The Electric potential of the Wheatstone Brigde depends on the LDR or NTC or PTC etc. If the potential is equal then the two led's remain dark. That changes as soon as the balance change to one side. Depending on positive or negative potential the red or the green LED will turn on. It can steer the direction of rotation of a electric motor as needed in SunChaser unit...or a day and night switch...or a temperature switch...or direction finder... Etc etc etc ... Use your imagination!
