Selecting a Motion Sensor

Selecting a Motion Sensor

LED motion sensors are a simple addition to lower energy costs without needing a complete lighting overhaul. They are ideal for rooms where lights are left on accidentally, such as offices, and for rooms that are often entered while your hands are full, like laundry rooms. While there are several types of motion sensors available, each type detects motion a little differently and each type has pros and cons.  There are also more technologies to choose from, depending on where and how you need to use them.

Active Sensors  

Active sensors use infrared energy, radar waves, or other methods to detect changes in the rooms they cover.  The three most common active sensors are ultrasonic, microwave, and tomographic. Ultrasonic sensors are the most used type in lighting and emit sound waves higher than a human can hear (although dogs and cats occasionally can). Microwave sensors emit microwave pulses. This type of sensor is extremely sensitive and is often used in security systems. However, since they can sometimes "see through" non-metallic objects and walls, they are prone to false alarms if not accurately calibrated. Tomographic sensors emit radio waves and are typically used in commercial areas that need a high level of security since they can cover a very large area. Once installed, an active sensor sends out pulses of energy and measures the time it takes for those energy pulses to bounce back when they hit objects in the room. It is similar to how a bat uses echolocation to see at night. These sensors are not restricted to line of sight and can detect slight movements. However, they too are prone to false alarms. Because of this continuous back and forth, these sensors consume a lot more power than passive sensors.

Passive Infrared Sensors

Passive Infrared (PIR) detects changes in infrared radiation, also known as heat, emitted by all warm-blooded creatures, as well as the sun.  PIR motion sensors contain a thin layer of pyroelectric material and two slots, which is what reacts to the IR radiation. The sensor remans idle while both slots are detecting the same amount of heat: the calibrated ambient amount of the room. When a person, or large enough animal, walks through the covered area it creates a "positive differential" charge between the two slots. These charges are what triggers the sensor. PIR sensors can be calibrated to go off only at certain heat levels, so small fluctuations do not cause the lights to come on.  This prevents the sensor from triggering when small animals enter the room or when the sun rises and warms the room. The coverage for PIR sensors is directional and limited to line-of-sight, so it's important to make sure no part of the space that is to be detected is blocked by partitions or shelves.

Dual Technology Sensors

Dual technology, or dual-tech motion sensors, combine ultrasonic and PIR sensing technology.  These sensors are less likely to cause false alarms and are typically used in areas where using just one technology isn't viable, such as offices, classrooms, and rooms with high ceilings or tall furniture. Dual-tech sensors only turn the lights on when both the ultrasonic and PIR sensors detect occupancy but require just one technology to remain on to help ensure the lights don't turn off while the room is occupied. This way the small movements, like someone typing, is picked up by the ultrasonic waves, but the person walking past the door in the hallway is ignored.

Occupancy VS Vacancy

Lighting motion sensors come in two main types: occupancy and vacancy.  Occupancy sensors automatically turn on the lights when the sensor is tripped and turn off after a programmed amount of time of no movement. This type of sensor is best used in high-traffic rooms like bathrooms and restaurant pantries. Vacancy sensors, also turn the light off when a room is vacant, and no motion is detected, but you must manually turn the light on when entering. Conference rooms and rooms with large windows that get a lot of natural daylight most of the day benefit from this type of motion sensor.

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