LEDs are compact, energy-efficient 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 compact fluorescent lamps (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. 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 an ever-expanding range of areas long dominated by more-traditional light sources. LEDs are a dynamic technology, and for those choosing between LEDs and conventional lighting options, the boundaries are constantly changing.
Integral Replacement Lamps
Integral lamps, which feature an LED/driver package that can be installed as a single unit in a conventional socket, are available in the full range of lamp types including A-lamps (the technical term for the commonly used light bulb), PAR (parabolic aluminized reflector) lamps (which are used to direct light in flood or spot patterns), and others. Compared to the halogen and CFL alternatives, LEDs offer longer life and higher efficacy (Table 1). LEDs are more expensive, but prices are falling. The challenge has been to develop products that provide the same amount of illumination as the standard incandescent products in the same size package—heat is the enemy of LEDs, and the more power you put in, the more light you get out, but the more heat you have to dissipate. As LEDs have become more efficient, the size of the incandescent equivalents that can be matched has improved. As of mid-2013, A-lamps are available in sizes up to 100-watt (W) incandescent equivalent, PAR38 lamps up to 90-W equivalent, and MR16 lamps up to 50-W equivalent. These lamps are also available in a range of color temperatures, and many products have a good color-rendering index (CRI) score, which indicates how well lamps render colors close to their natural appearance. CRI values above 80 are considered good. For more information about color, see Energy Star’s Color & Mood page.
Table 1: Comparing integral LED lamps to CFLs and incandescent lamps
Integral light-emitting diode (LED) lamps provide better efficacy and longer life than halogen and compact fluorescent lamp (CFL) alternatives.
Parking-Lot and Street Lighting
LEDs can be a good choice for parking and street lighting applications because they perform well in the cooler conditions that are typically found outside at night, and because LEDs provide a more even light distribution and produce less light pollution and light trespass—properties that improve aesthetics and contribute to energy savings. The DOE’s Better Buildings Alliance has published specifications for LED parking-lot lighting and for parking structure illumination. The alliance estimates that employing LEDs can cut energy use by 40 percent or more (savings vary by application).
A DOE case study of a Walmart parking lot (PDF) in Leavenworth, Kansas, illustrates many of the benefits of LEDs and describes savings of more than 50 percent. More parking-lot and structure lighting case studies can be found on the Federal Energy Management Program website. The Lighting Energy Efficiency in Parking Campaign—run by the DOE in partnership with Building Owners and Managers Association International, the Green Parking Council, and the International Facility Management Association—also provides information on lighting for parking garages and lots. The campaign website features case studies and links to financial analysis and savings tools. For streetlighting, the DOE Municipal Solid-State Street Lighting Consortium offers a number of resources and case histories.
LED Troffers and Tubes
For ambient lighting, LED troffers—more so than tubular LED lamps—have become an effective alternative to linear fluorescent fixtures. Found in most commercial office spaces, troffers are long, recessed lighting fixtures that are typically installed with the opening flush with the ceiling and with their inner surface serving as a reflector. The DOE’s Exploratory Study: Recessed Troffer Lighting (PDF) reported on the results of the testing of LED troffers and LED tubular products installed in a mock office space. In addition to providing objective measurements, the study also shared the observations of a group of lighting designers, engineers, and facility managers. Researchers concluded that LED troffers can compete with fluorescent fixtures in lighting-quality factors such as glare, light distribution, visual appearance, and color quality. The only caveat: Some of the products flicker when dimmed, so it’s important that LEDs be compatible with the dimming products they’re paired with.
In the study, tubular LED T8 products weren’t rated as highly as troffers. There was no efficacy benefit, and the color quality varied widely among the products tested, with CRI values ranging from the 60s to the upper 80s. Also, the LED tubes produced glare and an uneven light-distribution pattern. Because of concerns about safety with tubular LED products, a safety inspection was conducted, revealing that more than half of the products would not have passed due to labeling issues, confusing installation instructions, poor mounting or construction, and other complications.
The DOE study also looked at retrofit kits for troffers, which typically keep the fluorescent fixture’s housing, replace the ballast with an LED driver, and either use the existing fixture’s lens or louver or replace it with a new diffuser. Although there were quality-control issues, the researchers concluded that the retrofit kit approach avoids some of the safety concerns that arise with the tubular LED replacement lamps. The kit approach also enables users to change the appearance of their existing fixtures. The DOE urged those who are considering this option to check that the kit is approved by an organization that’s part of the US Occupational Safety & Health Administration’s Nationally Recognized Testing Laboratory Program and that it complies with Underwriters Laboratories’ standard 1598C. It also recommends that users check for any limitations on the troffers with which the kits can be used.
Although high-intensity discharge (HID) and fluorescent lighting still dominate in high-bay applications, LEDs are making inroads. They offer lighting levels that are similar or greater than HIDs or fluorescents—and the technology is still rapidly improving. LEDs offer longer life, similar color quality, more controllability, and the potential for better light-distribution patterns. So, for example, you can waste less light illuminating the tops of storage racks, and you can provide more-even light distribution.
The most promising early high-bay applications for LEDs were in cold storage because LEDs’ performance improves in colder conditions. Since then, products have become more efficient, and high-bay installations have expanded to more-general warehousing applications.
For applications other than cold storage, the main concern is heat: LED performance and life are sensitive to high temperatures, and in unconditioned spaces, temperatures can get pretty hot. For applications in which high temperatures are expected, it’s important to check the specs on the equipment. Products are available that are rated for operation at ambient temperatures up to 150° Fahrenheit (66° Celsius), but at a cost premium.
Another property of LEDs that makes them well-suited for high-bay areas is that they emit little infrared or ultraviolet radiation, so materials like food or fabrics may have a longer shelf life. Additionally, LEDs contain no mercury, which is a plus in a food-handling environment and could reduce end-of-life disposal costs.
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 dim or turn off lamps at unoccupied desks. An integrated office lighting approach has the potential to reduce lighting costs by 75 percent (Table 2). 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).
Table 2: Energy savings from integrated lighting in a 120-square-foot office space
Using efficient light-emitting diode (LED) task lamps to illuminate only the work area in use allows office managers to reduce the amount of overhead lighting needed. This integrated lighting approach leads to significant reductions in energy costs and a smaller overall carbon footprint.
In this application, one of the chief benefits of LEDs 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. LEDs are available as integrated packages for recessed cans or as replacement lamps that fit into existing units.
Table 3 shows a comparison of various types of recessed downlights. Most LED products outperform their CFL cousins, and most surpass the 42 lumens/W efficacy required for Energy Star fixtures. But the wide range in performance of available LED products means that users must choose with care.
Table 3: Recessed LED downlight options
The best light-emitting diode (LED) recessed downlights outperform compact fluorescent lamp alternatives, but the wide range of LED performance means that users must choose with care.
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. LEDs have also been successfully used for accent lighting in high-end hotels and to illuminate artwork in museums such as the Smithsonian American Art Museum in Washington, DC, and the J. Paul Getty Museum in Malibu, California. Compared to other energy-efficient alternatives—such as CFLs and ceramic metal halide—LED lamps offer higher efficacy, instant-on performance, better dimmability, and longer rated lifetime.
Exterior Signs and Architectural Lighting
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 that run around the top of a building or colored floodlights that 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.
Refrigerated Display Cases
LEDs have become an increasingly attractive option for use in refrigerated cases for several reasons. Unlike linear fluorescent systems, whose output drops in low temperatures, the efficiency of LEDs improves in cold operating environments. LEDs are also directional in nature, allowing for less wasted light. Because of these benefits, LED light strips are more than 40 percent more efficient than five-foot high-output fluorescent lamps and associated ballasts in refrigerated display cases.
LEDs can also be tied to occupancy sensors so that the cases are only illuminated when shoppers are present. This is a particularly easy savings opportunity for supermarkets that remain open 24 hours a day. Occupancy sensors aren’t typically used for cases that are illuminated by fluorescent lighting because frequent switching reduces the life of fluorescent lamps; however, it has no impact on LEDs. This approach also lengthens the life of LEDs: The more time the LEDs spend turned off, the longer the lamps will last.
The use of LEDs also reduces case compressor loads in several ways. Because the cases use lower-wattage lamps, there’s less heat to dissipate. Additionally, the heat sink for an LED can be positioned to allow at least some of the heat to dissipate outside the case. With fluorescent lighting, most of the waste heat must be offset with additional cooling inside the case. Also, when LEDs are used with occupancy sensors, they’ll spend less time in “on” mode and therefore contribute less to the cooling load.
In addition, LEDs provide an even light distribution,are dimmable, have a very long lifetime, and have been shown to appeal to shoppers.