Here are some DIY LDR switch circuits available on our website and the web. LDR switches are used to switch a relay or other device when light are present or absent. LDRs or Light Dependent Resistors ...

As you probably know the LDR is a light dependent resistor. Normally the resistance of an LDR is very high, sometimes as high as 1MΩ, but when they are illuminated with light resistance drops ...