A photoresistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can have a resistance as high as a few mega ohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. LDR can be used for Arduino/Raspberry-Pi/Robotics.