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

Automatic Street Light Circuit Uses LDR only

Here is our new simple Electronics project about 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 on and off the Street light 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 street lights 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.

Automatic Street Light Circuit Uses LDR only

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) off-stage. BT136 is a TRIAC that is used to control the main power 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 TRIAC join the current the bulb Turns on. TRIAC is a component that is used to control the light directly 110/220 volts AC main power.


Change in the circuit

You can also make it without DIAC (db3). I will work without DB3 perfectly.

Components used in this Circuit

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


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 to the Main power.

Advantages of LDR / wall Lights/ Street lights Switch

Streetlights consume a lot of power in the cities. Many times after sunrise the street lights remain on. Much amount of the energy is wasted in this way. The automatic street lights 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 are automatically on when the LDR finds light the wall lights off automatically. Once the street lights 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 manual mode if needed.

Related Articles