LDR – Light Dependent Resistor

Light Dependent Resistor or LDR is also known as photoresistor. The resistance of an LDR decreases with increasing intensity of incident light. Though it is called a photoresistor, actually it exhibits photoconductivity. When exposed to light, the resistance can fall from the order of megaohms to a few hundred ohms.

An LDR can be used in light activated switches. It can be used in automatic circuits which can switch on and off street lights and garden lights without a timer, depending on the ambient light. Light sensing headlights of vehicles in another situation in which LDR can be useful. They can also be used in security systems which trigger an alarm when a person crosses a laser beam.