JP2012256534A - Planar lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar lighting device of sidelight type capable of expanding uniform region of luminance of emitting light and improving its average luminance, while containing enlargement of the device.SOLUTION: The planar lighting device 10 is a sidelight type planar lighting device having a light guide plate 12 and light sources 17, 18 which are arranged along two opposed side end faces 13, 15 of the light guide plate 12, and is provided with a double-sided prism sheet 14 that is arranged on the emission face 19 side of the light guide plate 12. The rear face 20 of the light guide plate 12 includes a first region 22 in which an optical path changing means 21 is not formed and a second region 24 in which the optical path changing means 21 is formed, and a prescribed length B in light guide direction of the first region 21 satisfies relations of 0<B<(X-Y)/2 with the total length X in light guide direction of the light guide plate 12 and the length Y in light guide direction of an effective area 28 of the emission face 20.

Description

  The present invention relates to a planar illumination device suitable as a backlight of a liquid crystal display device, particularly as a backlight for a liquid crystal display device used in a naked-eye 3D display system.

  In recent years, a naked-eye 3D display system that allows an observer to visually recognize a stereoscopic (3D) image without using a dedicated instrument such as glasses has attracted attention. Conventionally, in such a naked-eye 3D display system, an image for the left eye and an image for the right eye displayed on the liquid crystal display device are respectively applied to only the left eye and only the right eye by the light distribution control of illumination light from the backlight. There has been proposed a technique for supplying and thereby realizing naked-eye 3D display (see, for example, Patent Document 1).

  As shown in FIG. 5, the display device 110 described in Patent Document 1 is disposed between a liquid crystal display panel 120, a backlight 130 that supplies light to the liquid crystal display panel 120, and between the liquid crystal display panel 120 and the backlight 130. A double-sided prism film 140. The backlight 130 includes a light guide plate 125, a right eye image solid light source 132 disposed on the first light input surface 131 of the light guide plate 125, and a left eye image solid disposed on the second light input surface 133. A light source 134 is included. Further, a linear prism is formed on the entire rear surface 136 of the light guide plate 125 as an optical path changing means.

  The double-sided prism film 140 includes a triangular prism row extending substantially parallel to the first and second light input surfaces 131 and 133 on the surface of the light guide plate 125 on the light output surface 135 side, and on the surface on the display panel 120 side, Cylindrical lens rows extending substantially parallel to the first and second light input surfaces 131 and 133 are provided. With this configuration, the light enters the light guide plate 125 from the first light input surface 131 and exits from the light output surface 135. The direction of the emitted light is converted into the direction of the right eye of the observer, and the direction of the light incident on the light guide plate 125 from the second light input surface 133 and emitted from the light output surface 135 is changed to the direction of the left eye of the observer. Functions to convert.

  The display system 110 alternately displays the right-eye image and the left-eye image on the display panel 120, and turns on the right-eye image solid-state light source 132 (at the same time for the left-eye) when displaying the right-eye image. When the left eye image is displayed, the left eye image solid light source 134 is turned on (at the same time, the right eye image solid light source 132 is turned off). A right eye image and a left eye image are selectively supplied to the eyes. The display system 110 includes a synchronous driving element 150 and an image source 160 for enabling such an operation.

Special table 2010-541020

  Conventionally, in a backlight for a naked-eye 3D display system as shown in FIG. 5, when a linear prism is formed on the entire back surface 136 of the light guide plate 125, the luminance is remarkably increased near the light input surfaces 131 and 133. There was a problem that illumination light could not be obtained. In order to deal with this problem, for example, it is conceivable that a portion with extremely high luminance near the light input surfaces 131 and 133 is shielded to be an ineffective area. In this case, the first light input surface 131 is used. In order to secure a necessary effective area between the second light input surface 133 and the second light input surface 133, the length of the light guide plate must be extended, resulting in a problem that the apparatus becomes larger. Further, in this method, since the utilization efficiency of the light emitted from the light sources 132 and 134 is also reduced, the total amount of light emitted from the effective area (and consequently the average brightness of the backlight) is reduced.

  In view of the above problems, the present invention is capable of expanding a uniform region of luminance of emitted light and improving the average luminance of the sidelight type planar lighting device while suppressing an increase in size of the device. An object is to provide a planar lighting device.

  The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further, while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

(1) In a sidelight type planar illumination device including a light guide plate and a light source disposed along two opposing side end surfaces of the light guide plate, a double-sided prism disposed on the output surface side of the light guide plate A first region in which a rear surface of the light guide plate is provided in a range having a predetermined length in a light guide direction from each of two side end surfaces on which the light source is disposed, and an optical path changing unit is not formed And a second region provided between the two first regions and formed with an optical path changing means, wherein the predetermined length B in the light guide direction of the first region is the light guide of the light guide plate A total length X in the direction and a length Y in the light guide direction of the effective area of the exit surface;
0 <B <(XY) / 2
A planar lighting device satisfying the following relationship (Claim 1).

(2) The planar illumination device according to (1), wherein the optical path changing means is a linear prism extending in parallel with a light incident surface of the light guide plate. ).

(3) The planar illumination device according to (1) or (2), wherein the second region on the back surface of the light guide plate is formed by a convex curved surface. 3).

The planar lighting device according to the present invention is configured as described above, and thus, in the sidelight type planar lighting device, enlarges a uniform region of luminance of emitted light while suppressing an increase in size of the device, and The average luminance can be improved.
The planar illumination device according to the present invention can be suitably used as a backlight for a liquid crystal display device of a naked eye 3D display system.

(A) is a side view which shows the principal part of the planar illuminating device in one Embodiment of this invention, (b) is a side view which shows the light-guide plate of the planar illuminating device shown to (a). (A) And (b) is a side view which shows another example of the light-guide plate with which the planar illuminating device in one Embodiment of this invention is provided, respectively. (A), (b), (c) is a side view which respectively shows another example of the light-guide plate with which the planar illuminating device in one Embodiment of this invention is provided. (A), (b) is the graph which showed the luminance distribution with respect to the light guide direction position of a light-guide plate by making the length of 1st area | region into a parameter, (a) is when only the left side light source is lighted. Luminance distribution, (b) shows the luminance distribution when only the right light source is turned on. It is a side view which shows an example of the conventional naked eye 3D display system.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, each figure which shows the whole or a part of a planar illuminating device is a schematic diagram which emphasizes the characteristic for description, and the relative dimension of each part shown in figure is not necessarily an actual scale. Does not reflect.

Fig.1 (a) is a side view which shows the principal part of the planar illuminating device in one Embodiment of this invention.
A planar illumination device 10 illustrated in FIG. 1A is a sidelight type planar illumination device including a light guide plate 12 and light sources 17 and 18. The light guide plate 12 is a plate-shaped light guide body having one main surface as an output surface 19 and a main surface (back surface) opposite to the output surface 19 as a reflection surface 20, and two opposing side end surfaces are incident. A plurality of light sources (for example, light emitting diodes) 17 and 18 are disposed along the light incident surfaces 13 and 15, which are used as the surfaces 13 and 15. Further, in the planar illumination device 10, a double-sided prism sheet 14 is disposed on the light exit surface 19 side of the light guide plate 12, and an optical sheet 16 is disposed on the reflective surface 20 side of the light guide plate 12.

  The light guide plate 12 is formed by molding a transparent resin material such as methacrylic resin or polycarbonate resin. All light incident on the light guide plate 12 through the light incident surfaces 13 and 15 is transmitted between the light exit surface 19 and the reflection surface 20. The light is propagated through the light guide plate 12 toward the light incident surfaces 15 and 13 facing each other while repeating reflection, and the propagation light is uniformly emitted from the emission surface 19 in the process. In this sense, in the planar lighting device 10, a direction orthogonal to the light incident surfaces 13 and 15 of the light guide plate 12 (the left-right direction in FIG. 1) is referred to as a light guide direction.

  In the following description, for each component of the light guide plate 12, the length in the light guide direction is also simply referred to as “length”, and the light guide is in a plane parallel to the main surface (the exit surface 19 and the reflection surface 20). The length in the direction orthogonal to the direction (the direction perpendicular to the paper surface in FIG. 1) and the length in the direction orthogonal to the main surface of the light guide plate 12 (the vertical direction in FIG. 1) are respectively “width”. Also referred to as “thickness”.

Here, the planar illumination device 10 is suitably used as a backlight of a liquid crystal panel in the naked-eye 3D display system as described above with reference to FIG. 5, and the double-sided prism sheet 14 is, for example, as shown in FIG. The double-sided prism film 140 shown in FIG. However, the present invention is not limited by the configuration of the double-sided prism sheet 14 and can have any appropriate configuration as long as the same function as that of the double-sided prism film 140 is achieved.

  In the planar illumination device 10, the optical sheet 16 disposed on the reflective surface 20 side of the light guide plate 12 may be a highly reflective sheet (for example, a reflectance of 98% or more), or a light absorbing member. In other words, it may be one that prevents the reflection of the light incident on the optical sheet 16 (and hence the incident light of the reflected light into the light guide plate 12) (for example, the reflectance is 30% or less).

  In the planar illumination device 10, the light incident on the optical sheet 16 includes light leaked from the reflection surface 20 of the light guide plate 12 and directly enters the optical sheet 16 without entering the light guide plate 12 from the light sources 17 and 18. Incident light, light emitted from the light guide plate 12 is reflected by the double-sided prism sheet 14 and incident on the optical member 16 through the light guide plate 12, and light emitted from the double-sided prism sheet 14 is reflected on the back surface of the liquid crystal panel or the like. Thus, light incident on the optical member 16 through the double-sided prism sheet 14 and the light guide plate 12 is included.

In the planar illumination device 10, the reflection surface 20 of the light guide plate 12 is provided in a range having a predetermined length B in the light guide direction from the light incident surfaces 13 and 15 as shown in FIG. And a second region 24 provided between the first region 22 on the light incident surface 13 side and the first region 22 on the light incident surface 15 side. Therefore, when the total length of the light guide plate 12 in the light guide direction is X, the length A of the second region 24 in the light guide direction is “X-2B”.

A plurality of linear prisms 21 extending substantially parallel to the light incident surfaces 13 and 15 are formed in the second region 24, and the first region 22 is formed of a flat surface on which the linear prisms 21 are not formed. Here, the linear prism 21 reflects a part of the light that has entered the light guide plate 12 through the light incident surfaces 13 and 15 and reached the reflection surface 20 to be emitted from the emission surface 19, and has an appropriate incident angle. This is for entering the double-sided prism sheet 14.

Further, in the planar illumination device 10, the exit surface 19 is configured to use a range having a predetermined length Y in the light guide direction as an effective area 28 and use the emitted light from the effective area 28 as illumination light. In addition, the area on the light incident surface 13 side and the area on the light incident surface 15 side outside the effective area 28 are non-effective areas 26 in which light emitted from these areas is not used as illumination light.
The predetermined length B in the light guide direction of the first region 22 of the reflection surface 20 is the total length X of the light guide plate 12 in the light guide direction and the length Y of the effective area 28 of the output surface 19 in the light guide direction.
0 <B <(XY) / 2 (1)
Is set to satisfy the relationship.

  Here, “(XY) / 2” corresponds to the length in the light guide direction from the light incident surfaces 13 and 15 of the ineffective area 26. Therefore, the above equation (1) means that the boundary between each first region 22 and the second region 24 is in the region corresponding to the non-effective area 26 of the reflection surface 20 of the light guide plate 12. . In other words, the length A in the light guide direction of the second region 24 of the reflection surface 20 is longer than the length Y in the light guide direction of the effective area 28 of the emission surface 20 (and is longer than the total length X of the light guide plate 12). (Short).

  In the planar illumination device 10, the light guide plate may be such that the second region 24a has a convex curved surface, like the light guide plate 12a shown in FIG. Preferably, the convex curved surface forming the second region 24a is formed such that the thickness of the light guide plate 12a is the thickest at the center in the light guide direction, and is, for example, a curved surface having an arc shape when viewed from the side. is there. Alternatively, the light guide plate may be such that the second region 24b forms a concave curved surface (for example, a curved surface having an arc shape when viewed from the side) as in the light guide plate 12b shown in FIG.

  Moreover, when forming the 2nd area | region of the light-guide plate 12 in convex shape, a 2nd area | region may consist of a curved surface of elliptical arc view in side view like the 2nd area | region 24c shown to Fig.3 (a). As shown in FIG. 3B, the second region 24d may be a flat surface configured in a triangular shape in side view, and the second region 24e shown in FIG. It may consist of a flat surface configured in the shape of a viewing platform. 3A to 3C, preferably, the convex curved surface forming the second region 24a is such that the thickness of the light guide plate 12a is the thickest at the center in the light guide direction. Is formed.

  In FIG. 3, illustration of linear prisms formed in the second regions 24c to 24e is omitted. Moreover, when forming the 2nd area | region 24 of the light-guide plate 12 in concave shape, you may make it into the shape which reversed the unevenness | corrugation of the shape shown to Fig.3 (a)-(c).

The effects of the planar illumination device 10 configured as described above will be described with reference to FIG. 4 and Tables 1, 2, and 3.
4A and 4B are graphs showing the luminance distribution with respect to the light guide direction position of the light guide plate 12 using the length B of the first region 22 as a parameter, and FIG. The luminance distribution when only the light source (for example, the light source 18) is turned on, and (b) shows the luminance distribution when only the right light source (for example, the light source 17) is turned on.

  The total length X of the light guide plate 12 used for the measurement is 108 mm, and the horizontal axes in FIGS. 4A and 4B are guided with the central portion of the light guide direction of the light guide plate 12 being 0 and the right direction being the positive direction. The light direction position is shown. In the measurement, LEDs were used as the light sources 17 and 18. Further, the length Y of the effective area 28 on the emission surface 19 was set to 92 mm. Therefore, the length “(XY) / 2” of each ineffective area 26 is 8 mm.

  The light guide plate 12 used for the measurement has a thickness in the first region 22 of 0.6 mm, and the second region 24 has a curved surface in which the light guide plate 12 has the thickest central portion in the light guide direction. Is.

In the measurement, the length B of the first region 22 is 0 mm (sample No. 1), 2 mm (sample No. 2), 4 mm (sample No. 3), 5 mm (sample No. 4), and 6 mm (sample No. 2). 5) and 6 mm of 8 mm (sample No. 6), numbers 1 to 6 attached to the curves indicated by different line types in FIGS. 4A and 4B are the samples. No. It is.

  For each sample, a plurality of linear prisms 21 arranged at a pitch of 89 μm are formed in the second region 24 (length A = X−2B). However, sample no. 1, the entire reflection surface 20 is configured as a second region 24.

  From FIGS. 4A and 4B, in general, the luminance in the vicinity of the light incident surfaces 13 and 15 (that is, around −50 mm in the case of FIG. 4A and around 50 mm in the case of FIG. 4B) is as follows. It can be seen that there is a tendency like this. That is, when the length B of the first region 22 is short, the luminance near the light incident surfaces 13 and 15 shows a remarkably high value, and as the length B of the first region 22 increases, the peak decreases and the luminance The distribution becomes uniform, but when the length B of the first region 22 is further increased, the luminance near the light incident surfaces 13 and 15 now shows a remarkably low value.

Tables 1 and 2 shown below summarize the results of evaluating the uniformity of luminance for the luminance distribution exhibiting such a tendency. Tables 1 and 2 are shown in FIG. 4A and FIG. This corresponds to 4 (b).

  Here, in Table 1 and Table 2, the uniform luminance region is a range showing a value within ± 10% with respect to the average value of the luminance at each point measured every 2 mm over the entire length of the light guide plate 12 in the light guide direction. It is. The average luminance indicates the average value of the luminance at each point in the luminance uniform region obtained in this way. From Table 1 and Table 2, sample No. 1 in which the first region 22 is not provided (B = 0 mm). Sample No. 1 provided with the first region 22 (B> 0 mm) with respect to the average luminance of 1. In 2-6, it turns out that average brightness | luminance is improving all.

  Further, with respect to the luminance uniform areas shown in Table 1 and Table 2, the results of newly integrating the areas that are the luminance uniform areas in both are shown in Table 3 together with the length of each luminance uniform area. .

  For example, when the planar illumination device 10 is used as a backlight in the naked-eye 3D display system as described above with reference to FIG. 5, such a naked-eye 3D display system alternately turns on and off the right LED and the left LED. Thus, 3D display is realized, so that the uniform luminance region shown in Table 3 is a region that can be suitably used as the effective area 28.

  From Table 3, sample No. 1 in which the first region 22 is not provided (B = 0 mm). 1, the length of the uniform luminance region is 88 mm, and the set effective area length Y = 92 mm cannot be secured, whereas the first region 22 having the length B = 2 mm, 4 mm, 5 mm, and 6 mm, respectively. Sample No. provided with 2 to 5, it can be seen that the length of the uniform luminance region is extended to 92 mm, 96 mm, 104 mm, and 92 mm, respectively, and it is possible to secure a necessary effective area in the luminance region. On the other hand, when the length of the first region 22 is extended to 8 mm (that is, the length of the ineffective area (XY) / 2), the length of the uniform luminance region is reduced to 84 mm. The necessary effective area cannot be secured.

  As a result, the effective area having the required length Y = 92 mm is secured by setting the length B of the first region 22 to 0 <B <6 mm (= (X−Y) / 2). It shows that it becomes possible. In particular, in the range of about 3 mm <B <about 5 mm, the length of the uniform luminance region has a sufficient margin with respect to the required effective area length Y. In other words, the predetermined length Y is It is possible to shorten the total length X of the light guide plate necessary for securing the effective area.

  As described above, in the planar illumination device 10 according to the present embodiment, a region with uniform luminance is expanded without extending the length of the light guide plate 12 and causing the device to be enlarged, and the average in the region is increased. The luminance can be improved.

  Further, in the planar illumination device 10, when the second region 24 is formed of a convex curved surface, the light guide plate from the light source 18 through the light incident surface 15 when one light source (for example, the light source 18) is turned on. The light extraction efficiency from the light exit surface 19 of the light incident on the light 12 is decreased on the light incident surface 15 side from the portion where the thickness of the light guide plate 12 is maximum, and is increased on the light incident surface 13 side, thereby making the luminance uniform. The property can be further improved. Of course, this is the same when the other light source (for example, the light source 17) is turned on.

Note that the luminance distribution shown in FIGS. 4A and 4B (and Tables 1 to 3) is measured by placing the optical sheet 16 having a reflectance of 98% on the reflective surface 20 side of the light guide plate 12. It is a thing. In the planar lighting device 10, the configuration using such a highly reflective sheet as the optical sheet 16 is advantageous for improving the luminance.
However, in the planar lighting device according to the present invention, even if the reflectance of the optical sheet 16 is 30% or less (for example, 0%), see FIGS. 4A and 4B (and Tables 1 to 3). As described above, similar effects can be obtained with respect to the expansion of the uniform luminance region and the improvement of the average luminance.

  As described above, when the reflectance of the optical sheet 16 is 30% or less (for example, 0%), the planar illumination device 10 is applied as a backlight of a liquid crystal panel in a naked-eye 3D display system. The light emitted from the right eye light source (for example, the light source 17) and visually recognized by the left eye of the observer, and the light emitted from the left eye light source (for example, the light source 18) and visually recognized by the observer's right eye. It is possible to reduce the crosstalk between the image for the right eye and the image for the left eye effectively.

  In this case, the entire optical sheet 16 may be made of a light absorbing member, and thereby the reflection of light incident on the optical sheet 16 may be suppressed almost completely. Alternatively, the optical sheet 16 has a two-layer structure in which a reflectance control member having a function of reflecting part of light and transmitting part of light and a light absorption member are laminated, and reflectance control is performed. The member may be disposed so as to face the reflecting surface 20. In this case, the optical sheet 16 is configured by adhering (or adhering) the reflectance control member and the light absorbing member with an adhesive (or adhesive), and the reflectance control member and the adhesive layer (or adhesive layer) A three-layer structure of a light absorbing member may be provided.

  Here, the light absorbing member used for the optical sheet 16 may be, for example, a black film formed by molding a resin material (for example, PET) in which a black pigment (for example, carbon black) is dispersed. The surface of a black film may be roughened. Moreover, the reflectance control member used for the optical sheet 16 may include a multilayer film structure formed by laminating a plurality of resin materials (for example, PET) having different refractive indexes. Alternatively, the reflectance control member may be formed by forming a metal film on a transparent substrate film. In this case, the transmittance and reflectance of the reflectance control member are controlled by the thickness of the metal film.

10: planar illumination device, 12: light guide plate, 13, 15: light incident surface, 14: double-sided prism sheet, 16: optical sheet, 17, 18: light source, 19: exit surface, 20: reflective surface, 21: linear Prism, 22: first area, 24: second area, 26: ineffective area, 28: effective area

Claims (3)

In a sidelight type planar illumination device comprising a light guide plate and a light source disposed along two opposing side end surfaces of the light guide plate,
A double-sided prism sheet disposed on the light exit surface side of the light guide plate, the back surface of the light guide plate having a predetermined length in the light guide direction from each of the two side end surfaces on which the light source is disposed A first region where the optical path changing means is not formed, and a second region provided between the two first regions and where the optical path changing means is formed,
The predetermined length B in the light guide direction of the first region is the total length X in the light guide direction of the light guide plate and the length Y in the light guide direction of the effective area of the exit surface,
0 <B <(XY) / 2
A planar illumination device characterized by satisfying the relationship:   The planar illumination device according to claim 1, wherein the optical path changing unit is a linear prism extending parallel to a light incident surface of the light guide plate.   The planar illumination device according to claim 1 or 2, wherein the second region on the back surface of the light guide plate is formed of a convex curved surface.

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