LDR Light Sensing Experiment

Objective

The aim of this experiment is to explore the behavior of a Light Dependent Resistor (LDR) by measuring its resistance under different lighting conditions and using it to sense light levels in a circuit.

Components Required

• 1 x Light Dependent Resistor (LDR)
• 1 x 10kΩ Resistor (for voltage divider)
• 1 x Multimeter (to measure resistance and voltage)
• 1 x Arduino or any microcontroller (optional for automation)
• 1 x Breadboard
• 1 x LED (optional for visual indication)
• 1 x Power supply (5V or battery)
• Connecting wires
• Light source (flashlight or natural light)

Theory

An LDR is a resistor whose resistance decreases with increasing light intensity. In the dark, the LDR has high resistance, and in bright light, it has low resistance. This property makes LDRs useful in circuits where light sensing is needed, such as in automatic street lights, alarm systems, or light meters.

Circuit Diagram

In this experiment, the LDR and a fixed resistor (10kΩ) form a voltage divider. The output voltage at the junction between the LDR and resistor changes with light intensity, allowing us to measure light levels.

Experimental Setup

1. Connect the LDR and 10kΩ resistor in series on the breadboard, forming a voltage divider.

2. Connect one end of the LDR to 5V (or the positive terminal of the battery), and the other end to the resistor.

3. Connect the free end of the 10kΩ resistor to ground.

4. Measure the voltage at the junction between the LDR and the resistor using a multimeter or Arduino analog input pin.

5. Vary the lighting conditions and observe the voltage or resistance change.

Procedure

1. Set up the voltage divider circuit using the LDR and the 10kΩ resistor as described.
2. Measure the output voltage at the junction of the LDR and the resistor using a multimeter.
3. Expose the LDR to varying levels of light, such as using a flashlight or shading the LDR with your hand.
4. Record the output voltage at different light levels.
5. (Optional) If using an Arduino, connect the junction to an analog input pin (e.g., A0) and write a simple code to display the light level based on the input voltage.

Arduino Code (Optional)

const int ldrPin = A0; // LDR connected to A0
int ldrValue = 0;

void setup() {
  Serial.begin(9600); // Begin serial communication
}

void loop() {
  ldrValue = analogRead(ldrPin); // Read the analog value from LDR
  Serial.print("LDR Value: ");
  Serial.println(ldrValue); // Print the value to the serial monitor
  delay(500); // Wait for 500ms
}

            

Results and Observations

As you change the light intensity on the LDR, observe how the output voltage varies. In low light, the voltage should be lower, while in bright light, the voltage should increase. The voltage divider converts the changing resistance of the LDR into a measurable voltage that can be used in a circuit to sense light levels.

Conclusion

This experiment demonstrates the use of an LDR in detecting light levels. The varying resistance of the LDR under different lighting conditions is converted into a measurable voltage through a voltage divider circuit. This simple sensor can be used in numerous light-based applications such as automatic lighting systems or light meters.