Solid-State Lighting

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It was near dusk as Liu Qi, president of the Beijing Olympic Committee Organizing Group, gazed at the massive “Bird’s Nest” Chinese national stadium in front of him. With the 2008 Beijing Summer Olympics scheduled to start in only three months, he was making an inspection tour of the stadium. Construction had just been completed.

But something didn’t look right.

Liu Qi looked back over his shoulder at the “Water Cube,” China’s national aquatic center, standing a few hundred yards from the stadium. The Water Cube gave off an iridescent blue and green glow. Earlier he had toured the facility and been mesmerized by the shifting multicolor patterns that had played across the exterior, provided by computer-controlled light-emitting diodes (LEDs). Looking back at the Bird’s Nest, he frowned. “What is the lighting being used for the stadium?” he asked his tour host.

“Why, it’s the standard fluorescent lamps called for in the design,” the man replied.

“I don’t like it; it’s too harsh,” said the president. He thought for a moment, then said “We want everything for the Olympics to be perfect. I want you to rip out the fluorescents and use LEDs for the Bird’s Nest, just like you did for the Water Cube.”

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The National Aquatic Center of China, also known as the “Water Cube.” The LED chips in the exterior architectural lighting were supplied almost entirely by U.S. companies. SOURCE: Courtesy of Cree.



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Solid-State Lighting I t was near dusk as Liu Qi, president of the Beijing Olympic Committee Organiz- ing Group, gazed at the massive “Bird’s Nest” Chinese national stadium in front of him. With the 2008 Beijing Summer Olympics scheduled to start in only three months, he was making an inspection tour of the stadium. Construction had just been completed. But something didn’t look right. Liu Qi looked back over his shoulder at the “Water Cube,” China’s national aquatic center, standing a few hundred yards from the stadium. The Water Cube gave off an iridescent blue and green glow. Earlier he had toured the facility and been mesmerized by the shifting multicolor patterns that had played across the exterior, provided by computer-controlled light-emitting diodes (LEDs). Looking back at the Bird’s Nest, he frowned. “What is the lighting being used for the stadium?” he asked his tour host. “Why, it’s the stan- dard fluorescent lamps called for in the design,” the man replied. “I don’t like it; it’s too harsh,” said the president. He thought for a moment, then said “We want everything for the Olympics to be perfect. I want you to rip out The National Aquatic Center of China, also known as the “Water Cube.” The LED chips in the exterior archi- the fluorescents and use LEDs for the tectural lighting were supplied almost entirely by U.S. Bird’s Nest, just like you did for the companies. SOURCE: Courtesy of Cree. Water Cube.” 2 Harvesting the Fruits of Inquiry

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And that’s how the American company Cree was contracted to light the last important The “Bird’s Nest” LED venue at the Olympics in Beijing. They had already supplied LEDs for the Water Cube, every Chinese national stadium in Beijing. video display in the main Olympic complex, and the tens-of-meters-long rolling video display SOURCE: Courtesy depicting the era of the Silk Road for the opening ceremony. All told, the entire event consumed of Cree. millions of LEDs worth many millions of dollars. An LED is a semiconductor device, related to the transistor, which directly converts electricity into light. In principle, close to 100 percent efficiency in the conversion of electricity to light is possible. This is radically different from conventional incandescent and fluorescent lamps, which have been limited for many decades, despite much effort, to about 5 percent and 25 percent efficiency, respectively. The first practical LEDs had very low efficiencies and were extremely expensive, about $200 each. During the 1970s efficiencies improved a little, but the price dropped dramatically— to a few pennies each. And so LEDs became widely used as indicators in clock radios and consumer electronics. LEDs suitable for lighting only became possible when new semiconductor materials investigated by scientists in academia and in industry reached sufficient maturity. The development of gallium nitride materials enabled the world’s first practical blue LEDs in 1993. Blue was the missing color—the holy grail—and its appearance on the scene finally enabled white LED light to be created, by mixing the blue with other colors. As researchers made progress, LED technology rapidly advanced and began to conquer incumbent technologies such as those for traffic lights. Red, yellow, and green LEDs used as little as 1/10 the electricity of the existing traffic light incandescent bulbs, saving roughly $1,000 of electricity per intersection each year. Today, roughly 80 percent of the traffic lights in the United States use LEDs. During the past decade, improvements in LED technology have followed a kind of Moore’s law (called “Haitz’s law”3 in the case of LEDs), rapidly increasing in performance and dropping in cost. Today, white LED lightbulbs are widely available in stores across the country. 3 Harvesting the Fruits of Inquiry

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The economic impact of these developments on employment will be significant. In 2007, the U.S. lighting industry employed 60,000 people nationwide and shipped $13.5 billion in lighting products. These products have good color quality and an extraordinarily long life (50,000 hours as compared to 5,000 hours for fluorescent lights and only 1,000 hours for incandescent lights). And LED lighting energy efficiencies are now surpassing those of fluorescents.4 Best of all, the costs continue to plummet with the passage of time: Bulbs that cost as much as $100 each when introduced in 2008 have seen their price drop to $10 per bulb by 2013.5 The development of this revolutionary new technology was supported by the National Science Foundation, the Department of Defense, and the Department of Energy. “There’s no doubt that Cree wouldn’t exist if it weren’t for the sustained frontier research funding that we received from the federal government in the early years, and the foresight and vision of the government program managers who realized the potential,” says Chris James, Cree’s vice president for strategy. “No venture capitalist would ever make the kind of high risk, decades-long investment that we needed.” What does the future hold? Current scientific research and development promises future LED lighting that is even more efficient and less costly. Research topics include how to allow electrons to move more easily in the LED layers (to reduce electrical resistive losses), how to reduce defects in the semiconductor material (to reduce parasitic channels in which electrons lose energy without emitting light), and how to “extract” more light from the LED once the light is created inside it—that is, to reduce the amount of light that is trapped and re-absorbed in the LED.6 While the best products currently on the market have energy efficiencies of around 25 percent, cool white LEDs have already demonstrated 50 percent in the lab.7 Ultimately, the industry believes it may achieve energy efficiencies of 70-80 percent, although much basic research will still be needed to reach those levels.8 According to a recent study for DOE by Navigant,9 by the year 2030, LEDs are expected to reduce the electricity used for U.S. lighting by 46 percent, resulting in annual savings of $30 billion, eliminating the need for ~50 large (1,000 megawatt) power plants, and reducing the emissions of 210 million metric tons of carbon every year. Moreover, the costs of LED lighting will continue to drop, as more light is coaxed out of every LED chip and as improvements in manufacturing techniques continue. It is believed that in the next dozen years the purchase price of LED bulbs will drop by a factor of 10.10 The economic impact of these developments on employment will be significant. In 2007, the U.S. lighting industry employed 60,000 people nationwide and shipped $13.5 billion in lighting products.11 LED lighting is an exciting new technology that is expected to have tremendous economic benefit for the lighting industry, which until recently had essentially been 4 Harvesting the Fruits of Inquiry

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reduced to selling products virtually indistinguishable from each other. The new performance possibilities represented by LED lighting should rejuvenate the industry as well as enhance human productivity and create wealth. And this is only the beginning. The very form and functionality of our lighting is destined to evolve into something difficult for us to currently imagine. Researchers are beginning to look at how to incorporate micromechanical optical components­ electrically activated miniature — mirrors and lenses—into the LED chip surface. This could allow beams of light from a lamp to be focused from a wide area to a spotlight. When combined with sensors, such lamps of the future could track peoples’ locations and activities as they move about a room, and adjust the intensity and distribution of the light to match the activities of a room’s occupant. Imagine living in such a world: instead of flicking on a light switch or adjusting a dimmer as you enter a room, the lamp could automatically adjust the color and spectral content of the light it emits to match the ambient light coming through the windows. Perhaps the lighting system could also respond to the mood and day/night biological rhythms of the perceiver—arriving home on a cold winter’s night, your home would be bathed in a warm, inviting glow as you stepped through the door. Or imagine how, as you enjoy the sunset of a summer evening, the lighting system might adjust to complement the orange and pink tones that streak the sky. This more intelligent and judicious allocation of light—the right photon in the right place at the right time—will not only improve the efficiency of our lighting but will also improve our everyday lives. 5 Harvesting the Fruits of Inquiry