Here's another circuit from Electronics For You, the Indian publication:
The relay is activated when light ceases to fall on the LDR. The resistance of the LDR increases and the BC557 transistor turns off. This allows the voltage on the common terminal of the 7806 to rise and the output voltage rises.
When the voltage rises above 9v, the base of the BC547 sees a turn-on voltage and the relay is energised.
This is a very complex circuit to perform such as simple task.
A much simpler circuit is shown below:
The relay is activated when light ceases to fall on the LDR. The resistance of the LDR increases and the BC557 transistor turns off. This allows the voltage on the common terminal of the 7806 to rise and the output voltage rises.
When the voltage rises above 9v, the base of the BC547 sees a turn-on voltage and the relay is energised.
This is a very complex circuit to perform such as simple task.
A much simpler circuit is shown below:
