When people are unlikely to remember to turn lights off, an occupancy sensor
is a great way to save money. This is an easy to install device that will turn
lights on and off automatically in an individual space such as a private office,
restroom, or storage area. Three types of sensors motion detecting
(ultrasonic), heat sensing (infrared), and sound sensing are available. Many sensors cost
less than $100, installed.
Sensors are mounted on the wall just like an ordinary light switch, or installed in the ceiling or high on a wall. The sensor turns the lights on when it senses someone coming into the room or area, and then turns the lights off some time after no longer sensing anyone present. Units come either with fixed, preset time delays and sensitivity levels, or with adjustable ones. You normally would want to buy a sensor which can be adjusted for both time delay and sensitivity.
You will need to carefully consider the time delays needed for the area, and the range, sensitivity, type, and mounting position of the sensor. For example, motion detectors may not be the right choice if occupants of the space sit very quietly at desks: people in such situations have been known to complain that they must deliberately move from time to time to prevent the sensor from shutting off the lights. Heat sensors, on the other hand, must be placed so that no obstruction blocks their sensing field.
The more hours the lights are off and the more watts controlled by the sensor, the greater the energy savings. Savings estimates of 20% to 40% are often cited, and even greater savings are possible when spaces are used for only limited times.
Among the very best places to install occupancy sensors are: private offices, conference rooms, dormitory and locker rooms, restrooms, stockrooms, and hotel and motel rooms. The lodging industry is experiencing success with sensors where not only lights but HVAC, too, may be controlled to keep occupants comfortable but save energy when the room is unoccupied.
Three types of sensors are available: motion, heat and audio. The area to be lit and the types of surfaces in the space will determine which sensor is most effective. The motion sensor keeps the lights on as long as there is movement. After motion has stopped (lapse time is adjustable), the detector switches the lights off. Heat sensors, which detect infrared radiation, and audio detectors, which are controlled by sound, operate in a similar manner.
