LEDs - The Next Generation Of Lighting  

The New York Times has a look at the slow evolution of LED lighting - Fans of L.E.D.’s Say This Bulb’s Time Has Come.

The nation’s Big Three of lighting — General Electric, Osram Sylvania and Royal Philips Electronics — are embracing a new era of more efficient technologies, like halogen, compact fluorescent and solid-state devices. Encouraged by legislation and the rising cost of energy, as well as concerns about greenhouse gases, consumers are swapping out incandescent bulbs.

The switch is forcing a fast change in strategy, as companies reposition their manufacturing lines. General Electric, for instance, said earlier this month that it was spinning off its unit that makes bulbs.

The bulb makers face a tough problem. Their businesses were built on customers who regularly replaced light bulbs. How do you make a profit when new lighting may commonly last 50 to 100 times as long as a standard bulb? Compact fluorescents, which use less than one-third the power and last up to 10 times as long as standard bulbs, have replaced incandescent bulbs in many homes and offices.

In some types of commercial buildings, L.E.D.’s are rapidly replacing older products. The industry seems convinced that new lower-cost L.E.D. bulbs, with their improved efficiency, will eventually become the chief substitutes for incandescent bulbs in homes.

L.E.D.’s, including new bulb types and applications, dominated the exhibits at Lightfair, the lighting industry’s annual trade event held in May in Las Vegas. Traditional tungsten bulbs were largely absent. L.E.D.’s were shown for street and parking lot lighting, under-counter lighting, residential bulb replacements and office lighting. They are being used in commercial refrigerators, as substitutes for fluorescents and for illuminating the outside of buildings, allowing for easy color changes. Television production studios are installing L.E.D.’s to save money and eliminate the need for climbing in the rafters to change bulbs or filters.

The problem, though, is the price. A standard 60-watt incandescent usually costs less than $1. An equivalent compact fluorescent is about $2. But in Europe this September, Philips, the Dutch company dealing in consumer electronics, health care machines and lighting, is to introduce the Ledino, its first L.E.D. replacement for a standard incandescent. Priced at $107 a bulb, it is unlikely to have more than a few takers.

“L.E.D. performance is there, but the price is not,” said Kevin Dowling, a Philips Lighting vice president and past chairman of the Next Generation Lighting Industry Alliance, an industry group that works with the Department of Energy. “Even at $10 to $15, consumers won’t buy L.E.D. bulbs,” Mr. Dowling said.

The L.E.D., a type of semiconductor, generates light when an electric current is passed through positive and negative materials. Energy is given off in the form of heat and light. Different colors and greater efficiency are created by altering the composition of the material. Typically, a compact fluorescent bulb uses about 20 percent of the energy needed for a standard bulb to create the same amount of light. Today’s L.E.D.’s use about 15 percent. Next-generation bulbs still in the labs do even better.

While compact fluorescents are beginning to replace standard light bulbs in many homes, lighting executives see those as an interim technology. They say the large size of the bulbs, the inability to dim many of them, the unpleasant color of the light and the five milligrams of mercury in each bulb will limit their appeal.

Philips is working to decrease the penetration of compact fluorescent bulbs. “We are not spending one dollar on research and development for compact fluorescents,” said Kaj den Daas, chairman and chief executive of Philips Lighting. Instead, the bulk of its R.& D. budget, which is 5.2 percent of the company’s global lighting revenue, is for L.E.D. research. Philips is betting the store on the L.E.D. bulbs, which it expects to represent 20 percent of its professional lighting revenue in two years.

Light-emitting diodes (LEDs) are better than compact fluorescent bulbs--LEDs use less energy, last longer, and contain no toxic mercury--but for general white-light illumination, they're still far too expensive for mass adoption. Now, researchers at Purdue University have taken a step toward making white LEDs with cheaper materials.

LEDs are semiconductors that emit photons when a charge is applied. To make white LEDs, you need an LED that emits blue light (the blue light is then either filtered or combined with red and green LEDs, to make white). Today's commercial LEDs generate blue light from a gallium nitride semiconductor expensively fabricated on a sapphire substrate. The Purdue group found a way to build blue gallium nitride LEDs by stacking metallic layers on silicon.

The benefits are several. Silicon is cheaper and available in larger diameters than sapphire is. Silicon also carries away heat effectively, meaning that it can remain in a finished LED device and allow the lamp to last longer and stay bright. Since sapphire is a poor thermal conductor, LEDs grown on the substrate have to be removed and transferred onto a different surface--costly extra steps, says Timothy Sands, director of the Birck Nanotechnology Center at Purdue, who led the research.

Although Sands says that he can't identify an exact cost savings until the devices are manufactured, the cheapness and scalability of silicon are reason enough for him to be "confident that it will be much cheaper [than sapphire]." Other improvements, such as better heat dissipation and reflectivity, also boost performance. The researchers have yet to report how the device's efficiency and total light output compare to that of current LEDs. "What's exciting is the impact this could have on energy savings" that would be derived from cheaper white-light LEDs replacing conventional lighting, Sands says.

The group achieved the trick using metallic layers. Since silicon absorbs light--a negative when the goal is to release it--Sands's group coated the silicon with a layer of zirconium nitride that reflects the downward-traveling light back to the top. To solve a second problem--that zirconium nitride reacts with silicon in a way that degraded the LED--they put a layer of aluminum nitride in between, which prevented these reactions. The last step is the addition of a layer of gallium nitride.