Light source apparatus

A light source apparatus comprising:

• a discharge lamp that encloses mercury and comprises a pair of electrodes arranged to face each other;
• and
• a power supply apparatus that supplies a first alternating current at a first predetermined frequency to the discharge lamp, the power supply apparatus inserts a second alternating current at a second predetermined frequency which is lower than the first predetermined frequency. and the power supply apparatus supplies the second alternating current to the discharge lamp,
• wherein, when the discharge lamp is placed horizontally, a first electric energy ratio A/B of the first alternating current is set to a first value C, and a second electric energy ratio A/B of the second alternating current is set to the first value C,
• when the discharge lamp is placed vertically, a first electric energy ratio A′/B′ of the first alternating current is set to the first value C, and a second electric energy ratio A′/B′ of the second alternating current is set to a third value E, the third value E being smaller than the first value C, and
• wherein the value A′ represents an electric energy that flows from one of the electrodes arranged in a lamp upper side to another one of the electrodes arranged in a lamp lower side of the pair of electrodes and the value B′ represents an electric energy that flows from the electrode arranged in the lower side to the electrode arranged in the upper side,
• wherein the power supply apparatus inserts the second alternating current into the first alternating current according to a predetermined insertion frequency,
• wherein the second electric energy ratio A′/B′ is set to the third value E,
• wherein the third value E is set to fall within a range of 1/3 ≦E<1, and the insertion frequency z×100% is set to fall within a formula:
• 4E+0.7 ≦z≦8E+5.