[FPD International] Clairvoyante Cuts LCD Power Consumption by 65%, Extends OLED Life

Oct 24, 2007
Tomohiro Ootsuki, Nikkei Electronics
An OLED panel to which Clairvoyante's technology was applied
An OLED panel to which Clairvoyante's technology was applied
[Click to enlarge image]

Clairvoyante Inc of the US will unveil two technologies at FPD International 2007, which opens from Oct 24, 2007, at Pacifico Yokohama, Yokohama City, Japan.

One is an original sub-pixel array for OLED panels. By lowering the current density of each sub-pixel, the life of OLED panels can be extended enough to be used for mobile devices, said Joel Pollack, CEO of Clairvoyante.

The other is a technology to control, for example, the backlights of LCD panels appropriately and reduce the power consumption of the panels by more than 50%.

Red and blue pixels are large

The first technology was adopted to a wide VGA (800 × 480 pixels) OLED panel of Samsung SDI Co Ltd of Korea. Samsung SDI plans to begin commercial production of it until the third quarter 2008, Clairvoyante said.

The power consumption of the OLED panel is 400mW. It covers 100% of the NTSC color gamut. Its screen size is 3.08 inches, luminance is 200cd/m2 and contrast ratio is 1000:1.

For LCD panels, Clairvoyante has been improving the luminance in the ratio to power consumption by adding white sub-pixels. However, the company does not use white sub-pixels in the new OLED panel. The pixel array is R(red)G(green)B(blue), and the areas of B and R sub-pixels are about twice as large as that of G because the luminous efficiencies of B and R are low.

"We have developed, for all that, a light-emission controlling method to reproduce colors accurately," Pollack said.

Syunichi Nishimura, Sr director of the Technical Business Development in Clairvoyante explained the reason why white color is not used.

"Other companies realized white color by using an RGB color filter, but its transmission efficiency of light is low," he said. "If white color is made without a color filter, the luminescence material is immature."

However, once materials for white color are prepared, Clairvoyante can provide a light-emission controlling method based on the premise of a sub-pixel array called RGBW, like LCD panels.

Humans perceive brightness relatively

As for the technology for LCD panels, the RGBW sub-pixel array enables to "reduce the power consumption by half in addition to a separate 15% cut, which add up to 65% reduction, Pollack said.

This is on the premise that users are watching a common TV program. The power consumption can be reduced by only 30% by controlling the backlights with a normal sub-pixel array, or RGB, Clairvoyante said.

The company can reduce the power consumption by more than 50% because it focused attention on the visual feature that humans perceive the brightness in a frame relatively. More specifically, brightness in each area of the frame is separately controlled by white sub-pixels in addition to the control of the backlights' brightness corresponding to the scenes of a movie.

When Nikkei Electronics had an interview in the headquarter of Clairvoyante, we could see a prototype of an LCD panel to which Casio Computer Co Ltd applied this technology. Though its power consumption was lower than that of other LCD panels, we could not find any apparent difference in, for example, contrast ratio.

"The technology itself can already be applied to production models. We will be able to announce many licensees in the near future," Pollack said.

He showed his confidence in the newly-developed technologies while making the following explanation.

"Though portable device manufacturers want to improve user experiences, they are worried about growing power consumption of LCD panels," he said. "Its primary cause is that less than 10% of the backlight's luminance reaches users. Moreover, when a popular touch panel is used, even that (10% of the luminance) will decrease by half. The sub-pixel array RGBW and the light-emission controlling method we have developed are essential to solve those problems."

The effect of decreasing power consumption. The vertical axis shows reduction rates. "PenTile" is a company's original pixel array. "DBLC" is an acronym of dynamic backlight control.
The effect of decreasing power consumption. The vertical axis shows reduction rates. "PenTile" is a company's original pixel array. "DBLC" is an acronym of dynamic backlight control.
[Click to enlarge image]
An LCD panel to which Clairvoyante's technology was applied. The graph (left) shows a time variation of power consumption.
An LCD panel to which Clairvoyante's technology was applied. The graph (left) shows a time variation of power consumption.
[Click to enlarge image]