Patent ID: 8148920

Claim:
A method of controlling a ballast for a high intensity discharge (HID) lamp, the method comprising the following steps of: (a) outputting an initial operating parameter to the ballast to turn on the HID lamp; (b) measuring an electric parameter at least at one predetermined time during a transient process after the HID lamp is turned on, and generating an HID starting transient electric characteristic value of the HID lamp based on the measured electric parameter; (c) determining whether the HID starting transient electric characteristic value is within a starting transient electric characteristic value range; and (d) when the HID starting transient electric characteristic value is within the starting transient electric characteristic value range, searching a plurality of stored rated power data for a lamp rated power corresponding to the HID lamp according to a corresponding associated relation between the starting transient electric characteristic value range and one of the plurality of stored rated power data, and searching for a ballast operating parameter corresponding to the lamp rated power according to corresponding associated relations between each of the stored rated power data and one of a plurality of stored ballast operating parameters, and outputting the corresponding ballast operating parameter to the ballast, to allow the HID lamp to operate in the lamp rated power, wherein the initial operating parameter and the corresponding ballast operating parameter each control a current output from the ballast.