Loosely defined as LEDs with at least a 1-W capacity, high-power LEDs are a hot technology that’s very much in the market spotlight. Since their emergence, they have found themselves in a diverse range of applications, and their many performance benefits have caught the attention of leading trade and consumer publications worldwide.
High-power LEDs represent a significant advance in lighting technologies and offer unparalleled user benefits in terms of energy efficiency, cost savings, and lighting performance (Fig. 1). They provide extremely efficient lumens-per-watt performance, in the realm of 80 lumens/W compared to just 15 lumens/W for incandescent lights and 70 lumens/W for compact fluorescent lamps (CFLs), generating substantial opportunities for energy savings.
Furthermore, the lifetime of a high-power LED can be 10 to 15 times longer than that of a traditional incandescent bulb and three to 10 times longer than a compact fluorescent light. This fact, combined with the enhanced durability of LED technology, results in major reductions in lighting maintenance expenses.
High-power LEDs also offer greater design flexibility than alternative lighting options. For example, LED systems are compact and deployable in conjunction with sensors and other lighting controls like dimmers, daylight controls, and dynamic color tuning.
These devices will become even more prevalent as regional, national, and municipal bodies transition from standard incandescent lighting to newer technologies (Fig. 2). Also, members of the European Union, Japan, Australia, Brazil, and Canada will be enforcing bans on incandescent bulbs by 2012.
In the United States, change has begun on a municipal level with cities nationwide switching traffic signals and street lights to LED technology. The move away from traditional lighting in the U.S. should accelerate as legislation such as Title 24 in California requiring energy-efficient lighting in buildings comes into effect.
While compact fluorescents and LED technologies both can meet energy-efficiency targets, only LEDs also meet hazardous material requirements. Compact fluorescents contain small amounts of mercury, and currently more than a dozen U.S. states have active or pending legislation that restricts the use of mercurycontaining lamps.
KNOW THY TECHNOLOGY
Standing on the cusp of a new era in lighting, driven largely by high-power LED technology, that misconceptions about the technology are still common. To effectively and efficiently integrate this evolving technology into the products of tomorrow, design engineers need an accurate understanding of the performance capabilities and design integration aspects of high-power LEDs. In the form of trueor- false statements, the following test outlines five common perceptions about highpower LED technology.
One:High-power LEDs exhibit high energy consumption.
False. One of the key benefits of highpower LED technology is its low energy consumption. It’s true that high-power LEDs consume more energy than standard LEDs. Even so, a look at some comparative figures demonstrates that high-power LEDs represent one of the lowest-consuming energy choices in the market.
A regular LED light consumes 75 to 150 mW while a high-power component consumes between 1 and 10 W. These are low energy consumption figures compared to 40 W for a low-power appliance bulb and 60 W for standard fluorescent fixtures. In some instances, the energy consumption of a 60-W incandescent-equivalent fluorescent is 15 W, which is much closer to that of high-power LEDs.
However, the mercury-free composition and longer life of LEDs often make them preferable over fluorescents. To combat the common misconception that highpower LEDs are high on energy consumption, many parties in the industry now refer to high-power LED technologies as highbright or HB LEDs.
Two:High-power LEDs aren’t a good choice for replacing incandescent lights in applications where color rendering is critical, and because white high-power LEDs employ a phosphor-coated blue chip structure, color performance is inconsistent.
False. Color rendering is measurable on a scale of 1 to 100, where 100 is a perfect match to sunlight across the visible spectrum. When the CRI rating falls below 80, the color perceived under this light won’t match an object’s true color.
Studies have shown that color matching is more important than lighting intensity in terms of viewing true colors. The human eye is not as sensitive to changes in light intensity as it is to even slight changes in color matching. This makes color rendering extremely important, especially in applications like lighting food in a refrigerator, a dressing room, or around a painting at a museum where accurate color perception is key.
Both white and color high-power LEDs now provide consistently high color rendering scores. Yet this wasn’t always the case, and it is a result of somewhat recent advances such as improvements in LED color rendering, made possible by advances in RGB LEDs. These devices feature red, green, and blue chips all in a single package that can produce white light or any color.
A good CRI score is generally greater than 90. Most compact fluorescent bulbs rate between 75 to 90. Incandescents garner up to 100. LEDs are just now reaching 90 and better, a goal that has been elusive since their inception roughly six years ago.
The CRI system doesn’t translate well to RGB LEDs, but a quick look at the spectrum of both a phosphor-converted white LED and an RGB LED will show how much more light is available in the emitted spectrum (Fig. 3). It is an intuitive leap to think that the more wavelengths of light present, the closer to true white light you will get.
Three:An advantage of high-power LEDs is that they are cool to the touch.
False, high-power LEDs do emit heat. This heat emanating from the solid-state core cannot escape in the form of infrared energy and requires thermal management for removal. The best type of thermal management for a LED system will vary depending on the application. A 1-W LED system may be able to remove heat by employing printed-circuit boards (PCBs) with extra copper while larger high-power systems require heatsinking technology.
The question then becomes, with the higher cost of thermal management, how a high-power LED will remain a viable alternative to some of the often cheaper, non-LED technologies. Thermally managed LEDs, though, offer longevity like no other products in the market.
Also, they are almost impervious to vibration and shock. They operate across extremely wide temperature ranges and offer output and color tuning that is unavailable in other standard lighting options. And, they have an inherent life span that easily exceeds current non-LED technology. All these factors create cost savings that significantly mitigate the investment in thermal management.
Four:Top LED providers now provide customized high-power LED solutions.
True. Not only has high-power LED technology evolved in recent years, the services offered by LED providers have expanded as well. What really sets a quality LED provider apart isn’t just the quality of its product but also the depth of its services.
A good LED provider can provide expert insights on how to implement LED technology into larger lighting systems. A quality supplier also should have the optical, thermal, and electrical system knowledge to identify the best possible LED solution for a specific application.
One way to gauge the quality of technical support is to pay close attention to initial interaction with a supplier. A good supplier should ask a broad range of questions about the system you are creating to make sure it is identifying technologies that closely match your specific needs.
The supplier will likely ask you about design challenges and about environmental and performance prerequisites. It will not only be able to tell you which LED best suits your needs, it will also provide information on how to integrate this technology with other system components like lenses, PCBs, wire harness, and panel-mounting technologies in plug-and-play modules.
Five: High-power LEDs are mainly for general-lighting applications.
False. With general lighting accounting for roughly 20% of electrical costs in the U.S., it is not surprising that much of the attention circling around high-power LEDs focuses on general-lighting applications. Cities stand to save as much as hundreds of thousands of dollars per year in lower energy, maintenance, and replacement costs by switching to high-power LED technology for applications like traffic signals, street lights, and parking structure lighting.
Yet new applications for high-power LED technology are emerging all the time, and many are quickly gaining in popularity. Some of the more popular include automotive (turn signal, headlight, dashboard backlighting, map lights, overhead lighting, running lights, license plate illumination, and accent lighting for decoration), appliances, backlighting, communications equipment, medical devices, security lighting, signage, and military designs.
In the years ahead, some of the most exciting high-power LED applications will be applications that combine with sensor applications—for example, lighting that switches on as you enter your driveway or approach a cooler at a grocery store.
Infrared LED technology is also a quickly expanding field. It includes innovative applications such as nighttime urban combat illumination, long-range emitters and detectors operating beyond 2500 ft., and ultra-high-speed agricultural sorting equipment. In the future, expect to see highpowered IR LEDs driving communications between appliances and between your vehicle and home, as well as changing the way we use night vision systems.
BRIAN COATES is the manager of highpower technology at Lumex and holds an EE degree from Northern Illinois University.