An illumination system includes an input interface, a phase angle control module, a lamp, and a driving module. The input interface is controllably switched between a first state and a second state. The phase angle control module is electrically connected to an AC power source and the input interface. When the input interface is at the first state, the phase angle control module modifies a voltage waveform of the AC power source to generate a delayed conduction angle in a half wave period of the voltage waveform. The driving module is stored with a control mode, wherein the driving module switches the control mode to control the lamp to emit light in accordance with the delayed conduction angle.