Abstract: A sine wave light-adjusting apparatus adjusts the input sine wave voltage and output a desired output sine wave voltage to a lamp according to the desired brightness of the lamp to achieve the light-adjusting effect by adjusting the switching period of a switch and utilizing a flywheel effect. The apparatus includes an energy-storing unit, a positive semi-period switching unit controlled by the microprocessor to execute the switching operation during the positive semi-period of the sine wave voltage, a negative semi-period switching unit controlled by the microprocessor to execute the switching operation during the negative semi-period of the sine wave voltage, a positive semi-period flywheel unit controlled by the microprocessor to conduct during the positive semi-period of the sine wave voltage, and a negative semi-period flywheel unit controlled by the microprocessor to conduct during the negative semi-period of the sine wave voltage.