JP2004342587A - Backlight and liquid crystal display using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device wherein unevenness of brightness and color of the display device is suppressed, and which has a high quality of display. <P>SOLUTION: This is a backlight provided with a cabinet 3, a first diffusing plate 1 arranged in the vicinity of the opening of the cabinet 3, a second diffusing plate 2 arranged between the light source 4 and the first diffusing plate 1, and a reflecting plate 7 arranged on the bottom face and the side face of the cabinet 3. As for the second diffusing plate 2, it is provided with a reflecting member 5 which is arranged in the corresponding position to the light source 4 and which reflects light from the light source 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight for supplying light to a display device and a display device using the backlight, and in particular, a direct-type backlight in which a light source is disposed immediately below a display surface, and a liquid crystal display using the backlight. It is suitable for application to an apparatus.

  In recent years, as a backlight of a display device such as a liquid crystal display device, a point light source such as an LED (Light Emitting Diode) or an LD (Laser Diode) has been adopted. The backlight using the point light source has three primary colors of red (R), green (G), and blue (B), which does not require the use of mercury, as compared with a conventional backlight using, for example, a cold cathode tube. By using, high color reproducibility can be obtained or the backlight can have a long life. On the other hand, when a point light source is adopted as the light source of the display device, the directivity of the emitted light is high, so that the luminance near the point light source is likely to be higher than the luminance at a position far from the point light source. There is a problem that luminance unevenness and color unevenness occur in display, and display quality is deteriorated. As a method of suppressing luminance unevenness and color unevenness in a backlight in which the point light source is disposed directly below a display panel, in a conventional backlight, a first and a second frame are disposed above a substrate on which a plurality of point light sources are disposed. By supporting the two light-diffusing sheets up and down at predetermined intervals, and integrally providing a fluorescent substance that emits fluorescence by the light of the point light source on one of the light-diffusing sheets, luminance unevenness is suppressed. (For example, see Patent Document 1).

  Further, as other conventional techniques, a light-transmitting sheet having a light-diffusing property, a light-emitting element disposed behind the light-transmitting sheet, and disposed between the light-emitting element and the light-transmitting sheet, A prism device having a prism surface having a plurality of rows of prism portions having a substantially V-shaped cross section and a prism sheet having a flat portion formed on a surface opposite to the prism surface constitutes a backlight device. Is arranged to be spaced apart from the light emitting element and the translucent sheet so as to face the light emitting element side, thereby suppressing luminance unevenness and color unevenness (for example, see Patent Document 2). .

JP 2000-133006 A (FIG. 2) JP-A-2002-49324 (FIG. 1)

  However, in the related art of Patent Document 1 described above, two light diffusion sheets are provided above the point light source to reduce luminance unevenness. In the second light diffusion sheet, the luminance near the position corresponding to the point light source becomes high, and there is a problem that luminance unevenness and color unevenness occur.

  Also, in the prior art of Patent Document 2 described above, the prism sheet and the translucent sheet are separated from each other with a distance above the point light source to reduce luminance unevenness. Is not provided, and even in this configuration, the luminance near the position corresponding to the point light source in the prism sheet and the translucent sheet becomes high, and luminance unevenness and color unevenness occur. There were also problems.

  The present invention has been made in view of the above problems, and in a backlight used for a display device, further suppresses luminance unevenness and color unevenness, a high-quality display backlight, and a display using the backlight. It is intended to provide a device.

  The backlight of the present invention supports a light source, a housing having an opening in at least a part of an upper surface, a first diffuser disposed close to the opening of the housing, and the light source. A backlight comprising: a second diffusion plate disposed between the first diffusion plate and a reflection plate disposed on a bottom surface and a side surface of the housing; A reflecting member that reflects light from the light source disposed at a position corresponding to the light source, a surface facing the light source that diffuses light from the light source disposed at a position corresponding to the light source; , A concave portion provided on a surface facing the first diffusion plate provided at a position corresponding to the light source, or a dense and sparse surface on a surface facing the first diffusion plate. It is characterized in that one of the formed uneven portions is formed.

  ADVANTAGE OF THE INVENTION According to this invention, in a backlight used for a display device, it is possible to perform display with high display quality by suppressing luminance unevenness and color unevenness.

Embodiment 1
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a backlight according to the first embodiment of the present invention, and FIGS. 2 to 4 are cross-sectional views of other backlights according to the first embodiment of the present invention.

  In FIG. 1, an opening is formed in at least a part of the upper surface of a casing 3 that supports a point light source 4 directly below a display surface, and the first diffusion plate 1 is placed close to close the opening. Arrange. Further, the second diffusion plate 2 is disposed between the first diffusion plate 1 and the point light source 4 and with a gap from the first diffusion plate 1. As the first diffusion plate 1 and the second diffusion plate 2, one having an uneven shape on both surfaces or one surface, or one having a light diffusion function such as a material using a milky white material is used. The first diffusion plate 1 and the second diffusion plate 2 are supported by the support member 6 and the housing 3. Several support members 6 are provided at substantially the center of the backlight. A reflection plate 7 for reflecting light from the point light source 4 is provided on the side and bottom surfaces of the housing 3, and an opening is provided at a position of the reflection plate 7 corresponding to the point light source 4, and a point is provided. The point light source 4 is arranged to guide the light of the light source 4 into the backlight. Further, a reflection member 5 is formed on a surface of the second diffusion plate 2 facing the point light source 4 at a position corresponding to the point light source 4. The reflection member 5 may be formed by printing after molding the second diffusion plate 2, or may be adhered with a reflection member having an adhesive force after molding. In the diffusion plate 2, either the surface facing the point light source 4 as shown in FIG. 1 or the surface facing the first diffusion plate 1 may be formed at a position corresponding to the point light source 4. In order to efficiently reflect the light from the point light source 4, it is preferable that the light source is formed on a surface facing the point light source 4 as shown in FIG.

  With the above-described configuration, the light emitted from the point light source 4 is temporarily reflected on the second diffusion plate 2 in a region close to the point light source 4 without directly entering the second diffusion plate 2. 5 is reflected. Thereafter, the light is repeatedly reflected between the reflection plate 7 disposed on the bottom surface of the housing 3 and the second diffusion plate 2. This makes it possible to disperse the light without concentrating the light in the vicinity of the position corresponding to the point light source 4 in the second diffusion plate 2. As a result, the light from the point light source 4 is further diffused after being incident on the second diffuser 2 and before being emitted from the first diffuser 1, and the light emitted from the first diffuser 1 is Luminance unevenness and color unevenness are suppressed, resulting in uniform brightness.

  Next, FIGS. 2 and 3 will be described. 2 and 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and differences will be described. 2 and 3 do not have the reflection member 5 in FIG. 1, and in FIG. 2, the second diffusion plate 2 has a surface facing the point light source 4 and is convex at a position corresponding to the point light source 4. In FIG. 3, a concave portion 9 is integrally formed on a surface of the second diffuser plate 2 facing the first diffuser plate 1 and at a position corresponding to the point light source 4.

  2 or 3 eliminates the need for the reflection member in FIG. 1, reduces the manufacturing cost, improves the reliability, and reduces the light from the point light source 4. The light is dispersed and emitted, for example, in the horizontal direction on the paper surface of FIG. 2 or FIG. Can be suppressed from being concentrated near the position corresponding to. As a result, the light from the point light source 4 is further diffused after being incident on the second diffuser 2 before being emitted from the first diffuser 1, and the light emitted from the first diffuser 1 is Luminance unevenness and color unevenness are suppressed, resulting in uniform brightness.

  Next, FIG. 4 will be described. 4, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals, and differences will be described. FIG. 4 shows a configuration in which the reflection member 5 or the convex portion 8 or the concave portion 9 is formed on the second diffusion plate 2 in FIGS. 1 to 3, and the second diffusion plate 2 faces the first diffusion plate 1. On the surface to be formed, uneven portions 10 are formed densely in the vicinity of the position corresponding to the point light source 4, and uneven portions 11 are formed sparsely in the position far from the position corresponding to the point light source 4.

  With the configuration shown in FIG. 4 described above, the reflection member in FIG. 1 is not required, the manufacturing cost can be reduced, and the reliability can be improved. For example, the light near the position corresponding to the point light source 4 is dispersed and emitted in, for example, the lateral direction on the paper of FIG. Concentration in the vicinity can be suppressed, and the same effects as in FIGS. 1 to 3 can be achieved. Although FIG. 4 shows the case where the concave and convex portions 10 and 11 are formed on the surface of the second diffuser plate 2 facing the first diffuser plate 1, the second diffuser plate 2 has a point light source. The same effect can be exerted even when it is formed on the surface facing 4.

  Further, FIG. 4 shows an example in which uneven portions 10 are densely formed in the vicinity of the position corresponding to the point light source 4 and sparsely formed in the position far from the position corresponding to the point light source 4. However, when the light emitted from the point light source 4 is mainly emitted in the horizontal direction on the paper of FIG. 4, the light is sparse near the position corresponding to the point light source 4 (an area where the light from the point light source is relatively small). The same effect can be obtained by forming the uneven portion 10 and forming the dense uneven portion 11 at a position far from the position corresponding to the point light source 4 (region where light from the point light source is relatively large). Becomes possible. In this case, in place of the uneven portions formed densely and densely, for example, a region where light from the point light source is relatively small is present on one or both of the surface facing the point light source and the surface facing the first diffusion plate 1. A light shielding pattern may be formed sparsely and densely in an area where light from the point light source is relatively large, or the light from the point light source may be formed in the second diffusion plate during molding of the second diffusion plate. A region with relatively little light may be made to have a high transmittance, and a region with relatively large light from a point light source may be made to have a low transmittance.

  In FIG. 4, the reflector 7 has a convex portion at the bottom center and the peripheral portion on the bottom surface of the housing 3, and a portion other than the central portion and the peripheral portion has a concave portion close to the bottom surface. It has become. With such a configuration, it is possible to further uniform the light from the point light source 4 and suppress luminance unevenness and color unevenness. In addition, the shape of the reflection plate may be used in combination with FIGS. 1 to 3 in the present embodiment. Further, in the reflection plate 7 shown in FIGS. 1 to 4, a regular reflection member for reflecting light in the horizontal direction in each drawing is disposed at a position near the point light source 4, and is located far from the point light source 4. By disposing a diffuse reflection member that reflects light in the upward direction in each figure at the center and / or the periphery of the bottom surface of the housing 3, it is possible to further suppress luminance unevenness and color unevenness. The shape and configuration of these reflectors may be used in combination with other embodiments described later. Further, the shape and configuration of the reflector may be independently applied to the backlight of each embodiment. In this case, too, the light from the point light source 4 is dispersed by the shape and configuration of the reflector, and The light is further diffused by the diffusion plate, so that luminance unevenness and color unevenness can be reduced.

  Further, the reflector 7 in FIG. 4 has a convex portion at the bottom center portion and the peripheral portion (region where the light from the point light source is relatively less) on the bottom surface of the housing 3, and other than the bottom central portion and the peripheral portion. (A region where the light from the point light source is relatively large) has a shape having a concave portion close to the bottom surface. However, the present invention is not limited to this, and the light from the point light source can be directed to the opening of the housing. Any shape may be used as long as a convex portion is formed in an area where the light from the point light source is small, and a concave portion close to the bottom surface of the housing is formed in an area where the light from the point light source is relatively large. Good.

  1 to 4, the distance between the point light source 4 and the second diffuser 2 shown in FIG. 1 is L1, the distance between the second diffuser 2 and the first diffuser 1 is L2, By adopting a configuration that satisfies the relationship of L1 ≦ L2, it is possible to more reliably suppress luminance unevenness and color unevenness. In the present embodiment, the reference points for the distances L1 and L2 are the center point in the thickness direction for the positions of the first diffuser and the second diffuser, and the point light source 4 for the position of the point light source 4. It is the position of the LED light emitting element (IC). When L2 is equal to or greater than L1, light can be sufficiently diffused between the first diffusion plate 1 and the second diffusion plate 2 as compared with the case where L2 is smaller than L1, resulting in uneven brightness, Color unevenness can be more reliably suppressed. Further, when L1 is a configuration using the reflection member 5 (in the case of FIG. 1), the reflection member 5, which is a light shielding member, can be formed small or attached with it by setting it small. As a result, the luminance of the backlight can be improved, so that it is preferable that the configuration satisfy the relationship of L1 ≦ L2.

Embodiment 2
A second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a sectional view of a backlight according to the second embodiment of the present invention. 5, the same components as those in FIGS. 1 to 4 are denoted by the same reference numerals, and differences will be described. FIG. 5 shows that, in addition to the configuration of FIG. 1, in the second diffusion plate 2, an uneven portion 12 is formed on the surface facing the first diffusion plate 1, and unevenness is formed on the surface facing the point light source 4. It is a smooth surface without being formed.

  With such a configuration, even on the surface of the second diffusion plate 2 where the reflection member 5 near the reflection member 5 provided on the surface of the second diffusion plate 2 facing the point light source 4 does not exist, By reflecting a part of the light from the point light source 4 on the surface and repeating the reflection several times between the reflector 7 disposed on the bottom surface of the housing 3 and the light, the light is brought close to the position corresponding to the point light source 4. Concentration can be further suppressed. As a result, the light from the point light source 4 is further diffused after being incident on the second diffuser 2 before being emitted from the first diffuser 1, and the light emitted from the first diffuser 1 is Luminance unevenness and color unevenness are suppressed, resulting in uniform brightness.

  The point light sources 4 in the first embodiment and the present embodiment are arranged in a row on a circuit board 16 as shown in FIG. 6 to constitute a light source unit 17, and are held on the bottom surface of the housing 3. I have. FIG. 6 is a perspective view for explaining the arrangement of the point light source 4 held in the housing 3, and the illustration of the first diffusion plate 1, the second diffusion plate 2, the reflection plate 7, the support member 6 and the like is omitted. are doing. In the light source unit 17, an arbitrary luminance distribution can be easily obtained also in the X direction shown in FIG. 6 by adjusting the arrangement intervals of the plurality of point light sources 4 in the arrangement direction. For example, as shown in FIG. 7, by using the light source unit 17 in which the point light sources 4 are arranged so that the center in the X direction is dense and the ends are sparse, the luminance distribution in the X direction in FIG. Can be controlled as shown in FIG. In FIG. 8, the luminance at the center in the X direction is higher than the luminance at the ends in the X direction, thereby enabling higher quality display.

  Further, since the distance between the light sources is large in a region where the arrangement of the point light sources 4 is sparse, unevenness in brightness and color in the vicinity of the point light sources 4 is particularly likely to occur. For this reason, by increasing the thickness of the device, it is necessary to increase the distance from the point light sources 4 to the emission surface, promote the mixing of light from each point light source 4, and improve the display quality. However, in the backlight and the liquid crystal display device according to the first embodiment and the present embodiment, the use of the second diffuser plate 2 promotes the diffusion and reflection of light and can take out sufficiently mixed light. Therefore, uneven brightness and uneven color can be easily reduced without increasing the thickness of the device.

  As the point light sources in the first and second embodiments, an LED is used, and a first point light source that emits red (R) light and a second point light source that emits green (G) light are used. A light source and a third point light source that emits blue (B) light can be used. An LED that emits monochromatic light of each of red (R), green (G), and blue (B) has higher luminous efficiency than an LED that emits white light, and the red, green, and green color filters used in the liquid crystal display device. By adjusting the blue transmission characteristics and the emission spectrum of the LED, a display device with high color reproducibility can be obtained. Therefore, it is preferable to use a combination of the above three point light sources.

Embodiment 3
A third embodiment of the present invention will be described with reference to FIG. FIG. 9 is a sectional view of a backlight according to the third embodiment of the present invention. 9, the same components as those in FIGS. 1 to 8 are denoted by the same reference numerals, and differences will be described. FIG. 9 shows a case where a line light source 13 such as a cold cathode tube is used instead of a point light source as a light source as in FIGS. The line light source 13 is supported on the bottom surface of the housing 3, and the first diffusion plate 1 disposed close to an opening formed in at least a part of the upper surface of the housing 3; A diffusion sheet 14 is formed therebetween. In this specification, a diffusion sheet refers to a sheet having a thickness of about 0.05 mm to 0.30 mm. A support plate 15 made of, for example, a transparent acrylic resin is used to support the diffusion sheet 14, and the support member 6 and the housing 3 support the diffusion sheet 14 and the support plate 15.

  With the above-described configuration, even in a backlight using a linear light source, as in the above embodiment, luminance unevenness and color unevenness can be suppressed, and a display with high display quality can be performed.

  Although only the present embodiment has been described with respect to an example in which the diffusion plate is constituted by the diffusion sheet and the support plate, the diffusion plates in the first and second embodiments are different from those in the third embodiment. Similarly, it is needless to say that the same effect can be obtained by using a diffusion sheet and a support plate. Furthermore, the diffusion plate in the above-described embodiment does not particularly need to have a thickness, and may be a member as thin as the diffusion sheet as long as the member has rigidity that can be supported by the support member and the housing. Good.

  In addition, the backlight according to the first to third embodiments and the liquid crystal are disposed outside the housing at positions corresponding to the openings formed in the housing, and the liquid crystal is provided between the two insulating substrates. By combining with a liquid crystal panel sandwiched therebetween, a liquid crystal display device with high display quality can be obtained.

  Further, also in the second and third embodiments, the distance between the point light source and the second diffusion plate shown in the first embodiment is L1, and the distance between the second diffusion plate and the first diffusion plate is L1. By setting the distance from the diffusion plate to L2 and satisfying the relationship of L1 ≦ L2, it is possible to more surely suppress luminance unevenness and color unevenness as in the first embodiment.

  Further, in the first to third embodiments, the case where the light source is supported on the bottom surface of the housing is described. However, the present invention is not limited thereto, and the light source is supported on the side surface of the housing. Also, in the case where the reflection member, the convex portion, the concave portion, or the concave / convex portion of the above embodiment is formed at a position where the second diffuser plate is most susceptible to the light from the light source, The same effect as the embodiment can be obtained.

  As described above, the display device using liquid crystal has been described as the display device in the above embodiment. However, the present invention is not limited thereto, and is applicable to any display device having a so-called backlight having a light source behind a display surface. Of course, there is no problem.

FIG. 2 is a cross-sectional view of the backlight according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view of another backlight according to the first embodiment of the invention. FIG. 5 is a cross-sectional view of another backlight according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view of another backlight according to the first embodiment of the present invention. FIG. 9 is a cross-sectional view of a backlight according to a second embodiment of the present invention. It is a perspective view explaining arrangement of a point light source in a 2nd embodiment of the present invention. It is a perspective view of a light source unit in a 2nd embodiment of the present invention. FIG. 13 is a diagram illustrating a luminance distribution in a direction in which a plurality of point light sources are arranged in a backlight according to a second embodiment of the present invention. FIG. 13 is a sectional view of a backlight according to a third embodiment of the present invention.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 first diffusion plate 2 second diffusion plate 3 housing 4 point light source 5 reflecting member 6 supporting member 7 reflecting plate 8 convex portion 9 concave portion 10 densely formed uneven portion 11 sparsely formed uneven portion 12 unevenness Unit 13 line light source 14 diffusion sheet 15 support plate 16 circuit board 17 light source unit

Claims (9)

A housing that supports the light source and has an opening in at least a part of the upper surface,
A first diffusion plate disposed close to an opening of the housing;
A second diffuser disposed between the light source and the first diffuser;
Reflectors disposed on the bottom and side surfaces of the housing,
A backlight with
In the second diffusion plate, a reflection member that reflects light from the light source disposed at a position corresponding to the light source, the light diffuses light from the light source disposed at a position corresponding to the light source. A convex portion provided on a surface facing the light source, a concave portion provided on a surface facing the first diffusion plate provided at a position corresponding to the light source, or a surface facing the first diffusion plate The backlight according to any one of claims 1 to 3, wherein one of uneven portions formed densely and sparsely is formed. 2. The backlight according to claim 1, wherein the reflection member is formed or attached on the second diffusion plate at a position corresponding to the light source and on a surface facing the light source. 3. 3. The backlight according to claim 1, wherein a surface of the second diffusion plate facing the light source is a smooth surface. 4. The backlight according to any one of claims 1 to 3, wherein the reflector has an uneven portion on a bottom surface of the housing. The backlight according to any one of claims 1 to 4, wherein the first diffusion plate and / or the second diffusion plate is formed by combining a diffusion sheet and a support plate. The backlight according to any one of claims 1 to 5, wherein the light source is a point light source. 7. The backlight according to claim 6, wherein respective arrangement intervals of the point light sources in the arrangement direction in which the plurality of the point light sources are arranged are densely arranged at a center portion and sparsely arranged at an end portion. The distance L1 between the second diffusion plate and the light source and the distance L2 between the first diffusion plate and the second diffusion plate satisfy a relationship of L1 ≦ L2. The backlight according to any one of claims 1 to 7. 9. The backlight according to claim 1, wherein a liquid crystal is provided outside the housing at a position corresponding to an opening formed in the housing, and a liquid crystal is provided in a gap between the two insulating substrates. A liquid crystal display device comprising: a liquid crystal panel sandwiched therebetween.

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