Discharge lamp lighting apparatus

A discharge lamp lighting apparatus, comprising:

• a discharge lamp in which a pair of electrodes each having a protrusion at a tip end thereof are arranged to face each other at an interval equal to or less than 2.0 mm in an arc tube, the arc tube enclosing mercury and halogen of 0.20 mg/mm3 or more;
• and
• a power supply device configured to supply an alternating current to the discharge lamp,
• the power supply device being configured to drive in a switchable manner between a regular lighting mode, in which the discharge lamp is being lit with a basic frequency selected within a range of 60 Hz to 1,000 Hz, and a low electric power lighting mode, in which the discharge lamp is being lit with an electric power value within a range of 25 to 80% with respect to a rated power consumption of the discharge lamp, and
• the power supply device being configured to control a power supply to the discharge lamp such that, in the low electric power lighting mode, after a secondary protrusion forming process in which a secondary protrusion forming alternating current having a frequency equal to or greater than the basic frequency in the regular lighting mode is supplied while lowering an electric power of the lamp, the frequency being selected within a range of 200 to 2,000 Hz,
• the low electric power lighting mode transitioning to a secondary protrusion maintaining process in which a secondary protrusion maintaining high frequency current having a frequency higher than the basic frequency in the regular lighting mode, the frequency being selected within a range of 100 Hz to 1,500 Hz, and a secondary protrusion maintaining low frequency current having a frequency lower than the frequency of the secondary protrusion maintaining high frequency current is alternately supplied as a secondary protrusion maintaining alternating current, wherein,
• during the secondary protrusion maintaining process, a secondary protrusion maintaining alternating current is supplied in which a boost current is superposed onto a regular lamp current with the selected frequency at a predetermined temporal interval, wherein
• a superposing ratio or a temporal interval of the boost current varies depending on any of a lamp electric power, a lamp voltage, a lamp current, and combined parameter thereof, wherein,
• when the superposing ratio of the boost current is varied, the superposing ratio is varied towards a target superposing ratio in a stepwise manner.