Backlight unit and liquid crystal display device using the same

A backlight unit for a liquid crystal display device includes: a lamp; a light guide plate adjacent to the lamp; a reflector under the light guide plate; a lamp housing covering the lamp, the lamp housing being combined with edges of the light guide plate and the reflector; and a housing pad under the lamp housing, the housing pad overlapping an edge of the lamp housing.

The present invention claims the benefit of Korean Patent Application No. 2004-30588, filed in Korea on Apr. 30, 2004, which is 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 display device, and more particularly, to a backlight unit and a liquid crystal display device using a backlight unit.

2. Discussion of the Related Art

As the information age progresses, flat panel display (FPD) devices having light weight, thin profile, and low power consumption characteristics are being developed and commonly used as a substitute for cathode ray tube (CRT) devices. Generally, display devices may be classified according to their ability for self-emission, and may include emissive display devices and non-emissive display devices. The emissive display devices display images by taking advantage of their ability to self-emit light, and the non-emissive display devices require a light source since they do not emit light by themselves. For example, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices are commonly used as emissive display devices. Liquid crystal display (LCD) devices, which may be categorized as non-emissive display devices, are commonly used in notebook and desktop computers because of their high resolution, capability of displaying color images, and high quality image display.

A LCD module of the LCD device includes an LCD panel for displaying images to an exterior and a backlight unit for supplying light to the LCD panel. The LCD panel includes two substrates facing and spaced apart from each other, and a liquid crystal material interposed therebetween. Liquid crystal molecules of the liquid crystal material have a dielectric constant and refractive index anisotropic characteristics due to their long, thin shape. In addition, two electric field generating electrodes are formed on the two substrates, respectively. Accordingly, an orientation alignment of the liquid crystal molecules can be controlled by supplying a voltage to the two electrodes, wherein transmittance of the LCD panel is changed based on polarization properties of the liquid crystal material. However, since the LCD panel is a non-emissive-type display device, an additional light source is required. Thus, a backlight unit is disposed under the LCD panel, wherein the LCD device displays images using light produced by the backlight unit. In general, backlight units may be classified into two types according to a disposition of the light source, such as side-type and direct-type. As display areas of the LCD devices become increasingly larger, direct-type backlight units including a plurality of light sources have become commonly used to provide high brightness.

FIG. 1is a schematic cross sectional view illustrating a backlight unit of an LCD module according to the related art.

InFIG. 1, an LCD module1includes a main support14supporting a LCD panel2of the LCD module1, a top case10covering the main support14and an edge of the LCD panel2, and a backlight unit30under the LCD panel2. The backlight unit30includes an optical element31and a light guide plate24.

Upper and lower polarizers42and40are disposed on upper and lower surfaces of the LCD panel2, respectively. Although not shown, the LCD panel2includes an upper substrate, a lower substrate facing the upper substrate, and a liquid crystal layer interposed between the upper and lower substrates, wherein the lower substrate includes a plurality of gate lines and a plurality of data lines having a matrix type, and a plurality of thin film transistors connected to each of the plurality of gate lines and plurality of data lines.

More specifically, the top case10is bent to cover sides of the main support14and the edge of the LCD panel2, and the main support14and the top case10are combined by a screw (not shown). Although the main support14generally is formed as a mold type, it may further include a metallic material having a characteristic of protection against heat, such as aluminum (Al), with respect to a high brightness television or monitor. A backlight unit30is disposed under the main support14and includes a backlight lamp20as a light source, a lamp housing16covering the backlight lamp20, a light guide plate24converting incident light from the lamp20into plane light, a reflector26on an backside of the light guide plate24, and the optical element31over the light guide plate24. The optical element31has a diffusion sheet32, an upper prism sheet36and a lower prism sheet34sequentially laminated over the light guide plate24. The LCD panel2is disposed over the optical element31, wherein the LCD panel2is substantially disposed over the optical element31through a protrusion14aof the support main14.

The backlight lamp20includes, for example, a cold cathode fluorescent lamp (CCFL) and light emitting from the lamp20enters the light guide plate24through an incident surface defined as a side portion of the light guide plate24.

The lamp housing16reflects light emitting from the backlight lamp20toward the incident surface of the light guide plate24because the lamp housing16includes a reflecting portion on an inner surface thereof. In addition, the light guide plate24is manufactured to have a sloped backside and a horizontal front side. The reflector26has a role of reducing light loss by reflecting light toward the light guide plate24such that incident light reflects through the backside of the light guide plate24. As a result, when the light emitting from the backlight lamp20enters the light guide plate24, the light is reflected with a predetermined angle on the sloped backside, thereby uniformly progressing with respect to an entire surface of the light guide plate24. At this time, the light emitted to the lower and side surfaces of the light guide plate24enters toward the entire surface by reflecting to the reflector26. In other words, the light emitting from the light guide plate24is diffused on an entire area by the diffusion sheet32.

In addition, when the incident light is perpendicularly disposed with the LCD panel2, light efficiency increases. Therefore, the upper and lower prism sheets36and34, may be laminated as two pieces to be perpendicularly disposed with the angle of the light emitting from the light guide plate24for the LCD panel2in order to increase light efficiency. The light through the diffusion sheet32may enter the LCD panel2through the upper and lower prism sheets36and34.

However, there is a gap A in an assembly structure of the mentioned backlight unit30, an interval between the optical element31and the LCD panel2forms the gap A.

As a result, the gap A leads to a bright line in a portion of the light guide plate24where light enters due to the sloped side of the optical element31. That is, the bright line is shown in the LCD panel2adjacent to the lamp20, wherein the bright line leads to problems such that brightness uniformity of the whole LCD panel2is reduced and the whole brightness is decreased. More particularly, in the case that the light guide plate24includes a prism pattern, the bright line phenomenon is exacerbated.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a backlight unit and a liquid crystal display device using a backlight unit that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a backlight unit that can be solved a bright line problem.

An advantage of the present invention is to provide a backlight unit having a high image quality.

Another advantage of the present invention is to provide an LCD having a backlight unit that can be used to solve a bright line problem.

Another advantage of the present invention is to provide an LCD using a backlight unit having a high image quality.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a backlight unit for a liquid crystal display device includes: a lamp; a light guide plate adjacent to the lamp; a reflector under the light guide plate; a lamp housing covering the lamp, the lamp housing being combined with edges of the light guide plate and the reflector; and a housing pad under the lamp housing, the housing pad overlapping an edge of the lamp housing.

In another aspect, a liquid crystal display device using a backlight unit includes: a backlight unit including: a lamp; a light guide plate adjacent to the lamp; a reflector under the light guide plate; a lamp housing covering the lamp, the lamp housing being combined with edges of the light guide plate and the reflector; and a housing pad under the lamp housing, the housing pad overlapping an edge of the lamp housing; and a liquid crystal display panel over the backlight unit, the liquid crystal display panel including a first substrate, a second substrate facing the first substrate and a liquid crystal layer interposed between the first substrate and the second substrate.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 2is a schematic cross sectional view showing a backlight unit of an LCD module according to the present invention.

InFIG. 2, a backlight unit130includes a backlight lamp120as a light source, a light guide plate124converting the light emitting from the backlight lamp120into a plane light and disposed adjacent to an edge of the backlight lamp120, a reflector126reflecting the light from the light guide plate124to upper portion and disposed under the light guide plate124, and a lamp housing116covering the backlight lamp120, wherein edges of the light guide plate124and the reflector126are inserted in edges of the lamp housing116to attach with each other.

At least one optical element131is disposed over the light guide plate124and an LCD panel102attached over the optical element131. Upper and lower polarizers142and140are also over the optical element131. The optical element131may include a diffusion sheet132, an upper prism sheet136and a lower prism sheet134. An edge of the LCD panel102is disposed in a main support114over the lamp housing116and another edge of the LCD panel102is covered by a top case110.

It is noted that the backlight unit130further includes a housing pad160between the lamp housing and a bottom case150, wherein the housing pad160pushes up the lamp housing116corresponding to a portion of the light guide plate124in which light enters. The housing pad160can reduce a gap B between the LCD panel102and the optical element131. For example, the housing pad160may include a tape that is attached to the lamp housing116and may have a plate shape.

In other words, the housing pad160may be utilized to remove the gap B between the LCD panel102and the optical element131by being inserted between the lamp housing116and the bottom case150. Therefore, a bright line due to the gap B between the LCD panel102and the optical element131can be effectively reduced.

For example, the housing pad160may include a polyethylene terephthalate (PET) material and a thickness of the housing pad160is about 0.1 millimeter. Further, the housing pad160may be manufactured in various sizes and shapes and inserted between the bottom case150and the lamp housing116. More specifically, the housing pad160may be inserted between the bottom case150and a backside edge of the lamp housing116.

The LCD panel2, the backlight unit130, the top case110and the bottom case150form a LCD module100which may be referred as an LCD device.

According to the present invention, a backlight unit130and an LCD using a backlight unit does not experience the bright line phenomenon when a housing pad is added between the lamp housing116and the bottom case150.

Although not shown, the LCD panel includes a first substrate, a second substrate facing the first substrate, and a liquid crystal layer interposed between the first and second substrates.

Additionally, a simple process of the backlight unit and a LCD using the same is accomplished without modifying the driving method and the structure thereof, thereby improving productivity in accordance with reduction of a defect rate.