Gradual progress for high-brightness LEDs

17 Jun 2002

Solid-state lighting can offer enormous energy savings in comparison with conventional lighting technology, but high-brightness LEDs still have some way to go before they begin to achieve significant market penetration. Jacqueline Hewett finds out more.

From Opto & Laser Europe May 2002

During the first five months of 2002, two of the main players in the light-emitting diode (LED) market - LumiLEDs and Osram Opto Semiconductors - showcased concept vehicles fully equipped inside and out with high-brightness (HB) LEDs. In a market dominated by large firms, two of the other major players, Nichia and Cree, have also announced technological breakthroughs: an increase in the output power of surface-mount white LEDs and the production of green-emitting LEDs, respectively.

As rival companies race to develop similar technologies, the value of today's HB LED market already exceeds $1.2 bn (EURO 1.4 bn). And it is set to increase to $3 bn by 2005, according to analyst Strategies Unlimited. While new advances continue to be made, HB LEDs are already penetrating niche markets. Consumers are set to reap the rewards with significant savings in energy, and therefore, in cost.

An eye-opening example is the case for using HB LEDs in traffic lights, which would consume 85% less electricity than using conventional incandescent bulbs. If the 100 million traffic lights in the US switched to LEDs there would be a staggering saving of $190 m in energy costs per year, and an annual reduction in national energy consumption of 3 billion kW/ h. And the story does not end there. There are 100 million exit signs in the US today, containing incandescent lamps that consume a total of 20 billion kW/ h of electricity per year. By switching the signs to LED lighting, approximately three-quarters of this energy could be saved. Additionally, using HB LEDs to replace neon offers a conversion efficiency of 80%. In other words, rather than using 100 W of neon, you could now be using 20 W of red LEDs instead.

Driven by the potential cost savings, the US government has launched an initiative to try to accelerate time-to-market. The 10 year plan, called the Next Generation Lighting Initiative, is part of the National Energy Bill and offers researchers the chance to get their hands on $30 m next year alone to develop the technology.

The advantages of using HB LEDs for general illumination, or solid-state lighting (SSL), may be enormous, but where does SSL fit in to an established global lighting market with an estimated value of $12 bn in 2001? While experts agree that there is a market for white light, the consensus is that significant market penetration will not be seen for at least another five years. Bob Steele of Strategies Unlimited explained: "LED lighting is still a very small part of the total world lighting market - less than 0.5%. In 2001 it was valued at $50 m but we expect it to grow to more than $250 m in the next five years. And that figure could easily be exceeded if the technology continues to accelerate."

Steele added that although SSL is expected to see growth in the next five years, it is unlikely to take over a huge fraction of the lighting business as a whole for another 10 years. "To us it seems more like a 10 year problem than a five year problem to really compete on a large scale with other forms of lighting," he said.

The key to SSL's growth lies in markets with high margins but low volume requirements. There has recently been a flurry of activity in single-colour HB LEDs for niche market applications. "Most of the applications are in coloured LEDs at the moment," said Steele. Researchers are now channelling their efforts in this direction.

Although new sectors are constantly emerging, however, there are several applications in which the use of HB LEDs is already well established. These include display backlighting, the automotive industry, signs and traffic signals.

The largest sector of these is display backlighting, particularly for use in mobile phones. All mobile phones use LEDs for their displays. Typically these have been low-cost greenish-yellow, but there is now significant interest in other colours.

Asia, particularly Japan, is leading the way in this area. Companies are using high-brightness blue, green and amber LEDs which have really taken off in Japan, although very little activity has been seen so far in the US and Europe.

Larger displays are also set to benefit from this technology. In March this year, LumiLEDs announced that it had teamed up with Mitsubishi Electric Corporation to produce the first thin-film transistor liquid-crystal display (TFT-LCD) modules. Using their Luxeon HB LED range, the two firms claim that the TFT-LCD modules will provide higher brightness levels, better colour fidelity and longer lifetimes than traditional backlighting solutions such as cold-cathode fluorescent lamps. The first monitors are expected to become available by the end of this year.

Nichia in Japan is also engaged in the development of white LED technology. Earlier this year the company announced that it had developed surface-mount white LEDs achieving a luminous intensity that was 50% greater than current products. Nichia is currently ramping up the production of these devices.In the automotive industry a number of applications have been developing over the past 10 years, both for external and, more recently, internal lighting. The first exterior applications to emerge were brake and indictor lights. Michael Godwin, product market manager for Osram Opto Semiconductor, explained: "The first exterior light was red, because the lumens per watt were better than in incandescent bulbs. This offered the opportunity for growth in this area."

The fundamental quantity of lumens per watt is a crucial factor in the successful market penetration of HB LEDs. The right combination of lumens per watt - a measure of the efficiency of a device - and lumens per US dollar is the holy grail that all researchers are striving towards.

Over the past five years, with red-emitting HB LEDs matching the efficiency of incandescent lamps of the same wavelength, European car manufacturers have been quick to adopt the technology. Steele commented: "For exterior lighting, we now see a European market approaching 90% for the centre high-mounted stop light (CHMSL), or third brake light."

And the simple reason for this is cost. In the US, where Steele says that the law requiring a third brake light has been in existence for 12-14 years, CHMSLs initially used incandescent bulbs. They are now gradually switching to LED-based devices. Europe, however, passed the law requiring a third brake light later than the US, in the latter part of the 1990s.

"By the late 1990s, the LED CHMSLs had come down in price dramatically and it was an easier proposition to sell in Europe," said Steele. "In the US, and also Japan, penetration is approximately 20%. Europe really leads on this one." Car interiors also benefit from this technology, with HB LEDs now being used in instrument clusters, radios, air conditioning, switches and reading lights. But the main drive in the present market is to increase the brightness of the LEDs for use as vehicle headlights.

And competition in this area has been increasing, particularly between LumiLEDs and Osram. LumiLEDs has based the headlights on its concept car on its proprietary Luxeon Star high-power LED-based light sources, which offer an efficiency of 30 lm/W from a single LED chip. Osram uses its TOPLED technology, which operates at a comparable efficiency level.Both companies cite the same advantages for making this change. LED technology provides improved reliability, compact packaging, flexible optical designs and - most importantly - power savings throughout the vehicle. With efficiency levels constantly improving, the factor that is again holding up penetration into the market is amount of lumens per dollar.

"In a lot of cases it is simply down to the cost," explained Godwin. "We will see slow growth and penetration, perhaps over five to 10 years. The savings make it a viable option," he added.

Although LEDs are making inroads into the automotive market, they already have a foothold in a related market. According to Steele: "Traffic and road signs would probably be the largest single-colour application at present. Another area that is growing quickly is what we call channel letters - where you have these big plastic letters lit from the inside, usually by neon." This application is now at a point where is it becoming very cost competitive.

And the reason for this is not only the reduction in power consumption. Steve Johnson, lighting research group leader at Lawrence Berkeley National Laboratory, US, explained: "The reason LEDs are cheaper than incandescent bulbs is that you are only producing red in the LED, whereas incandescent bulbs have to be filtered. The cost is in generating all the light that you are not using. You are only using a small part of what you are producing."

This cost reduction has paved the way for single-coloured LEDs to enter both the signs and traffic-signal markets. Emission of light in one waveband is an inherent advantage of HB LEDs used in these areas. LEDs have other advantages, however, which will aid their transition into markets such as street lighting.

Johnson continued: "The thing about LEDs is that you have the function of focus. Other sources distribute in all directions unless we put a reflector there. With LEDs, they don't uniformly distribute in all directions. What is sometimes lost is that we don't have to generate the same number of lumens, or the same amount of light, as compact fluorescent sources because we can focus the light."

Even though HB LEDs are now being used in a variety of niche applications, both the HB LED and SSL markets are still in the early stages. But with the HB LED market growing at a rate of more than 50% a year, there are likely to be many more applications for these devices that we are not yet aware of.

It seems as though everything is in place for progress and the future of SSL is now in the hands of the developers. Steele said: "Growth in areas such as signs, vehicles and backlights will generate the revenue, volume and profit that will enable work to be done on SSL to develop higher efficiencies. SSL will benefit from all of these activities. Just ramping up manufacturing volumes helps to bring costs down."

And with programs such as the US Next Generation Lighting Initiative, developers will be able to advance the technology to bring costs down and efficiencies up. These are exciting times in this young market. Steele said: "There's a lot of activity, there's a lot of research, there's a lot of government and industrial activity. There is still a lot to be done but I am very optimistic. This really is a new approach to lighting."