Patent number 8596852 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to a backlight unit for a liquid crystal display (LCD) using a light emitting diode (LED) and a light guide plate, more particularly, which can obtain high definition through a high contrast ratio and be reduced in thickness.
"Recently, with the trend of a thinner and high-performing image display device, a liquid crystal display is prominently utilized in televisions, monitors and the like. A liquid crystal panel does not generate light on its own so that the liquid crystal display requires a backlight unit (BLU). The BLU has adopted as its light source a cold cathode fluorescent lamp (CCFL) which is inexpensive and easy to assemble together. The BLU using the CCFL performs separate driving such as local dimming or impulsive driving. Besides, the CCFL-based BLU is not environment-friendly due to use of a mercury gas, and low in response rate. To overcome this drawback, the CCFL has been replaced by light emitting diodes (LEDs) as the light source for the BLU.
"Meanwhile, in a method to drive the BLU by local dimming, the liquid crystal panel of the liquid crystal display is divided into a plurality of areas and brightness of the BLU light source can be adjusted according to the divided areas by a value of a grey level. That is, light emitting diodes (LEDs) of the BLU corresponding to a brighter area in the displayed image are turned on, and the LEDs corresponding to the rest of the image are turned on with low brightness or completely turned off. In the impulsive driving, the BLU is time-synchronized with the liquid crystal panel. Here, a plurality of light source areas arrayed in rows and columns on a BLU board are turned on sequentially.
"In general, the BLU includes a direct-type BLU and an edge-type BLU. In the latter, a bar-shaped light source is disposed at an edge of the liquid crystal panel to irradiate light thereonto through a light guide plate. On the other hand, in the former, a surface light source is disposed below the liquid crystal panel to directly irradiate light thereonto.
"FIG. 1 is a perspective view illustrating a conventional edge-type BLU using an LED. Referring to FIG. 1, the BLU 10 includes a light guide plate 11, LED light sources 15 and 17 disposed along edges of the light guide plate 11, respectively, and a reflective plate 19 disposed underneath the light guide plate 11. Each of the LED light sources 15 and 17 includes a printed circuit board 17 and a plurality of LEDs 15 arranged on the board 17. Light incident on the light guide plate 11 from the LEDs 15 is internally total-reflected and scattered, and then transferred to the liquid crystal panel. This edge-type BLU 10 can be manufactured in a relatively small thickness but not suitable for separate driving such as local dimming.
"FIG. 2 is a perspective view illustrating a conventional direct-type BLU using an LED. Referring to FIG. 2, the BLU 20 includes a PCB 21 and a plurality of light emitting diodes 23 arranged thereon. A diffusing plate 25 is disposed between a liquid crystal panel (not illustrated) and the LEDs to diffuse light. The LEDs 23 directly irradiate light onto the liquid crystal panel. This direct-type BLU 20 can perform separate driving such as local dimming. In order to achieve such local dimming, each of the LEDs 23 can be controlled to be turned on/off. Alternatively, the BLU is divided into predetermined areas, e.g., A1, A2, and A3 areas to drive the LEDs 23 according to the divided areas. However, the LEDs 23, when driven respectively, entail high consumption power, costs for a heat radiating structure for coping with high temperature and complicated circuits. Meanwhile, the LEDs, when driven according to the divided areas, experience less local dimming effects due to difficulty in dividing the areas and thickness (H) of the BLU. Notably, here, the BLU should be sufficiently thick to assure uniform light, thereby disadvantageous for thinning the BLU and the liquid crystal display."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a high-quality backlight unit capable of easily achieving separate driving such as local dimming or impulsive driving and suitable for a thin product.
"According to an aspect of the invention, the invention provides a backlight unit for a liquid crystal display disposed below a liquid crystal panel to irradiate light thereto, including a plurality of separate light guide plates defining respective blocks; and groups of LEDs each disposed along an edge of each of the light guiding plates, each of the LED groups emitting light toward a corresponding one of the light guide plates, wherein the each LED group is turned on and off according to the corresponding block.
"According to an embodiment of the invention, each LED group is disposed at an interface between adjacent ones of the blocks. Each LED group for emitting light toward one of the blocks overlaps with an adjacent one of the LED. This reduces a gap between the adjacent ones of the light guide plates. Preferably, the adjacent LED block is provided at an edge with a cutout for giving a space to the overlapping LED group. This allows each LED group for emitting light toward one of the blocks to easily overlap with the adjacent one of the LED. The cutout has a face selected from an inclined face, a round face and an angled face.
"According to a preferred embodiment of the invention, the light guide plates are arranged in a matrix. Preferably, the backlight unit further includes bar-shaped printed circuit boards disposed along the edges of the light guide plates, respectively, wherein each LED group is arranged on each of the bar-shaped printed circuit boards. Each of the printed circuit boards is disposed to span some of the light guide plate blocks which are arrayed in a row in a direction parallel with the edge of the blocks.
"According to another embodiment of the invention, the LED groups can be driven by local dimming. Here, the liquid crystal panel has a plurality of divided areas, and the LEDs have brightness adjusted according to the blocks, by a peak value of a grey level in each of the divided areas.
"According to further another embodiment of the invention, the LED groups can be driven impulsively. The blocks are time-synchronized with the liquid crystal panel and turned on sequentially."
URL and more information on this patent, see: Yoo,
Keywords for this news article include: Circuit Board, Light-emitting Diode,
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