Light guide plate and backlight module using the same

A light guide plate has a light incident surface, a light emitting surface and a bottom surface. The bottom surface or the light emitting surface has a plurality of light guide units disposed thereon. Each of the light guide units has a first curved surface and a second curved surface connected with the first curved surface. Both of the first curved surface and the second curved surface are concave surfaces or convex surfaces. In a cross section perpendicular to the light incident surface and passing through the first curved surface and the second curved surface, the first curved surface and the cross section intersect in a first curved line, and the second curved surface and the cross section intersect in a second curved line. A curvature radius of the first curved line is greater than that of the second curved line.

BACKGROUND

1. Field of the Invention

The present invention relates to a plane light source device, and more particularly to a backlight module and a light guide plate used in the backlight module.

2. Description of the Related Art

With the development of flat panel display technique, flat panel displays (FPDs) that have advantages of light in weight, small in size and low power consumption are becoming more and more popular. Typically, the flat panel displays include liquid crystal displays (LCDs), plasma panel displays (PDPs), organic light emitting diode displays (OLED displays) and electrophoretic displays (EPDs). Among the flat panel displays, the liquid crystal displays are most widely used.

The liquid crystal display includes a liquid crystal display panel and a backlight module. The backlight module is used to provide a plane light source to the liquid crystal display panel. Generally, the backlight module may be classified into a direct type backlight module and a sidelight type backlight module based on a transmission mode of light.

FIG. 1Ais a schematic view of a conventional sidelight type backlight module.FIG. 1Bis a schematic side view showing a light guide plate ofFIG. 1A. Referring toFIGS. 1A and 1B, the conventional backlight module100includes a light source110, a light guide plate120, a reflective sheet130and an optical sheet140. The light guide plate120includes a light incident surface122, a light emitting surface124and a bottom surface126. The light emitting surface124is opposite to the bottom surface126. The light incident surface122is connected between the light emitting surface124and the bottom surface126. The light source110is disposed adjacent to the light incident surface122. The reflective sheet130is disposed under the bottom surface126. The optical sheet140is disposed above the light emitting surface124. In addition, a plurality of sandblasted structures125is formed on the light emitting surface124, and a plurality of V-shaped light guide units127is formed on the bottom surface126.

When a portion of light rays (such as light ray112) provided by the light source110transmits to a surface127aof the V-shaped light guide unit127, the portion of light rays (such as light ray112) would be totally reflected, and a light emitting angle of the portion of light rays (such as light ray112) is relatively small when emitting from the light emitting surface124. In the conventional backlight module100, the portion of light rays (such as light ray112) which is totally reflected can be utilized. In addition, the light rays (such as light ray114) transmitting to the sandblasted structures125would be diffused. However, a portion of the diffused light rays (such as light ray115) could not emit from the light emitting surface124. Accordingly, light emitting efficiency of the conventional light guide plate120would be reduced, and light utilization efficiency of the conventional backlight module100would be decreased. In addition, the sandblasted structures125would make it difficult to control the light emitting angle of the light rays. Consequently, brightness and uniformity of the light rays emitting from the light guide plate120are not easily adjusted, and the light emitting surface124of the light guide plate120may appear some bright areas (or bright strips) and dark areas (or dark strips).

BRIEF SUMMARY

The present invention relates to a light guide plate that can improve light utilization efficiency.

The present invention also relates to a backlight module for providing a plane light source having relatively high brightness.

To achieve at least one of the above-mentioned advantages, the present invention provides a light guide plate. The light guide plate has a light incident surface, a light emitting surface and a bottom surface. The bottom surface is opposite to the light emitting surface. The light incident surface is connected between the light emitting surface and the bottom surface. The bottom surface or the light emitting surface has a plurality of light guide units disposed thereon. Each of the light guide units has a first curved surface and a second curved surface connected with the first curved surface. Both of the first curved surface and the second curved surface are concave surfaces or convex surfaces. In a cross section perpendicular to the light incident surface and passing through the first curved surface and the second curved surface, the first curved surface and the cross section intersect in a first curved line, and the second curved surface and the cross section intersect in a second curved line. A curvature radius of the first curved line is greater than that of the second curved line.

In an embodiment of the present invention, a joint of the first curved surface and the second curved surface is located at a first reference plane parallel with the light incident surface.

In an embodiment of the present invention, the curvature radius of the first curved line is R1, and 100 micrometers<R1<∞. The curvature radius of the second curved line is R2, and 100 micrometers<R2<300 micrometers.

In an embodiment of the present invention, an included angle defined between a tangent of any one of points on the first curved line and a second reference plane parallel with the bottom surface and the light emitting surface is in the range from 0.1 degrees to 15 degrees. An included angle defined between a tangent of any one of points on the second curved line and the second reference plane is in the range from 10 degrees to 60 degrees.

In an embodiment of the present invention, the light guide units are protruded out from the bottom surface. In each of the light guide units, the second curved line is nearer to the light incident surface relative to the first curved line. In addition, both of the first curved line and the second curved line are convex lines.

In an embodiment of the present invention, the light guide units are concaved in the bottom surface. In each of the light guide units, the first curved line is nearer to the light incident surface relative to the second curved line. In addition, both of the first curved line and the second curved line are concave lines.

In an embodiment of the present invention, the light guide units are protruded out from the light emitting surface. In each of the light guide units, the first curved line is nearer to the light incident surface relative to the second curved line. In addition, both of the first curved line and the second curved line are convex lines.

In an embodiment of the present invention, the light guide units are concaved in the light emitting surface. In each of the light guide units, the second curved line is nearer to the light incident surface relative to the first curved line. In addition, both of the first curved line and the second curved line are concave lines.

In an embodiment of the present invention, a maximum length of each of the light guide units along a first direction is L1, a maximum length of each of the light guide units along a second direction is L2, the first direction is parallel with a long axis of the light incident surface, the second direction is perpendicular to the first direction, and 1≦L1/L2≦∞.

In an embodiment of the present invention, the light guide units are spaced from each other.

In an embodiment of the present invention, intervals between each two adjacent light guide units are different.

In an embodiment of the present invention, each two adjacent light guide units abut against each other.

To achieve at least one of the above-mentioned advantages, the present invention provides a backlight module. The backlight module includes a light source, an optical sheet and the above light guide plate. The light source is disposed adjacent to the light incident surface. The optical sheet is disposed above the light emitting surface.

In an embodiment of the present invention, the optical sheet is selected from the group consisting of a prism sheet and a diffusion sheet.

In an embodiment of the present invention, the backlight module further includes a reflective sheet disposed under the bottom surface of the light guide plate.

In the present invention, the light emitting angles of the light rays can be regulated by adjusting the curvature radiuses of the first curved line and the second curved line. Therefore, the light guide plate has relatively high light emitting efficiency. Accordingly, the backlight module using the light guide plate has relatively high light utilization efficiency. In other words, brightness of a plane light source provided by the backlight module of the present invention can be improved.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe various exemplary embodiments of the present light guide plate and backlight module using the light guide plate in detail.

FIG. 2is a schematic cross-sectional view of a backlight module according to an embodiment of the present invention.FIG. 3is a schematic three-dimensional view showing a light guide plate ofFIG. 2. Referring toFIGS. 2 and 3, the backlight module200of the present embodiment includes a light source210, an optical sheet220and a light guide plate300. The light guide plate300has a light incident surface310, a light emitting surface320and a bottom surface330. The bottom surface330is opposite to the light emitting surface320. The light incident surface310is connected between the light emitting surface320and the bottom surface330. The light source210is disposed adjacent to the light incident surface310. The optical sheet220is disposed above the light emitting surface320. The optical sheet220can be, but not limited to, a prism sheet. For example, the optical sheet220can be a diffusion sheet or a combination of the prism sheet and the diffusion sheet.

The bottom surface330of the light guide plate300has a plurality of light guide units340disposed thereon. Each of the light guide units340has a first curved surface342and a second curved surface344connected with the first curved surface342. In a cross section (as shown inFIG. 2) that is perpendicular to the light incident surface310and passes through the first curved surface342and the second curved surface344, a curvature radius of the first curved surface342is greater than that of the second curved surface344. In specific, in the cross section that is perpendicular to the light incident surface310and passes through the first curved surface342and the second curved surface344, the first curved surface342and the cross section intersect in a first curved line343, and the second curved surface344and the cross section intersect in a second curved line345. The curvature radius of the first curved line343is, for example, R1, and the curvature radius of the second curved line345is, for example, R2, wherein 100 micrometers<R1<∞, and 100 micrometers<R2<300 micrometers. A joint of the first curved surface342and the second curved surface344is located at a first reference plane P1that is parallel with the light incident surface310. In each of the light guide units340, the first curved line343is, for example, nearer to the light incident surface310relative to the second curved line345. In other words, the first curved surface342is nearer to the light incident surface310relative to the second curved surface344. The light guide units340are, for example, concaved in the bottom surface330. Both of the first curved line343and the second curved line345are, for example, concave lines. In other words, both of the first curved surface342and the second curved surface344are concave surfaces. In addition, the first curved surface342and the second curved surface344of each of the light guide units340can be cylinder surfaces respectively. Each two adjacent light guide units340abut against each other.

In this embodiment, an included angle θ1defined between a tangent of any one of points on the first curved line343and a second reference plane P2parallel with the bottom surface330and the light emitting surface320is in the range from 0.1 degrees to 15 degrees. An included angle θ2defined between a tangent of any one of points on the second curved line345and the second reference plane P2is in the range from 10 degrees to 60 degrees.

The light source210can be a cold cathode fluorescent lamp (CCFL), a light emitting diode (LED) or other suitable light sources. The light source210is used for providing light rays212into the light guide plate300. Due to each of the light guide units340being concaved in the bottom surface330, both of the first curved surface342and the second curved surface344being concave surfaces and the first curved line343with the greater curvature radius being nearer to the light incident surface310of the light guide plate300relative to the second curved line345(i.e., in each of the light guide units340, the first curved surface342being located at left of the first reference plane P1, and the second curved surface344being located at right of the first reference plane P1), most of the light rays212can be reflected to the light emitting surface320of the light guide plate300by the first curved surfaces342of the light guide units340, and then emit from the light emitting surface320of the light guide plate300. Therefore, the light guide plate300of the present embodiment has relatively high light emitting efficiency. In the present embodiment, light emitting angles of the light rays212emitting from the light emitting surface320can be regulated by adjusting the curvature radius of the first curved line343and the second curved line345. Although the light emitting angles of the light rays212emitting from the light emitting surface320are relatively greater, the light emitting angles of the light rays212are relatively uniform. Therefore, the light emitting angles can be corrected by the optical sheet220(such as prism sheet), and thus light emitting angles of the light rays212emitting from the optical sheet220can be decreased to increase light converging efficiency of the light rays212emitting from the optical sheet220. In addition, because the light emitting angles of the light rays212emitting from the light emitting surface320are relatively uniform, light leakage can be reduced. Therefore, light utilization efficiency of the backlight module200can be improved. Accordingly, the brightness and the uniformity of a plane light source provided by the backlight module200of the present embodiment can be improved without increasing power consumption.

The backlight module200can further includes a reflective sheet230disposed under the bottom surface330of the light guide plate300. The reflective sheet230can reflect the light rays212passing through the light guide units340back to the light guide plate300. Therefore, the light utilization efficiency of the backlight module200can be further improved.

In the present embodiment, the first curved surface342and the second curved surface344of each of the light guide units340are the cylinder surfaces. However, in another embodiment, the first curved surface342and the second curved surface344can be spherical surfaces.FIG. 4Ais a schematic bottom view of a light guide plate according to another embodiment of the present invention.FIG. 4Bis a schematic bottom view of a light guide plate according to still another embodiment of the present invention. Referring toFIGS. 4A and 4B, the light guide plates300aand300bare similar in principle to the light guide plate300ofFIG. 3, and the difference between the light guide plates300aand300band the light guide plate300lies in that each of first curved surfaces342aand342band second curved surfaces344aand344bof light guide units340aand340bof the light guide plates300aand300bis a spherical surface. In addition, similar to the light guide plate300, in a cross section that is perpendicular to the light incident surface310and passes through the first curved surface342a/342band the second curved surface344a/344b, the first curved surface342a/342band the cross section intersect in a first curved line, and the second curved surface344a/344band the cross section intersect in a second curved line. A curvature radius of the first curved line is greater than that of the second curved line. The curvature radius of the first curved line is, for example, R1, and the curvature radius of the second curved line is, for example, R2, wherein 100 micrometers<R1<∞ and 100 micrometers<R2<300 micrometers. An included angle defined between a tangent of any one of points on the first curved line and a second reference plane P2(as shown inFIG. 2) is in the range from 0.1 degrees to 15 degrees. An included angle defined between a tangent of any one of points on the second curved line and the second reference plane P2is in the range from 10 degrees to 60 degrees.

In the light guide plate300a/300b, a maximum length of the light guide unit340a/340balong a first direction A1is L1, and a maximum length of the light guide unit340a/340balong a second direction A2is L2. Herein, the first direction A1is parallel with a long axis of the light incident surface310, the second direction A2is perpendicular to the first direction A1, and 1≦L1/L2≦∞. In specific, as the value of L1/L2getting smaller, a profile of the light guide unit becomes approximating to that of the light guide unit340aofFIG. 4A. As the value of L1/L2getting larger, the profile of the light guide unit becomes approximating to that of the light guide unit340bofFIG. 4B. The light guide plates300aand300bhave advantages similar to the light guide plate300ofFIG. 2, which will not be repeated again. The light guide plate300of the backlight module200ofFIG. 2can be replaced by one of the light guide plate300aand the light guide plate300b.

FIG. 5is a schematic cross-sectional view of a light guide plate according to another embodiment of the present invention. Referring toFIG. 5, the light guide plate300cof the present embodiment is similar in principle to the light guide plate300. The difference between the light guide plate300cand the light guide plate300would be described as follows. In the light guide plate300, each two adjacent light guide units340abut against each other. However, in the light guide plate300c, each two adjacent light guide units340disposed on the bottom surface330of the light guide plate300are spaced from each other. In addition, intervals D1, D2, D3, D4and D5between each two adjacent light guide units340can be different. For example, the interval nearer to the light incident surface310is greater than the interval farther away from the light incident surface310. In other words, D1>D2>D3>D4>D5. The light emitting uniformity of the light guide plate300ccan be improved by regulating the intervals D1, D2, D3, D4and D5between each two adjacent light guide units340.

In alternative embodiment, the intervals D1, D2, D3, D4and D5between each two adjacent light guide units340can be the same. In the light guide plate300c, the first curved surface342and the second curved surface344of each of the light guide units340can be cylinder surfaces or spherical surfaces. In addition, the light guide plate300of the backlight module200ofFIG. 2can be replaced by the light guide plate300c.

FIG. 6is a schematic cross-sectional view of a light guide plate according to another embodiment of the present invention. Referring toFIG. 6, the light guide units340dof the light guide plate300dof the present embodiment are protruded out from the bottom surface330. In a cross section that is perpendicular to the light incident surface310and passes through the first curved surfaces342dand the second curved surfaces344d, a first curved surface342dand the cross section intersect in a first curved line343d, and a second curved surface344dand the cross section intersect in a second curved line345d. Both of the first curved line343dand the second curved line345dare convex lines. In other words, both of the first curved surface342dand the second curved surface344dare convex surfaces. In each of the light guide units340d, the second curved line345dis nearer to the light incident surface310relative to the first curved line343d. That means that the second curved surface344dis nearer to the light incident surface310relative to the first curved surface342d. A curvature radius of the first curved line343dis greater than that of the second curved345d. The curvature radius of the first curved line343dis, for example, R1, and 100 micrometers<R1<∞. The curvature radius of the second curved line345dis, for example, R2, and 100 micrometers<R2<300 micrometers. In addition, an included angle θ1defined between a tangent of any one of points on the first curved line343dand the second reference plane P2is in the range from 0.1 degrees to 15 degrees. An included angle θ2defined between a tangent of any one of points on the second curved line345dand the second reference plane P2is in the range from 10 degrees to 60 degrees.

Due to each of the light guide units340dbeing protruded out from the bottom surface330, both of the first curved surface342dand the second curved surface344dbeing convex surfaces and the second curved line345dwith the smaller curvature radius being nearer to the light incident surface310relative to the first curved line343d(i.e. in each of the light guide units340d, the first curved surface342dbeing located at right of the first reference plane P1, and the second curved surface344dbeing located at left of the first reference plane P1), most of the light rays212can be reflected to the light emitting surface320of the light guide plate300dby the first curved surfaces342dof the light guide units340d, and then emit from the light emitting surface320of the light guide plate300d. Therefore, the light guide plate300dof the present embodiment has relatively high light emitting efficiency, and light emitting angles of the light rays212emitting from the light guide plate300dcan be uniformed. The light guide plate300dof the present embodiment has advantages similar to the light guide plate300ofFIG. 2. The light guide plate300of the backlight module200ofFIG. 2can be replaced by the light guide plate300d. In addition, in the light guide plate300d, the first curved surface342dand the second curved surface344dof each of the light guide units340dcan be cylinder surfaces or spherical surfaces. The light guide units340dcan be spaced from each other on the bottom surface330.

In above embodiments, the light guide units are all disposed on the bottom surfaces. However, in the present invention, the light guide units can be disposed on the light emitting surface. Embodiments about the light guide units disposed on the light emitting surface would be described as follows.

FIG. 7is a schematic cross-sectional view of a light guide plate according to another embodiment of the present invention. Referring toFIG. 7, the light guide units340eof the light guide plate300eof the present embodiments are protruded out from the light emitting surface320. In a cross section that is perpendicular to the light incident surface310and passes through a first curved surfaces342eand a second curved surfaces344e, the first curved surface342eand the cross section intersect in a first curved line343e, and the second curved surface344eand the cross section intersect in a second curved line345e. Both of the first curved line343eand the second curved line345eare convex lines. In other words, both of the first curved surface342eand the second curved surface344eare convex surfaces. In each of the light guide units340e, the first curved line343eis nearer to the light incident surface310relative to the second curved line345e. That means that the first curved surface342eis nearer to the light incident surface310relative to the second curved surface344e. A curvature radius of the first curved line343eis greater than that of the second curved345e. The curvature radius of the first curved line343eis, for example, R1, and 100 micrometers<R1<∞. The curvature radius of the second curved line345eis, for example, R2, and 100 micrometers<R2<300 micrometers. In addition, an included angle θ1defined between a tangent of any one of points on the first curved line343eand the second reference plane P2is in the range from 0.1 degrees to 15 degrees. An included angle θ2defined between a tangent of any one of points on the second curved line345eand the second reference plane P2is in the range from 10 degrees to 60 degrees.

In the present embodiment, each of the light guide units340eis protruded out from the light emitting surface320. Both of the first curved surface342eand the second curved surface344eare convex surfaces. The first curved line343ehaving the greater curvature radius is nearer to the light incident surface310relative to the second curved line345e. That is, in each of the light guide units340e, the first curved surface342eis located at left of the first reference plane P1, and the second curved surface344eis located at right of the first reference plane P1. As such, most of the light rays212transmitting to the second curved surface344ewould emit from the second curved surface344e. Most of the light rays212transmitting to the first curved surface342ewould be reflected to the bottom surface330, and then emit from the second curved surface344eafter being reflected at least one time.

Most of the light rays212can emit from the second curved surface344e. Therefore, the light guide plate300eof the present embodiment has relatively high light emitting efficiency, and light emitting angles of the light rays212emitting from the light guide plate300ecan be uniformed. The light guide plate300eof the present embodiment has advantages similar to the light guide plate300ofFIG. 2. The light guide plate300of the backlight module200ofFIG. 2can be replaced by the light guide plate300e. In addition, in the light guide plate300e, the first curved surface342eand the second curved surface344eof each of the light guide units340ecan be cylinder surfaces or spherical surfaces. The light guide units340ecan be spaced from each other on the light emitting surface320.

FIG. 8is a schematic cross-sectional view of a light guide plate according to another embodiment of the present invention. Referring toFIG. 8, the light guide units340fof the light guide plate300fof the present embodiment are concaved in the light emitting surface320. In a cross section that is perpendicular to the light incident surface310and passes through the first curved surface342fand the second curved surface344f, the first curved surface342fand the cross section intersect in a first curved line343f, and the second curved surface344fand the cross section intersect in a second curved line345f. Both of the first curved line343fand the second curved line345fare concave lines. In other words, both of the first curved surface342fand the second curved surface344fare concave surfaces. In each of the light guide units340f, the second curved line345fis nearer to the light incident surface310relative to the first curved line343f. That means that the second curved surface344fis nearer to the light incident surface310relative to the first curved surface342f. A curvature radius of the first curved line343fis greater than that of the second curved345f. The curvature radius of the first curved line343fis, for example, R1, and 100 micrometers<R1<∞. The curvature radius of the second curved line345fis, for example, R2, and 100 micrometers<R2<300 micrometers. In addition, an included angle θ1defined between a tangent of any one of points on the first curved line343fand the second reference plane P2is in the range from 0.1 degrees to 15 degrees. An included angle θ2defined between a tangent of any one of points on the second curved line345fand the second reference plane P2is in the range from 10 degrees to 60 degrees.

In the present embodiment, each of the light guide units340fis concaved in the light emitting surface320. Both of the first curved surface342fand the second curved surface344fare concave surfaces. The second curved line345fhaving the smaller curvature radius is nearer to the light incident surface310of the light guide plate300frelative to the first curved line343f. That is, in each of the light guide units340f, the first curved surface342fis located at right of the first reference plane P1, and the second curved surface344fis located at left of the first reference plane P1. As such, most of the light rays212transmitting to the second curved surface344fwould emit from the second curved surface344f. Most of the light rays212transmitting to the first curved surface342fwould be reflected to the bottom surface330, and then emit from the second curved surface344fafter being reflected at least one time.

Most of the light rays212can emit from the second curved surface344f. Therefore, the light guide plate300fof the present embodiment has relatively high light emitting efficiency, and light emitting angles of the light rays212emitting from the light guide plate300fcan be uniform. The light guide plate300fof the present embodiment has advantages similar to the light guide plate300ofFIG. 2. The light guide plate300of the backlight module200ofFIG. 2can be replaced by the light guide plate300f. In addition, in the light guide plate300f, the first curved surface342fand the second curved surface344fof each of the light guide units340fcan be cylinder surfaces or spherical surfaces. The light guide units340fcan be spaced from each other on the light emitting surface320.

In summary, each of the light guide units of the light guide plate of the present invention has the first curved surface and second curved surface. The light emitting angles of the light rays can be regulated by adjusting the curvature radiuses of the first curved line and the second curved line. Therefore, the light guide plate has relatively high light emitting efficiency, and the light emitting angles of the light rays emitting from the light guide plate can be uniformed. In this regard, the backlight module using the light guide plate has relatively high light utilization efficiency. Accordingly, the brightness and the uniformity of the plane light source provided by the backlight module of the present invention can be improved without increasing power consumption.