Street light circuit.

admin March 8, 2012 219 Comments


The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises. In fact you can this circuit for implementing any type of automatic night light.

The circuit uses a Light Dependent Resistor (LDR) to sense the light .When there is light the resistance of LDR will be low. So the voltage drop across POT R2 will be high.This keeps the transistor Q1 ON. The collector of Q1(BC107) is coupled to base of Q2(SL100). So Q2 will be OFF and so do the relay. The bulb will remain OFF.

When night falls the resistance of LDR increases to make the voltage across the POT R2 to decrease below 0.6V. This makes transistor Q1 OFF which in turn makes Q2 ON. The relay will be energized and the bulb will glow.

Circuit diagram with Parts list.



  • POT R2 can be used to adjust the sensitivity of the circuit.
  • You can use bulb of any wattage, provided that relay should have the sufficient rating.
  • The circuit can be powered from a regulated 9V DC power supply.
  • Click Here! to get the power supply circuit for this project.
  • The relay K1 can be a 9V SPDT relay.
  • Jaahnavi
    October 2, 2018

    hello sir. can i get the full report of this project? i need as the reference to my project.

  • John
    August 31, 2018

    Send me the list of components and their specification for automatic street light, especially the relay used in the circuit

  • kavya
    December 28, 2016

    I am ready to do the project. Can I know the full details of the project

  • umakanta
    April 24, 2016

    Sir, kindly pliz sent me the full detail of the circuit diagram so as i can make a project on for my daughter. pliz explain me in a simplist way so that i can made

  • Rabindranath Mukhopadhyay
    October 28, 2015

    Please state what is the variation in the diagram and components in regards of different load

  • Nagendra Kumar
    October 21, 2015

    Dear sir
    I have made this circuit but relay is not connect properly. relay do fluctuation
    please help me what can i do for issue

    Nagendra Kumar.

  • mahesh
    September 3, 2015

    please tell me what are the components required for street light circuit,send the details about the components and the circuit diagram for designing

  • AsiahFarnan
    June 18, 2015

    hello sir. can i get the full report of this project? i need as the reference to my final year project. May we use the fully circuit diagram of this project using the arduino? You can email me at : Thankyou for replying me. (:

      May 8, 2017


  • John Ong
    April 24, 2015

    Hi sir, can i get the full report for me as a reference ?

  • Bayo
    March 27, 2015

    is it not possible to have the circuit work with a 9v battery or possibly 12v cos I am just looking at the circuit to be independent of mains supply?? I want a Circuit that’s independent of mains, please say something about the request?

  • Gowtham. A
    March 24, 2015

    Hi sir.
    I am a student of diploma in electricals and electronics 4th sem. i need the project related to human counting and fan and light control. please help me getting this project. It should include content sheet, circuit diagrams, introduction, brief explaination of parts, applications, advantages and disadvantages, final conclusion.

  • adeelsafdar
    March 18, 2015

    sir i m a student of electrical engineering 6th semester;;;; i m interestd in that project; i want the circuit ,block diagram of that project as well as applications

  • adeelsafdar
    March 18, 2015


  • February 24, 2015

    does that spdt changes/rectify ac signals to dc signals???

  • Gaurav K Parashar
    February 5, 2015

    can we construct this circuit on the bread board or do we need any other medium to construct it.

  • zohra amreen
    January 1, 2015

    please send me the apparatus required, its specifications, principle used along with all the details exactly in the way the project must be written to my email I’d
    thanks for assistance

  • parimal maji
    December 25, 2014

    what build 100w lamp on and off with clap?

  • bhupesh
    December 21, 2014

    i want to know the name of the parts which are used in the automatic street light of 230 volts bulb, plz reply

  • syaza
    December 19, 2014

    can you please email me full detail of this project ?

  • Preeti
    November 1, 2014

    i need full details of this project.

  • Francis
    October 15, 2014

    Why is the circuit includes a 9v dc? What is it for? Can i eliminate it if i want to create the project?

    September 20, 2014


    • Mayur Bhalshankar
      October 18, 2014

      it is not so expensive.
      you can do it within 100 rupees.

  • September 3, 2014

    Prplease send me catv stb schematic diagram with desciption.

  • kiran
    August 7, 2014

    i want full informatiom about this projest plz send as posible as early

  • Kisho
    May 16, 2014

    To make a working clap switch .Sir, i have no facilitys to watch videos on youtube, so can please send me the circute diagrame and the camponants with valus wanted to make the circute please sir. It is very urgent to me to make a exhibit to my school anual exhibition so please help me sir.Please

  • Kisho
    May 16, 2014

    Sir, i have no facilitys to watch videos on youtube, so can please send me the circute diagrame and the camponants with valus wanted to make the circute please sir. It is very urgent to me to make a exhibit to my school anual exhibition so please help me sir.Please

  • Ramkisan kumawat
    May 9, 2014


  • Danial
    May 4, 2014

    I couldn’t find bc107 and sl100 transistors. Please tell me their alternatives.

  • Neha
    May 1, 2014

    Can u send me ckt diagram of that using led instead of bulb

  • Neha
    April 30, 2014

    Can u plz give me the connection of spdt relay…
    Sir I am using 12V supply and 12 V spdt relay without modifying any components…is it ok..??

    • June 25, 2014

      madam there is five terminals of relay system. three terminal side is used for output, while the other in between two terminals of output is used as common. which is used to connect anyone terminal of input terminals.

  • srikanth
    April 25, 2014

    hello sir , we are doing project on ip encryptors, in this when one encryptor gone bad, other one should come into the action that is the theam. so we are using relay circuitry for shifting the control signal when encryptor fails to boot,so to drive that control signal we are using driver ic, but we are in confusion, where to place that ic, wheater before the relay or after the relay. please send your reply to mail !!!!!!!!!!!!!!!!

  • April 18, 2014

    i have more details adout street light circuit

    • Surjeet
      June 30, 2014

      can u give me info about the components needed in ths ckt and also the cost for each component i will be vry thankful to you.

  • sravan
    March 25, 2014

    i want to efficient power saver for street lights using ldr,rtc,leds light with solar power ppt pdf send to( sir

  • garry
    February 28, 2014

    can we use this circuit on 12v supply because i have 12v relay ?????

  • February 20, 2014

    Sir,i need complete working procedure of this project,pls do reply.

  • ashish
    February 17, 2014

    can any one give the pcb layout of this circuit

  • arpan
    February 16, 2014

    sir please give me full description about the whole circuit thanks

  • December 25, 2013

    wouldn’t using an op-amp give a better accuracy?

    • Seetharaman
      December 26, 2013

      Here accuracy is not very important as the circuit is only a binary control if it measuring analog information and calculating then an opamp is a must. for this circuit approximate light intensity is used for changeover which can be set by trial and error by the pot.

  • Archana
    December 17, 2013

    we want to use micro-controller in this circuit and also want to replace bulb by LED.So what will be the estimated cost of this project? and what modifications will be required?Plz reply fast…

    • Seetharaman
      December 23, 2013

      No need to make the circuit complicated by micro control etc. the circuit is very simple and fail safe with very few components. You can use the relay’s potential free contact to switch on anything

      • yadhvi
        November 1, 2014

        seetha ram sir can u pls give ur mail id…I need a help from u

      • Manirathnam
        July 17, 2015

        sir, i am a college student. i just want to do this project. i had a doubt that how the voltage drop occurs with the LDR device. can you please explain it sir. by connecting what device the voltage drop may occurs. please reply me sir. and i need your mail id to contact you.. please….

  • Tanvi
    October 25, 2013

    plz give me layout of street light mini project…..:-)

  • omjee kr
    October 16, 2013

    it is nice circuit.

  • vennela
    October 13, 2013

    plz sir we want full details and description on this topic plz… sir…

  • felistus
    October 5, 2013

    hi pliz may you email me the calculations involved in choosing size of resistors, capasitors and transistors. Im doing a school project on this topic. Your help will be greatly appreciated

  • Tridip Sarma
    September 24, 2013

    i want to project report of the circuit… i want its working principle in details… like how transformer BC107 and SL100 works… why relay is used.. and it is also work in above 9v supply… if not then why we used like that… and i also want to components specifications in details… and also uses in practical field… and also advantage, disadvantage and conclusion…

  • snehu
    September 24, 2013

    i have to design this project as soon as possible on pcb. plz help me for circuit diagram n pcb layout

  • September 10, 2013

    i selected this as my minor project.
    so plz send me the clear description of this project.
    it was urjent for me,so i wish u will send replay soon.

  • Sulakshana
    September 3, 2013

    Can we get the components required easily in market?

  • Pradeep Kumar
    September 3, 2013

    How to made solar led circuit mini project. what are neccessary equipment to made it and how & where we will get these equipment.

  • surbhi varshney
    August 29, 2013

    pls provide synopsis

  • rahul
    August 3, 2013

    so simple ,explain the workings


  • August 1, 2013

    please give me full discription in this project please sir its urgent

  • July 16, 2013

    Project is so simple and interesting. if any one want to get more information about working of circuit, contact me

    • faseeh janjua
      October 20, 2013

      can I use bc 548 ..insted of bc107??

  • chandhru
    July 15, 2013

    nice commands thanks

    June 15, 2013

    PLZ send me datasheet o0 9v SPDT relay

  • Gautam
    April 17, 2013

    I am working on the project of automated street light controller using LDR.
    My project is almost done but i have to sumbit a project report on the same and there is very little information about this topic.
    Can u please help me with it.

    • Punit sharma
      May 10, 2013

      Plz brother told me how i can make this project its so urgent

  • Avinash reddy
    March 30, 2013

    wow,its amaizing I have done this project by replacing that 230v ac supply with a battery of 9v and bulb with a is working thank you for your circuit.

    • sai
      September 29, 2013

      hi frnd pls send me this project details we r done this project but output is not coming means light does not glow can u send the pcb board connection for undersatnding

    • Neha
      May 1, 2014

      Can u send me ckt diagram of that

  • D.shekar
    March 24, 2013

    Sir, i take it as a mini project n started work on dis so pls send me ful descipton of dis…

  • Automatic stritelight control using ldr
    March 21, 2013

    Sir, plese me ful discription this project

  • Chandan singh
    March 1, 2013

    what is the cost of this circuit. plz replay me.

  • aarti gupta
    February 26, 2013

    sir plz help me out.
    plz send me the report of this

  • baskar
    February 24, 2013

    plz…send me the ful report of this project…..i need it quickly fr my project….

  • sahil vaid
    February 23, 2013

    hello sir it is amazing circuit but what is the value of relay when i give 230 v power supply

    February 20, 2013

    please sir could you mail me full description of the working of this circuit d the estimated costs of the various components…. i need enlightment…. thanks

  • Sahithya
    February 17, 2013

    Please send me the full report of this project.
    We have chosen and started work on this project but we didnt get the output.
    We have to submit this project by 25th.
    So please send it as soon as possible.

  • sreeram
    February 14, 2013

    we are selecting mini projects for our 6th sem(BTECH).and it is also high time for deciding on our topic.hence we would be most obliged if you could
    mail me the approximate cost and availability of the components.
    plz attach the full report also,if available.

    • arun
      March 4, 2013

      please reply me alternatly using another transisters in thise circuits. becou’s thise are not available nearly in my village (above circuit added components works surly) i take thise project in my class
      please give for more inporamtion sir

  • Mallikarjun N Sidaraddi
    February 13, 2013

    >sir why we use 9v battery in the circuit.
    althoug all the circuit is operating in AC main current,plz tell me breafely why we use battery in the circuit.
    >plz send full report plz sir.

  • rashmi gawande
    February 9, 2013

    plzzzzzz send the full report sir as soon as fast

  • Rajat Sood
    February 8, 2013

    sir, please mail me full description of this project!
    I have to make it for my presentation!!!

  • February 3, 2013

    sir,we want description about automatic street lamp circuit using relays and also applications, uses

    February 2, 2013

    Plz give me full description of SPDT relay.I want to make this as a project.

  • theju
    January 9, 2013

    sir please tell me that in which place is this “automatic street lighting controllers using ldr and relay” are using practically……

  • kavitha
    December 31, 2012

    i need to know abuot cad format for this circuit sir please reply.

  • kavitha
    December 31, 2012

    sir i need the circuit diagram in cadd format sir.. please help sir and give a detailed descpiption for this sir please.

  • Kavitha
    December 31, 2012

    sir i need a full description about the circuit diagram sir please reply sir.. and i need the circuit diagram in cadd format sir please explain about this sir please.

  • agbesi moses
    December 30, 2012


  • November 19, 2012

    You can can get exactly 9volt if you make use of step down transformer of 9Volt that’s if you want to get a proper results

  • Seetharaman
    October 26, 2012

    Hi you can use a 6 volt relay but not 12 volt relay, as the voltage across it will be around 8.4 volts may not produce sufficient magnetic pull for the relay contact to change over.

  • sagar
    October 25, 2012

    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?

  • October 22, 2012

    plz send full report plz sir

  • jitendra soni
    October 21, 2012

    can i get full description of this project.can u mail me.

  • mehboobelahi
    October 14, 2012

    sir why we use 9v battery in the circuit.
    althoug all the circuit is operating in AC main current,plz tell me breafely why we use battery in the circuit

  • rohin
    October 11, 2012 is giving so much circuit but people are not satisfy with them.they always want another circuits for their need.

  • Thnku sir for this simple project plz email me report sir plz
    October 9, 2012

    Plz email me report sir

  • October 3, 2012

    sir,we want automatic street light controller by using timer and counter.we want controlling the street light as follows,day time-6.30a.m to 6 p.m-light off,6.30 p.m to 7.30 p.m-light glows alternately,7.30 p.m to 6 a.m-light on,6 a.m-7 a.m-light glows alternately.So please send related circuit diagram,we are waiting for your circuit diagram.

  • Mrudveeka Josyula
    September 27, 2012

    sir i want full description about this circuit

  • Mrudveeka Josyula
    September 27, 2012

    sir is there any design procedure for the values of resistors ? plz post it as early as possible sir

  • Mrudveeka Josyula
    September 27, 2012

    sir can we use a solar panel instead of 9vdc supply

  • Aabha
    September 23, 2012

    gm sir
    i am student of 7th sem.i want to made this project as MINOR pls send full information like ckt diagram,block diagram,rating of elements and full description…..

  • Navatha Reddy
    September 21, 2012

    thank you sir for giving this circuit after many attempts i got this.and i want detailed description of working of this circuit to my email sir.

  • prithvi
    September 14, 2012

    what is the wiring of relay plz show me the diagram somebody plz….
    got time only until 19th

  • Prithvi
    September 14, 2012

    sir,I’m doing this project and my bulb is glowing only when the upper two terminals(2 contacts) are plz help me get output sir..n plz anybody who got the output for this, plz hello me out guys. …

  • k.siva
    September 3, 2012

    respected sir ,i want the ratings for this components like resistors and ldr etc

  • benoy
    August 25, 2012

    Dear sir
    can I use a 15w. CFL as the 230V Lamp ? /is it strictly need a BULB?

  • harish
    August 22, 2012

    sanjay what you want after getting the output

  • August 13, 2012

    i hav very short time to give seminar on this topic plz give reply sir. and i have done this project i got output also

  • sanjay
    August 13, 2012

    sir during rainy season salt formation will be there on ldr so that light will glow day time also. how can we avoid this problem?
    and how to arrange the circuit on the street light in all seasons? i want to test this by connecting it to a street light. plz give me answer sir..

  • harish
    July 29, 2012

    soumya all r there na which component u want

  • July 24, 2012

    this 1 project is very simple and easy……..4 ec student 3 rd sem….
    electronics workshop………300 costs…..

  • Soumya sk
    July 5, 2012

    Sir,i need the names of components used in street light

  • Binny
    June 22, 2012

    I want to make any intresting and easy project at my home during my summer vacations. Will you guys plz suggest me any gud1…
    I m now B.Tech 2rd year student in ECE stream….
    Plzzz guys hlp me….

  • harish
    June 15, 2012

    please sir i want full report of this circuit with power circuit also

  • harish
    June 15, 2012

    Can u suggest any additional features that can be added to the circuit above? Iā€™d be really grateful.

  • Priya
    June 11, 2012

    Can u suggest any additional features that can be added to the circuit above? I’d be really grateful.

  • Johnsheen
    June 7, 2012

    This circuit is working very well. I have connected it to a flickering Flash light. I have a Farm house where the wild Elephants are the uninvited guests. I am using Xenon flash light to threaten the Elephants as they are very bright and consume less power. Also I am going to connect a Audio system which will play during the nights creating a feeling of presence of people inside the house.

  • harish
    June 7, 2012

    i got out put sir thanks
    i want som more projects like this
    to my mail

  • Seetharaman
    June 7, 2012

    Hi Harish THE PROBLEM MAY BE WITH YOUR ldr. WHAT IS THE DARK AND DAYLIGHT VALUES OF THE LDR. You can use 220k or 470k instead of 100k if your LDR values are high. To check whether the electronics is OK. disconnect LDR and fix a 47K resistance. now turn the pot from one end to other, at one point of the pot, the change should occur(relay energising and de energising). if it is not happening your wiring is wrong may be c b e is wrongly connected or may be the transistors are defective. connect a diode 1N4007 in parallel with the relay such that diode anode is conncted to 9vlt positive bus to protect Q2.

  • harish
    June 6, 2012

    reply me sir it tooo urgent for me mr seetharaman

  • harish
    June 6, 2012

    tha lamp glowing even though the light on ldr what is the problem sir

  • harish
    June 6, 2012

    can we use any resistor instead of 100 k preset

  • harish
    June 6, 2012

    its too urgent for me sir

  • harish
    June 6, 2012

    sir i got out put bt the lamp glowing allways even though i changed a intensity of lamp on ldr

  • harish
    June 6, 2012

    how much should be the preset

  • harish
    June 6, 2012

    seetharaman sir sir am given total connections same as ckt bt am not getting out put

  • harish
    June 6, 2012

    sir please help me i am not getting correct relay connections

  • k.anil varma
    May 18, 2012


  • pank
    May 17, 2012

    hello sir
    i want to apply the things which is wrote there…
    can you tell me the required items with specific details…
    also approximate cost in making it…

    i will be very much thankful to you…
    for your help….

  • pank
    May 17, 2012

    hello sir
    i want to apply the things which is wrote there…

    can you tell me the required items with specific details…
    also approximate cost in making it…

    and more clear diagram concept…

    i will be very much thankful to you
    for your help….

  • Seetharaman
    April 19, 2012

    Hi Jainson increase the supply voltage to 12 volt DC regulated one capable of atleast 300mA. you have to provide a black tube of 6 to 8″ in length on the LDR such that it looks at open sky without getting the rays from the nearby light sources. The circuit is quite reliable and it works nicely.

  • olawale
    April 18, 2012

    please i want to know more about projects on automatic street ligth.

  • Jainson
    April 16, 2012

    i made d project … the relay dnt gets switched with change in intensity of light….i used 12v relay….plz help

  • Kayode olawale micheal
    April 7, 2012

    Please can i get the write up for this project?

  • shyam
    March 13, 2012


    Could u give the relay specifications..


  • Tete Erastus Focho
    March 9, 2012

    very impressed sir, need material to start my work. thanks to your inspiration. hope in times to come i will really make good use of your infos

    best regards

  • Enayat
    February 18, 2012

    Sir, I need the names of components used in automatic street light

  • Amar
    February 2, 2012

    Respected Sir, can i use IR sensor for automatic street light? How?

  • amol
    January 17, 2012

    sir i need to use microcontrooler in the circuit….plz help me

  • manali
    January 4, 2012

    hi! is 100K preset value of R2 or it is a set value??? if it is not then what is the set value???

  • December 24, 2011

    sir, we require an automatic street light circuit using ldr and npn transistors in darlington connection &relay .please send us the report.

  • sharon
    December 3, 2011

    i want to inverter diagrom

  • seetharaman
    November 19, 2011

    Hi Ram SPDT is singe pole double throw contact, nothing but a relay with a change over contact. (volt DC is the supply for the circuit to operate. It should have been shown as 9vols DC plus (+9volts) and negative to common shown as ground (emitter of Q1 & Q2).

  • ram
    November 19, 2011

    iam not able to understand about SPDT relay and 9V dc plz give me the clarification

  • Thenmozhi
    October 20, 2011

    pls suggest me component for ldr and pot resistor to simulate this circuit in pspice

  • Taofik
    October 17, 2011

    Sir, pls help discuss on the issue of the movement detector. PLEASE!

  • Taofik
    October 12, 2011

    Sir, I haven’t heard from you yet. PLS IT’S URGENT!

  • seetharaman
    October 11, 2011

    Hi Ishan you can use 2N2222, 2N2221, 8050, 2N1711, BC167, BC237, BC317 any NPN small signal transistor can be used.

  • Ishan
    October 8, 2011

    Sir, It’s not possible to find BC 107 in my country. is there any other equivalent transistor for this BC 107 ? thanks

  • Taofik
    October 6, 2011

    Infact how do we go about the movement detector circuit? what form of sensor can be best used? should it be sound or metal or what? pls it’s urgent.

  • Taofik
    October 6, 2011

    Owing to your comment on August 13th, I would like you to please send a circuit that will give room for a movement detector in your circuit, such that during off peak periods say after 10pm, the illumination will be reduced or using the 50% idea as u’ve said, but whenever an obstacle gets nearer, it gives full illumination or 100%.

    my email add:
    Pls it’s urgent.

  • seetharaman
    September 16, 2011

    Hi Luckydile 220uF will be a very large value delay will be larger, still you can try. if 4.7uF is available you can try.

  • Luckydile
    September 13, 2011

    sir pls,i’ve got this topic as a,the 10microfarad 12V capacitor u added to cut off transient responses is not available around here.pls tel me another capacitor that wil do the job or wil 220microfarad 16V capacitor do? Thank you sir.

  • Luckydile
    September 13, 2011

    pls sir,i’ve got this topic as a,the 10microfarad 12V capacitor u added to cut off transient responses is not available around here.pls tel me another capacitor that wil do the job or wil 220microfarad 16V capacitor do? Thanks so much.

  • September 8, 2011

    sir i am student of electronics engineering i have need component of the ultrasonic motion detector.

  • September 5, 2011


  • seetharaman
    September 2, 2011

    Hi James you can connect 2nos hi bright white LEDs in series and a resistance of 47 ohms 1/4 watt also in series connect them in place of the relay shown, such that anode of LED is towards 9 volt +ve.

  • September 1, 2011

    Hi there, great circuit! Can the relay be swapped for an LED. If so which way will it be connected?


  • seetharaman
    August 24, 2011

    Hi Kecik you can but the circuit will not work if you shout near microphone the relay at the most can chatter, that is all.

  • KecikSpoon
    August 23, 2011

    sir, can i change the LDR to electret microphone.???

  • seetharaman
    August 13, 2011

    Hi Nandita for traffic sensing you can use Doppler Shift sensing method or IR movement detector or any movement detector. To avoid special circuits for florescent light dimming, use two lights in each fitting you need switch off one for 50% illumination. for switching you can use SSR or standard mechanical relays. You use a dark detector during dusk switch on both the lights after 4 hours it will switch off one light and with movement detector it can come on. once no movement is detected it will again switch off. during dawn both will go off. This will work when suddenly it becomes dark even during day time due to dark clouds

  • Nandita
    August 12, 2011

    Sir, Im a final year Btech student, and would like to do an extension of this project. ie..The streetlight is fully bright during the peak hours of traffic, say from 6pm to 10pm.After 10pm it automatically goes to a power saving mode with 50% brightness, and then when a vehicle or pedestrian approaches, it again goes to 100% brightness. Hoping for your valuable suggestions.

  • bharadwaj
    July 31, 2011

    give the circuit for mobile controlled street light system………….?????????

  • eswar
    July 9, 2011

    thank you sir, this very useful circuit to me .i have more intrest about electronic projects .

  • VG Krishna, Hyderabad
    June 19, 2011

    Sir, I assembled the above circuit along with the additions suggested by Sri Seetharaman (May 14, 2011 above -to avoid chattering and transient response)and using the light in my courtyard and it is working excellent. Whenever we go out (by locking the house) we switch it on and by the time we return during night, the light automatically is on during dusk. Very good facility and security to the house. The circuit is simple and better than other circuits which use a Triac (I also assembled the same) wherein I find lot of flicker in the incandescent light during the transition period(day/night). I Thank Circuitstoday for giving the above circuit.

  • Abhijan
    June 9, 2011

    Thank you sir, Thanks a lot!! šŸ™‚

  • Seetharaman
    June 2, 2011

    Hi Abhijan Pl refer my comment dated 28th April. Adjust R2 for you requirement. If you want small delay you can add a capacitor of 10 to 100uF between Q2 base and common ground. If you want to have a small difference in light level between switching on and off add a 100k resistance between Q2 collector and Q1 base.

  • Abhijan
    June 1, 2011

    Hello sir. The circuit is really helpful. I had a doubt though. I have a 12V bulb and a DC supply from the battery of the vehicle itself. How can I modify this circuit so that I can use the LDR system to automatically switch on the light with decrease in Visible light!

  • Seetharaman
    May 14, 2011

    Hi Edwardson you are right you can fix a 10uF 12 volt capacitor in parallel to R2 that will take care of transient response. This simple circuit itself is having enough hysteresis hence chattering will not be a problem. Still if you feel it is not sufficient can add around 1M resistance between Q2 collector and Q1 base.

  • Edwardson
    May 12, 2011

    Correct me if I’m mistaken but this circuit seems to be prone to at least two conditions:

    1. “chattering” — when ambient light level is at or crossing the trip point, the relay/load can rapidly switch on and off, the reason being that there’s no hysteresis built into the circuit. For better performance the ambient light level at which the load is switched on will be slightly lower than the level at which it is switched off.

    2. abrupt, transient, and large changes in ambient light level will “fool” the circuit into switching the load on/off. Example: during the night, lightning and car head lamps might make the circuit turn off the load for the duration of the high ambient light level. So there’s a need for a low pass filter to make the circuit reject these transients. A simple RC network connected to the base of Q1 might be sufficient.

  • May 5, 2011

    thanks macha.

  • Seetharaman
    April 28, 2011

    Hi Mouly no change is required you can increase the supply voltage to 12volt with 12 volt relay.

  • Mouly
    April 27, 2011

    Dear Sir,i can only find 12v relay in my place.Can i use 12v relay?any changes should i make in the circuit.Waiting for reply

  • ifeanyi
    April 26, 2011

    i am a final year student,i was given a project on the design of a street light using a low energy LED i dont know how to get the circuit diagram and also the procedure to follow in actualising the project.plz if you can help me with the circuit diagram send it to my email i need it urgently thank you in address:-

  • Seetharaman
    April 21, 2011

    Hi Rajashree + of nine volt is given to line indicated as 9V DC. – is given to the common shown as ground. BC 107 is a small signal NPN transistor in T018 casing. SL100 is a medium power medium current transistor in T05 casing. Since the relay used is 9volt the supply also should be minimum 9 volt to operate it.

  • Rajashree
    April 20, 2011

    Please tell me how 9v dc supply is given? And about sl 100 and bc 107? Why it is used and their properties? Please give the calculations of 9v dc suply to the circuit.

  • pranab mandal
    April 13, 2011

    sir how can i connect relay in my ckt

  • Seetharaman
    March 2, 2011

    Hi Deepanshu Q1 is sensing comparator and Q2 is relay driver.When the light is falling on LDR it resistance becomes low biasing Q1. it conducts the base bias available for Q2 through R3. Q2 stops conducting and the relay is switched off. once the light falling on LDR reduces its resistance increased reducing the bias for Q1 and stops conduction. since Q1 is not conducting the bias for Q2 is made available, the relay conducts and the light is switched on. The light sensitive level to operate the relay can be adjusted with preset R2.

  • deepanshu
    March 1, 2011

    sir,i m a ist year student…i want to know wat is the need of transistors in the above circuit…if possible,please send me details about the working of these two transistors….w8ing 4 ur reply..
    thank you

  • Navas basheer
    February 23, 2011

    hi,i am doing a project on this same topic with an extension that it has an automatic intensity control circuit. the brightness must be adjusted when any car or object passes the street light..waiting for your valuable suggestion šŸ™‚

  • val
    February 2, 2011

    sir what is the replacement of bc 107 and sl 100… wala kc mabili d2 na ganyan

    • admin
      February 2, 2011

      BC107 = 2N2222 = BC548

      SL100 = BD139 = BD135

  • melkamu
    January 14, 2011

    i need the connection diagram of led street light b/c i need it to done in my country b/c as my country is a developing country and we use high power consumption lamp and they have not longer life so please tell me how to done this.
    thank you

  • Balu Bhargav
    January 11, 2011

    Sir can we design an intelligent street light controller which switches itself on when a vehicle is detected? and then switches off by itself after the vehicle passes away?

  • shaivya
    November 30, 2010

    i used ur ckt n developed a ckt of automatic car headlight dipper…
    thnx 4 uploading ur ckt….
    having minor viva tomorrow…
    will tell u how it went related 2 ur ckt…

    November 22, 2010

    sir ,
    when a light falls on ldr its resistance increase and current increases then ldr has high resistance in the absence of light
    then how the street light works

  • Seetharaman
    November 14, 2010

    Hi Vikas 230volt AC to 15 volts SMPS are available in the market at reasonable cost. you can buy that and use with LED circuit. (why you require 15volts for the LED ?). can you kindly elaborate your requirement

    November 13, 2010

    Sir i am polytechnic stud. plese give me complyt cicuit diagram and project report to street light to 230 volt ac and pass to 15 volt dc supply for led

  • Ramesh
    August 23, 2010

    Sir, I am doing my diploma in industrial electrical, I have to make diagram using Contactor, RCD or MCB, Timer for automatic switch on, six 400 watt flood lights,

  • seetharaman
    August 22, 2010

    Hi bu i am just back from my pilgrimage you can use 2N2218 2N2219 BD135, 2N1711 any medium power NPN T05 casing or T0220 casing transistor will do.

  • abu
    August 21, 2010

    pa ada alternatif SL 100

  • abu
    August 21, 2010

    Is there any alternatif for SL100?

  • abu Farih
    August 19, 2010

    tanya ke seetharaman
    pa ada ganti tuk SL 100,thanks

  • nafzy
    August 4, 2010

    this project can make base on microcontroller?

  • naufil
    August 3, 2010

    respected sir can we make this project(microcontroller base street light control )?
    if yes than how to implement it?give some brief information about circuit diagram?
    i look forward for positive speedy reply.thanking you. sir it’s urgent.

  • July 13, 2010

    can i use a single automatic switch for the whole street lightings? what type of sensor will i use? thanks in advance..

  • Ivan
    July 6, 2010


    Only 12v relay is available in our area so what modifications has to be done to make the circuit work with a 12v power supply.


  • chidiebere madubuko
    June 17, 2010

    how i mine going to use the street light to light up 15 point of light 200watt each.

  • Yogi
    June 13, 2010

    Sir, Thank you very much for this circuit. I am a first year BTEC student. I have a question regarding the nine volts voltage applied in the light-detecting bit of the system. It is: How does the street light in our roads actually access a 9v supply? Do they use a step-down transformer and rectifier? Thank you sir.

  • seetharaman
    March 23, 2010

    Hi Sunita You can use the Dew sensitive switch appeared in this column in “Circuits Today”(which uses LM358 dual OP amp). You can modify the circuit and use. Instead of using dew sensor replace it with LDR. output you can use an opto-coupled triac to control the Street Lighting. If you have any doubt please contact.

  • March 23, 2010

    sir,i am the student of B Tech 2nd year, I gonna do a mini project of topic ‘Automatic Street Light Switching Device’. I am using an integrated circuit ICLM358. sir please design the circuit diagram using this IC.

  • March 12, 2010

    sir, thanks for the circuit, I have made a prototype of street light circuit for our project, and guess what? I got the highest grade in our class. thank you very much sir!

    March 7, 2010

    sir its so interesting……………..think you………..

  • March 3, 2010

    sir?can I use 220v AC source, instead of 230v? thank you…

  • jenny
    August 29, 2009

    Can I model the street lighting circuit using pspice?

  • July 16, 2009

    How can we get a 9v DC in street lighting system which is totally working in ac supply. Is there any method to generate 9v Dc from universal ac mains 110-230 Vac without any resistor losses and heating issues. kindly help me.

    February 26, 2009

    sir please tell me which relay i can use

    • admin
      March 3, 2009

      Author: The value of relay is added in the notes.thanks for pointing out.

      • mehboobelahi
        October 14, 2012

        sir why we use 9v battery in the circuit.
        althoug all the circuit is operating in AC main current,plz tell me breafely why we use battery in the circuit.

        • January 24, 2013

          sir this circuit be play.

        • nakul
          May 2, 2013

          respected sir
          my self nakul gaba , a student of ECE diploma 4th semester.
          i have selected this project for my minor project work and i successfully made it but the probelum is about project report ……..please kindly send me the complete project report of this topic on my email id.
          i am very thankful to circuitstoday for my project ,thank you .

          • January 1, 2014


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