How can an energy-efficient, pinpoint light source best light up a room, or a part of one? That was the question recently asked in a five-week-long lighting-design class offered by the Department of Architecture at the University of California at Berkeley.

A new generation of LEDs will save energy on interior lighting.

Architecture 249X, titled "Technology and Design of Solid-State Lighting Systems," is headed by Susan Ubbelohde, associate professor of architecture. Usually Ubbelohde teams with architecture professor Cris Benton, but this year she chose to focus the semester-long lighting class on LED-based lighting, working with coteachers Steve Johnson, head of Berkeley Lab's Energy-Efficient Lighting Group, and his postdoctoral students Neil Fromer and Akos Boberly.

The light-emitting diode is familiar to most people from the pinpoint sources used in older computer and calculator displays and other electronics applications. Now these solid-state lights are showing up in other kinds of lighting applications, for example as energy-efficient traffic lights and airport runway lighting. The technological race is on to improve the light intensity of LEDs and decrease their manufacturing cost so that they can light rooms and perhaps supplant the incandescent bulb as a major source of electrical light.

A recent report prepared for the U.S. Department of Energy estimates that by 2025 the cumulative savings from solid-state lighting could reach anywhere from 505 to 1,848 trillion watt-hours (terawatt-hours) of electricity, depending on how rapidly LED lights are adopted in the marketplace — savings that could be worth up to $128 billion.

At Berkeley Lab there's a growing cross-disciplinary research effort, funded by the Department of Energy, to make technical improvements to LEDs so that they will become practical and inexpensive enough for lighting. Many other labs, both publicly funded and in the private sector, are working on LEDs as well. Technical hurdles remain to the large-scale production and use of these devices for room lighting, but experts feel it's a matter of a few years before those problems are solved, and LEDs come into general use as an energy-efficient room lighting technology.

Then what? LEDs won't plug into incandescent or fluorescent lamp sockets, so how can they be arrayed in a room to distribute their energy-efficient light to best advantage? Lighting designers will need to develop new fixtures that distribute LED light as efficiently as possible, and the 16 UC Berkeley undergraduates and their instructors have already come up with some answers to these questions. "The class provided a quick immersion in lighting design aimed at teaching students as much as possible through design, rather than through doing research," said Ubbelohde.

According to Berkeley Lab's Fromer, "we're beginning to see a push to get LEDs into the marketplace as a replacement for existing lights" — and because LED lights have qualities that differ from incandescent sources, they require a different approach to design.

Most lighting applications in typical homes and offices are either task or ambient lighting. The first need is met by desk lamps and other lighting devices designed for working in a focused area, such as reading, computer work, fine tool work, and the like. Ambient lighting needs are met by lights that illuminate spaces such as rooms, offices, and other enclosures.

LEDs are pinpoint sources with a focused distribution in the forward direction, while the familiar incandescent bulb emits light from a spherical surface. Instead of household 120-V alternating current, LEDs require a low-voltage, direct-current source. This means, among other things, that portable LED-based lights can run on batteries for a long time — outdoors enthusiasts have already discovered LED lights on the market for camping.

The students heard lectures from Berkeley Lab's Steve Johnson and Akos Boberly on lighting design and how LED lights differ from existing lighting technology. They went to local buildings to look at examples of task and ambient lighting design, searching for current applications of LED technology. Fromer provided assistance with the technology and wiring for these unusual sources.

By week three of the class, the students were expected to have an initial design for an LED task light of their own. They did three rounds of design work: an initial study model, followed by a mock-up and a prototype.

"I was impressed with their work, especially for a five-week project," says Ubbelohde. "Every team had a design strategy to use these tiny points of light to light up a larger area. We arbitrarily limited them to using five or six LEDs, limiting their options, but even within those constraints, there was a great range."

Johnson concurs. "We were so impressed with some of the designs that I invited interested students to explore the possibility of further developing and testing their designs at Berkeley Lab, and getting help to commercialize them."

A design by Enrique Sanchez and Beau Trincia showcases a single LED source by encasing it in a translucent diffusing cylinder attached to an adjustable gooseneck.

	A single LED source, by Sanchez and Trincia

A bedside lamp by Chu-Pang (Benson) Chen and Octavio Gutierrez can change from a blue night-light to a white reading light.

A combined night-light and reading lamp, by Chen and Gutierrez

Because the tiny LEDs are portable and easy to reconfigure, a user can pull the lamps off the wire and replace them anywhere he or she needs light. Ryota Shirai designed fixtures that look like lanterns. "Electricity is running through the hardware itself," he explains. "There is no wire connection through the fixture frame, so the light is removable and can be put it anywhere along the frame."

Hanging LED lanterns, by Shirai

Other designs also emphasize portability. "The lights are small and easy to power, so they are adaptable to a variety of uses," says Ubbelohde. One consisted of modular plastic snap-together parts with rechargeable batteries that the user could set on a table or use as a flashlight. Another placed the LED source on a tripod with an adjustable neck.

Still others came up with swingable or collapsible units that could point light in any direction and fold up into a unit small enough for a pocket or briefcase. One unique design had several LEDs embedded in a plastic sheet mounted on a rail, allowing the user to move the lights anywhere over a desk or workbench.

"All of the designs are much smaller and more compact than those you see using compact fluorescent lamps," notes Boberly.

Researchers are still improving LEDs in the laboratory for use as a room light source, says Johnson, but the UCB class showed that it's possible to begin designing lighting environments with them right away. The experience that students gain in exercises like this will help future lighting designers use energy-efficient LEDs when they become available on a commercial scale, perhaps not too many years in the future.

Additional information

• More about the Building Science Group in UC Berkeley's Department of Architecture
• More about lighting research in the Building Technologies Department of Berkeley Lab's Environmental Energy Technologies Division