LDR Light Sensor

This LDR Light Sensor, also called a Light Dependent Resistor or photoresistor, is a simple and reliable component for measuring ambient light in electronic circuits. The sensor is typically built using cadmium sulphide material, whose resistance decreases when light falls on its surface and increases in darkness. Because it behaves like a variable resistor, it can be used directly in voltage-divider circuits with microcontrollers such as Arduino Uno, Nano, ESP8266, ESP32, Raspberry Pi Pico and many other development boards. In practical projects, the LDR is commonly connected with a fixed resistor to generate an analog voltage that represents the surrounding brightness. This voltage can be read by an ADC pin or compared with a threshold using a transistor, op-amp or comparator circuit. In bright light the LDR resistance becomes low; in low light or darkness it rises significantly, allowing simple automatic ON/OFF control for lamps, garden lights, street-light models, display dimming and light-triggered alarms. The 5mm round package is easy to mount on breadboards, PCBs and through-hole prototype boards. It has two non-polar leads, so it can be connected in either direction, making it beginner-friendly for school labs and DIY electronics kits. The sensor offers a visible-light response suitable for general ambient light detection rather than precision lux measurement. Actual resistance values may vary by batch and lighting conditions, which is normal for CdS photoresistors. What you get is one 2-pin LDR light sensor/photoresistor. For microcontroller use, pair it with a resistor such as 10kΩ to form a voltage divider. For relay or high-power load switching, use a suitable driver transistor, comparator module or microcontroller interface circuit.