Automatic Street Light Circuit

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

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 fall on LDR sensor of this project.


So in this circuit we are going to uses a LDR (Light Dependent Resistor) as a sensor to sense the light. In the day time due to light the resistance of LDR will be very low. So the voltage drop be high. This keeps the TRIAC (BT136) on 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 joints 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 with Main power.

Advantages of LDR / wall Lights/ Street lights Switch

Street lights consume a lot of power in the cities. Many times  after sunrise the street lights remain on. Much amount of 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 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 the manual mode if needed.

19 Comments on “Automatic Street Light Circuit”

  1. Can you make an inverter circuit(1.5v to 220v or say 6 to 12v to 220 v)that will run more than 2 hours in a single charge?(4 pcs.1.5 v battery can be connected parallel for higher current if thats the case.)tnx.

  2. Sir according to ohm’s law when resistance is increase current is decrease then how do the light on.???..if we use 2 transistor as a switch then what happens in the ckt???

    1. But…. and I may be wrong here, but my understanding of an LDR (Light Dependent Resistance) is that it’s resistance is dependent on there being light. Ergo, no light, no resistance (and the bulb gets energized). No?

      A big thanks to the author of this article. I am purchasing the components tomorrow (including the DIAC DB3) and will report on its performance in due course.

  3. Thank you for every other wonderful post. The place
    else could anybody get that type of information in such a perfect
    approach of writing? I have a presentation next week, and I’m at the search for such information.

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