Processors and memory chips keep growing in capacity, but batteries don't improve fast enough to keep up. So the only way to increase the battery life of mobile devices such as PDAs and smart phones is to reduce the amount of power they consume. Working with a new generation of displays based on organic light-emitting diodes (OLEDs), researchers at Hewlett-Packard have found a way to do that: dimming the parts of the screen that aren't in use.

"We have energy-aware central processors; why don't we have energy-aware interfaces?" asks Parthasarathy Ranganathan, a senior research scientist at HP Labs. The prevailing approach to energy-saving displays -- leaving the entire screen illuminated while a device is active but turning it off after a minute or two of inactivity -- is less than ideal, since it uses a lot of energy when the screen's on and, when it's off, forces the user to push a button to return to his or her task. Instead, Ranganathan's team developed special software that monitors a PDA's screen when it's in use and automatically dims the unimportant pixels -- for example, everything in the background behind an active pop-up menu or dialogue box.