Backlight assembly and liquid crystal display having the same

A backlight assembly is suitable for emitting uniform flat light. The backlight assembly causes light from a lamp to travel in the form of flat light using a light guide plate disposed to have one plane facing the lamp. The light guide plate includes one or more rounded portions at one or more edges of an incident plane thereof onto which the light from the lamp is incident, and the one or more rounded portions cause the light from the lamp to travel into the light guide plate.

This application claims the benefit of Korean Patent Application No. 10-2006-0060494, filed on Jun. 30, 2006 and Korean Patent Application No. 10-2006-0060495, filed on Jun. 30, 2006), which are hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight assembly for emitting flat light, and a liquid crystal display having the same.

2. Discussion of the Related Art

Flat display devices are generally divided into emissive type flat display devices and non-emissive type flat display devices. The emissive type flat display devices include plasma display devices and electro-luminescent display devices. In contrast, the non-emissive type flat display devices include liquid crystal displays (LCDs), as a representative example thereof.

The LCDs control an amount of transmission of light that is incident from the outside, because they do not spontaneously emit the light. For this reason, the LCDs have difficulty in displaying an image in a dark place. To solve this problem, each LCD is equipped with a backlight assembly, which emits flat (or two-dimensional) light. The backlight assembly irradiates the light to the rear surface of a liquid crystal panel of the LCD. Further, the backlight assembly is used in flat panel graphic displays, such as lighting signs, in addition to the non-emissive type display devices, such as LCDs.

This backlight assembly is divided into a direct type and an edge type according to the arrangement of a light source. The direct-type backlight assembly has a plurality of light sources disposed below a radiating surface of the light. The light sources directly emit light to the rear surface of a light irradiating target (i.e. a liquid crystal panel). Meanwhile, the edge-type backlight assembly includes a light source installed on one side of a light guide plate, and the light guide plate guides the light from the light source to the entire surface of the liquid crystal panel. The light guide plate causes the light generated from the light source to radiate to the rear surface of the target (i.e. the liquid crystal panel) in the form of flat light.

In comparison with the direct-type backlight assembly, the edge-type backlight assembly remarkably reduces power consumption. As the size of the LCD having the edge-type backlight assembly is gradually increased, the brightness of an image displayed by the LCD is decreased. In this aspect, the edge-type backlight assembly is applied to a relatively small size of LCD such as the monitor of a lap-top computer or a small-sized desk top computer.

FIG. 1is an exploded perspective view illustrating a related LCD having an edge-type backlight assembly, andFIG. 2is a sectional view taken along line I-I′ of the related LCD ofFIG. 1. Referring toFIGS. 1 and 2, the related LCD includes a liquid crystal panel10displaying an image, a backlight assembly20providing flat light to the rear surface of the liquid crystal panel10, and a top case11enclosing an edge of the liquid crystal panel10and sides of the backlight assembly20.

The backlight assembly20includes a bottom cover80fastened with a support main40. A lamp60, a lamp housing61, a reflector70, a light guide plate50, and a set of optical sheets30are received into the support main40, and are supported by the bottom cover80. The support main40supports the liquid crystal panel10.

The light guide plate50allows light emitted from the lamp60to travel to the liquid crystal panel10in the form of flat light. To this end, the light guide plate50is made of material having superior light transmittance. In addition, the light guide plate50has a prism pattern capable of increasing an amount of the flat light. Although not illustrated, the prism pattern is formed on the rear surface of the light guide plate50.

The lamp60is disposed near one side of the light guide plate50so as to be in one plane by the light guide plate50. The light emitted from the lamp60is incident onto one side (hereinafter, referred to as “incident plane”) of the light guide plate50. The lamp60is provided with electrodes63at opposite ends thereof. An entire length of the lamp60does not exceed the incident plane of the light guide plate50. This functions to prevent the size of the LCD from exceeding an effective screen of the liquid crystal panel10.

The lamp housing61reflects some of the light, which is emitted from the lamp60toward to the other directions than the incident plane of the light guide plate50, to the incident plane of the light guide plate50, thereby increasing the efficiency of using the light emitted from the backlight assembly.

In the related LCD having the edge-type backlight assembly, the electrodes63of the lamp60correspond to opposite ends of the incident plane of the light guide plate50. An amount of the light that is incident onto the opposite ends of the incident plane of the light guide plate50is relatively smaller, compared to the other portion of the incident plane of the light guide plate50. As such, an amount of the light that exits from corner regions (black regions ofFIG. 1) of the light guide plate50on the side of the incident plane of the light guide plate50is relatively smaller, compared to the other surface regions of the light guide plate50. In other words, the related edge-type backlight assembly has no alternative but to emit a remarkably small amount of light from some of the surface regions corresponding to the electrodes63of the lamp60. As a result, the image displayed on the liquid crystal panel10inevitably has shadows (dark portions). The non-uniform brightness caused by the shadows degrades a quality of the image displayed by the LCD.

In order to inhibit the shadows from being generated, the edge-type backlight assembly is provided with a plurality of diffusion sheets. However, these diffusion sheets have difficulty in making the LCD lightweight, thin, and inexpensive, and furthermore cannot sufficiently inhibit the shadows and the non-uniform brightness caused by the shadows.

In addition, the light incident onto the incident plane of the light guide plate50includes the light (hereinafter, referred to as “direct light”) that is directly incident from the lamp60, and the light (hereinafter, referred to as “reflected light”) that is reflected by the lamp housing61. The reflected light is incident onto the incident plane of the light guide plate50at a large angle with respect to the surface of the light guide plate50, compared to the direct light. As such, the light guide plate50allows a lot of light to be irradiated in the proximity of the incident plane of the light guide plate50. More specifically, as illustrated inFIG. 2, the light guide plate50has a spectral region (i.e. bright lines (bright band)) Ws where a lot of light is irradiated, and a spectral region (i.e. dark lines (dark band)) Bs where a relatively small of light is irradiated. In other words, the related edge-type backlight assembly has difficulty in irradiating uniform flat light to the liquid crystal panel. The non-uniformity of this flat light leads to the bright lines (bright band) and the dark lines (dark band) within the image displayed on the liquid crystal panel10. As a result, the LCD using the edge-type backlight assembly not only has difficulty in displaying the image having uniform brightness but also has no choice but to deteriorate the image quality.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a backlight assembly capable of emitting flat light that substantially obviates one or more of the problems due to limitations and disadvantages of the related art, and a liquid crystal display using the same.

An advantage of the present invention is to provide a backlight assembly, which is suitable for emitting uniform flat light.

Another advantage of the present invention is to provide a backlight assembly, which is suitable for displaying an image of uniform brightness.

Another advantage of the present invention is to provide a liquid crystal display, which is suitable for displaying a good quality of image.

According to an aspect of the present invention, there is provided a backlight assembly, which including a lamp, and a light guide plate having a plane facing the lamp that causes light from the lamp to travel in the form of flat light. The light guide plate includes one or more rounded portion at one or more edges of the plane facing the lamp. The one or more rounded portion cause the light from the lamp to travel into the light guide plate. Alternatively, the one or more rounded portions may include a pattern.

According to another aspect of the present invention, there is provided a liquid crystal display, which comprises a backlight assembly including a light guide plate having a plane facing a lamp that causes the light from the lamp to travel in the form of flat light, and a liquid crystal panel controlling an amount of flat light transmitted from the light guide plate to display an image. The light guide plate includes one or more rounded portions at one or more edges of an incident plane thereof onto which the light from the lamp is incident.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, components having the same operations and functions are designated by the same reference numerals.

FIG. 3is an exploded perspective view illustrating a liquid crystal display (LCD) having a backlight assembly according to a first embodiment of the present invention.FIG. 4is a partial detailed view illustrating parts of the lamp160and the light guide plate150in part A ofFIG. 3. The LCD ofFIG. 3includes a liquid crystal panel110displaying an image, a backlight assembly120providing flat light to the rear surface of the liquid crystal panel110, and a top case111enclosing an edge of the liquid crystal panel110and sides of the backlight assembly.

The liquid crystal panel110includes a thin film transistor array substrate and a color filter substrate that are bonded together such that a uniform cell gap is maintained, and a liquid crystal layer interposed between the thin film transistor array substrate and the color filter substrate.

The backlight assembly120includes a support main140, which has the shape of a frame and received in a box-like bottom cover180. The support main140is fixed to the bottom cover180by screws or hooks. The liquid crystal panel110is located in the support main140. In other words, the liquid crystal panel110is supported by the support main140.

A reflector170, a light guide plate150, and a set of optical sheets130are sequentially stacked in a space defined by the bottom cover180and the support main140. The backlight assembly120further includes a lamp160disposed on one side (hereinafter, referred to as “incident plane”) of the light guide plate150so as to form one plane of the light guide plate150, and a lamp housing161enclosing the lamp160together with the incident plane of the light guide plate150.

The lamp160is driven by drive voltage from the outside, thereby emitting light. The lamp160is formed to be long along a lengthwise direction of the light guide plate150. The lamp160is provided with electrodes163on opposite ends thereof. An entire length of the lamp160including the electrodes163is limited so as not to exceed a length of the incident plane of the light guide plate150. This functions to prevent a geometry of the LCD from being too increased, compared to an effective screen of the liquid crystal panel110.

The lamp housing161reflects some of the light, which is emitted from the lamp160and then travels to the other directions than the incident plane of the light guide plate150. The reflection of the lamp housing161causes the lamp160and the backlight assembly120to increase the efficiency of using the light.

The optical sheet set130diffuses and collects the flat light traveling from the surface of the light guide plate150to the rear surface of the liquid crystal panel110. The optical sheet set includes a diffusion sheet that diffuses the light radiating from the light guide plate150to the rear surface of the liquid crystal panel110, a prism sheet that collects the light diffused by the diffusion sheet, and a protection sheet that protects the prism sheet. The optical sheet set130makes more uniform the flat light to be irradiated to the liquid crystal panel110.

The reflector170reflects the light, which travels from the rear surface of the light guide plate150to the bottom cover180, onto the rear surface of the light guide plate150again. The reflection of the reflector170causes the backlight assembly120to further increase the efficiency of using the light. In other words, the reflector170prevents the light from leaking out toward the rear surface of the light guide plate150, thereby minimizing the loss of light.

The light guide plate150causes direct light that is directly incident from the lamp160and reflected light that is reflected by the lamp housing to travel to the rear surface of the liquid crystal panel120in the form of flat light. For the purpose of changing the path and shape of light, the light guide plate150may have a thickness gradually reduced in proportion to a distance from the incident plane thereof. In addition, the light guide plate150may have a prism pattern (not shown) in order to improve a characteristic of changing the light path (i.e. a characteristic of refracting the light). This prism pattern may be formed on the rear surface of the light guide plate150. The light guide plate150may be made of a material capable of transmitting the light. This transmittable material may be an acrylic transparent resin such as polymethyl methacrylate (PMMA), which has a refractive index of about 1.49, and a specific gravity of about 1.19. Further, for the purpose of a light weight, an olefinic transparent resin having a specific gravity of about 1.0 may be used. Further, the light guide plate150may have a thickness between about 2 mm and about 3 mm, with the size depending on a size of the LCD.

Furthermore, the light guide plate150may have rounded portions150A at opposite ends of the incident plane thereof which correspond to the electrodes163of the lamp160. In other words, as inFIG. 4, opposite corners of the light guide plate150located on the side of the incident plane of the light guide plate150may be rounded, thereby having the rounded portions150A. The rounded portions150A do not require a separate process, because they may be formed by an injection molding process of the light guide plate150. Further, a distance between the rounded portions150A may be longer than that between the electrodes163of the lamp160. Also, the round portions150A are formed of the structure having a convex surface. In this way, the rounded portions150A provided at the regions corresponding to the electrodes163scatter the light that is incident from the lamp160and the lamp housing161onto the opposite ends of the incident plane of the light guide plate150(i.e. the opposite corners of the light guide plate150located on the side of the incident plane of the light guide plate150). This scattered light sufficiently radiates toward the corners of the liquid crystal panel110, which correspond to the rounded portions150A of the light guide plate150at the rear of the liquid crystal panel110. This configuration can further increase an amount of the light traveling from the corners of the light guide plate150, which are adjacent to the electrodes163of the lamp160, to the corners of the liquid crystal panel, which correspond to the rounded portions of the light guide plate150at the rear of the liquid crystal panel. As a result, in the case of the image displayed on the liquid crystal panel110, the brightness at the corners thereof is similar to that at the other region thereof. Furthermore, the LCD can not only provide an image having uniform brightness, but also improve a quality of the image.

FIG. 5is an exploded perspective view illustrating an LCD having a backlight assembly according to a second embodiment of the present invention.FIG. 6is a partial detailed view illustrating parts of the lamp and the light guide plate in part B ofFIG. 5. The LCD ofFIG. 5has the same configuration as that ofFIG. 3, except that the light guide plate150is replaced by a light guide plate152. The components ofFIG. 5having the same structures, functions and operations as those ofFIG. 3will be designated by the same reference numerals. The structures, functions and operations associated with the components ofFIG. 5are obviously disclosed through the description ofFIG. 3, and so the description thereof will be omitted.

The light guide plate152may include patterned rounded portions152A. The patterned rounded portion152A, which may be formed at opposite ends of the incident plane of the light guide plate152which correspond to the electrodes163of the lamp160(i.e. the opposite corners of the light guide plate152located on the side of the incident plane of the light guide plate152), may have a predetermined curvature. Each patterned rounded portions152A may be provided with a prism pattern. As inFIG. 6, the prism pattern may be formed perpendicular to the rear surface of the light guide plate152, thereby collecting the light. Instead of this prism pattern, the patterned rounded portions152A of the light guide plate152may have a dotted pattern or a pyramid pattern. Further, the patterned rounded portions152A do not require a separate process, because they may be formed by an injection molding process of the light guide plate152. In this manner, the patterned rounded portions152A provided at the regions corresponding to the electrodes163scatter and collect the light that is incident from the lamp160and the lamp housing161onto the opposite ends of the incident plane of the light guide plate152(i.e. the opposite corners of the light guide plate152located on the side of the incident plane of the light guide plate152). This scattered and collected light sufficiently radiates toward the corners of the liquid crystal panel110, which correspond to the rounded portions152A of the light guide plate152at the rear of the liquid crystal panel110. This configuration can further increase an amount of the light traveling from the corners of the light guide plate152, which are adjacent to the electrodes163of the lamp160, to the corners of the liquid crystal panel110, which correspond to the rounded portions of the light guide plate152at the rear of the liquid crystal panel110. As a result, in the case of the image displayed on the liquid crystal panel110, the brightness at the corners thereof is similar to that at the other region thereof. Furthermore, the LCD can not only provide an image having uniform brightness, but also improve a quality of the image.

FIG. 7is an exploded perspective view illustrating an LCD having a backlight assembly according to a third embodiment of the present invention.FIG. 8is a sectional view taken along line II-II′ of the LCD ofFIG. 7. The LCD ofFIGS. 7 and 8has the same configuration as that ofFIG. 3, except that the light guide plate150is replaced by a light guide plate154. The components ofFIGS. 7 and 8having the same structures, functions and operations as those ofFIG. 3will be designated by the same reference numerals. The structures, functions and operations associated with the components ofFIGS. 7 and 8are obviously disclosed through the description ofFIG. 3, and so the description thereof will be omitted.

The upper side (i.e. upper edge) of the incident plane of the light guide plate154may be rounded. In other words, the light guide plate154may be provided with a rounded portion154A at the upper edge of the incident plane thereof. The rounded portion154A may be formed along the upper side (i.e. upper edge) of the incident plane of the light guide plate154. The rounded portion154A does not require a separate process, because it may be formed by an injection molding process of the light guide plate154. Also, the round portion150A is formed of the structure having a convex surface.

This rounded portion154A scatters the direct light from the lamp160and the indirect light from the lamp housing161, and diffuses the light traveling into the light guide plate154. The light traveling into the light guide plate154is uniformly distributed within an angle of about 90° with respect to a rear surface (or a front surface) of the light guide plate154. The flat light reflected from the surface of the light guide plate154is made uniform without leaning to one side in a band shape. Thus, the backlight assembly can emit the uniform flat light to the liquid crystal panel110. The uniform flat light from the backlight assembly prevents bright lines (bright band) and dark lines (dark band) from being detected from the image displayed on the liquid crystal panel110. Thus, the LCD can improve a quality of the image. Alternatively, the rounded portion154A of the light guide plate154may have any one of a prism pattern, a dotted pattern, and a pyramid pattern. In this case, the prism pattern, the dotted pattern, or the pyramid pattern may be formed on the round154A.

FIG. 9is a characteristic graph for explaining the relation between incident light Lin and transmitted light Lou at the rounded portion154A ofFIGS. 7 and 8. InFIG. 9, the Y-axis represents a surface of the light guide plate154, and the X-axis represents a direction perpendicular to surface of the light guide plate154. The incident light Lin that is incident onto the rounded portion154A of the light guide plate154is refracted at any one of the angles between 0° and 90° with respect to the surface of the light guide plate154according to a curvature of the rounded portion154A. This is because the angle between the rounded portion154A and the incident light Lin is varied according to a position of the incident light Lin that is incident onto the roundeded portion154A. Thus, the light that is incident onto the rounded portion154A travels in the light guide plate154in the state in which it is uniformly diffused within an angle of 90°.

FIG. 10is an exploded perspective view illustrating an LCD having a backlight assembly according to a fourth embodiment of the present invention.FIG. 11is a sectional view taken along line III-III′ of the LCD ofFIG. 10. The LCD ofFIGS. 10 and 11has the same configuration as that ofFIG. 3, except that the light guide plate150is replaced by a light guide plate156. The components ofFIGS. 10 and 11having the same structures, functions and operations as those ofFIG. 3will be designated by the same reference numerals. The structures, functions and operations associated with the components ofFIGS. 10 and 11are obviously disclosed through the description ofFIG. 3, and so the description thereof will be omitted.

The upper and lower sides (i.e. upper and lower edges) of the incident plane of the light guide plate156may be rounded. In other words, the light guide plate156may be provided with the first rounded portion156A at the upper edge of the incident plane thereof, and the second rounded portion156B at the lower edge of the incident plane thereof. The first rounded portion156A may formed along the upper side (i.e. upper edge) of the incident plane of the light guide plate156, whereas the second round156B is formed along the lower side (i.e. lower edge) of the incident plane of the light guide plate156. The first and second rounded portions156A and156B do not require a separate process, because they may be formed by an injection molding process of the light guide plate156. Also, The first and second rounded portions156A and156B are formed of the structure having a convex surface.

The first and second rounded portions156A and156B scatter the direct light from the lamp160and the indirect light from the lamp housing161, and diffuse the light traveling into the light guide plate156. The light traveling into the light guide plate156is uniformly distributed within an angle of about 90° with respect to a rear surface (or a front surface) of the light guide plate156. The flat light reflected from the surface of the light guide plate156is made uniform without leaning to one side in a band shape. Thus, the backlight assembly can emit the uniform flat light to the liquid crystal panel110. The uniform flat light from the backlight assembly prevents bright lines (bright band) and dark lines (dark band) from being detected from the image displayed on the liquid crystal panel110. Thus, the LCD can improve a quality of the image.

Alternatively, the first and second rounded portions156A and156B of the light guide plate156may have any one of a prism pattern, a dotted pattern, and a pyramid pattern. In this case, the prism pattern, the dotted pattern, or the pyramid pattern may be formed on the first and second rounded portions156A and156B.

As described above, according to the present invention, the backlight assembly forms the rounded portion at one or more edges of the incident plane of the light guide plate, thereby scattering the incident light. Thus, the brightness of the light radiating from the corner regions of the light guide plate which correspond to the electrodes of the lamp can be similar to that of the light radiating from the other region. Further, the angles of the light traveling into the light guide plate are uniformly distributed within an angle of 90° with respect to the front surface (or rear surface) of the light guide plate. Thus, the backlight assembly can emit the light uniformly distributed in the form of flat light without a lopsided portion. The uniform flat light from the backlight assembly prevents the shadows (dark portions), bright lines (bright band) and dark lines (dark band) from being detected from the image displayed on the liquid crystal panel. Thus, the LCD can improve a quality of the image.