JP5386258B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device using an LED as a backlight, and more particularly to a relatively large liquid crystal display device used in a TV or the like that is thin and consumes less power.

  In a liquid crystal display device, there are a TFT substrate in which pixel electrodes and thin film transistors (TFTs) are formed in a matrix, and a counter substrate in which color filters are formed at locations corresponding to the pixel electrodes of the TFT substrate, facing the TFT substrate. The liquid crystal is sandwiched between the TFT substrate and the counter substrate. An image is formed by controlling the light transmittance of the liquid crystal molecules for each pixel.

  Liquid crystal display devices are used in various fields because they can be made thin and light. Since the liquid crystal itself does not emit light, a backlight is disposed on the back of the liquid crystal display panel. A fluorescent tube has been used as a backlight in a liquid crystal display device having a relatively large screen such as a television. However, LEDs (Light Emitting Diodes) have started to be used in order to make the liquid crystal display device thinner or to increase the color display area.

  There are two types of backlight light source arrangements: a direct type that places the light source directly under the liquid crystal display panel and a sidelight type that places the light source on the side of the light guide plate. In order to increase the brightness of the screen, a direct light source has been often used.

  Although it has been performed by a conventional cathode ray tube TV or the like, it is not always necessary to make the screen brightness uniform in the application of the TV or the like, and the peripheral luminance can be made smaller than the central luminance. In “Patent Document 1”, a fluorescent tube is used as a light source of a direct type backlight, and the density of the dot pattern formed on the reflection surface is changed between the center and the periphery, whereby the brightness of the screen periphery is changed from the brightness of the screen center. A configuration for reducing the size is also described. In addition, “Patent Document 1” describes a configuration in which the brightness of a screen is adjusted by using an LED as a light source of a direct type backlight and changing the density of the LED depending on a place.

  In “Patent Document 2”, in a relatively small liquid crystal display device, a sidelight type backlight is used, and the density of LEDs arranged on the side of the light guide plate is changed between the vicinity of the center and the vicinity of the periphery. It describes that the brightness of the screen is adjusted.

  “Patent Document 3” describes a configuration in which a plurality of seamless light guide plates are formed in a first direction in a sidelight type light guide plate. The light guide plate described in “Patent Document 3” is a single light guide plate that is continuous in a second direction perpendicular to the first direction.

JP WO2004 / 038283 JP 2002-75038 A JP 2001-93321 A

  The direct type backlight can easily increase the brightness of the screen, but it is difficult to reduce the thickness of the liquid crystal display device. FIG. 27 is a schematic cross-sectional view of a liquid crystal display device having a direct type backlight in which the light source is an LED. The LED 30 is disposed on the back cover 90. In the direct type backlight, a diffusion plate 60, a diffusion sheet, and the like are used, but are omitted in FIG.

  In FIG. 27, the distance d from the bottom of the LED 30 to the lower side of the liquid crystal display panel needs to be about 25 mm to 35 mm. In FIG. 27, if the distance d between the liquid crystal display panel 10 and the LED 30 is reduced while the pitch P of the LEDs 30 is kept constant, luminance unevenness occurs. In order to reduce the distance d, the pitch P of the LEDs 30 needs to be reduced so that the luminance unevenness does not occur. However, reducing the pitch P of the LEDs 30 means that the number of LEDs 30 needs to be increased, which is a problem in terms of manufacturing cost.

  FIG. 28 is a schematic cross-sectional view of a sidelight type liquid crystal display device. In FIG. 19, the light guide plate 50 is disposed on the back cover 90, and the LEDs 30 are disposed on the side surfaces of the light guide plate 50. Light from the LED 30 is directed toward the liquid crystal display panel 10 by the light guide plate 50. Actually, a diffusion sheet or the like exists between the liquid crystal display panel 10 and the light guide plate 50, but is omitted in FIG.

  In FIG. 28, the distance d from the lower side of the light guide plate 50 to the lower side of the liquid crystal display panel 10 is 10 to 15 mm, which can be made smaller than in the case of a direct type backlight. However, since the light of the LED 30 is incident from the side of the light guide plate 50, the light use efficiency is lower than that of the direct type. In order to obtain the same screen brightness as that of the direct type, as shown in FIG. 28, the number of LEDs 30 must be increased as compared with the case of the direct type.

  For example, in a 42-inch liquid crystal display device, in order to obtain a predetermined brightness, a direct-type backlight requires 500 LEDs 30. On the other hand, in order to obtain the same brightness on the same screen, it is necessary to use 700 LEDs 30 when using a sidelight type backlight. That is, in the sidelight system, the thickness of the liquid crystal display device can be reduced, but the number of LEDs 30 must be increased, and the power consumption of the LEDs 30 increases.

  An object of the present invention is to reduce the thickness of a liquid crystal display device without increasing the number of LEDs and without increasing power consumption as compared with a direct type backlight.

  The present invention overcomes the above problems, and specific means are as follows.

  (1) A liquid crystal display device having a liquid crystal display panel and a backlight, wherein the backlight has a rectangular light guide plate in which rectangular light guide plate blocks are arranged in a matrix, and corresponds to the light guide plate block The LED is disposed, and the size of the light guide plate block at the end of the light guide plate is larger than the size of the light guide plate block at the center of the light guide plate.

  (2) The liquid crystal display according to (1), wherein a size of the light guide plate block at a lateral end portion of the light guide plate is larger than a size of the light guide plate block at a central portion of the light guide plate. apparatus.

  (3) The liquid crystal display according to (1), wherein a size of the light guide plate block at a longitudinal end portion of the light guide plate is larger than a size of the light guide plate block at a central portion of the light guide plate. apparatus.

  (4) A liquid crystal display device having a liquid crystal display panel and a backlight, the backlight having a rectangular light guide plate in which rectangular light guide plate blocks are arranged in a matrix, and corresponding to the light guide plate block The LED is arranged, and a large-sized light guide plate block having a larger area than the light guide plate block at the center is arranged at the end of the light guide plate than the size of the light guide plate block at the center of the light guide plate, The liquid crystal display device, wherein the number of LEDs arranged in the light guide plate block and the number of LEDs arranged in the large light guide plate block are the same.

  (5) When the area of the light guide plate block at the center is S1 and the area of the large light guide plate block is S2, S2 / S1 is larger than 1 and 1.67 or less ( The liquid crystal display device according to 4).

  (6) A liquid crystal display device having a liquid crystal display panel and a backlight, wherein the backlight has a rectangular light guide plate in which rectangular light guide plate blocks are arranged in a matrix, and corresponds to the light guide plate block A plurality of LEDs are arranged, and a large-sized light guide plate block having a larger area than the light guide plate block at the center is arranged at the end of the light guide plate, rather than the size of the light guide plate block at the center of the light guide plate. The number of LEDs arranged in the light guide plate block is the same as the number of LEDs arranged in the large light guide plate block, and the electric power input to the plurality of LEDs arranged in the light guide plate block in the center And a power input to a plurality of LEDs arranged in the large light guide plate block is equal.

  According to the present invention, the number of the light guide plate blocks can be reduced as a whole by using the light guide plate having the light guide plate blocks arranged in a matrix and enlarging the light guide plate blocks arranged in the peripheral portion. The number of can also be reduced as a whole. Therefore, since the number of LEDs can be reduced as a whole, the power consumption of the liquid crystal display device can be reduced.

  Further, according to the present invention, it is not necessary to positively change the number of LEDs in each light guide plate block, so that it is possible to easily control the brightness area. By performing brightness region control, the power consumption of the liquid crystal display device can be reduced. Furthermore, according to the present invention, since the light guide plate is constituted by the light guide plate blocks arranged in a matrix, the thickness of the backlight can be reduced.

It is a general-view figure of a liquid crystal display device. 1 is an exploded perspective view of Example 1. FIG. It is a perspective view of a division | segmentation light-guide plate. 1 is an exploded sectional view of Example 1. FIG. 1 is a detailed cross-sectional view of Example 1. FIG. It is a schematic diagram which shows the relationship between a light-guide plate block and LED. It is a top view of the light-guide plate as a comparative example with respect to this invention. It is a circuit diagram which shows the method of carrying out area | region control of the brightness for every light-guide plate block. 3 is a plan view of a light guide plate of Example 1. FIG. 4 is an enlarged plan view of a part of the light guide plate of Example 1. FIG. 2 is a schematic diagram of a large light guide plate block of Example 1. FIG. It is a schematic diagram which shows the leakage of the light from the specific light-guide plate block to the adjacent light-guide plate block. It is a schematic diagram which shows the area | region control of brightness. 6 is a plan view of a light guide plate of Example 2. FIG. 6 is an enlarged plan view of a part of a light guide plate of Example 2. FIG. It is a schematic diagram of the large sized light-guide plate block of Example 2. FIG. 6 is a plan view of a light guide plate of Example 3. FIG. 6 is a plan view of a light guide plate that is a first example of Embodiment 4. FIG. 6 is a plan view of a light guide plate that is a second example of Embodiment 4. FIG. 6 is a plan view of a light guide plate that is a third example of Embodiment 4. FIG. 10 is a plan view of a light guide plate that is a fourth example of Embodiment 4. FIG. 6 is a plan view of a light guide plate that is a fifth example of Embodiment 4. FIG. 10 is a plan view of a light guide plate that is a sixth example of Embodiment 4. FIG. 10 is an exploded perspective view of Example 5. FIG. FIG. 10 is a perspective view of a light guide plate of Example 5. It is sectional drawing which shows the relationship between the light-guide plate of Example 5, and LED. It is sectional drawing of a direct type | mold backlight. It is sectional drawing of a sidelight type backlight.

  FIG. 1 is a liquid crystal TV showing an example in which the liquid crystal display device according to the present invention is used. In FIG. 1, the display frame 2 leaves the display screen 1 and surrounds the periphery of the liquid crystal display panel. A backlight 3 is disposed on the back surface of the liquid crystal display panel. The backlight 3 shown in FIG. 1 has a configuration having a light guide plate having a plurality of light guide plate blocks and LEDs arranged in each light guide plate block.

  FIG. 2 is an exploded perspective view of the liquid crystal display panel 10 and the backlight from which the display frame and the like are removed in the liquid crystal display device shown in FIG. In FIG. 2, a TFT substrate 11 on which a display area in which TFTs and pixel electrodes are arranged in a matrix, scanning lines, video signal lines and the like and an opposite substrate 12 on which color filters and the like are formed are bonded with an adhesive (not shown). Are bonded through. A liquid crystal (not shown) is sandwiched between the TFT substrate 11 and the counter substrate 12.

  A lower polarizing plate 14 is attached to the lower side of the TFT substrate 11, and an upper polarizing plate 13 is attached to the upper side of the counter substrate 12. A state in which the TFT substrate 11, the counter substrate 12, the lower polarizing plate 14, and the upper polarizing plate 13 are bonded together is referred to as a liquid crystal display panel 10. A backlight is disposed on the back surface of the liquid crystal display panel 10. The backlight is formed of a light source unit and various optical components.

  In FIG. 2, the LEDs 30 are arranged on the wiring board 40 in the light source unit. A divided light guide plate 53 having a light guide plate block 51 or a large light guide plate block 511 is disposed on the wiring substrate 40 on which the LEDs 30 are disposed. The LEDs 30 arranged on the wiring board 40 correspond to the respective light guide plate blocks. The LEDs 30 are arranged in the same number in each light guide plate block.

  The light guide plate 50 shown in FIG. 2 is formed of four rectangular light guide plates 53. The length L2 of the divided light guide plate 53 located at both ends of the light guide plate 50 (display surface of the liquid crystal display panel 10) is two rows of divided light guide plates located at the center of the light guide plate 50 (display surface of the liquid crystal display panel 10). It is larger than the length L1. The length L2 of the divided light guide plates 53 at both ends is 1.5 times the length L1 of the central divided light guide plate. Therefore, by using the divided light guide plates 53 having a long length at both ends, four divided light guide plates 53 that are normally required are completed by four.

  The shape of the divided light guide plate 53 is shown in FIG. FIG. 3A is a perspective view of the central divided light guide plate 53 in FIG. 2, but the shapes of the divided light guide plates at both ends are essentially the same except that the length is different. In the divided light guide plate 53, four light guide plate blocks 51 are formed. The length of each light guide plate block 51 is L1 like the length of the divided light guide plate 53, and the width of each light guide plate block 51 is W1. Therefore, the width of the divided light guide plate 53 is 4W1.

  FIG. 3B is a cross-sectional view taken along the line KK of FIG. Each light guide plate block 51 is partitioned by a groove 52. Each light guide plate block 51 functions as an independent light guide plate by the groove 52. As shown in FIG. 3B, the shape of the groove 52 is substantially V-shaped, and the depth d is about 0.5 mm.

  Returning to FIG. 2, the same number of LEDs are arranged in each light guide plate block. Accordingly, the luminance of the screen in FIG. 2 is lower at both ends than at the center. However, in applications such as TV, even if the peripheral luminance is about 60% of the central luminance, there is almost no discomfort on the screen. As shown in FIG. 2, by reducing the width of the light guide plate block in the periphery, the number of light guide plate blocks is reduced as a whole, while the number of LEDs arranged in each light guide plate block is constant, As a whole, the number of LEDs used can be reduced. Therefore, the power consumption of the LED can be suppressed.

  In FIG. 2, three diffusion sheets 15 are arranged on the light guide plate 50. Since each diffusion sheet 15 is as thin as about 60 μm, the three diffusion sheets 15 are actually placed on the light guide plate 50. Fine irregularities are formed on the surface of the diffusion sheet 15, and this diffuses light from the light guide plate 50. Further, the fine irregularities on the surface have a role of a kind of prism, and also have a function of directing light incident obliquely on the diffusion sheet 15 toward the liquid crystal display panel 10.

  The number of the diffusion sheets 15 is an example, and may be one, two, or more than three as necessary. In addition to the diffusion sheet 15, a prism sheet may be disposed if necessary. The prism sheet has a function of improving the luminance of the screen by directing light from the backlight incident from an oblique direction toward the liquid crystal display panel 10.

  The liquid crystal display panel 10 is disposed on the uppermost diffusion sheet 15. Even after the assembly, the liquid crystal display panel 10 and the diffusion sheet 15 are spaced apart by, for example, about 50 μm. This is to prevent the diffusion sheet 15 and the lower polarizing plate 14 from being rubbed and scratched.

  4 is an exploded cross-sectional view of the liquid crystal display device shown in FIG. In FIG. 4, the liquid crystal display panel 10 and the three diffusion sheets 15 are as described in FIG. In FIG. 4, a light guide plate 50 is disposed below the diffusion sheet 15. The light guide plate 50 is formed of four divided light guide plates 53. The length L2 of the divided light guide plates at both ends is larger than the length L1 of the divided light guide plates in the two central rows.

  As described in FIG. 3, each divided light guide plate 53 further includes four light guide plate blocks. The divided light guide plates at both ends include a light guide plate block 511 having a length L2, and the center two rows of light guide plates 51 include a light guide plate block 51 having a length L1. Since the length L2 of the light guide plate block 511 included in the divided light guide plates at both ends is 1.5 times the length L1 of the light guide plate block 51 included in the central divided light guide plate, originally, five required divisions are required. Four light guide plates are used.

  Each divided light guide plate 53 has a wedge-shaped cross section, and has a thick part and a thin part. The thick part is about 3 mm, and the thin part is less than 1 mm. Since the thin part of the divided light guide plate 53 enters the step formed in the thick part of the previously arranged split light guide plate 53, the appearance looks like a single light guide plate 50.

  In FIG. 4, the light guide plate 50 is placed on the wiring board 40 having the LEDs 30. The arrangement interval of the LEDs 30 varies depending on the length of the light guide plate block. The LEDs 30 are arranged on the side surfaces of the thick sections of the divided light guide plates 53. Light from the LED 30 that has entered from the side surface on the thick side of the light guide plate 50 changes its direction toward the liquid crystal display panel 10 and exits within the light guide plate 50.

  FIG. 5 is a cross-sectional view showing a state in which the components shown in FIG. 4 are assembled. FIG. 5 shows a cross section of the light guide plate block 51 corresponding to the divided light guide plates in the center two rows of FIG. In FIG. 5, the LEDs 30 arranged on the wiring board 40 are arranged on the thick side surface of the light guide plate block 51. The LEDs 30 are combined for each divided light guide plate 53. There is no need to combine each LED 30 or each light guide plate block 51.

  In FIG. 5, the light from the LED 30 incident from the side surface of the light guide plate block 51 is reflected by, for example, the lower surface of the light guide plate block 51 and travels toward the liquid crystal display panel 10. However, since the lower surface of the light guide plate block 51 is a diffusing surface, the light incident from the LED 30 goes in various directions, but most of the light goes in the direction of the liquid crystal display panel 10.

  In order to direct the light from the LED 30 toward the liquid crystal display panel 10 efficiently, the lower surface of the light guide plate block 51 needs to have a predetermined inclination. Therefore, when the light guide plate 50 is large, the surface of the light guide plate 50 on which the LEDs 30 are arranged becomes thick. In the present invention, since the light guide plate 50 is divided, the thickness can be reduced.

  FIG. 6 is a schematic diagram showing the relationship between the light guide plate block 51 and the LEDs 30. 6A is a schematic cross-sectional view, and FIG. 6B is a perspective view. In FIG. 6A, the cross section of the light guide plate block 51 is simplified and described as being triangular. The LED 30 is disposed on the thick side of the side surface of the light guide plate block 51. For clarity, FIG. 6A shows that the LED 30 is separated from the side surface of the light guide plate block 51. In practice, however, the LED 30 is used to increase the light use efficiency of the LED 30. Arranged as close to the side as possible.

  In FIG. 6B, three LEDs 30 are arranged on the side surface of the light guide plate 50. FIG. 6B describes the light guide plate block 51 near the center of FIG. 4, but three LEDs 30 are also arranged for the light guide plate blocks 511 at both ends in FIG.

  In FIG. 4, the ratio between the length L1 of the light guide plate block 51 near the center and the length L2 of the light guide plate blocks 511 at both ends is L2 / L1 = 1.5, and the number of LEDs arranged in each light guide plate block is If the number is constant, the brightness at both ends of the screen is about 1 / 1.5 = 67% of the brightness at the center of the screen. However, such a brightness difference is also present in conventional CRT TVs, and the screen does not feel strange. Further, as will be described later, since light leaks between the light guide plate blocks, the brightness does not change abruptly between the light guide plate blocks.

  FIG. 7 is a plan view of a light guide plate 50 partitioned by a light guide plate block 51 in a TV having a screen size of 42 inches as a comparative example. In FIG. 7, the light guide plate block 51 has a length L1 of 66 mm and a width W1 of 59 mm. The light guide plate has a horizontal diameter XL of 944 mm and a vertical diameter YL of 528 mm. Therefore, in FIG. 7, a total of 128 light guide plates are arranged in a matrix, with 8 light guide plate blocks in the vertical direction and 16 in the horizontal direction. The light guide plate 50 is formed by arranging eight horizontally long divided light guide plates having 16 light guide plate blocks 51 in the horizontal direction in the vertical direction. However, the method of creating the light guide plate 50 is not limited to this. That is, the shape of the divided light guide plate can be arbitrarily selected. The following description is based on the light guide plate block.

  In FIG. 7, the screen size of 42 inches has a horizontal diameter XD of 930 mm and a vertical diameter YD of 523 mm. Therefore, the light guide plate is larger by about 14 mm in horizontal diameter and about 5 mm in vertical diameter. In consideration of the assembly accuracy of the liquid crystal display panel 10, the light guide plate 50, and the LED 30, the outer shape of the light guide plate 50 is slightly larger than the screen size.

  As shown in FIG. 7, if light guide plate blocks 51 of the same size are used and the same number of LEDs 30 are arranged in each light guide plate block 51, the luminance of the screen becomes uniform. On the other hand, in order to reduce the power consumption of the backlight, when reducing the luminance around the screen, it is possible to take a means of reducing the number of LEDs 30 arranged in the peripheral light guide plate block 51. In this case, the number of LEDs for each light guide plate block varies depending on the location of the screen.

  As a driving method of the liquid crystal display device, there is an area control method for controlling the brightness of the backlight for each place according to the image on the screen. If the area control is performed, it is only necessary to turn on the backlight or the LED of only a necessary portion, so that the power consumption of the backlight can be reduced and the contrast can be improved.

  Such area control is performed by storing video information for one frame in a frame memory, identifying a bright part and a dark part of the screen, and turning on the LED 30 only in the area corresponding to the bright part. I can do it. In the light guide plate partitioned by the light guide plate block, the region control can be performed for each light guide plate block.

  The circuit of the LED 30 for each light guide plate block 51 for performing the area control is, for example, as shown in FIG. FIG. 8 shows a case where three LEDs 30 are arranged in each light guide plate block 51. In FIG. 8, a DC power source 110 is used for the LED 30. The current flowing through the LED 30 is controlled by a signal from the control circuit 100. In this case, if the number of LEDs 30 is different for each light guide plate block 51, the control signal needs to be changed accordingly. Therefore, there is a problem that the area control system becomes complicated.

  In the present invention, FIGS. Or since the number of LED30 arrange | positioned at each light-guide plate block is constant as shown in a following example, it also has the advantage that area | region control can be performed easily. An embodiment of the present invention will be described below taking a large TV as an example.

  FIG. 9 shows an example in which the number of light guide plate blocks is reduced as a whole by using large light guide plate blocks at the top and bottom of a 42-inch TV screen. In FIG. 9, the range where the large light guide plate block 511 is used is hatched. The same applies to the following drawings. In FIG. 9, the light guide plate blocks are arranged 7 in the vertical direction and 16 in the horizontal direction, and a total of 112 light guide plate blocks are used. Therefore, compared with the case shown in FIG. 7, the number of light guide plate blocks can be reduced by 16, and the figure of LED can be reduced by 48. Therefore, the cost of the LED 30 can be reduced and the power consumption by the LED 30 can be reduced.

  FIG. 10 shows an example in which the lower three blocks of the light guide plate 50 in FIG. 9 are displayed. The width of the light guide plate block is the same W1 in the case of the normal light guide plate 51 and in the case of the large light guide plate 511, for example, 59 mm. The length of the light guide plate block is L2 for the large light guide plate block 511, for example, 99 mm, and is 66 mm for the normal light guide plate block 51, for example, 66 mm.

  In each light guide plate, three LEDs 30 are arranged. Since the intensity of the light emitted from the light guide plate block is inversely proportional to the area of the light guide plate block, assuming that the luminance of the normal light guide plate 51 is 100, the luminance of the large light guide plate is 67. However, since light from the light guide plate block leaks at the boundary 520 between the normal light guide plate block 51 and the large light guide plate block 511, the luminance does not change abruptly at the boundary 520.

  Although the luminance in the large light guide plate block 511 is reduced by about 33% with respect to the luminance in the normal light guide plate block 51, the luminance does not change abruptly at the boundary, so that the screen does not feel strange. In order to further alleviate the change in luminance, the density of the embossments 57 (or dots) used as the light diffusion pattern formed in the large light guide plate block 511 as shown in FIG. 11 can be changed.

  The embossment 57 is disposed on the back side of the light guide plate block 511, that is, on the opposite side of the liquid crystal display panel. The light quantity emitted from the surface of the light guide plate block 511 is increased in the portion where the density of the texture 57 is large. Therefore, in FIG. 11, the light emitted from the light guide plate block 511 decreases as shown by the arrow E due to the influence of the grain density. In this way, by increasing the density of the texture closer to the normal light guide plate block 51, the luminance portion in the large light guide plate block 511 can be gradually changed to make the change in luminance less noticeable. .

  FIG. 12 shows an example of luminance when the LED 30 of only one light guide plate block 55 is illuminated in the light guide plate 50 divided into blocks. As shown in FIG. 12, although only one light guide plate block 55 is actually illuminated, the surrounding light guide plate block 56 is also brightened. This is because light leaks from the light guide plate block 55 to the other light guide plate block 56.

  Due to the presence of such light leakage, as shown in FIG. 9, even in a place where the normal light guide plate block 51 and the large light guide plate block 511 are arranged, the screen luminance changes abruptly at that portion. There is no. Therefore, even when white is displayed on the entire screen, luminance unevenness does not occur.

  On the other hand, in the present invention, since the light guide plate block is used, the fineness of the area control of the light guide plate block and the brightness can be a problem. FIG. 13 is an explanatory diagram showing how the light guide plate block affects an actual image when brightness area control is performed. FIG. 13A shows an image to be actually displayed. FIG. 13A shows a case where a bright portion 70, for example, the moon is displayed on a dark background.

  As described above, in the present invention, brightness area control can be easily performed. FIG. 13B is an example of the luminance of the backlight when brightness area control is performed corresponding to the image of FIG. 13A. In FIG. 13B, the LED 30 of the light guide plate block corresponding to the moon on the screen is lit. FIG. 13C shows the correspondence between the image and the brightness of the backlight that performs brightness area control. The light guide plate block corresponding to the moon on the screen is bright. As shown in FIG. 13C, appropriate brightness can be obtained by lighting the LEDs 30 of the plurality of light guide plate blocks corresponding to the bright portions.

  FIG. 14 shows an example in which the number of light guide plate blocks is reduced as a whole by using large light guide plate blocks on both sides of a 42-inch TV screen. In FIG. 14, the light guide plate blocks are arranged 8 in the vertical direction and 15 in the horizontal direction, and a total of 120 light guide plate blocks are used. Therefore, compared with the case shown in FIG. 7, the number of light-guide plate blocks can be reduced by 8, and the figure of LED can be reduced by 24. Therefore, the cost of the LED 30 can be reduced and the power consumption by the LED 30 can be reduced.

  FIG. 15 is an example in which the lower right four blocks of the light guide plate 50 of FIG. 14 are displayed. The length of the light guide plate block is the same L1 in the case of the normal light guide plate 51 and in the case of the large light guide plate 511, for example, 66 mm. The width of the light guide plate block is W2 for the large light guide plate block 511, for example, 88.5 mm, and the width of the normal light guide plate block 51 is, for example, 59 mm for W1.

  In each light guide plate, three LEDs 30 are arranged. Since the intensity of the light emitted from the light guide plate block is inversely proportional to the area of the light guide plate block, assuming that the luminance of the normal light guide plate 51 is 100, the luminance of the large light guide plate is 67. However, since light from the light guide plate block leaks at the boundary 522 between the normal light guide plate block 51 and the large light guide plate block 511, the luminance does not change abruptly at the boundary 522.

  Although the luminance in the large light guide plate block 511 is reduced by about 33% with respect to the luminance in the normal light guide plate block 51, the luminance does not change abruptly at the boundary, so that the screen does not feel strange. In order to further alleviate the change in luminance, the density of the embossments 57 (or dots) used as the light diffusion pattern formed on the large light guide plate block 511 as shown in FIG. 16 can be changed.

  The embossing 57 is disposed on the back side of the light guide plate block, that is, on the side opposite to the liquid crystal display panel. The amount of light emitted from the surface of the light guide plate block 511 increases in the portion where the wrinkle density is high. Accordingly, in FIG. 16, the light emitted from the light guide plate block 511 decreases as indicated by the arrow F due to the influence of the grain density. In this way, by increasing the density of the texture closer to the normal light guide plate block 51, the luminance portion in the large light guide plate block 511 can be gradually changed to make the change in luminance less noticeable. .

  FIG. 17 shows an example in which the number of light guide plate blocks is reduced as a whole by using large light guide plate blocks 511 on the upper and lower sides and both sides of the screen of a 42-inch TV. In FIG. 14, the light guide plate blocks are arranged 7 in the vertical direction and 15 in the horizontal direction, and a total of 105 light guide plate blocks are used. Therefore, compared with the case shown in FIG. 7, the number of light guide plate blocks can be reduced by 23, and the number of LEDs can be reduced by 69. Therefore, the cost of the LED 30 can be reduced and the power consumption by the LED 30 can be greatly reduced.

  The example of the luminance distribution at the boundary between the normal light guide plate block 51 and the large light guide plate block 511, the relaxation of the luminance distribution, and the like are the same as those described in the first and second embodiments. In the first and second embodiments, one type of large light guide plate block 511 may be used in addition to the normal light guide plate block 51, but in this embodiment, three types in addition to the normal light guide plate block 51 are used. Large light guide plate block 511 must be used.

  That is, a vertically long light guide plate block 511 is used above and below the screen, and a wide light guide plate block 511 is used on both sides of the screen. Furthermore, in the corner portion, it is necessary to use a light guide plate block 511 that is larger than the normal light guide plate block 51 in both the vertical diameter and the horizontal diameter. Further, since the large-sized light guide plate block 511 at the corner portion has only light leaking from the large-sized light guide plate block having low luminance from the upper direction (or the lower direction) and the horizontal direction, the luminance at the corner portion is further reduced. To do.

  As described above, it is necessary to determine the vertical diameter L2 and the horizontal diameter W2 of the large light guide plate block 511 and the vertical diameter L1 and the horizontal diameter W1 of the normal light guide plate block 51 in anticipation of luminance reduction in the corner portion.

  Examples 1 to 3 are examples of the arrangement of light guide plate blocks that are subject to screen brightness up and down or left and right. However, there are actually various screen sizes, and a large light guide plate block cannot always be arranged on the screen. That is, it is disadvantageous in cost to design and manufacture the light guide plate block for each screen size. Therefore, there are cases where it is desired to use a light guide plate block designed and manufactured with another screen size for a light guide plate block with a different screen size.

  On the other hand, if the luminance ratio corresponding to the normal light guide plate block and the large light guide plate block is about 40%, the luminance unevenness due to the light guide plate block is hardly recognized. The present embodiment is an example in which the arrangement of the large light guide plate block 511 is not arranged with respect to the screen.

  FIG. 18 shows an example in which the large light guide plate block 511 is arranged on the upper side of the screen. In FIG. 18, the width of the light guide plate block is the same for both the normal light guide plate block 51 and the large light guide plate block 511 and is W1. The length L2 of the large light guide plate block 511 is 1.5 times the length L1 of the normal light guide plate block 51. In this case, the amount of light emitted from the large light guide plate block 511 is usually 67% of the amount of light emitted from the light guide plate block 51.

  Note that the change in the luminance distribution is substantially inconspicuous until the length L2 of the large light guide plate block is up to about 1.67 times the length L1 of the normal light guide plate block 51. In order to further improve the luminance distribution, the texture density distribution on the bottom surface of the light guide plate block 511 can be changed as shown in FIG. As a result, the light guide plate blocks for one horizontal row can be omitted, and the number of corresponding LEDs can be reduced.

  FIG. 19 shows an example in which a large light guide plate block 511 is arranged on the lower side of the screen. This is an example of lowering the luminance on the lower side of the screen, but in this case as well, the configuration in which the change in luminance is inconspicuous can be achieved in the same manner as described with reference to FIG. As a result, the light guide plate blocks for one horizontal row can be omitted, and the number of corresponding LEDs can be reduced.

  FIG. 20 is an example in which a large light guide plate block is used on the left side of the screen. In FIG. 20, by setting W2 / W1 to 1.67 or less, the luminance distribution can be made substantially inconspicuous. In order to make the luminance distribution less noticeable, for example, a texture 57 having a density distribution as shown in FIG. 16 can be formed on the back surface of the large light guide plate block 511. FIG. 21 shows an example in which a large light guide plate block 511 is used on the right side of the screen. The operation is exactly the same as described in FIG.

  FIG. 22 shows an example in which large light guide plate blocks 511 are used on the upper side of the screen and the right side of the screen. In the examples of FIGS. 18 to 21, one type of large light guide plate block 511 may be used, but in this embodiment, three types of large light guide plate blocks 511 are required. However, when the large light guide plate block 511 used in another screen size can be used, the arrangement of the light guide plate block as shown in FIG. 22 may be advantageous.

  FIG. 23 shows an example in which large light guide plate blocks 511 are used on the lower side of the screen and the left side of the screen. It can be used in exactly the same way as described in FIG. In addition, when the large light guide plate block 511 is used on the upper side of the screen and the lower side of the screen, it is needless to say that the same can be done when the large light guide plate block 511 is used on the lower side of the screen and the right side of the screen. .

In the first to fourth embodiments, the light guide plate 50 is formed using a divided light guide plate 53 having a plurality of light guide plate blocks 51 or large light guide plate blocks 511. There are various modifications to the method of forming the divided light guide plate 53. For example, in the example of FIG. 9, the divided light guide plate 53 in which 16 large light guide plate blocks 511 are arranged in the horizontal direction and the light guide plate block 53 in which 16 normal light guide plate blocks 51 are arranged in the horizontal direction are combined. Can also be used.

  On the other hand, all the light guide plate blocks 51 or the large light guide plate blocks 511 can be formed on one light guide plate 50. FIG. 24 shows an example in which all the light guide plate blocks are formed in one light guide plate 50. FIG. 24 is the same as FIG. 2 except for the light guide plate 50. In FIG. 24, the light guide plate 50 is formed with four light guide plate blocks 51 in the y direction and four in the x direction. Large light guide plate blocks 511 are formed on both rows, and normal light guide plate blocks 51 are formed on the two central rows.

  FIG. 25 is a perspective view of the integrated light guide plate 50. In FIG. 25, a groove 52 indicating the boundary of the light guide plate block 51 or the large light guide plate block 511 extends in the x direction. The shape of the groove 52 is the same as that shown in FIG. A dotted line extending in the y direction is a portion where the thickness is thin in the light guide plate block 51 or the large light guide plate block 511, and the boundary between the light guide plate block 51 or the large light guide plate block 511 in this portion. Is formed. Each light guide plate block has a wedge-shaped cross section. For example, a thick portion is about 3 mm and a thin portion is less than 1 mm.

  The boundary of each light guide plate block is formed by the groove 52 extending in the x direction or the thinned region of the light guide plate block extending in the y direction. Since the light is not completely blocked, the light of a specific light guide plate block leaks to the adjacent light guide plate block. This action eliminates the luminance step between the light guide plate blocks 51 and forms a smooth luminance distribution.

  FIG. 26 is a cross-sectional view showing a state in which the wiring board 40 having the light guide plate 50 and the LEDs 30 in the present embodiment is assembled. FIG. 26 shows the light guide plate block 51 in a row near the center. The optical sheet and the liquid crystal display panel 10 are disposed on the light guide plate 50 shown in FIG. 26, but are omitted in FIG. In FIG. 26, the LED 30 is disposed on the side surface of the thick portion of the light guide plate block 51 having a wedge-shaped cross section.

  As shown in FIG. 26, the light guide plate block 51 having a wedge-shaped cross section is connected to the previous light guide plate block 51 in the thinner plate thickness. Since this connection portion exists, the light from the LED 30 leaks to the previous light guide plate block 51, and the brightness between the light guide plate blocks 51 is prevented from changing abruptly. As shown in FIG. 24, a large number of LEDs 30 are attached to the wiring board 40. However, since all the light guide plate blocks 51 are integrally formed, the combination of the light guide plate 50 and the LEDs 30 can be performed only once. I can do it.

  As described above, in the present invention, a light guide plate having light guide plate blocks of different sizes may be assembled as a divided light guide plate including a plurality of light guide plate blocks, or a light guide plate including a plurality of light guide plate blocks is integrated. You may shape it.

  DESCRIPTION OF SYMBOLS 1 ... Display screen, 2 ... Display frame, 3 ... Backlight, 10 ... Liquid crystal display panel, 11 ... TFT substrate, 12 ... Opposite substrate, 13 ... Upper polarizing plate, 14 ... Lower polarizing plate, 15 ... Diffusion sheet, 30 ... LED, 40 ... Wiring board, 45 ... Dark part, 50 ... Light guide plate, 51 ... Light guide plate block, 52 ... Groove, 53 ... Divided light guide plate, 55 ... Bright block, 56 ... Light leaked block, 57 ... Wrinkle, 70 ... Bright image, 80 ... Reflective sheet, 90 ... Back cover, 100 ... Control circuit, 110 ... DC power supply, 511 ... Large light guide plate block, 520 ... Boundary between large light guide plate block and normal light guide plate block.

Claims (3)

A liquid crystal display device having a liquid crystal display panel and a backlight,
The backlight has a rectangular light guide plate in which rectangular light guide plate blocks are arranged in a matrix, and LEDs are arranged corresponding to the light guide plate blocks,
A plurality of the light guide plate blocks are integrally formed, thereby causing light leakage between the adjacent light guide plate blocks,
The size of the light guide plate block at the horizontal end, the vertical end, or the horizontal and vertical ends of the light guide plate is larger than the size of the light guide plate block at the center of the light guide plate. and rather large, than the size of the light guide plate blocks in the center portion,
The number of LEDs arranged in the light guide plate block in the center of the light guide plate and the light guide plate block at the horizontal end, vertical end, or horizontal and vertical ends of the light guide plate A liquid crystal display device having the same number of LEDs . When the area of the light guide plate block at the center is S1, and the area of the light guide plate block at the horizontal end, the vertical end, or the horizontal and vertical ends of the light guide plate is S2, S2 / The liquid crystal display device according to claim 1, wherein S1 is greater than 1 and equal to or less than 1.67 . Power input to the plurality of LEDs arranged in the light guide plate block at the center and the light guide plate block at the horizontal end, the vertical end, or the horizontal and vertical ends of the light guide plate The liquid crystal display device according to claim 1, wherein powers input to the plurality of LEDs are equal .

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