How to Make a Dark Sensor

Hello everyone . This is my frist instructable on this site ..This idea came in my mind when i was reading of automatic street light . Here i have show an easy way to make a dark senensor it sence dark and then a light will glow automaticly . It is also helpfull in making of LFR-line following robot. The part are very cheap and can find on a simple electronic store..also

1.Battery (3v-4.5v) 2.LDR 3.Transistor (BC547B NPN) 4.LDR 5.LED

here is a vedio by wich you can learn how to make it easily