Hi!

The circuit shown can be used to turn on the light in the garden, or some light panels / advertisements in the evening; or early in the morning when they need to be turned off; automatic switching on or off of the warning lights and more.

The circuit contains two amplifier stages with transistors.

The first floor detects the state of local lighting through the LDR photoresistor. In the dark, the value of photoresistor is about 50KΩ and in bright light below 500Ω. Together with the resistor RV1 forms an adjustable voltage divider from which the control signal based on the transistor is applied.

In the dark, the relay is triggered. When the photoresistor receives a light beam, it will increase the current that will be injected based on the transistor and cause a collector current. The threshold is set by adjusting the RV1 semi-adjustable. As the illumination decreases, the value of the LDR (photoresistor) resistance increases, the transistor Q1 will lock, Q2 will enter the conduction and will allow the relay to start, simultaneously with the LED lighting.

P.S. I'm not the original author of this circuit, I just drew it.