This application is a basic electronics application. We will use the BC547, a transistor that is widely used in the electronics world.
It is used as an LDR voltage divider with a 100K resistor. When more light falls on the LDR, the resistance remains low. As the light begins to decrease as the light falls on the LDR, its resistance begins to increase. And the VBE voltage of the BC547 transistor increases. When the threshold voltage of 0.7 volts is exceeded, the collector current also increases and the LED connected on the collector line of the transistor starts to light.
This application is a basic application and can be used in many electronic circuits. This circuit, which has an illuminance sensor with an LDR half, can be used to turn on nightlights.