Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-05-14
2004-09-14
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S061000, C349S063000, C349S065000, C362S035000
Reexamination Certificate
active
06791639
ABSTRACT:
BACKGROUND
1. Technical Field
The present invention is generally directed to a LCD (liquid crystal display) panel and device for use in a portable personal computer (PC). In particular, the present invention is directed to a LCD panel and LCD device that provides improved brightness and viewing angle of light emitted from a portable LCD panel.
2. Description of Related Art
There has been remarkable progress in the use of liquid crystal display devices as image displays for PCs and various other applications. The liquid crystal display devices of this kind are typically constructed such that a backlight unit, which comprises a planer light source for illumination from the backside of the liquid crystal display panel, illuminates an entire liquid crystal layer having a given expanse with light having a uniform brightness thereon, wherein an image formed in the liquid crystal layer is made visible using polarizing sheets.
This backlight design typically employs a HCFL (hot-cathode fluorescent lamp) or a CCFL (cold-cathode fluorescent lamp) as the light source. Light from so-called “linear light source” such as a fluorescent tube must be projected onto the full surface of the liquid crystal display panel, and two general configurations for the backlight have been developed: (i) a directly-below type; and (ii) a side light type (edge lit type). A directly-below backlight unit employs one or more fluorescent tubes disposed directly below the LCD panel, with a light control plate and a diffusing plate disposed between the fluorescent tube(s) and the LCD panel.
A side light type unit has a fluorescent tube along one or two sides of a light guide plate that is made of a transparent resin. The light guide plate directs light incident on the edges of the light guide plate toward the surface of the liquid crystal display panel by reflecting microstructured portions formed on the backside of the light guide plate. This backlight design is suitable for use as a display device for portable equipment such as a notebook PC or the like, since it can be made thin as compared to a backlight device comprising a directly-below structure.
A desired characteristic for a liquid crystal display device is that the display be bright even from a wide viewing angle. One method of increasing the brightness of the screen is to increase the luminance of the backlight. Increasing the backlight luminance, however, has the disadvantage of increased power consumption, especially in the case of battery powered portable equipment, wherein power consumption should be limited.
Typically, to increase the viewing angle of a display, a diffusing plate is used in the liquid crystal device. The diffusing plate redistributes light from the light guide plate as light having a wider angular distribution. A diffusing plate comprises a light diffusing layer, made of a light transmissive resin and light scattering particles such as acrylic particles, silica particles or the like, on or in the surface of a transparent substrate such as a PET film. When light emitted from a light source (such as a fluorescent tube or the like) is transmitted through the diffusing plate, however, the luminance is substantially reduced. Consequently, by removing the diffusing plate, the luminance, or brightness, of the liquid crystal display device can be increased.
As noted above, however, the diffusing plate provides an important function of increasing the angular distribution of the light from the backlight to provide a wider viewing angle. Thus, it is not desirable to remove the diffusing plate.
There are patents that disclose the use of lenticular lens sheets in conjunction with liquid crystal displays. This use of microlens has generally been directed toward projection displays (see, U.S. Pat. Nos. 5,764,319, 5,548,349, and 5,859,675), especially for “color-filterless” projection displays where a lenticular sheet with a lens pitch equal to the pixel pitch is used to focus and direct Red, Green, and Blue light which are incident on the lenticular sheet from different angles through spatially separate Red, Green, and Blue subpixels in the display.
A color filterless backlight system for direct view LCDs is described in U.S. Pat. No. 4,798,448 and U.S. patent application Ser. No. 09/664,719 filed Sep. 19, 2000, entitled “FLAT BACKLIGHTING SYSTEM”, which is commonly assigned and incorporated herein by reference. U.S. Pat. No. 5,101,279 to Kurematsu et al. describes using a lenticular sheet in combination with a LCD to increase the amount of light transmitted through the open aperture. In this patent, the longitudinal axes of the cylindrical lenses comprising the lenticular extends in the direction of the optical switching portion (open aperture) dimension of greater distance. This configuration has a number of disadvantages. Nearly all LCDs use a vertical triad structure, i.e., each pixel is composed of a Red, Green, and Blue subpixel, each of which extends vertically across the whole of a square pixel and occupies ⅓ of the pixel area in the horizontal direction. For the configuration described by Kumematsu et al., the lenticular longitudinal axis would be vertical and the pitch would equal ⅓ of the pixel pitch. It would be advantageous to make the pitch of the lenticular equal to the pixel pitch (and not the subpixel pitch) since less precision is needed in forming and aligning the lenticular sheet to the display. If a vertical lenticular is placed behind the display, and no additional structure is added to the front, the width of the output light distribution would be increased in the horizontal direction, but be unchanged in the vertical direction.
It is typical for notebook displays to use a tapered light guide with the CCFL along the top or bottom edge of the display. This is advantageous since nearly all displays are used in a “landscape” mode so the top or bottom edge is longer than the side edges. Thus, placing a single CCFL along the longer edge results in a brighter display than placing a single CCFL along the shorter edge. As described below, with a tapered light guide having the CCFL along the bottom (or top) edge, the light output distribution in the vertical direction can be adjusted to be much less than that in the horizontal direction, so having a vertical lenticular present which further increases the width of the output light distribution in the horizontal direction is very undesirable.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide a liquid crystal display panel and a liquid crystal display device capable of improving the brightness and viewing angle of the light emitted from a portable liquid crystal display panel.
In one aspect of the present invention, a display panel for a direct view display device comprises: a first substrate comprising a light transmissive material for receiving light emitted from the light source; a second substrate comprising a light transmissive material for receiving light transmitted through the first substrate and emitting the light from an image display screen thereof; an optical device layer, disposed between the first and second substrates, comprising an optical device for controlling light emitted from the light source; and light converging means for converging the light emitted from the light source on the optical device layer.
The light converging means preferably converges light emitted from the light source onto the optical device layer so that the converged light can be transmitted through the optical device layer without being blocked, e.g., by scanning lines. Further, the focusing of light in one dimension increases the angular width of the output distribution in that direction, which increases the viewing angle without using diffusing plates. In other words, since light having a wide angular distribution can be emitted from the display panel without using any diffusing plates, unlike the conventional method, it is possible to increase the luminance while maintaining adequate brightness off the display normal to provide a wide viewing angle
Colgan Evan George
Doany Fuad Elias
Singh Rama Nand
Suzuki Masaru
Chowdhury Tarifur R.
Trepp Robert M.
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