A dimming controller for controlling dimming of a light-emitting diode (LED) light source includes a monitoring terminal and a control terminal. The monitoring terminal receives a switch monitoring signal indicative of an operation of a power switch which transfers power from an AC power source to a bridge rectifier when the power switch is on. A power converter receives input power from the bridge rectifier and provides output power to the LED light source. The control terminal generates a control signal to adjust the output power according to the switch monitoring signal so as to control dimming of the LED light source.