We all know that one way to save energy is to turn off the lights when we leave a room. But how often do we remember to do that? In business offices and industrial facilities, it is frequently the case that the last person leaving the premises will turn off all the lights. If you look at the skyline of any large city at night, you will usually see floor after floor of offices buildings brightly lit, even though the offices have long been closed for the day.
Along with other changes being brought about by a desire for greater energy efficiency, reduced energy costs and compliance with restrictions on incandescent lighting, there is growing interest in the use of occupancy sensors. Occupancy sensors work by dimming or completely extinguishing lights when there are no people in proximity of the controlled lights.
How does the system really know whether someone is present? A common way "occupancy" is sensed is by using an infrared image sensor (Figure 1) and a microprocessor to analyze an area for specific thermal images, or signatures. When no heat signature for the human body is detected, the system concludes that no one is in the area and shuts off the lights. Acoustic sensors – detecting human-related sounds – are also used in some occupancy sensors, and both IR and acoustic sensors may be combined.
Figure 1: The AMN34111 infrared sensor is an example of a device designed to sense human presence in a wide area. (Source: Panasonic Electric Works)
Occupancy sensors are available today as standalone units that can be wired into existing lighting systems to control light fixtures. There is a trend, however, to add occupancy sensing directly into the fixture and the light source itself, as well as other appliances such as air conditioners, to give products autonomous control.
A broad array of motion sensors on the market today can help designers implement occupancy sensing very economically. The AMN Design Manual is a valuable resource for additional information on occupancy sensing applications.