Phase-cut dimmable,we also call it Leading edge/triac dimming is the use of thyristor circuit, starting from the AC phase 0, the input voltage chopper, until the thyristor on, there is no voltage input. Its principle is to change the sinusoidal waveform by adjusting the conduction angle of each half wave of AC, so as to change the effective value of AC current,and achieve the purpose of dimming.

Leading edge dimmer has the advantages of high precision, high efficiency, small size, light weight, easy long-distance operation, etc. It dominates the market. Most manufacturers produce this type of dimmer. Leading-edge phase-controlled dimmers generally use thyristor as switching devices, so they are also called triac dimmable.