The present invention relates generally to video display systems. More specifically, the present invention relates to the use of holographic diffusers to provide backlighting in liquid crystal display (LCD) video systems.
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present invention that are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Many video display units create video images by using a light source to illuminate an image displayed on a panel. One example of such a video display unit is a liquid crystal display (LCD) system, which uses a backlight to illuminate an image that is displayed on an LCD panel. In particular, large LCD TVs generally employ backlighting as a form of illumination, which may be provided by a number of long narrow cold cathode fluorescent lamps (CCFLs), or alternatively, hot cathode fluorescent lamps (HCFLs), forming a lamp plane array. However, the light distribution from multiple lamps is not uniform when applied to the LCD panel. For example, from the perspective of a viewer, a non-uniform light distribution results in some areas of the LCD panel appearing brighter than other areas. This is generally an undesirable characteristic in video image quality.
The current art employs several methods for increasing the uniformity of light distribution in LCD devices. One solution to reduce the problems related to uneven lighting is to first diffuse the light output from the multiple light sources through an optical diffuser, typically glass, in order to more uniformly distribute the light source in as small a space as possible before applying the light to the LCD panel. Another solution for increasing light distribution uniformity is by decreasing the spacing between each lamp, thus requiring additional lamps. In addition, a light pipe layer may be employed between the lamp plane and the diffuser in order to conduct and distribute light in a more desirable way prior to diffusion. Disadvantageously, the aforementioned methods require integrating additional components (e.g., the additional lamps and light pipe layer, etc.), thus increasing the manufacturing and production costs of the LCD device. Another method for increasing light distribution uniformity is by increasing the distance between the lamps and the diffuser. However, this results in a thicker LCD which may result in a less attractive product in the eyes of a consumer (a thicker LCD device may be deemed inferior when compared alongside thinner competing LCD products).
To avoid the drawbacks of the prior art, there is a need for an LCD display system having improved light distribution uniformity without sacrificing economic and market competitiveness.
These and other features, aspects, and advantages of the present technique will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developers' specific goals, such as compliance with system-related and and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
An exemplary embodiment of the present invention provides a holographic optical diffuser (holographic diffuser) for improving uniformity of light distribution in LCD backlighting. Holographic diffusers provide a high level of diffusion transmission efficiency and can be used to control the diffuse area of illumination from various light sources. For example, some holographic diffusers are capable of providing a diffusion transmission efficiency of 90% or greater.
In one exemplary embodiment, glass diffusers of conventional LCD panel devices are replaced with a holographic diffuser that is aligned so that a strong diffusion axis is orthogonal to the direction of the backlight lamps, and a weak diffusion axis is parallel to the direction of the backlight lamps. As such, the light output is diffused strongly along the orthogonal diffusion axis in the direction necessary to “smear” the lamp images together, creating the effect of a uniform illumination source. Furthermore, because only a relatively small amount of the light output is diffused along the weak diffusion axis, there is decreased loss of the useful light output in the direction parallel to the lamps and, therefore, the overall brightness of the backlight is increased.
The application of a holographic diffuser to provide improved uniformity in LCD backlighting is advantageous in several ways. As discussed above, holographic diffusers are more efficient than other conventional diffusers and, therefore, more light is available for illumination of the LCD panel. This may reduce or eliminate the need for additional components (e.g., the additional lamps and light pipe layer, etc.), thereby reducing the overall cost of manufacturing the LCD device. Moreover, in a manufacturing context, the benefits of the holographic diffuser can be utilized in several ways:
(1) the distance between the lamp plane and the diffuser can be decreased while maintaining uniformity, thereby allowing for a thinner LCD panel;
(2) the distance between each lamp can be increased while maintaining uniformity, thereby reducing the number of lamps in the lamp plane and lowering production costs;
(3) the distance between the lamp and diffuser can be maintained with improved backlight illumination uniformity; and
(4) the distance between each lamp can be maintained with improved backlight illumination uniformity.
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Specifically, in the illustrated embodiment, the display device 10 includes an illumination system 12, an LCD panel 14, and a screen 18. The illumination system 12 is adapted to generate white or colored light to provide a backlight for the LCD panel 14 and the screen 18. The illumination system 12 may include any suitable form of lamp or bulb capable of producing white or generally white light. In the illustrated embodiment, the illumination system 12 may include a plurality of cold cathode fluorescent (CCFL) lamps forming a lamp plane. In other embodiments of the present invention, hot cathode fluorescent (HCFL) lamps may be used in place of CCFL lamps. Furthermore, in one or more embodiments utilizing a plurality of either CCFL or HCFL lamps, the CCFL or HCFL lamps may be arranged in such a manner that each of the plurality of lamps is parallel with the others. It will be appreciated, however, that the above-described exemplary embodiments are not intended to be exclusive, and that in alternate embodiments, other suitable lighting sources (e.g., light emitting diodes, incandescent light bulbs or the like) may also be employed in the illumination system 12.
The LCD panel 14 is adapted to intake and modulate the light provided by the illumination system 12, thereby forming viewable images which are, thereafter, distributed and displayed across the screen 18. In the illustrated embodiment, the LCD panel 14 includes a holographic optical diffuser adapted to diffuse or spread the light produced by the illumination system 12. As will be appreciated by those skilled in the art, the holographic diffuser may be capable of providing a diffusion transmission efficiency of 90% or greater. The holographic diffuser is aligned so that a first diffusion axis diffuses a substantial portion of the light in a direction that is perpendicular to the direction of the light source of the illumination system 12 (e.g., perpendicular to the direction of a plurality of CCFLs), and a second diffusion axis diffuses a relatively small amount of the light weakly in the same direction of the light source (e.g, parallel to a plurality of CCFLs). From the perspective of a viewer, the the diffusion of the light output from the illumination system 12 by the holographic diffuser of the LCD panel 14 creates the effect of a uniformly distributed illumination source, which is then applied onto the screen 18 to provide properly diffused backlighting for the screen 18. The configuration of the lighting source of the illumination system 12 and operation of the holographic diffuser will be described in more detail below.
In one or more exemplary embodiments of the present invention, the LCD panel 14 may further include a light pipe layer operatively positioned between the illumination system 12 and the holographic diffuser. For example, the light pipe layer may be adapted to funnel or conduct the light output from the illumination system 12 in a more desirable way prior to diffusion by the holographic diffuser.
The LCD panel 14 may include additional imaging components adapted to generate and enhance images appearing on the screen 18. Such imaging components may include a thin film transistor (TFT) LCD, super twisted nematic (STN) LCD, multidomain vertical alignment (MVA) LCD, pattern vertical alignment (PVA) LCD or the like. An LCD device may generally include two thin polarized panels on either side of a thin liquid-crystal gel that is divided into pixels. In the illustrated embodiment, images may be formed by the display unit 10 as the LCD panel 14 applies appropriate voltages to appropriate image pixels disposed across the panel 14, wherein each pixel is be adapted to receive a respective voltage and to darken in proportion to the amount of voltage applied. By way of example, to create a bright detail, a low voltage is applied to the corresponding pixels and, conversely, for darker shadow details, a higher voltage is applied. In this manner, the uniformly distributed light output provided by the LCD panel 14 is provided to the screen 18, so as to from images perceivable by a viewer. The opacity of each pixel on the LCD panel 14 determines the amount of light that passes through. It should be noted that LCDs are not completely opaque and that even the darkest (e.g., blackest) pixels may still allow some degree of light to pass through.
In one or more exemplary embodiments of the present invention, the LCD panel 30 may further include a light pipe layer (not shown in
As discussed above, a display device 10 (
The diffused light output 36 (
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
Number | Date | Country | Kind |
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200810067698.3 | Jun 2008 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US08/81161 | 10/24/2008 | WO | 00 | 12/3/2010 |