A method for controlling a discharge lamp by a power controlling device on an automobile vehicle includes a starting step and a switching step. The device supplies electricity to the lamp. In the starting step, the discharge lamp starts to emit a light such that the device supplies a first electricity. In the switching step, the device switches from the first electricity to a second electricity so that the lamp maintains to emit the light with the second electricity, which is smaller than the first electricity. In the switching step, a temperature of the lamp is decreased with a temperature gradient, which is equal to or smaller than a predetermined gradient.