JP2005031637A - Backlight structure for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight structure for a liquid crystal display which is downsized with a simple construction and further brings about no uneven brightness. <P>SOLUTION: The backlight structure of the liquid crystal display part, wherein the backlight of a liquid crystal display element is constructed by using a light emitting body and a diffusion part is disposed between the light emitting body and the liquid crystal display element, is provided with an inner wall on the side of a space in the inside of which the diffusion part is formed and an outer wall which is a liquid crystal display element bonding surface, wherein the inner wall is equipped with a refraction part and the outer wall is equipped with recessing parts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight for liquid crystal display, and more particularly to a backlight structure using a point light emitting element such as an LED as a light source of the backlight.

Conventionally, it has been proposed that an LED is used as a light source of a liquid crystal display device using a direct type backlight, which is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-281656 and 2001-305535. The backlight is known. Such a conventional technique is called a direct type, and is a liquid crystal display device using an LED as a backlight of a liquid crystal display device and using a point light source. Then, by arranging the LED at a predetermined position of the reflecting plate, for example, at the center portion, the light source obtained from the LED is diffused throughout the display portion. Here, the reflection plate has a concave surface shape or a multi-bending surface shape, and has a structure capable of uniformly irradiating the irradiation surface by changing the point light emission of the LED to the surface light emission as described above.
JP 2001-281656 A JP 2001-305535 A

  Further, as another diffusion method, as the light guide plate method, a light guide plate is used, and the light source is irradiated from the side surface of the light guide plate, whereby the irradiation surface can be uniformly irradiated.

  However, when illuminated from a plurality of light sources, such as the backlight structure using a plurality of point light sources such as the above-described conventional LEDs as described above, the luminance of the light emitting surface is difficult to be uniform because it is a point light source, The light emitted from the LED floats up in a spot shape and is not practical. In particular, it is difficult to obtain a uniform light emitting surface only by the structure of the reflecting surface in the following points. That is, the uniformity in the direct type greatly depends on the size, the directivity angle of the light source, the diffusion angle of the diffusion plate, and the like. Increasing the directivity angle of the light source and diffusing and mixing the light source through the diffuser plate can be solved by increasing the diffuser angle of the diffuser plate, but the directivity angle of the light emitting surface deteriorates and the light emitting surface The brightness of is reduced.

  In addition, the structure for guiding the light reflected by the diffusion sheet or the inner wall (reflecting plate) of the holder to the light emitting surface (peripheral portion) having low brightness makes the shape of the reflecting plate complicated and requires a diffusion plate. Therefore, the general configuration of the direct backlight structure has the shape shown in FIG.

  In addition, in the prior art, the luminance of the portion where the luminous intensity of the LED, which is a point light source, is high (the central part of the light emitting surface) is high, and the luminance of the portion where the luminous intensity of the LED is low (the edge of the light emitting surface) is Is low.

  The shape of FIG. 5 is highly dependent on the height a of the light source (distance from the light source to the diffusion plate 1) and the thickness of the diffusion plate 1, so that the light emitting surface 4 is bright and a thin shape is obtained for an LED or the like. When the point light source 3 having a high luminous intensity is used, the light emitted from the point light source 3 floats on the light emitting surface 4 in a spot shape. As a countermeasure, the diffuser plate 1 is thickened and the position of the point light source 3 is increased. Will do.

  In view of the above problems, the present invention can make the luminance of the light emitting surface uniform, reduce the height of the light source, and adjust the thickness of the diffusion plate 1 and the height of the point light source 3 in the direct backlight structure. An object is to provide a liquid crystal display backlight structure capable of adjusting the luminance of the light emitting surface 4.

  In order to solve the above problems, the present invention is configured as follows. That is, in a liquid crystal display backlight structure, a direct-type backlight has a point light source (such as an LED), and a structure of a diffuser plate on which light emitted from a plurality of or a single light source is incident is the plurality of light sources The cross section of the case is provided with a recess between the point light source and the point light source, and has a refracting portion from the recess to the inner wall, and a recess on the light emitting surface side. It is characterized by having.

  According to the above configuration, in claim 1, in the backlight structure of the liquid crystal display unit in which the backlight of the liquid crystal display element is configured using the light emitter, and the diffusion portion is provided between the light emitter and the liquid crystal display element, The diffusing portion has an inner wall on the space side formed inside thereof, a bonding surface of the liquid crystal display element is an outer wall, the inner wall is provided with a refracting portion, and the outer wall is provided with a recess. The backlight structure of the liquid crystal display unit is used.

  With the above configuration, the uneven brightness of the liquid crystal display element due to the backlight of the point light source, which has been a problem in the past, is improved. In this configuration, the shape of the diffusing unit 10 can be mainly handled only by the refracting unit 11 and the recessed part 30, so that a special reflecting plate is not prepared or an arrangement space for the LEDs is not individually secured. Both can be provided at a low cost with a simple configuration.

  Examples of the present invention will be described. In the basic structure of the backlight structure for liquid crystal display in the present invention, the light source plate type point light source space is arranged directly under the liquid crystal display element, and the light of the point light source is deformed by the diffusing part so that there is no unevenness in the display part. A uniform brightness is obtained.

  Specifically, the liquid crystal display device of the present invention will be described with reference to FIG. In FIG. 1, an LED 3-3 serving as a light emitter is disposed on a case 20, and there is a diffusion part 10 having a predetermined space inside the LED 3-3. On the upper surface, a light emitting surface 4 serving as a backlight of liquid crystal is disposed. With such a structure, the issuing surface 4 can obtain a backlight using the LED 3-3 disposed immediately below as a light source by the diffusing unit 10, and forms a direct-type backlight structure.

  Next, the most characteristic shape of the diffusing part in the present invention will be described. The light source of the LED 3-3 can be refracted on the inner wall of the diffusing part 10 directly above the LED 3-3. A refracting portion 11-11 having a shape is formed. Specifically, in the inner wall 21 of the diffusing unit 10, the other diffusing unit 10 is formed so that the thickness of the other diffusing unit 10 is reduced from right above the two LEDs 3-3 to the inside of each LED 3-3. The refracting portion 11-11 is connected in a tapered shape, and light is refracted by the corner of the refracting portion 11-11 and the tapered portion.

  Moreover, the cross-sectional shape of the outer wall of the diffusion portion 10 is substantially rectangular or elliptical, and a liquid crystal display element is attached to the upper surface. In the present invention, the concave portion 30-30 is formed on the upper surface of the outer wall at a predetermined position on the attachment surface. The position and shape of the concave portion 30-30 are formed so that the light refracted by the refracting portion 11-11 can be used as a backlight from the light emitting surface 4 without unevenness.

  Next, the characteristic configuration of the backlight will be described with reference to FIGS. FIG. 2 is a cross-sectional structure showing the backlight configuration of the present embodiment. FIG. 2 shows a cross-sectional structure of the MM cross section of FIG. The optical path of the irradiation light irradiated from LED3 used as a point light source is demonstrated. As shown in FIG. 2, the light emitted from the LED 3 to the diffusing portion is incident on the diffusing portion 10, but the light incident on the refracting portion 11 of the diffusing portion 10 is refracted as shown in the optical path 101. The angle φ degree of the refracting portion 11 is determined so that the remaining transmitted and absorbed light is reflected and incident on the C portion.

  Further, by making the angle φ of the refracting part 11 and each corner of the refracting part 11 into a curved surface, the light intensity incident on the C part can be adjusted by changing the optical path of the irradiation light emitted from the LED 3. Moreover, the brightness | luminance of the light emission surface 4 can be adjusted by shortening the a dimension of FIG. In addition, in order to equalize the luminance of the light emitting surface 4 efficiently, it is preferable that the LED 3 is disposed so that the vertex B of the refracting portion 11 is located in a portion extending vertically from the central portion A of the LED 3.

  Next, the angle φ of the refracting portion 11, the distance a from the LED 3 to the diffusing portion 10, and the thickness of the diffusing plate will be described with reference to FIG. As shown in FIG. 3, the distance between the inner walls 21a and 21b of the backlight case 20 is L, the distance a from the upper end of the LED 3-3 to the refracting portion 11, the distance between the LEDs 3-3 is K, and the LED 3-3 The inner angle at which the line V connecting the line V extending vertically from the center and the points B and D of the refracting portion 11a intersects is θ, the plate thickness of the backlight case 20 at the O portion of the light emitting surface 4 is d1, and the LED 3-3 The thickness of the backlight case 20 in the region indicated by the arrow B of the line V extending vertically upward from the center is defined as d2. Further, for convenience of explanation, the central portion of the LED 3-3 is A, the point where the optical path 102 of the irradiation light irradiated from the LED 3-3 is reflected by the diffusing portion 10, the reflected light is at the center of the O portion of the light emitting surface 4. Let C be the intersection of the vertical perpendicular W and the inside of the backlight case 20.

  In such a configuration, the irradiation light irradiated from the LED 3-3 is reflected once at the refracting portion B point of the diffusion plate and then incident on the point C, that is, the irradiation light indicated by the optical path 102 in FIG. To obtain it, the following configuration is adopted. The relationship between the plate thicknesses is d1 <d2 (1), the angle B is ∠ABC ≧ 90 ° (2), and the angle θ is θ = 90 ° − (∠BCD + ∠DBC) (3). Further, ∠ABC = 180 ° − (θ + ∠DBC) (4), and when equation (3) is substituted into equation (4), ∠ABC = 90 ° + ∠BCD (5).

  Further, the thicknesses of d1 and d2 of the diffusing unit 10 are directly related to the luminance of the light emitting unit. The relationship between the thickness of the diffuser and the luminance changes linearly. That is, when the thickness is thick, the luminance is low (dark), and when the thickness is thin, the luminance is high (bright). Therefore, the dimensions of d1 and d2 are determined so that the expression (1) is satisfied and the luminance at the point α = the luminance at the point β.

  Further, an elliptical semicircular recess (curved recess) 30 shown in FIG. 3 is provided on the light emitting surface side in the direction of the V-axis arrow B, and the light irradiated to the diffusing unit 10 is diffused in the diffusing unit 10. The light within the focal length of the recess 30 is a parallel light beam. By using parallel rays, the illuminance can be increased to the reciprocal of the area ratio, and the darkness of the light emitting surface in the direction of the V-axis arrow B can be made uniform with the concave portion 30 to prevent uneven brightness. Yes.

  In this embodiment, an example of the luminance distribution of the light emitting surface obtained by calculation is shown in FIG. In FIG. 4, the horizontal axis x represents the distance from the inner walls 21a to 21b of the backlight case 20, and the vertical axis y represents the relative luminance when the luminance at the 2 / L point on the light emitting surface is 1. The calculation model in FIG. 4 is two LEDs, the transmittance of the diffusion plate is 45%, the reflectance is 45%, the absorption is 10%, the distance between the diffusion plate inner walls 21a-21b is 24.6 mm, and the center portion of the LED 3 The distance between them is 16 mm, the thickness of the diffuser is d1 = 1 mm, d2 = 3.8 mm, θ = 52 ° of the diffusing portion refracting portion, ∠ABC = 128 ° It consists of parts.

  In FIG. 4, (a) shows the luminance distribution of the present embodiment, and (b) shows the luminance distribution of the conventional embodiment. As can be seen from FIG. 4, the luminance of the light emitting surface 4 is made uniform as a whole in the embodiment shown in (a) as compared to the conventional light emitting surface shown in (b).

  Table 1 shows a table in which a value obtained by dividing the maximum luminance value by the minimum luminance value is evaluated as uniformity in terms of luminance uniformity. The uniformity in the conventional embodiment is 1.99 in the present embodiment compared to 1.99, and the uniformity is improved.

  In the embodiment of the present invention, two LEDs 3-3 are provided as a light source. However, the number and position are not limited to the embodiment described above, and it is sufficient that at least one LED 3-3 is provided. As long as a sufficient light source can be secured as a light, the light source is not limited to an LED, and a light source such as another light bulb may be used. Further, the portion where the LED 3-3 is disposed may not be the above case but may be a member such as a wiring board, for example, and the case or the like may be provided with a reflector or a reflective material as described in the prior art. By providing, it is good also as a structure which diffuses the light source from a downward direction separately.

The top view of the backlight structure for liquid crystal displays made into the Example of this invention is shown. 1 is a side sectional view of a backlight structure for a liquid crystal display according to an embodiment of the present invention. An explanatory view of a backlight structure for a liquid crystal display as an example of the present invention is shown. The characteristic view of the backlight for liquid crystal displays made into the Example of this invention is shown. The top view of the backlight structure for the conventional liquid crystal display is shown.

Explanation of symbols

In the drawings, the same reference numerals indicate the same or corresponding parts.
3 LED
4 Light emitting surface 10 Diffusion part 20 Case 21 Inner wall 11 Refraction part 30 Concave part

Claims (1)

In a backlight structure of a liquid crystal display section in which a backlight of a liquid crystal display element is configured using a light emitter and a diffusion section is provided between the light emitter and the liquid crystal display element, the diffusion section is formed inside the backlight section. A backlight structure for a liquid crystal display section, comprising an inner wall on the space side, an attachment surface of the liquid crystal display element as an outer wall, a refracting portion on the inner wall, and a recess on the outer wall.

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