Automatic night light

Automatic night light circuit

A cheap and simple automatic night light using few transistors and NE555 timer is shown here. The circuit will automatically switch on the AC lamp when night falls and the lamp will be automatically switched off after a preset time.

The working of this night light circuit very simple. An LDR is used as the sensor here. At day time the resistance of the LDR will be low and so do the voltage drop across it, the transistor Q1 will be in the conducting mode. When darkness falls the resistance of LDR increases and so do the voltage across it. This makes the transistor Q1 OFF. Base of Q2 is connected to the emitter of Q1 and so Q2 is biased on which in turn powers the IC1. NE555 is wired as monostable multivibrator that is automatically triggered at power ON. This automatic triggering is achieved with the help of capacitor C2. The output of IC1 remains high for a time determined by resistor R5 and capacitor C4. When output of IC1 goes high transistor Q3 is switched ON which triggers triac T1 and the lamp glows. A 9V battery is included in the circuit in order to power the timer circuit during power failures. Resistor R1, diode D1, capacitor C1 and Zener D3 forms the power supply section of the circuit. R7 and R8 are current limiting resistors.

Circuit diagram of automatic night light.

night light cicuit

Automatic night light circuit



  • The circuit can be assembled on a vero board.
  • Preset R2 can be used to adjust the sensitivity of the circuit.
  • Preset R5 can be used to adjust the ON time of the lamp.
  • With R5 @ 4.7M the ON time will be around three hours.
  • The wattage of L1 must not exceed 200W.
  • Heat sink is recommended for BT136.
  • IC1 must be mounted on a holder.
Show Comments

62 thoughts on “Automatic night light

  1. Ramkumar

    If I want to on the lamp in night after the light completes its working time of 3 hrs how should i on the lamp

  2. JBD

    I did this circuit. then i use 2.2M Preset series with a resistor about 2.2M but when i finished making… when i shut the lights off nothing happened but when i feel like ground then the light from the bulb turn on and when i open my flashlight and i place it near to LDR the bulb light turn off and when i turn off the flashlight , the light from the bulb didnt turn on.. help

  3. b delaram

    there should be something wrong with the circuit design,it can not work .all componets used are checked.I think the left part of circuit from B1 to point 2 of IC is the cause of circuit failur.

    thanks a lot

  4. Manoj

    sir this i have a problem that when i switch on ac supply the bulb is glowing during day time also. What to do i am a polytechnic student i would like to design circuits please help me, I would be grateful please please…

  5. srd mathur

    your circuit is just awesome but
    can you please provide the PCB layout of this circuit.
    as soon as possible.


    can you please suggest me a software to make its PCB layout.


  6. Hema

    I designed a simple project for my son (6th std) using the motion light sensor, and it worked very well. But the problem was that when it was exposed to sun, the light which was supposed to glow only when someone crosses the area, is switched ON fully though no obstruction was there and it does not work. Can you please tell me if there is anyway by which I can control it. Please help me in this regard as the project has to be displayed in school in the morning hours and we cannot get a very dark space for displaying it.


  7. sagar

    sir i have made the same connections as above but instead of 9V relay,I used 12V relay n gave 9V dc battery as in figure but i m not getting output.wud 12V relay make any difference? shuld i change it to 9V relay to get output?

  8. Aswin Jose

    hey everyone.. I made this automatic night light and its working good now.. i’am using it for my house lighting now.. The problem i commented earlier was solved by removing the light sensoring part described in the circuit and added a new one which uses another 555 ic(the circuit is available in circuitstoday,”darkness dectetor”)… now it works perfect.. I made simple changes in the entire circuit not all the area, as i’m using a relay to drive my lamp..
    But sometimes i found that the lamp is not switching of even after preset time.. and the problem is with R5.. as i cannot find 4.7M pot i’m using a 4M steady resister., the funny thing is that i made 4M by adding four 1M resistance in series(Local stores always runs out…)so that simple loose connection or bad soldering make the circuit go wrong, anyone who is going behind the circuit ,please take care about connections and soldering..
    Any way thanks circuitstoday.,and thanking Mr.Seetharaman for his help…

  9. priya

    what changes are to be done in the above ckt to make it work as an automatic street light ckt?….will removing the timing pot R5 be enough for that?…pls reply asap

  10. Aswin Jose

    Please help me.. I already assembled everything in a box and its ready to be installed in my house.. But the problem i explained in my last comment.. Its a trouble, any help please..
    Thank you

  11. Aswin Jose

    Hey.. Please help.. Once the problem is solved, my circuit will be perfect and i can use it for my household lighting..

  12. Aswin Jose

    Hey Seetharaman.. Thanks for all your help.. My circuit works well.. I’m using a 9v transformer, I used 4x1N4007 diodes along with 1000uF 16v capacitor to make 9vac to DC.. I think its just fine.. If any mistake please correct me..

    But now i’m facing a problem that once when the lamp is switched on at dark and switched off after the preset time at night, it is not turning back on when its dark in next day evening.. the light sensing unit is working good but its not triggering the timer so that to power the base of transistor to light the lamp.. so what i’m doing now is that i’ll simply short the two legs of LDR just with a pin or something once (which literally makes the circuit full off stage)and the problem is solved.. Once the shorting is removed the circuit work very fine.. but i have to do the same when its dark again the next day.. It also occurs when there s a power failure, the timer fails to work and i have to short the LDR making full conductivity, and then it works.. any suggestion?? a little help will make my circuit work perfect.. Please can you think of any solutions??

    thanking in advance

  13. Seetharaman

    Hi Aswin there is 9 volt AC available in the circuit. I thought you will be using the battery supply to illuminate the lamp, hence a transistor to take care if SCR is used in DC it will get latched up.

  14. Seetharaman

    Hi Aswin NE555 can sink 200mA load. its pin 3 is open collector. hence it can can switch on a relay between positive rail and pin3. I am using it as time delay relay for AC using a power relay driven directly by 555.

  15. Aswin Jose

    Hello., i connected relay as recommented by Mr.seetharaman.. But i’m sorry that i burned three 555 ic’s.. I connected relay with a freewheling diode to pin 3 of ic.. The thing is that the relay is not properly switched to on,but just vibrates.. Why is it so.? I think 555 can drive a relay without transister.. Ples reply for my last doubt too.. Waiting help.. Thanking you

  16. Aswin Jose

    Hai Seetharaman… you told about using TIP3055 insted of BT136.. Why so?? Can we use it to drive AC lamp just like we did with triac.?? or can we just switch a 9volt lamp??


  17. Aswin Jose

    Thank You Seetharaman for your helpfull reply… so glad that you are always around to help people like me in this website… Let me try the circuit with the modifications and I will have my comments. Take care
    thank you

  18. Seetharaman

    Hi Aswin you can use a suitable fixed resistance in place of variable. you can use a 100uF / 16volts electrolytic capacitor in parallel with the relay coil to avoid chattering.

  19. Aswin Jose

    Thanks for all your help… But when i use a relay, it used to chatter some times.. and for a few times when it goes to one state(say off state,in day light) but never switches back on when its dark…But the thing is that the circuit is doing its job but was unable to drive the relay..when i check i found that the relay is just vibrating but not working as it should be.. so i have to switch off the entire circuit and switch it on back. I think we can add a capacitor parallel to relay to get rid of chattering and this switch on problem.. But what should be the value of capacitor?? and at last one more doubt, can i use a 4M or 5M resistors insted of variable resistance in place of R5(4.7M) so that i can have more switch on time…

  20. Seetharaman

    Hi Aswin you can use a 9 volt relay and ensure that a diode (free wheeling diode)is used in parallel with the relay to protect the IC. and a 27 ohms 1/2 watt resistance is used in series with the relay to protect it against a higher voltage of 12volts instead of nine.

  21. Aswin jose

    Hey.. Thanks for your help.. I think that we can use a 6v 100ohm relay in that place of 9v bulb so that we can still drive an ac lamp.. Correct me please if i’m wrong..

    Thank you

  22. Seetharaman

    Hi Aswin in the above ircuit the bulb is connected between neutral and 230volt AC. In that place you can use a low voltage lamp within 300mA rating, direct to Pin3 of NE555 and 9volt positive bus, no need for T1.

  23. Aswin Jose

    Hey Seetharaman… i would like to know what did you mean by the statement “use a 9 volt lamp and connect it to battary +”.. in your last comment. I was always looking forward to make the circuit work in dc source,and thanks for helping… and also i will be glad if you can provide information to make this lighting work with a relay, so that we can replace T1.

    Thanks in Advance

  24. Seetharaman

    Hi Nidhi you can delete R1 D2 D3. Connect B1 + to R2, use a 9 volt lamp and connect it to battary + and replace T1 with TIP3055. You can also adopt this circuit for 12 volt system.

  25. nidhi

    can we make the same circuit using a dc battery only i.e. without using an ac supply a voltage regular circuit,please reply please…

  26. Lucas Liu

    Great Light!
    Do you aways wanted to fill the void at the back of a stage with something? Do you still useing tower LED panels but these are a bit fiddly to set up and can’t be folded? The LED vision curtain does the job much better.Sure to be a massive hit for years to come, order yours from our outlet store now(

  27. Seetharaman

    Hi Sadham it can be between 1k (with bright light) and around 100k (in dark). A standard 5mm LDR will be OK.

  28. DJ

    It’s best project.It can use for verious applications…
    sir i requested u that please give me circuit analysis

    thank you.

  29. aswin

    i like this post and i tried it.. bt i dnt kno why.,the bulb i connected(60watt) is nt glowing any time.,nt at dark not at light.. i dont y???
    i did as perfect as i could.. i checked the circuit board i assembled many times bt still nt working.. i checked the comments and i had already done a google to find more of this circuit.. bt no hope… please somebody help me.. it not working at all.. i kno its too late to add a comment… bt please help me

    thank you

    • Alectronic

      You did nothing wrong.
      The circuit is a HOAX. I build it too and it didn’t work either.
      The NE555 (also TLC555 cmos version) never triggers. Only activates when you make pin 2 shortly grounded (shorting pins 1 and 2). Carefull high voltage !! And even then the Triac just barely triggers. So the light never works. Only works when you short Q3 emitter with collector.
      Q1 and Q2 LDR circuit works splendid. But the 555 won’t do anything here.
      It’s a fake circuit !!

  30. aswin

    i kno tht nw i’m late to add a comment. Bt i’m troubling wth this circuit. I assembled the circuit.. Bt the bulb is nt glowing even in dark nor anytime.. I checked all round circuit and its perfct.. I read all comments in this topic and i had a googling abt this circuit. I’m totaly unhappy. Ples smebdy help me.. Ples

  31. Seetharaman

    Hi Jirah this can be assembled in standard PCB. Ensure that the PCB is cleaned dried after assembly with iso-propyl alcohol, this will ensure there is no leakage path in the PCB, which will affect your timing as the components are of high value hence the inter track insulation should be quite high.


    I purchased the components for the above circuit. All components are available except R5, 4.7M preset. It is told in the market (hyderabad)that presets are available upto 1 M only. Whether can I use 1 M preset in series with 3.7M general resistance in the circuit (making it a total of 4.7 M resistance)?. Ofcourse, the no. of
    components will increase. The preset adjustment can be used upto 1 M, over and above the constant 3.7M general resistance. Whether this will do?
    2. Please clarify, in the notes point 4, it is mentioned R5 as 47 M. Is it 4.7 M or 47 M ?

    • admin Post author

      With a 3.7M series to 1M preset the ON time cannot be adjusted below 2.5 hrs.
      (1.1RC is the ON time for a Monostable)

      In the notes its 4.7M. I have corrected it there. That was a type error from my part. Thanks for pointing out.

  33. Seetharaman

    hi krishna C1 & C4 are electrolytic capacitors 12 to 16 working voltage. C2 & C3 are ceramic disc capacitors 12 to 16 working voltage. R3,6,7 & 8 are 1/4 watt, R2 and R5 are preset pots, 10mm LDR preferred. You can remove B1 and D2, the problem will be when ever a power failure occurs the timer will get reset.


    I want to build the circuit. Kindly clarify:
    1) What type of capacitors are C1 to C4?
    2)What is the wattage for R2 to R7?
    3)Whether 8 / 10 mm LDR can be used?
    4)Suppose I dont want to provide the timer circuit through battery then what components are to be removed from the circuit. I think they are B1 (battery) and D2.
    Kindly reply.


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