Backlight assembly and liquid crystal display device having the same

A backlight assembly includes a plurality of light emitting diodes (LEDs), a light guiding plate disposed on the same plane as the LEDs, and a plurality of optical correcting portions formed on a side of the light guiding plate and spaced apart from each other by a predetermined distance to change an optical path.

This application claims the benefit of the Korean Patent Application No. 2006-60073 filed in Korea on Jun. 30, 2006, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight assembly for a flat panel display device, and more particularly, to a backlight assembly that is capable of improving its luminance uniformity and a liquid crystal display device with such a backlight assembly.

2. Discussion of the Related Art

A liquid crystal display (LCD) device is a flat display device for displaying an image, and has been widely utilized as a monitor for a computer, a television set or the like, because of its advantage of thin profile, light weight and low power consumption. The LCD device typically includes a liquid crystal panel for displaying an image and a backlight assembly for emitting light to the liquid crystal panel.

The backlight assembly may be classified into an edge-type and a direct-type according to the disposition of a light source. The edge-type backlight assembly includes a light guiding plate and a light source disposed on a side surface of the light guiding plate. The light guiding plate serves to guide light emitted from the light source frontward. The direct-type backlight assembly is suitable for a large-sized (e.g., more than 12-inch) LCD device, and includes a plurality of light sources formed on a rear surface of the liquid crystal panel. The light emitted from the light sources is directly emitted to the liquid crystal panel.

The light source of the backlight assembly may be selected from any one of an electro luminescence (EL), a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), and a light emitting diode (LED). The LEDs include red, green and blue LEDs and also white LEDs. Since the LEDs have the advantage of maintaining the uniformity of the light while reducing a thickness of the LCD device, the LEDs can contribute to a high luminance backlight assembly.

FIG. 1is an exploded perspective view illustrating an edge-type LCD device having LEDs, andFIG. 2is a top view illustrating luminance of the LCD device ofFIG. 1according to the related art. As shown inFIGS. 1 and 2, the related art edge-type LCD device includes a liquid crystal panel10, and a backlight assembly20that emits light to the liquid crystal panel10.

Referring toFIG. 1, the backlight assembly20includes a bottom cover90, a reflective plate70, a light guiding plate50, a plurality of optical sheets30, and a plurality of LEDs60. The LEDs60are disposed at a side of the bottom cover90and spaced apart from each other. The backlight assembly20further includes a printed circuit board (PCB)61provided with an electric conductive pattern to supply electric power to the LEDs60, and a housing62enclosing the LEDs60to guide the light generated from the LEDs60to the light guiding plate50.

Referring toFIG. 2, the LEDs60and the light guiding plate50are disposed on an identical plane such that the light generated from the LEDs60is incident on a side surface of the light guiding plate50. Moreover, the LEDs60have an emission angle of about 100°, and thus the light emitted from the LEDs60is incident on the incident surface of the light guiding plate50. Due to the medium difference at the incident surface of the light guiding plate50, the light path is changed.

However, in the related art LCD, the emission angle of the light emitted from the LEDs60and incident on the incident surface of the light guiding plate is reduced by the medium difference. As a result, bright portions A and dark portions B are alternately generated at the incident surface area of the light guiding plate50, causing hot spots where the luminance is not uniform at areas where the LEDs60are disposed.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a backlight assembly and a liquid crystal display (LCD) device having the backlight assembly that substantially obviate one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a backlight assembly in which luminance uniformity can be enhanced by changing a shape of the light incident portion of a light guiding plate to diffuse the light, and an LCD device having such a backlight assembly.

Another object of the present invention is to provide a backlight assembly in which heat dissipation efficiency is improved, and an LCD device having such a backlight assembly.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the backlight assembly includes a plurality of light emitting diodes (LEDs), a light guiding plate disposed on the same plane as the LED, and a plurality of optical correcting portions formed on a side of the light guiding plate and spaced apart from each other by a predetermined distance to change the optical path.

In another aspect of the present invention, the LCD device includes a plurality of light emitting diodes (LEDs), a light guiding plate disposed on the same plane as the LED, a plurality of optical correcting portions formed on a side of the light guiding plate and spaced apart from each other by a predetermined distance to change the optical path, and a liquid crystal panel disposed on the light guiding plate to display an image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3is an exploded perspective view illustrating an edge-type LCD device according to a first exemplary embodiment of the present invention.FIG. 4is a perspective view of portion A ofFIG. 3, illustrating an exemplary light guiding plate and an LED.

As shown inFIGS. 3 and 4, the edge-type LCD device according to the first exemplary embodiment includes a liquid crystal panel100and a backlight assembly120emitting light toward the liquid crystal panel100. Although not shown, the liquid crystal panel100includes a TFT array substrate, a color filter substrate, and a liquid crystal layer interposed between the TFT array substrate and the color filter substrate.

The backlight assembly120includes a bottom cover190, a plurality of LEDs160disposed on the bottom case190and spaced apart from each other, a light guiding plate150disposed on the same plane as the LEDs160to convert point light generated from the LEDs160into surface light, a reflective plate170disposed on a rear surface of the light guiding plate150to reflect the light toward the liquid crystal panel100, and a plurality of optical sheets130disposed in front of the LEDs160to diffuse and focus the light. The backlight further includes a printed circuit board (PCB)161on which an electric conductive pattern for applying electric power to the LEDs160is formed, and a housing162enclosing the LEDs160and reflecting the light toward the light guiding plate150. The LEDs160may be red, green and blue LEDs. Alternatively, the LEDs160may be white LEDs emitting white light.

In order to enhance the light efficiency of the light guiding plate150, a plurality of prism patterns having a plurality of protrusions may be formed on the front and/or rear surface of the light guiding plate150. The light guiding plate150may be formed of poly methyl methacrylate resin having a high light transmittance or glass having high thermal-resistance. The light guiding plate150may be formed as a flat type or a wedge type. When the light guiding plate150is formed of glass, the thermal deformation of the light guiding plate150can be minimized.

Moreover, the light guiding plate150includes a plurality of protrusions200and a plurality of light incident surfaces151, which are formed on a side of the light guiding plate150. The plurality of light incident surfaces151face the LEDs160, respectively. Each of the protrusions200has a triangular section. As shown inFIG. 4, each protrusion200includes two protruding surfaces on which reflective sheets201are attached by adhesive or a two-sided tape. The reflective sheets201are exemplary only. Alternatively, reflective layers formed of Ag, for example, may also be coated on the protruding surfaces of the protrusions200. The LEDs160are disposed to correspond to the light incident surfaces151. That is, the LEDs160are disposed between the protrusions200. In addition, the protrusions200may be integrally formed with the light guiding plate150during the manufacturing process of the light guiding plate150.

According to the first exemplary embodiment, the light emitted from the LEDs160is incident on the side of the light guiding plate150. Then, the light is reflected in the light guiding plate150and directed to the optical sheets130. At this point, some of the light reflected in the light guiding plate150may be directed to the light incident surfaces151and the protrusions200. The light directed to the protrusions200is reflected to an area around the protrusions200according to the shape of the protrusions200and by the reflective sheets201. Therefore, the luminance at the area around the protrusions200that do not correspond to the LEDs160can be enhanced by the light reflected to the area around the protrusions200. That is, the hot spot problem is thus solved by varying the shape of the light guiding plate150.

FIG. 5is a top view illustrating an exemplary light path of the edge-type LCD device ofFIG. 3. As shown inFIG. 5, the plurality of protrusions200spaced apart from each other by predetermined intervals and corresponding to the LEDs160are formed at the side of the light guiding plate150. The reflective sheets201are attached on the surfaces of the protrusions200. The light emitted from the LEDs160is incident on the incident surfaces151of the light guiding plate150. At this point, the light incident on the protrusions200is reflected and scattered by the reflective sheets201, thereby enhancing the luminance around the protrusions200. As described above, by varying the shape of the light guiding plate150, the hot spot problem in the related art can be solved.

FIG. 6is an exploded perspective view illustrating an edge-type LCD device according to a second exemplary embodiment of the present invention.FIG. 7is a perspective view of portion B ofFIG. 6, illustrating an exemplary light guiding plate and an LEDFIG. 8is a top view illustrating an exemplary light path of the edge-type LCD device ofFIG. 6.

As shown inFIGS. 6 through 8, an edge-type LCD device of the second exemplary embodiment is similar to the first exemplary embodiment ofFIGS. 3 through 5except for a light guiding plate250. Therefore, the description of the identical parts will be omitted herein and the like reference numbers will be applied thereto.

The light guiding plate250includes a side which corresponds to the LEDs160and is formed with optical correcting portions300that are spaced apart from each other. The optical correcting portions300include protruding surfaces that face the LEDs160, respectively. Moreover, as shown inFIG. 7, each protruding surface of the optical correcting portion300is shaped in accordance with an optical path of the LEDs160. In this exemplary embodiment, the protruding surface is concave and is provided with a diffusion pattern that is formed in a radial structure. The diffusion pattern includes a plurality of round-shaped grooves301. Thus, the light emitted from the LEDs160is diffused while passing through the optical correcting portions300, thereby solving the hot spot problem in the related art.

As described above, referring toFIG. 8, the light is diffused by the optical correcting portions300formed on the side of the light guiding plate250and provided with the rounded grooves301(ofFIG. 7) each having the diffusion pattern303(ofFIG. 7). Accordingly, the luminance can be made uniform throughout the entire surface of the light guiding plate250. That is, by enlarging the light emission angle of the LEDs160using the optical correcting portions300, the hot spot problem can be solved.

FIG. 9is an exploded perspective view illustrating an edge-type LCD device according to a third exemplary embodiment of the present invention.FIG. 10is a perspective view of portion C ofFIG. 9, illustrating an exemplary light guiding plate and an LED.FIG. 11is a top view illustrating an exemplary light path of the edge-type LCD device ofFIG. 9.

As shown inFIGS. 9 through 11, an edge-type LCD device of the third exemplary embodiment is similar to that ofFIGS. 3 through 5except for a light guiding plate350. Therefore, the description of the identical parts will be omitted herein and the like reference numbers will be applied thereto.

The light guiding plate350includes one side that corresponds to the LEDs160and is formed with optical correcting portions400spaced apart from each other. Each of the optical correcting portions400has a rectangular-shaped section. Portion where the optical correcting portion400meets a light incident surface351may be rounded so that the light emitted from the LEDs160can be effectively directed to the optical correcting portions400. Such portion may also be formed with other shapes. A dot pattern401is formed on the optical correcting portion400to diffuse the light. The shape of the dot pattern401may be formed in a variety of shapes. A rate of the dot pattern401per unit area may also be adjusted. The dot pattern401as shown is merely an example in this embodiment, and therefore other patterns may be utilized to diffuse the light.

The LEDs160are disposed to correspond to the light incident surfaces351between the optical correcting portions400. The light emitted from the LEDs160is incident on the incident surfaces351and diffused by the rounded portion between the incident surfaces351and the optical correcting portions400. At this point, the light directed toward the optical correcting portions400is diffused by the dot pattern401to enhance the luminance of areas around thereof.

As described above, referring toFIG. 11, the plurality of the optical correcting portions400are integrally formed at the side of the light guiding plate350. Accordingly, the luminance of the dark portions can be improved, thereby improving the luminance uniformity of the light guiding plate350.

According to the first exemplary embodiments of the present invention, by providing the reflective sheets on the surfaces of the protrusions formed on the light guiding plate, the light can be reflected toward the low luminance areas by the reflective sheets, thereby improving the luminance uniformity of the light guiding plate. According to the second exemplary embodiment of the present invention, since the optical correcting portions protruding from a side of the light guiding plate and provided with the rounded grooves having the diffusion pattern, the light emitted from the LEDs can be diffused to improve the luminance uniformity of the light guiding plate. According to the third exemplary embodiment of the present invention, since the optical correcting portion protruding from the light guiding plate and having the dot pattern, the light emitted from the LEDs can be diffused to improve the luminance uniformity of the light guiding plate.

It will be apparent to those skilled in the art that various modifications and variations can be made in the backlight assembly of the present invention and LCD device having the same without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.