Automatic Street Light Circuit Uses LDR only

August 23, 2025 admin Electronics Projects, LDR 0

AUTOMATIC STREET LIGHT CIRCUIT

In this article, we are going to make an automatic street light circuit. You must want to know how the streetlights turn on automatically in the evening and off in the morning. We want to tell you that nobody manually turns these lights on or off physically.  In this article, we are describing a circuit for an automatic street light or street light controller project by using LDR (light-dependent resistor).

Here is our new simple electronics project about the automatic street light control system. In this project, we did not use any relay for on/off. We have just used a TRIAC as a relay to turnthe street light on and off automatically.

Automatic street light circuit Features

  • It is a simple and powerful concept, which uses TRIAC as a switch to switch ON and OFF the streetlights automatically.
  • Automatically switches ON lights when the sunlight goes below (e.g., in the evening)
  • It automatically switches OFF lights when sunlight falls on the LDR sensor of this project.

So in this circuit, we are going to use an LDR (light-dependent resistor) as a sensor to sense the light. In the daytime due to light, the resistance of LDR will be very low. So the voltage drop is high. This keeps the TRIAC (BT136) offstage. BT136 is a TRIAC that is used to control the main power of 110/220V directly. The bulb will remain OFF.

As night falls the resistance of LDR increases, and it turns on the TRIAC points M1 and M2. When M1 and M2 of the TRIAC join the current, the bulb turns on. A TRIAC is a component that is used to control the light directly with 110/220 volts AC main power.

Change in the circuit

You can also make it without DIAC (DB3). I will work without DB3 perfectly.

AUTOMATIC STREET LIGHT CIRCUIT

Components used in this Circuit

    • TRIAC:  BT134/BT136/BT139
    • Resistor: 220k 1/4 watts
    • LDR: Light-dependent resistor

WARNING

The Light Sensor Switch works on 110/220V AC directly, and if you are not accustomed to working with mains voltage or do not have experience in working with 220V AC mains voltage, please stay away from this project while it is connected with main power.

Advantages of LDR/Wall Lights/Street lights Switch

Streetlights consume a lot of power in the cities. Many times after sunrise the streetlights remain on. A large amount of energy is wasted in this way. The automatic streetlights using LDR work according to the light. LDR detects the light. The lights are turned on if the light is below a specific value.

The system is highly sensitive. When the LDR goes dark, the street lights automatically turn on; when the LDR finds light, the wall lights automatically turn off. Once the streetlights are placed in this system, there is no need to monitor them anymore. They function on their own. They are less costly and reliable. This system can handle heavy loads up to 7A; if you use BT139, then it can handle 18A main current.  The system can be changed to the manual mode if needed.

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