An electronic ballast for a high intensity discharge lamp (HID) includes a power
converters, a controller, and a lamp power switch. In the power converter, an input
DC voltage is converted into a ballast output power for lighting the HID lamp.
The controller has a function to control the power converter and change the ballast
output power. The lamp power switch detects a lamp output parameter indicated after
the HID lamp starts discharge, identifies a lamp power of the HID lamp according
to the lamp output parameter, and gives an identification signal indicating the
lamp power. In response to this identification signal, the power converter outputs
the ballast output power which matches with the lamp power identified.
