JP2006162827A - Surface light source device, and transmission display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device in which uniform illumination free of unevenness can be performed irrespective of positions for observing a screen. <P>SOLUTION: The light source device is equipped with light emitting tubes 13 arrayed at equal intervals with spaces L, and a uniformization sheet 14 which uniformizes the light emitted from the light emitting tubes 13 by diffusion. When the transmittance of the light made incident on the uniformization sheet 14 from a normal direction of the sheet is defined as T, the relations of the vertical transmittance T, the spaces of the light emitting tubes 13, and the distance D between the light emitting tubes 13 and the uniformization sheet 14 are so set as to satisfy the relations 0.8T≤0.7×2×cos<SP>2</SP>(tan<SP>-1</SP>(L/2D))-0.8×2×cos<SP>2</SP>(tan<SP>-1</SP>(L/D))≤1.2T. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface light source device and a transmissive display device used for illumination of a liquid crystal display device or the like.

Various surface light source devices have been proposed and put into practical use as surface light sources for illuminating a transmissive liquid crystal display (LCD panel) or the like from the back. The surface light source device mainly includes an edge light type and a direct type by converting a light source that is not a surface light source into a surface light source.
For example, in the direct type, light is introduced using a cold cathode tube (light emitting tube) in parallel from the back, and the distance between the cold cathode tube and a transmissive display unit such as an LCD panel is appropriately increased, In the meantime, a diffusion plate was used, and a plurality of sheets for converging light were used.
In such a conventional method, the convergence characteristics are insufficient for the large number of optical sheets required, and the LCD panel is improved to compensate for this, and the image quality is also improved even for incident light from an oblique direction. It was set as the structure which does not drop.

However, this method has a problem in that the light use efficiency is reduced and the configuration of the LCD panel is complicated, resulting in an increase in cost.
In particular, in the direct type, the light depends on whether it is a part close to the cold cathode tube (a position close to the cold cathode tube or a position close to a gap part of the cold cathode tubes arranged in parallel). Unevenness (light source unevenness) easily occurs in intensity (luminance). In order to suppress this, if the distance between the cold cathode tube and the LDC is made large, there is a problem that the thickness of the display becomes thick. In addition, when the diffusion is increased or the transmission amount is limited in order to suppress unevenness, there is a problem that the amount of light used is reduced.

For example, in the surface light source devices described in Patent Documents 1 and 2, uniformity is maintained by providing a light-shielding portion (lighting curtain, light-shielding dot layer). In this method, the amount of light used is as described above. Decreased.
Also, a method using a sheet provided with lenticular lenses on both sides is reported, for example, in Patent Document 3, but this is a configuration for performing diffusion control in two directions and has no function of converging light. Therefore, there is a problem in that unevenness of brightness occurs depending on the position where the screen is observed because the optical axis varies depending on the location of the LCD depending on the positional relationship with the cold cathode tube.
JP 05-119703 A JP 11-242219 A Japanese Patent Laid-Open No. 06-347613

  An object of the present invention is to provide a surface light source device and a transmissive display device that can perform uniform illumination without unevenness regardless of the position where the screen is observed.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to the Example of this invention is attached | subjected and demonstrated, it is not limited to this.
The first aspect of the present invention is a direct-type surface light source device that illuminates the transmissive display unit (11) from the back, and the light sources (13) arranged at equal intervals at a distance L and the distance from the center of the light source. And a homogenization sheet (14) that diffuses and equalizes the light emitted from the light source, and is arranged in a direction normal to the sheet. When the transmittance of incident light is T, 0.8T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) A surface light source device (12, 13, 14, 15, 16) characterized by satisfying the relationship of 1.2T.

  Invention of Claim 2 is provided with the diffusion sheet (16) which is provided in the output side rather than the said uniformization sheet (14), and has the effect | action which diffuses light in the surface light source device of Claim 1. It is the surface light source device (12, 13, 14, 15, 16) characterized.

The invention of claim 3 is a direct type surface light source device for illuminating the transmissive display unit (11) from the back, and the light sources (13) arranged at equal intervals with a distance L and the distance from the center of the light source. And a homogenization sheet (14) that diffuses and equalizes the light emitted from the light source, and is arranged in a direction normal to the sheet. When the transmittance of incident light is T, 0.9T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) A surface light source device (12, 13, 14, 15, 16) characterized by satisfying the relationship of 1.1T.

  The invention of claim 4 comprises a transmissive display unit (11) and the surface light source device (12, 13, 14, 15, 16) according to any one of claims 1 to 3. A transmissive display device (10).

According to the present invention, the following effects can be obtained.
(1) 0.8T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.2T Therefore, a surface light source device that emits uniform illumination light can be obtained by combining with a diffusion sheet.

(2) 0.8T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.2T And a diffusion sheet that is provided on the emission side of the homogenization sheet and has a function of diffusing light, can emit uniform illumination light.

(3) Relation of 0.9T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.1T Therefore, a surface light source device that emits illumination light that is uniform and has high brightness can be obtained.

  The purpose of uniform illumination without unevenness was realized by defining the relationship between the spacing between the light sources, the distance between the light source and the homogenizing sheet, and the transmittance in the normal direction of the homogenizing sheet.

FIG. 1 is a diagram showing an embodiment of a transmissive display device according to the present invention.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
The transmissive display device 10 in this embodiment includes an LCD panel 11, a reflecting plate 12, an arc tube 13, a uniformizing sheet 14, a reflective polarizing sheet 15, a diffusion sheet 16, and the like, and an image formed on the LCD panel 11. This is a transmissive liquid crystal display device that illuminates information from the back by a surface light source device that includes a reflecting plate 12, an arc tube 13, a uniformizing sheet 14, a reflective polarizing sheet 15, and a diffusing sheet 16.

  The LCD panel 11 is an element formed by a so-called transmissive liquid crystal display element, and can display a 30-inch size and 800 × 600 dots. The direction along the longitudinal direction of the arc tube 13 is used as the horizontal direction, and the direction in which the arc tubes 13 are arranged is used as the vertical direction.

The arc tube 13 is a light source of a cold cathode tube forming a light source part of a backlight. In this embodiment, six are arranged in parallel at equal intervals of L = 50 mm. Further, the distance D between the arc tube 13 and the homogenizing sheet 14 described later is D = 25 mm.
A reflector 12 is provided on the back surface of the arc tube 13, and the design allows the incident light illuminance to each part of the screen to be made uniform.
The reflective polarizing sheet 15 is a sheet that is disposed between the LCD panel 11 and the homogenizing sheet 14 and increases the luminance without narrowing the viewing angle. In this embodiment, DBEF (manufactured by Sumitomo 3M Limited) is used.

The diffusion sheet 16 is a sheet that is provided on the emission side from the homogenization sheet 14 and assists the diffusion function of the homogenization sheet 14. In this embodiment, the diffusion sheet 16 is disposed between the homogenizing sheet 14 and the reflective polarizing sheet 15. The diffusion sheet 16 is also called a bead diffusion plate and contains almost no diffusing agent inside. The diffusion bead is dispersed on the surface to form a fine uneven shape on the surface, and according to the curvature of the diffusion bead. Diffuses outgoing light. Therefore, the diffusion sheet 16 can adjust the diffusion degree by the diffusion beads. The haze value of the diffusion sheet 16 in this example is 83.6%.
A uniformizing sheet 14 is provided between the arc tube 13 and the diffusion sheet 16.

FIG. 2 is a perspective view showing the homogenizing sheet 14.
The homogenizing sheet 14 is a sheet that diffuses and homogenizes the light emitted from the arc tube 13, and a lenticular lens shape composed of two types of unit lenses is formed on the emitting side in order to emit light uniformly. ing.
On the exit side of the homogenizing sheet 14, a large number of unit lens sets 141 in which two types of unit lenses 141a and 141b are regularly arranged in parallel are arranged. Note that the direction in which the unit lenses are aligned is the same as the direction in which the arc tubes 13 are aligned (see FIG. 1).
The two types of unit lenses 141 a and 141 b formed on the exit side of the homogenizing sheet 14 in the present embodiment have a shape of a part of a continuous elliptic cylinder whose major axis is orthogonal to the sheet surface of the homogenizing sheet 14. Yes, forming a lenticular lens shape.

When the homogenization sheet 14 is near the arc tube 13 (when light is incident from the normal direction), about half of the light is returned to the light source side, and between the arc tubes 13. When it is near the position (when light enters from an oblique direction), the unit lens shape formed on the emission side is formed so that the light is emitted in the normal direction. Therefore, measuring the transmittance T (hereinafter referred to as the vertical transmittance) T of light that is incident perpendicularly to the homogenizing sheet is emitted to the emitting side, and thus the ability to homogenize the light of the homogenizing sheet 14 is briefly demonstrated. It can be a parameter to represent. That is, when the vertical transmittance T is large, light incident from the normal direction is transmitted as it is, so that it can be said that the ability to make uniform is low. On the other hand, when the vertical transmittance T is small, it can be said that the ratio of returning to the light source side without transmitting the light incident from the normal direction is large, and the ability to equalize is high.
The vertical transmittance T of the homogenizing sheet 14 in this embodiment is T = 0.4.

  Here, of course, good results are not always obtained if the vertical transmittance T is small. Further, the uniformizing sheet 14 is not necessarily uniform without any light source unevenness under any conditions. For example, even when the homogenization sheet is fixed to a certain object, if the distance D from the center of the light source to the incident surface of the homogenization sheet and the distance L between the light sources are different, the luminance distribution of the emitted light Changes. Similarly, even if the distance D and the interval L are fixed, if the shape of the homogenizing sheet changes, the luminance distribution of the emitted light changes.

Therefore, paying attention to the mutual relationship between the vertical transmittance T, the distance D, and the interval L, specific conditions that should be satisfied in order to obtain uniform illumination are derived. Hereinafter, this condition will be described.
FIG. 3 is a diagram schematically showing typical light emitted from the arc tube 13. In FIG. 3, for the convenience of explanation, the arc tube 13 is denoted by reference numerals 13-1 to 13-4.
First, the incident point A immediately above the intermediate position between the arc tube 13-1 and the arc tube 13-2 will be examined. At this incident point A, if the incident lights L1 and L2 incident from the arc tube 13-1 and the arc tube 13-2 are examined, it is simple and sufficient for the examination of luminance unevenness. Here, the incident angle θ _A of the incident lights L1 and L2 incident on the incident point A is given by θ _A = tan ⁻¹ (L / 2D).
On the other hand, the incident point B directly above the arc tube 13-3 will be examined. At this incident point B, if the incident lights L3 to L5 incident from the arc tube 13-2 to the arc tube 13-4 are studied, it is simple and sufficient for the examination of luminance unevenness. Here, the incident angle θ _B of the incident lights L3 and L5 incident on the incident point B is given by θ _B = tan ⁻¹ (L / D).

Then, using these θ _A and θ _B , light emitted from the incident points A and B in the normal direction of the uniformizing sheet 14 is obtained, and the mutual relationship among the vertical transmittance T, the distance D, and the interval L is the minimum. The conditions that can ensure the uniformity of the above were experimentally determined as the following equation (1).
0.8T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.2T Equation ( 1)
Moreover, the following formula | equation (2) was obtained as conditions which can obtain illumination light with higher uniformity than Formula (1).
0.9T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.1T Equation ( 2)
In the present embodiment, as described above, T = 0.4, D = 25 mm, and L = 50 mm, which satisfy both the expressions (1) and (2).

Here, for convenience of explanation, 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) = G.
In order to explain the contents of the equations (1) and (2), the result of calculating the value of G by changing L every 5 mm from 5 to 100 mm with D = 25 mm which is the same as in this embodiment is shown in Table 1. Shown in In addition, Table 2 shows the result of calculating the value of G by changing D every 5 mm from 5 to 100 mm, assuming that L = 50 mm, which is the same as in this example.

FIG. 4 is a graph showing the results of Table 1.
FIG. 5 is a graph showing the results of Table 2.
In the graphs of FIGS. 4 and 5, ranges satisfying the expressions (1) and (2) are shown as the range of G, respectively. In the surface light source device in the range satisfying the formula (2), sufficiently uniform illumination light could be obtained without disposing the diffusion sheet 16. Even in the surface light source device of this example, even if the diffusion sheet 16 is omitted, a sufficiently uniform surface light source device can be obtained.
On the other hand, in the surface light source device that does not satisfy Expression (2) but is in a range satisfying Expression (1), when the diffusion sheet is not used, the light source unevenness is slightly confirmed, but the diffusion sheet is made uniform. By disposing on the light output side, the light source unevenness could not be confirmed, and uniform illumination light could be emitted.

  According to the present embodiment, since the vertical transmittance of the homogenizing sheet and the dimensional relationship with the arc tube are defined, high luminance illumination can be obtained without luminance unevenness. Moreover, it is not necessary to produce a large number of prototypes by trial and error in the shape of the uniformized sheet, and as a result, the surface light source device and the transmissive display device can be provided at low cost.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
(1) In the present embodiment, the example in which the homogenization sheet has a shape close to the lenticular lens shape on the surface on the emission side is shown, but the present invention is not limited to this. It may be a so-called lens array shape arranged in the dimension direction (a square lens shape), or may be a prism sheet in which the prism shape is arranged on the exit side, and does not depend on the shape of the uniformizing sheet.

(2) In this embodiment, the surface light source device and the transmissive display device are shown by combining the homogenizing sheet 14, the diffusion sheet 16, and the reflective polarizing sheet 15. However, the present invention is not limited to this. The diffusion sheet 16 may be omitted, or a surface light source device and a transmissive display device may be formed by combining various optical sheets other than these and the uniformizing sheet 14.

(3) In the present embodiment, an example in which the arc tube 13 that can be regarded as a linear light source is used as the light source has been shown. However, the present invention is not limited to this. Also good.

It is a figure which shows the Example of the transmissive display apparatus by this invention. It is a perspective view which shows the homogenization sheet | seat 14. FIG. FIG. 4 is a diagram schematically showing typical light emitted from the arc tube 13. It is the figure which showed the result of Table 1 in the graph. It is the figure which showed the result of Table 2 in the graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission type display apparatus 11 LCD panel 12 Reflector 13 Light emission tube 14 Uniform sheet 141 Unit lens assembly 141a, 141b Unit lens 15 Reflective polarizing sheet 16 Diffusion sheet

Claims (4)

A direct-type surface light source device that illuminates a transmissive display unit from the back,
Light sources arranged at equal intervals at intervals L;
A uniformizing sheet that is fixed so that the incident surface is located at a position away from the center of the light source by a distance D, and diffuses and uniformizes the light emitted from the light source;
With
When the transmittance of light incident on the uniformized sheet from the normal direction of the sheet is T,
0.8T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.2T
Satisfying the relationship
A surface light source device. The surface light source device according to claim 1,
Provided with a diffusion sheet provided on the emission side than the homogenization sheet and having an action of diffusing light,
A surface light source device. A direct-type surface light source device that illuminates a transmissive display unit from the back,
Light sources arranged at equal intervals at intervals L;
A uniformizing sheet that is fixed so that the incident surface is located at a position away from the center of the light source by a distance D, and diffuses and uniformizes the light emitted from the light source;
With
When the transmittance of light incident on the uniformized sheet from the normal direction of the sheet is T,
0.9T ≦ 0.7 × 2 × cos ² (tan ⁻¹ (L / 2D)) − 0.8 × 2 × cos ² (tan ⁻¹ (L / D)) ≦ 1.1T
Satisfying the relationship
A surface light source device. A transmissive display;
The surface light source device according to any one of claims 1 to 3,
A transmissive display device.

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