Light detector Circuit using LM358 Op amp IC


A Light detector Circuit using LM358 Op amp IC is a simple electronic circuit that can detect the presence or absence of light. It is widely used in various applications such as automatic switching of appliances, security systems, and even in everyday objects like cupboards and wardrobes. In this article, we will discuss how to build a light detector circuit using the LM358 Op amp IC.

Hardware Required

1×LM358 OP – Amp IC
1xRed LED
1×Small LDR
1×10 KΩ Potentiometer
1×10 KΩ Resistor
1×220 Ω Resistor
1×9V Battery with Cap

Circuit Diagram:



In the Light detector Circuit using LM358 Op amp IC, we connect the LDR to pin 3 of the LM358 Op amp IC, which is the non-inverting terminal. When light hits the LDR sensor, the resistance through the LDR decreases, resulting in a higher voltage on pin 3. This high voltage output at pin 1 indicates the presence of light.

To make the circuit more versatile, we add a variable resistor at pin 2. By adjusting the variable resistor, we can manipulate the sensitivity or set the value of the light intensity to be detected. When the variable resistor is set to a low resistance, the voltage on pin 2 increases. This higher voltage on the non-inverting terminal (pin 3) requires a higher input signal to overcome the voltage on pin 2, resulting in a higher output. This setting indicates a high intensity of light.

Conversely, when the resistance of the variable resistor is increased, the sensitivity of the light detector circuit increases. This is because a lesser voltage is required on pin 3 to trigger a higher output.


The simple Light detector Circuit using LM358 Op amp IC has numerous applications:

  1. Automatic Appliance Switching: The circuit can be used to automatically switch on or off appliances based on the detection of light. For example, it can be employed to turn on outdoor lights when it gets dark.
  2. Security Systems: The light detector circuit can be integrated into security systems to trigger alarms or activate surveillance cameras when there is a significant increase or decrease in light intensity.
  3. Cupboards or Wardrobes: It can be used in cupboards or wardrobes to turn on the lights inside when the door is opened, providing convenience and energy efficiency.
  4. Photovoltaic Systems: The circuit can be utilized in photovoltaic systems to monitor the intensity of sunlight and regulate the charging of batteries or the operation of solar panels.
  5. Plant Growth: The light detector circuit can be employed in indoor gardening setups to monitor the light intensity and ensure optimal conditions for plant growth.

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