LEDs — Beyond the Hype

As president of LED Lighting Technologies, Dr. M. Nisa Khan consults in the solid-state lighting industry and educates consumers about LED lighting. She has a bachelor’s degree in physics and mathematics, and master’s and Ph.D. degrees in electrical engineering. Email her at nisa.khan@iem-asset.com

Despite the economic slowdown, the light-emitting diode (LED) lighting industry continues to expand. By 2014, the LED market is expected to reach $20.5 billion, according to Strategies Unlimited (SU), a Mountain View, CA research firm, with LCD-display backlighting and illuminated sign applications as the main drivers. Interestingly, the high-brightness LEDs (HB-LED) market, which SU said experienced a modest 5% growth ($5.3 billion total sales) in 2009, is generously projecting 52% growth in 2010.
Sign-industry applications of LED-based lamps also continue to expand, though signmakers still face various technological challenges. Discordantly, LEDs are universally pitched, and, as a result, numerous shops have upgraded designs and systems to include such lamps. However, they’re still not ubiquitously proven as the better cost and performance choice, meaning, controversies remain.
LED enthusiasts — both newcomers and deep-rooted believers — are convinced this technology, although presently disruptive, will, in the long run, be a winner for most illumination applications. Several prominent companies presently argue the LED advantage has arrived.
This experience is similar to several I had in the ’80s and ’90s, while working in fiberoptics communication (integrated vs. hybrid solutions in optoelectronics). Then, the incumbent technologies, while often more reliable and less costly, were eclipsed by new, “superior” technologies.
Fortunately, I was acquainted with AT&T Bell Labs’ Dr. Enrique Marcatilli, a pioneer in fiberoptics communication technologies who, even after having retired, often visited the Crawford Hill Bell Labs facility (Holmdel, NJ).
Dr. Marcatilli once recollected how, when optical fibers were first invented, they were so lossy that comparable copper wire losses were minuscule.
Further, the possibilities and limitations of fiber – the “new” signal transmission medium — was poorly understood by period scientists, even decades after. Nevertheless, Marcatilli told how certain NYC municipalities discussed removing all the underground, copper-wire, telecommunication-signal transmission systems and replacing them with optical fibers. Because the technology was yet unproven, such conversations riled some citizens.
The optical-fiber hype proved to be true beyond all claims. Today, optical fibers carry trillions of bits per second over transoceanic distances, an impossible feat with copper wire.
Will we see similar developments in LED lighting? Perhaps. First, we must inventory LEDs’ unquestionable or arguable advantages, that is, areas where fluorescent and incandescent incumbent lights can’t compete.
For example, LEDs are clear winners for distance-viewing, full-color, electronic message centers (EMCs). And, there are advantages for certain sign applications, such as channel letters and some cabinet signs.
An illuminated sign needs to be bright enough to be easily read, but, unlike a searchlight, it doesn’t need to illuminate anything else. Sign designers must incorporate this thinking when specifying LED illumination. Thus, builders of back, or edge-illuminated, LED-lamped channel letters or cabinet signs must comprehend that LED lamps’ directional nature prevents them from illuminating large spaces (or extended distances) and, therefore, must position the lamps near the translucent sign faces, to provide adequate surface illumination.
Interestingly, LEDs aren’t inherently directional – the common wafer-manufacturing process makes them so, although, some chip design improvements will widen the viewing angle. Further, the refractive-index difference between the semiconductor material and its surroundings cause additional directionality. This mismatch may be corrected, but the process adds cost and optical loss.
Some writers commonly describe conventional, illuminated LEDs as point (light) sources, but the term is incorrect. Point sources are omni-directional, whereas LEDs are directional and more suited for such applications as illuminated signs and displays, than for illuminating living spaces.
Organic LEDs (OLEDs) are better suited for sign/display illumination because they comprise a broader source area and may be directly integrated in the signface.
Unlike LCD and plasma screens, OLED technology creates its own light, thus eliminating the need for CCFL or LED backlights.
Historically, fabrication and lifetime challenges have restrained OLED’s popularity, but this may soon reverse. Display Search (Austin, TX), a global, market-research and consulting firm, reported that 2009 marked a record OLED year, with sales revenues of $826 million, up 35% from 2008. It notes, also, that active-matrix OLEDs (AMOLEDs) overtook passive-matrix (PMOLED) systems for the first time.
An active matrix (AM) display structure controls the backplane transistors’ current for each system pixel. AMOLED displays are brighter, faster and sharper than passive matrix (PM) OLED systems, thus, better suited for video. They also produce faster display action, with a broader viewing angle.
DisplaySearch also stated that increased AMOLED demand for mobile-phone main displays was the key growth driver for 2009.
OLEDs and LEDs have become mainstream for various display technologies, but for different reasons. The demand for both will increase because there are fundamental advantages that incumbent systems can’t match.
Because OLED lighting can be sheet fabricated, its uses include large-area, direct light sources — emissive screens — to illuminate general areas as well as backlight LCD-type screens.
AMOLED TVs have the similar high-contrast benefits of plasma, but are much thinner and produce beautiful, bright, saturated colors. At CEATEC 2008, Sony displayed its OLED prototype TV that measured two business cards thick. You could bend it (within reason) without distorting the image or damaging the screen.
Samsung offers two digital cameras equipped with AMOLED viewing screens, which, the company says, provides higher contrast, faster refresh rates and longer battery life than standard, backlit, LCD-screen cameras. Kodak, which claims high OLED knowledge and systems, offered the first OLED equipped camera, its LS633 model, in 2003.
Presently, many mobile computing and communication devices are AMOLED equipped.
Larger OLED screens are slow to arrive because of manufacturing infrastructure and changeover costs. Thus far, the largest, commercially available OLED TV is Sony’s $2,500, 11-in. (diagonal), XEL-1. LG displayed a 15-in. model at CES 2010, but no pricing was available.
Although large-format, self-emissive OLED displays are detained, you can now find LED-lit LCD-based TVs and other displays in most retail stores. Expectedly, they’re overtaking the CCFL-lit LCD screens.
Manufacturers now offer two types of such screens: backlit and edge lit. Backlighting’s advantage is local dimming, accomplished via an array of LED elements. It produces nice contrast and strong black levels; it’s also much more power efficient than traditional plasma and LCD TVs.
Edge lit LCD TVs comprise a line of LED lamps around the screen edges, and these focus their light inward (toward the center of the TV), onto a thin, multi-layer sandwich of clear and translucent plastic sheets that are designed to diffuse the light evenly behind the LCD panel, to produce a bright, white light source. The advantages of edgelit TVs over traditional CCFL-lit LCD TVs are primarily in thickness and power efficiency; however, such systems lack local-dimming capabilities and, in terms of black levels and contrast, are not significantly different from CCFL-lit LCD TVs.
Companies such as Samsung, LG, Toshiba and others are busy improving their LED-lit LCD TVs. Samsung is choosing LED edge lighting for the future, which enables a feature-packed full 1080p HDTV that is just 0.3 inches thick (the C9000 series) — some now including 3-D capabilities with 2-D to 3-D conversion.
Imagine such screens in electronic-digital signage applications. Two, back to back, would measure slightly more than one-half inch.
The backlights are HB-LEDs and, because such lamps are only available from a handful of manufacturers, they’re much more costly than a comparable CCFL arrangement. The price should drop as the technology matures.
Most agree that LED-backlit screens are an improvement on CCFL-backlit systems and that LED backlighting will soon become the default method for TV, computer screen and other consumer electronic device display.
As content generation, data transport and delivery, consumer audio/video reception and interaction (live or otherwise) all are brought to us through mostly digital and some analog technologies — several things are simultaneously important: consumption, management, portability and size, among other things. Therefore, high-quality illumination or picture qualities can often a take back seat to some of these features.
Because LED-illuminated signage, display and illumination applications produce many features and, also, better integrate with other technologies than conventional light sources, the positive “hype” I mentioned earlier may be purposeful.
Despite LED’s illumination challenges, one must consider its vast usability and, therefore, predict its ongoing popularity will continue — along with OLED systems. Expectedly, scientists and manufacturers will solve the problems we face today. Most exciting will be the arrival of large-format, flexible OLEDs with plastic logic, that is, all polymer transistors integrated with display technologies in end-user products.
Imagine, then, large-format, bendable, full-color television screens — electronic digital signage — wrapped around stadium or mall pillars. n