WO2008156236A1

WO2008156236A1 - Light guide panel having light mix-member for lcd back light unit and lcd back light unit thereby

Info

Publication number: WO2008156236A1
Application number: PCT/KR2007/005970
Authority: WO
Inventors: Chul Goo Chi; Sung Hyun Joo; Jae Han Kim; Seong Hoon Lee; O Yong Jeong; Man Suk Kim
Original assignee: Cheil Industries Inc.
Priority date: 2007-06-18
Filing date: 2007-11-26
Publication date: 2008-12-24
Also published as: TW200900765A

Abstract

Disclosed herein is a light guide plate for an LCD back light unit. More specifically, provided is a light guide plate for an LCD back light unit, which employs a three-color or white LED as a light source to render white light. The light guide plate comprises a rear surface provided with geometric prisms to reflect or refract light emitted from a light source, side surfaces on which light is incident, and a front surface from which the light is emitted, the front surface connected to the side surfaces while facing the rear surface, wherein the front surface includes an optical mix -member. Further disclosed herein is an LCD back light unit using the light guide plate.

Description

[DESCRIPTION] [Invention Title]

LIGHT GUIDE PANEL HAVING LIGHT MIX-MEMBER FOR LCD BACK LIGHT UNIT AND LCD BACK LIGHT UNIT THEREBY

[Technical Field]

The present invention relates to a light guide plate for a back light unit of a liquid crystal display (hereinafter, referred to simply as a "LCD") device and an

LCD back light unit using the light guide plate. More specifically, the present invention relates to a light guide plate for an LCD back light unit which employs a tri-color or white LED as a light source to render white light, and to a back light unit for an LCD device using the light guide plate.

[Background Art]

In general, an LCD device refers to a device which displays numerals or images through application of an electric field to liquid crystals disposed between two glass substrates, in which the liquid crystals are made of a material having an intermediate phase between a liquid and a solid.

Since the LCD device is not a self-luminescent device, it must be provided with a back light unit as a light source to generate light. An image is displayed in such a manner that transmittance of light generated from the back light unit is adjusted in a liquid crystal panel, in which liquid crystals are uniformly arranged. FIGs. 1 and 2 are exploded perspective views illustrating a conventional

LCD back light unit.

According to a position of a light source 105 that emits light, an LCD back light unit 10 is classified to a direct-type back light unit in which the light source 105 is directly positioned at a rear side of an LCD panel 100 and an edge-type back light unit in which the light source 105 is positioned at a side of the LCD panel 100.

According to a shape of a light guide plate, the edge-type back light unit is sub- classified to a wedge-type back light unit and a flat-type back light unit. FIG. 1 illustrates a flat-type back light unit in which the light source 105 is arranged at both sides of the LCD panel 100. FIG. 2 illustrates a wedge-type back light unit in which the light source 105 is arranged at one side of the LCD panel 100. As shown in FIGs. 1 and 2, a conventional LCD back light unit includes the light source 105, a light guide plate 1 10 (or 1 12), a reflection plate 1 15, a diffusion sheet 120, prism sheets 125 and a protective sheet 130.

The light source 105 serves to emit light initially in the LCD device. Various types of light source can be used, however the LCD device generally employs a cold cathode fluorescence lamp (CCFL), which has a low power consumption and emits highly bright white light, or a light emitting diode (LED) with a high brightness, as the light source. At present, the CCFL is commonly used. However, the CCFL has problems in that it is under environmental regulation due to mercury contained therein and is expensive due to an inverter required to operate the CCFL. On the other hand, the LED has advantages in that it is free from mercury and has a long life-span, as compared to the CCFL. However, the LED has a drawback in that light emitted from a tri-color LED must be uniformly mixed to render white light. The light guide plate 1 10 is provided below the LCD panel 100 (112) and at one side of the light source 105. The light guide plate 110 serves to convert spot light generated from the light source 105 into plane light and then project the plane light forward to the LCD panel.

The light guide plate 110 of FIG. 1 has a flat cross-section and the light guide plate 1 12 of FIG. 2 has a wedge cross-section.

The reflection plate 115 is provided on a rear side of the light guide plate 110 (or 112). The reflection plate 115 serves to reflect light emitted from the light source 105 toward the LCD panel 100 disposed in front of the reflection plate 115.

The diffusion sheet 120 is provided on a front side of the light guide plate 110 (or 112). The diffusion sheet 120 serves to uniformize light passing through the light guide plate 110.

While passing through the diffusion sheet 120, the light is diffused in horizontal and vertical directions, and brightness is rapidly deteriorated. In this regard, the prism sheets 125 are used to refract and concentrate the light, thereby enhancing brightness.

The protective sheet 130 is provided above the prism sheets 125. The protective sheet 130 serves to prevent scratches on the prism sheets 125 and to prevent Moire effect from occurring when using the prism sheets 125 arranged in two layers in the vertical and horizontal directions. Although not shown in FIGs. 1 and 2, the conventional back light unit further includes a mold frame (housing) that serves as a case to allow respective components of the back light unit to be fixed and to thereby make the back light unit be assembled in an unitary form, and a lamp cover (back cover) to protect the back light unit while serving to maintain the strength of the back light unit and support the back light unit.

FIGs. 3 and 4 are enlarged sectional views illustrating a path of light in the flat-type light guide plate 110 after being generated from the light source 105. FIGs. 5 and 6 are enlarged sectional views illustrating a path of light in the wedge-type light guide plate 112 after being generated from the light source 105.

As shown, the light source 105 is generally located at one edge of the back light unit 10 (for an LCD TV, the light source is often located directly at the rear side of a panel). As a result, light is not uniformly transmitted through the overall surface of the unit, so that the edge of the back light unit can be brighter than any other portions of the back light unit. In order to prevent this phenomenon, the light guide plate 1 10 (or 1 12) is used. The light guide plate is generally made of a transparent acrylic resin, which is not easily breakable due to its high strength, and has deformation resistance, light weight and high transmittance of visible light. In other words, the light guide plate 110 (or 112) serves to allow light emitted from the light source 105 to be uniformly projected to the overall surface of the light guide plate 110 (or 112). In practice, however, in a case where the back light unit 10 is disassembled and light is allowed to emit from the light source 105 located at one side of the light guide plate 110 (112), the light is not uniformly projected to the overall surface of the light guide plate 110 (112), but is concentrated on both ends of the light guide plate 110 (112). This is because the light guide plate 110 guides the light from the light source 105 to the opposite side of the light guide plate 110.

As shown in FIGs. 4 and 6, the rear surface of the light guide plate 110 (112) is subjected to a specific treatment to cause scattered reflection of light in the light guide plate 110 such that light can be transmitted through the overall surface of the light guide plate 110. Specifically, the rear surface of the light guide plate 110 is formed with a prominence/depression pattern 113 which has a predetermined shape designed in consideration of a distance from the light source 105 and the like. When the prominence/depression pattern 113 is formed on the rear surface of the light guide plate 110, plane light having higher brightness and uniformity is emitted through the overall surface of the light guide panel of the LCD device.

In the case where the CCFL is used as the light source, since the light source emits white light in itself, brightness and uniformity are considered as main issues. However, because of the above problems associated with the CCFL, an attempt to use LED as a light source has been continuously made. In the case where the LED is used as the light source, the light source emits three colors (i.e., red, green and blue) of light, rather than white light, and the three colors of light must be then mixed to render uniform white plane light. In order to realize such plane light, three colors of light must be mixed perpendicular to a path of the light. Accordingly, the present invention provides a light guide plate having a structure to allow three colors of light to be appropriately mixed.

[Disclosure] [Technical Problem] The present invention has been made to solve the foregoing problems of the prior art and it is one aspect of the present invention to provide a light guide plate for an LCD back light unit that exhibits superior uniformity of light and excellent visibility by which light emitted from three colors of light sources are mixed with one another to render white light. It is another aspect of the present invention to provide a light guide plate for an LCD back light unit that exhibits superior uniformity of light and excellent visibility by which light emitted from a white LED used as a spot light source are mixed with one another.

It is yet another aspect of the present invention to provide an LCD back light unit using the light guide plate.

It should be noted that the present invention is not limited to the aspects described above, and that other objects and features of the present invention will be apparent to those skilled in the art according to the following description.

[Technical Solution]

In accordance with one aspect of the present invention for achieving the above aspect, there is provided a light guide plate for a liquid crystal display device, comprising: a rear surface provided with geometric prisms to reflect or refract light emitted from a light source; side surfaces on which light is incident; and a front surface from which the light is emitted, the front surface connected to the side surfaces while facing the rear surface wherein the front surface includes an optical mix-member.

Preferably, the optical mix-member allows light to be mixed perpendicular to a path of light and includes a plurality of lenticular lenses repeatedly disposed.

[Advantageous Effects]

As apparent from the fore-going, in a case where a tri-color LED is used as a light source, the light guide plate for an LCD back light unit according to the present invention comprises an optical mix-member to allow light emitted from light sources to be uniformly mixed and to thereby render white light.

In the case where a white LED is used as a light source, the optical mix- member serves to remove a hot spot (a bright portion) near the white LED and to thereby emit uniform plane light.

As such, the present invention provides a light guide plate for an LCD back light unit capable of rendering uniform white plane light using a tri-color or white LED as a light source.

[Description of Drawings]

The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGs. 1 and 2 are exploded perspective views illustrating a conventional LCD back light unit;

FIGs. 3 to 6 are enlarged sectional views illustrating a path of light in a light guide plate after being generated from a light source; FIG. 7 is a perspective view illustrating a light guide plate for an LCD back light unit according to one embodiment of the present invention;

FIG. 8 is a perspective view illustrating a light guide plate for an LCD back light unit according to another embodiment of the present invention;

FIG. 9 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to one embodiment of the present invention;

FIG. 10 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to another embodiment of the present invention; FIG. 1 1 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to yet another embodiment of the present invention; and

FIGs. 12 and 13 are sectional views illustrating a path of light in a light guide plate for an LCD back light unit according to the present invention.

[Best Mode]

Details of other aspects and exemplary embodiments of the present invention are encompassed in the following detailed description and the accompanying drawings.

The advantages, features and their achieving methods of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It should be noted that the present invention is not limited to embodiments of the present invention, and that various modifications and variations can be made without departing from the scope of the present invention. The embodiments are provided for clear understanding of those skilled in the related art without limiting the scope of the present invention, which is defined only by the accompanying claims, through which like components are denoted by like reference numerals.

For clear description of the present invention, dimensions of components constituting the present invention are exaggerated in the drawings. In the following description, if one component is expressed as being "positioned within" or "connected with" another component, it means that the component may be positioned in contact with the other component or spaced a predetermined distance from the other component. In the case where the component is spaced the predetermined distance from the other component, it should be noted that description of a third component used to fix or couple the component to the other component can be omitted. Hereinafter, preferred embodiments of the light guide plate for an LCD back light unit according to the present invention will be described with reference to the accompanying drawings in greater detail.

FIG. 7 is a perspective view illustrating a light guide plate for an LCD back light unit according to one embodiment of the present invention. As shown in FlG. 7, the embodiment is directed to a flat-type back light unit in which light is incident on both sides thereof. According to the embodiment, a light guide plate 300 for an LCD back light unit comprises: side surfaces 301, on which light is incident; a front surface 104, from which the light is emitted, wherein the front surface 104 is connected to the side surfaces 301 ; and a rear surface 305, on which the light is reflected, wherein the first surface 303 is provided with an optical mix-member 310.

The optical mix -member 310 is composed of lenticular lenses 312 repeatedly disposed. The optical mix-member 310 is disposed perpendicular to a longitudinal direction of the light source and has preferably a height in the range of

0.1 to 10% of a total height of the optical mix-member 310.

A light source 306 disposed at the both side surfaces 301 of the light guide plate 300 is a tri-color LED which emits three colors (i.e., red, green and blue) of light. The optical mix-member 310 allows the three-colors of light to be mixed to finally render white light.

When a white LED is used as the light source, the optical mix-member 310 serves to remove a hot spot (a bright portion) near the LED.

A plurality of geometric prisms 320 are disposed on the rear surface 305 and serves to reflect light emitted to the rear surface 305 toward the front surface 303. The prisms 122 are disposed such that they have a longitudinal direction perpendicular to a direction of light emitted from the light source.

As shown in FIG. 7, the prisms 320 have a triangular cross-section. Alternatively, the cross-section of the prisms 320 may be in the form of a tetrahedron, trapezoidal concave wedge or trapezoidal convex wedge. Light emitted from the light source 306 is incident on the side surface 301, is reflected from the rear surface 305 and then directed toward the front surface 303. While passing though the optical mix-member 310 (i.e., the lenticular lenses 312), formed on the front surface 303, the light is mixed perpendicular to a path of light.

FIG. 8 is a perspective view illustrating a light guide plate for an LCD back light unit according to another embodiment of the present invention.

As mentioned above, the embodiment shown in FIG. 7 is directed to the flat-type light guide plate 300 in which light is incident on the both side surfaces thereof. On the other hand, the embodiment in FIG. 8 is directed to a wedge-type light guide plate 400 in which light is incident on one side surface thereof. The wedge-type light guide plate 400 is formed such that a rear surface 405 is inclined upwardly toward a front surface 403.

In the case where light is incident on one side surface only, since the intensity of light becomes weaker along with an increase in a distance from a light source 406, prisms disposed on the rear surface 405 increases in length along with an increase in a distance from the rear surface 405. Since prisms 420 serving to refract light increase in length along with an increase in a distance from the light source, they prevent deterioration in intensity of light and thus improve uniformity of light. FIG. 9 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to one embodiment of the present invention.

As shown in FIG. 9, the optical mix-member 310 is formed on the front surface of the light guide plate 300, serves to induce mixing of light in a horizontal direction and is composed of a plurality of lenticular lenses 312.

The lenticualr lenses 312 induce the incident light to be mixed in a horizontal direction and enable mixing of red, green and blue of light emitted from three colors of LED light sources to render white light.

When a white LED is used as a light source, the optical mix-member 310 removes a hot spot (a bright portion) near the LED to thereby uniformly distribute light.

In order to realize desirable mixing of light, it is preferable that the lenticular lenses 312 have a curvature radius in the range of 10 to 250 μm. When the curvature radius is excessively small, mixing of light is insufficient. When the curvature radius is excessively large, there is a danger that the pattern of the lenticular lenses is exposed.

In the present embodiment, the uniform-dimension lenticular lenses 312 are disposed without a space between the adjacent lenses. Alternatively, the lenticular lenses may increase in length along with an increase in a distance from the center of the light guide plate.

FIG. 10 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to another embodiment of the present invention. FIG. 11 is a sectional view illustrating an optical mix-member in a light guide plate for an LCD back light unit according to yet another embodiment of the present invention.

As shown in FIG. 10, the optical mix-member 310 comprises a plane part 315 which has a predetermined width d disposed between the adjacent lenticular lenses 314. As shown in FIG. 1 1, the optical mix-member 310 may be formed with two lenticular lenses 316, 318 that differ from each other in curvature radius.

FIG. 12 is a sectional view illustrating a path of light in a light guide plate for an LCD back light unit according to another embodiment of the present invention.

As shown in FIG. 12, while passing through the optical mix-member 310, (i.e., the lenticular lenses 312) after being emitted from a tri-color LED as the light source 306, the light is refracted. Since the refraction direction is perpendicular with the surface, the light emitted toward the front surface is mixed perpendicular to a path of light. As a result, light emitted from the tri-color LED are mixed with one another and white light is thus finally rendered toward the front surface. FIG. 13 is a sectional view illustrating a path of light in a light guide plate for an LCD back light unit according to yet another embodiment of the present invention.

As shown in FIG. 13, while passing through the optical mix -member 310, (i.e., the lenticular lenses 312) after being emitted from a white LED employed as the light source 306, the light is refracted. Since the refraction direction is perpendicular with the surface, light emitted to the front surface are mixed perpendicular to the direction of the light. As a result, light emitted from the white LED are mixed with one another and white light is thus finally rendered toward the front surface. Accordingly, a portion (i.e., a hot spot), where it looks bright near the LED, is removed, and a uniform plane light is thus emitted toward the front surface.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 5/5

[Fig. 11]

310

\

316

[Fig. 12]

Claims

[CLAIMS]

[Claim 1]

A light guide plate for a liquid crystal display device, comprising: a rear surface provided with geometric prisms to reflect or refract light emitted from a light source; side surfaces on which light is incident; and a front surface from which the light is emitted, the front surface connected to the side surfaces while facing the rear surface, wherein the front surface includes an optical mix-member.

[Claim 2]

The light guide plate according to claim 1 , wherein the optical mix-member is disposed perpendicular to a longitudinal direction of the light source.

[Claim 3]

The light guide plate according to claim 1 , wherein the optical mix-member has a height in the range of 0.1 to 10% of a total height of the optical mix-member.

[Claim 4]

The light guide plate according to claim 1, wherein the optical mix-member includes a plurality of lenticular lenses repeatedly disposed.

[Claim 5] The light guide plate according to claim 4, wherein the lenticular lenses have a curvature radius in the range of 10 to 250 μm.

[Claim 6]

The light guide plate according to claim 4, wherein the lenticular lenses increase in height along with an increase in a distance from the center of the light guide plate.

[Claim 7]

The light guide plate according to claim 4, wherein the lenticular lenses are

10 uniformly spaced apart from each other.

[Claim 8]

The light guide plate according to claim 1, wherein the optical mix-member includes a plurality of lenticular lens units having different curvature radiuses repeatedly disposed.

[Claim 9]

The light guide plate according to claim 1, wherein each of the geometric prisms has a cross-section in the form of a triangle, tetrahedron, trapezoidal concave wedge or trapezoidal convex wedge.

[Claim 10]

A back light unit for a liquid crystal display device, comprising: a light source including a light emitting diode (LED); and the light guide plate according to claim 1.

[Claim 11]

A liquid crystal display device comprising the back light unit according to claim 10.

11