Passive Infrared sensors detect heat energy in a room. By sending an array of infrared lasers from its location in a room it can detect when one crosses the ‘line of sight’ of the sensor. These sensors are very appropriate for locations where traffic is unobstructed by objects, but also spaces that are not too open. According to the National Lighting Product Information Program, passive infrared occupancy sensors detected medium sized motion in an open space office area at 35% of the locations. This data does not reflect the effectiveness of passive infrared technology but rather the planning required to appropriately place these sensors based on the technology they use.
In the same study, ultrasonic occupancy sensors were also tested. The results revealed that medium sized motion was detected at 98% of the locations. Ultrasonic occupancy sensors works similar to a submarine’s sonar technology. The ultrasonic sensor sends high frequency waves that return to the sensor after traveling across a space. Once irregularities of these patterns occur, the sensor is triggered. Once activated, the lights will turn on, and once the wave patterns return to a static state for a certain time the lights will turn off. Ultrasonic occupancy can be used in more locations than passive infrared occupancy sensors because the waves they send out can move around barriers while infrared lasers are calibrated to static position. Most ceiling mounted occupancy sensors use ultrasonic waves. Applying these occupancy sensors to an automated lighting setup in an open office area is very effective. The waves are capable if returning occupancy based information with in
subdivided areas by partitions or a traditional cubicle setup.
When integrating occupancy sensors into a cost effective automated lighting design, one should consider the usage of both types. While the ultrasonic is useful in more locations, it also ranges from 15%-33% more expensive than a passive infrared occupancy sensor. For this reason a cost efficient design will have passive infrared sensors where acceptable and ultrasonic sensors in other locations.