Skip to Content

Energy-Saving Screens

December 1, 2004

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.

In studies with human volunteers, Ranganathan’s team found that Pocket PC devices equipped with the energy-saving software could last 1.3 to 8 times longer on a single charge than those without the software. Not only that, but “95 percent of our users preferred the new interfaces, even without the energy advantages,” Ranganathan says. “Deemphasizing low-interest areas means you’re emphasizing high-interest areas” – which seemed to help users focus on their immediate tasks.

The method is not effective with most of today’s standard liquid-crystal displays, which are illuminated by fluorescent bulbs that remain on even if a particular group of pixels is dark. But in OLED screens, each pixel emits its own light, so “if you turn off a pixel, you don’t have to spend power on it,” explains Ranganathan. Since phones and PDAs with OLED screens are expected to become commonplace within two years, the new software could soon be a standard feature of the operating systems of mobile devices.

Keep Reading

Most Popular

Workers disinfect the street outside Shijiazhuang Railway Station
Workers disinfect the street outside Shijiazhuang Railway Station

Why China is still obsessed with disinfecting everything

Most public health bodies dealing with covid have long since moved on from the idea of surface transmission. China’s didn’t—and that helps it control the narrative about the disease’s origins and danger.

individual aging affects covid outcomes concept
individual aging affects covid outcomes concept

Anti-aging drugs are being tested as a way to treat covid

Drugs that rejuvenate our immune systems and make us biologically younger could help protect us from the disease’s worst effects.

Europe's AI Act concept
Europe's AI Act concept

A quick guide to the most important AI law you’ve never heard of

The European Union is planning new legislation aimed at curbing the worst harms associated with artificial intelligence.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.