You’re probably aware of the different kinds of lighting controls that are out there. Dimmers and timers are two examples. They operate just as you would imagine. Dimmers adjust light levels and timers will turn lights off after a specified period of time.
Another kind of lighting control is the sensor. There are two general types of lighting sensors, photo sensors, and motion sensors. Photo sensors detect the presence (or absence) of light. They are usually used for outdoor lighting so that a light will automatically turn on when the sun sets and then automatically turn off when the sun rises.
Motion sensors, as you would imagine, detect motion. A motion sensor is an electronic mechanism used for detecting moving things in a given area, human beings in particular. They are used to control lighting as well as automate the operations related to other connected devices.
Lighting fixtures and systems can integrate sensors which makes them even more efficient. Motion sensors are used to identify when someone approaches a given area. This results in lights being turned on. These sensors can be used to save costs on energy bills by dimming or turning off lights when no one is around. It can also be used as a security measure, with lights coming on to let you know when someone is nearby.
There are two commonly used types of motion sensors used for occupancy and intrusion detection; PIR (Passive Infrared) sensors and microwave sensors.
Microwave vs PIR Motion Sensors: How do they work?
A microwave sensor is an electromagnetic radiation motion-detecting device. They emit electromagnetic waves with the help of a transmitter that is then reflected back to the sensor. The receiver in the sensor then analyzes the echo time of the waves that are bounced back.
Echo time is defined as the time taken for the signal to be reflected back to the sensor. It is used to calculate the distances from all the stationary objects in the detection zone. The distance calculation is used to establish a baseline to work from. When a person moves into the detection area, it causes a disturbance in the microwave beam. This changes the echo time and triggers the lights to turn on. The sensor quickly detects any movement inside its range by evaluating this data.
There are two types of waves analyzed by the sensor:
Normal Wave – If there are no moving objects in the pathway of the wave, the waves reflected back to the sensor will be normal. Essentially, this means that there is no change from the baseline.
Altered Wave – If the sensor detects a moving object in the room, the waves reflected are going to be altered. The changed wave will alter the calculated echo time. This will trigger the security systems/lights linked to the sensor.
More sophisticated microwave sensors can identify whether a person is traveling towards or away from the sensor or moving randomly.
PIR Motion Sensors
A PIR (passive infrared) sensor can measure infrared light emitted from bodies in its line of sight.
A pyroelectric sensor is the main component of a PIR motion sensor. Humans and animals produce heat energy as infrared radiation. The PIR sensor has two pyroelectric sensors that can identify heat energy within its nearby environment. It generates an electrical signal when the environment is cooled or heated. Both sensors are positioned next to each other. The sensor module also has a specially constructed cover known as a Fresnel lens. This lens focuses the infrared signals on the pyroelectric sensor.
The ambient temperature of a room is measured by PIR sensors by using a number of detection beams. Once a change in the temperature is identified through one of the beams, the sensor is then triggered, and the lights are switched on. Once all of the beams recognize the same temperature again, the lights will turn off.
PIR sensors are not programmed to be constantly sensing. They are designed to cycle, which means the light must go off before it starts to sense again.
This is often because the light itself may interfere with the sensor.
What are the advantages and limitations of each type of motion sensor?
Microwave Motion Sensor
They can be used in almost any environment. They have consistent detection across all temperatures. They don’t rely on heat signatures, making them more trustworthy in hot and cold environments.
They are accurate and highly sensitive with a wide range of detection. This means that they don’t have many false positive results.
They can penetrate walls, glass, plastic, and holes. This means that they can cover a wider area. Microwave sensors do not require a precise line of sight.
Microwave sensors may have difficulty with smaller indoor spaces because they can perceive movement through walls. Due to this sensitivity, they might be triggered by movement that you are not trying to detect.
They are more expensive than PIR sensors but can come with more advanced settings and features.
PIR Motion Sensor
They are energy efficient and relatively inexpensive.
They don’t release any sort of electromagnetic wave. Therefore, there is no issue with interference around sensitive testing equipment.
They detect motion accurately at any time of the day or at night.
Ambient temperatures can significantly affect sensitivity. This is because a PIR sensor flags the variation in heat to detect movement. They are under-sensitive to higher background temperatures. They are over-sensitive to lower temperatures.
What are the best applications for each type of sensor?
Microwave Motion Sensor
They are more suited to oddly shaped rooms and areas with a lot of barriers because they don’t require a precise line of sight.
Their advanced controls can also allow precise settings for use in a parking lot or a warehouse lighting layout.
Best used for security lights, warehouses, restaurants, gas stations, conference halls, underground parking, outdoor lighting, and parking lots.
PIR Motion Sensor
PIR sensor has a light that is considerably more efficient and effective for garden and home protection.
They are a good choice in distinctly specified places where they can’t be disregarded. These types of places include entryways, halls, pathways, and alleyways.
Best used for offices, stairwells/staircases, corridors, basements, conference halls, and bathrooms.
Motion sensors are a great option for residential and commercial spaces. Not only do they enhance security and safety, but they also save on energy costs by switching lights on/off when needed. They are also easy to install if they are not included with the light fixtures themselves. Whether in a retrofit or new construction, this makes them convenient for lighting contractors or designers.
About the Author
Dwayne Kula is President of LED Lighting Supply. On any given day, Dwayne is writing content for the site and helps manage the marketing initiatives that are on-going. He has a Software Engineering degree and still dabbles in writing software for the company as needed. When not working, he enjoys spending time with his family, working out, playing the occasional game of golf and exploring New England.