Patent ID: 7548031
Filing Date: 2009-06-16
Classification: H05B

Abstract:
1. An apparatus for a discharge lamp containing no mercury or a small amount of mercury, which gradually reduces electric power supplied to the discharge lamp in accordance with a time lapse during a transient time period, where the discharge lamp reaches a stable lighting state, comprising: means for detecting a change value of a lamp voltage from an initial lamp voltage value; and means for controlling electric power which switches in a stepwise manner, when the change value reaches at least a threshold value, a temporal change rate of electric power supplied to the discharge lamp during the transient time period in accordance with one of an increase of the change value and a time lapse; wherein the means for controlling includes a time constant circuit comprising a capacitor and a plurality of resistors, the time constant circuit operating when the change value relating to the lamp voltage reaches at least the threshold value, and a charge time constant of the capacitor is switched in accordance with one of an increase of the change value and an increase of a voltage of the capacitor to control the temporal change rate of the electric power during the transient time period in the stepwise manner, and wherein, the electric power during the transient time period is controlled in accordance with a first time constant when the change value relating to the lamp voltage reaches at least the threshold value, and the electric power during the transient time period is controlled in accordance with a second time constant smaller than the first time constant.