BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a sectional view illustrating a liquid crystal display with a backlight unit according to the prior art;
FIG. 2 illustrates the conventional backlight unit, in which FIG. 2(a) shows the light and shade distribution of a liquid crystal panel, FIG. 2(b) shows the lighting status of the backlight unit, and FIG. 2(c) shows the luminance distribution of the backlight unit;
FIG. 3 is a view illustrating the light amount distribution curve of the conventional backlight unit;
FIG. 4 is a sectional view illustrating a backlight unit according to an embodiment of the present invention;
FIG. 5 is a view showing the light amount distribution curve of the backlight unit according to an embodiment of the present invention;
FIG. 6 is a plan view illustrating exemplary forms of the partitions according to various embodiments of the present invention;
FIG. 7 is a view showing the light amount distribution according to the height of the partition;
FIG. 8 is a view schematically showing the luminance distribution above the backlight unit according to the present invention; and
FIG. 9 is a configuration view illustrating a liquid crystal display with the backlight unit according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same or similar components are designated by the same reference numerals throughout.
FIG. 4 is a sectional view illustrating a liquid crystal display having a Backlight Unit (BLU) according to an embodiment of the present invention. Referring to FIG. 4, the liquid crystal display 500 includes a liquid crystal panel 107, a BLU 100 and an optical sheet 105 disposed between the display and the BLU. The BLU 100 is a direct type, which is disposed under the liquid crystal panel 107 to irradiate light to the back surface of the liquid crystal panel 107. The BLU 100 includes a plurality of LEDs 103 and a circuit 102 for driving and controlling the LEDs. The plurality of LEDs 103 are disposed on the substrate 101 and constitute a light source unit of the BLU (the arrangement of the plurality of LEDs 103 on the substrate 101 is referred to as “LED light source unit”).
The LED light source unit is divided into a plurality of light source regions A1, A2 and A3, and each of the light source regions A1, A2 and A3 includes at least one LED. For example, each of the light source regions A1, A2 and A3 can have at least one of each of red, green and blue LEDs. Using a set of the red, green and blue LEDs allows emission of white light with superior color reproducibility. In another embodiment, each of the light source unit regions A1, A2 and A3 can have at least one white LED. The white LED can be obtained, for example, by using a blue LED chip with yellow phosphor.
In addition, the LED light source unit can be driven partially by the light source regions. For example, only the LEDs in a light source region A2 can be turned on while the LEDs in other light source regions A1 and A3 can be turned off or turned on at lower luminance. This partial driving method can be applied to implement local dimming or impulsive driving as described later.
As shown in FIG. 4, partitions 104 are formed on the substrate 101. These partitions 104 are disposed at the boundaries between the light source regions A1, A2 and A3. The partitions 104 serve to block the light, emitted from each of the light source regions A1, A2 and A3, from entering other regions. In particular, the sideward light emitted from each of the light source regions is reflected or absorbed by the partitions 104, thus minimally affecting other light source regions as possible. Therefore, the luminance distribution of the BLU 100 is more clearly distinguished among the light source regions. Such a feature is clearly shown in FIG. 5.
FIG. 5 schematically illustrates the light amount distribution curve of the BLU 100. The light amount distribution on the diffusion plate 105a disposed over the BLU 100 is relatively clearly distinguished between the high-luminance region (the central portion in FIG. 5) and the low-luminance regions (the left and right portions in FIG. 5) (compare with FIG. 3). That is, as the partitions 104 are installed at the boundaries between the light source regions, the light distribution above the BLU (or the diffusion plate) is more clearly distinguished among the regions. This allows accurately confining and lighting only a desired portion of the entire back surface of the liquid crystal panel.
FIG. 6 is a plan view illustrating the arrangement of the partitions according to various embodiments of the present invention. As shown in FIG. 6(a), the plurality of partitions 104 can extend in a horizontal direction (Y-axis direction), in parallel with each other. This partition arrangement is useful especially for driving LEDs through the impulsive driving method. Alternatively, the plurality of partitions can extend in a vertical direction (X-axis direction), in parallel with each other (not shown).
Alternatively, as shown in FIG. 6(b), the partitions 104 can be arranged in a matrix on the substrate 101. In this case, each of the regions on the substrate divided by the partitions 104 (i.e., the regions surrounded by the partitions 104) may correspond to one of the light source regions A1, A2 and A3 (FIG. 4) driven separately. This kind of partition arrangement can be useful especially for driving the LEDs through the local dimming method. The partitions can be arranged variously other than the examples shown in FIG. 6. For example, the partitions can be arranged in a honeycomb, forming hexagonal cells (not shown).
The light distribution above the BLU can vary according to the height h of the partitions and the height H of the BLU (H: distance from the substrate 101 to the diffusion plate 105a) With a greater height h of the partition and a lower height H of the BLU, the light distribution on the diffusion plate 105a is more clearly distinguished by the regions. If the height of the partition is too low, the effect of distinction among the regions due to the partitions decreases. Conversely, if the height of the partition is too high, the effect of clear distinction in the light distribution increases but a greater amount of light is absorbed by the partition, and in turn, the liquid crystal display may have a large overall thickness.
FIG. 7 is a view illustrating the light intensity distribution above the BLU according to the height of the partitions. As shown in FIG. 7, the higher the partition is, the clearer the distinction in the light intensity distribution among the regions. That is, with higher partitions, the light intensity in the area above the BLU corresponding to the lighted light source region A2 becomes higher, and the light intensity in the area above the BLU (left and right parts in FIG. 7) corresponding to the unlighted (or of low luminance) light source regions A1 and A3 becomes lower. Considering the light distribution distinction effects and the light absorption by the partitions, it is preferable that the partition 104 has a height of 5 to 25 mm. However, if the BLU has varying thicknesses, the height of the partition 104 can be adjusted differently.
FIG. 8 is a view schematically showing the luminance distribution above the BLU 100. As shown in FIG. 8, among the light source regions A1, A2, A3, the portion on the BLU 100 corresponding to the lighted light source region A2 forms a high-luminance region 127b, whereas the portions on the BLU 100 corresponding to the unlighted light source regions A1 and A3 form low-luminance regions 127a. The high-luminance region 127b and the low-luminance region 127a are distinguished clearly, and they do not have intermediate luminance regions therebetween (compare with FIG. 2(c)).
As shown in FIGS. 5 to 8, the light distribution above the BLU 100 (the light distribution on the diffusion plate 105a) has a profile that is distinguished by the regions. The light distribution clearly distinguished by the regions allows a more effective partial driving method, and more significant effects (clear and lively image, the synchronization between the BLU and the liquid crystal panel in time, etc.) intended by such partial driving method.
The BLU according to the present invention is suitable especially for local dimming or impulsive driving methods. In these methods, the liquid crystal panel has a plurality of divided regions, and the LED light source unit irradiates light separately to the divided regions of the liquid crystal display. For example, referring to FIG. 4, each of the light source regions A1, A2 and A3 of the LED light source unit can irradiate light to corresponding one of the divided regions of the liquid crystal display. In the local dimming method, the luminance of each of the light source regions can be controlled according to the gray level peak value of each of the divided regions. In the impulsive driving method, a plurality of light source regions divided by the partitions 104 can be synchronized in time with the divided regions of the liquid crystal panel, allowing sequential lighting.
FIG. 9 is a view illustrating a liquid crystal display having the BLU according to an embodiment of the present invention. In this embodiment, the BLU is driven by the local dimming method. Referring to FIG. 9, a plurality of LEDs 103 arranged on the substrate 101 irradiate light to the back surface of the liquid crystal panel 107 (for convenience, the optical sheet is not shown). The plurality of the LEDs 103, i.e., the LED light source unit is divided into a plurality of light source regions driven separately, and partitions 104 are disposed at the boundaries between the plurality of light source regions.
The liquid crystal panel 107 is divided into a plurality of regions (the divided regions are indicated by the dotted lines), which produces images, respectively. The LED light source unit irradiates light separately to the divided regions of the liquid crystal panel 107. At this time, the luminance of each of the light source regions (of the LED light source unit) is adjusted according to the gray level peak value of each of the divided regions (of the liquid crystal panel). That is, the light source region corresponding to one of the divided regions, which should have relatively higher luminance, is lighted with a higher current duty radio than other light source regions. Alternatively, the duty ratio of the light source regions corresponding to the other divided regions can be lowered.
The operation of the BLU by the local dimming is explained with reference to FIG. 9.
When a video signal is inputted to a signal processor 130, the signal processor 130 supplies an image signal for driving each pixel of the liquid crystal panel. In addition, the signal processor 130 processes the video signal to generate a gray level signal for each of the divided regions of the liquid crystal panel 107. The gray level signal is supplied to a controller 122 of the circuit 102. The gray level signal can be the gray level peak value of each of the divided regions.
The controller 122 controls the operation of the LED driver 112 inside the circuit 102 according to the gray level signal. The LED driver 112 drives the LED light source unit in accordance with the control of the controller 122 such that at least some of the light source regions have different luminance from other light source regions. Each of the light source regions of the LED light source unit operates to exhibit the luminance corresponding to each of the gray level peak values. With this method, the luminance of each of the light source regions can be adjusted according to the gray level peak value of each of the divided regions of the liquid crystal panel.
Using such local dimming method allows increasing the contrast ratio of the display while achieving a lively image. In particular, as the partitions are installed at the boundaries of the light source regions, the luminance distribution of the BLU is more clearly distinguished among the regions. This in turn further maximizes the effects of local dimming method and reduces unnecessary light loss.
According to the present invention as set forth above, partitions are installed between light source regions partially driven, thereby allowing a light distribution of the BLU, which is clearly distinguished by the light source regions. This in turn allows more effective matching of the BLU with a liquid crystal panel, reducing unnecessary light loss. Furthermore, accurately confining and lighting only a portion of the liquid crystal panel allows a higher contrast ratio, a clearer image, and further enhanced image quality. Moreover, this allows obtaining a desired form of luminance distribution according to the shape or the structure of the partitions.
While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
Patent Application
20070247833
