The recommended occupancy sensors also have a photocell built into them that will keep lights off when natural lighting levels are adequate. There are several types of occupancy sensors available. The infrared wall switch units are installed into the switch plates of current lights. These units turn the lights off and on by detecting differences in the heat given off by a human body and the surroundings. They work best in enclosed offices where the light switch area has a clear view of the entire area.
Ultrasonic sensors work by bouncing ultrasonic sound waves off objects in the room.
The lights are turned on when the sound waves return at a faster or slower rate indicating that someone has entered the room. Applications for these sensors include bathrooms and larger office spaces. It is estimated that the area being considered in this facility will need approximately 16 infrared wall switch units and 3 ultrasonic sensors. These cost estimates are based on local manufacturers' representatives' quotes. The occupancy sensors that were recommended also feature a special daylight sensor that also helps to reduce lighting electrical energy.