Backlight module

A backlight module (10) includes a light source and a light guide plate (12). The light source defines a number of light units (11) for emitting light beams. The light guide plate includes a light incident surface (121), an emission surface (123) adjacent to the light incident surface, a bottom surface (124) opposite to the emission surface, a plurality of side surfaces (122) between the emission surface and the bottom surface, and a plurality of diffusion units (13) formed on the bottom surface. A dot size of each diffusion unit/dot is inversely proportional to a summation of the sum of reciprocals of squares of distances between the diffusion unit and each of the light units and the sum of reciprocals of squares of distances between the diffusion unit and corresponding images of each of the light units formed, respectively, by the side surfaces.

BACKGROUND

1. Technical Field

The present invention relates to backlight modules typically used in liquid crystal displays (LCDs) and, more particularly, to backlight modules with highly uniform illumination.

2. Description of the Related Art

Color LCD devices have been widely used in various applications, such as in portable personal computers, LCD televisions, video built-in type LCDs, etc. A conventional LCD device mainly includes a backlight module and a liquid crystal panel. An under-lighting system or an edge-lighting system is used as the backlight module. In an under-lighting system, a light source is disposed under a diffusion plate, and the diffusion plate is disposed under the liquid crystal panel. In an edge-lighting system, a light source is disposed at a side surface of a light guide plate (LGP), and the LGP is disposed under the liquid crystal panel.

Typically, an edge-lighting system includes an LGP and a light source. The LGP is formed from a planar transparent member, such as an acrylic resin plate or the like. Light beams emitted from the light source are transmitted through a side surface (i.e., light incident surface) of the LGP into the LGP. Most of the incident light beams are internally reflected in the LGP between a light emission surface and an opposite bottom surface of the LGP and are then transmitted more or less uniformly out through the light emission surface of the LGP. A plurality of light diffusion dots, having a light scattering function, are advantageously formed on the bottom surface, in order to increase the uniformity of illumination of the backlight module. The light source is usually at least one linear source, such as a cold cathode fluorescent lamp (CCFL), or at least one point source, such as a light emitting diode (LED).

The configuration of the diffusion dots is key to good optical performance of the LGP. Thus, various configurations of diffusion dots of LGPs have been devised recently.FIGS. 9 and 10show a conventional backlight module including an LGP22, a CCFL21, a reflection sheet25, a prism sheet27, and three side reflectors29(only one shown). The LGP22has a light incident surface223, a bottom surface222, an emission surface221, and three side surfaces224,225. The CCFL21is arranged adjacent to the light incident surface223. The reflection sheet25is placed under the bottom surface222. The prism sheet27is set above the emission surface221. One of the side reflectors29is arranged adjacent to the side surface224. The other two side reflectors29are aligned respectively adjacent to their two corresponding side surfaces225. A plurality of diffusion dots26are provided on the bottom surface222, generally in a regular array of rows and columns. The diffusion dots26are ordered in a manner such that sizes thereof in a first main region A of the bottom surface222increase with increasing distance away from the CCFL21, and sizes thereof in a second region B of the bottom surface222adjacent to the side surface224are the same. The sizes of the diffusion dots26in region B are substantially the same as a size of those diffusion dots26in region A that are adjacent to region B. The diffusion dots26in any column of the array parallel to the CCFL21have a similar size.

Generally, CCFL21light intensity in region A decreases with increasing distance away from the CCFL21. Thus, the configuration of the diffusion dots26in region A can increase the uniformity of illumination on the emission surface221of the LGP22, because intensity of light beams emitted from the emission surface221is substantially proportional to the sizes of the corresponding diffusion dots26.

However, illumination in both regions A and B is uneven. One reason for this is because light beams are reflected by the side reflector29from region A back into region B, and the columns of the diffusion dots26in region B are spaced different respective distances from the side reflector29. That is, the diffusion dots26in respective different columns in region B receive light beams having different intensities. Therefore, light beams do not emit uniformly from the part of the emission surface221corresponding to region B. Another reason is that the two side reflectors29that are adjacent to the two side surfaces225have a similar effect to the above-described operation of the side reflector29that is distal from region A. This contribution by these side reflectors29results in further uneven illumination between the side surfaces225, in both regions A and B. Therefore, light beams do not emit uniformly from the part of the emission surface221corresponding to both regions A and B (i.e., the entire emission surface221of the LGP22). In summary, respective distributions of the diffusion dots26in regions A and B result in non-uniform illumination over the whole emission surface221of the LGP22.

Furthermore, if the CCFL21is replaced by a series of point sources such as LEDs, the uniformity of illumination of the backlight module is generally unsatisfactory. That is, the limited lighting characteristics of the LEDs result in a plurality of darker areas, generally between adjacent LEDs, being created in the LGP22. In conclusion, it is very problematic to provide even illumination throughout the entire emission surface221of the LGP22.

What is needed, therefore, is a backlight module that overcomes the above-mentioned problems and thereby provide more even illumination throughout the entire emission surface of a given LGP.

SUMMARY

A backlight module, according to one preferred embodiment, includes a light source and a light guide plate. The light source defines a plurality of light units for emitting light beams. The light guide plate includes a light incident surface configured for receiving the light beams from the plurality of light units; an emission surface adjacent to the light incident surface, the emission surface being structured and arranged (i.e., configured) for emitting the light beams; a bottom surface opposite to the emission surface; a plurality of side surfaces connectively extending between the emission surface and the bottom surface; and a plurality of diffusion units formed on the bottom surface, the diffusion units being respectively configured for scattering the light beams. A size of each diffusion unit is inversely proportional to summation of the sum of reciprocals of squares of distances between the diffusion unit and each of the light units and the sum of reciprocals of squares of distances between the diffusion unit and corresponding images of each of the light units formed respectively by the side surfaces.

Other advantages and novel features will become more apparent from the following detailed description of present backlight module, when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe preferred embodiments of the present backlight module, in detail.

Referring toFIGS. 1 and 2, a backlight module10, according to a first embodiment, includes a plurality of point sources11(i.e., point light sources) arranged in a line and an LGP12used for transmitting light received from the point sources11. The point sources11can be LEDs, mercury lamps, or like apparatuses. In this embodiment, the point sources11are LEDs.

The LGP12is a rectangular transparent plate and includes a light incident surface121; three side surfaces122; a top emission surface123, adjacent and perpendicular to both the light incident surface121and the side surfaces122; and a bottom surface124, opposite to the emission surface123and adjacent both the light incident surface121and the side surfaces122. A plurality of diffusion dots13are formed on the bottom surface124. A thickness of the LGP12is preferably in the range from approximately 1 millimeter to 10 millimeters. The point sources11are disposed adjacent to the light incident surface121. The backlight module10further includes three reflectors (similarly to reflectors29ofFIG. 9) positioned on corresponding side surfaces122, adjacent thereto and/or in contact therewith, of the LGP12so that the side surfaces122are reflective surfaces. Alternatively, a plurality of reflective films can be respectively coated on the corresponding side surfaces122of the LGP12in order to make the side surfaces122reflective.

Transparent glass material or synthetic resin may be used for making the LGP12. Various kinds of highly transparent synthetic resins may be used, such as acrylic resin, polycarbonate resin, vinyl chloride resin, etc. The selected resin may be molded into a plate using known molding methods such as extrusion molding, injection molding, or the like. In particular, polymethyl methacrylate (PMMA) resin provides excellent light transmission, heat resistance, dynamic characteristics, molding performance, processing performance, etc. Thus, it is especially suitable as a material for the LGP12.

The diffusion dots13are, advantageously, generally hemispherical. That is, a bottom elevation (i.e., view from bottom upwards) of each diffusion dot125is a circle, the circle defining a dot area. In alternative embodiments, the diffusion dots13may be generally sub-hemispherical, cylindrical, parallelepiped-shaped, pyramidal or frustum-shaped. The diffusion dots13are, beneficially, arranged convexly on the bottom surface124(i.e., protruding directly from the bottom surface124) in a generally uniform array of rows and columns. The diffusion dots13can be formed by means of an integral molding technique or a printing technique. In this embodiment, the diffusion dots13are formed by the integral molding technique and are formed integrally with the LGP12.

Also, referring toFIG. 3, the dot area of each diffusion dot13is inversely proportional to the summation of the sum of reciprocals of squares of distances between the diffusion dot13and each of the point sources11and the sum of reciprocals of squares of distances between the diffusion dot13and corresponding images of each of the point sources11formed by the side surfaces122. This relationship is expressed by the following equation:

D=r0+k∑j=1m⁢∑i=1n⁢fh⁢1(X-Xji)2+(Y-Yji)2+∑i=1n⁢1(X-Xi)2+(Y-Yi)2,
wherein D designates the dot size, such as radius, of the diffusion dot13; (X, Y), (Xi, Yi), and (Xji, Yji), respectively, represent coordinates of the diffusion dot13, coordinates of the point sources11, and coordinates of images of the point sources11relative to the side surfaces122in a Cartesian coordinate system; m equals the number of side surfaces122; n corresponds to the number of point sources11; fhdesignates the reflectivity of a corresponding side surface122; i and j each represent the series of integers1,2,3, etc.; and r0and k are constants whose values are related to predetermined specifications of the LGP12, the point sources11and distances between the point sources11and the LGP12. Generally, r0can be used for limiting the smallest dot size of the diffusion dot. In practice, optimal values of r0and k can be determined via simulating operation of the LGP12, using optical simulating software such as SPEOS software. The systematic variation of the dot sizes D of the diffusion dots13enable the backlight module10to provide highly uniform illumination.

As an embodiment shown inFIG. 3, the point sources11and the bottom surface124are in the Cartesian coordinate system. The point sources11are arranged in the Y-axis, and the central light source11is an origin of the Cartesian coordinate system. Thus, when r0is 10 microns, k is 0.005, and the width of the LGP10in the Y-axis is 20 centimeters, the dot size D of each diffusion dot13can be determined according to the above-mentioned equation. Specifically,FIG. 4illustrates the sizes D (unit: micron) of the diffusion dots13with a distance of 0.01 meters away from the Y-axis (unit: meter);FIG. 5illustrates the sizes D of the diffusion dots13with a distance of 0.03 meters away from the Y-axis;FIG. 7illustrates the sizes D of the diffusion dots13with a distance of 0.05 meters away from the Y-axis; andFIG. 8illustrates the sizes D of the diffusion dots13with a distance of 0.07 meters away from the Y-axis. The changing trend of the diffusion dots13is illustrated throughFIGS. 4 to 8.

FIG. 8is a view of a backlight module50, according to a second embodiment. The backlight module50is similar to the backlight module of the backlight module10, except that the point sources11are replaced by at least one linear source51, such as a CCFL. Because the linear source51can be regarded as a combination of innumerable point light units511, each with a length dl, the size D of the diffusion dots53can be expressed by the following equation:

It is to be understood that the above-described embodiment is intended to illustrate rather than limit the invention. Variations may be made to the embodiment without departing from the spirit of the invention as claimed. The above-described embodiments are intended to illustrate the scope of the invention and not restrict the scope of the invention.