Notebook LCDs: Power Thieves

Cutting screen power is the key to longer notebook battery life, Intel exec says.

Sean Captain, PC World

MONTEREY, CALIFORNIA-- Vendors focus on CPUs to save power in notebooks, but the LCD is a far greater power sink, an Intel executive says.

Displays account for over 30 percent of a notebook's power use, says Kamal Shah, an engineering program manager at Intel Labs. In contrast, the CPU consumes only about 10 percent of a notebook's power, while the graphics and hard drive use about 8 percent each.

Shah spoke at the Flat Information Displays Conference, sponsored by ISuppli/Stanford Resources here this week.

Tackling the Backlight

While Intel and other chip makers focus on squeezing more CPU performance from fewer watts, the display system still offers plenty of room for improvement, Shah said. For example, at most only 8 percent of the light from an LCD's fluorescent backlight actually reaches the user's eye, he noted.

Reducing display power usage is one challenge of the Mobile PC Extended Battery Life Working Group, an alliance of Intel, Microsoft, and several PC and LCD makers, formed in 2002. The group's aim is to reduce the display's power use from the typical 4.5-to-5 watt range to 3 watts.

In 2002, no notebook displays met the target. In 2003, eight displays qualified, according to Shah, who described both current and future efforts to cut power use.

He also described the Display Power Savings Technology built into Intel's 855GME chip set. When it processes screen images, the integrated graphics processor exaggerates their brightness to compensate for a dimmer backlight level. Shah says the technology perfectly reproduces the original image's brightness level while saving up to a quarter of the power. Further savings come from adjusting the backlight to match ambient lighting conditions, Shah said. For example, you need less power to read a screen when on a nighttime flight than while working in a well-lit office. Toshiba, for example, provides some of its notebooks with a sensor that reads the ambient light and adjusts the display's backlight accordingly.

OLED to the Rescue?

Other power-saving methods are still theoretical.

For example, Shah proposed outfitting notebooks with a camera and facial recognition software to determine when users turn away or even walk away from the screen, and then dim or shut off the backlight until someone returns.

He also spoke enthusiastically about Organic Light-Emitting Diodes. Unlike LCDs, which lose light when it moves through liquid crystals and color filters, OLED screens use a thin material that glows when an electrical charge is applied, eliminating the need for a separate backlight.

OLEDs are a hot topic at the Monterey conference, as in past years. They have begun to emerge, initially implemented in small devices. Kodak uses an OLED for its EasyShare LS633 digital camera, for example. But several conference participants noted that issues of cost and longevity will keep OLEDs from replacing LCDs in notebook or desktop monitors for the next few years at least.