Light guide plate having high-density dots

A light guide plate (10) includes a pair of opposite incidence surfaces (101, 103), an emission surface (108) and a bottom surface (109) opposite to the emission surface. A plurality of dots (11) is distributed on the bottom surface, and each dot is shaped as a rectangle or a square with one corner thereof cut away. Thus, a clearance between adjacent dots is relatively small. That is, a distribution of the dots is relatively compact, and this ensures that the light guide plate can provide emission of light beams with good uniformity. Furthermore, adjacent rows of dots are offset, and this offset can avoid bright lines. Thus, the light guide plate can provide improved display quality. Therefore, the light guide plate can be advantageously applied in back light systems of liquid crystal display devices.

RELATED APPLICATIONS

BACKGROUND

1. Field of the Invention

The invention relates generally to light guide plates used in back light systems of liquid crystal display devices and, more particularly, to a light guide plate having high-density dots.

2. Discussion of Related Art

Back light systems are used in liquid crystal display devices for converting linear light sources, such as cold cathode ray tubes, or point light sources, such as light emitting diodes, into area light sources having high uniformity and brightness.

A conventional back light system includes a light source, a light guide plate, a reflection plate, a diffusion plate and a prism sheet. The light source can be located beside one end or beside two opposite ends of the light guide plate and is used to emit incident light beams into the light guide plate. The light guide plate is used to lead travel of the incident light beams therein and ensure that most of the incident light beams can be emitted from an emission surface thereof. The reflection plate is located below a bottom surface of the light guide plate and is used to reflect some of the incident light beams that are emitted from the bottom surface into the light guide plate. This reflection enhances the utilization ratio of the incident light beams. The diffusion plate and the prism sheet are located on the emission surface of the light guide plate, in turn, and are used to improve uniformity of the emitted light beams.

As shown inFIG. 10, a conventional surface light source device includes a light guide plate1, a line light source2, an end edge reflection layer4, a light diffusion layer6, a white back face reflection layer5, and a curved reflection plate7. The line light source2is positioned on a first end edge of the light guide plate1. The end edge reflection layer4is provided on a second end edge of the light guide plate1, and the light diffusion layer6is provided upon a light emitting surface of the light guide plate1. The white back face reflection layer5is provided on a back surface of the light guide plate1. The curved reflection plate7is further provided to enclose the line light source2so as to effectively utilize light beams emitted by the line light source2.

Furthermore, a light diffusion/transmission section3is provided on the back surface of the light guide plate1. The light diffusion/transmission section3is formed by means, for example, of gravure printing, offset printing, and/or screen printing or transfer and, as formed, includes a plurality of dots. The dots can have arbitrary shapes, such as round, square or chain dot-shapes, and are used to break up what would otherwise be a total reflection condition of the incident light beams. This light diffusion ensures that most of the light beams can pass through the light-emitting surface of the light guide plate1.

Referring toFIG. 11, a distribution of the dots on the back surface of the light guide1is shown. In a region from the first end edge of the light guide plate1to a position at which the surface emission luminance of the light guide plate1is lowest, the ratio of dot area of the light diffusion/transmission section3to the whole area of the back surface of the light guide plate1gradually increases with an increase in distance from the first end edge along a first direction. The first direction is perpendicular to the end edges of the light guide plate1and parallel to the side edges of the light guide plate1. In a region from the position at which the surface emission luminance of the light guide plate1is lowest to the second end edge of the light guide plate1, the ratio is constant along the first direction. The ratio of the dot area of the light diffusion/transmission section3to the whole area of the back surface of the light guide plate1is made constant along a second direction perpendicular to the first direction.

The light diffusion/transmission section3can enhance, to a certain extent, the uniformity of the emitted light beams from the light guide plate1. However, two corners of the first end edge of the light guide plate1are electroshock areas of the line light source2, and the brightness of the emitted light beams at the two corners is relatively low. Furthermore, a clearance between adjacent dots of the light diffusion/transmission section3is relatively big. That is to say, the distribution density of the dots is relatively small, and, as such, the light diffusion/transmission section3can't disperse light beams as effectively as would be desired. Thus, it is difficult to achieve entire or even substantial uniformity of the emitted light beams from the whole area of the light guide plate1.

Furthermore, clearances between adjacent columns of dots are straight and tend to produce bright lines in use. Thus, the light guide plate1can't provide an optimal display quality.

What is needed, therefore, is a light guide plate that can provide emission of light beams with good uniformity.

What is also needed is a light guide plate that can provide improved display quality.

SUMMARY

In one embodiment, a light guide plate includes a pair of opposite incidence surfaces, an emission surface, and a bottom surface opposite to the emission surface. A plurality of dots is distributed on the bottom surface, and each dot is shaped as a rectangle or as a square with one corner thereof cut away. Thus, each dot has a cut part or portion. A distribution density of the dots at a middle area of the bottom surface, which is parallel to the incidence surfaces, and a distribution density of the dots at four corners of the bottom surface are larger than that at other area of the bottom surface. Each dot at the middle area and at the four corners is bigger than each dot located at other areas of the bottom surface. Furthermore, adjacent rows of dots can be offset.

Compared with a conventional light guide plate, a clearance between adjacent dots of the present light guide plate is relatively small. That is, a distribution of the dots is relatively compact, and this compact distribution ensures that the light guide plate can readily disperse light beams. Furthermore, the cut parts of the dots can enhance the utilization ratio of the incident light beams, thereby improving the uniformity of the emitted light beams. Thus, the emitted light beams tend to display good uniformity.

Secondly, the distribution density of the dots at the middle area of the bottom surface is relatively large, and each dot thereat is relatively big. This combination of dot distribution density and size further ensures that the light guide plate can disperse light beams effectively. Thus, the uniformity of the emitted light beams is further improved.

Thirdly, the distribution density and the size of the dots at the four corners of the bottom surface are each relatively large, thereby enhancing the brightness of the light beams emitted at the four corners. Thus, the uniformity of the emitted light beams, as a whole, is further improved.

Fourthly, adjacent rows of dots are offset, and this row patterning can help avoid bright lines. Thus, the present light guide plate can provide improved display quality. Therefore, the present light guide plate can be advantageously applied in back light systems of liquid crystal display devices.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the present light guide plate, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe embodiments of the present light guide plate in detail.

Referring toFIGS. 1-4, in general, andFIGS. 1 and 4, in particular, a light guide plate10, in accordance with a preferred embodiment of the present device, is flat and includes a pair of opposite incidence surfaces101,103, an emission surface108and a bottom surface109opposite to the emission surface108. A light source includes a pair of lamps20located beside the incidence surfaces101,103respectively.

The light guide plate10is made of transparent material, such as acrylic resin, polycarbonate, polyethylene resin, or glass. The incidence surfaces101,103are parallel to each other and are used to receive incident light beams emitted from the lamps20and lead them into the light guide plate10. The emission surface108and the bottom surface109are parallel to each other and perpendicular to the incidence surfaces101,103. The emission surface108is used to lead/direct emitted light beams out of the light guide plate10. The light guide plate10further has a pair of reflection plates30associated therewith. The reflection plates30are located beside two side surfaces105,107, respectively, of the light guide plate10. Alternatively, the reflection plates30can take the form of reflective films coated on the two side surfaces105,107thereof, respectively. The reflection plates30/reflective films are used to reflect the light beams emitted from the side surfaces105,107back into the light guide plate10. The light guide plate10, the lamps20, and reflection plates/films30, when considered together, define a lighting device40.

Referring toFIGS. 2,3, a plurality of dots11are distributed on the bottom surface109of the light guide plate10by means of printing or injection. Each dot11can essentially be rectangular or square, thereby allowing for close packing of dots11via rows120and/or columns122. In the one preferred embodiment ofFIGS. 1-3, the dots11are square. Referring toFIG. 4, at least one corner of each dot11is advantageously cut away, and thus each dot11has at least one cut part111. In the illustrated embodiment, one corner of each dot11is cut away, thereby defining a cut part111.

When the incident light beams travel to the cut parts111of the dots11, the incident light beams are reflected and diffused, thereby traveling along multiple directions and being emitted from the emission surface108of the light guide plate10. This emission can enhance the utilization ratio of the incident light beams and can improve the uniformity of the emitted light beams.

The dots11are distributed on the bottom surface in multiple rows and multiple columns. Referring toFIG. 2, a distribution state of the dots11at the bottom surface109is as follows: a distribution density of the dots11at a middle area of the bottom surface109which is parallel to the incidence surfaces101,103and a distribution density of the dots11at four corners of the bottom surface109are each larger than that at other areas of the bottom surface109. Further, each dot11at the middle area and the four corners is bigger than each dot11at the other areas. Furthermore, a distribution density of the dots11at two ends of the middle area is the largest, and the dots11thereat are the biggest. Therefore, the brightness of the light beams emitted from the four corners, the middle area is enhanced. Thus, the uniformity of the emitted light beams, as a whole, is further improved.

Referring toFIG. 4, in the preferred embodiment illustrated, adjacent rows120of dots11can be offset relative to one another, advantageously by a half of a length/width of the dot11. It is to be further understood that any fractional amount of offset could potentially be used, including varying the degree (fractional amount of width and/or length of the dot11) of offset used between adjacent pairs of rows120on a given bottom surface109, and still be within the scope of present system. In fact, it is recognized that varying the offset between adjacent pairs of rows120could potentially enhance the utilization ratio of the incident light beams and/or help avoid bright lines. Alternatively, each column122of the dots11could have no offset and be within a same straight line, as shown inFIG. 5. The third kind of distribution, as shown inFIG. 6, is similar to the second kind of distribution inFIG. 5, except that the dots11at each column122are rotated, relative to the symmetry of the dots, about 90 degrees, in turn, relative to any adjacent dot11within that particular column122and/or the dots11in adjacent column122. Rotation of the dots11within adjacent columns and/or rows at an angle other than 90°, in order to aid the light utilization ratio, is also considered to be within the scope of the present system. The fourth kind of distribution, as shown inFIG. 7, is similar to the third kind of distribution inFIG. 6, except that adjacent rows120of dots11can be offset from one another, advantageously by a half of the length/width of the dot11. The fifth kind of distribution, as shown inFIG. 8, is similar to the third kind of distribution inFIG. 6, except that the dots11at each row120are rotated 90 degrees, in turn, relative to any adjacent dot within that particular row120and/or the dots in adjacent rows120. The sixth kind of distribution, as shown inFIG. 9, is similar to the fifth kind of distribution inFIG. 8, except that adjacent rows of dots11can be offset from one another, advantageously by a half of the length/width of the dot11. While only offsetting of adjacent rows of dots11has been illustrated, the offsetting of adjacent columns of dots11, additionally or alternatively, is also considered to be within the scope of this system.

Compared with a conventional light guide plate, each dot11of the present light guide plate10is rectangular or square and has a cut part111. Thus, a clearance between adjacent dots11is relatively small. Accordingly, a distribution of the dots11is relatively compact, and this compactness ensures that the light guide plate10can disperse light beams in a preferable and effective manner. Furthermore, the cut parts111can enhance the utilization ratio of the incident light beams, thereby improving the uniformity of the emitted light beams.

Secondly, the distribution density of the dots11at the middle area of the bottom surface109is relatively large, and each dot11thereat is relatively big. This dot density and size further ensures that the light guide plate10can disperse light beams preferably. Thus, the uniformity of the emitted light beams is further improved.

Thirdly, the distribution density of the dots11at the four corners of the bottom surface is relatively large, and each dot11thereat is relatively big. As such, the brightness of the light beams emitted at the four corners is enhanced. Thus, the uniformity, as a whole, of the emitted light beams is further improved.

Fourthly, adjacent rows of dots11, as shown inFIGS. 4,7,9can be offset to help avoid bright lines. Thus, the present light guide plate10can provide improved display quality.

Therefore, the present light guide plate10, incorporating all or some of the above-mentioned features, can be advantageously applied in back light systems of liquid crystal display devices.

In addition, the present light guide plate10can be wedge-shaped and the dots11can be distributed, additionally or alternatively, on the emission surface108, using any of the various dot distributions discussed with respect toFIGS. 4-9. Each light source or lamp20can, for example, be in the form of an incandescent or fluorescent lamp, a field emission device, a CRT (cathode ray tube), a LED (light emitting diode), or a plurality of LEDs. When the light source20is a lamp, a distribution state of the dots11at the bottom surface109is, advantageously, as follows: a distribution density of the dots11at an area near to the lamp20is smaller than that at other area far from the lamp20, and the dots11at the area near to the lamp20is smaller than that at the other area far from the lamp20.