Abstract:
A planar light source device ( 6 ) for a liquid crystal display device. The planar light source device includes a light source device ( 2 ) and a light guide plate ( 67 ). The light source device includes a light-emitting element ( 21 ), and an optical guiding member ( 20 ) that is hollow and has a reflective surface. The reflective surface receives light rays emitted by the light-emitting element, and guides the light rays out from a plurality of generally aligned through holes ( 23 ) defined in a front light-emitting surface ( 28 ) of the optical guiding member. The light guide plate has a light incident surface adjacent to the light source device. The planar light source device can greatly diminish possible dark regions on the light-emitting surface of the light guide plate, and provide uniform illumination for an LCD.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention generally relates to a light source device and a planar light source device used in a liquid crystal display (LCD) device. 
   2. Prior Art 
   In general, an LCD device has the advantages of thinness, light weight, and low power consumption. For this reason, LCD devices are widely utilized in various types of electronic equipment, from pocket calculators to large-scale office automation equipment. 
   Conventionally, planar light source devices are designed for use in an LCD device for backlighting purposes. The planar light source device generally includes a light guide plate (LGP) and at least one light source. The LGP has at least one light incidence surface, and one light-emitting surface. In operation, light rays emitted by the light source(s) enter the LGP through the light incident surface(s) thereof, and are guided through the LGP to emit from the light-emitting surface. Each light source may be a linear light source or a point light source. The point light source is generally a light emitting diode (LED), which emits light rays over a region subtending an angle of about 140°. Generally, a plurality of LEDs is arranged adjacent to the light incident surface(s) of the LGP to ensure high illuminance and high uniformity of light emitting from the light-emitting surface. This kind of light source device is disclosed in U.S. Pat. No. 6,386,720 issued on May 14, 2002. 
   However, the lighting characteristics of ordinary LEDs are limited, and the uniformity of illumination of the planar light source device may not be sufficient. Referring to  FIG. 10 , a conventional planar light source device  1  utilizes two LEDs  11 ,  12  as light sources to illuminate an LGP  10 . Each of the LEDs  11 ,  12  emits light rays over a region subtending an angle of about 140°. As seen, some dark regions (“shadows”) A, B, C are created on a light-emitting surface of the LGP  10 , because few light rays reach these regions. The number of LEDs  11 ,  12  can be increased to diminish the shadows A, B, C. However, this is achieved at the cost of supplying more LEDs  11 ,  12  and having higher power consumption. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a planar light source device having high uniformity of illumination and low power consumption. 
   A planar light source device in accordance with the present invention comprises a light source device and a light guide plate. The light source device comprises a light-emitting element and an optical guiding member having a light-emitting surface. The optical guiding member receives light rays emitted by the light-emitting element and guides the light rays out from a plurality of aligned light-emitting exits defined in the light-emitting surface. The light guide plate has a light incident surface adjacent to the light-emitting surface of the optical guiding member. 
   The planar light source device can reduce or even eliminate dark regions being created on the light-emitting surface of the light guide plate, and provide uniform illumination for an associated LCD. 
   Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded, isometric view of a first embodiment of a planar light source device according to the present invention; 
       FIG. 2  is a slightly enlarged, isometric view of a light source device of the planar light source device of  FIG. 1 ; 
       FIG. 3  is a schematic, cross-sectional view of the light source device of  FIG. 2  taken along line III—III thereof; 
       FIG. 4  is similar to  FIG. 3 , but showing a second embodiment of a light source device according to the present invention; 
       FIG. 5  is an isometric view of a third embodiment of a light source device according to the present invention; 
       FIG. 6  is an isometric view of a fourth embodiment of a light source device according to the present invention; 
       FIG. 7  is an isometric view of a fifth embodiment of a light source device according to the present invention; 
       FIG. 8  is an isometric view of a sixth embodiment of a light source device according to the present invention; 
       FIG. 9  is an isometric view of a seventh embodiment of a light source device according to the present invention; and 
       FIG. 10  is a schematic top elevation of a conventional planar light source device, showing dark regions thereof. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a planar light source device  6  according to the first embodiment of the present invention includes a transparent plate-shaped LGP  67  and a light source device  2 . The light source device  2  is arranged adjacent to a light incident surface (not labeled) of the LGP  67 , for providing illumination thereto. 
   Referring to  FIGS. 2 and 3 , the light source device  2  includes an optical guiding member  20  and two LEDs  21 ,  22 . The optical guiding member  20  functions as a linear light source, and is substantially a hollow box. The optical guiding member  20  comprises a light-emitting surface  28 , a back surface  24  opposite to the light-emitting surface  28 , a bottom surface  27  adjoining the light-emitting surface  28 , and an upper surface  29  opposite to the bottom surface  27 . The optical guiding member  20  further comprises two opposite side surfaces  25 ,  26  adjoining the above-described surfaces  24 ,  27 ,  28 ,  29 , and an internal light reflective surface (not labeled). A plurality of uniform, aligned through holes  23  are defined in the light-emitting surface  28  of the optical guiding member  20 . The through holes  23  function as light exits. Two openings  21 ′,  22 ′ are defined in the side surfaces  25 ,  26  of the optical guiding member  20  respectively. The LEDs  21 ,  22  are fixed in the openings  21 ′,  22 ′ respectively, so that exposed faces of the LEDs  21 ,  22  are coplanar with the side surfaces  25 ,  26  respectively. Wires (not shown) connect the LEDs  21 ,  22  to a power source or a controller (not shown). 
   The light-emitting surface  28  is optically coupled with the light incident surface of the LGP  67 . The through holes  23  are spaced apart at substantially equal intervals, and have substantially the same area. A length of the array of the through holes  23  is less than a length of the light incident surface of the LGP  67 , and a height of each through hole  23  is less than a height of the light incident surface, so that the light source device  2  is optically coupled with the light incident surface efficiently. 
   In operation, light rays em it from the LEDs  21 ,  22  into the optical guiding member  20 . The light rays are reflected any number of times by the reflective inner surface of the optical guiding member  20 . The light rays then exit from the through holes  23  and enter the LGP  67 . Because the light rays are randomly reflected in the optical guiding member  20 , the light rays emitting therefrom have more uniform, broad radiant angles compared with the light rays emitted by the LEDs  21 ,  22 . This reduces or even eliminates dark areas or “shadows” being created in the LGP  67 . More importantly, the number of through holes  23  can be much greater than the number of LEDs  21 ,  22 . That is, the optical guiding member  20  effectively converts the LEDs  21 ,  22  into a plurality of point light sources. This can greatly reduce the possibility of shadows being created in the LGP  67 , and make light rays emitting from the LGP  67  more uniform. 
   Referring to  FIG. 4 , in a planar light source device  3  according to the second embodiment of the present invention, two LEDs  31 ,  32  are fixed in a back surface  34  of an optical guiding member  30 . Light rays emitted by the LEDs  31 ,  32  are guided by the optical guiding member  30 , and emit from a light-emitting surface  38  through a plurality of through holes  33  thereof. 
   Referring to  FIG. 5 , a light source device  4  according to the third embodiment of the present invention includes an optical guiding member  40 , and two LEDs  41 ,  42 . The optical guiding member  40  is substantially a hollow arch-shaped box, which comprises a planar light-emitting surface  48 , an arch-shaped back surface  44  adjoining the light-emitting surface  48 , and two opposite side surfaces  45 ,  46 . The optical guiding member  40  further comprises an internal light reflective surface (not shown). A plurality of uniform, aligned through holes  43  are defined in the planar light-emitting surface  48  of the optical guiding member  40 . The through holes  43  function as light exits. Two openings (not labeled) are defined in the side surfaces  45 ,  46  of the optical guiding member  40  respectively. The LEDs  41 ,  42  are fixed in the openings respectively, so that exposed faces of the LEDs  41 ,  42  are coplanar with the side surfaces  45 ,  46  respectively. 
   Further alternative embodiments of the planar light source device according to the present invention may comprise various permutations and combinations of the above-described first through third embodiments. Still further alternative embodiments are described below: 
   The optical guiding member  20  ( 30 ,  40 ) can be replaced with a transparent, solid body having a light reflective outer surface and a plurality of aligned optical holes. The reflective outer surface reflects light rays impinging thereon until the light rays exit the optical holes. Two concavities are defined in the two opposite sides of the optical guiding member  20  ( 30 ,  40 ). The LEDs  21 ,  22  are fixed in the concavities respectively. Alternatively, the LEDs  21 ,  22  may be arranged adjacent to outsides of the two opposite sides respectively, such that the LEDs  21 ,  22  emit light rays into the optical guiding member  20  ( 30 ,  40 ). Further or alternatively, referring to  FIG. 6 , in a fourth embodiment of the present invention, the optical guiding member can be cylindrical. Similarly, the optical guiding member can be semi-cylindrical. 
   Referring to FIG  7 . in a fifth embodiment of the present invention, the through holes can progressively increase in size from each of opposite ends of the array thereof to a center of the array. Alternatively, referring to FIG  8 . in a sixth embodiment of the present invention, only one LED may be provided in the light source device. In this case, sizes of the through holes can progressively increase from an end of the array thereof adjacent to the LED to the opposite end of the array distal from the LED. Alternatively, referring to FIG  9 , in a seventh embodiment of the present invention, the through holes can be arranged at different intervals apart, such that the intervals progressively decrease in length from the two opposite ends of the array to the center of the array. 
   The LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ) may be arranged adjacent to outsides of the respective side and back surfaces  25 ,  26  ( 34 ,  45 ,  46 ), such that the LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ) are optically coupled with the openings  21 ′,  22 ′ and emit light rays into the optical guiding member  20  ( 30 ,  40 ). Alternatively, the LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ) may be fixed in two concavities defined in the inner surface of the optical guiding member  20  ( 30 ,  40 ). Alternatively, more than two LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ) may be provided. However, the number of LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ) would be less than the number of through holes  23  ( 33 ,  43 ). In addition, an interval between any two adjacent through holes  23  ( 33 ,  43 ) would be smaller than an interval between two adjacent corresponding LEDs  21 ,  22  ( 31 ,  32 ,  41 ,  42 ). 
   It is to be further understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.