W1 is for changing the conduction angle of the bidirectional silicon controlled to adjust the brightness; R1 is the protective resistance that prevents the diode and silicon from getting broken when the resistance is zero; When the resistance of W1 is at the maximum, the conduction time of the capacitor C1 charging the silicon controlled is longer and the conduction time of silicon is shorter, so the brightness is lower; The brightness will become higher with the resistance reducing and the conduction time of silicon increasing; Adopts ordinary rectifier diode.