motion light circuit

Motion-Sensing Security Light

Fascinating electronics hobby circuit, Tricky Security Light, presented here is nothing but a motion sensing security light built around one commonly-available passive infrared sensor (PIR) module. A motion-sensing light is one that is activated by a motion sensor rather than by a conventional light switch. Motion-sensing lights are great for lighting areas that you only use briefly, since they only stay on as long as you need. By automatically turning off after a few minutes, they prevent wasted electricity and help conserve energy resources. Besides, motion-sensing lights for your home are great deterrents from burglars, who are startled by the sudden illumination and may believe someone awakes inside the home.

motion sensing security light Alas, I cannot offer such great ‘green’ benefits with my design because this is only a funny/tricky gizmo to throw all night-invaders in the deep of trouble. Don’t panic! Please be patient, and let me describe the working of this security light. When powered, it instantly switch on the white light source to illuminate its surroundings, for example the corridor, stairway, backyard, garage, etc (nothing more happens in this standby mode). However, if the motion sensor detects a motion, the light source shuts off gradually, and revert to its initial state within a finite time after the last detected movement. No doubt, the unexpected darkness followed by another sudden illumination will hamper the invader.

motion light circuit

As can seen in the circuit diagram, the electronics is very simple and straight forward. In the prototype, only one white LED (3.6V/1W) is used as the light source. After construction, the whole circuit should be housed in a suitable enclosure. The finished unit can be used indoors or outdoors, and can mount to either walls or ceilings of the detection area. The tricky security light can be powered from any external 12-volt dc power source with atleast 500mA output current capacity. Since the input supply is 12-volt, it is possible to connect two – three white LEDs (in series configuration) in lieu of the existing light source. No more changes required here (except in the value of resistor R5), but you should remember to increase the output current of the external 12-volt dc power source upto the actual demand.

Circuit Description

In standby mode, output from the PIR sensor module is 0V, the gate of T1 is at 0V level and T1 is off. Capacitor C1 is now charged via R2 and D1, whereupon T2 comes on so that the light source (LED1) is switched on. When PIR sensor module detects motion, T1 whose gate is linked to the PIR sensor module, cuts off T2, so that the light source turns off. However, C1 is discharged fairly slowly through R4, so that the light source is not turned off immediately (goes out slowly). This turn-off delay may be varied by altering the values of C1 and R4.

3w led

Note that, in a PIR sensor module, its output goes to high-level (near 3.3V) for a finite duration after the motion detection, and revert to low-level (0V) thereafter. This time period can be changed by adjusting the on-board potentiometer of the PIR sensor module (refer PIR sensor-related articles and tutorials published elsewhere in this website). Finally, resistor R5 limits the operating current of the light source (LED1). Prototype was tested with a 33-Ohm power resistor (33R / 3W) as R5.


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  • V.Sambath kumar

    Hi Marianne,

    Regarding the value of R1, i asked you a doubt now you are asking the same question to me. i dont know what you mean, i commented your article
    Desk top pc linear power supply circuit but you have not responded.
    no number is seen in the pir pcb ,the shop keeper told me that it is a
    infra red motion sensor.i have asked you some doubts that also you have not answered, and now your are travelling in a different route as if you want to find out some thing.

    Regards V.Sambath kumar

  • V.Sambath kumar

    Hi, Marianne,
    Let me first thank you for your feed back.
    I purchased the pir sensor from Bangalore , pin 1 vcc pin 2 D-out pin3 gnd, pirpcb come With 2 pre sets .For T2 i am using IRF540N, By mistake for R 1 i used 120 ohms Now changed to 10k it is working but the Led brightness level is not that good . what should i do.I am using PIR sensor first time.what are the uses of the presets in the pir unit.

    Regards V.Sambath kumar.

    • marianne

      Hi Sir,

      Thanks for the response. I will be using this prototype in our microscopes in our laboratory as a switch, should i increase the value of R1? For the PIR, may i know what’s the specific model of the PIR used in tthe ckt above (i.e, D203S)? Again, thanks for the response. I am hoping that my inquiries will be answered. It woukd be a big help. Thanks a lot.

  • marianne

    Hi Sir,

    May I know what kind/description on PIR sensor used in this ckt? Your response will be much appreciated. Thanks a lot!


  • V.Sambath kumar

    V.Sambath kumar,

    Hi Sir,

    Can we change R1 with a 10k or 15k preset which may help to adj the
    sensitivity of triggering signal for T1.

    Regards Sambath

  • tkhareendran

    @Raman: You can switch the electric bulb through a relay circuit driven by the motion sensor. Hope this gives you some ideas. Have a look at:

  • Peter

    looks great. I’m new to this stuff, so please bear with me! I want to illuminate a few LEDs at the same time, triggered by motion sensor but a) I only want this to happen after dark and b) I want the LEDs to illuminate slowly then go out slowly after say three minutes. Is this a straightforward enhancement to your circuit?

    Thanks in anticipation…

    • T.K.Hareendran

      @Peter: Thanks!Although this circuit is adaptable for your particular requirement, I would like to prefer a “revised” design. I will try to post the revision here in due time. Needless to say, the design and test process might take sometime and might even require multiple attempts. So please be patient. Have a nice time…

  • Susan

    Thank you sir for taking the time out to help with all the explanations and logistics of this project… It worked fantastically!!! Once again, my sincere thanks! Susan

  • T.K.Hareendran

    Recheck your wiring to ensure that all components are wired in right order. Especially the mosfet,pir sensor, etc. I will add a troubleshooting guide here to help all readers.

    • T.K.Hareendran


      It’s assumed that you are familiar with PIR sensor modules (otherwise, please read related articles published elsewhere in this website).


      After finishing the wiring, power the circuit from a 12V dc source.

      Do not connect the PIR sensor

      Ensure that LED1 lits up well

      If not, recheck the pin orientation of T2, and D1

      (If you are using an equivalent mosfet as T2, then try to change R3 to a lower value, for example 10K)

      If everything upto this is okay, then attach the pir sensor

      Output of the pir sensor in active state is near 3.3v. Check the same.

      If LED1 not goes out after a little delay during the motion detection, check the pin orientation of T1 and/or remove resistor R1 from the circuit. If the circuit is working well now, you can continue without R1.

      Normally, LED1 always lights up and goes off when a motion is sensed by the pir sensor. You may need to adjust the “delay” and “sensitivity” pots of the pir sensor for better performance.

      If you are using near-similar or equivalent components to build the circuit, performance may be erratic!

    • Susan

      Thank you so much… I rechecked my wiring. The PIR sensor works but the white light stays on… It does not dim…

  • Susan

    Hi Sir, I have built this on a breadboard. I have been unable to turn this light on and have redone the circuitry a couple of times. I was hoping you can look this over to see if I have made a mistake or did something improperly.

    Thanks, Susan

  • Pradeep

    OK sir I refer hall arrival then after contact you if any quary.

    • Pradeep

      I refer hall circular. I have correctly install all parts and our MODULE as mentioned in circular but as mention light is not perfectly off when motion is not detected ( the unit is on as low lighting all time and when any motion detection it glow to bright lighting)

      Please help to correct it.

      Thanking you,


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