Occupancy Sensors

Occupancy sensors reduce energy consumption by automatically shutting off lights when rooms are empty. Sensors are required for new buildings under the Massachusetts Energy Code. MHC is installing sensors in many locations because they are a cost-effective retrofit, substantially reducing energy costs.

How a lighting occupancy sensor works

Each unit has a passive infra-red (PIR) sensor that detects even slight motion. A Fresnel lens gives the sensor a panoramic view.

MHC mostly uses sensors that are "dual technology" in that they also sense noise. Triggering either the motion OR the noise sensor will keep the lights on. After the lights go off there is a two-second period where just a noise will bring them back on.

Behind the lens is a green LED that indicates when the sensor has "seen" or heard" something.

We need to get three things right for a sensor to work properly: location, type, and setup.

  1. Location: The sensor must be located where it can best "see" the occupants of the room. In cases where a wall switch would be obstructed, they can be mounted on the ceiling or high on the wall.
  1. Type: The dual-technology sensors we use trigger on motion and sound for extra sensitivity. Ultrasonic types are also available, that can "see" reflections around corners.
  2. Setup: There are up to 12 parameters that can be adjusted: time delay, switch action, and sensitivity.

Switch action is adjustable, usually set so that if you manually turn lights off you have to manually turn them on again. All ceiling and high-wall sensors act this way because they have a separate switch. In some areas, like rest rooms and utility closets, sensors are set to automatically come on whenever motion is sensed. These sensors can be turned off by pressing the button at the bottom of the switch. The detector will reset to auto mode after a few seconds and turn on the lights the next time someone enters.

If your sensor is not working properly (either shutting off the lights when you need them, or not going off at all) please dial ext. 2012 to report the problem. We'll adjust it to get things working right.

For more information on sensors.