CN103900031B - A kind of guiding device for liquid crystal display - Google Patents

Abstract

The invention discloses a light guide device for a liquid crystal display, comprising: a rectangular parallelepiped light guide plate, the rectangular parallelepiped light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, and a bottom surface opposite to the bottom surface a light-emitting surface; a wedge-shaped light guide plate, the wedge-shaped light-guiding plate has a light-incident surface, a bottom surface adjacent to the light-incidence surface, a light-exit surface arranged parallel to the light-incidence surface, and a light-exit surface arranged opposite to the bottom surface The inclined surface; wherein, the light incident surface of the cuboid light guide plate coincides with the light exit surface of the wedge-shaped light guide plate, the bottom surface of the cuboid light guide plate is coplanar with the bottom surface of the wedge-shaped light guide plate, and the wedge-shaped light guide plate The inclined surface of the light plate gradually inclines from the light incident surface of the wedge-shaped light guide plate to the light exit surface of the wedge-shaped light guide plate to form a convex cylindrical surface. The light guide device proposed by the present invention reduces the light leakage of the wedge-shaped light guide plate by changing the inclined surface of the wedge-shaped light guide plate into a convex inclined surface.

Description

A light guide device for liquid crystal display

technical field

The invention relates to the technical field of liquid crystal displays, in particular to a light guide device for liquid crystal displays.

Background technique

Existing liquid crystal display devices usually include a liquid crystal display panel and a backlight module. The liquid crystal display panel is composed of a thin film transistor substrate, a color filter substrate, and a liquid crystal layer arranged between the two substrates. To provide the light source required by the liquid crystal display panel.

The LightGuidePlate (LGP for short) is an important component in the backlight module. Its main function is to guide the light emitted by the light source to exit from a plane, and at the same time improve the luminance and uniformity of the luminance of the liquid crystal display panel. In the existing liquid crystal display devices of small and medium sizes, the wedge-shaped light guide device can realize the light and thin design of the backlight module structure. FIG. 1 is a front view of a conventional wedge-shaped light guide device 100 . As shown in FIG. 1 , the light from the LED light source 102 can enter the wedge-shaped light guide device 100 and exit from the light-emitting surface 101 of the wedge-shaped light guide device 100 . However, there is a problem that light incident on the inclined plane 103 of the wedge-shaped light guiding device 100 is refracted from the inclined plane 103 , resulting in light leakage from the wedge-shaped light guiding device 100 . For example, the light rays A, B, and C from the LED light source 102 are incident on the inclined plane 103 of the wedge-shaped light guide device 100. The total reflection angle of the inclined plane 103 is refracted from the inclined plane 103 , causing light leakage from the wedge-shaped light guide device 100 , resulting in reduced brightness of the light emitting area of the backlight module, and finally affecting the display performance of the liquid crystal display panel.

Contents of the invention

The purpose of the present invention is to provide an improved light guide device for liquid crystal display, which can make the light guide device have less light leakage rate and higher light extraction rate.

To achieve the above object, the present invention is achieved through the following technical solutions:

A light guide device for a liquid crystal display, comprising:

A cuboid light guide plate, the cuboid light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, and a light exit surface opposite to the bottom surface;

A wedge-shaped light guide plate, the wedge-shaped light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, a light exit surface parallel to the light incident surface, and an inclined surface opposite to the bottom surface;

Wherein, the light incident surface of the cuboid light guide plate coincides with the light exit surface of the wedge-shaped light guide plate, the bottom surface of the cuboid light guide plate is coplanar with the bottom surface of the wedge-shaped light guide plate, and the inclined surface of the wedge-shaped light guide plate A convex cylindrical surface is gradually inclined from the light incident surface of the wedge-shaped light guide plate to the light exit surface of the wedge-shaped light guide plate.

Further, the cuboid light guide plate and the wedge-shaped light guide plate are made of polymethyl methacrylate (PMMA).

Further, the inclined surface of the wedge-shaped light guide plate has a vertical section in the shape of an arc, and the radius of curvature of the arc is the distance between the light incident surface of the wedge-shaped light guide plate and the light-emitting surface of the wedge-shaped light guide plate The ratios are in the range of 2.125 to 6.875.

Further, the ratio of the radius of curvature of the arc to the distance between the light incident surface of the wedge-shaped light guide plate and the light exit surface of the wedge-shaped light guide plate is 3.375.

Further, the light guide device further includes a reflection plate disposed under the bottom surface of the cuboid light guide plate and the bottom surface of the wedge-shaped light guide plate.

Further, the light guide device further includes a diffuser plate arranged on the light emitting surface of the cuboid light guide plate.

Further, the light guiding device further includes a brightness enhancement film disposed on the diffuser plate.

Further, the cuboid light guide plate and the wedge-shaped light guide plate are integrally formed.

Correspondingly, the present invention also proposes another light guide device for a liquid crystal display, the light guide device comprising:

A cuboid light guide plate, the cuboid light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, and a light exit surface opposite to the bottom surface;

A wedge-shaped light guide plate, the wedge-shaped light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, a light exit surface parallel to the light incident surface, and an inclined surface opposite to the bottom surface;

Wherein, the light incident surface of the cuboid light guide plate coincides with the light exit surface of the wedge-shaped light guide plate, the bottom surface of the cuboid light guide plate is coplanar with the bottom surface of the wedge-shaped light guide plate, and the inclined surface of the wedge-shaped light guide plate A convex inclined surface is gradually formed from the light incident surface of the wedge-shaped light guide plate to the light exit surface of the wedge-shaped light guide plate, and the inclined surface has a V-shaped vertical section.

Further, the angle between the two sides of the V-shaped vertical section is greater than 120 degrees.

Further, the cuboid light guide plate and the wedge-shaped light guide plate are made of polymethyl methacrylate (PMMA).

Further, the light guide device further includes a reflection plate disposed under the bottom surface of the cuboid light guide plate and the bottom surface of the wedge-shaped light guide plate.

Further, the light guide device further includes a diffuser plate arranged on the light emitting surface of the cuboid light guide plate.

Further, the light guiding device further includes a brightness enhancement film disposed on the diffuser plate.

Further, the cuboid light guide plate and the wedge-shaped light guide plate are integrally formed.

Correspondingly, the present invention also proposes a liquid crystal display, the liquid crystal display having the light guide device described in the above solution.

In the light guide device proposed by the present invention, by changing the inclined surface of the wedge-shaped light guide plate from the inclined plane of the prior art to a convex inclined surface, the incident angle of the light traveling on the inclined surface of the wedge-shaped light guide plate is larger than that of the light at the The total reflection angle of the inclined surface produces total reflection, which not only reduces the light leakage of the wedge-shaped light guide plate, but also improves the utilization rate of light in the light guide device, so that the light guide device requires a normal viewing angle. Brightness is improved.

Description of drawings

Fig. 1 is the front view of existing wedge-shaped light guiding device;

2 is a perspective view of a light guide device for a liquid crystal display according to a first embodiment of the present invention;

3 is a front view of a light guide device for a liquid crystal display according to a first embodiment of the present invention;

Fig. 4 is a schematic diagram comparing the refraction of light on the inclined surface of the light guide device according to the first embodiment of the present invention and the refraction on the inclined plane of the light guide device of the prior art;

Fig. 5 is the front view of four kinds of light guiding devices;

Fig. 6 is a comparative analysis diagram of light leakage and light output of the four light guide devices in Fig. 5 obtained by simulation;

FIG. 7 is a graph of the relationship between light leakage and light output of the four light guide devices in FIG. 5 obtained through simulation;

Fig. 8 is a schematic diagram of light traveling in two different light guiding devices;

9 is a perspective view of a light guide device for a liquid crystal display according to a second embodiment of the present invention;

10 is a front view of a light guide device for a liquid crystal display according to a second embodiment of the present invention;

11 is a front view of a light guide device for a liquid crystal display according to a third embodiment of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention. In addition, it should be noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings but not all structures.

A first embodiment of the invention is shown in Figures 2-4.

2 is a perspective view of a light guide device 200 for a liquid crystal display according to the first embodiment of the present invention; FIG. 3 is a front view of the light guide device 200 for a liquid crystal display according to the first embodiment of the present invention. As shown in FIG. 3 , the light guide device 200 in this embodiment includes: a cuboid light guide plate 220 and a wedge-shaped light guide plate 210 . The cuboid light guide plate 220 has a light incident surface 224 , a bottom surface 223 adjacent to the light incident surface 224 , and a light exit surface 221 opposite to the bottom surface 223 . The wedge-shaped light guide plate 210 has a light incident surface 212, a bottom surface 213 adjacent to the light incident surface 212, a light exit surface 214 arranged parallel to the light incident surface 212, and a light exit surface 214 opposite to the bottom surface 213. The inclined surface 211. Wherein, the light incident surface 224 of the cuboid light guide plate 220 coincides with the light exit surface 214 of the wedge-shaped light guide plate 210, the bottom surface 223 of the cuboid light guide plate 220 is coplanar with the bottom surface 213 of the wedge-shaped light guide plate 210, The inclined surface 211 of the wedge-shaped light guide plate 210 gradually inclines from the light-incident surface 212 of the wedge-shaped light guide plate 210 to the light-exit surface 214 of the wedge-shaped light guide plate 210 to form a convex cylindrical surface.

In the first embodiment, the cuboid light guide plate 220 and the wedge-shaped light guide plate 210 are made of polymethyl methacrylate (PMMA). As a preferred manner, the cuboid light guide plate 220 and the wedge-shaped light guide plate 210 may be integrally formed.

In a preferred implementation of this embodiment, the wedge-shaped light guide plate 210 may further include a horizontal connection portion 240, and the horizontal connection portion 240 extends from the light incident surface 212 and the bottom surface 213 of the wedge-shaped light guide plate 210 to the light source 230. extend. With the help of the horizontal connection portion 240 , the light from the light source 230 is better guided into the light guiding device 200 , thereby helping to increase the light flux in the light guiding device 200 .

In the first embodiment, by changing the inclined surface 211 of the wedge-shaped light guide plate 210 from the wedge-shaped inclined plane of the prior art into a convex cylindrical surface with a radian, the inclined surface 211 of the wedge-shaped light guide plate 210 The incident angle of the light at 211 is greater than the total reflection angle of the light on the inclined surface 211 to produce total reflection, which can not only reduce the light leakage of the wedge-shaped light guide plate 210, but also improve the utilization rate of light in the light guide device 200 , so that the brightness required by the front viewing angle of the light guide device 200 is improved.

4 is a schematic diagram comparing the refraction of light on the inclined surface 211 of the light guide device 200 according to the first embodiment of the present invention and the refraction on the inclined plane 261 of the light guide device in the prior art. Referring further to FIG. 4 on the basis of FIGS. 2-3 , the wedge-shaped light guide plate 210 is made of polymethyl methacrylate (PMMA) material, and the medium refractive index of the PMMA material is 1.4935, and the total reflection angle is 43.352° . In FIG. 4 , when the light a directed toward the upper side of the inclined surface of the wedge-shaped light guide plate 210 reaches the inclined plane 261 of the light guide device in the prior art, the included angle between the normal of the light a and the inclined plane 261 is 42° (less than full reflection angle), light a will pass through the inclined plane 261 and cause light leakage. And when the light a directed toward the upper side of the inclined surface of the wedge-shaped light guide plate 210 reaches the inclined surface 211 according to the first embodiment of the present invention, the included angle with the normal line of the inclined surface (curved surface) 211 is 48° (greater than total reflection Angle), so the light a will be totally reflected back to the inside of the wedge-shaped light guide plate 210 without causing light leakage.

Continuing to refer to FIG. 4, when the light b directed toward the lower side of the inclined surface of the wedge-shaped light guide plate 210 reaches the inclined plane 261 of the prior art light guide device, the included angle with the normal to the plane is 66°, which is greater than the total reflection angle, so The light b will be totally reflected back into the wedge-shaped light guide plate 210; and when the light b reaches the inclined surface 211 according to the first embodiment of the present invention, the included angle with the normal of the inclined surface (curved surface) 211 is 60°, still is greater than the total reflection angle, so the light b will also be totally reflected back into the wedge-shaped light guide plate 210 . That is to say, although the angle formed by the light b incident on the lower side of the inclined surface of the wedge-shaped light guide plate 210 and the normal line of the inclined surface (curved surface) 211 is smaller than the angle formed by the light b and the inclined plane 261, but Since the two included angles are greater than the total reflection angle, the light b will be reflected back into the wedge-shaped light guide plate 210 , so that light leakage from the wedge-shaped light guide plate 210 will not be caused.

5-8 are comparison diagrams of various optical parameters obtained by simulation for the existing light guide device and the light guide device according to the first embodiment of the present invention under the premise of using the same manufacturing material. Here, simulation software (such as Tracepro simulation software) is used to simulate the optical characteristics of the four light guide devices LGP1-LGP4.

Fig. 5 shows the front views of four kinds of light guide devices LGP1-LGP4, wherein, LGP1 is a light guide device of the prior art; and LGP2-LGP4 are all light guide devices according to the first embodiment of the present invention, the only difference is Sloped surfaces (curved surfaces) have different radii of curvature. As shown in Figure 5, the radius of curvature R of the inclined surface (curved surface) of the light guide device LGP2 is 5.5 mm, the radius of curvature R of the inclined surface (curved surface) of the light guide device LGP3 is 2.7 mm, and the inclined surface of the light guide device LGP4 (Surface) The radius of curvature R is 1.7mm. The four light guide devices shown in Figure 5 are all made of PMMA material, the refractive index of the medium is 1.4935, and the total reflection angle is 43.352°. The distance between them is 0.8mm (the unit of length in Figure 5 is mm).

FIG. 6 is a comparative analysis diagram of light leakage and light output of four light guide devices LGP1-LGP4 obtained by simulation. According to the comparison of various optical data in Figure 6, it can be seen that the light guide device LGP1 has more light leakage in the area of the wedge-shaped light guide plate, while the light leakage of the light guide devices LGP2-LGP4 in the area of the wedge-shaped light guide plate is relatively small, reflecting Better optical properties of the light guide device. In particular, the area of the wedge-shaped light guide plate of the light guide device LGP3 has the smallest light leakage and the largest effective light output, which is the most suitable wedge-shaped light guide plate design among the four light guide devices.

FIG. 7 is a graph showing the relationship between light leakage and light output of four light guide devices LGP1-LGP4 obtained through simulation. Wherein, the horizontal axis represents the four light guide devices LGP1-LGP4, and the vertical axis represents the amount of light leakage in the wedge-shaped light guide plate area of the light guide device, and the unit is watts (W). According to the comparison of the two curves in Figure 7, it can be seen that the inclined surface of the wedge-shaped light guide plate changes from an inclined plane to a curved surface, which can effectively reduce the light leakage in the area of the wedge-shaped light guide plate and increase the effective light output in the visible area of the light guide device. For example, compared with the existing light guide device LGP1, the light guide device LGP2-LGP4 according to the first embodiment of the present invention reduces the amount of light leakage in the area of the wedge-shaped light guide plate to varying degrees, especially the light guide device LGP3. In terms of the two parameters of effective light extraction and effective light extraction, it reflects a large data advantage and shows that the optical performance of the light guide device is effectively enhanced.

It can be further seen from the simulation data shown in Figures 6 and 7 that the curvature of the inclined surface (curved surface) of the light guide device according to the first embodiment of the present invention is not as large as possible, and there is an optimal curvature that makes the wedge-shaped light guide plate Areas with minimal light leak effects. For example, the curvature of the inclined surface (curved surface) of the light guide LGP4 is larger than that of the light guide LGP3, but the light leakage problem in the wedge-shaped light guide plate area of the light guide LGP4 is more serious. The reason for the above-mentioned light leakage problem can be further referred to the description of FIG. 8 , which shows a schematic diagram of light traveling in the light guide device LGP3 and the light guide device LGP4 . It can be seen from FIG. 8 that the same light a will exit the wedge-shaped light guide plate area in the light guide device LGP4 and cause light leakage, but will be totally reflected back into the wedge-shaped light guide plate in the light guide device LGP3 for reuse. Therefore, in practice, you can initially set a curvature radius R so that the angle between the light a and the surface normal is slightly larger than the total reflection angle, and then slightly change the curvature radius R or other parameters for simulation comparisons, and you can quickly find the best The scheme of the radius of curvature R.

To sum up, compared with the existing light guide device LGP1, the light guide device LGP2-LGP4 according to the first embodiment of the present invention not only effectively reduces the light leakage in the wedge-shaped light guide plate area, but also enhances the light guide to different degrees. Optical properties of the device.

9-10 show a second embodiment of the invention.

FIG. 9 is a perspective view of a light guide device 900 for a liquid crystal display according to a second embodiment of the present invention; FIG. 10 is a front view of a light guide device 900 for a liquid crystal display according to a second embodiment of the present invention. As shown in FIG. 10 , the light guide device 900 in this embodiment includes: a cuboid light guide plate 920 and a wedge-shaped light guide plate 910 . The cuboid light guide plate 920 has a light incident surface 924 , a bottom surface 923 adjacent to the light incident surface 924 , and a light exit surface 921 opposite to the bottom surface 923 . The wedge-shaped light guide plate 910 has a light incident surface 912, a bottom surface 913 adjacent to the light incident surface 912, a light exit surface 914 arranged parallel to the light incident surface 912 and opposite to the bottom surface 913. The inclined surface 911. Wherein, the light incident surface 924 of the cuboid light guide plate 920 coincides with the light exit surface 914 of the wedge-shaped light guide plate 910, the bottom surface 923 of the cuboid light guide plate 920 is coplanar with the bottom surface 913 of the wedge-shaped light guide plate 910, The inclined surface 911 of the wedge-shaped light guide plate 910 gradually inclines from the light incident surface 912 of the wedge-shaped light guide plate 910 to the light-emitting surface 914 of the wedge-shaped light guide plate 910 to form an outwardly convex inclined surface, and the inclined surface 911 has a V shape. vertical section of .

In the second embodiment, the cuboid light guide plate 920 and the wedge-shaped light guide plate 910 are made of polymethyl methacrylate (PMMA). As a preferred manner, the cuboid light guide plate 920 and the wedge-shaped light guide plate 910 may be formed integrally.

In a preferred implementation of this embodiment, the wedge-shaped light guide plate 910 may further include a horizontal connection portion 940, the horizontal connection portion 940 is directed from the light incident surface 912 and the bottom surface 913 of the wedge-shaped light guide plate 910 to the light source 930. extend. With the help of the horizontal connection portion 940 , the light from the light source 930 is better guided into the light guiding device 900 , thereby further increasing the light flux in the light guiding device 900 .

It can be seen from FIG. 10 that, unlike the first embodiment, the inclined surface 911 in the second embodiment is not a convex cylindrical surface but has a V-shaped vertical section. Preferably, the angle β between the two sides of the V-shaped vertical section is greater than 120 degrees.

In the second embodiment, by changing the inclined surface 911 of the wedge-shaped light guide plate 910 from the inclined plane of the prior art to an outwardly convex inclined surface with a V-shaped vertical section, the The incident angle of the light on the inclined surface 911 of 910 is greater than the total reflection angle of the light on the inclined surface 911 to produce total reflection, which can not only reduce the light leakage of the wedge-shaped light guide plate 910, but also improve the light transmission in the light guide device. The utilization rate of 900 improves the brightness required by the front viewing angle of the light guide device 900 .

Fig. 11 shows a third embodiment of the present invention.

FIG. 11 is a front view of a light guide device 1100 for a liquid crystal display according to a third embodiment of the present invention. As shown in FIG. 11 , the light guide device 1100 in this embodiment includes: a cuboid light guide plate 1120 and a wedge-shaped light guide plate 1110 . The cuboid light guide plate 1120 has a light incident surface 1124 , a bottom surface 1123 adjacent to the light incident surface 1124 , and a light exit surface 1121 opposite to the bottom surface 1123 . The wedge-shaped light guide plate 1110 has a light incident surface 1112, a bottom surface 1113 adjacent to the light incident surface 1112, a light exit surface 1114 parallel to the light incident surface 1112, and a light exit surface 1114 opposite to the bottom surface 1113. The inclined surface 1111 of. Wherein, the light incident surface 1124 of the cuboid light guide plate 1120 coincides with the light exit surface 1114 of the wedge-shaped light guide plate 1110, the bottom surface 1123 of the cuboid light guide plate 1120 is coplanar with the bottom surface 1113 of the wedge-shaped light guide plate 1110, The inclined surface 1111 of the wedge-shaped light guide plate 1110 gradually inclines from the light-incident surface 1112 of the wedge-shaped light guide plate 1110 to the light-exit surface 1114 of the wedge-shaped light guide plate 1110 to form a convex cylindrical surface.

In the third embodiment, the structure of the cuboid light guide plate 1120 and the wedge-shaped light guide plate 1110 in the light guide device 1100 is the same as that of the corresponding light guide plates in the first embodiment, and will not be repeated here.

It can be seen from FIG. 11 that, unlike the first embodiment, the light guide device 1100 in the third embodiment further includes: the bottom surface 1123 of the cuboid light guide plate 1120 and the wedge-shaped light guide plate 1110 The reflection plate 1160 under the bottom surface 1113 of the cuboid light guide plate 1120; As a preferred manner, the light guide device 1100 further includes a brightness enhancement film 1190 disposed on the diffusion plate 1180 .

The optical performance of the light guide device 1100 can be further optimized by adding a reflection plate 1160 , a diffuser plate 1180 and a brightness enhancement film 1190 to the above light guide device 1100 .

In addition, the present invention also proposes a liquid crystal display, which has the light guide device as described in one of the first, second and third embodiments above.

In the light guide device proposed by the present invention, by changing the inclined surface of the wedge-shaped light guide plate from the inclined plane of the prior art to a convex inclined surface, the incident angle of the light traveling on the inclined surface of the wedge-shaped light guide plate is larger than that of the light at the The total reflection angle of the inclined surface produces total reflection, which not only reduces the light leakage of the wedge-shaped light guide plate, but also improves the utilization rate of light in the light guide device, so that the light guide device requires a normal viewing angle. Brightness is improved.

Note that the above are only preferred embodiments of the present invention and applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the present invention, and the present invention The scope is determined by the scope of the appended claims.

Claims (8)

1. A light guide device for a liquid crystal display, comprising: A cuboid light guide plate, the cuboid light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, and a light exit surface opposite to the bottom surface; A wedge-shaped light guide plate, the wedge-shaped light guide plate has a light incident surface, a bottom surface adjacent to the light incident surface, a light exit surface parallel to the light incident surface, and an inclined surface opposite to the bottom surface; Wherein, the light incident surface of the cuboid light guide plate coincides with the light exit surface of the wedge-shaped light guide plate, the bottom surface of the cuboid light guide plate is coplanar with the bottom surface of the wedge-shaped light guide plate, and the inclined surface of the wedge-shaped light guide plate From the light incident surface of the wedge-shaped light guide plate, the light-emitting surface of the wedge-shaped light guide plate is gradually inclined to form a convex cylindrical surface, and the inclined surface of the wedge-shaped light guide plate has a vertical section in the shape of an arc, and the arc of the arc The ratio of the radius of curvature to the distance between the light incident surface of the wedge-shaped light guide plate and the light exit surface of the wedge-shaped light guide plate is in the range of 2.125 to 6.875. 2 . The light guide device for a liquid crystal display according to claim 1 , wherein the cuboid light guide plate and the wedge-shaped light guide plate are made of polymethyl methacrylate (PMMA). 3. The light guide device for a liquid crystal display according to claim 1, wherein the radius of curvature of the arc is between the light incident surface of the wedge-shaped light guide plate and the light exit surface of the wedge-shaped light guide plate The ratio of the distances is 3.375. 4. The light guide device for liquid crystal display according to claim 1-3, characterized in that, the light guide device also includes a bottom surface arranged on the bottom surface of the cuboid light guide plate and the bottom surface of the wedge-shaped light guide plate below the reflector. 5. The light guide device for a liquid crystal display according to claim 1-3, wherein the light guide device further comprises a diffuser plate disposed on the light emitting surface of the cuboid light guide plate. 6 . The light guide device for a liquid crystal display according to claim 5 , wherein the light guide device further comprises a brightness enhancement film disposed on the diffuser plate. 7 . 7 . The light guide device for a liquid crystal display according to claim 1 , wherein the rectangular parallelepiped light guide plate and the wedge-shaped light guide plate are integrally formed. 8. A liquid crystal display having the light guiding device as claimed in any one of claims 1-7 above.