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January 27, 2012 -
Today's tip comes from James Piper, contributing editor for Building Operating Management magazine: Properly installed occupancy sensors won't leave occupants in the dark or reduce lamp life.
One of the biggest complaints concerning the occupancy sensor is that it can leave occupants in the dark if it falsely believes that the space is unoccupied. Most occupancy sensors work by detecting motion. Once detected, the sensor turns the lights on for a preset amount of time. Each time that motion is detected, the sensor's timer is reset. If no motion is sensed and the timer reaches its preset interval, the lights are turned off. If the space is still in use, the occupants can be left in the dark.
In most cases, the failure to detect occupants is the result of installation or application errors. To be effective the sensor needs to be able to see all or most of the space. Sensors have a limited viewing range and angle. Objects within the space or unusual room configurations can partially block the view of sensors, resulting in false readings. By selecting the right type of occupancy control and by properly placing that control, most false readings can be eliminated. If there still are concerns about leaving occupants in the dark, a single, low wattage fixture can be left switched on at all times to provide backup lighting.
A related concern is that, as a result of their frequent on off cycles, occupancy sensors kill lamp life. While there is no question that this frequent cycling does reduce lamp life as measured by total operating hours, it can actually extend the calendar life of the lamps, particularly in applications where light is only needed a small fraction of the time.
This has been a Building Operating Management Tip of the Day. Thanks for listening.