Canon Develops Reflective LCD Panel with Reduced Light Absorption of Color Filter Able to Double Brightness

Jul 14, 2006
Naoki Tanaka, Nikkei Microdevices
The prototype reflective LCD panel (Left: the latest three-subpixel configuration, Right: the previous two-subpixel configuration).
The prototype reflective LCD panel (Left: the latest three-subpixel configuration, Right: the previous two-subpixel configuration).
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Canon Inc. has developed a new reflective LCD panel that achieves brightness twice as high as that of the existing RGB LCD panel by reducing the light absorption of the color filter by half. The panel was manufactured by adding subpixels of "white" to the color display method proposed by Canon which uses a two-color filter of "green" and "magenta." Although the new display panel uses a polarizing plate, it can achieve the brightness theoretically on par with that of a color electronic paper (color filter method) without using a polarizing plate. The actual measurement of the prototype panel showed the reflectivity of 40% or more.

The color display method employing two-color filter that underlies this technology utilizes the coloring phenomenon (interference color) caused by birefringence. Although green is reproduced according to the same principle as that of the existing RGB LCD panels, red and blue are displayed by utilizing birefringence. Since this method can reduce the number of subpixels from previous three to two, the light absorption of the color filter can be suppressed. Thus, the panel can achieve the light use efficiency and the resolution 1.5 times as high as those obtained by the existing method.

Generally, it is reported that the color representation using birefringence shows poor color purity due to the lack of steep spectrum. In particular, it is difficult to reproduce saturated red since red tends to be tinged with yellow. In the latest method, however, red and blue are displayed by the magenta pixels that block the waveband of green, thus enabling the representation by the three primaries with high purity.

To implement this method, Canon has adopted the VA-LCD mode. LCD TVs and other products using the VA-mode usually utilize only the brightness modulation region of birefringence. This time, by setting the cell thickness to be greater, a larger retardation (optical path difference) region can be used to provide color representation by means of birefringence.