Automatic light On Off Circuit

Now a day the automation play vital role in our daily life and it also make easy the daily routine task. Automatic light On Off Circuit by using LDR is very important in our daily life. It operation totally depend upon the LDR  





4-82 ohm resistor

5-LED bulb

6-bulb holder


8-Wire piece

Construction and Working  

In the circuit of the automatic light on off switch we will used LDR (Light dependent resistor or Diy dark sensor)as a sensor which sense the light in the day time .In the day time due to sunlight the resistance of LDR is very low ,so the voltage drop is high.Due to this the TRIAC remain off.BT138 is a TRAIC which is used in power controlling circuit directly .

When the night fall ,the resistance of LDR increase and it turn on the TRIAC and as are result the bulb turn on.

automatic light ON Off Circuit

Alternate Circuit

automatic Light ON Off circuit


  • By using this project a lot of energy consumption in the day time due to street light remain on will reduced
  • This automation system can be used up to 7 A and if we used BT 139 then this system can be used up to 18 A
  • The system can be change to manual when we need according to the need ..

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