Demand for electronic book readers such as Amazon.com's Kindle and Sony's Digital Reader may be on the upswing, but the technology still has some hurdles to leap before it banishes print media to the recycling bin. The current generation of e-readers doesn't make good use of ambient light (making them less energy efficient and more difficult to read in sunlight), and few can reproduce full-color copy. This could be changing now that a team of engineers has developed a new prototype electronic paper that can rapidly reveal or hide enough pigments to form 1,000 different colors, paving the way for, among other things, more vivid e-book readers that will also be able to play video.

The prototype is an "electrofluidic display" (EFD) that uses voltage to pull water-based spots of colored ink out of a reservoir in the center of the screen's pixels and spread their colors over those pixels, which are coated with highly reflective aluminum, according to the researchers, led by the University of Cincinnati's Novel Devices Laboratory in paper published yesterday on Nature Photonics's Web site. When voltage is removed the ink returns to the reservoir in the center of the pixel, and the screen goes blank.

The key to the EFD's color are the pigments supplied by Sun Chemical Corp., which began working with Novel Devices Laboratory in 2006, says lead researcher Jason Heikenfeld, an assistant electrical engineering professor in the University of Cincinnati's electrical and computer engineering department. "One could argue that the ultimate reflective display device would simply place the best colorants used by the printing industry directly beneath the front viewing substrate of a display," he adds.

While Novel Devices Laboratory's prototype EFD can reflect about 55 percent of ambient light (more than any other e-reader screen currently on the market), their goal is to create a screen that can reflect 85 percent of available light. For e-readers to become a widespread technology, they need to, among other things, Heikenfeld says, make better use of ambient light and reproduce full-color copy.

Other types of e-readers use a variety of different approaches to creating their display screens. The most common is "electrophoretic" display developed by E Ink Corporation and used by Sony, iRex Technologies, and others in their e-readers. An electrophoretic display uses an electric field to rearrange white and black titanium dioxide particles (rather than colored pigments) within the millions of capsules that comprise the e-reader's screen. The downside is that electrophoretic displays can reflect only 40 percent of ambient light. Adding color requires makes them even dimmer because filters must be added to the display.

Japan's Fujitsu Frontech Limited and Fujitsu Laboratories Limited staked their claim in the color e-reader market last week with the release of its FLEPia device. The companies claim that the FLEPia can display 260,000 colors in high definition, but that comes at a premium because the FLEPia costs $1,000. By comparison, Amazon's new black-and-white Kindle 2, which hit the streets in February, sells for $359. (The EFD is too early in its development for Heikenfeld to say how much it will sell for.)

Heikenfeld and his colleagues in February formed Gamma Dynamics LLC to develop and commercialize products based on their electrofluidic display. Their goal is to continue to improve the quality of the e-reader screen, Heikenfeld says, "until it can mimic the appearance of pigment on paper."

Ink reservoir image © University of Cincinnati's Novel Devices Laboratory