Introduction to Occupancy Sensors
All lighting systems are operated with lighting controls i.e. devices that switch lights on and off or devices that dim light output. The most common and basic lighting control is a simple on-off switch, which, when flipped, opens and closes the lighting circuit and switching on or off the lamps.
While the basic switch is economical in terms of initial cost, they can actually become quite expensive over time in terms of total ownership cost. If you look at most large city skylines at night, we see an almost majestic view of skyscrapers dotted with thousands of lights, each of them a window offering a view of an office or space that is lighted but unoccupied. Lighting system operation costs money, and yet organizations lose profits every day by paying to operate lighting systems when nobody’s there to work. It’s like paying workers to sit and do nothing.
A solution is the adoption of automatic lighting controls that switch the lights based on occupancy. Occupancy sensors are automatic switching devices that sense human occupancy and control the lighting system accordingly, either by turning on/off the lighting system.
Energy, a basic product for which the electric utility charges, is the result of a lighting system used over time: Power (watts) x Time (hours) = Energy (kilowatt-hours). If we reduce the hours of operation for a lighting system, then we can significantly reduce energy use and associated costs. By turning off the lights when occupants are not present using occupancy sensors, we reduce energy waste that can result in a reduction in lighting energy consumption. According to the California Energy Commission, “Energy saving potential is highly dependent on baseline assumptions and operation, but values of 35% to 45% are typical.”
In an occupancy or PIR -based motion detector, the PIR sensor is typically mounted on a printed circuit board which also contains the necessary electronics required to interpret the signals from the chip. The sensor is mounted in a location where it can view the area to be monitored. Infrared energy is able to reach the sensor through the opaque window because the plastic used is transparent to infrared radiation. This plastic sheet or bubble prevents the introduction of dust which could obscure the sensor's field of view.
A person entering the monitored area is detected when the infrared energy emitted from the person's body is focused by a lens or a mirror segment and overlaps a section on the chip which had previously been looking at some much cooler part of the protected area. As the person moves, so does the hot spot on the surface of the chip - moving hot spots cause the electronics connected to the chip to de-energize the relay, operating its contacts and illuminating the lamp circuit.
Relays can be incorporated in the lighting circuit to have more than one detector operating the same lights i.e. both end of a corridor or to switch between dimmed lighting when areas are unoccupied and full output when movement is detected. A good electrician should be able to advise you on what relay would be required to suit your conditions and use. |
