Use NE555 to make light-controlled automatic lights

The circuit for making light-controlled automatic lights using NE555 is shown in Figure 3-10.
    In the picture, the time base integrated circuit NE555 is connected as a Schmitt trigger. During the day, the outside light is strong, the photoresistor RG
shows low resistance, and pins 2 and 6 of the time base circuit are high level, greater than 2/3 VDD. , in reset state. Its output pin 3
outputs low level, the thyristor VS is turned off without triggering current, and the lamp H does not light up. At night, RG loses light and becomes high resistance,
so the trigger terminal pin 2 of the time base circuit is at low level (less than 1/3 VDD), the time base circuit is set, and its output terminal pin 3 jumps to
high level, which is controllable. Silicon vs is turned on by receiving the trigger current from R2, and the electric lamp H is energized and emits light.
    Rl and C1 in the circuit form an interference pulse absorption circuit to prevent short-term light (such as lightning flashes, vehicle lights
, etc.) from interfering with the normal operation of the circuit. Since the Schmitt trigger composed of the time base circuit has a hysteresis voltage of 1/3 VDD, it
can prevent the light from flashing when the circuit is in a critical state. The varistor RV connected in parallel to the thyristor is used to eliminate
various spikes in the power grid to protect the thyristor VS from damage due to overvoltage.