The Cadmium Sulfide (CdS) or Light Dependent Resistor (LDR) whose resistance is inversely dependent on the amount of light falling on it, is known by many names including the photo resistor, photoconductor, photoconductive cell, or simply the photocell. The photoresistor finds many uses as a low cost photo sensitive element use in photographic light meters as well as in other applications such as smoke, flame and burglar, detectors, card readers and lighting controls for street lamps.
LDR Symbol:
LDR Structure Map:
LDR Resistance vs Light:
When an LDR light sensor is exposed to light, the resistance reduces, this is known as dark resistance. Conversely, when resistor is exposed to darkness, the resistance decreases.
Features:
- Light Sensitivity
- High Resistance in Darkness
- Compact and Cost-Effective
- Easy Integration with Microcontrollers
- Slow Response Time
- Simple Circuitry
Applications:
- Automatic Lighting Systems: Streetlights and night lights that turn on in low light
- Light-Activated Switches: Controls for devices based on ambient light
- Brightness Control: Used in screens and displays for auto-brightness adjustments
- Security Systems: Triggers alarms when light is disrupted, e.g., in laser security systems
- Solar Tracking Systems: Detects sunlight direction for optimal solar panel positioning
- Camera Light Meters: Measures light for optimal camera exposure
- Toy and Hobby Projects: Common in light-sensitive toys and DIY projects
- Ambient Light Sensors: Adjusts lighting based on room brightness
- Optical Smoke Detectors: Used to sense changes in light due to smoke
- Count and Sorting Devices: Detects objects passing by, based on light blockage
