Circuit for automatic adjustment of light, how it works

The circuit shown in the figure can automatically adjust the brightness of the light with the intensity of the light. It is mainly through the photodiode V11 photoelectric coupling used to control the size of the collector current of transistor V8, that is, to control the capacitance C charging fast and slow, but also control the single junction transistor conduction moment, changing the voltage at both ends of the lamp, so that the brightness of the light is regulated. When the light is strong, the photodiode control V8 collector current decreases, capacitance C charging slows down, the single junction transistor conduction moment shifted back, the control angle increases, the voltage at both ends of the lamp decreases, the brightness of the light is weakened. When the light is weak, the opposite is true.