The LED EvolutionLED performance, color quality, output, and consistency have come a long way, but improvements are still to be had with this ever-evolving technology.

Source: ARCHITECTURAL LIGHTING Magazine

Publication date: 2007-09-01

Solid-state lighting (SSL) technology is one of the fastest-evolving illumination sources. Use of light emitting diodes (LEDs) is well-established in a variety of applications that many people take for granted: automobile interiors and dashboards, cellular phone keypads and screens, televisions, computers, and other electronic devices, as well as theatrical stage lighting, street lighting, and architectural lighting.

Lately, the SSL industry has been focused on developing LED lamps and luminaires for general lighting applications in buildings as building owners and occupants grow increasingly aware of and concerned about energy use and costs and seek more efficient solutions. In the past five years alone the technology has progressed so rapidly that architects and lighting designers are tested to constantly keep up with all the latest developments. The challenge for the SSL industry lies in developing general-use LED luminaires and lamps that will deliver high-efficacy, high-quality (warm) white light at a cost-effective price point.

COLOR QUALITY, COST, AND EFFICACY

Currently, the SSL industry is working toward producing lower-cost, daylight-equivalent white light LED sources that exhibit minimal color shift and degradation, longer life, and greater light output for general use. While the costs of LED sources are decreasing continually, the price for white light is not yet low enough to make LED lamps or luminaires cost-effective for most applications. “Step one is to get the cost down so there's not such a huge gap between incandescent, fluorescent, and LED,” according to Kraig Kasler, vice president of product management and marketing for GE Illumination.

Lighting quality is an equally important aspect from the designer's viewpoint, but as Kasler points out, even if high-quality LED light becomes available, few designers will be able to use it unless costs also have fallen to acceptable levels.

On the other hand, Kathy Abernathy of North Providence, Rhode Island-based Abernathy Lighting Design and chair of the International Association of Lighting Designers' (IALD) Energy and Sustainability Committee, points out that using LED luminaires, even in limited applications, allows peripheral savings in HVAC load and costs because of their minimal heat output, which is attractive both to designers and their clients.

Delivering the warm-white light end-users are accustomed to receiving from incandescent lamps at high enough outputs, combined with low color temperature variation and high efficacy has been a big challenge. While cool-white LEDs provide stable, efficient light output, warm-white LEDs have greater color instability and color variation, and lower efficacies.

Warm-white LED technology is still new, and manufacturers of luminaires and LED chips still have a lot of work ahead of them. Because LED light is not naturally white, developers have had to find ways to create white light, and the two main processes available deliver different types of white light with different benefits and drawbacks. Applying different phosphor coatings is one method, but certain phosphors decrease LED efficacy. Color-mixing RGB systems are another method, but because each LED color degrades at different rates in application, color quality and efficacy are inconsistent. Some lighting companies are experimenting with different phosphors to discover which can deliver the best mix of desired light color with high efficacy, while others are developing better RGB color-mixing systems.

GE Lighting's Lumination VIO high-power LED uses a proprietary chip and phosphor system to effect a color shift of less than 100K within the overall Kelvin scale over a 50,000-hour rated life, which the manufacturer says also overcomes color control issues and provides high efficiency at warmer color temperatures. Philips Lumileds has developed a new phosphor technology, Lumiramic, that allows specific colors and temperatures of white LEDs to be produced. The company plans to introduce Luxeon products incorporating Lumiramic phosphor technology early in 2008. Ledon's Tempura LED spotlight, utilizing Philips TIR Systems' Lexel RGB color-mixing technology, allows the color temperature of the light to be adjusted from 2500K to 6500K while providing a constant luminous flux of 1000 lumens and consuming between 40 and 75 watts.

Heat in application also affects LED performance. When too much heat is generated in an LED fixture, the lamp's lumen output and useful life decrease. Managing heat in the fixture and understanding the environmental conditions of the lighting application are critical to the success of the LED product. Manufacturers use conductive materials to create a heat sink in their LED products that pull heat away from the light source; the better the heat sink, the more stable the LED's lumen output, color, and life.

Both higher efficiencies and lower costs will deliver the payback that designers, end-users, and building owners are looking for. According to Kevin Dowling, vice president of technical innovation for Philips Solid-State Lighting Solutions, consistency, quality, and amount of light output in warm-white LEDs have all improved dramatically in the past 18 months.

MEASURING PERFORMANCE

Absence of standards has made it difficult for designers to decipher the life expectancy and other performance aspects of white LEDs and white LED luminaires. A safety standard from United Laboratories (UL) recently was published. Along with UL and the U.S. Department of Energy (DOE), several other organizations, including the Illuminating Engineering Society of North America (IESNA), the Institute of Electrical and Electronics Engineers (IEEE), the International Commission on Illumination (CIE), the National Electrical Manufacturers Association (NEMA), and the American National Standards Institute (ANSI), are working on standards for measuring LED life, efficacy, lumens per watt, chromaticity, and color shift. Late in September 2007, DOE's Energy Star program released standards for LED lighting, which will go into effect September 30, 2008, with requirements for light output, efficacy, warmth of light, and light focus.

“DOE is accelerating their efforts in this standards area, because they know what happened when CFLs [compact fluorescent lamps] came online years ago. There were few standards and inaccurate claims, and that really inhibited the adoption of CFLs,” Kasler says.

One of the issues of debate has been manufacturers claiming their LED's efficacy, life expectancy, and light output based on the testing lab performance of the LED source, not its real-world performance in a complete lighting system. The DOE's most recent round of solid-state luminaire testing, released in August 2007, indicates that the problem of accurate reporting has not significantly improved.

Rensselaer Polytechnic Institute's Lighting Research Center (LRC) also offers guidelines for the effective use of SSL through its Alliance for Solid-State Illumination Systems and Technologies (ASSIST) program.

The SSL industry is acting quickly to develop standards for this lighting category, in part because the technology itself is evolving so quickly but also because the DOE and the aforementioned industry groups are confident that LEDs offer one of the best means of reducing the energy usage of lighting—one of the largest electricity consumers in the United States. Lighting represents about 22 percent of all energy use in the U.S.—one-fifth of national electrical consumption, according to the DOE. Four to five performance standards are expected to be completed this year.

SO LONG, INCANDESCENTS?

Though it is unlikely that general service incandescent lamps will be banned outright, the lighting efficacy standards under consideration in Congress this session would set minimum standards so high that most incandescents would become ineligible for use by 2012 at the earliest. Though there are alternatives to incandescents that are less expensive than LEDs at this point in time, the lack of incandescent sources efficient enough to meet the standards proposed will leave a huge gap in the market, one that potentially could be at least partially filled by LED lamps and luminaires.

However promising LED technology is, though, it is important to understand that most of the people who currently purchase incandescent lamps do so because it is an inexpensive light source—and LEDs still are an expensive option that do not yet reliably deliver the high-quality light for which incandescent sources are appreciated.

FORM FACTORS AND APPLICATIONS

There is a slight division in the lighting industry regarding the form LED luminaires should take. Some manufacturers are focusing on producing products that will accommodate existing lighting infrastructure and resemble conventional decorative and task lighting fixtures, while others are designing new formats that deliver lighting in unexpected and innovative ways that previously could not be accomplished with old lighting technologies.

LED fixtures designed to resemble conventional light fixtures range from recessed down-lights and pendants to undercabinet lights and tracklights. LED Lighting Fixtures has introduced its LR6 downlight, a complete recessed downlight trim kit with LED light engine, designed to fit into standard recessed housings. Winona Lighting's POPS fixtures offer conventional sconce, chandelier, and pendant light fixture configurations, but are integrated with LED light sources in several colors, including warm white, and have a playful, contemporary vibe.

LEDs can be used to provide illumination in nearly any kind of application, such as io Lighting's Luxrail LED-based handrail, designed to illuminate a path or stairs while providing ADA-compliant gripping surfaces. The fact that LEDs can be incorporated into just about any material, including fabrics, means that lighting could be made to emanate from the very surfaces and shapes of a building, from architectural elements to furniture. “LEDs have such unique characteristics that lend themselves well to new forms of lighting; new form factors, new bulb types that will perform much better than existing bulb sources,” Dowling says.

Some industry experts think that maintaining the same old form factors for lamping and luminaires with such a promising technology is short-sighted and wastes the potential of LEDs. “Trying to replace an existing light bulb in a socket with an LED light bulb is a waste of the LED's talent,” says Dr. Nadarajah Narendran, director of solid-state lighting for the LRC. “If you can look at applications where LEDs can be of better service to the end-user, that becomes a better value proposition.” But he concedes, there is a market for both.

GOOD INVESTMENTS

The lighting industry is investing heavily in LED technology. Several big-name lighting companies have acquired smaller, specialized LED development companies in the past few years. Royal Philips Electronics, for example, has acquired a number of LED developers, including Lumileds, TIR Systems, and Color Kinetics, and Cooper Lighting recently acquired io Lighting. Several industry partnerships between conventional lamp manufacturers and LED chip or semiconductor manufacturers also have been arranged, including cross-licensing agreements.

The DOE also has been investing in solid-state lighting research and development with $7 million in funding going to a variety of projects and industry partnerships. According to Jim Brodrick, DOE's solid-state lighting portfolio manager, nearly $200 billion or more can be saved if the DOE is successful in achieving general illumination with LEDs.

“These investments are advancing LED technology as well as associated technologies required to make LEDs useful, such as controls, power, thermal management, and optics,” says Jim Anderson, director of technology and projects for Philips Solid-State Lighting Solutions.

Every major lighting manufacturer wants to have some play in LED technology for when the market catches on; missing the boat could be disastrous. “I think probably over the next five to six years or so, we will see the market go to about 20 to 25 percent LED,” Narendran predicts. “Market transformation takes a long time. To get to 50 percent may take much longer.”

All in all, LED technology appears to be progressing in the right direction for adoption in general illumination and architectural applications, according to Kasler. “Efficiencies are getting better, costs are coming down, people are being forced to talk about the quality of light,” he says.