Motion Sensors for Lights

Motion sensors that switch lights on and off and can save you a lot of energy and money. They can also reduce light pollution because the lighting is only on when it is wanted.

Forget about jargon, such as the Internet of Things, “smart buildings”, mesh networks and protocols, this blog describes simple ways to improve the efficiency of your lighting installation by using motion or movement sensors. It also gives you tips on how to use them.

Motion sensors can be used anywhere indoors; even in damp areas such as bathrooms. They are especially useful for stairs, corridors and meeting rooms which are not used very often. Why have the lights on if no-one is using them?

Motion sensors can also be used outdoors. A lot of outdoor lights such as floodlights or door lights have the sensor integrated and already built in.

Most sensors are fitted as stand-alone units remote from the light fittings. Other sensors are built in to LED fixtures so you can simply retrofit them into existing sockets.

Basically, there are two types of motion sensor.

• By far the most common type is Passive Infra-Red, also known as PIR.
• The other type is microwave which has some advantages, and disadvantages, over PIR.

As mentioned, most movement sensors are passive infra-red, PIR. These work by transmitting a beam and detecting any change when it reflects back. They sense the warmth from a person, animal or vehicle when it crosses or interrupts the IR beams. The sensors are directional and often have optional blanking plates to limit the detection angle. For example, up and down a corridor.

You can have narrow beams and wide beams and the detection coverage is affected by the mounting height. Drawing of different beam angles from a sensor. It depends on the geometry of the installation.

Note that PIR works by line of sight. A small partition or corner might block detecting movement beyond it.

PIR detectors work less well in hot environments where the ambient temperature is similar to that of a person; typically, around 35C. For example, a PIR detector may not work so well in a boiler room or a sauna.

Microwave sensors work in a similar way but do not use beams. Instead, they look at changes to the “echo pattern” of the space and detect movement by changes in the pattern.

Unlike PIR, they are not affected by temperature. There are two other aspects of microwave sensors that may, or may not, be an advantage. Firstly, they can detect movement through glass panes or stud walls. Therefore, movement beyond a window, glass partition or an adjacent office might trigger them. Secondly, they are much more sensitive to movement. They can detect small movements like someone typing on a keyboard. However, some sensors might be triggered by a draught causing a window blind to move.

They tend to be used in more industrial applications.

Both these types of sensor can be used as presence detection or absence detection in meeting rooms. These are similar concepts but differ in the way the lights are switched on and off. “Corridor hold” is where nearby lights are also switched on. This gives a feeling of security to users who are working in nearly empty premises. 

• Water resistant. For use in bathrooms, wet rooms or outdoors, your sensor should have a protection of IP44, or higher. Maybe a link to a future blog on IP Rating.
• Time delay ON. You can set the time delay typically from 30 seconds to 15 minutes. This makes them ideal for stairwells, bathrooms, store cupboards etc. Some can set the time delay remotely using a mobile phone or simple IR handset
• An adjustable head, so that you alter the detection distance. Together with blanking plates, it might be able to detect movement along a long corridor from a low mounting height such as 2.5m.
• Twin beams that can detect the difference between movement from an animal like a cat or fox and that of a child or vehicle.
• Solar powered and wireless. You don’t need to replace batteries nor power the sensor from the luminaire or a separate supply. Instead, the sensor has an internal energy storage element which can operate the device for several days even without any natural or artificial light.
• Modern movement sensors consume very little energy, maybe less than 0.5W. Those which are not powered from the light fittings often have rechargeable batteries. Read the data sheet carefully to see what power supply the sensor requires.

Installing the sensors needn’t be difficult although there are some which can connect to lighting control systems either wirelessly or hard wired.

Most sensors send a simple ON/OFF to the light fitting but some can also send other types of signals such as:

• DALI
• 1 – 10v.
• Platforms such as Interact.
• Bluetooth
• Casambi.

If there is a control system, you need to check what kind of driver or ballast is inside the existing luminaire. Some can only be switched on or off but many have extra terminals for control wires or a receiver for a wireless signal. Read the label on the driver/ballast carefully and you will see what control signal they will accept. Typical ones are: DALI, 0 – 10v, dmx etc. 

You can fit a sensor next to each fitting but it might be more economical to use one sensor to control a group of luminaires. E.g a small office or a corridor. This can be done wirelessly but, at that point, you might need some specialist advice.