Showing up on the market
E-paper displays are already showing up in consumer applications, even though consumers may not recognize them. Jennifer Colegrove, an analyst at market researcher iSuppli, identified several product categories in addition to e-book readers, including displays for wearable and carryable products like watch dials, mobile phones, credit cards and security-system cards; instrumentation applications like the capacity meter on Lexar JumpDrive USB drives; and signage. Point-of-sale devices like electronic shelf labels can be updated remotely, Colegrove explains, or promotional signage can be updated by time of day -- breakfast specials in the morning, for example, and dinner in the evening.
EPD screens have great advantages for consumer electronics applications, says Colegrove: their very low power consumption means devices can run for days or weeks rather than hours. In active-matrix configurations, they can produce very high resolutions, and they are readable over a wide illumination range, even in sunlight.
But there are disadvantages, too. Although the displays need power only when they're redrawn, the redraw itself is much slower than an LCD screen, which makes the technology unusable for faster moving images, such as animation effects and video. Because they're reflective, EPD signage needs to be illuminated in dark areas, which makes it less attractive than electroluminescent technologies like LEDs. And even though EPD screens can be read in direct sunlight, the screen contrast is much lower than backlit LCD screens.
The resolution of EPD screens is improving rapidly. Active-matrix displays like those used on the current generation of e-book readers can work at relatively high resolutions (the Kindle screen displays 167 pixels per inch), and Seiko Epson recently showed off an A4-size (13.4-in.) display prototype with 3104 by 4128 resolution, about 385 ppi, that uses E Ink's electrophoretic ink on a Si-TFT glass substrate.
E-paper displays are currently limited to black-and-white, and they display only a limited range of gray tones (the Kindle display renders four levels of gray, iRex Technologies' iLiad reader renders 16).
These current limitations lead at least one industry observer to predict that the acceptance of e-paper displays will take a while: "E-paper is still five years from being a mainstream technology," says Len Kawell, a distinguished engineer at Microsoft. "E-paper is very slow to change state, to turn the page, almost a second -- there's that flash, that visual artifact, of the switch to black and back as the screen is cleared and redisplayed."
Kawell, who is currently working on enhancing Windows Mobile, has been interested in e-book readers for more than a decade. He bought a Kindle when they first came out and feels that the screen's contrast is too low. "While it looks like paper, it's still got a shiny, reflective screen," he says. "You get a lot of reflection from the plastic screen surface, and it's difficult to get lighting that's bright enough to read but doesn't cause a glare problem."
The slow display causes "some weird UI-ness," he continues. "Typing is difficult because the letters are slow to echo to the screen. There's a lot of work to be done yet. You're moving physical objects around and that takes physical time, not like LCD displays that change the state of electrons."