Users of LCD-equipped devices have favored fast colors over the better readability and longer battery life achieved with reflective (non-backlit) displays. But with e-paper encroaching on their turf, several LCD makers are pushing back by resurrecting reflective techniques.
Pixel Qi, a startup spun off from the One Laptop per Child initiative, is providing the display for a $75 laptop that OLPC intends to ship later this year. The Pixel Qi dual-mode transflective LCD doesn't boast the paper-white background of E Ink's Vizplex--text displayed on the screen looks like it's printed on a mirror--but it does have a low-power monochrome mode, plus it can be switched to a color mode that supports full video frame rates at a fraction of the power required by backlit LCDs.
Kent Display's bistable cholesteric LCD locks crystals in
either a planar texture state (which reflects ambient light) or a focal-conic state (which scatters it).
"Pixel Qi is very good in bright sunlight but works in dim light as well, plus it offers full-motion video and vivid colors," said Richard Doherty, principal analyst at Envisioneering (Seaford, N.Y.). "If you want the fast response time of an LCD, Pixel Qi looks very good, but if you are satisfied with multisecond page turns for reading books, then E Ink rules the roost for a while longer."
Kent State spinoff Kent Displays Inc. uses a a roll-to-roll process to manufacture cholesteric reflective LCDs that are low-cost, flexible and very thin. Kent has licensed the technology to Varitronix (Hong Kong) and to Fujitsu Frontech, maker of the Flepia color e-book reader (sold only in Japan).
Cholesteric LCDs use bistable states of the bulk LCD material, which can maintain either a planar texture (which reflects ambient light) or a focal-conic texture (which scatters it). The displays achieve a very low cost point by using a passive-matrix backplane that still maintains millisecond refresh times. Kent has demonstrated its cholesteric LCDs on substrates of glass, plastic and even fabric. Hitachi and Kodak have also shown prototypes of cholesteric LCDs.
Nematic chemical formulations use the surface characteristics of the LCD crystals, instead of the bulk state, to enable bistable displays in "twisted" or "untwisted" modes. Nemoptic Displays (Paris) offers nematic displays mounted on glass. ZBD Displays (Windsor, U.K.) uses a similar mechanism to lock pixels in its Zenithal bistable display using inexpensive passive backplanes on plastic or glass.
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