinguishing the lamp light emitting tube to cut off a starter in the case where the light emitting tube leaks during operation of a lamp.
CONSTITUTION: When a high pressure Na lamp light emitting tube 1 leaks so that noble gas sealed therein leaks into an outer tube 8, the noble gas is ionized in an electric field of a high electric discharge gap, thus starting glow discharge. The glow discharge is transferred to arc discharge, and accordingly, a first conductor 2 and a second conductor 3 are short-circuited for a short period. The light emitting tube 1 stops electric discharge because a voltage applied to both electrodes is abruptly decreased. A filament 6 is incandescently fused due to a short-circuiting current flowing in an electric discharge gap 10 and the filament 6. Since a starter 7 cannot be operated owing to the fusing, the light emitting tube 1 cannot be discharged electrically. Consequently, it is possible to prevent an overcurrent from flowing in a stabilizer 9 for a long period.
MATSUNO HIROMITSU
IKUTA YASUSHI
MIYATA KENJI
