A Light Dependent Resistor (LDR) is also called a photoresistor or a cadmium sulfide (CdS) cell. It is also called a photoconductor. It is basically a photocell that works on the principle of photoconductivity. The passive component is basically a resistor whose resistance value decreases when the intensity of light decreases. This optoelectronic device is mostly used in light varying sensor circuit, and light and dark activated switching circuits. Some of its applications include camera light meters, street lights, clock radios, light beam alarms, reflective smoke alarms, and outdoor clocks.

The LDR 5mm Light Dependent Resistor PhotoResistor sensor works best in both Light and dark region. Light-dependent resistors or photoresistors are a staple of electronics. If you need a way to sense the level of ambient light then there is no easier way to do it. As the light on the sensor increases then the resistance across the two leads decreases.

Two Cadmium Sulphide (CDs) PhotoConductive Cells with spectral responses similar to that of the human eye. The Cell resistance falls with increasing light intensity. Applications of this product include smoke detection, Automatic lighting control, batch counting, and burglar alarm systems.