What It Is and How It Works

The LDR Light Sensor Module is a compact light-detection board built around an LDR (light-dependent resistor, also known as a photoresistor). The resistance of the LDR falls as the light falling on it increases, and rises again in darkness. An onboard LM393 comparator compares the LDR signal against a threshold set with the blue onboard potentiometer, so you can adjust exactly how bright or dark the surroundings must be before the output switches.

The module gives you two ways to read light:

• Digital output (DO) — goes HIGH/LOW when the light level crosses the threshold you set with the potentiometer.
• Analog output (AO) — gives a continuous light-level reading that you can read with an Arduino.

Power and output indicator LEDs show at a glance when the module is powered and when the digital output has switched, making testing and debugging quick and easy.

Specifications

How to Use with Arduino

Connect the module to your Arduino UNO R3 DIP as follows:

Use analogRead on A0 to read AO for a continuous light-level measurement, or digitalRead on D2 to read DO for a simple light/dark trigger. Turn the blue potentiometer to set the dark/light threshold at which DO switches. Pair the module with a 5mm LED, a 1-Channel Relay Module or an MB102 Breadboard to build your circuit quickly.

Applications

• Automatic street lights
• Light-sensitive night lamp
• Smart desk lamp
• Morning light alarm
• Light-following robot
• Greenhouse ventilation
• Security and home automation projects

Frequently Asked Questions

What is an LDR sensor module?

It is a small board that uses a light-dependent resistor (LDR/photoresistor) to detect light intensity. Its resistance falls as light increases. With an onboard LM393 comparator, it converts the light level into digital and analog outputs that you can read with an Arduino or any other microcontroller.

What is the difference between the digital and analog outputs?

The digital output (DO) goes HIGH or LOW when the light level crosses the threshold set with the potentiometer — best for simple on/off triggers such as switching a lamp. The analog output (AO) gives a continuous reading of the actual light level, which you read with analogRead for finer measurements.

How do I adjust the sensitivity?

Turn the blue onboard potentiometer with a small screwdriver. It sets the threshold at which the digital output switches. Watch the output indicator LED while turning it to find the exact light level that triggers your project.

Can it work with 3.3V boards?

Yes. The module runs on 3.3V–5V DC, so it works with 3.3V boards as well as 5V Arduino boards.

What projects can beginners build with it?

Beginner-friendly projects include automatic night lamps, smart desk lamps, light-sensitive alarms, morning light alarms and simple light-following robots — all possible with just the module and an Arduino.

Is it suitable for outdoor use?

The module is not waterproof, so it is not suitable for unsheltered outdoor use. Use it indoors or inside a sheltered, weatherproof enclosure if your project goes outside.