PURPOSE: To prolong the lifetime of a high pressure discharge lamp by accommodating therein a plurality of light emitting tubes in its single outer tubing in the condition that they are connected parallelly in electrical terms, allowing either of the light emitting tubes to make electric discharge and emit light, and thereby providing possibility of starting the other tube in case one tube goes in leakage without risk of generating electric discharge in the outer tubing.
CONSTITUTION: An inert gas is encapsulated in an outer tubing 1 so that the discharge in outer tubing occurs in case a voltage exceeding the discharge starting voltage of light emitting tubes 5a, 5b is impressed. Thus the outer tubing is filled with inert gas to such a level that a voltage around the discharge starting voltage of light emitting tube does not initiate the electric discharge in outer tubing, so that the other tube can be started certainly even in the event of leakage at one of the tubes when no discharge in outer tubing will take place.
OKAMURA KAZUYOSHI
UCHIDA KAZUO
