This article was published in the June 2013 issue of LEDs Magazine.
View the Table of Contents and download the PDF file of the complete June 2013 issue, or view the E-zine version in your browser.
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While some may still consider LEDs to be a relatively new lighting technology, many LED installations have been operating successfully for more than five years. Implemented well in a purpose-built luminaire, LEDs can reliably offer high-quality light over long lifetimes while consuming low amounts of energy.
However, to switch to LEDs from incandescent lighting, why not opt for the seemingly quick fix of replacing conventional lamps with LED bulbs, instead of purchasing purpose-built luminaires? LED replacement lamps are now widely available in a range of standard formats and typically consume much less energy than incandescent lamps.
Here’s the catch: while some LED replacement lamps can save significant energy, they can also perform poorly over their rated lifetime, as the quality of light degrades perceptibly. You might assume that a solution rated for 50,000 hours will perform in its last hour exactly as it did in its first — that it will look identical to the human eye — but that assumption could prove problematic.
Mounting anecdotal evidence from lighting designers and specifiers suggests that, in some installations, LED replacement lamps fail to live up to manufacturers’ lifetime claims of ≥35,000 hours. Moreover, recent studies made on behalf of the U.S. Department of Energy (e.g., “Demonstration of LED retrofit lamps,” June 2012) reveal installations where LED replacement lamps have:
• Displayed highly visible color shifts after as few as 4000 hours of use;
• Displayed unwanted behavior, such as visible flickering; or
• Suffered from accelerated rates of lumen depreciation.
Don’t let this deter you from implementing an LED lighting strategy: you just need to pick the right one. Well-designed LED luminaires are far superior to LED replacement bulbs for many professional settings.
Professional applications demand stable color temperature and light intensity. In retail environments, color tones are carefully specified to match merchandise displayed; a color shift can weaken customer appeal and lower sales. In hospitality and restaurant environments, lighting schemes must welcome and/or comfort the guest. In museums and galleries, color tones are selected precisely to highlight specific works of art.
These settings demand the best possible quality of light: true, consistent color over time, with no flickering or degradation and minimal risk of failure. Merely replacing conventional bulbs with LED bulbs cannot meet these requirements. First, visible flicker (often a result of incompatible dimming systems) is not uncommon with LED replacement lamps. Second, many professional settings require always-on lighting, which can create thermal challenges with LED replacement bulbs. The waste heat LEDs generate in normal operation can rapidly degrade or even destroy the internal electronics as well as the LED and its phosphor coating (which converts the LED’s native blue color to white) unless it’s properly channeled away from the bulb. In a purpose-built LED luminaire, a fixture’s thermal design is specified to support continuous operation without heat damage.
Thus, to achieve the desired results, the luminaire must exhibit both consistency and reliability. Consistent light output maintains a stable color temperature, intensity (measured in lumens), color rendering capability and beam pattern over the luminaire’s rated lifetime. To be considered reliable, the luminaire must operate for its rated lifetime without failing or exhibiting undesired behavior such as flickering or visible dark spots in the light source.
Speaking of the light source, the luminaire’s color stability is affected most strongly by that of the LED light source. While poor thermal management and degraded optics can cause color shift, if the LED light source is not color-stable to begin with, the luminaire cannot compensate.
The global lighting industry does not yet have a framework for predicting color stability over time, but many luminaire manufacturers follow the lead set by Xicato. Xicato designs its LED modules from the ground up for color, consistency, and reliability, and guarantees performance over time. The company’s Luminaire Thermal Validation Program ensures that heat is properly managed for rated lifetime and performance, while breakthrough technologies enable LED modules that deliver the best possible quality of light, without fail.
