Article
Most of us who work in commercial or institutional spaces rarely think 
about lighting, and that’s a problem for any facility’s energy bills. 
Occupancy/vacancy sensors can help by becoming a lighting system’s 
brains – these devices think about lighting, so we don’t have to. 
Selecting the right kind of sensor for each location is important, 
though, because not every sensor “sees” in the same way.

Picking the Right Occupancy Sensor for Any Application

Chuck Ross
Most of us who work in commercial or institutional spaces rarely think about lighting, and that’s a problem for any facility’s energy bills. Occupancy/vacancy sensors can help by becoming a lighting system’s brains – these devices think about lighting, so we don’t have to. Selecting the right kind of sensor for each location is important, though, because not every sensor “sees” in the same way.

Sensors judge whether a space is occupied or not by detecting motion. The devices use one of three different technologies to make that assessment, according to Terry Arbouw, director of product development and innovation at Hubbell Control Solutions.

Passive infrared (PIR) technology works by detecting movement of heat emitted by human bodies against the background space. This requires them to have an unobstructed line of sight to do their job. The sensors incorporate a segmented lens that divides the coverage area into zones, and heat movement between zones indicates occupancy.

“PIR sensors are ideal for detecting major motion, like walking,” Arbouw says. “They work best in small, enclosed spaces with high levels of occupant movement.”

In contrast, ultrasonic technology uses soundwaves to detect movement. Ultrasonic (US) sensors bounce these waves off of objects and analyze the frequency shift between the emitted soundwaves and those that are reflected back. When a person or object moves within a space, that frequency shifts, which the sensor interprets as occupancy. These sensors have a limited range, but they can detect minor motion like typing, and don’t require direct line of sight. This makes US sensors a good fit for an office space filled with cubicles or a bathroom with stalls, according to Arbouw.

More recently, sensors incorporating both PIR and US capabilities have come to market. These dual technology products bring maximum reliability to occupancy detection. Both PIR and US sensing components have to detect movement for these devices to switch lighting systems on.

“Dual technology sensors minimize the risk of lights coming on when the space is unoccupied, which is commonly referred to as ‘false triggering,’” Arbouw says. “Dual technology sensors offer the best performance for most applications.”
Photo courtesy of Hubbell Lighting
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