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An Inexpensive Wireless Lighting Control System to Improve Energy Efficiency

WiLight, a new wireless lighting control system developed by two researchers in the Lawrence Berkeley National Laboratory (Berkeley Lab) Environmental Energy Technologies Division (EETD), was a finalist for the 2006 Technology Breakthrough Award. The award competition is managed by the University of California, Berkeley College of Engineering's Center for Entrepreneurship and Technology.

Developed by EETD's Francis Rubinstein and Dennis DiBartolomeo, WiLight dims or switches overhead lighting according to occupant preference or a building-wide demand-response signal. The system was designed to be low cost to encourage building owners to retrofit facilities with this energy-efficient technology. Using a battery-less transmitter instead of a normal wall switch, the occupant can turn on and off or dim overhead lighting wirelessly. Using a radio bridge, a building manager can manually control the lighting system, or the lights can dim or switch off automatically in response to a signal from a demand- response server. Figure 1 is a picture of the system's control circuitry.

Francis Rubinstein looking at the interior ofWiLight transceiver.

Figure 1. Francis Rubinstein with the transceiver of the WiLight wireless lighting control system. (Photo by Anthony Ma, EETD)

The WiLight transmitter uses a clever energy-scavenging technique developed by EnOcean Inc. to eliminate the need for batteries. The transmitter harvests the mechanical energy of the user's clicking of the switch to charge up a radio transmitter that signals the transceiver to dim or switch the lights. This strategy avoids the maintenance headache of replacing batteries and reduces the system's environmental impact.

WiLight and Demand Response

WiLight can read a wireless signal from a building's demand response system to automatically dim lighting during a power grid emergency or when electricity prices are high. To accomplish this, the WiLight system works with CLIR (client logic integrated relay) technology currently being developed at Berkeley Lab with support from the California Energy Commission's Demand Response Research Center. CLIR is a demand-response client that allows buildings to automatically read a signal, sent from a utility server on the internet, indicating electricity grid status. If the grid is nearing an overloaded, emergency state, the CLIR box uses the WiLight radio bridge to send a radio frequency (RF) signal to the building indicating the level of crisis (moderate or severe). WiLight can read the signal and automatically reduce specified non-essential energy uses, for example by lowering lighting intensity to pre-set levels or raising air-conditioning unit thermostat settings. See schematic in Figure 2.

A Price Server connects to the Internet, which connects to a Building Demand Response Server. This server determines the Demand Response (DR) mode (normal, moderate, severe) and sends the correct mode to a receiver. The receiver radios the DR mode to a transmitter and a transceiver. The transceiver is composed of a radio, intelligence, dual relays and anolog dimming. The dual relays control the bi-level lights (2 x 20 Amps) while the analog dimming controls the dimmable lights (up to 50 analog dimming ballasts.

Figure 2. The economical WiLight system accepts a variety of inputs to increase efficiency and reduce energy use of building lighting.

Many buildings in California now have bi-level switching, as required by Title 24 energy-efficiency standards. This means that all, half, or none of the lights in a room can be on. WiLight works with the bilevel circuitry so that the demand-response technology can automatically choose lower light levels during a grid emergency. If a user turns on lights during the emergency, WiLight allows the lights to illuminate at the pre-specified lower lighting level but not at the maximum level until the grid emergency is over. WiLight is compatible with existing lighting products and protocols and can work with emerging wireless technologies. "This makes WiLight an extremely inexpensive control system for retrofitting large commercial buildings," says Rubinstein, "since the cost of additional wiring has been the major disincentive to lighting control systems in large existing commercial spaces."

Commercial Building Energy Use

Berkeley Lab studies suggest that lighting controls could reduce energy used for lighting in commercial buildings by nearly one-half, by automatically turning off or lowering electric lighting when there is sufficient daylight to make electric lights unnecessary.

Nationwide, there are 60 billion square feet of commercial floor space. Rubinstein estimates that if 30 percent of those buildings adopted lighting control systems by 2025, the nation could reduce its energy use by 700 billion kilowatt-hours, saving about $50 billion and reducing greenhouse gas emissions by 140 million metric tonnes, equivalent to the emission of 93 million automobiles.

— Allan Chen

For more information, contact:

  • Francis Rubinstein
  • (510) 486-4096; Fax (510) 486-4089

This research was funded by California Energy Commission's Public Interest Energy Research (PIER) Program, and the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy.

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