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Challenges that face LED use in general lighting applications.
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Editor’s note: In last month’s magazine, ST columnist Bob Klausmeier addressed “Display Lifespan and Service” (see November 2007, page 46). Bob wrote, “Commonly, LED manufacturers caution that luminance declines after the first year of use, but real-world data suggests these projections are considerably understated, even though the life-expectancy question hasn’t been answered.” Bob exampled many long-life, LED-lamped displays, including the daily-use, Las Vegas-based Bellagio display, installed in 1999.
In the same issue, on page 32, columnist Marcus Thielen includes information from the Dept. of Energy’s (DOE) LED lamp study. The DOE has released an independent research report that says commercially available LED lamps, such as compact fluorescent lamp (CFL) replacements reach between 11 and 19.5 lumen/watt luminous efficiency, contrary to higher claims. The DOE concluded available LEDs can’t replace CFL or fluorescent (neon) lamps, regarding efficiency (www.eere.energy.gov). Although some circles regard this announcement as headline news, readers should note the DOE evaluation regarded fully fabricated lamps applied to common lighting uses, such as household lamp replacements. The DOE report says, “The pilot tests examined two ‘downlights’ – the type of spotlight that is typically recessed into a ceiling – as well as a task light and an under-cabinet light.”
Apparently, there are difficult, technological obstacles to overcome before applying high-brightness LEDs or other solid-state lighting (SSL) to general lighting applications, including the backlighting systems in plasma or LCD displays. Here, Kahn explains these obstacles.
After having seen color LEDs used as a light source in numerous electronic products for many decades, I’ve observed white LEDs slowly penetrate general lighting markets (including flat-panel displays illumination) in the last few years. The penetration is slow, because, unlike indicator or mixed-batch (RGB) LED lamp systems, humans prefer general (room or sign) illumination and retail-display lighting to have a certain desirable white glow and brightness that’s difficult to achieve in solid-state lighting.
The LED or solid-state lighting (SSL) market growth has been remarkable in the last five years, but, white, high-brightness LEDs (HB-LEDs) for general-illumination and retail-merchandise applications still face tough challenges.
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