Testing LDR

LDR (light dependent resistance) can be very easily tested by using a digital multimeter. We are aware that the resistance of an LDR varies according to the light falling on it .In bright light LDR resistance will be around 500 Ohms and in darkness the resistance will be around                 200 K.Ohm. For a proper testng we need to measure the resistance of the LDR in bright light and in darkness.

Testing in bright light
Keep the multimeter at Resistance checking mode. The LDR must be subjected to a bright light source (day light is enough).Now the multimeter will show a low resistance reading around   500 Ohms.

Testing in darkness
Keep the multimeter at Resistance checking mode. The LDR must be subjected to darkness by covering it with an opaque paper. Now the multimeter will show a high resistance reading around 200K.Ohm

IF both the tests are OK we can conclude that the LDR is working fine