Green Technology
Saving Energy with Vacancy Sensors
Cutting electricity costs can be even easier than switching a light.
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June 24, 2008 by Steven Castle

Want to save electricity but can’t afford a full-blown lighting control system? One of the best and least expensive ways to save energy in your home is to install occupancy or vacancy sensors, in rooms where lights may be left on. 

A vacancy sensor detects when someone is no longer in a room and shuts the light off automatically (turning them on requires a manual switch). Occupancy sensors can turn the lights on and off automatically. Both type of sensors can be installed easily to replace standard light switches, and are ideal for bathrooms, bedrooms, closets, garages, basements, hallways and utility spaces—anywhere a light can be inadvertently left on and forgotten. They can be used with incandescent or fluorescent lights.

Best of all, the sensors are good for the environment. “For every switch that is replaced by a vacancy sensor, carbon dioxide emitted into the environment is reduced,” says Carlos Villalobos, product manager for Watt Stopper/Legrand. “If 100 million households were to control just one 60-watt bulb with one vacancy sensor, this would represent almost 500 million kilowatt hours (kWh) in energy savings—about $50 million per year—and a reduction of almost a billion pounds of carbon dioxide.”

If you want to find out more about occupancy and vacancy sensors, the Home Lighting Control Alliance has an informative white paper that describes how they work, basic and advanced features, and how they are typically installed and set up.

Some highlights from the white paper:

  • Vacancy sensors work by sensing changes in heat (such as body heat) against background radiation.
  • The sensor includes a lens that determines the coverage area (field of view), sensitivity (ability to detect levels of motion such as body or hand movements) and range (distance from the sensor motion can be detected).
  • Sensors feature adjustable time-delay settings that allow the homeowner to set the amount of time that will occur between the sensor detecting an absence of people and shutting the lights off.
  • Dual-relay sensors allow the switching of two loads, like a bathroom light and fan, from one location. “Housed in a single-gang device, dual-relay sensors give installers the option of two loads or adding a load without having to install a larger electrical box,” says Villalobos.
  • Multiway sensors that switch from more than one location are available as well; coverage is extended to the area covered within line of sight of any one of the connected sensors.
  • Some occupancy sensors, offering both automatic-ON and automatic-OFF are available with light -level sensing so that the lights do not turn on automatically if there is sufficient daylight in the room, an added energy-saving feature for rooms that receive a lot of sunlight throughout the day.
  • Some sensors are also available with a dimmer switch for dimming.


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Steven Castle - Contributing Writer
Steven Castle is Electronic House's managing editor. he has been writing about consumer electronics, homes and energy efficiency topics for two decades. He is also the co-founder of GreenTech Advocates.

Watt Stopper/Legrand’s application-specific wall switch vacancy sensors are designed to replace standard wall switches. They are engineered to comply with California’s rigorous Title 24-2005 residential energy code.


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