JP2006064899A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is excellent in display characteristics and which is equipped with a backlight unit having a plurality of point light sources. <P>SOLUTION: The liquid crystal display device 100 is equipped with the backlight unit 101 irradiating a liquid crystal panel from the anti-viewer's side with light. The backlight unit 101 is equipped with an LED light source 110 and a light transmission plate 108 guiding light emitted from the LED light source 110 to the entire surface so that the liquid crystal panel is irradiated with the guided light. Also the LED light source 110 is constituted of a high luminous intensity LED 110a and low luminous intensity LEDs 110b, 110c. These LEDs are symmetrically located with respect to a center line A-A in a longitudinal direction of a light incident surface of the light transmission plate 108. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a backlight unit having a plurality of point light sources.

  In transmissive and anti-transmissive liquid crystal display devices, a backlight unit is disposed on the non-viewing side of the liquid crystal panel. The backlight unit typically includes a light source and a plurality of optical members for effectively emitting light from the light source to the liquid crystal panel. Since this backlight unit is easy to reduce in thickness, it is a sidelight type in which a linear or dotted light source is attached along the side end surface of a transparent plate-shaped light guide plate made of acrylic resin or the like. Things have become mainstream.

  In such a sidelight type backlight unit, illumination light is incident from a side end face of the light guide plate (hereinafter referred to as a light incident surface), is repeatedly reflected inside the light guide plate, and propagates the illumination light. In addition, the planar light is generated by using the illumination light of the light source by emitting the light from the light emitting surface.

  Conventionally, a fluorescent tube has been used as the light source. However, light-emitting diodes (hereinafter referred to as LEDs) have come to be used because of consideration for environmental problems, long life, and good light emission.

Since the light of the LED has high directivity, the light just before the light emitting surface of the LED is bright, and it becomes dark as the radiation angle increases. In order to solve this, there has been provided a device devised so that uniform illumination can be obtained by diffusing light using a reflector (reflector) or the like (see Patent Document 1). Moreover, in order to eliminate the difference in brightness between the central part and the peripheral part of the light exit surface of the light guide plate, a light output control pattern is provided on the light guide plate to perform light distribution (see Patent Document 2).
JP-A-9-092886 JP 2002-107716 A

  In a backlight unit using an LED, a design in which a conventional fluorescent tube is replaced with an LED is performed. Since a portion having an effective light emission length uniformly emits light in a fluorescent tube, a plurality of LEDs having the same luminous intensity are arranged when this is replaced with LEDs. However, it is not optimal to arrange LEDs having the same luminous intensity in this manner from the viewpoint of effectively using light from a light source.

  For example, in the liquid crystal display device, the display characteristics are improved by making the luminance in the central part higher than that in the peripheral part. That is, the light emitted from the backlight unit has a luminance distribution in which the central luminance is high and the peripheral luminance is low. When light having such a luminance distribution enters the liquid crystal panel, it is viewed brighter for the viewer than when light with uniform luminance is emitted from the entire surface.

  Thus, in order to obtain a desired luminance distribution for the backlight unit, a light control pattern is provided on the light guide plate to perform light distribution. However, since the required luminance distribution differs depending on the product, the light guide plate has to be designed differently for each product. Further, the structure of the light guide plate becomes complicated, and there is a problem that the light transmittance is significantly reduced.

  Moreover, it is possible to change the luminous intensity of LED by changing the electric current supplied to each LED. However, when the current is changed, the chromaticity of the LED also changes, and the display characteristics deteriorate. Increasing the number of LEDs or increasing the applied current of LEDs has also increased the overall luminance. However, in this case, there are problems such as an increase in power consumption, an increase in the amount of heat generated by the light source, and an accelerated deterioration of the light source.

  The present invention has been made in the background as described above, and an object of the present invention is to provide a liquid crystal display device having excellent display characteristics.

  The liquid crystal display device according to the present invention is a liquid crystal display device including a light unit that irradiates light to a liquid crystal panel, and the light unit is emitted from three or more point light sources and the three or more point light sources. A light guide plate that guides light to the entire surface and irradiates the liquid crystal panel, and the three or more point light sources include a high light intensity point light source and a low light intensity point light source. Thereby, the luminance distribution of the light emitted from the light unit can be easily adjusted.

  The three or more point light sources are driven with substantially the same current value. Thus, display characteristics can be improved with a simple configuration.

  The luminous intensity of the high luminous intensity point light source is preferably 1.5 to 3 times the luminous intensity of the low luminous intensity point light source. Thereby, the luminous intensity of the point light source can be determined according to the desired luminance distribution.

  The three or more point light sources are particularly effective when arranged in a line along the longitudinal direction of the light incident surface of the light guide plate.

  The low luminous intensity point light sources are disposed at both ends of the three or more light sources in the longitudinal direction of the light incident surface of the light guide plate. Accordingly, the luminance at the center of the light unit can be increased and the luminance at the periphery can be decreased, and the display characteristics can be further improved.

  Of the three or more point light sources, the point light sources having the same luminous intensity are arranged symmetrically with respect to the longitudinal center line of the light incident surface of the light guide plate. Thereby, display characteristics can be improved. Note that the same luminous intensity does not have to be exactly the same, and it is sufficient that the luminous intensity ratio falls within the range of 0.9 to 1.1.

  The three or more point light sources are particularly effective when they are light emitting diodes.

  According to the present invention, a liquid crystal display device having excellent display characteristics can be provided.

  Hereinafter, embodiments to which the present invention can be applied will be described. The following description is to describe the embodiment of the present invention, and the present invention is not limited to the following embodiment. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Moreover, those skilled in the art can easily change, add, and convert each element of the following embodiments within the scope of the present invention. In addition, in each drawing, the same code | symbol is attached | subjected to the same element and the duplication description is abbreviate | omitted as needed for clarification of description.

  A liquid crystal display device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an exploded perspective view for explaining the entire configuration of a liquid crystal display device which is an example of the display device of the present invention. FIG. 1 schematically shows a liquid crystal display device 100 having a sidelight type backlight unit. In FIG. 1, reference numeral 101 denotes a backlight unit that emits planar light, and 102 denotes a liquid crystal panel that displays an image. The liquid crystal panel 102 is driven by a source driver IC 103 and a gate driver IC 104, and can display an image by controlling transmission of light from the backlight unit 101. A holder 105 holds and protects the liquid crystal panel 102 and the backlight unit 101 from the outside. The holder 105 is made of resin or metal.

  The liquid crystal panel 102 can control light transmittance by enclosing liquid crystal between two glass substrates and controlling an electric field applied to the liquid crystal. The two glass substrates are maintained at a predetermined interval by bead spacers or columnar spacers. A polarizing plate is attached to each of the outer surface of the non-viewing side glass substrate and the outer surface of the viewing side glass substrate. For example, in a TN type liquid crystal panel which is a typical example of a liquid crystal panel, polarizing plates on the non-viewing side and the viewing side are arranged so that their transmission axes are vertical or parallel. The direction of polarization of the linearly polarized light that has passed through the non-viewing-side polarizing plate is controlled by the liquid crystal, and the transmittance of light transmitted through the viewing-side polarizing plate is controlled.

  The liquid crystal panel 102 has a display area composed of a plurality of pixels and a peripheral area formed around the display area. A source driver IC 103 and a gate driver IC 104 are connected to the peripheral area. Each pixel in the display area of the liquid crystal panel 102 displays one of RGB colors. A monochrome display displays a monotone that changes from white to black. An active matrix type liquid crystal panel has an array substrate on which switch elements such as TFTs (Thin Film Transistors) are formed on an array, and a counter substrate disposed to face the array substrate.

  In a color liquid crystal panel, a color filter layer is formed on a counter substrate. In the display area on the array substrate, a plurality of source lines and gate lines are arranged in a matrix. The source line and the gate line are disposed so as to overlap each other at a substantially right angle. The voltage input from the source driver IC 103 is sent to the pixel electrode through the source / drain of the TFT turned on by the gate driver IC 104, and the pixel electrode on the array substrate and the common electrode on the counter substrate are connected. A voltage is applied to the liquid crystal in between. By changing this voltage, the voltage applied to the liquid crystal can be changed, and the light transmittance is controlled. The source driver IC 103 and the gate driver IC 104 are typically connected to the array substrate by TAB (Tape Automated Bonding), but may be provided directly on the glass substrate of the array substrate.

  As the liquid crystal panel 102, a simple matrix type having no switching element is known in addition to the above active matrix type. Other types of liquid crystal panels include TN (Twisted Nematic) type liquid crystal panels, STN (Super Twisted Nematic) type liquid crystal panels, and IPS (In Plane Switching) type in which pixel electrodes and common electrodes are formed on the same substrate. Liquid crystal panels are known. The present invention is applicable to various types of liquid crystal panels as described above.

  The backlight unit 101 is disposed by laminating a diffusion sheet 106, a prism sheet 107, a light guide plate 108, and a reflection sheet 109 in this order from the viewing side. The backlight unit 101 is a side light type, and includes an LED light source 110 in which a plurality of LEDs (Light Emitting Diodes) as light sources are arranged in a line along the side end surface of the light guide plate. Here, an example in which three LEDs are arranged is shown.

  The diffusion sheet 106, the prism sheet 107, the light guide plate 108, the reflection sheet 109, and the LED light source 110 are accommodated in the frame 111. L-shaped convex positioning portions (not shown) are formed at the four corners of the viewing side surface of the light guide plate 108. The diffusion sheet 106, the prism sheet 107, and the liquid crystal panel 102 are fitted with the positioning portions. And disposed on the light guide plate 108.

  The diffusion sheet 106 diffuses incident light and emits it. As the diffusion sheet 106, for example, the surface of the base sheet coated with a binder in which a light diffusing agent such as beads is dispersed, or the light diffusing layer in which the light diffusing agent is dispersed is laminated on the surface of the base sheet. Alternatively, conventional materials such as those in which a plurality of irregularities are formed on the surface of the base sheet can be used by embossing the surface of the base sheet made of synthetic resin.

  The prism sheet 107 improves the brightness of the display front by condensing light. The prism sheet 107 can be formed by forming an uneven structure with an organic resin on a base film such as polyethylene terephthalate. The prism sheet 107 is typically formed with a plurality of triangular prism structures, anisotropic diffraction gratings, and the like. Although only one sheet is shown here, two prism sheets may be used as a set, and the ridge lines of each prism sheet may be arranged to be orthogonal to each other.

  The LED light source 110 is arranged so that the LEDs are arranged along a predetermined end surface (light incident surface) of the light guide plate 108. The light guide plate 108 guides and diffuses the light from the LED light source 110 and emits planar light. A dot pattern is provided on the non-viewing side of the light guide plate 108. This dot pattern is formed by dot printing or processing. Or the uneven structure may be provided in the back surface of the light-guide plate.

  The reflection sheet 109 makes the light emitted from the non-viewing side of the light guide plate 108 reenter the light guide plate 108. The reflection sheet 109 is provided on the non-viewing side of the light guide plate 108. As the reflection sheet 109, a conventional sheet such as a coating made of a white pigment or a coating with a fine resin hollow powder can be used.

  Here, the optical action of the backlight unit 101 will be described. An example in which a dot pattern is formed on the back surface of the light guide plate 108 is shown. Light from the LED light source 110 enters the light guide plate 108 and propagates through the light guide plate 108 while repeating total reflection. A part of the light that does not satisfy the total reflection condition due to the dot pattern is emitted from the light emitting surface of the light guide plate 108 to the viewing side. Further, a part of the light is emitted from the non-viewing side of the light guide plate 108, reflected by the reflection sheet 109, and reenters the light guide plate 108. Light from the light exit surface of the light guide plate 108 is collected in a direction perpendicular to the display surface of the liquid crystal panel 102 by the prism sheet 107 and enters the diffusion sheet 106. The diffusion sheet 106 has a function of diffusing incident light and emitting it to the viewing side.

  Here, with reference to FIG. 2, the LED light source 110 concerning this embodiment is demonstrated. FIG. 2 is a schematic plan view of the liquid crystal display device 100 of FIG. 1 as viewed from the viewing side. In FIG. 2, illustration of components that are not visible after being stacked is omitted. For the sake of explanation, the holder 105 is not shown.

  In the LED light source 110 according to the present embodiment, two types of LEDs having different luminosities are used as the light source. For example, in FIG. 2, when three LEDs are used, a high luminous intensity LED 110a having a luminous intensity of 1200 mcd and a low luminous intensity LED 110b and 110c having a luminous intensity of 500 mcd are used in combination. These LEDs emit light having different luminosities with the same current. That is, those having different light emission efficiency with respect to current are used. Further, the high-intensity LED 110a and the low-intensity LEDs 110b and 110c emit white light having the same chromaticity when driven with the same current.

  Usually, the chromaticity of the LED changes according to the drive current. Generally, it changes to the blue side at a high current and to the yellow side at a low current. In the present embodiment, LEDs 110a, 110b and 110c having the same emission color and different emission efficiencies are used. Therefore, even if it is going to provide the difference in luminous intensity in several LED, since it can drive with the same electric current, the luminescent color of each LED can be made the same. That is, since all the LEDs 110a, 110b, and 110c can be driven with the same current, there is no chromaticity shift between the LEDs. As a result, color unevenness can be suppressed and the display characteristics of the liquid crystal display device can be improved.

  Moreover, since it can drive with the same electric current, you may connect each LED in series. Thereby, the number of wirings can be reduced, and a simpler configuration can be obtained.

  For the LED light source 110 having such a configuration, for example, by using three LEDs, the overall luminance of the backlight unit 101 is maintained at a desired value, while the central luminance is increased and the peripheral luminance is decreased. The case where the luminance distribution is created so as to improve the display characteristics of the liquid crystal display device 100 by making the luminance of the central portion higher than that of the peripheral portion will be described.

  First, the high-intensity LED 110a is arranged on the center line AA in the longitudinal direction of the light incident surface of the light guide plate 108 along the light incident surface. Then, the low-luminance LEDs 110b and 110c are arranged symmetrically about the high-luminance LED 110a. That is, the distance between the high luminous intensity LED 110a and the low luminous intensity LED 110b is made equal to the distance between the high luminous intensity LED 110a and the low luminous intensity LED 110c. Each LED is arranged along the light incident surface of the light guide plate 108. The light emitting surface of the LED is disposed on the light guide plate 108 side. That is, the light emitting surface of the LED is arranged to face the light incident surface. The light incident surface of the light guide plate 108 and the light emitting surface of the LED are parallel to each other.

  The light emitted from the LED has high directivity, bright immediately before the light emitting surface, and darkens as the radiation angle increases. When only one high-intensity LED 110a is used, the brightness of the X and Y portions in FIG. 2 becomes darker than the central portion. Therefore, low-luminance LEDs 110a and 110c are arranged in order to compensate for the luminance of the dark portion.

  Conventionally, the luminance distribution of the backlight unit has been adjusted by forming a concavo-convex pattern or a wrinkle pattern on the surface of the light guide plate 108 and reflecting and diffusing light. However, as described above, the luminance distribution can be adjusted without changing the design of the light guide plate 108 by arranging the high luminous intensity LED 110a and the low luminous intensity LEDs 110b and 110c in combination. That is, the central luminance can be high and the peripheral luminance can be lowered while maintaining the overall luminance of the backlight unit 101 at a desired value.

  Thereby, the display characteristics of the liquid crystal display device 100 can be improved. That is, the light emitted from the backlight unit 101 has a luminance distribution in which the central luminance is high and the peripheral luminance is low. When light having such a luminance distribution is incident on the liquid crystal panel 102, it is viewed brighter for the viewer than when light with uniform luminance is emitted from the entire surface.

  Further, the luminance distribution of the backlight unit 101 can be easily adjusted by changing the light emission efficiency of the high-intensity LED 110a and the low-intensity LEDs 110b and 110c, respectively. For example, when the luminance at the center is made higher, an LED having a higher luminous efficiency is used at the center. On the other hand, when lowering the peripheral luminance, LEDs having lower light emission efficiency are used symmetrically with the LED having high light emission efficiency in the middle.

  The luminance distribution of the backlight unit 101 can be easily changed simply by changing the LED arrangement. For example, when the brightness in the display surface of the liquid crystal display device 100 is uniformly increased, as shown in FIG. 3, along the light incident surface on the center line AA in the longitudinal direction of the light incident surface of the light guide plate 108. The low-intensity LED 110d is arranged. Then, the high luminous intensity LEDs 110e and 110f are arranged symmetrically with respect to the low luminous intensity LED 110d. Accordingly, the luminance can be improved by the left and right high-luminance LEDs 110e and 110f, and the luminance of the low-luminance portion Z can be compensated by the central low-luminance LED 110d.

  In order to increase the overall luminance, the number of LEDs may be increased. In this case, the high-intensity LED and the low-intensity LED may be arranged symmetrically with respect to the center line AA in the longitudinal direction of the light incident surface of the light guide plate 108. That is, LEDs having the same luminous intensity are arranged symmetrically with respect to the center line AA. For example, when four LEDs are used as shown in FIG. 4, the high luminous intensity LEDs 110 g and 110 h are arranged symmetrically with respect to the center line AA in the longitudinal direction of the light incident surface of the light guide plate 108. Then, the low-luminance LEDs 110i and 110j are arranged symmetrically with respect to the center line AA at positions that are separated from the distance from the high-luminance LEDs 110g and 110h to the center line.

  By doing so, the luminance can be increased and the backlight unit can have a desired luminance distribution. Further, as described above, the arrangement of the high-intensity LED and the low-intensity LED can be changed so that the liquid crystal display device 100 has a desired luminance distribution.

  Moreover, each LED may be arrange | positioned at equal intervals, and it is also possible to arrange | position at unequal intervals. Thereby, the luminance distribution of the backlight unit 101 can be set more finely. The difference in luminous intensity between the high luminous intensity LED and the low luminous intensity LED can be determined according to the luminance distribution of the liquid crystal display device 100. That is, the luminous intensity of each LED is determined to make the liquid crystal display device 100 have a desired luminance distribution. For example, the luminous intensity of the high luminous intensity LED with high luminous efficiency can be 1.5 to 3 times the luminous intensity of the low luminous intensity LED.

  When applied to a large liquid crystal display device, in order to obtain a desired luminance, an LED light source may be arranged in an L shape on two adjacent side surfaces of the light guide plate. At this time, as shown in FIG. 5, the high-intensity LED along the light incident surface of the light guide plate 108 so as to be symmetric with respect to the center lines AA and BB of the respective sides where the LEDs are arranged. And a low-intensity LED may be arranged. The present invention is also applicable to a front light unit in which a light unit is arranged on the viewing side of the liquid crystal panel.

It is a disassembled perspective view which shows the structure of the liquid crystal display device concerning embodiment. It is a schematic plan view explaining arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment. It is a schematic plan view explaining other arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment. It is a schematic plan view explaining other arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment. It is a schematic plan view explaining other arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Liquid crystal display device 101 Backlight unit 102 Liquid crystal panel 103 Gate driver IC
104 Source driver IC
105 Holder 106 Diffusion sheet 107 Prism sheet 108 Light guide plate 109 Reflection sheet 110 LED light source 111 Frame

Claims (7)

A liquid crystal display device comprising a light unit for irradiating light to a liquid crystal panel,
The light unit includes three or more point light sources and a light guide plate that guides light emitted from the three or more point light sources to the entire surface and irradiates the liquid crystal panel.
The three or more point light sources include a high luminous intensity point light source and a low luminous intensity point light source.   The liquid crystal display device according to claim 1, wherein the three or more point light sources are driven with substantially the same current value.   3. The liquid crystal display device according to claim 1, wherein a light intensity of the high light intensity point light source is 1.5 to 3 times a light intensity of the low light intensity point light source.   4. The liquid crystal display device according to claim 1, wherein the three or more point light sources are arranged in a line along a longitudinal direction of a light incident surface of the light guide plate.   5. The liquid crystal display device according to claim 1, wherein the low luminous intensity point light source is disposed at both ends of the three or more light sources in a longitudinal direction of a light incident surface of the light guide plate.   The liquid crystal according to claim 1, wherein among the three or more point light sources, the point light sources having the same luminous intensity are arranged symmetrically with respect to the center line in the longitudinal direction of the light incident surface of the light guide plate. Display device.   The liquid crystal display device according to claim 1, wherein the three or more point light sources are light emitting diodes.

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