How I Made Darkness Detector Circuit Using LDR and Transistor

Hi, in this post I will share with you how I made a darkness detector circuit using a transistor. It worked well for me and hope you can also make this project at home or in school or college projects. It is very simple, easy, and can be built on a low budget.

So, before going ahead let me tell you what is a dark detector device or circuit?

What is Darkness Detector

In simple terms, it is a device that detects darkness. It is sensitive to light so it is able to detect the darkness. It uses a simple dark detector circuit which can be made in many ways, using a transistor or using a ‘555 timer’. It is made with the help of LDR [Light Dependent Resistor or Photoresistor]

What is LDR or Photoresistor

Photoresistor or LDR is a passive component that decreases resistance with respect to receiving luminosity on the component’s sensitive surface. The resistance of a photoresistor decreases with the increase in incident light intensity.

Applications of dark sensor

So this can be used in various ways. We can use it in automatic lights that can be automatically switched ON in the evening or when there is darkness. Or we can use it in security alarms and there are a lot of other applications.

Components used in darkness detector circuit

Below I am listing the darkness detector circuit components, I used in this circuit.

  • One pcs LDR [light-dependent resistor]
  • One pcs LED [Light Emitting Diode]
  • One pcs carbon resistor 30k ohms
  • One pcs battery 6V
  • N-N-N Transistor
  • Connections Wires
  • Soldering iron and other helping apparatuses.

You can also buy Technical Hut Automatic Street Light DIY Breadboard kit for Students

Package include:- Breadboard 400 points – 1 Piece, BC547 Transistor – 1 Piece, LDR – 1 Piece, 5mm led – 1 Piece, 1k ohm resistor – 3 Piece, 10k ohm resistor – 1 Piece, 9v Battery with cap – 1 Piece, Single stand jumper – 1 meter

Procedure | How to make darkness detector

Make the circuit according to the diagram shown below and make sure all the connections are tight. After checking if the circuit is working fine then solder the connections.

Darkness detector circuit diagram

darkness detector circuit diagram
Automatic Light detector using resistor and transistor. Image source:

Darkness Detector Demo

Here is the video I found on youtube and I am sharing it with you. This is how a darkness detector works. This is the live demo of the dark detector as an automatic light detector.

That’s it, you have a darkness detector now. You can use it in automatic lights or after some modifications [Using speaker or other things] we can modify it for the application as a security alarm.

Also Read: Sun Tracking Solar Panel Project Without Using Microcontroller


I hope you liked this post and if you are looking to make a school or college project on the darkness detector topic so it would surely help you. If you need any further help, you can contact me I’ll help you out.

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