Backlight module having colored reflective structure and liquid crystal display using same

An exemplary backlight module (20) includes a light guide plate (22) having a light incident surface (224), a plurality of light sources (23) adjacent to the light incident surface, a frame (24) for receiving the light sources and the light guide plate, and a colored reflective structure (220) disposed in the frame. Some of the light beams emitting from the light sources are transmitted to the colored reflective structure and converted to reflected light beams having a corresponding color. The reflected light beams further mix with light beams emitting from the light sources and generate light beams in desired color system. A liquid crystal display (200) using the backlight module is also provided.

FIELD OF THE INVENTION

The present invention relates to backlight modules, and more particularly to a backlight module having a colored reflective structure and a liquid crystal display (LCD) using the backlight module.

GENERAL BACKGROUND

LCDs are widely used in various modern information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. The wide usage of the LCD is due to its advantages such as portability, low power consumption, and low radiation. LCDs are passive optical devices. Therefore in general, a backlight module is needed to provide sufficient illumination for an LCD panel of the LCD, so as to enable the LCD panel to display images.

Generally, a backlight module includes a light source and a light guide plate (LGP). The LGP is for guiding light beams emitted by the light source, so that the light beams transmit to a predetermined display area. The light source can for example be a cold cathode fluorescent lamp (CCFL) or one or more light emitting diodes (LEDs). A typical LED is small, and light beams emitted by an LED are more focused. Therefore the LED is more suitable for a small sized product, such as an LCD used in a mobile phone, a portable media player, a PDA, or the like.

In general, it is difficult to manufacture a white light emitting diode (WLED) that can emit white light beams with high purity. Typically, light beams emitted by a WLED are slightly yellowish. That is, the light beams are mostly white but also partly yellow. These white-yellowish light beams are liable to reduce the display quality of the LCD. One means employed to convert the white-yellowish light beams to pure white light beams is to use an LGP that has a plurality of colored particles incorporated therein. This solution utilizes principles of colored light mixing to achieve white output light having high purity.

FIG. 5is an isometric view of a conventional backlight module. The backlight module10includes a light guide plate (LGP)13and a plurality of light sources12. The LGP13is made by injection molding, and includes a top light emitting surface132, a bottom surface133, a light incident surface131adjacent to the light emitting surface132and the bottom surface133, and a plurality of embedded colored particles130. The colored particles130are typically blue particles, which are sprayed into a molten LGP preform during the injection molding process. Each of the light sources12is a white light emitting diode (WLED). The light sources12are disposed adjacent to the light incident surface131of the LGP13.

Light beams emitting from the light sources12are transmitted into the LGP13via the light incident surface131, with the light beams being white-yellowish. In the LGP13, some of the white-yellowish light beams are scattered by the colored particles130, and converted to blue light beams. The blue light beams mix with other white-yellowish light beams that are not scattered, and accordingly white light beams having high purity are generated. The white light beams emit from the light emitting surface132of the LGP13, and enable an LCD employing the backlight module10to display high quality images.

The backlight module10solves the need to provide pure white light beams. However, the material of the colored particles130is different from that of the LGP13. Therefore when the colored particles130are sprayed into the molten LGP preform, the colored particles130block cross-linking of molecular structures of the material of the LGP preform. Thus the structural integrity of the formed LGP13is weakened.

It is, therefore, desired to provide a backlight module and an LCD employing the backlight module which can overcome the above-described deficiencies.

SUMMARY

In one aspect, a backlight module includes a light guide plate having a light incident surface, a plurality of light sources adjacent to the light incident surface, a frame for receiving the light sources and the light guide plate, and a colored reflective structure disposed in the frame. Some of the light beams emitting from the light sources are transmitted to the colored reflective structure and converted to reflected light beams having a corresponding color. The reflected light beams further mix with light beams emitting from the light sources and generate light beams in desired color system.

In another aspect, a liquid crystal display includes a liquid crystal panel and a backlight module adjacent to the light crystal panel. Some of light beams emitting from the backlight module is converted to new light beams having a corresponding color by a colored structure. The new light beams further mix with the light beams emitting from the backlight module and generate light beams in desired color system for illuminating the light crystal panel.

Other novel features and advantages of the above-described backlight module and liquid crystal display will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe preferred and exemplary embodiments of the present invention in detail.

FIG. 1is an exploded, isometric view of an LCD200according to a first embodiment of the present invention. The LCD200includes a liquid crystal panel29, and a backlight module20that functions as a surface light source to illuminate the liquid crystal panel29. The backlight module20includes a light guide plate (LGP)22, a frame24, and three light sources23. All of the light sources23are white light emitting diodes (WLEDs).

The frame24includes a first sidewall241, a second sidewall244opposite to the first sidewall241, a third sidewall242adjacent to the first sidewall241and the second sidewall244, and a fourth sidewall243opposite to the third sidewall242. The first sidewall241, the third sidewall242, the second sidewall244, and the fourth sidewall243are arranged end-to-end to cooperatively form a four-sided closed structure for containing the LGP22. Moreover, the first sidewall241includes three notches249, which are configured to contain the three light sources23.

The LGP22is preferably made of polymethyl methacrylate (PMMA), and includes a top light emitting surface222, a bottom surface223, and four side surfaces224adjacent to both the light emitting surface222and the bottom surface223. One of the side surfaces224that is adjacent to the light sources23functions as a light incident surface. Each of the other three side surfaces224includes a colored reflective layer220formed thereon. Each colored reflective layer220includes colored reflective material228, and is applied on the corresponding side surface224by painting or coating. Typically, the colored reflective material228is particles of blue pigment. The colored reflective layer220reflects light beams incident thereto. The color of reflected light beams corresponds to the color of the colored reflective material228. In this embodiment, the reflected light beams are blue because the colored reflective material228is blue pigment particles.

FIG. 2is an enlarged plan view of the colored reflective layer220of one of the side surfaces224that is adjacent to the light incident surface224. The colored reflective material228is distributed in the colored reflective layer220with a varying distribution density. In particular, the distribution density of the colored reflective material228gradually reduces from a first end of the colored reflective layer220at the light incident surface224to an opposite second end of the colored reflective layer220far away from the light incident surface224. As regards the colored reflective layer220of the other side surface224that is adjacent to the light incident surface224, the distribution density of the colored reflective material228varies as described above. That is, the distribution density of the colored reflective material228gradually reduces from a first end of the colored reflective layer220at the light incident surface224to an opposite second end of the colored reflective layer220far from the light incident surface224. As regards the colored reflective layer220of the other side surface224at an opposite side of the LGP22to the light incident surface224, the distribution density of the colored reflective material228is uniform.

In assembly of the LCD200, the LGP22is lowered down and arranged in the frame24, so that the light incident surface224faces the first sidewall241, and the other three side surfaces224face the second sidewall244, the third sidewall242, and the fourth sidewall243, respectively. Then each of the light sources23is lowered down and contained in the corresponding notch249of the first sidewall241, such that the light sources23are held firmly in position adjacent to the light incident surface224of the LGP22. The liquid crystal panel29is lowered down and positioned on the assembled backlight module20.

In operation, light beams230emitting from the light sources23are transmitted into the LGP22via the light incident surface224, the light beams230being white-yellowish. Some of the white-yellowish light beams230pass though the LGP22and are reflected by the colored reflective material228of the colored reflective layers220. Accordingly, these white-yellowish light beams230are converted to blue light beams. The blue light beams mix with other white-yellowish light beams that are not reflected, and accordingly white light beams231having high purity are generated. The white light beams231emit from the light emitting surface222of the LGP22, so as to illuminate the liquid crystal panel29. Thereby, the LCD200is able to display high quality images.

Because the light sources23are disposed adjacent to only one of the side surfaces224of the LGP22, the luminous flux of the white-yellowish light beams230within the LGP22decreases gradually from the light incident surface224to the side surface224that is at the opposite side of the LGP22. Accordingly, the white-yellowish light beams230reaching the two side surfaces224that are adjacent to the light incident surface224gradually decrease in intensity from the first ends of the side surfaces224at the light incident surface224to the second ends of the side surfaces224far from the light incident surface224. Therefore the gradually reducing distribution density of the colored reflective material228in said two side surfaces224corresponds to the gradually reducing intensity of the white-yellowish light beams230. Accordingly, at any given region within the LGP22, the intensity of the blue (reflected) light beams is proportional to the intensity of the white-yellowish light beams230. As a result, the mixing of the white-yellowish light beams230with the blue light beams is suitably proportioned, so that the white light beams231emitting from each portion of the light emitting surface222have high purity. Thus, the white light beams231emitting from all portions of the light emitting surface222can have high purity.

In further and/or alternative embodiments, other means can be employed in order to help ensure that the white light beams231emitting from the light emitting surface222have high purity. In a first example, for the colored reflective layer220at each of the two side surfaces224that are adjacent to the light incident surface224, a thickness of the colored reflective layer220gradually reduces from the first end at the light incident surface224to the second end far from the light incident surface224. In a second example, for the colored reflective layer220at each of said two side surfaces224, a reflectivity of the colored reflective material228gradually reduces from the first end of the colored reflective layer220at the light incident surface224to the second end of the colored reflective layer220far from the light incident surface224. In a third example, a colorizing capability of the colored reflective material228gradually reduces from the first end of the colored reflective layer220at the light incident surface224to the second end of the colored reflective layer220far from the light incident surface224.

In summary, the LCD200generates the blue reflected light beams via the colored reflective layers220, and mixes the blue reflected light beams with the white-yellowish light beams230so as to generate pure white light beams230to illuminate the liquid crystal panel29. Because the colored reflective layers220are disposed on the three side surfaces224of the LGP22, no extra material is sprayed into the LGP prefrom during injection molding of the LGP22. Therefore the structural integrity of the formed LGP13is optimal, so that the LGP22can withstand shock or vibration that may be sustained by the LCD200.

FIG. 3is an exploded, isometric view of an LCD300according to a second embodiment of the present invention. The LCD300is similar to the above-described LCD200. However, the LCD300includes a liquid crystal panel39and a backlight module30. The backlight module30includes an LGP32, a frame34, three light sources33adjacent to the LGP32, and a colored reflective film36. The colored reflective film36is U-shaped, and has colored reflective material360coated on the inner sides thereof. The structure and function of the colored reflective film36are similar to those of the colored reflective layers220of the LGP22of the LCD200. The frame34includes four sidewalls349, which are arranged end-to-end to cooperatively form a four-sided closed structure. The LGP32includes a top light emitting surface322, and four side surfaces324adjacent to the light emitting surface322. One of the side surfaces324that is adjacent to the light sources33functions as a light incident surface.

In assembly, the colored reflective film36is lowered down and disposed on or attached to inner surfaces of the corresponding sidewalls349of the frame34. Then the LGP32is lowered down and contained in the frame34, so that the side surfaces324except for the one functioning as the light incident surface closely abut the colored reflective film36. Then the light sources33are also lowered down and contained in the frame34, such that the light sources33are held firmly in position adjacent to the light incident surface324of the LGP32. The liquid crystal panel39is lowered down and positioned on the assembled backlight module30.

Light beams emitting from the light sources33are transmitted into the LGP32. Some of the light beams are transmitted to the colored reflective film36via the corresponding side surfaces324of the LGP32, and are converted to reflected light beams. The reflected light beams then mix with the light beams that are not reflected, and white light beams having high purity are generated. The white light beams emit from the light emitting surface322, so as to enable the LCD300to display high quality images.

FIG. 4is an exploded, isometric view of an LCD400according to a third embodiment of the present invention. The LCD400is similar to the above-described LCD200. However, the LCD400includes a liquid crystal panel49and a backlight module40. The backlight module40includes an LGP42, a frame44, three light sources43, and a reflector45. The LGP42includes a top light emitting surface422, a bottom surface423, and four side surfaces424. One of the side surfaces424functions as a light incident surface.

The frame44includes a first sidewall441, a second sidewall444opposite to the first sidewall441, a third sidewall442adjacent to the first sidewall441and the second sidewall444, and a fourth sidewall443opposite to the third sidewall442. The first sidewall441, the third sidewall442, the second sidewall444, and the fourth sidewall443are arranged end-to-end to cooperatively form a four-sided closed structure. Inner surfaces of the second sidewall444, the third sidewall442, and the fourth sidewall443all include a respective colored reflective layer440formed or attached thereon. Each of the colored reflective layers440has colored reflective material448. The structure and function of each colored reflective layer440are similar to those of the colored reflective layers220of the LGP22of the LCD200. The reflector45includes a colored reflective layer (not labeled) coated on a top surface thereof. The colored reflective layer includes colored reflective material448. In an alternative embodiment, the reflector45can instead include colored reflective material448embedded therein.

In assembly, the reflector45is lowered down and arranged in the frame44. Then the LGP42is lowered down and contained in the frame44, so that the bottom surface423abuts the reflector45, the light incident surface424faces the first sidewall441, and the other three side surfaces424face the second sidewall444, the third sidewall442, and the fourth sidewall443respectively. The light sources43are then lowered down and contained in the frame44, so that the light sources43are adjacent to the light incident surface424of the LGP42. The liquid crystal panel49is lowered down and positioned on the assembled backlight module40.

Light beams emitting from the light sources43are transmitted to the LGP42. Some of the light beams are transmitted to the colored reflective layers440of the frame44via the side surfaces424of the LGP42, some of the light beams are transmitted to the reflector45via the bottom surface423of the LGP42, so as to generate reflected light beams. The reflected light beams are then mixed with the light beams that are not reflected, and white light beams having high purity are generated. The white light beams further emit from the light emitting surface422, and enable the LCD400to display high quality images.

Furthermore, according to light beam mixing principles, in the LCDs200,300, and400, if the light beams emitting from the light sources23,33, and43are in other color systems, the colored reflective material228,360, and448can be substituted by other material accordingly. For example, if the light beams emitting from the light sources23,33, and43are white-bluish, the colored reflective material228,360, and448can be yellow pigment, so as to generate mixed light beams having high purity. In addition, the colored reflective material can be disposed in another element of the liquid crystal panel, such as in a polarizer (not shown); or even disposed in other thin films of the backlight module, such as in a brightness enhancement film (BEF) or a diffuser, and the backlight module can be either direct type or side-edge type.