LED to the Future

Stephen DeAngelis

May 26, 2009

When most of us hear the term “light emitting diode” or LED, we think either about the little lights that tell us that our electronic gizmos are on or solar-powered landscape lighting that dimly mark walkways around people’s homes. For a few years now, there have been scientists touting the benefits of LED technology as a major breakthrough in energy savings. LED lights are “about four times more efficient than conventional incandescent lights and more environmentally friendly than compact fluorescent bulbs. The LEDs also are expected to be far longer lasting than conventional lighting, lasting perhaps as long as 15 years before burning out” [“Advance brings low-cost, bright LED lighting closer to reality,” e! Science News, 17 July 2008]. It is estimated that wide-spread use of LED lighting could cut electricity consumption by 10 percent. Getting people to use them, however, still presents a problem. Brightness, for one thing, used to be a problem for LEDs, “but recent advances have made them as bright as incandescent bulbs.” Cost is another challenge.

Last Christmas in the United States, there was a big push by many retailors to sell LED lights for decorating houses and trees, but they were more expensive than traditional strings of lights. One reason that LED lights are more expensive is that are normally “created on a substrate, or first layer, of sapphire. Researchers [at Purdue University] solved this problem, according to the e! Science News article, “by developing a technique to create LEDs on low-cost, metal-coated silicon wafers.” These breakthroughs are being achieved at just the right time. Earlier this year, “the European Commission formally adopted new regulations that will phase [incandescent] bulbs out in Europe by 2012. America will do so by 2014. Some countries, such as Australia, Brazil and Switzerland, have got rid of them already.” [“A brilliant new approach,” The Economist, 19 March 2009] The Economist article explains how LEDs work:

“An LED is made from two layers of semiconductor, an ‘n-type’ with an excess of negatively charged electrons, and a positive “p-type” which has an abundance of ‘holes’ where electrons should be but aren’t. When a current is applied across the sandwich, the electrons and holes team up at the junction of the two materials and release energy in the form of light. The colour depends on the properties of the semiconductor, and these can be tuned to produce light that is similar to natural daylight but with virtually no ultraviolet or heat. Light-emitting diodes have progressed from simple red indicators on electronic products to become torches, streetlights and car headlights. Now the first mains-voltage LEDs designed as direct replacements for incandescent bulbs are arriving on the market. Some, such as the Philips Master LED range, promise energy savings of up to 80% and a working life of 45,000 hours.”

The article underscores what I mentioned earlier — right now LEDs are not cheap. The problem remains the cost of the sapphire layer used in most LED lights. Cambridge University researchers, like those at Perdue University, have come up with a way to use cheaper silicon wafers and gallium nitride.

“Gallium nitride is a semiconductor used to create bright-blue LEDs. These can be made to emit white light by coating the device with a phosphor compound that absorbs part of the blue light and re-emits it as yellow. When combined with the rest of the blue this forms a cool, white light. Most of the white LEDs now on the market are based on gallium nitride. At present these LEDs are made in machines similar to those used to make silicon chips, by depositing layers of gallium nitride on sapphire-based wafers. Sapphire is robust enough to withstand a process that first heats it to 1,000°C and then cools it to room temperature without causing cracks and other defects. It is, however, quite expensive. What Colin Humphreys and his colleagues at Cambridge have come up with is a reliable way to deposit gallium nitride on much cheaper silicon wafers, which they estimate could cut production costs to a tenth of what they are at the moment.”

The most widely used alternative to incandescent lights is compact fluorescent lighting (CFL). Getting people to switch over to compact fluorescent lighting, however, has been a struggle. Some people don’t like their appearance; others don’t like the color of light they emit; still others don’t like the cost. Environmentalists don’t like CFLs because they contain mercury. Using them outdoors has also been a challenge because they don’t like cold weather. LEDs could change all that. “Unlike compact fluorescents bulbs,” reports Eric A. Taub, “they contain no mercury and they work well in cold weather. They provide a more pleasing light than fluorescents.” [“Industry Looks to LED Bulbs for the Home,” New York Times, 10 May 2009]. According to Taub, manufacturers demonstrated their wares at a recent lighting show.

“Manufacturers displayed LEDs incorporated into large warehouse, garage and street-lighting fixtures, flexible light ribbons, and replacements for the halogen reflector lamps used in kitchens and offices. Strips of flexible LEDs from Osram Sylvania put light in places where it could not otherwise fit. Later this year, the company will market tiny LED chandelier lights that use 6 watts instead of the 15 watts typical of an incandescent version. It says they will last 25,000 hours instead of 1,500 for an incandescent bulb. Also this fall, Osram, Lighting Science and Philips will introduce 25,000-hour LED lamps that look like traditional bulbs but use just 8 watts of electricity to produce the same amount of light as a 40-watt bulb. Much of the industry’s effort is aimed at making LED lamps that emit as much light as a 60- or 75-watt incandescent bulb. Cree, a leading maker of LEDs, showed a new version of its LED ceiling fixture that uses 6.5 watts, compared with 11 watts for last year’s model, to create the light of a standard 65-watt lamp.”

Most people won’t rush out and buy LEDs because their cost still remains high. The processes developed by researchers have yet to be commercialized. A 40-watt equivalent bulb still costs around $20. Taub points out that manufacturers have been slow to get onboard the LED band wagon because long-lasting bulbs will basically put them out of the lucrative replacement bulb business. The cost of LED bulbs is likely to come down, but analysts don’t expect them to ever be as cheap as incandescent bulbs — unless, of course, you consider life-cycle costs. In the long run, LEDs will save people money and reduce the energy needed to light the world. Even the developing world will benefit from the higher cost LEDs. According to The Economist article, “low-cost LEDs [could] … bring light to new areas. Philips, for instance, is planning to launch a small solar-powered LED reading light for Africa, where an estimated 500m people live without electricity. The simplest version, which it hopes to sell for less than $15, is designed to allow children to do their homework in the evenings without a candle or smoky kerosene lamp. Bringing down the cost of LEDs this way really will let in the light.” Fifteen dollars is still a lot of money in poor countries, but the expected lifespan and low energy consumption of LED products still makes them attractive for the developing world.

I first wrote about LED technology in a blog entitled Technology-based Reductions in Energy Consumption Touted. That post contains links to additional information, including information about an unsung Japanese scientist named Shuji Nakamura who invented LEDs. Right now, it looks like LEDs are the best bet for being the light of the future. If that proves to be true, Nakamura may become as famous as Thomas Edison.