Field of the Invention
The present invention relates to a backlight unit and a liquid crystal display device including the same, and more particularly, to a direct-type backlight unit and a liquid crystal display device including the same.
Discussion of the Related Art
Portable electronic devices such as mobile terminals and notebook computers typically include flat panel display devices.
Example flat panel display devices include a liquid crystal display device, a plasma display panel, a field emission display device, a light emitting diode display device, and an organic light emitting diode display device.
Among the flat panel display devices, the liquid crystal display device has advantages such as highly developed mass-production technology, easy driving means, low power consumption, high definition resolution, and large screen size.
Since the liquid crystals themselves do not emit light, the liquid crystal display device includes a separate light source such as a backlight unit provided with a light-emitting diode (LED) on a rear surface to irradiate light toward the surface of the liquid crystal panel in order to display an identifiable image.
Backlight units may be categorized into direct-type backlight units and edge-type backlight units. In a direct-type backlight unit, light sources are arranged below a liquid crystal panel. In an edge-type backlight unit, a light source is arranged to face a side of a light guide plate, and a plurality of optical sheets are arranged between the liquid crystal panel and the light guide plate.
FIG. 1 is a cross-sectional view illustrating a related art liquid crystal display device that includes a direct-type backlight unit. The direct-type backlight unit has a structure where a plurality of optical sheets 5 and a diffuser plate 4 are disposed below a liquid crystal panel 6, and a plurality of light sources 1 are arranged below the diffuser plate 4. Light generated from the light sources 1 is scattered and refracted through the diffuser plate 4 and the optical sheets 5, and then spreads toward an entire surface of the liquid crystal panel 6. The liquid crystal display device also includes a bottom cover 7, a guide panel 8, and a case top 9 to secure the light sources 1, diffuser plate 4, optical sheets 5, and liquid crystal panel 6.
If the light sources 1 are arranged below the diffuser plate 4 as shown in FIG. 1, a deviation of light supplied to an edge area of the liquid crystal panel 6 and the other areas is generated, which results in non-uniform display color across the surface of the liquid crystal panel 6.
FIG. 2 is a cross-sectional view illustrating a related art liquid crystal display device that includes a direct-type backlight unit having a support side 3. As shown in FIG. 2, support sides 3 having a shape tilted with respect to bottom cover 7 are arranged at both sides of the light sources 1. A path of light generated from the light sources 1 is changed by the support side 3 in order to increase light supplied to an edge area of liquid crystal panel 6. The liquid crystal display device also includes a guide panel 8 and a case top 9 to secure the diffuser plate 4, optical sheets 5, and liquid crystal panel 6.
As the liquid crystal display device's bezel becomes narrow, the support side 3 is arranged on a rear surface of an active area where an image is displayed on the liquid crystal panel 6 as shown in FIG. 2. This results in non-uniformity of light in area S between the light source 1 and the support side 3, which causes the user to perceive relative darkness in area S.
FIG. 3 illustrates an image of light provided to a front surface of an area under “A-A” of the direct-type backlight unit of FIG. 2. In FIG. 3, a dark red color indicates that luminance is high as relatively more light is provided, and a faded red color indicates that luminance is low as relatively less light is provided. The amount of light reaching the area S of FIGS. 2 and 3 is less than light reaching the other areas. When an image is displayed by the liquid crystal panel, the image formed in area S is relatively darker than the image formed in other areas.
As described above, the related art direct-type liquid crystal display device has a problem that a dark area is generated in the edge area of the liquid crystal panel by non-uniform light supply.
It is difficult to provide a large sized screen of 100 inches or more as a single display device. Technology called a VideoWall, MultiVision, or multiple unit display device has been developed.
The MultiVision display device is a display device that provides a large sized screen by continuously arranging a plurality of unit display devices in horizontal and vertical directions. The MultiVision display device displays different images on each unit display device or displays one image which is divided on each unit display device.
Particularly, when multiple images are displayed by a display device, more important images are generally displayed in a center area of the display device and the less important images are displayed towards edge areas of the display device.
Therefore, if one image is divided for display on unit display devices in the MultiVision display device, the more important image is displayed by the unit display device arranged at the center of the overall display device. As a result, a dark area is generated in the edge area of the unit display device that is arranged at the center.
In this way, if one image is divided for display through unit display devices of the MultiVision display device, problems occur in that a dark area may occur in an important image, and a user may perceive quality deterioration more seriously than when the unit display devices each display different images.