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If you're like most people, it happens every day: Somebody in your house forgets to turn off the lights in a room, sometimes for hours. The result is energy waste. Literally, wasted money.

Compact fluorescent lamps, or CFLs, are frequently touted for their energy-saving benefits. This bulb , in fact, saves up to 75% on energy compared to incandescent bulbs of comparable light output, yet even this bulb is an energy-waster if left on when it isn't needed.

Homeowners now have another energy-saving, quick-payback strategy to get excited about: vacancy sensors. Ideal for bathrooms, bedrooms, closets, garages, hallways and utility spaces, vacancy sensors install just like a standard wall switch and also function like one: To turn the lights on, just flick the switch. However, if you forget to turn off the lights, the sensor will detect that the room is unoccupied and turn off the lights automatically after a preset period of time. The result is energy savings-ongoing cost savings on the homeowner's electric bill.

“After California updated its energy code in 2005, recognizing vacancy sensors as an alternative to high-efficacy (fluorescent) lighting in many rooms, manufacturers began offering a wide range of products, features and aesthetic looks to satisfy virtually any need in the home,” says Carlos Villalobos, product manager for Watt Stopper/Legrand.

This special report by the Home Lighting Control Alliance describes how vacancy sensors work, basic and advanced features, and how they are typically installed and set up.

Basic Features

Residential vacancy sensors are typically passive-infrared (PIR) devices that fit into a single-gang electrical box and simply replace a traditional wall switch. They work by sensing changes in heat (such as body heat) against background radiation. If human occupancy is not detected, the sensor waits a period of time, and then shuts the lights off.

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). According to Villalobos, well-designed sensors can see a full 180° and detect motion in an area of up to 600 square feet. Note that PIR sensors need a direct, unblocked line of sight to “see” whether there are people in a room or not, however.

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. The shorter the time delay, the higher the energy savings; the longer the time delay, the less risk to user safety or comfort (the lights won’t suddenly go out because somebody is standing still for a few minutes).

“Different length delays are appropriate for different applications,” says Villalobos. “A long time delay, such as 30 minutes, works well in a bathroom where an occupant might take an extended shower or bath out of view of the sensor. A laundry room could use a shorter delay and a hallway could use an even shorter delay. The key is to avoid false-off switching in spaces where there might be minimal movement when the area is occupied.”

Advanced Features and Options

Some applications may pose special switching requirements. One example is a homeowner wanting to switch two loads separately from a single location, such as a bathroom fan and light. For this type of application, dual-relay sensors offer a solution and can be useful for retrofits. “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. “They are ideal for bathroom applications—one half of the switch button to control the light, the other to control the exhaust fan; the sensor takes care of keeping both of them off it the bathroom is vacant.”

Another type of room posing special switching requirements is a room with multiple entrances, such as a Jack and Jill bathroom, hallway or staircase, may not be suited to switching from a single location, but instead require three- or four-way control with multiple switching locations. For this type of application, multi-way sensors are available as a solution; coverage is extended to the area covered within line of sight of any one of the connected sensors. Lighting is kept on for the time-delay period of the last sensor in the group to detect the presence of people. “Be certain that the model selected offers full multi-way control,” Villalobos advises. “Occupants should be able to turn lighting on or off from any of the connected sensors.”

Some sensors are available with built-in low-wattage LED nightlights to soothe children and help people navigate the dark and find the light switch.

And other sensors are occupancy sensors offering both automatic-ON and automatic-OFF; some of these 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.

Finally, some sensors are available with a dimmer switch for dimming.

Installation and Setup

Qualified electrical installers should find wiring wall-switch sensors to be straightforward because they are self-contained devices, says Villalobos.

All controls should be properly grounded and specific load requirements should be confirmed before installation.

Generally, setup may involve a few one-time adjustments. If the device has the option of automatic-ON or manual-ON, this parameter may need to be configured for one option or the other. In most cases, the only adjustment is time delay. If the sensor includes a built-in light sensor, it should be factory-set to the maximum light level, ensuring the daylighting option does not activate until it is required; the light level setting can be decreased until the ideal setting is achieved.

“The contractor should test the sensors as the final step of the installation process,” says Villalobos. “But once the sensor is set up, you can confidently walk away knowing that it will operate consistently over time, as sensors do not require any maintenance.”

Big Energy Savings, Small Environmental Footprint

“For every switch that is replaced by a vacancy sensor, carbon dioxide emitted into the environment is reduced,” says Villalobos. “If 100 million households were to control just one 60W bulb with one vacancy sensor, this would represent almost 500 million kWh in energy savings—about $50 million per year at the average U.S. residential rate of about 10 cents per kWh—and a reduction of almost a billion pounds of carbon dioxide.”

California's Title 24 Energy Code Encourages Vacancy Sensors

In 2005, California released a major update to its Title 24 energy code. The 2005 version contains significant residential lighting provisions related to controls, a major departure since residential energy codes normally don't regulate lighting, usually just HVAC. Basically, when designing a home, all of the hardwired lighting must be high-efficacy OR controlled. Right now, high-efficacy means compact fluorescent.

For example, in a bathroom, either the lighting must be compact fluorescent or controlled by a vacancy sensor, which is a manual-ON occupancy sensor. The sensor detects when there are no people in the room, and then automatically shuts the lights OFF.

In many spaces, there is a three-way choice. In a media room, bedroom, dining room and other spaces, either the lighting must be compact fluorescent or controlled by a dimmer or controlled by a vacancy sensor. Then switch all high- and low-efficacy lighting separately.

Table 1. Title 24's lighting requirements in a nutshell