About the lighting dimming switch circuit diagram

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

The characteristic of the dimming switch of the illuminator is that after the switch is turned off, the light does not disappear immediately, but gradually fades out and finally goes out within one or two minutes. The use of such a switch allows a person to leave the room or go to bed without lighting in the presence of light. When the light switch K is closed, the light is turned on as usual. The line on the right of K is shorted by the switch and does not work. When the light is turned off, K is turned on. The 220V AC voltage is rectified by D1~D4 to the anode and cathode of the unidirectional thyristor SCR. At the same time, the positive pole of the power supply provides a trigger current to the thyristor control electrode through the capacitor C, the resistors R2, R3 and the diode D5, so that the lamp continues to emit light. For capacitor C, this is a charging process in which the charging current is gradually reduced, that is, the SCR trigger current is gradually reduced. When the C charge is sufficient, the trigger current is zero and the lamp is extinguished. The dimming time of the lamp depends on the charging time constant (R2+R3)·C. Using the data shown in the figure, R3 is adjusted, and the fade-out time is adjustable in about 1~3 minutes.
Resistor R1 action: When switch K is closed, the charge stored in capacitor C can be discharged through R1, so that the voltage across C is reduced to zero to ensure that C can be recharged to make the lamp dim when the lamp is turned off next time.