When it comes to displays, three technologies dominate the field—liquid crystal displays (LCDs), light-emitting diodes (LEDs), and organic LEDs (OLEDs). Plasma display panels (PDPs) and polymer LEDs (PLEDs)have some challenges ahead, though success is possible. And, keep your eye on the active-matrix OLED (AMOLED) market.
LCDs have overtaken PDPs to claim the lion’s share of the flat-panel display market. OLEDs remain a dark-horse candidate for both flat-panel and discrete lighting applications. And, LEDs are making tremendous progress as white-light sources and in other applications like traffic lights and backlighting for flat-panel displays.
PDPs have enjoyed some market penetration with lower prices in applications that require diagonals of 34 in. or less. They suffer from much higher power-dissipation levels and lower resolution levels. However, studies show that efficacy and manufacturing improvements can make PDPs more competitive with LCDs.
LCD panels presently feature luminous efficacies of about 5 lm/W, while those for PDPs now feature 2 to 2.5 lm/W. Prototype PDPs with luminous efficacies of 5 lm/W have already been demonstrated, and some experts say that 10 lm/W is quite possible.
A comprehensive “apples-to-apples” analysis by DisplaySearch compared PDPs with diagonals of 50 to 52 in. to 52-in. LCDs. Results show that PDP costs would remain lower than those for LCDs and could be 29% lower at 5 lm/W and 59% lower at 10 lm/W (Fig. 1).
Meanwhile, researchers at the UCLA Henry Samueli School of Engineering and Applied Science have achieved up to18 lm/W from a red phosphorescent PLED to backlight PDP displays. They’re using a novel and simple combination of a polymer powder and a liquid mixture that’s added to a proprietary Canon material. So far, they’ve achieved luminous efficacies of 20 lm/W for white LED outputs and 30 lm/W for green emissions. Look for Canon to make these LED arrays available within two to three years.
LCDs Reign Supreme
LCD flat-panel displays are getting larger and less expensive. The largest is an LCD TV with a 108-in. diagonal from Sharp. Some experts believe the technology is close to reaching a finite limit on size. Yet there’s still more room for improvement. Last year, TPO Displays Corp. developed a process that resulted in the world’s thinnest daylight-readable module—just 0.95 mm thick.
The module is made on a low-temperature polysilicon (LTPS) process. TPO leveraged a cutting-edge chemical etching process that allows both bi-panes of the glass to be thinned to just 0.2 mm and enables the use of 0.25-mm ultra-thin light guides and very thin capacitors. The module is ideal for 2.0-in. QVGA (640 by 480 pixels) LCDs, exceeding the requirements for telecom, PDA, and digital still camera applications where the design footprint is a major consideration.
LCD panels of 15 in. or less now use LEDs instead of the tried-and-true cold-cathode fluorescent lamp (CCFL) for backlighting. That’s because LEDs cost less, they use materials that are more environmentally friendly, and they use less power. Also, they provide higher efficiency and longer lifetimes.
The increased brightness levels of white-light LEDs have made them feasable for use in the back- and edge-lighting of LCDs as well. Look for LEDs to backlight LCD panels greater than 15 in. In fact, many CCFL suppliers also offer LED backlighting options.
Unlike other flat-panel displays like LEDs or OLEDs, LCD technology isn’t self-emitting. It instead uses backlighting, which tends to increase power dissipation and limit the panel’s thinness. Although much progress has been made in manufacturing slimmer LCD panels, there’s a limit to how thin they can be since they need a backlighting source.
Yet this could change, as Sharp Corp. plans to develop a 1-in. thick LCD panel that will be integrated into mainstream displays produced at the company’s tenth-generation fab facility, scheduled to begin operation in March 2010. Sharp already has demonstrated a 52-in. prototype panel with a thickness of 20 to 29 mm. The company believes such a display will dissipate half the power of conventional LCD TVs and one-fourth the power of plasma-panel TVs.
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