In 2014, the Royal Swedish Academy of Sciences awarded the Nobel Prize in Physics to a group of scientists for their 1990s invention of efficient blue light-emitting diodes (LEDs), which enabled LEDs to generate white light.
The recipients were Isamu Akasaki, Meijo University and Nagoya University, Japan; Hiroshi Amano, Nagoya University; and Shuji Nakamura, University of California, Santa Barbara.
The lighting industry is in the midst of a tremendous and disruptive technological shift, driven by continuing advances in efficacy, long life and cost reduction that make LEDs an attractive choice for general lighting.
Today, LED luminaires are offered for virtually every application and are supported by industry groups, energy-efficiency program rebates, and a growing body of knowledge and standards. Performance, quality and cost have reached a competitive level and are expected to continue to improve at an even faster pace. As the category matures, the luminaire product offering is stratifying in a similar fashion to conventional lighting, with commodity and specification segments. In the specification segment, this period of extreme competition is driving manufacturers to add value, and they are showing a high degree of attentiveness to customer feedback and the resulting innovation.
The changing luminaire
Luminaires are designed around the form factor and light emission of light sources. The first generation of LED luminaires essentially incorporated LED packages into designs originally developed for conventional light sources. Though LEDs are very small light sources, manufacturers still had to design luminaires that supported the number of LEDs and associated heat sinking required to deliver the desired light output.
As efficacy and thermal performance of LED packages improve, manufacturers are enjoying greater flexibility in mechanical and optical design because fewer LEDs and less heat sinking are required. Lower wattage needs drive smaller luminaires and smaller apertures with greater lumen potential. As a result, the lighting industry is now developing new form factors that take advantage of the LED’s small size.
Meanwhile, optics—used to direct light out of the luminaire and into the desired emission pattern—are no longer centered on reflectors built around the light source. The directional light emission of LEDs has sparked a number of new optical approaches, such as total internal reflection (TIR). Typically constructed of injection-molded acrylic, TIR optics can be attached directly to the light-emitting end of the light source (typically smaller high-output sources), resulting in high optical efficiency and precise beam control. Some luminaires combine TIR with reflector-based optics.
Other developments include edge lighting, light guides and micro or imprinted optics in which complex structures enhance transmission, diffusion and optical control. Edge lighting is leading the slimming trend in luminaires.
Smaller luminaires also allow shapes that include custom lengths and complex angles, providing greater design flexibility. The development of flexible and translucent circuit boards permits freer deployment of luminaire shapes.
A final interesting development is the ability to integrate LEDs into building materials and textiles, turning them into luminaires.
From retail to manufacturing, color perception matters, and the color we see is largely dependent on the spectral composition of light. LED color performance has improved remarkably.
Approaches have been developed to produce a more balanced color spectrum. One is new phosphor mixes that emphasize deep reds. Another is an intentional shift from the black body locus to produce a more balanced spectrum with warm white products. A third is the use of violet LEDs instead of blue for white light production, which not only improves perceived color quality but also arguably enhances perception of white.
This latter point is interesting because white is a very popular color, but it is not part of the color rendering index (CRI) rating. Many paint, textile and other manufacturers use fluorescent-whitening agents to produce a “whiter than white” appearance in their products. These agents absorb ultraviolet and violet light and re-emit blue light, causing fluorescence and enhanced perception of whiteness. While many conventional lamps produce such an emission, the output of LED sources is precisely engineered, often with no violet emission. A 2014 study—conducted by Kevin Houser at Penn State University’s Department of Architectural Engineering, and funded by LED product manufacturer Soraa Inc.—found that blue-pumped LEDs (used in a majority of white-light products) do not excite fluorescent-whitening agents as well as violet-pumped LEDs.
One problem with LEDs and color is the limitations of the CRI metric itself when applied to this technology. While it has served as a reliable color-rendering indicator for conventional light sources since 1964, it does not reliably address the variety of ways in which LEDs produce white light. As a result, the international lighting community, including the Illuminating Engineering Society, is looking at new methods for measuring color quality of white-light sources. Two proposed alternatives include the color quality scale and the gamut area index.
One of the most exciting advances in LED lighting is in the area of controllability. A majority of products are offered with 0–10 volts direct current (V DC) dimming standard. Reduction of perceivable flicker and dimming down to ≤1 percent are areas of focus in manufacturer development efforts. Driver manufacturers are beginning to offer higher grade products with greater dimming and electrical performance.
LED technology is leading the way in the digitization of lighting. With intelligent drivers, lighting can be programmed for constant light output over the life of the luminaire, saving energy while potentially extending the product’s life. Luminaires can be programmed with custom light output and wattage settings to support precise design requirements. They can be programmed to indicate end of life. Luminaires can be individually zoned and rezoned in groups and calibrated and controlled using software. Sensors and controllers may be integrated into the luminaire, potentially simplifying installation while offering the benefits of a packaged solution. Devices may communicate using low-voltage control wiring or radio-frequency wireless signals. While some solutions offer intelligent room-based, luminaire-integrated lighting control, the most advanced enable communication between rooms and to a central control station, allowing energy and performance monitoring and measurement.
Additionally, in some products, the color temperature (tone) of white light can be adjusted manually or automatically with varying degrees of range and precision. This allows the color appearance of the light to be controlled, to calibrate and tune it during commissioning, to support changing application needs and to address color shift that may occur as the LEDs age with operation. Some products dim to a very warm color temperature, which is suited for applications where users will expect the lighting to dim similarly to incandescent lighting. For very discerning clients, some configurations also allow adjustment of hue and saturation separately from color temperature.
Because LEDs are highly sensitive to thermal and electrical conditions, LED source efficacy and life is highly dependent on luminaire design and construction. For this reason, LED luminaires are highly engineered and typically highly integrated devices. At end-of-life, owners will be replacing complete luminaires, imposing a higher cost. Additionally, luminaires installed today will be less efficient than luminaires installed a short time from now, creating an incentive to wait.
The ideal scenario is for the luminaire to be serviceable and upgradeable with standardized electrical connections. Some manufacturers offer serviceable components, but they must confidently indicate how long they will have available stock, as LED packages are continually being phased out due to ongoing improvement. Drivers may be available over a longer term, but, due to a lack of standards, the driver must typically be replaced by the same driver or one approved by the original manufacturer. Replaceable drivers should feature a quick disconnect for relatively easy replacement.
The Zhaga Consortium is creating voluntary specifications defining electrical and physical connections. Products manufactured according to these specifications provide some assurance of modularity and future-proofing. Otherwise, the best way for owners to realize the full value of their investment is to select high-quality products offering the greatest confidence in performance and longevity.
In the end, as with end-of-life indication, the success of industry efforts at modularization will depend on demand among owners, not to mention other issues.
Risks and rewards
Lighting is going high-tech, presenting new opportunities and threats for electrical contractors. The biggest challenge is that the LED is still a young technology. Attracted by the opportunities and disruption LEDs cause, many new suppliers and products have entered the lighting market, some good, some not so good, and their longevity is uncertain.
Continuing advances in the technology have been extremely disruptive to lighting product development and cycles. New LED chips may create the need for new drivers, which may have different control compatibilities (and capabilities), while also affecting optical, thermal and luminaire design. The product cycle for an LED product could be as short as about a year and as long as about two years. During a long project cycle, what is initially specified may not be available (or compatible) later, requiring contractors to pay attention.
Key voluntary industry standards—IES-LM79, IES-LM80 and ANSI C78.377—provide standardized testing of light output, efficacy, lumen maintenance up to 6,000–10,000 hours (which is then extrapolated to L70 or some other point using IES-TM21), and color characteristics. However, standards covering LED electrical and operating characteristics, electrical connections, and dimming interfaces have not been developed during this very innovative period, but would likely be beneficial.
At this time, the most beneficial step electrical contractors can take is to familiarize themselves with the technology, products and manufacturers. While owners respond to price, this is still a get-what-you-pay-for period in the LED market. Those who have the expertise to understand the technology’s issues, find reliable suppliers, match lighting and controls, and qualify good products will be more likely to have satisfied customers.
Various government and industry organizations offer a number of tools that can be helpful, including the Next Generation Luminaires Design Competition, Lighting for Tomorrow residential product design competition, Lightfair Innovation Awards, CALiPER testing reports, Gateway project demonstrations, Lighting Facts, DesignLights Consortium’s Qualified Products List, Energy Star and more. These can be helpful, but the best assurance of quality performance, particularly regarding aspects such as color and visual comfort, comes from expert observation. Conduct mockups when possible; request samples; see for yourself.
In the end, the LED is just another technology. Its ultimate limitation is how well it is applied within a well-designed system that not only reduces the electric bill, but satisfies users. As always, electrical contractors can benefit from general lighting education to understand what goes into the installation and what comes out of it.