How do Microwave and PIR sensors work?


These motion detectors emit microwave signals and measure the time taken for the signal to be reflected back to the sensor, this is known as the echo time. The echo time is used to calculate the distances from all the stationary objects in the detection zone, to establish a baseline to work from. A person moving into the detection zone causes a disruption in the microwave beam, changing the echo time and triggering the lights.


These sensors detect heat. They do this by measuring the ambient temperature of the room using several detection beams. When a difference in temperature is detected by one of the beams, the sensor is activated, switching on the lights. When all the beams sense the same temperature again, the lights will switch off.

PIR Detection Range Diagram

A Comparison

When choosing the best sensor for your application, there are many aspects to take into account;

Sensitivity Under sensitive in higher background temperatures.
Over sensitive in lower temperatures.
Consistent detection over all temperatures.
DetectionCan be insensitive when walking directly towards the sensor.Can sense movement through walls.



Tri-Sensor PIR

As mentioned above, a standard PIR operates differently at different temperatures, not triggering when it gets hotter but in the colder months triggering for every small, distant, movement.

To combat the PIRs temperature detection fault, Green Lighting developed a PIR sensor with Tri-Sensor Technology. The P-Lux LED Lantern Range, incorporates a sensor that combines a PIR with a thermometer, allowing the lantern to automatically adjust the PIRs sensitivity depending on the ambient temperature.

This, combined with a photocell and the Lux-Up, Lux-Down feature of the P-Lux, makes these lanterns some of the best on the market, functioning perfectly all year round.

For more information on the P-Lux range, why not have a read of our Product Focus blog?


Adjustable Microwave Sensors

To combat Microwaves Sensors tendency to be overly sensitive, we have developed a fitting that can be adjusted to suit your personal needs. This Microwave Ceiling Bulkhead has been manufactured so that it can detect movement from any angle from a distance of up to 6m, with a sensitivity which can be adjusted easily with the flick of a switch. This fitting also incorporates a photocell which, thanks to its easily customisable settings, can be altered to react to difference light levels to fit its desired purpose. This fitting has been designed so it is only on when it needs to be, saving energy and, therefore, money for the end user.


  • Hi there hope you can help me,at the moment I have a outside light with a sensor added to it,the sensor is in a ceiling in a porch so no rain can go on keeps going on & off,I’ve adjusted the dusk to dawn to no change.
    All I want is this light to come on when I approach the front door to see the the key hole.
    Can you tell me the best sensor (ceiling one) I need outside please. Thank you Barry

  • I believe I need a Microwave sensor floodlight for the inside of our double garage. The sensor needs to pick up and trigger inside when the up and over door/s start to open, so that they will light the garage to drive into. Previously having tried a PIR sensor light, this would not notice the cold doors opening. Am I correct in my thinking. Also I wish to have the sensor pointed at the doors just inside, but the light shining into the garage in almost opposite direction. I needs to be bright, possibly 50 watt 4-6000 Kelvin, would this work?

    • Hi Malcolm,
      It does sound like a microwave sensor would be the correct choice for you. A microwave sensor should be sensitive enough to pick up the movement of the doors while facing into the garage. You could also use an external microwave sensor and link this to lights in your garage. As for brightness and colour temperature, that will depend entirely on the job itself. I hope this helps.

  • Hi I have installed a number of pirs to a security lighting circuit. I keep getting constant triggering. I feel the ir illuminators of the CCTV cameras could be causing this.
    Do you offer a black stand alone microwave sensor?
    Thanks Chris

    • Hi Chris,

      From what you’ve described it’s possible that the illuminators of the CCTV cameras could be triggering the PIRs of your security lighting.

      Unfortunately, we don’t at this time offer a black microwave sensor at this time. Your best bet would probably be an electrical wholesaler, who would be able to source that for you.

      Kind regards,

  • Would you recommend fitting a light with built in microwave sensor to an outside wall, would there be a problem that the sensor will be prone to triggering off from small trees and bushes moving in the wind and the sensor facing the wrong angle?

    • Hi Dave,

      I’ve checked with our technical team and there wouldn’t be an issue with the sensor facing the wrong angle. They did say however that there would be a chance that small movements from trees and bushes could affect it.

      If you’ve got any further questions, please don’t hesitate to ask.

      Kind regards,

  • Hi, I have a hotel with 40+ corridor lights in public and staff areas, each currently consuming 18w 24 hours a day (About 17.25 Kw) My questions are

    1… Could I replace these lights with lighting with Microwave detectors that would turn the lights on as guests and staff walk into the corridors and off as they leave?

    2 .. Would they be sensitive enough to trigger say when a guest opens their bedroom door to light the corridor before they leave their room ?

    3.. Can they be set to remain on for long enough for the guest to exit the corridors into their rooms?

    4.. How reliable are the detectors as obviously if they don’t come on their are health and safety issues.

    • Hi Steve,

      1. You could replace your current lighting with ones with inbuilt microwave sensors that would fit your requirements.
      2. Our microwave lighting has a detection area of up to 12m x 6m, so would be able to pick someone up as they open their room door to leave.
      3. These fittings also have adjustable hold time (how long it remains on for) which has the following options; 5s, 30s, 90s, 3 mins, 20 mins and 30 mins. I’d imagine either 90s or 3 mins would be suitable for your requirements.
      4. We supply these to housing developers who use them in corridors in blocks of flats and they have proven reliable in that application since we launched the product.

      I’ve added the link for our microwave lights for you to browse above, which includes a datasheet and fitting instructions, the latter details the adjustable settings for the fitting on page 3.

      If you require any further help, please don’t hesitate to contact me. If our corridor light fits your requirements, you can use discount code ALEX15 if purchasing online.

      Kind regards,

  • Hello, I am looking to replace my fluorescent T8 tube figments in my carports with LED. At present I have twin 6ft 70w fluorescent tubes in each car port, housed in a weatherproof IP65 ceiling-mounted fitment. What LED tubes can you recommend and what would you recommend as a suitable fitting ? I’m looking for something of good quality and comes with built-in microwave sensor, assuming microwave would be more suitable than PIR. Thanks, Peter

    • Hi Peter,

      For what you’re using your current fittings for, you are correct in saying that microwave would be best. We don’t currently have either T8 tubes or a suitable fitting on our website but I can send you across datasheets for both if you email

      Kind regards,

  • I’m looking for a high penetration long range (10m) microwave sensor to be placed under a desk to detect the occupancy of a row of workstations. As I need the data to be transmitted to a gateway via Zigbee HA1.2, I will feed the 230VAC output to the input of a Zigbee relay. The relay will then update the gateway. Do u have a microwave sensor fit for this purpose?

    • Hi Edwin,

      Unfortunately we don’t have any products in our range that would be suitable for the requirements you have.

      Kind regards,

  • Hi

    I have a standard pir sensor in the garden switching 4 outside lights around my garage. It’s over sensitive and is switching to the movement of the washing line and garden bushes etc. What sensor could you recommend that only reacts to a human presence. Kind regards

    • Hi Gareth,

      A PIR would be most suitable for what you’ve described. To avoid the issues you’re having currently I would recommend either relocating your PIR sensor if at all possible so that it doesn’t sense the washing line and garden bushes or alternatively source a PIR that you can alter the settings on to be able to adjust it to suit your requirements.

      Kind regards,

  • Had my garden sheds broke into the other week. CCTV captured the toe rags in the act however I had no security lighting and the footage on the CCTV was too grainy for positive ID. Since I have placed an Enlite FLH50p/40 floodlight this is bright enough illuminating the shed adequately but the PIR seems only to be active within 8 meters, from its position 2.9meters above the ground .. My shed and garden fence are 12.5 meters from the PIR. (4.5 meters short in the killing zone) Another point we get a lot of false triggering day and night time… The neighbours have tall shrubs either side of my garden. The garden width 7 meters from fence to fence. I have placed masking tape on either side of the PIR cover to narrow the beam somewhat but it still triggers… is there a PIR that would cover the distance required or is PIR sensors like ripples on a pond strong around the sensor and gradually getting weaker the further away from the sensor they travel. Would a microwave PIR help me in the distance and false triggering issues
    All measurements given are correct just been out and measured up.
    Thank you,

    • Hi Keith,

      Sorry to hear that your shed was broken in to the other week.

      With the detection range I know with our products with a PIR, the higher they’re mounted the shorter the detection range becomes. So I would say that this might be the same with the product you’ve fitted but as it’s not one of ours I can’t say with 100% certainty.

      Have you adjusted the settings on the floodlight at all? I’ve researched the product you mentioned and it looks like there are dials on the back of the fitting which allow you to adjust PIR sensitivity, light level the fitting will activate and also how long it’s on for. We have similar on our floodlights and adjusting the sensitivity and light level settings should hopefully reduce the issues you’re currently having.

      I hope this has helped and if you have any more questions please don’t hesitate to ask me.

      Kind regards,

  • Really this post is best & creative. I read your full article this is good and excited. Thank you for share this information. Hi I have installed a number of pirs to a security lighting circuit. I keep getting constant triggering. I feel the ir illuminators of the CCTV cameras could be causing this. Do you offer a black stand alone microwave sensor?

    • Hi Hossain,

      Thank you for the positive feedback on this post.

      Regarding a stand alone microwave sensor, unfortunately this isn’t something we do I’m afraid.

      Kind regards,

  • Hi
    I have a pir situated about 4 meters and side on from a gas flue. Naturally in winter this can be triggered if the wind is blowing in the wrong direction. Would fitting a microwave detector prevent spurious triggering?


    • Hi Simon,

      I’ve had a look into this for you and I think a microwave sensor would prevent the issues you’re having. Alternatively, you could use a light and wire a separate PIR sensor in and locate it in a different location to avoid false triggering.

      Kind regards,

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