High pressure discharge lamp lighting apparatus

A high pressure discharge lamp lighting apparatus for lighting a discharge lamp, comprising:

• a discharge container made of quartz glass that encloses 0.20 mg/mm3 or more of mercury and halogen in a range of 10−6 μmol/mm3-10−2 μmol/mm3;
• a pair of electrodes arranged in the discharge container, with a projection is formed at a tip of each of the electrodes, wherein the projections face each other at an interval of 2.0 mm or less;
• and
• a power supply apparatus which performs constant electric power control over the discharge lamp;
• the power supply apparatus supplies a first alternating current of stationary frequency selected from a range of 60-1000 Hz to the discharge lamp;
• wherein the power supply apparatus inserts a second alternating current of lower frequency, which is lower than the stationary frequency, periodically into the first alternating current;
• wherein, when a lighting current value of the discharge lamp is smaller than a predetermined lower limit, the lower frequency is set as a predetermined minimum frequency;
• when the lighting current value is larger than a predetermined maximum value, the lower frequency is set as a predetermined maximum frequency;
• and when the lighting current value is between the lower limit and the maximum value, the lower frequency is set as a first selected frequency corresponding to the lighting current value;
• wherein the first selected frequency increases based on an increase of change value as the lighting current value increases.