LDR - Light Depending Resistor

LDR - Light Dependent Resistor (also known as a Photoresistor or Cadmium Sulfide / CdS cell) is a light-sensitive passive electronic component whose electrical resistance decreases as the intensity of incident ambient light increases. In complete darkness, an LDR exhibits a very high resistance (often in the megaohms range), whereas exposure to bright light drops its resistance down to a few hundred ohms. Because of its simplicity, low cost, and reliable performance, the LDR is widely used in light detection, automatic night-light switching, optical counting, and solar tracking systems.

Features

• Light-sensitive semiconductor sensor (CdS cell) with rapid response to visible light wavelengths
• Inverse resistance-to-light relationship: high resistance in darkness, low resistance in light
• Highly sensitive to changes in ambient illumination levels
• Bi-directional passive component with non-polarized leads for effortless circuit integration
• Easily forms a voltage divider circuit with a fixed resistor to provide analog light intensity readings
• Compact, lightweight, and durable epoxy-coated package
• Seamlessly interfaces with microcontrollers (Arduino, ESP32, ESP8266) via analog pins or digital comparator modules (LM393)
• Low power consumption and cost-effective design

Applications

• Automatic street light control circuits and dusk-to-dawn outdoor lighting
• Smart home light intensity detection, automatic display backlighting, and ambient lighting adjustment
• Dual-axis and single-axis solar panel tracking systems to maximize solar energy efficiency
• Object detection, optical line-following robots, and beam-break intrusion alarm systems
• Camera light meters, shadow detectors, and optical pulse/counting devices
• Microcontroller-based academic, polytechnic diploma, and university engineering thesis projects

Important Notes:

• An LDR is a passive variable resistor, not an active voltage sensor; to read light values with an analog pin (like Arduino A0), connect it in a series voltage divider configuration with a static resistor (e.g., 10kΩ).
• LDRs are sensitive to the visible spectrum and ambient temperature; high ambient thermal noise can slightly alter resistance readings.
• Avoid bending the leads repeatedly at the base of the epoxy head to prevent physical cracking or internal disconnection.
• For applications requiring precise numerical lux calibration, calibrated photodiode sensors (e.g., BH1750 or TSL2561) are recommended over standard photoresistors.
• Keep the surface of the clear epoxy head clean and free of dust or opaque moisture for accurate light measurement.

Package includes

• 1 x LDR - Light Dependent Resistor (5mm Photoresistor)