Automatic Night Light

The LDR in this circuit must be placed outdoor. At day time the light falls on LDR. (+)ve charge reaches the transistor's base through LDR. There will be more (+)ve charge than (–)ve charge at transister’s base.
So t1 turn off. And LED doesn’t glow .

At night LDR doesn’t transfer (+)ve Charge. So there will be more (+)ve charge than (–)ve charge at transistor's base. So the transistor, turns on and LED glows

Through these operations the LED glow at night and doesn't glow at day.