GL5549 Light Dependent Resistor (LDR) – 100kΩ–200kΩ

The GL5549 Light Dependent Resistor (LDR), also known as a photoresistor, is a simple light-sensitive electronic component whose resistance changes according to the amount of light falling on its surface. As the light level increases, its resistance decreases; in darkness, its resistance increases significantly. With a light resistance of approximately 100kΩ–200kΩ and a dark resistance of up to 10MΩ, the GL5549 is ideal for light-sensing circuits, automatic lighting, alarms, electronic kits, microcontroller projects, and classroom experiments. Its simple two-lead, non-polarised design makes it particularly suitable for students learning about sensors and input devices.

Key Features

• Light-sensitive variable resistance
• Light resistance: 100kΩ–200kΩ
• Dark resistance: approximately 10MΩ
• Maximum power: 100mW
• 3.4mm lead spacing
• Non-polarised – can be connected either way
• Simple two-lead through-hole component
• Suitable for analogue sensor circuits

What’s Included

• 1 × GL5549 Light Dependent Resistor

How an LDR Works

An LDR changes resistance in response to light. In brighter conditions, its resistance decreases, allowing more current to flow through a suitable circuit. As the surroundings become darker, its resistance increases.
This changing resistance can be converted into a changing voltage by combining the LDR with a fixed resistor to form a voltage divider. The resulting voltage can then be used by a transistor, comparator, PICAXE, Arduino, or other microcontroller to determine the surrounding light level.

Common Applications

• Automatic night lights
• Light and dark sensors
• Security lighting
• Light-activated alarms
• Robotics and automation
• Solar tracking experiments
• Light-level measurement
• PICAXE and Arduino projects
• Electronic kits and classroom experiments

Classroom Use / Learning Outcomes

Students can use the GL5549 to:
• Understand how sensors respond to environmental conditions
• Measure resistance at different light levels
• Investigate analogue input signals
• Construct voltage divider circuits
• Program a microcontroller to respond to light levels
• Create automatic light and dark activated systems
• Explore input-process-output control systems

Teacher Benefits

• Simple and engaging introduction to sensors
• Easy for students to test using a multimeter
• Non-polarised design simplifies circuit construction
• Suitable for breadboards and PCB projects
• Excellent for demonstrating analogue inputs
• Can be incorporated into a wide variety of design projects

Perfect For

• Light-sensitive circuits
• Automatic night lights
• PICAXE projects
• Arduino projects
• Robotics and automation
• Electronic kits
• Breadboard experiments
• STEM and classroom electronics