JP2009272251A - Back light unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-type backlight unit in which both electric power-saving and a high contrast ratio can be made compatible, and a boundary between light-emitting regions is less likely to be conspicuous. <P>SOLUTION: The backlight unit includes a plurality of light guide plates 20 which have side faces and light-emitting faces, respectively, and are arranged while the side faces are opposed to each other, and a plurality of point light sources 22 which are arranged on respective side faces of the light guide plates, and by which light is simultaneously made incident on the plurality of respective light guide plates. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a backlight unit that includes a light source and a light guide plate and is used as a backlight of a liquid crystal display device or the like.

  Usually, a liquid crystal display device includes a liquid crystal display panel and a backlight unit that illuminates the liquid crystal display panel. A large-sized liquid crystal display device has a direct backlight, and a small-sized liquid crystal display device has a light guide plate backlight.

  In recent years, large liquid crystal display devices have been increasingly thinned, and direct type backlight units have been thinned by integrating the number of components. However, the direct type backlight unit needs to uniformly diffuse the light from the light source, and a space is required between the light source and the diffusion plate. As a result, there is a limit in reducing the thickness of the backlight unit in principle.

  On the other hand, in the backlight unit using the light guide plate method, the light source is arranged around the light guide plate and arranged in the frame portion of the screen. Therefore, the light guide plate type backlight unit can be made thinner than the direct type. Attempts have been made to use a light guide plate type backlight unit for a large liquid crystal display device, but there is a technical problem in forming a large light guide plate.

  As will be described later, in recent years, a local dimming technique has been developed in which the light emission region of the backlight is divided and individually driven. However, since the light guide plate type backlight unit has a light source arranged around the display screen, in principle, the light emitting areas cannot be two-dimensionally arranged and does not support local dimming.

  As described above, in order to achieve further thinning of the large-sized liquid crystal display device, a backlight unit of a system different from the conventional one is necessary.

In addition to the reduction in thickness, power saving of a liquid crystal display device is also an important issue. With the replacement of the light source of the backlight from the cold cathode fluorescent lamp (CCFL) to the light emitting diode (LED), attempts have been made to save power by adjusting the light source. In particular, a local dimming technique is known as a technique that enables high contrast and low power consumption of a liquid crystal display device (Non-Patent Document 1).
This is a next-generation backlight that uses a backlight unit in which a plurality of LEDs are arranged for each area of the light-emitting surface, and controls the light-emitting areas of the backlight according to video information by individually driving the light sources. Light drive technology. Thereby, in addition to the power saving of the liquid crystal display device, the contrast can be improved and the display quality can be improved.

As a backlight system for a large-sized liquid crystal display device that achieves both reduction in thickness and power saving, for example, a backlight system in which a large number of light guide plates and a large number of light sources are arranged in a plane has been proposed (Patent Literature). 1).
Seetzen et al., ACM Trans. Graph. 23, 3, pp. 760-768, 2004 JP 2007-293339 A

However, the above-described backlight system has a problem that the boundary between the light guide plates is easily noticeable because the amount of light changes in the divided portions of the light guide plates.
The present invention has been made in view of the above points, and an object of the present invention is to provide a backlight unit that can achieve both thinness, power saving, and high contrast ratio, and the boundary of the light emitting region is not noticeable.

  In order to achieve the above object, a backlight unit according to an aspect of the present invention has a plurality of light guide plates each having a side surface and an output surface and arranged in a state where the side surfaces face each other, And a plurality of point light sources that respectively enter the light into the plurality of light guide plates at the same time.

  A backlight unit according to another aspect of the present invention includes a plurality of light guide plates each having a side surface and an emission surface and arranged in a state where the side surfaces face each other, and the light guide plate disposed on a side surface of each of the light guide plates. A plurality of point light sources that allow light to enter the light source, and the boundary between the light guide plates and the boundary between the light emitting regions that adjust the amount of light emitted from each point light source are different from each other.

  According to the above configuration, it is possible to provide a backlight unit that can achieve both a thin shape, power saving, and a high contrast ratio, and the boundary between the light emitting regions is less noticeable.

Hereinafter, a liquid crystal display device including a backlight unit according to an embodiment of the present invention will be described in detail with reference to the drawings.
1 is an exploded perspective view showing a liquid crystal display device including a backlight unit according to the first embodiment, FIG. 2 is a cross-sectional view of the liquid crystal display device, and FIG. 3 is an enlarged view of a light guide plate and LEDs of the backlight unit. FIG. 4 is a plan view showing a light emitting region to which each LED contributes in the arrangement of the light guide plate and the LED.

  As shown in FIGS. 1 and 2, the liquid crystal display device includes a rectangular liquid crystal display panel 10 and a backlight unit 12 disposed to face the back side of the liquid crystal display panel. The liquid crystal display panel 10 includes a rectangular array substrate 15, a rectangular counter substrate 14 that is opposed to the array substrate 15 with a gap, and a liquid crystal layer 16 sealed between the array substrate and the counter substrate. I have.

  As shown in FIGS. 1 to 4, the backlight unit 12 includes a large number of light guide plates 20 separated from each other, and a large number of LEDs 22 each functioning as a point light source. Each light guide plate 20 is formed in a rectangular shape, for example, a square, and has a square emission surface 20a, four side surfaces 20b, and a bottom surface 20c located on the opposite side of the emission surface, and is formed of, for example, a transparent synthetic resin. Has been. Each of the multiple light guide plates 20 is arranged in a state where the side surface thereof is adjacent to and opposite to the side surfaces of the other light guide plates, in this case, in a surface contact state, and is arranged in a plurality of columns and a plurality of rows. The exit surfaces 20a of the multiple light guide plates 20 are aligned and located in the same plane. The large number of light guide plates 20 constitute a rectangular light guide plate having a size corresponding to the size of the liquid crystal display panel 10 as a whole.

  The backlight unit 12 has a rectangular printed circuit board 24. The light guide plate 20 is supported on the printed circuit board by, for example, bonding and fixing the bottom surface 20 c on the printed circuit board 24.

  A number of LEDs 22 are mounted on a printed circuit board 24 and electrically connected to the printed circuit board. The plurality of LEDs 22 are provided to face the side surfaces of the respective light guide plates 20, and are arranged at four corners of each light guide plate 20 here. In the present embodiment, each corner of each light guide plate 20 is cut into an arc shape to form a recess 21. By combining the corners of the four light guide plates 20, a substantially circular through hole 26 is defined by the recess 21. The LEDs 22 are respectively disposed in the through holes 26 and are opposed to the corners of the four light guide plates 20 positioned around the LEDs 22. Then, the LED 22 causes the emitted light to enter the four light guide plates 20 simultaneously.

  As shown in FIG. 4, the light emission area of the backlight by each LED 22 is a square area centering on the LED, and is a square area composed of four areas 1a, 2a, 3a, 4a indicated by broken lines. ing. Unlike the boundary between the adjacent light guide plates 20, the boundary of the light emitting region, that is, the contour is shifted by a half pitch.

  Each light guide plate 20 has a plurality of light emitting regions divided into the same number as the number of LEDs 22 entering the light guide plate. That is, in this embodiment, the light guide plate 20 has four light emitting areas 1a, 1b, 1c, and 1d (na, nb, nc, and nd) corresponding to the four LEDs.

FIG. 5 shows a three-dimensional shape of the light guide plate 20, and FIG. 6 shows a cross section along the diagonal of the light guide plate 20. 5 and 6, dotted lines indicate contour lines of the bottom surface 20 d of the light guide plate 20, and the bottom surface 20 d is formed in a shape that becomes shallower from the four corners toward the center. The inclination of the bottom surface 20d is formed such that the contour lines are perpendicular to the straight line connecting the LED and the center of the light guide plate 20. Thereby, the light guide plate 20 has a structure in which the short sides of the wedge-shaped light guide plate are combined.
In addition, as shown in FIG. 7, you may make it the inclination of the bottom face 20c of each light-guide plate 20 have the same height of the bottom of an equidistant point from LED22.

  In the backlight unit, an optical sheet 30 such as a lens sheet or a diffusion sheet is laid on the emission surface 20a of the plurality of light guide plates 20 in an overlapping manner. A reflection sheet (not shown) is provided so as to overlap the bottom surfaces 20 c of the plurality of light guide plates 20.

  The backlight unit 12 is provided adjacent to and facing the array substrate 15 of the liquid crystal display panel 10 with the optical sheet 30 interposed therebetween. By turning on the LEDs 22, light enters the light guide plates 20 from the LEDs. The light propagates through the light emitting regions of the plurality of light guide plates corresponding to the respective LEDs 22 and is radiated to the liquid crystal display panel 10 from the emission surface 20a via the optical sheet 30.

  The backlight unit 12 includes a control unit 32 that controls lighting of the LEDs 22. The control unit 32 is connected to the printed circuit board 24 and to a control unit (not shown) of the liquid crystal display device. The control unit 32 includes a light emission amount adjustment unit 34 that adjusts the light emission amount of the LED 22 for each light emission region of the corresponding light guide plate 20 based on the video luminance signal sent from the control unit of the liquid crystal display device. That is, the control unit 32 performs dimming of each light emitting area of the backlight according to the video information by individually driving the plurality of LEDs 22.

  Since the backlight unit 12 configured as described above includes a plurality of light guide plates and a plurality of light sources opposed to the side surfaces of the light guide plates, the backlight unit 12 is thinner than a direct type backlight. Can be achieved. It is possible to reduce power consumption by using LEDs as light sources, and by individually driving a plurality of LEDs 22 in accordance with video information and dimming each light emitting area of the backlight. Furthermore, a plurality of LEDs are provided to face a plurality of side surfaces of each light guide plate, and the light emission region of the light guide plate when each LED is lit is formed so as not to coincide with a divided portion of each light guide plate, that is, a boundary. As a result, the boundary of the light emitting region can be made inconspicuous.

  As a result, it is possible to achieve both a thin shape, power saving, and a high contrast ratio, and in the area dimming drive, it is possible to obtain a backlight unit that is excellent in luminance uniformity of the light emitting area and in which the boundary of the light emitting area is less noticeable. Further, by applying this backlight unit to a liquid crystal display device, it is possible to provide a high-quality large-screen liquid crystal display device that satisfies high contrast, low power consumption, and thinness.

Next, a backlight unit according to another embodiment of the present invention will be described.
FIG. 8 shows an arrangement of the light guide plate and the light source of the backlight unit according to the second embodiment. As shown in FIG. 8, the plurality of LEDs 22 as point light sources are provided at the boundary between adjacent light guide plates, and are arranged to face the central portions of the four side surfaces of the light guide plate 20, respectively.

  The light emission area of the backlight by each LED 22 is a square area centering on the LED, and is a square area composed of two areas 1a and 2a indicated by broken lines. Unlike the boundary between the adjacent light guide plates 20, the boundary of the light emitting region, that is, the contour is shifted by approximately 45 degrees.

  Each light guide plate 20 has a plurality of light emitting regions divided into the same number as the number of LEDs 22 entering the light guide plate. That is, in this embodiment, the light guide plate 20 has four light emitting areas 1a, 1b, 1c, and 1d (na, nb, nc, and nd) corresponding to the four LEDs.

  FIG. 9 shows the arrangement of the light guide plate and the light source of the backlight unit according to the third embodiment. As shown in FIG. 9, the plurality of LEDs 22 as point light sources are provided at the boundary between adjacent light guide plates, face the four corners of the light guide plate 20, and further each of the four side surfaces of the light guide plate 20. Are arranged to face each other at the center. Eight LEDs 22 are arranged for one light guide plate 20.

  As shown by the broken line in FIG. 9, the light emission area of the backlight by each LED 22 is a star-shaped area extending over the four light guide plates 20 around the LED, or a diamond-shaped area that forms two light guide plates on both sides of the LED. It has become. The boundary of the light emitting region, that is, the contour is different from the boundary between the plurality of adjacent light guide plates 20.

  Each light guide plate 20 has a plurality of light emitting regions divided into the same number as the number of LEDs 22 entering the light guide plate. That is, in this embodiment, the light guide plate 20 has four light emitting areas 1a to 1h corresponding to eight LEDs.

  In the second and third embodiments, the other configuration of the backlight unit is the same as that of the first embodiment described above, and the same reference numerals are given to the same portions, and detailed description thereof is omitted. To do. In the second and third embodiments, the same effects as those in the first embodiment can be obtained.

  FIG. 10 shows an enlarged view of the light guide plate and LEDs of the backlight unit according to the fourth embodiment. In the first embodiment described above, recesses are formed in the corners or side edges of the light guide plate 20, and the LEDs are arranged in the through holes made of the recesses. According to this, the recess 21 formed in the light guide plate 20 is formed as a bottomed recess in which the exit surface 20a side of the light guide plate is closed. Each LED 22 is disposed in the recess 21, and its emission side portion is covered with the light guide plate 20. As described above, the light guide plate is extended immediately above the LED 22 for the purpose of improving the uniformity of luminance from the light guide plate according to the light distribution characteristics of the LED.

  In the fourth embodiment, the other configuration of the backlight unit is the same as that of the first embodiment described above, and the same reference numerals are given to the same portions, and detailed description thereof is omitted. And also in 4th Embodiment, the effect similar to 1st Embodiment can be acquired.

  The present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  For example, the light guide plate is not limited to a square, and may have another shape such as a rectangle or a rhombus. In this case, the same effect as described above can be obtained.

FIG. 1 is an exploded perspective view showing a liquid crystal display device including a backlight unit according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the liquid crystal display device. FIG. 3 is an enlarged perspective view showing a light guide plate and LEDs of the backlight unit. FIG. 4 is a plan view of the backlight unit showing a positional relationship between the light guide plate and the LEDs. FIG. 5 is a plan view showing a bottom surface of the light guide plate. 6 is a cross-sectional view of the light guide plate along line AA in FIG. 5. FIG. 7 is a plan view showing a bottom surface of a light guide plate according to a modification. FIG. 8 is a plan view schematically showing an arrangement relationship between a light guide plate and LEDs of a backlight unit according to the second embodiment of the present invention. FIG. 9 is a plan view schematically showing an arrangement relationship between a light guide plate and LEDs of a backlight unit according to a third embodiment of the present invention. FIG. 10 is an enlarged perspective view showing a light guide plate and LEDs of a backlight unit according to the fourth embodiment of the present invention.

Explanation of symbols

10 ... Liquid crystal display panel, 12 ... Backlight unit, 20 ... Light guide plate,
20a ... emitting surface, 20b ... side surface, 20c ... bottom surface, 22 ... LED, 21 ... recess,
24 ... Printed circuit board, 32 ... Control unit, 34 ... Light emission amount adjustment unit

Claims (9)

  A plurality of light guide plates each having a side surface and an output surface and arranged in a state where the side surfaces face each other, and a plurality of points arranged on the side surfaces of each of the light guide plates and allowing light to enter the plurality of light guide plates simultaneously And a backlight unit for a display device.   A plurality of light guide plates each having a side surface and an emission surface, and arranged in a state where the side surfaces face each other, a plurality of point light sources arranged on the side surfaces of each of the light guide plates and allowing light to enter the light guide plates, A backlight unit for a display device, wherein a boundary of the light guide plate and a boundary of a light emitting region for adjusting a light emission amount from each point light source are different from each other.   The backlight unit according to claim 1, wherein the point light source is disposed at a boundary portion between adjacent light guide plates.   4. The backlight unit according to claim 1, wherein each of the light guide plates has a plurality of light emitting regions divided into the same number as the number of point light sources entering the light guide plate. 5.   5. The backlight unit according to claim 1, further comprising: a light emission amount adjustment unit that adjusts the light emission amount of the point light source for each light emission region of the corresponding light guide plate based on a video luminance signal. Each of the light guide plates is formed in a rectangular shape having a plurality of side surfaces, and the plurality of side surfaces are arranged side by side in a plurality of rows and a plurality of columns in a state facing the side surfaces of the other light guide plates,
The backlight unit according to any one of claims 1 to 5, wherein the plurality of point light sources are respectively disposed at corners of the light guide plates. Each of the light guide plates is formed in a rectangular shape having four side surfaces, and a plurality of side surfaces are arranged in a plurality of rows and a plurality of columns in a state of facing the side surfaces of the other light guide plates,
The backlight unit according to any one of claims 1 to 5, wherein the plurality of point light sources are respectively disposed on four side surfaces of the light guide plates. Each of the light guide plates is formed in a rectangular shape having a plurality of side surfaces, and the plurality of side surfaces are arranged side by side in a plurality of rows and a plurality of columns in a state facing the side surfaces of the other light guide plates,
The backlight unit according to any one of claims 1 to 5, wherein the plurality of point light sources are respectively disposed at corners and four side surfaces of each light guide plate.   The backlight unit according to claim 6, wherein the light guide plate has a recess formed at a corner, and the point light source is disposed in the recess.

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