Casio's Transmissive LCD Used Outdoors w/o Backlighting

Jul 2, 2008
Masao Oonishi, Nikkei Microdevices
The 5.7- (left) and 3.5- inch (right) models of "Blanview LCD"
The 5.7- (left) and 3.5- inch (right) models of "Blanview LCD"
[Click to enlarge image]
The new panel reflects outside light more efficiently and has a higher transmittance.
The new panel reflects outside light more efficiently and has a higher transmittance.
[Click to enlarge image]

Casio Computer Co Ltd developed "Blanview LCD," a transmissive LCD panel that does not need backlighting when used outdoors.

The company increased the transmittance of the panel by about 30% and cut its power consumption for outdoor use by about 50%, compared with its existing model. In addition, it developed a new structure that efficiently takes in outside light into the LCD panel so that the transmissive LCD panel can be used outdoors without backlighting like a reflective LCD panel.

The Blanview LCD panel is aimed mainly at business-oriented and industrial mobile devices such as handy terminals. Thus far, semi-transmissive LCD panels have been the LCD panels for outdoor use.

In semi-transmissive LCD panels, pixels are divided into transmissive and reflective parts. Images are displayed on the transmissive part with backlighting indoors and on the reflective part without backlighting outdoors.

However, the low transmittances of semi-transmissive LCD panels reduce the efficiency of backlighting, increasing the power consumption of the panels. Also, the quality of their images displayed on the transmissive part is not high enough.

On the other hand, to used a normal transmissive LCD panel outdoors, the luminance of the backlighting has to be enhanced to counter outside light, resulting in larger power consumption.

To develop the Blanview LCD panel, Casio Computer improved the transmittance of the existing transmissive LCD panel by 30% by the following two methods. First, the aperture ratio of the panel was increased by, for example, narrowing the width of the wiring lines. Second, the optical design was changed so that the spectral characteristics of the color filter become white.

Also, the coloration problem was alleviated. The company used amorphous Si (a-Si) TFT and TN liquid crystals.

With the enhanced transmittance, outside light incident through the apertural areas of the panel reaches the backlighting part and efficiently reflects off light guide plates, light reflectors, etc, realizing a high visibility without backlighting outdoors.

When used indoors, the power consumption of the backlighting that provides a surface brightness of 200cd/m2 to a 3.5-inch panel is 200mW, about 50% of that of the existing model, Casio Computer said.

From July 2008, the company will ship samples of the following models in series: 2.7- and 3.5-inch vertical models (240 × 320 pixels); 3.5-, 4.1-, 5- and 5.7-inch horizontal models (320 × 240 pixels); and a 6.5-inch horizontal model (640 × 480 pixels).