Working with light-emitting diode (LED)-based luminaires presents an additional set of challenges for lighting specifiers. As a result, there are different issues the lighting designer and architect must consider when thinking about including a solid-state fixture on a project. I see three major trends at work today that address this situation:

  • Printed circuit board (PCB) replacement is not offered. Entire fixture, including all of its components, is deemed a “throw away” when it reaches the end of useful life.
  • The fixture manufacturer, who sells PCB with fixtures, offers replacement PCBs. These can be purchased up front when the fixtures are purchased (i.e., “attic stock”) or replacement modules are available to be purchased in the future. The manufacturer promises to deliver the same lumen output and chromaticity, no matter the LED package and arrangement on the PCB.
  • LED takes on the form of a conventional lamp, complete with Edison base, so replacements are done the old-fashioned way.
  • Knowing which approach the light fixture manufacturer is taking with its luminaires is not only important for the designer and the client to know what is required in terms of replacement, but also outlines the remedy if a fixture should fail in advance of expected life.

    TECHNICAL DATA Lighting designers should expect the same technical data from LED-based luminaires as they expect from conventional screw-based lamps and light fixtures. Independently tested photometrics, Underwriters Laboratory listings, and IP ratings are all good qualifiers. However, there are additional questions that should be asked by the lighting specifier to ensure a quality LED product and a knowledgeable LED manufacturer and/or supplier. A manufacturer should be able to answer the following questions:

  • What is the rated life at the lighting industry standard of 70 percent of lamp lumen output?
  • What is the stability of chromaticity over life?
  • What is the color-shift range between LEDs on the PCB?
  • What is the maximum allowable ambient temperature the fixture can withstand without negatively affecting life or color stability?
  • Does the fixture have the proper heat sink to thermally manage the diode so the junction temperature does not exceed the manufacturer's recommended maximum allowable?
  • If lighting designers required fixture manufacturers to provide this data before specifying a product, the crowd of booths at Lightfair would thin substantially, while the quality of products for those remaining would increase.

    MOCK-UPS REQUIRED Reviewing samples prior to specifying also is of critical import. Not only is it imperative to evaluate the quality of the fixture itself, but the quality of light as well, which is vital, especially when dealing with LEDs. This is significant because optically controlling LEDs can be difficult given the precise nature of the LED package. For example, if the phosphor on the chip is not deposited uniformly, color separation in the beam can occur when coupling the LED with a very precise refractor. Also, color shift between LEDs may be too extreme for a particular application (i.e., grazing a white wall). Lastly, glare needs to be controlled. The days of LEDs not being bright enough are long gone. Now designers and manufacturers are faced with how to control brightness effectively.

    Mock-ups are critical to the success of any lighting design with conventional luminaires and particularly with LED-based luminaires. If two to three name specifications are desired or required, then be sure to compare the fixtures side by side. This is important because lighting manufacturers sell fixtures with PCBs, meaning either they are sourcing their own PCBs, or having them made to their specifications by another manufacturer. With this supply chain model it means designers no longer can rely on the “tried and true” lamp they have specified a thousand times before.

    ACCURATE TECHNICAL DATA LED-based lighting fixtures are like machines; each cog in the wheel is dependent on the next. The PCB, heat sink (housing), optical assembly, and driver are all interrelated. One of the most exciting attributes associated with LEDs is the ability to redefine the architecture of a light fixture. Fixtures can take on a minimalist scale and offer industrial designs that were not possible when designing around bulbous light sources.

    This is particularly relevant when it comes to architectural detailing. Just because an LED fixture has a different footprint does not mean the basic principles of lighting design do not need to be considered. For example, LED fixtures often have a slimmer profile. But this does not mean they can be installed in tight fitting spaces, especially for exterior installations, without following the fixture manufacturer's exterior certifications, such as wet list and IP ratings. Just as you would ask of a conventional fixture—is the fixture rated for face-up applications or for submersion—the same care must be given to LED luminaires. This new miniaturization paradigm enables lighting designers to create architectural details that are more minimalist in scale than ever before. It is important to allow enough airflow around the fixture to enable the heat sink to operate as it should. This gets back to fixture manufacturers providing the proper guidance by listing the maximum allowable ambient temperature requirements on the specification sheet. This is of critical importance to an LED-type light. While properly designed fixtures promise longevity, these luminaires are electromechanical devices that potentially could fail. While solid-state lighting is extremely robust as compared to conventional lamps and sources, it is advisable to design the architectural detail to allow for accessibility; fixtures should not be permanently installed, as access will be required at some point.

    WARRANTIES AND UPDATES The longevity of an LED is greater than conventional light sources. We can expect anywhere from three to 25 times longer life than lamps we specify today. Lamp manufacturers define “rated life” in their catalogs as, “the point at which half of the lamps have burned out.” This further promotes LEDs as a viable source option because LEDs do not “burn out” or catastrophically fail. The lumen output just depreciates over time until it is a small glowing point source. That is why LED fixture manufacturers should state in their literature how the life of their product is defined. For example, if average rated life is 50,000 hours at 70 percent of lumen output, that means that at 50,000 hours into the life of the LED, the lumens have depreciated 30 percent. The LED is far from burning out at this point. If we are depending on the LED-based luminaire to deliver functional illumination, then we know that 30 percent less light may deem the lighting system ineffective for the application.

    But what if a fixture should fail in advance of rated life? From my experience, it is typically due to an electronic component on the PCB, or a solder joint/connector, or a bad batch of LEDs (which can occur if something has gone wrong during the manufacturing process), or inappropriate application. If there should be an unfortunate failure, will a replacement fixture match existing luminaires in terms of light output and color? Probably not, but this is not a new issue in the world of lighting. Lamp lumen depreciation is a fact of life for all conventional lamps. This is why group relamping or group refixturing has always been advocated. If that is not an option, spot relamping surely will reveal brightness differences between the new and the old fixtures.

    Color shift between lamps also is not a new phenomenon in the lighting industry. Phosphor differences in fluorescent technology, differing MR16 dichroic coating processes, and the trials and tribulations of the ever-evolving metal halide lamp over the years have caused many designers and manufacturers angst at one time or another. But there have been significant strides to address this problem. As consistency has increased with the aforementioned lamps, so goes LED technology. The quality of white light and consistency between LED packages has made quantum leaps in the past several years.

    So, what about warranties? Should fixture manufacturers provide extended warranties to match the expectations of the technology? This is a tricky question. Can a fixture manufacturer get its suppliers to warrant their components for the same warranty duration? If so, then a warranty is realistic. However, if the same warranty cannot be applied to all components, then a warranty is a useless guarantee.

    LED-based light fixtures are an amazing breakthrough, but they are not “miracle” light sources—they do not solve all challenges of lighting design and working with other types of sources. I certainly would not have dedicated my professional life to this technology if I did not whole-heartedly believe in it, but all design professionals and manufacturers must keep themselves informed and ask the right questions to keep pushing the technology forward. As a lighting community, we must work together to guard against the potential failures and work toward solutions and standards that result in successful projects and happy clients. There are imperfections to be sure. The task at hand is to figure out how to manage with (and around) these challenges.

    Ann Reo is the founder of io Lighting. A trained architect and experienced lighting designer, Reo has a successful track record in both luminaire and lighting design. She has been awarded several U.S. patents for fixture design as well as several national lighting design awards. io Lighting was awarded Best New Product in 2004 at Lightfair's New Product Showcase.