30 since the lamp 13 is not on when a high voltage pulse from the igniter circuit 14 is further superimposed on the above mentioned voltage v 3 a voltage v 4 is applied to the high pressure discharge lamp 13 thus starting up the lamp next at a time u201c t1 u201d high voltage small current glow discharge is started and this state further changes to high voltage small current arc discharge at a time u201c t2 u201d the lamp voltage increases with increases in a temperature of the lamp at a time u201c t3 u201d the ac conversion circuit 31 starts operating and the high pressure discharge lamp 13 changes to an ac lighting mode after this when a stationary voltage v 4 is reached at a time u201c t4 u201d the power control circuit 30 supplies constant electric power to the high pressure discharge lamp 13 by activating constant power control the frequency of a rectangular wave from u201c t3 u201d onward is generally called the inverter frequency operation modes of the discharge lamp after it has been lit up i e after u201c t4 u201d in fig3 are described next there are typically four operation modes of the discharge lamp 1 an.