KDDI Corp released the W64SA, an au-branded mobile phone manufactured by Kyocera Corp, in August 2008.

One of the features of the handset is the "color therapy" function, which displays illumination in two colors by using LEDs arranged on the back side of the main display.

When asked about the technology that enables the illumination used for the color therapy function, the development team at the Corporate Communication Systems Equipment Division of Kyocera pointed out two factors, an LED mounting method and a chassis cover molding method.

LED mounting method based on LCD panel backlight technology

First, let's look at the LED mounting method. In order to realize the illumination function, the handset has four LEDs on the back side of the main display. As for the light emission method, the company utilized the technology adopted for the backlight of small- to middle-size LCD panels, said Kazuhiro Suzumura at the Mechanical Planning Department of the Corporate Communication Systems Equipment Division of Kyocera.

Specifically, a light guide plate and a reflection plate are used to expand the light-emitting area of the LEDs arranged in the edge portion of the emission block. If the LEDs are arranged right under the emission block, the emission area cannot be expanded and the emission block increases in thickness, Suzumura said.

In the outer side of the emission block, only the reflection plate is used with no light guide plate so that the end section of the emission block is dimly lit, said Masanori Tsujimura at the Domestic Products Department of the Corporate Communication Systems Equipment Division of Kyocera.

The emission block is about 0.6mm thick, which is equivalent to the thickness of an LCD or monochrome OLED panel used as a sub-display, Suzumura said. The light guide and reflection plates are the same as those used for LCD panels, and not made of a special material developed for this handset, he said.

Chassis cover made by two-color molding

The chassis cover of the main display is manufactured by two-color molding. The chassis cover comes in four colors, white, black, pink and yellow. The black cover is attached to a translucent plastic of a similar color, while the covers in the other colors use a translucent plastic on the outer side and a white plastic on the inner side.

"The white plastic transmits light from the LEDs and prevents the internal components from being seen through the cover," Suzumura said.

If the color of the chassis is too dark, then the light emitted from the LEDs cannot be seen clearly. If the color is too light, on the other hand, the components and irregularities inside the chassis may be visible, Kyocera said.