Photoresistor
![](/Images/godic/202501/31/LDR_1480405_6_7_HDR_Enhancer_13713.jpg")
![Three photoresistors with scale in mm](/Images/godic/202501/31/Photoresistors_-_three_sizes_-_mm_scale3713.jpg")
![The internal components of a photoelectric control for a typical American streetlight. The photoresistor is facing rightwards, and controls whether current flows through the heater which opens the main power contacts. At night, the heater cools, closing the power contacts, energizing the street light.](/Images/godic/202501/31/Streetlight_control3713.jpg")
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 can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.