If you're looking to buy an e-reader, you can choose between a beautiful but battery-draining liquid crystal display (LCD), like the one in Apple's new iPad, or a slow-switching but easy to read black-and-white one, like the one in Amazon's Kindle. At the Society for Information Display's annual conference this week in Seattle, Qualcomm MEMS Technologies is demonstrating prototypes of a screen that meets somewhere between these extremes. It shows video in color, and under full sunlight, but without draining the battery. The display will be in products by the end of the year.

The backlights in conventional LCDs consume the majority of the power in portable electronic devices. That's because a significant amount of that light is lost in polarizers and filters inside the device. These displays also require continuous power to maintain an image. "Batteries are evolving slowly, and there's increasing pressure to reduce this power consumption," says Brian Galley, senior director of product management at Qualcomm MEMS Technologies.

The iPad has raised the bar, says Paul Semenza, senior analyst at Display Search, by showing that LCDs are getting more energy-efficient while the glass they're built on is getting tougher and lighter. "Once things go full color, and go video, it's difficult to go back," he says.

Qualcomm's Mirasol display, which can play video in color, extends battery life by 51 percent relative to an LCD, according to a report by Pike Research.

Many companies are working to develop better reflective displays, which provide considerable power savings because they don't require a backlight and, in most cases, can maintain an image without needing additional power. E-Ink has been a leader in this area but has yet to come out with a color, video-capable display, though company representatives at the conference say one will be ready at the end of the year.

E-Ink pixels contain electrically charged black and white particles; when a small voltage is applied, one or the other moves to the surface to make the pixel reflect light or appear black. To make a color screen, filters are added to the top. Early versions of E-Ink's color screen appeared washed out because of light lost due to the filter, and were relatively slow to refresh, taking about a quarter of a second to refresh a page. Black-and-white E-Ink prototypes at the conference have higher resolution, faster-switching screens that looked crisp; company representatives say these improvements will lead to better color technology, too.

The pixels in Qualcomm's Mirasol displays can switch fast enough to show video, and don't use filters to generate color. These displays generate color by harnessing the interference effects that occur when light bounces off certain structures.