Leading edge dimming usually uses silicon controlled rectifier（SCR） as a switching device, so it is also called silicon controlled dimmer (Phase-cut dimmer). Its working principle is to wait for the trigger to turn on from the zero phase of AC voltage, and when it turns on, AC power is transmitted to the load. The sine wave shape is changed by adjusting the conduction angle of each half wave of alternating current, so that the effective value of alternating current is changed to achieve the purpose of dimming.
The forward phase-cut(FPC) dimmer have the following advantages：low in dimming cost、compatible with existing lines、and does not need to be rewired, so it dominates the market. Most manufacturers also produce this type of dimmers.
The back-edge(reverse) phase-cut dimmer(RPC) turns on immediately after the half-waveof AC voltage starts, and turns off immediately when the half-wave voltage reaches the set turn-on angle. Similar to front-end dimming, dimming is achieved by adjusting the conductionangle.