I previously add another project named, "Line Following Robot". And this one is , "Light following". Except this everything is identical (I mean circuit diagram). For track the light I use Two LDR faces oppositely (Left-Right) and connect them to microcontroller's two ADC channel. They continuously convert the voltage across LDR and compare. If left one is greater then right one, then it move left and vice versa. If both are same then move forward. If no light is there it stop.