Abstract:
A backlight for a liquid crystal display includes a light guide plate located adjacent to a liquid crystal display panel. A light collector is located at one end of the light guide plate and has an exposed surface for receiving ambient light. The light collector has a reflector secured inside it. The received ambient light is reflected by the reflector along the light guide plate. The reflector may include three arcuate shaped reflecting elements. The light guide plate has a reflective surface which reflects the light toward the liquid crystal display panel.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to backlights for liquid crystal displays. 
     A typical liquid crystal display (LCD) has a liquid crystal display panel and a backlight arranged behind the display panel. The backlight includes a light guide plate, which is located behind the display panel, an edge light, which is arranged at one end of the backlight, and a light collector, which is arranged at the other end of the backlight. The light guide plate is typically made of an acrylic. A light emitting diode (LED) or an electroluminescence (EL) may be employed as the edge light. The light collector has a lens-like shape and transmits ambient light, such as sunlight or artificial light, to the light guide plate. Examples of backlights are described in “Recent Trends in Liquid Crystal Backlights,  Monthly Display , June 1997: 75-85.” 
     An LCD may be applied to the view finder of, for example, a video camera or a digital still camera. In such cases, outdoor usage may incur problems. When strong sunlight shines on the display panel from behind the user on a sunny day, the amount of light transmitted to the light guide plate decreases. This may lead to a decrease in the brightness of the display panel. In some cases, the decrease in brightness can make the images on the display panel barely visible. 
     Accordingly, it is an objective of the present invention to provide a liquid crystal display backlight that collects ambient light efficiently. 
     SUMMARY OF THE INVENTION 
     To achieve the above objective, the present invention provides a liquid crystal display backlight comprising: a light guide plate; a light collector arranged on at least one end of the light guide plate and having an exposed surface for receiving ambient light; and a reflector arranged within the light collector. 
     The present invention further provides a liquid crystal display comprising: a liquid crystal display panel; a light guide plate located adjacent to the liquid crystal display panel; a light collector arranged on at least one end of the light guide plate and having an exposed surface; and a reflector arranged in the light collector. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a side view showing an LCD employing a backlight according to a first embodiment of the present invention; 
     FIG. 2 is an enlarged perspective view showing the backlight of FIG. 1; 
     FIG. 3 is a perspective view showing a backlight according to a second embodiment of the present invention; 
     FIG. 4 is a perspective view showing a backlight according to a third embodiment of the present invention; 
     FIG. 5 is a perspective view showing a reflector of the backlight of FIG. 4; 
     FIG. 6 is a perspective view showing a backlight according to a fourth embodiment of the present invention; 
     FIG. 7 is an exploded perspective view showing an LCD employing a backlight according to a fifth embodiment of the present invention; 
     FIG. 8 is an enlarged perspective view showing the backlight of FIG. 7; and 
     FIG. 9 is a perspective view showing a backlight according to a sixth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, like numerals are used for like elements throughout. 
     First Embodiment 
     A liquid crystal display (LCD)  100  employing a backlight  10  according to a first embodiment of the present invention will now be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the LCD  100  has a liquid crystal display panel  1 . The LCD  100  further includes a polarizing film, or lens film  2 , a diffuser  3 , and the backlight  10 , which are sequentially arranged behind the display panel  1 . 
     The backlight  10  includes a light guide plate  4  arranged behind the diffuser  3 , and a light collector  5 , which is preferably formed integrally with the left end of the light guide plate  4 . An edge light  8 , which is preferably a light emitting diode (LED) or an electroluminescence (EL) element, is arranged at the right end of the light guide plate  4 . The edge light  8  is used when ambient light is not collected through the light collector  5 . The light guide plate  4  preferably has a V-shaped profile such that the light guide plate  4  is thinner at locations further from the light collector  5 . However, the light guide plate  4  may also be rectangular. One side of the light guide plate  4  faces the diffuser  3 . The other side of the light guide plate  4  is molded or printed so that it has a diffusing reflection surface  4   a . Preferably, silk screen printing is performed by forcing ink through the pores of a meshed fabric and onto a printing subject. In comparison to offset printing, which could also be used, silk screen printing forms a diffusing reflection surface  4   a  (i.e., ink layer) having a thickness that is five to ten times greater. The silk screened diffusing reflection surface  4   a  is believed to have superior weather resistance and chemical resistance properties. 
     The light collector  5  preferably has a profile similar to a convex lens to guide ambient light, such as sunlight or artificial light, toward the light guide plate  4 . Furthermore, the light collector  5  is made of a material having high transparency, such as an acrylic, glass, or polycarbonate. A reflector  6 , which preferably includes three reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3 , is arranged within the light collector  5 . The number of the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  may be changed. The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are preferably made of a material having high reflectance, such as aluminum, which also has desired molding properties. The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  extend in the longitudinal direction of the light collector  5  (perpendicular to the plane of FIG.  1 ). 
     The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  will now be described with reference to FIG.  2 . The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are arranged such that the light collected by the light collector  5  is transmitted toward the light guide plate  4 . More specifically, the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are arranged such that the ambient light reflected by the reflecting elements  6 - 2 ,  6 - 3  are collected by the reflecting element  6 - 1 . 
     The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are embedded in the light collector  5  and molded or silk screen printed to define reflection surfaces. Further, the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are formed preferably through insert molding, press fitting, or deposition. When performing insert molding, the reflector  6  is positioned in a mold. Liquefied resin is then poured into the mold and solidified. It is preferable that the light collector  5  be made of an acrylic when carrying out insert molding. Insert molding is most preferable since the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  can be formed thin and at low cost. When performing press fitting, the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are heated. The heated reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are then pressed against the acrylic light collector  5 . This melts the light collector  5  and embeds the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  longitudinally in the light collector  5 . When performing deposition, metal is deposited into notches having the same shape as the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  to form the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3 . Alternatively, preformed reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  may be inserted into the notches. 
     Each reflecting element  6 - 1 ,  6 - 2 ,  6 - 3  has a parabolic profile. A gap  7  extends between the reflecting elements  6 - 2 ,  6 - 3 . The reflecting surfaces of the reflecting elements  6 - 2 ,  6 - 3  face the exterior of the light collector  5 . The reflecting element  6 - 1  is arranged between the reflecting elements  6 - 2 ,  6 - 3  such that its reflecting surface faces the gap  7 . 
     Incident light in the light collector  5  is reflected by the reflecting elements  6 - 2 ,  6 - 3  and collected by the reflecting element  6 - 1 . The reflecting element  6 - 1  reflects the collected light into the light guide plate  4  through the gap  7 . The light is collimated when passing through the gap  7 . The diffusing reflection surface  4   a  then illuminates the display panel  1  from behind. Accordingly, ambient light is efficiently transmitted to the light guide plate  4 . Thus, images can be viewed on the display panel  1  even if the display panel  1  is subjected to sunlight from behind the user on a sunny day. 
     Second Embodiment 
     A second embodiment according to the present invention will now be described with reference to FIG.  3 . The second embodiment is a modification of the first embodiment. As shown in FIG. 3, a light collector  5   a  may have a flat outer side surface (light collecting surface), as opposed to the curved rim of the first embodiment shown in FIG.  2 . 
     Third Embodiment 
     A third embodiment according to the present invention will now be described with reference to FIGS. 4 and 5. In this embodiment, the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are rotatable. The light collector  5  has a convex lens-like shape and includes a bore  11 , which extends longitudinally. A cylinder  12  is accommodated in the bore  11 . The reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  are preferably secured to the inner surface of the cylinder  12 . The positional relationship of the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  is the same as the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  of the first embodiment. The cylinder  12  is formed independently from the light guide plate  4  and is preferably formed from a transparent material, which may be the same type of material as the light guide plate  4 . The cylinder  12  is rotated manually to adjust the position of the reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  to maximize or optimize the amount of light transmitted to the light guide plate  4 . 
     Fourth Embodiment 
     A fourth embodiment according to the present invention will now be described with reference to FIG.  6 . The fourth embodiment is a modification of the embodiment illustrated in FIG.  5 . As shown in FIG. 6, a light collector  5   a  may have a flat rim (light collecting surface). Thus, the forth embodiment is a combination of the second and third embodiments. 
     Fifth Embodiment 
     As shown in FIG. 7, in a fifth embodiment of the present invention, a backlight  20  has a plurality of reflectors  6  (five shown). Each reflector  6  preferably includes three reflecting elements  6 - 1 ,  6 - 2 ,  6 - 3  like the above embodiments. More specifically, as shown in FIG. 8, a plurality of reflectors  6  are arranged longitudinally along the light collector  5 . The reflectors  6  are preferably spaced from one another at equal intervals (θ1=θ2=θ3=θ4) along the rim of the light collector  5  in a direction substantially perpendicular to the longitudinal direction. Each reflector  6  may be rotatable like the reflector  6  of the third embodiment. 
     Sixth Embodiment 
     A sixth embodiment of the present invention will now be described with reference to FIG.  9 . The backlight  20  illustrated in FIGS. 7 and 8 is modified in this embodiment. As shown in FIG. 9, each reflector  6  is associated with a light collector  5 - 1 ,  5 - 2 ,  5 - 3 ,  5 - 4 ,  5 - 5 . Each light collector  5 - 1 ,  5 - 2 ,  5 - 3 ,  5 - 4 ,  5 - 5  has a convex lens-like shape. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.