Feature

LED lighting: panel debates quality versus cost

LED lighting can be great—but LEDs won’t make a replacement for screw-in light bulbs any time soon.

By Ron Wilson, Executive Editor -- EDN, 5/8/2009

A wide-ranging panel discussion at EDN’s Designing with LEDs seminar last week explored many of the issues LEDs will face as they move into commercial and residential lighting applications. There is great promise, the panelists insisted, but the path won’t be easy. Francis Nguyen, senior product marketing manager at OSRAM, Willem Sillevis-Smitt, director of strategic marketing at Philips Lumileds, and Paul Scheidt, product manager at Cree Components, discussed the issues.

Conference chair and EDN editor Margery Conner opened the discussion with a simple question—why can’t we just use banks of ordinary 5mm industrial white LEDs for lighting?

The answer turned out to be less than simple. For one thing, Scheidt said, a typical 5mm LED produces about 6 lumens. So a big commercial fixture would require thousands of LEDs, creating interesting problems for driver designers, and in the end consuming about the same power as a florescent fixture of the same output. “The big advantage for LEDs in lighting applications comes when you design the LEDs for that purpose,” Scheidt said. “Then you can achieve output efficiency, directability of the beam, and reliability that you can’t get any other way.”

Nguyen offered a cautionary tale. “I walk through a neighborhood that has lots of those solar-powered LED yard lights,” he said. “And I started noticing recently that more and more of them are burned out. Well, those fixtures actually do use standard 5mm white LEDs. What happens—you can see this if you take one apart—is that the blue light from the LED is intense enough, especially if you overdrive it, to degrade the epoxy encapsulant. The epoxy turns yellow, and then it starts to crack. Once you get a crack, the LED will fail. So this is not a good use of these LEDs.”

The next question was more challenging. How will LED lighting avoid the same sort of problems that compact florescent lamps (CFLs) experienced early in their market life? Sillevis-Smitt weighed in first, explaining that like LEDs, CFLs had started out as high-priced lamps designed for long life. But the lure of the incandescent-bulb replacement market, coupled with the entry of low-cost producers from Asia, quickly drove vendors to trade away the long life in exchange for lower cost. This led to a complex situation in which consumers often don’t understand the characteristics of the lamp they are buying. In fact in many applications, inexpensive CFLs aren’t really direct replacements for ordinary light bulbs at all. But not knowing this, consumers buy the wrong bulb for their purpose and get frustrated when it doesn’t work. That is exactly the situation regulators are now trying to prevent with new standards, Sillevis-Smitt said.

Nguyen added that first of all, designers needed to understand that LED lamps required conductive cooling, while incandescents are designed to survive with only radiative cooling. So LEDs physically could not be screw-in replacements for incandescent bulbs in all applications. And today, he said, the cost per Lumen of LEDs is very much too high to replace incandescents or even CFLs. “Fixtures must exploit the long life of properly-designed LED lighting to have a competitive position,” he said.

Scheidt agreed with both statements. “The EnergyStar standards will be critical to the development of this market,” he said. Also, he underlined that the strength of LED lighting is not its cost, or even its efficiency, but the features that it can offer beyond just illumination. “We have to break people away from the expectation of a screw-in light bulb for very low cost,” he said.

A question from the floor then revisited the issue of low-cost entrants from outside the US. “Everybody uses low-cost manufacturing in Asia today,” Sillevis-Smitt responded. “The difference in cost of LED lighting is in the choice of materials. For instance, you can choose to use inexpensive epoxy that will fail, or you can choose to replace it with any of a number of compounds that are resistant to light degradation but are more expensive.”

“The package, the phosphor [that goes over the LED and adds a yellow component to the LED’s blue emission to product white light] and the die are the key components in a lamp,” Scheidt said. “There are lots of trade secrets and IP in this business, and most of the suppliers are quite vertically integrated. There’s only a core set of companies that have the IP for white LEDs. That could limit competition from low-cost producers who don’t know how to do it well.”

Another questioner pointed out that consumers have had access to long-life light bulbs, and have steadfastly refused to pay a premium for them. Also, for the most part, the questioner said, people stop using the dimmer switches in their homes as soon as the novelty wears off. So what is the hope of LEDs establishing a higher price point based on these features?

Scheidt responded that 70 percent of the lighting-fixture market in the US is commercial, not residential. Further, incandescent lamp sales are declining as people switch to more energy-efficient lamps. Only the US appears to be lagging in that trend. Sillevis-Smitt added that if you explore homes in Europe, you will find no incandescent bulbs, and pretty much every lamp will be on a dimmer. “In Europe, consumers compare against a gu10 halogen lamp and they see a two-year repayment on their investment,” he said. “And if you offer them added features, people are willing to pay additional money to enhance their lifestyles.”

A series of questions asked about what the maximum light output of the lamps really was, and whether it was a function of lifetime. Sillevis-Smitt answered that getting the best lifetime out of the lamps meant reading the datasheet, where output-vs.-life data was available. “In general, higher junction temperature and higher current will mean lower life,” he warned. “There are several failure modes on LEDs, but which one is most likely depends on the architecture of the particular lamp.

“In theory, physics says you could get about 230 Lumens/Watt at perfect efficiency,” eiaid. “Most products today are in the neighborhood of 100 Lumens/W, and we have so-called cool white lamps [emitting light with a higher color temperature] in the lab producing about 130-160 Lumens/W.”

Sillevis-Smitt added that outside the US, users preferred slightly warmer light, and the theoretical perfect efficiency would produce only about 200 Lumens/W at the lower color temperature. Nguyen agreed that pretty much all the major players had something in the neighborhood of 150 Lumens/W in the lab. But these are hand-built devices.

All in all, the panelists seemed confident in the future of LED lighting, but definitely not as a screw-in replacement for incandescent lamps. They warned also, at least between the lines, not to use the US as a judge of the global market, because economic conditions, cost and availability of electricity, and even preference in color temperature differed here from most of the world.