Abstract: A dimmer for an incandescent lamp, wherein a phase angle controlling dimmer for performing one time ignition operation every one period of a power supply waveform is used, the ignition angle is varied continuously to perform an optical adjustment operation, each of the electrical powers of positive half cycle and negative half cycle is supplied to individual filaments of a bulb so as to enable an optical adjustment of less variation in color temperature to be attained.

Abstract: An object of the present invention consists in enabling an optical adjustment having a less amount of variation in color temperature while raising fast a color temperature even if the optical adjustment is carried out and enabling an optical adjustment where reduction in color temperature is scarcely acknowledged while maintaining the color temperature after the color temperature reaches a specified value. There is provided a dimmer for performing one time igniting operation for every one period of the power supply waveform, each of the electrical power of the positive half cycle and the electrical power of the negative half cycle is supplied to a separate filament, a raising time of the optical adjustment at each of the filaments is displaced and the variation in the color temperature through the optical adjustment operation is reduced.