February 26th, 2020 by Chris Chapman

There are plenty of different motion-sensitive lights on the market right now, and it’s easy to see why. They’re used to reduce wasted energy at businesses by ensuring the lights go out when there’s nobody around, and they can also make great security lights for homeowners. Many people don’t realise that there are actually two very different kinds of motion detection which work in very different ways. Knowing the difference between them could help you make the right choice when you’re looking at new lighting – this article will explain how they work and what the best places to use them are.

Benefits of Motion Sensor Lighting

The most common use of motion-sensitive lights is as security lights. They’re installed in gardens up and down the country to protect homeowners, as well as in car parks and building sites. These models tend to be high-powered floodlights which instantly light up a wide area. However, motion detectors are also installed in smaller, less powerful indoor lights as well.

Indoor motion-sensitive lights can be used to reduce the amount of energy you waste at work. They’ll only turn on when somebody is using the room, and there’s no need to worry about forgetting to turn them off. If you have a stairwell or a corridor that doesn’t need to be lit all day, installing lighting with motion sensors is a guaranteed way to slash your energy costs.

PIR Sensors

PIR stands for passive infrared. It uses an infrared sensor which constantly monitors everything within range. The sensor is made with two small slots in it, which you can think of as its eyes. When nothing is moving in front of the sensor, both ‘eyes’ pick up the same amount of infrared radiation. When a warm body enters the sensor’s field of view, one of the eyes will pick up the movement before the other one. This means the two eyes are picking up different heat signatures, so the sensor knows something is moving across its field of view which triggers the light. When the warm body leaves the sensor’s field of view, the reverse happens – the heat signature drops and returns to normal, so the light knows to turn off.

As they only detect heat signatures, PIR sensors aren’t usually triggered by inanimate objects being blown across their field of view by the wind. This means they make good security lights for home gardens, car parks, and building site offices – while they will be set off by passing wildlife, they won’t be triggered by every little thing that blows by.

You can use PIR sensors indoors, of course, but remember they do need to have a direct line of sight to work.

Microwave Sensors

Microwave sensors work similarly to sonar. They send out constant microwave signals into their environment and measure how long it takes for that signal to bounce back. When something moves within the detection zone, the signal is disrupted, slightly delaying the amount of time it takes to reach the sensor. The sensor recognises this and triggers the light to switch on.

Microwave sensors are less reliant on having a direct line of sight than PIR sensors, making them better for very large or awkwardly-shaped rooms. Some highly-sensitive models can emit a signal that can travel through glass and thin walls, so they work well in ladies’ toilets or other areas that have a lot of cubicles.

PIR vs Microwave Sensors – Which is Best?

As with most things, neither PIR or microwave sensors are objectively better than the other. They each have their own advantages and are better at different things.

Lights with PIR sensors are the best for use as security lights as they only pick up movement from living things, meaning they give fewer false alarms. Technically, microwave sensors can be adjusted so that they’ll only pick up movement from human-sized things, but this happens at the factory before they’re installed into the lights.

Location is everything with a PIR sensor as the target needs to pass through their field of view to be detected. This means they’re ideal for clearly-defined areas like corridors and alleyways where you can’t really avoid them.

Microwave sensors don’t need a line of sight to detect movement, so they’re better suited to oddly-shaped rooms with a lot of obstacles in them like warehouses and toilets. As they don’t rely on heat signatures, they’re also more reliable in very hot areas where PIR might not be effective. Microwave sensors are also much more sensitive, so are suitable for cases when you need to detect very fine movements. However, this can also be a negative as it means they can be triggered by blowing leaves and other small objects, so if you’re looking for a garden security light you may be better off with a PIR-sensing model.