DR is an electronics sensor that sense presence of light. When Light is fall on the top surface of the LDR, its resistance becomes lower and when there is low light, its resistance becomes higher. Means, the resistivity is inversely proportion to the intensity of light exposed on LDR active surface. This chance in resistance can be used to changes in voltage and current. Actual look of LDR is show in image 1 . Circuit diagram of LDR with single resistor can be used to detect light. When LDR is connect to resistor in series, as show in image 1. When light fall on LDR, voltage dropped across output decrease and when light decreases, voltage dropped across output will increase. This voltage drop can be used to control switching like transistor, relays, hyristors or any other switches and can controlthrough microcontroller inputs.