The working of the circuit is very simple. During daytime, light falls on the LDR1 and it offers a low resistance. As a result, both the transistors (T1 and T2) do not conduct and the LEDs (LED1 through LED25) do not glow. On the other hand, during nighttime, the light does not fall on LDR1 and it offers a high resistance. As a result, transistors T1 and T2 conduct and the LEDs (LED1 through LED25) glow.
Assemble the circuit on a general-purpose PCB and enclose in a cabinet. Connect the LEDs (LED1 through LED25) and LDR1 on top of the box. Place the unit such that during daytime the sunlight falls directly on LDR1. For powering the circuit, use a 12V battery or any 12V adaptor.