The next time you walk into an empty meeting room or office on a sunny day, notice whether the lights are on. If yes, and the room has windows, you might wonder why someone — or some automatic system — hasn't turned them off to save energy.

It's a sunny day and the room is empty. Why are the lights on?

The problem of measuring and controlling lighting within buildings is more complicated and subtle than it appears. Decades after scientists recognized the large potential for saving energy by taking advantage of daylighting to give the electric lights a rest, automated technologies and systems that can do the job are only now close to appearing on the market. Researchers from Berkeley Lab's Environmental Energy Technologies Division (EETD), the high-tech start-up company Dust Networks, and SVA Lighting are now working together on technology to do exactly this — a technology that will save hundreds of millions of dollars annually on lighting energy costs.

Dana Teasdale of Dust Networks, Francis Rubinstein and David Watson of Berkeley Lab's Environmental Energy Technologies Division, and Steve Purdy of SVA Lighting Design have been working on a Department of Energy-funded research project to develop wireless networking technology solutions for the problem of using daylighting effectively to reduce lighting energy in buildings.

Dust Networks provides a wireless mesh networking technology consisting of "smart motes," which create a low-power, connected network of devices such as sensors, control devices, and computers. The company was founded by in 2002 by a team including Kristofer Pister, a professor of electrical engineering and computer sciences at the University of California at Berkeley, who first coined the expression "smart dust" as a way of describing tiny, expendable sensors.

Smart mote technology is now finding its way into commercial and industrial applications for making buildings more comfortable, reducing energy costs, and optimizing materials and energy use in industrial processes. Wireless motes have a wide variety of applications for controlling and monitoring systems and processes, but researchers expect their use as a tool for energy efficiency and environmental comfort in buildings to be widespread once products appear on the marketplace — a prospect that could be just a few years away.

Saving lighting energy through daylight and user controls

Lighting commercial buildings in the United States currently consumes about 3.7 quadrillion Btus (British thermal units) of primary energy a year, equivalent to the output of over 175 modern power plants. According to Berkeley Lab estimates, if buildings could automatically dim electric lights in daylit spaces, and building occupants could manually dim local lighting according to preference, the U.S. energy savings could amount to more than half a quadrillion Btus per year — about 14 percent of annual energy use for lighting in commercial buildings.

However, the effective use of these strategies requires a smart-building infrastructure — properly located sensors to measure how much daylight is available in a room and lighting fixtures that can respond quickly and reliably to on-demand user control, plus automated systems, software-based control algorithms, and a network to tie all of these devices and systems together.

Solutions for new construction and major renovation

Francis Rubinstein, a scientist in EETD's Berkeley Lab, has been applying networking systems to daylighting and lighting control problems for years. Starting in 2000, Rubinstein's team of researchers at Berkeley Lab began developing an integrated-building equipment network called IBECS to allow facilities managers to automatically control devices such as lighting in commercial buildings from a computer workstation, over a network installed within the building.

Originally developed for wired installations, the IBECS integrated-building equipment network is being revised for wireless technology.

They developed a set of wired prototypes, including a digital interface for dimmable lighting fixtures, a light sensor, switches, and a user interface for controlling the network from a PC. Their research demonstrated that automated network control of lighting systems could be cost effective in new construction and major renovation projects, where the cost of adding control wiring is not prohibitive.

The team's work on the network has continued. IBECS was recently expanded to allow control of off-the-shelf Digitally Addressable Lighting Interface (DALI) ballasts; DALI-based lighting products are in the marketplace now, so this enhancement of IBECS allows facilities engineers to customize control systems for their buildings using commercially available lighting products.

For advanced controls to penetrate the much larger existing-building market requires eliminating additional control wiring altogether, then demonstrating a new technological solution's effectiveness in real settings.

Dust settles on the problem

Rubinstein teamed with Dust Networks Inc. in 2003 to begin using wireless-mesh networking technology to extend lighting control to the huge existing-building market.

"The reason we began looking at wireless technology for lighting control is that wiring and installation costs are barriers to deploying control systems in existing buildings," says Rubinstein. "Existing commercial buildings use over 95 percent of all electricity for lighting, but it is not cost effective to add control wiring to the ceiling to control lighting loads. To capture the energy savings possible from daylighting and other strategies in these buildings requires technology that is reliable and inexpensive enough to be retrofitted to commercial buildings."

Components for smart wireless daylighting

The project team developed several components for lighting control using Dust Networks' SmartMeshTM technology. These included an analog control module and "mote-integrated dimmable ballasts" (MDBs), which will work in existing lighting systems.

The ballast is the unit in a fluorescent lighting system that provides power to the fluorescent tube at the proper frequency. Located in the lamp's housing, it is a featureless metal box containing electronic circuitry. Dimmable ballasts are an advanced design that allow lights to be tuned continuously from full brightness to a very low level (usually about five percent of total brightness), to save electricity when less light is needed or to reduce lighting glare.

Berkeley Lab researchers worked with the lighting industry in the 1970s to develop and test the first electronic ballasts as replacements for less efficient magnetic versions prevalent in the market at the time. Today, energy-efficient, nondimming electronic ballasts are common off-the-shelf products, accounting for a majority of the market share of ballasts for fluorescent lighting.

The Dust Networks mote shown here is part of a prototype lighting control system being tested to demonstrate wireless control of office fluorescent lighting for greater energy efficiency and control.

In the current research, the development team built prototype MDBs, standard dimmable ballasts that embed Dust Networks' mote technology as an integral component. An antenna on the mote extends outside the fixture, allowing the building control system to communicate wirelessly with that particular mote.

No wiring makes it cheaper

With mote-embedded MDBs no low-power wiring is needed, which reduces the cost of installing the control system and makes the technology easier to install in existing buildings. The facilities staff can replace old ballasts with new MDBs over time, adding economical lighting-control capability to the building during routine maintenance.

"The cost of wiring in advanced lighting systems has traditionally been a major economic impediment to their widespread adoption. The use of wireless technology substantially reduces the installed cost of these systems," says Berkeley Lab's David Watson.

The lights are controlled wirelessly by the motes, which receive instructions from Dust Networks' SmartMesh Manager, a single-board computer that connects the entire network of motes to a PC running lighting-control software.

An environmental sensor too

The research team has also developed a wireless environmental sensor that measures the lighting level in a room, tells whether it is occupied or empty, and transmits this information to the control system through a mote. The multisensor version of this device also contains a temperature sensor to help manage the room's heating and cooling needs.

With the initial phase of technology development completed, the research team will now turn its attention to developing more advanced second-generation systems and testing these devices in buildings.

A wireless network installation is estimated to cost 30 percent less than a wired network installation. Much of the savings is in labor (and there is no cost for wire).

Preliminary analysis of the costs and benefits indicates that installing this wireless control system in an existing 16,000 square-foot building costs about 30 percent less than a comparable wired system. The wireless system will pay for itself in three years.

If tests of the wireless technology in buildings prove successful, energy management and control in buildings will join the wireless revolution, and the marketplace will have a new wireless solution for saving energy in commercial buildings.

Additional information

• Technical details are in the report Adapting Wireless Technology to Lighting Control and Environmental Sensing, by Dana Teasdale of Dust Networks, Francis Rubinstein and Dave Watson of Lawrence Berkeley National Laboratory, and Steve Purdy of SVA Lighting (pdf).
• More about IBECS, the integrated building equipment communications network developed by Berkeley Lab's EETD
• More about Dust Networks
• More about the lighting research group at Berkeley Lab