Light-emitting diode (LED) technology is rapidly improving and is becoming more common in business settings. Although LEDs are not ready for all general illumination applications, they may be a good choice for a variety of uses, including parking-lot lighting, commercial signage, desk lamps, undercabinet fixtures, refrigerated cases, and recessed downlighting. Today’s high-quality LEDs are more efficient than traditional incandescent bulbs and outperform compact fluorescent lamps (CFLs) in some applications, but it will likely take several years before they surpass linear fluorescent lights.
LEDs are compact, solid-state light sources that offer longer operating lifetimes than many other sources. They are also vibration-resistant, provide directional light output, turn on instantly, and perform well at cold temperatures. LEDs are easier to dim than CFLs, but not all LED products are dimmable; of those that are, not all of them work on all existing dimming circuits. In the past, LEDs were limited to niche applications such as traffic signals, exit signs, and other uses where monochromatic LEDs displaced highly inefficient filtered incandescent lighting. But in recent years, as the performance of white-light LEDs has improved and the costs have come down, this lighting technology has become competitive in a wider range of areas long dominated by more-traditional light sources. LEDs are a dynamic technology, and for those choosing between LEDs and conventional sources for a given application, the boundaries are constantly changing.
LED efficiency is approaching that of high-pressure sodium (HPS) and metal halide (MH) lamps, and LED fixtures can be designed with better light distribution. Some users have found LEDs accep for parking lots and street lighting, even if light levels are lower. A recent utility company study in Oakland, California, found that LED luminaires saved 35 percent on energy use while providing a more even light-distribution pattern, longer lifetime, and superior color rendering than HPS luminaires. LED light levels were lower than those provided by the HPS lamps, but they were deemed to be acceptable. Because LED fixtures currently have a considerably greater initial cost, the simple payback period is over a decade, although this is expected to decrease as prices come down in the future.
A number of streetlighting case studies are available through the U.S. Department of Energy’s (DOE’s) Gateway Demonstrations program. For parking lots, the DOE provides the fact sheet LED Site (Parking Lot) Lighting Technology Procurement Project (PDF). It has also posted the results of a field test performed at a supermarket in California, Application Assessment of Bi-Level LED Parking Lot Lighting (PDF), that was prepared by Pacific Gas and Electric Co. as part of the utility’s Emerging Technologies program. When considering LED fixtures for this application, make sure that light distribution and light levels will be adequate for your needs.
Though often neglected, overhead exit signs—which must be on 24 hours a day—can consume significant amounts of energy if illuminated with an incandescent bulb. Because LEDs are directional and monochromatic, there is no need for filters or reflectors, which diminish the output of the already inefficient incandescent light source. When illuminated by LEDs, exit signs will consume up to 90 percent less energy and require light replacement once a decade, instead of twice a year. For more information, refer to our exit signs topic.
Replacing fluorescent or incandescent lights for task lamps or undercabinet fixtures in offices can save significant amounts of energy. The directional nature of LEDs allows task lamps to be oriented to illuminate only the working area without wasting energy through the use of a reflector or by lighting unused areas. These savings can be further enhanced by delamping unnecessary overhead lighting and using occupancy sensors, which would dim or turn off the lamps at an unoccupied desk. An integrated office lighting approach has the potential to reduce lighting costs by 75 percent (Table 1). Even a modestly sized company can save thousands of dollars by using this lighting strategy, which can yield a simple payback period of just a few years in existing buildings. For more information, refer to the California Public Interest Energy Research Program’s technical brief on integrated office lighting (PDF).
In this application, one of the chief benefits of the LED is the directionality of the light output. Reflector-style incandescent lamps are shaped and coated to emit light in a defined cone, but “A”-style incandescent lamps and CFLs emit light in all directions, leading to significant light loss unless the luminaire is designed with internal reflectors. Therefore, the downlights that use CFLs typically offer a fixture efficiency of only about 50 to 60 percent. CFL reflector lamps lead to better fixture efficiency, but the lamps themselves are less efficient than bare spiral lamps. Enter the LED, boasting directional light output that enables the production of very efficient fixtures that emit almost all the light produced. LEDs can also dim more smoothly and deeply than CFLs, though not all LEDs are dimmable, and those that are may not be dimmable on all dimming circuits.
Table 2 shows a comparison of various types of recessed downlights. It is notable that there is a high-efficiency LED product available—more efficient than the best CFL alternatives. But the table also shows a low-efficiency LED product—less than half the efficacy of a CFL—that is also on the market, highlighting the need to choose carefully.
Retail accent lighting is a growing area for LEDs because they can vary in color, create sparkle, and aim the light precisely on an object or area. LEDs have been used in high-end retail stores for their “high-tech” aesthetic, interesting effects, and design flexibility; in cosmetics shops because they do not radiate heat; and in jewelry cases because of the sparkling appearance a point source of light lends and because their small size enables them to be used unobtrusively.
Using LEDs for marquee lighting and exterior commercial signage can result in better visibility, lower maintenance costs, and considerable energy savings. Many businesses have also begun to use LEDs for architectural lighting applications. Traditional architectural lighting may include neon border lights running around the top of a building or colored floodlights used to illuminate building exteriors, facades, or signs. Many high-profile businesses, such as the Hard Rock Casino and Hotel in Las Vegas, now use LEDs to provide this sort of exterior nighttime lighting. Even a traditional neon “open” sign can be replaced with a comparable LED unit for very little additional cost, while saving 75 percent or more on energy expenses. And because an LED sign will last two to five times longer than a comparable neon sign, it can be a decade or more before replacement becomes necessary.
Conventional refrigerated display cases are illuminated by fluorescent lights. LEDs offer several advantages in this type of setting, the most important being that they perform very well in cold temperatures. This is in contrast to fluorescent lamps, for which output drops appreciably. Also, fluorescent lighting dissipates waste heat (mostly infrared radiation) inside the case, whereas some of the heat generated by an LED system can be transferred outside the case, resulting in reduced refrigeration energy needs. And because LEDs are directional in nature, less light is wasted, which means even greater energy savings. As a solid-state technology, LEDs are easy to dim as well.
In November 2006, Walmart became the first major retailer to announce plans to use LED lighting in refrigerated display cases. In 500 stores, the company is installing low-wattage LEDs connected to occupancy sensors that will automatically dim the lights when no shoppers are nearby. Compressor loads can also be reduced because LEDs with lower wattage than fluorescents can be installed and because the heat sink for an LED can be placed so that at least some of the waste heat is dissipated outside the case. The technology has shown significant savings in the field. In a 2007 case study (PDF) published by Watt Stopper/Legrand, Walmart reported cutting its display-case energy use (lighting and refrigeration) by more than 90 percent from this change.
Although LED performance is getting better, it is still hard to distinguish good products from bad: A recent DOE report found that more than half of the LED products it tested came with “inaccurate or misleading literature.” Several programs are helping users to sort through the exaggerated claims. In September 2008, the Energy Star criteria for LEDs took effect and the Energy Star label is beginning to help users identify effective LED products. The second effort is the DOE’s Commercially Available LED Product Evaluation and Reporting (CALiPER) program, which provides objective test results for selected commercially available products. For the latest independent data on LED lighting performance, visit the DOE’s Solid-State Lighting web site. In addition, some manufacturers are also participating in SSL Quality Advocates, a voluntary DOE program that uses a lighting facts label to report data in a uniform, useful way based on established standards. As more manufacturers participate, it will become easier to compare products on a common basis.
LEDs are poised to move beyond niche commercial applications into more general lighting purposes. In the near term, LEDs will continue to expand into such areas as recessed downlighting, refrigerated cases, shelf-mounted undercabinet lighting, por desk or task lamps, commercial signs, and architectural illumination. Even though LED technology is advancing quickly, it will likely be a number of years before the technology is cheap and efficient enough to displace linear fluorescents for general indoor illumination.
As the LED market continues to mature, the Energy Star program will set higher benchmarks and widen the range of products evaluated. With a uniform industry standard, consumers should expect to see less of the widely varying—and often dubious—vendor claims that have plagued the industry in the past.
In an effort to accelerate the development of integral LED products, the DOE launched the L Prize competition to develop high-efficiency bulb replacement products. Integral LED lamps include the light source, the driver, and the connector (for example, Edison screw-base, pin-base, or GU) in one package. Many LED products are designed to replace conventional lamps such as A-line lamps, MR16s, or PARs. Some of them are fairly efficient, but most do not put out enough light to replace the incandescent versions that their manufacturers claim they can. In addition, the Energy Star program has developed criteria for integral lamps of all sorts—A-lamps, reflector lamps, PAR and MR lamps, and nonstandard lamps. The ratings will go into effect August 31, 2010. Details are available on the Energy Star web site (PDF).