Abstract:
A liquid crystal display is provided. The liquid crystal display includes a liquid crystal display panel having pixels configured to form an image; and a backlight system proximate to the liquid crystal display panel and configured to illuminate the pixels of the liquid crystal display panel. The backlight system includes a light guide including a plate portion generally parallel to the liquid crystal display panel and a first side portion extending generally perpendicularly from the plate portion, a light source configured to emit light into the light guide via the first side portion, and a heat sink coupled to the light source and configured to remove heat generated by the light source during operation.

Description:
TECHNICAL FIELD 
     The present invention generally relates to a liquid crystal display having a backlight system, and particularly relates to a liquid crystal display with a folded backlight system. 
     BACKGROUND 
     Many efforts have been made to study and develop various types of display devices as substitutes for cathode ray tubes (CRTs), such as liquid crystal display devices (LCDs), plasma display panels (PDPs), electro-luminescence displays (ELDs), and vacuum fluorescent displays (VFDs). For example, LCDs have been actively developed as flat display panels in laptop computers, desktop computers, and large-sized information displays because of their high quality images, lightness, thinness, compact size, and low power consumption. Thus, the demand for LCDs increases continuously. 
     LCDs typically include an LCD panel on which images are formed and a backlight system for illuminating the images on the LCD panel. Generally, the backlight system includes one or more light sources and may include a light guide. When a light guide is present, the light sources are typically arranged adjacent to one or more edges of the light guide. The light guide receives and mixes the light from the light sources and directs the light to illuminate the LCD panel. The design and operation of backlight systems is a particularly important consideration. Some backlight systems may suffer from the following common disadvantages: uneven luminance and/or luminance spots; brightness issues; heat management issues; sizing constraints; and color mixing issues. 
     Accordingly, it is desirable to provide a more compact backlight system with a compact design that provides adequate color mixing, luminance characteristics, and heat management. In addition, it is desirable to provide improved LCDs with such a backlight system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY 
     In accordance with an exemplary embodiment, a liquid crystal display is provided. The liquid crystal display includes a liquid crystal display panel having pixels configured to form an image; and a backlight system proximate to the liquid crystal display panel and configured to illuminate the pixels of the liquid crystal display panel. The backlight system includes a light guide including a plate portion generally parallel to the liquid crystal display panel and a first side portion extending generally perpendicularly from the plate portion, a light source configured to emit light into the light guide via the first side portion, and a heat sink coupled to the light source and configured to remove heat generated by the light source during operation. 
     In accordance with another exemplary embodiment, a backlight system includes a light guide including a plate portion and a first side portion extending generally perpendicularly from the plate portion, a light source configured to emit light into the light guide via the first side portion, and a heat sink coupled to the light source and configured to remove heat generated by the light source. 
     In accordance with yet another exemplary embodiment, a liquid crystal display includes a liquid crystal display panel comprising pixels configured to form an image; and a backlight system proximate to the liquid crystal display panel and configured to illuminate the pixels of the liquid crystal display panel. The backlight system includes a light guide having a plate portion generally parallel to the liquid crystal display panel and having a perimeter with at least four sides, fold portions coupled to each of the at least four sides of the plate portion, and side portions coupled to each of the fold portions, and extending essentially perpendicular from the plate portion, the side portions and the plate portion forming a cavity, a light source configured to emit light into the light guide via the side portions, and a heat sink coupled to the light source and configured to remove heat generated by the light source during operation. The liquid crystal display further includes circuitry arranged within the cavity and configured to drive the liquid crystal display panel and the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a cross-sectional view of a liquid crystal display (LCD) with a backlight system in accordance with an exemplary embodiment; 
         FIG. 2  is a partial, rear plan view of the backlight system of  FIG. 1 ; 
         FIG. 3  is a close-up view of a portion of  FIG. 1 ; and 
         FIG. 4  is a partial cross-sectional view of a backlight system in accordance with an alternate exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     Broadly, liquid crystal displays are provided that include backlight systems with light guides. The backlight systems can be used in a wide variety of applications, including, but not limited to, vehicle lighting, search lights, task lights and projection systems. The display system can particularly be utilized in vehicle applications, such as an airplane cockpit, as well as other applications where viewing angles, space, thermal, and/or structural issues are of concern. In accordance with exemplary embodiments, the light guides of the backlight systems can include side portions that extend generally perpendicularly from a plate portion. The extended side portions allow placement of the light sources in a position for efficient heat removal. Additionally, the side portions can have a length sufficient for mixing light from colored light sources, and can create a cavity with the plate portion to accommodate circuitry. Fold portions can couple the side portions to the plate portions and provide additional optical advantages. 
       FIG. 1  is a cross-sectional view of a liquid crystal display (LCD)  100  in accordance with an exemplary embodiment. Generally, the LCD  100  includes an LCD panel  110  and a backlight system  120  that illuminates the LCD panel  110 , as will be discussed in greater detail below. The LCD panel  110  generally includes a liquid crystal layer sandwiched between two glass substrates and divided into pixels. Typically, thin film transistors (TFTs) are mounted on the glass substrates to switch the pixels “on” and “off” such that images are formed on the LCD panel  110 . In addition to the depicted LCD panel  110  and backlight system  120 , the LCD  100  can include one or more color filters, diffusion plates, and/or prism sheets. 
     The backlight system  120  includes a light guide (or “waveguide”)  130 , a light source  160 , a reflector  170 , a heat sink  180 , and circuitry  190 . As discussed in further detail below, the light guide  130  directs light from the light source  160  to illuminate the LCD panel  110 .  FIG. 2  is a rear view of the LCD  100  with the heat sink  180  ( FIG. 1 ) removed and will be discussed in conjunction with  FIG. 1 . 
     The light source  160  may include one or more light emitting diodes (LEDs). Typically, the LEDs include linear or planar arrays of red, green or blue LEDs, although white and other colors of LEDs are also possible. In other embodiments, the light source  160  can be one or more fluorescent lamps. As best shown in  FIG. 2  and discussed in further detail below, the light source  160  typically extends around the perimeter of the backlight system  120 , for example, around all four perimeter sides. Although the light source  160  is depicted as extending around all four perimeter sides of the backlight system  120 , in alternate embodiments, the light source  160  may only be provided on one, two, or three of the sides of the backlight system  120 . 
     In the depicted embodiment, the light guide  130  includes a plate portion  132  with a generally rectangular shape as viewed from the top and bottom sides, one or more side portions  134  extending from the perimeter of the plate portion  132 , and one or more fold portions  136  that couple the side portions  134  to the plate portion  132 . The plate portion  132  is formed into the shape of a substantially flat plate by a material having high transmissivity with respect to every range of relevant wavelength, for example, a transparent acrylic resin. 
     This arrangement, as best shown in  FIG. 1 , can be referred to as a “folded backlight” system since the side portions  134  extend at an angle to the plate portion  132 . Consequently, by incorporating such a backlight system  120  into a display device, for example, the LCD  100 , the outside dimensions of the display device with respect to the area of the data display space of the display device can be decreased. Namely, the display device can have smaller outside dimensions compared to a conventional display device having a data display space of the same area. This compact arrangement can be accomplished, while maintaining the luminance advantages of an edge-lit backlight system. 
     In the depicted embodiment, the side portions  134  are approximately 90° relative to the plate portion  132  and extend towards the light source  160 . Again, as best shown in  FIG. 2 , the side portions  134  are provided on each of the perimeter sides of the backlight system  120  and generally correspond to the arrangement of the light source  160 . The fold portions  136  and their relationship to the plate portion  132  and side portions  134  are discussed in further detail below. 
     The side portions  134  and the plate portion  132  of the light guide  130  form an interior cavity  142  that houses the circuitry  190 . The circuitry  190  drives the backlight system  120  and/or the LCD panel  110 . In many conventional LCDs, the circuitry is positioned behind the backlight system, thereby disadvantageously creating additional thickness. The length  139  of the side portions  134  can be adjusted as necessary to accommodate additional or less circuitry  190 . 
     Generally, the plate portion  132 , side portions  134 , and fold portions  136  may be formed of a transparent polymer material such as acrylic or polycarbonate. Alternatively, glass, such as fused silica, F2, or BK7 can be used, as well as a combination of these materials. 
     The reflector  170  is positioned between the light guide  130  and the circuitry  190  within the cavity  142 . The reflector  170  is preferably a reflective white sheet, but may also be diffusely or specularly reflective, and may contain any of several reflective materials or structures such as polymers, metals, metallic films, paints, fibers, structured glass or ceramics. The reflector  170  extends parallel to the plate portion  132  and to each of the side portions  134 . 
     The heat sink  180  is positioned proximate to the light source  160  and functions to draw heat away from the light source  160 . Generally, the heat sink  180  can be any suitable material, such as for example, aluminum, copper, other metals or certain crystalline structures. Composite materials may also be used, especially when the composite includes particles or components with high thermal conductivity properties. The folded nature of the light guide  130  enables a more efficient and effective use of the heat sink  180  and particularly enables heat to be removed at a distance from the LCD panel  110 . This separation between the LCD panel and the combination of heat sink  180  and light sources  160 , for example 0.25 to 0.5 inches or more, enhances thermal heat dissipation by allowing the heat sink surface area or cross-section to be larger and to operate at higher temperatures without adversely impacting the temperature and therefore the optical performance of the LCD panel  110 . In addition, the isolation from the LCD panel  110  also makes it more practical for circuitry  190  to share the same heat sink  180 . 
     Now that the structure of the LCD  100  has been introduced, the operation of the LCD  100  will be described. The light source  160 , which in this example is driven by circuitry  190 , emits ray  135 , for example. Ray  135  enters the light guide  130  on a bottom face  138  of the side portion  134 . Due to the perpendicular nature of the side portion  134 , the optical coupling between the light guide  130  and the light source  160  can approximate an edge-lit back light, even though the light source  160  is positioned behind the light guide  130 . Ray  135  passes from the side portion  134  into the fold portion  136 , and then from the fold portion  136  into the plate portion  132 . The light passing through the fold portion  136  is discussed in greater detail below in reference to  FIG. 3 . Ray  135  may pass directly out of the plate portion  132  as light  137  that illuminates the LCD panel  110 , or may be totally internally reflected within the plate portion  132  until extracted as light  137 . The plate portion  132  can include one or more extraction features (not shown) to assist in extracting the light. Any light that leaks out of the rear side of the plate portion  132  can be reflected back into the plate portion  132  by the reflector  170 . 
     As noted above, the light source  160  typically includes multiple colors of LEDs. These colors may include red, green, blue and white LEDs and the light that enters the side portion  134  (e.g., ray  135 ) is typically separated into colors. The side portion  134  can have a length  139  sufficient to enable the colored light to mix such that a white light is formed prior to reaching the plate portion  132  and being emitted from the light guide  130 . Generally, the longer the side portion  134 , the more color mixing occurs. The provision of multiple colors of light source  160  allows the colors to mix as needed for achieving backlight or display output having the desired mixed color or chromaticity. In one embodiment, the length  139  of the side portions  134  can be “tuned” to produce the desired amount of color mixing. Additional color mixing may or may not occur in the plate portion  132 . 
       FIG. 3  is a close-up view of section  300  of  FIG. 1  and particularly depicts the fold portion  136 . In the depicted embodiment, the fold portion  136  has the cross-sectional shape of a right triangle with one leg  302  being coupled to the side portion  134  and one leg  304  being coupled to the plate portion  132 . The fold portion  136  can be any suitable material, such as for example, polycarbonate. Similarly, the fold portion  136  can be the same or different material as the plate portion  132  and/or the side portion  134 . 
     Generally, the legs  302 ,  304  of the cross-sectional shape of the fold portion  136  are the same lengths and correspond to the thicknesses of the side portions  134  and the plate portion  132 , respectively. The outer side  306  (or third leg of the cross-sectional shape) can include a reflective material, for example a coating or an adjacent mirror, such that any light that would otherwise escape from the fold portion  136  is reflected back into the light guide  130  and is directed to the plate portion  132 . 
     The fold portion  136  can be coupled to the plate portion  132  and the side portions  134  by low index regions  308 . The low index regions  308  typically have a refractive index low enough to maintain total internal reflection (TIR) of the light propagated within the light guide  130 . In one embodiment, the low index regions  308  can be formed by an adhesive that adheres the fold portion  136  to the plate portion  132  or the side portions  134 . The adhesive can be, for example, a layer of adhesive or spots of adhesive with air gaps in between. In other embodiments, the low index region  308  can be formed by air, clear PTFE, silicone, or any suitable material. The presence of the low index region helps to minimize the loss of useful light at the fold region by preventing light from entering the plate portion  132  at angles which do not meet the conditions for TIR within plate portion  132 . 
     Although the depicted light guide  130  is a multi-piece light guide, in an alternate embodiment, the light guide  130  can be a single piece. In other words, the light guide  130  can be physically folded to form the side portions  134  and fold portions  136 , or the light guide  130  can be molded into the plate portion  132 , side portions  134 , and fold portions  136 . Moreover, although the cross-sectional shape of the fold portions  136  in  FIGS. 1 and 3  is triangular, the fold portions  136  can have other cross-sectional shapes, such as for example, semi-circular or trapezoidal. Even as a single piece, light guide  130  may still include low index regions  308 . For example, air spaces may be provided by cutting, casting or otherwise shaping the single piece to include full or partial channels within the structure, and these air spaces may alternately filled with suitable index materials. In still further embodiments, the light source  160  can be positioned within the cavity  142 , and light from the light source  160  can enter the light guide  130  on an inner side of side portion  134 . 
       FIG. 4  is a partial cross-sectional view of a backlight system  400  in accordance with an alternate exemplary embodiment. As in the embodiments described above, the backlight system  400  includes a light source  460  and a light guide  430 . The light guide  430  includes a plate portion  432 , one or more side portions  434 , and one or more fold portions  436 . 
     In this embodiment, the side portions  434  have tapered, rectangular cross-sections. In other words, the side portions  434  have a first end  450  coupled to the fold portion  436  and a second end  455  adjacent the light source  460 . The first end  450  has a thickness or area greater than that of the second end  455 . The tapered side portions  434  can function as collimators and/or compound parabolic concentrators, and can include tapering as shown in  FIG. 4  or along the orthogonal axis. The introduction of angular tapering makes the optical output of the side portions  434  more collimated or directional. 
     Collimated light produced by the tapered side portions  434  can be preferable for optimizing the material selection and performance of the fold portion  436  and plate portion  432  of light guide  430 . By reducing the angular spread of light which enters the fold portion  436 , less light will escape from the fold region and the effectiveness of any low index region, if present, will be enhanced. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.