Patent ID: 8193740

Claim:
A controller for controlling a discharge lamp provided with: a closed vessel having gas encapsulated therein; a cathode constituted of a filament located in the closed vessel; an anode located in the closed vessel; and an aperture member, which has a first opening positioned on a discharge path between the cathode and the anode, said controller comprising: a variable resistor, which is interposed between the anode and a power source and has a resistance value that is configured to be switched between a high resistance value and a low resistance value and is set to the low resistance value during steady discharge; and control means capable of performing, regarding a first time, a second time, a third time, a fourth time and a fifth time numbered with the elapse of time, operations of: starting power supply to the filament at the first time; applying main voltage from the power source to the anode in a state where the resistance value of the variable resistor is set to the high resistance value at the second time; starting application of trigger voltage for discharge to the anode or the aperture member in a state where the resistance value of the variable resistor is set to the high resistance value at the third time; lowering power supply to the filament at the fourth time without setting the resistance value of the variable resistor to the low resistance value; and setting the resistance value of the variable resistor to the low resistance value at the fifth time.