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How far can motion sensors save energy used for lighting?

Posted by Alex Barrett on 30 September 2016 at 12:45 pm

It is well known that switching off unused lights can save a large amount of energy. Around three percent of home energy usage comes from lighting [1]. While energy use can thus be reduced by switching to energy efficient light bulbs, there is no substitute for ensuring that lights are switched off when not in use. Motion sensors provide a valuable tool to ensure that only the lights that are needed at any given time are in use.

Motion sensors are commonly used to trigger outside lights when someone approaches a house. Now many organisations are using similar systems, called occupancy sensors, to control lighting within offices and public buildings. It has been estimated that the use of motion sensors in commercial buildings can reduce energy use by up to 30% [2]. These systems work best in large buildings, so are mostly used by businesses and organisations. However, similar systems can be of value to private homeowners.

Occupancy sensors can be used to create different patterns of lighting, depending on which parts of a large room are in use, and switch on lights ahead of you as you move through a building. Task lights, such as those over counters and work surfaces, can be activated by movement on those surfaces, but remain off when the area isn’t in use. The lights will then switch off automatically after there has been no movement for a while, cutting down on energy use [3].

One common concern with using motion sensors is that switching a light on and off repeatedly might shorten the life of the bulb. This is partially true for compact fluorescent lamps (CFLs). Switching them on and off rapidly can have an effect on their life, but the total number of times they are switched on and off does not. Since motion sensor systems are set on a timer they keep the light on for a set period of time after it is triggered, so this is unlikely to be a problem.

CFL lights can take a while to become bright when switched on. This means that it will take longer to reach full brightness after a motion sensor is triggered. Light emitting diodes (LED) do not have this issue as they achieve full brightness as soon as they are switched on. The life of an LED bulb is not adversely affected by being switched on and off at all. While these are more expensive in the short term they have a much longer life than CFLs and are more energy efficient overall. Thus they are a better choice for use with motion sensors.

Motion sensors also have applications for public lighting. Street lights can be kept off, or dimmed, most of the time. Motion sensors detect the approach of a pedestrian and tell the lights ahead of them to come on, so that an area is already brightly lit once they arrive. This was not possible with older sodium streetlights, since they take much longer to become bright. New LED streetlights allow much more flexibility in controlling urban lighting. Street light control systems are yet to be put into widespread use, although LED street lights are now being installed in various parts of the UK.

This technology, on both large and small scales, has the potential to reduce urban energy use and massively cut light pollution [4]. It is a good way to ensure that energy use reflects what is actually needed on a day to day basis.


1)  Energy Saving Trust

2) The Carbon Trust



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3 comments - read them below or add one

NEF Jemma

NEF JemmaComment left on: 13 October 2016 at 4:12 pm

I used to take calls on the local Energy Saving Trust advice line. I once took a call from a homeowner who was mystified by their high electricity bill. It turned out to be down to the 500W halogen security floodlights they were leaving on all night. Clearly sensors are going to help in this situation and any energy consumed by the sensor is going to be immaterial by comparison to leaving high wattage bulbs on for long periods...

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GaryComment left on: 2 October 2016 at 10:02 pm

That is exactly what I was thinking.  We turn lights off anyway and have r motion detector lights for front door (we are set back 30m from any road), a security light and back garden lights and i think they are useful for that but indoors we are now completely LED.  The average room is now between 10W and 20W for normal lighting.  Compare the potential saving with that wattage with the price of detectors and i doubt they would economic...

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cannonballdazeComment left on: 30 September 2016 at 6:44 pm

What's the energy consumption of a typical motion sensor itself ? 

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