A light source driving apparatus to drive at least one light source module includes a switch unit for coupling in series with an AC power source and the light source module; a clock synchronization unit for coupling to the AC power source and to provide a clock synchronization signal in accordance with an AC voltage of the AC power source; a control unit coupled to receive the clock synchronization signal and to provide to the switch unit an adjusting signal according to a timing of the clock synchronization signal; and a feedback unit coupled to the control unit and to detect a load state of the light source module, the feedback unit configured to provide to the control unit a feedback signal having a value representative of the detected load state of the light source module. The control unit is configured to modulate a pulse width of the adjusting signal according to the feedback signal and a preset brightness value of the light source module, the switch unit responsive to the adjusting signal to open and close to apply the AC voltage to the light source module in accordance with the modulated pulse width.