Ultra-Low Power: Changing the Rules of the Game

by Robert Zehner

Last summer, as fuel prices across the U.S. peaked at over $4.00 per gallon, stories about a group of auto enthusiasts known as "hypermilers" began to crop up on television and in newspapers. Rather than pursuing maximum speed or handling, hypermilers modify their driving style to achieve maximum mileage. Hypermiling techniques range from mild (gentle acceleration and braking) to suicidal (drafting semi-trailers on the highway with the engine off), but skilled practitioners can coax 40–50 miles out of a single gallon of gasoline.

This month's issue of Information Display is dedicated to ultra-low-power displays – the hypermilers of the display industry. As with their automotive equivalents, these display technologies aim to deliver an entirely different kind of high performance. It is not about frames per second; it is about pages (or prices, or ads) per battery charge.

This difference is exemplified by comparing two popular consumer devices from the past year, both of which I carry with me when I travel: Apple's iPhone 3G and Amazon's Kindle electronic book reader. Both have always-on cellular data capability, for when the urge strikes to surf the Web or buy the latest best-seller, but that's where the similarity ends. The iPhone is a mini movie theatre, packing feature-length films onto its 3.5-in. backlit LCD. But, after a few hours of film, it is time for a re-charge. The Kindle, on the other hand, regularly delivers 3–4 days between charges, seemingly independently of how much I read, and despite sporting a display that is over three times the size and pixel count of the iPhone. And for battery longevity, even the Kindle pales in comparison to its close competitor, the Sony PRS-505 Reader, another of my frequent traveling companions. The PRS-505 relies on USB instead of wireless for its data, allowing it to go 20 days or more between top-ups. I'm embarrassed to say that by the time the Reader's battery is dead, I've often forgotten where I put the charger.

Some might point out that this is not an apples-to-apples comparison, but that is exactly the point. The hypermiling Kindle and Reader, and their electrophoretic displays, are purpose-built for immersive reading, for settling in with a book, or two, or three on a Sunday afternoon or a trans-Pacific flight. In return, at least for now, they sacrifice full-motion-video capability.

Electronic books are just one category where ultra-low power consumption confers a big advantage. This month's featured articles show us how three different display technologies are being successfully applied to create digital billboards, in-store elec-tronic pricing labels, and smart cards. In each case, the displays possess image stability – they maintain an image, even after all power sources have been removed. As a result, ZBD has been able to construct an in-store point-of-purchase display with a 5-year battery life, and E Ink and Epson foresee a similar battery life for a credit card with a one-time-password display. All three displays are also reflective, which means that they largely rely on ambient lighting rather than powering their own internal light source. Elimination of the backlight allows cholesteric-signage-maker Magink to cut the power required for an outdoor electronic billboard by up to 90%, when compared to LED or backlit-LCD solutions.

These ultra-low-power technologies may not be ready to replace the LCD in your living room TV. However, as the hypermilers have shown on the road, it is possible to break new ground in battery life, if you are willing to change the rules of the game.