Occupancy sensors

Occupancy sensors should be a part of any research laboratory lighting system, mainly because many offices attached to labs are left unoccupied for a significant amount of time each day, typically with the lights on. Reducing this load will result in measurable savings. If a laboratory does not "sweep" lights off during nighttime hours, weekends and holidays, the sensor will ensure that the lights are off when the space is unoccupied. It is probable that more energy savings will be derived from having the lighting system turned off by sensors at these times than will be realized during normal working hours.

The occupancy sensor is an energy-saving control device that turns lights on and off depending on the occupancy of the space being controlled. When people are in the room, the lights are enabled on, and when the room is vacated for a set period of time (usually 15 minutes) the device turns off the lights. This provides energy savings ranging from 10 percent to 50 percent, depending on the habits of the occupants of the space.

Occupancy sensors have been available for laboratory installation since the late 1970s. The technology uses both passive infrared (PIR) and ultrasonic (US) detectors. New, hybrid products are now being manufactured that employ both PIR and US technologies. The designer may select either technology. As a rule of thumb, PIR is most efficient in small areas, such as individual offices or supply rooms, and US is most effective in large spaces, such as a lab or classroom. Dual technology sensors, composed of both the passive infrared and ultrasonic technologies, are triggered by either heat or motion but require the absence of both to shut off, alleviating false triggering problems. Hybrid sensors are more expensive initially but may prove more efficient and cost effective over the life of the system than a single technology sensor. An occupancy sensor specialist can be consulted to determine which type of sensor will provide optimal performance and to select locations for mounting.

Designers must account for false triggering of sensors, which could occur when someone walks past the door of a controlled room and is "picked up" by the sensor, or when a sensor turns off lights in an occupied room where the occupant has remained still for the sensor's shutoff time period.

The laboratory lighting system designer should rarely if ever experience a problem involving interference with sensitive equipment from lighting sensors. There have been some isolated reports of interference with laboratory equipment, particularly in the 27-kilohertz range, but these problems have been solved by simply changing the frequency of the sensors to a higher range, usually 40 kilohertz or higher.

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