Solid-State Lighting Becoming Practical

Paula Doe, SEMI, San Jose, www.semi.org -- Semiconductor International, 6/13/2008 8:27:00 AM

Semiconductor-based lighting could cut the energy used by lighting in half, says the U.S. Department of Energy (DOE, Washington, D.C.). Because lighting accounts for about one-fifth of all electricity used in the United States, that could add up to some $98B in energy savings by 2020. DOE figures just replacing the country’s 60 W bulbs with 10 W LEDs would save enough electricity to power all of Las Vegas for a year — twice. Indeed, the government is so keen on the idea it is offering up to $20M in prize money to developers of viable commercial fixtures meeting its standards.

That dream is now a lot closer than people thought only a couple of years ago, as solid-state lighting technology made surprisingly big progress over the past year or so in getting more useable light out of the devices. That — and growing consumer and corporate interest in reducing carbon emissions — is starting to make the technology viable in an increasing number of market niches. The LED market jumped 60% in 2007 to $330M, according to Strategies Unlimited (Mountain View, Calif.), which projects a $1.4B market by 2012.

“Quite recently, LEDs have been coming into the general illumination market, where they’re replacing incandescent and halogen bulbs in retail displays, commercial premises and outdoor lighting, though the cost is still generally too high for residential,” said Robert Steele, director, optoelectronics, for Strategies Unlimited. “Light per LED package has doubled in the past two years, while cost has gone down 10% or so, so we’re getting more than twice the lumens per dollar. It’s not a stretch to see 10× more light output within five years, for a 10× decrease in cost.” Government incentives will also likely spur demand, as utilities in California plan a $2B dollar incentive program to start within a year and as mandated performance standards effectively phase out incandescent bulbs within 5-10 years.

One supplier claiming real progress is Cree LED Lighting Solutions (Morrisville, N.C.), with its recessed downlight fixture that it claims puts out the equivalent of a 65 W incandescent bulb while using only 12 W. CTO Gerry Negley said hotels, restaurants, hospitals and offices are opting for them for the high quality of the light and the reduction in electricity and maintenance costs. Payback period for one Friendly’s restaurant in Waverley, Mass., was within one year, Negley said.

Bucking the conventional approach of choosing the blue LED and the yellow phosphor top coating to get the best white light, the company instead chose the most efficient blue LED and the most efficient yellow phosphor coating, although that makes yellow, not white, light, and then adds an efficient red LED to make white. Negley noted that the company has demonstrated efficacy as high as 113 lm/W. “It was very expensive,” he said, “but in a couple of years, it will be common.”

1. Makers of solid-state lighting have improved light output markedly over the past two years, particularly for cool white light. (Source: Strategies Unlimited)

Luminus Devices (Billerica, Mass.) is also now pushing into the solid-state lighting market, said founder and CTO Alexei Erchak. His company has been mass-producing its high-brightness LEDs for projection TVs and projectors since 2006, and will start to supply them for LCD backlights later this year. It now aims at other applications that require lots of light from a single source. A single, large, higher-power chip simplifies the optical design and may prove less costly than assembling the typical array of small LEDs. The company recently raised an additional $72M in venture capital to expand into new general lighting markets.

While most light escapes from a typical small-chip LED from the sides and edges, Luminus tops its devices with a photonic lattice pattern to extract more light from the chip’s surface so it can make a larger device, allowing it to run at higher power and with greater total light output. Erchak noted, however, that an equally important aspect of Luminus’ technology is the packaging, where the company uses new materials and processes to manage the heat effectively enough to maintain reliability despite putting up to 100 W into a single device.

2. Photonic lattice gets more light out from the surface, allowing larger device. (Source: Luminus Devices)

Semi supply chain to bring down costs

Despite major recent strides, there’s still plenty of opportunity to bring down LED costs. Yields remain a problem, noted Steele, as the chips vary by wavelength, light output and voltage, and then they’re topped with a squirt of phosphor in epoxy that adds even more variability, leaving a lot of chips that don’t meet standards on one of the three measures.

>“We haven’t found the right chip or package yet,” Negley said. “The LED community is just starting to understand what the lighting community needs.” He argued that the key issues now are developing better drivers to convert down to the low 3 V level needed for the LEDs and better encapsulants that don’t optically degrade in light and heat. “With most materials, we know how they behave with temperature, but we don’t know how they behave with light,” he said, noting that the LED operating conditions are far more severe than those for photovoltaics. “It’s a question of finding the right polymer engineers and making them understand the problem.”

“We’re finding lots of companies to look at,” said Robert Walker, principal, Sierra Ventures (Menlo Park, Calif.). “We see the best opportunities around the infrastructure; for example, the thermal and electrical parts of the system, like the current drivers.” He noted that driver burnout is often where LED systems fail, as both the heat of the real operating environments and the extreme lifetimes expected require new approaches from suppliers. “People aren’t used to making stuff to last 50,000 hours,” he noted.