JP2012033276A - Planar lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar lighting device in which matching with characteristics of a liquid crystal display device to be used in combination with the lighting device becomes easy and a required viewing angle can be obtained.SOLUTION: Since the inclination angles of a pair of inclined planes 162, 163 which constitute each prism of a downward prism sheet 16 are constructed to be different from each other for the opposed inclined planes, the prism angles of the downward prism sheet 16 become unsymmetrical across the edge line 161 of the prism against the optical axis direction of emission light from the emitting face 12a of a light guide plate 12. Then, the emission light from the emitting face 12a of the light guide plate 12 become unsymmetrical against the extension direction of the edge line 161 of the prism of the downward prism sheet when it is deflected by the downward prism. As a result, the emission luminance with two ridges of the planar lighting device becomes unsymmetrical.

Description

  The present invention relates to a planar illumination device used as illumination means such as a liquid crystal display device, and more particularly to a sidelight type planar illumination device.

In recent years, liquid crystal display devices have been widely used as display devices for electronic devices such as personal computers and mobile phones. Since a liquid crystal is not a self-luminous display element unlike a cathode ray tube or the like, for example, in a transmissive liquid crystal display device, an illuminating means for irradiating light to the liquid crystal panel is indispensable. Even in the transmissive liquid crystal display device, auxiliary illumination means is provided to enable use in a dark place. A sidelight type planar illumination device having a light guide plate and a light source disposed on the side of the light guide plate as main components has an advantage that it can be easily thinned. It is suitably used as an illuminating means, and a cold cathode discharge tube or the like that is a linear light source has been used as the light source.

On the other hand, in recent years, with the improvement in performance of white light emitting diodes (LEDs), the above-mentioned cold cathode discharge tube has been replaced with a white LED as a point light source in order to further reduce the size and thickness of a planar lighting device and reduce power consumption. The number of replaced planar lighting devices has also increased.
For example, in the planar lighting device 100 as shown in FIGS. 6A and 6B, the light guide plate 101 is a plate-like light guide made of a transparent resin material such as methacrylic resin or polycarbonate resin, and one of them. The main surface functions as the exit surface 101a. The opposing main surface functions as a reflecting surface, reflects light incident on the surface, and causes at least part of the light to enter the exit surface 101a with an incident angle less than the critical angle. Diffuse reflection means or regular reflection means 101b is provided.

The light guide plate 101 further includes a first prism sheet 103 and a second prism sheet 104 disposed on the light output side of the first prism sheet 103 on the light exit surface 101a side. A diffusion film 105 is disposed between the light guide plate 101 and the first prism sheet 103, and a reflective polarizing plate (DBEF) 106 is disposed on the light exit side of the second prism sheet 104. Further, a reflection sheet 107 is disposed on the light reflection plate 101 on the regular reflection means 101b side. In FIG. 6, the housing frame for positioning the above-described components and bringing them together is drawn.

By the way, the first and second prism sheets 103 and 104 are sheet-like members made of a transparent resin material such as a PET film, for example, and are arranged in one direction made of methacrylic resin or polycarbonate resin on one main surface 103a or 104a thereof. An extended, multi-row triangular prism is formed. Triangular prisms have apex and valley angles formed at right angles, and the cross-sectional shape is an isosceles triangle. On the other hand, the other main surfaces 103b and 104b of the first and second prism sheets 103 and 104 are formed as flat surfaces.

The first prism sheet 103 has a light incident surface 101c on which the light source 102 is disposed, with the prism surface 103a facing the light exit surface 101a of the light guide plate 101, and the prism extending direction is the light guide plate 101. Are arranged so as to be orthogonal. On the other hand, the second prism sheet 104 has its flat surface 104b opposed to the exit surface 101a side of the light guide plate 101, and the prism extending direction of the prism surface 104a is the light incident surface 101c of the light guide plate 101. Are arranged in parallel. Note that the diffusion film 105 and the DBEF 106 are appropriately arranged according to the characteristics required for the planar illumination device 100.

In the planar illumination device 100 configured as described above, the light emitted from the emission surface 101a of the light guide plate 101 is polarized by the first and second prism sheets 103 and 104, and the light emission luminance of the planar illumination device is increased. Bimodality appears (peaks appear at two points of the entire light emitting surface (omnidirectional)). And a display device incorporating such a planar illumination device having bimodality can improve visibility from two different directions (see Patent Document 1). In the case where the first and second prism sheets 103 and 104 are not used, a normal planar illumination device that does not have bimodality in light emission luminance is configured.

JP 2007-294465 A (paragraphs [0020], [0023], [0034], [0035])

By the way, it is not easy to match the characteristics of a liquid crystal display device used in combination with a conventional planar illumination device having bimodality in light emission luminance, and a display device including the planar illumination device In order to obtain a required viewing angle in the state configured as above, it is necessary to change the arrangement of the diffusion film 105 and the DBEF 106 as appropriate, or to change specifications such as using a plurality of them. Moreover, even if such adjustment is performed, the required viewing angle may not be satisfied.
This invention is made | formed in view of the above problems, The place made into the objective is to solve the said subject by devising the shape of the prism sheet which comprises a planar illuminating device. .

(Aspect of the Invention)
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) A downward prism sheet and an upward prism sheet, each including a light guide plate and a light source disposed on one end face of the light guide plate, wherein a plurality of prisms are disposed in parallel on the output surface side of the light guide plate Are stacked so that the ridge lines of the prisms intersect each other, and the inclination angles of the pair of inclined surfaces constituting each prism of the downward prism sheet are configured to be different from each other in the opposing inclined surfaces. A planar lighting device (Claim 1).
In the planar illumination device described in this section, the light emitted from the exit surface of the light guide plate is polarized by the downward prism and the upward prism, and the light emission luminance of the planar illumination device is given bimodality. . In addition, the inclination angle of the pair of inclined surfaces constituting each prism of the downward-facing prism sheet is configured to be different between the opposed inclined surfaces, so that the optical axis direction (guided light) of the outgoing light from the outgoing surface of the light guide plate is reduced. The prism angle of the downward prism sheet becomes asymmetric with respect to the ridge line of the prism with respect to the normal direction of the exit surface of the optical plate. Then, when the outgoing light from the outgoing surface of the light guide plate is deflected by the downward prism, it becomes asymmetric with respect to the direction in which the ridge line of the prism of the downward prism sheet extends. As a result, the light emission luminance having the bimodality of the planar illumination device is also asymmetric (strength is generated).

(2) The planar illumination device according to (1), wherein a cross-sectional shape of the multiple prisms of the downward prism sheet is the same throughout the downward prism sheet.
In the planar illumination device described in this section, since the cross-sectional shape of the multiple prisms of the downward prism sheet is the same throughout the downward prism sheet, the light emitted from the output surface of the light guide plate is multiple. The deflection direction when deflected by each of the prisms is made uniform over the entire downward-facing prism sheet, and the bimodality of the planar illumination device clearly appears.

(3) In the above items (1) and (2), the inclination angle of the pair of inclined surfaces constituting each prism of the downward prism sheet is the deviation of the light transmittance of the display surface of the liquid crystal display device used in combination. A planar illumination device that is formed in a manner that compensates for the luminance deviation caused by the above (claim 3).
The planar illumination device described in this section is an aspect that complements the luminance deviation caused by the deviation of the light transmittance of the display surface when the outgoing light from the emission surface of the light guide plate is deflected by the downward prism sheet. Thus, the deviation of the light transmittance of the display surface of the liquid crystal display device is corrected by the downward prism sheet.

(4) In the above items (1) to (3), the surface in which the extending direction of the multiple prisms of the downward prism sheet is arranged to be orthogonal to the light incident surface on which the light source of the light guide plate is disposed Lighting device (Claim 4).
In the planar illumination device described in this section, when the light emitted from the light exit surface of the light guide plate is deflected by the downward-facing prism sheet, bimodality appears in a direction parallel to the light entrance surface of the light guide plate. It becomes.

(5) The planar illumination device according to (1) to (4) above, wherein the downward prism sheet and the upward prism sheet are arranged in this order from the exit surface of the light guide plate.
In the planar illumination device described in this section, light emitted from the light exit surface of the light guide plate is deflected by each of the multiple prisms of the downward prism sheet. Further, the upward prism sheet is diffused or condensed by a plurality of prisms extending in a direction intersecting the prism of the downward prism sheet, and diffused in a direction orthogonal to the direction in which the prism ridge line of the upward prism sheet extends. Become.

(6) In the above item (5), the planar illumination device in which the downward prism sheet is arranged so that the ridge line of the prism intersects with another downward prism sheet instead of the upward prism sheet .
The planar illumination device described in this section is configured so that the light emitted from the exit surface of the light guide plate is changed by the downward prism sheet arranged in place of the upward prism sheet of the planar illumination device of the above (5). Since the ridgeline is deflected in the direction perpendicular to the extending direction, each of the multiple prisms extending in the direction intersecting with the prism of the downward prism sheet disposed in place of the upward prism sheet of the other downward prism sheet In combination with the deflection action of, the four peaks appear (peaks occur at four points of the entire light emitting surface).

(7) In the above items (1) to (4), the planar illumination device is arranged in the order of the upward prism sheet and the downward prism sheet from the exit surface of the light guide plate.
In the planar illumination device described in this section, the light emitted from the light exit surface of the light guide plate is diffused by the multiple prisms of the upward prism sheet. Further, the high-luminance range is narrowed in the direction in which the prism ridge of the downward prism sheet extends, and the ridge of the prism of the downward prism sheet extends. It appears widely in the direction orthogonal to the direction.

(8) The planar lighting device according to (7), wherein the upward prism sheet is laminated so that the ridgelines of the prisms intersect each other.
In the planar illumination device described in this section, light emitted from the light exit surface of the light guide plate is first diffused by the mutually intersecting prisms of the upward prism sheet that is laminated. Further, it is deflected by each of the multiple prisms of the downward prism sheet.

  (9) In the above items (1) to (8), the extending direction of the multiple prisms of each prism sheet arranged in order from the exit surface of the light guide plate is relative to the adjacent prism sheet. They are arranged so as to be orthogonal. In addition, as the cross-sectional shape of the prism of the downward prism sheet, a triangle, a trapezoid, or other polygon is appropriately employed.

  Since the planar illumination device of the present invention is configured as described above, it becomes easy to match the characteristics of the liquid crystal display device used in combination with the planar illumination device, and a necessary viewing angle can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The structure and characteristic of the planar illuminating device which concern on the 1st Embodiment of this invention are shown, (a) is a schematic diagram which shows the lamination | stacking state of the component of a planar illuminating device, (b) is this invention. (C) is a graph comparing the luminance distribution of the planar illumination device of (a) with a planar illumination device having another structure as a reference example. d) visually shows the luminance distribution of the planar illumination device of (a). The another structure and characteristic of the planar illuminating device which concerns on the 1st Embodiment of this invention are shown, (a) is a schematic diagram which shows the lamination | stacking state of the component of a planar illuminating device, (b) is Sectional drawing of the principal part of the downward prism sheet which concerns on embodiment of this invention, (c) is the graph which compared the luminance distribution of the planar illuminating device of (a) with the planar illuminating device of the other structure which is a reference example. , (D) visually shows the luminance distribution of the planar illumination device of (a). It is the graph which compared the luminance characteristic of the structure shown by FIG. 1, FIG. 2 of the planar illuminating device which concerns on embodiment of this invention with the planar illuminating device of the other structure which is a reference example. The structure and characteristic of the planar illuminating device which concerns on the 2nd Embodiment of this invention are shown, (a) is a schematic diagram which shows the lamination | stacking state of the component of a planar illuminating device, (b) is this Sectional drawing of the principal part of the downward prism sheet which concerns on embodiment of invention, (c) showed the luminance distribution of the planar illuminating device of (a) about the direction parallel to the light-incident surface of a light-guide plate, and the orthogonal direction. The graph (d) visually shows the luminance distribution of the planar illumination device (a). The structure and characteristic of the planar illuminating device which concerns on the 3rd Embodiment of this invention are shown, (a) is a schematic diagram which shows the lamination | stacking state of the component of a planar illuminating device, (b) is this The principal part sectional drawing of the downward prism sheet which concerns on embodiment of invention, (c) is the graph which compared the luminance distribution of the planar illuminating device of (a) with the planar illuminating device of the other structure which is a reference example, (D) shows visually the luminance distribution of the planar illumination device of (a). (A) It is a schematic diagram which shows the structure of the conventional planar illuminating device, (b) is the schematic diagram which looked at the planar illuminating device of (a) from the direction which looks at the light-incidence surface of a light-guide plate from the front. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, parts that are the same as or correspond to those in the prior art are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 1A schematically shows a laminated structure of the planar lighting device 10 according to the embodiment of the present invention. In the planar lighting device 10, a diffusion film 14, a downward prism sheet 16, an upward prism sheet 18, and a DBEF 20 are laminated in this order on the light exit surface 12 a side of the light guide plate 12, and on the regular reflection means 12 b side of the light guide plate 12. The reflective sheet 22 is arranged.
1A is a schematic view of the planar illumination device 10 as viewed from the front direction of the light incident surface 12c of the light guide plate 12 as in FIG. 6B (hereinafter, FIG. The same applies to a), FIG. 4A, and FIG. 5A.

Here, like the conventional light guide plate 101 (see FIG. 6), the light guide plate 12 is a plate-like light guide formed by molding a transparent resin material, and one main surface functions as the emission surface 12a. . Further, the opposing main surface functions as a reflecting surface, reflects light incident on the surface, and causes at least a part of the light to enter the exit surface 12a with an incident angle less than the critical angle. Diffuse reflection means or regular reflection means 12b is provided (see FIG. 6). Suitable transparent resin materials for the light guide plate 12 include methacrylic resin, polycarbonate resin, polystyrene resin, polyolefin resin, amorphous polyolefin resin, polyester resin, polystyrene resin, transparent fluororesin, epoxy resin, and the like. Further, the light incident surface 12c which is one side end surface of the light guide plate 12 is provided with a point light source such as a white LED or a rod-like light source (see reference numeral 102 in FIG. 6A). Is omitted.
Then, in the planar illumination device 10 (10A) of FIG. 1A, a downward prism sheet 16 and an upward prism sheet 18 in which a plurality of prisms are arranged in parallel on the exit surface 12a side of the light guide plate 12 are provided. The ridgelines of the prisms are stacked so as to intersect each other. In the illustrated example, the downward prism sheet 16 and the upward prism sheet 18 are arranged in such a manner that the ridge lines of the prisms are orthogonal to each other.

Further, the downward prism sheet 16 is disposed so that the extending direction of the ridge lines 161 of the multiple prisms is orthogonal to the light incident surface 12 c of the light guide plate 12. And as FIG.1 (b) shows, it is comprised so that the inclination angle of a pair of inclined surface 162,163 which comprises each prism may differ in the opposing inclined surface. The cross-sectional shape of the multiple prisms of the downward prism sheet 16 is the same throughout the downward prism sheet. The material of the downward prism sheet 16 is a sheet-like member made of a transparent resin material such as a PET film, for example, like the conventional prism sheets 103 and 104 (see FIG. 6). A multi-triangular triangular prism made of polycarbonate resin extending in one direction is formed. In addition, the code | symbol 164 of FIG.1 (b) has shown the trough part of the prism.

In the example of FIG. 1B, the apex angle (ridge line angle) and valley angle of the prism are both right angles, but the angle formed between the surface connecting the ridge lines 161 and the inclined surface 162 is 50 ° ± 0.5. The angle formed between the surface connecting the ridge lines 161 and the inclined surface 163 is set to 40 ° ± 0.5 °. The pitch of the ridge lines 161 of the prism is 0.07 mm, and the height (depth) of the prism is 0.0345 mm.
Further, the planar illumination device 10 (10B) of FIG. 2A differs from the planar illumination device 10 (10A) of FIG. 1A in that the inclination angle of the prism of the downward prism sheet 16 is different. It is what. Specifically, as shown in FIG. 2B, the apex angle (ridge line angle) and valley angle of the prism are both right angles, but the angle formed between the surface connecting the ridge lines 161 and the inclined surface 162. Is 47.5 ° ± 0.5 °, and the angle between the surface connecting the ridge lines 161 and the inclined surface 163 is set to 42.5 ° ± 0.5 °. The pitch of the ridge lines 161 of the prism is 0.07 mm, and the height (depth) of the prism is 0.0349 mm.
The inclination angle of the pair of inclined surfaces 162 and 163 constituting each prism of the downward prism sheet 16 is determined by the liquid crystal display device used in combination with the planar illumination device 10 (10A, 10B) (FIG. 1A, FIG. 2 (a) is disposed in a manner that complements the unevenness in luminance caused by the uneven light transmittance on the display surface, and is appropriately set.

On the other hand, the upward prism sheet 18 has the same shape and material as the conventional prism sheets 103 and 104 (see FIG. 6), and in particular, the flat surface 18b is formed on the light guide plate 12 in the same manner as the second prism sheet 104. The prism extending direction of the prism surface 18 a is arranged in parallel to the light incident surface 12 c of the light guide plate 12.
In addition, about the diffusion film 14, DBEF20, and the reflection sheet 22, it is the same as the conventional diffusion film 105, DBEF106, and the reflection sheet 107, respectively.

Now, according to the first embodiment of the present invention configured as described above, the following operational effects can be obtained.
First, in the planar illumination device 10 according to the embodiment of the present invention, the light emitted from the emission surface 12a of the light guide plate 12 is polarized by the downward prism 16 so that the emission luminance of the planar illumination device is two peaks. Sex is imparted. In addition, since the inclined angles of the pair of inclined surfaces 162 and 163 constituting each prism of the downward-facing prism sheet 16 are different between the opposing inclined surfaces, the emitted light from the emitting surface 12a of the light guide plate 12 The prism angle of the downward prism sheet 16 is asymmetric with respect to the ridgeline 161 of the prism with respect to the optical axis direction (normal direction of the exit surface of the light guide plate). And when the outgoing light from the outgoing surface 12a of the light guide plate 12 is deflected by the downward prism, it becomes asymmetric with respect to the direction in which the prism ridge 161 of the downward prism sheet extends. As a result, as shown in FIGS. 1C, 1D, 2C, and 2D, the light emission luminance having the bimodality of the planar illumination device is also asymmetric.

Further, according to the first embodiment of the present invention, the cross-sectional shape of the multiple prisms of the downward prism sheet 16 (16A, 16B) is the same throughout the downward prism sheet 16, so that the light guide plate 12 The deflection direction when the outgoing light from the outgoing surface 12a is deflected by each of the multiple prisms is made uniform over the entire downward prism sheet 16, and the bimodality of the planar illumination device 10 clearly appears. It becomes.
Further, the inclination angle of the pair of inclined surfaces 162 and 163 constituting each prism of the downward prism sheet 16 (16A and 16B) is determined by the light transmittance of the display surface of the liquid crystal display device used in combination with the planar illumination device 10. Therefore, when the outgoing light from the outgoing surface 12a of the light guide plate 12 is deflected by the downward prism sheet 16, the display of the liquid crystal display device is performed. The uneven light transmittance of the surface can be corrected by the downward prism sheet 16.

In addition, the extending direction of the multiple prisms of the downward prism sheet 16 (16A, 16B) is arranged so as to be orthogonal to the light incident surface 12c on which the light source of the light guide plate 12 is arranged. When outgoing light from the outgoing surface 12 a is deflected by the downward prism sheet 16, bimodality appears in a direction parallel to the light incident surface 12 c of the light guide plate 12.
Further, by arranging the downward prism sheet 16 (16A, 16B) and the upward prism sheet 18 in this order from the exit surface 12a of the light guide plate 12, the light emitted from the exit surface 12a of the light guide plate 12 is directed downward. The prism ridgeline 161 of the upward prism sheet 18 extends by being deflected by each of the multiple stripe prisms and further diffused by the multiple prisms extending in the direction intersecting with the prisms of the downward prism sheet of the upward prism sheet 18. It is diffused in a direction orthogonal to the direction.

The above effects are also apparent from FIGS. 1C and 2C showing the luminance distribution of the planar illumination device 10 according to the embodiment of the present invention. In FIG. 1C and FIG. 2C, the line graphs indicated by reference numerals 10A and 10B indicate the luminance distribution of the planar lighting device 10 (10A and 10B) according to the embodiment of the present invention. .
Further, in FIGS. 1C and 2C, as a comparative example, the first and second prism sheets 103 and 104 are excluded from the planar illumination device 100 shown in FIG. The normal planar illumination device (circled number 1) to which no peak is imparted, the first and second prism sheets 103 and 104 are removed from the planar illumination device 100, and the diffusion film 105 (see FIG. 6). ) Is different from the normal and the surface illumination device (circled number 2) arranged oppositely (the diffusion layer faces downward), the second prism sheet 104 of the surface illumination device 100, and the first prism sheet 103 Similarly, the luminance distribution of the planar illumination device (circled number 3) with the prism facing downward is shown.

As shown in FIG. 1D, the planar lighting device 10A in FIG. 1 has a light source side (light incident surface 12c of the light guide plate 12) in front, and the left and right emission luminance distribution is 44% vs. 56%. As shown, bimodality appears. Further, as shown in FIG. 2D, the surface illumination device 10B of FIG. 2 has a light emission luminance distribution of 47% on the left and right sides with the light source side (the light incident surface 12c of the light guide plate 12) in front. Bimodality appears so as to be 53%.
Further, FIG. 3 shows the planar illumination shown in FIG. 6 together with the luminance distribution (indicated by reference numerals 10A and 10B) of the planar illumination device including the downward prisms 16A and 16B shown in FIGS. Except for the first prism sheet 103 from the device 100, the luminance distribution of a normal planar illumination device that is not given bimodality in light emission luminance is denoted by reference numeral P1, and the first prism sheet 103 of the illumination device 100 is denoted by P1. Similarly to the second prism sheet 104, the luminance distribution of the planar illumination device with the prism facing upward is indicated by a symbol P2.

Next, a planar illumination device according to the second embodiment of the present invention will be described with reference to FIG. Here, the same or corresponding parts as those in the first embodiment of the present invention are denoted by the same reference numerals, and detailed description thereof is omitted.
The planar lighting device 10 (10C) according to the second embodiment of the present invention is replaced with the upward prism sheet 18 according to the first embodiment, as shown in FIG. The downward prism sheet 17 is arranged so that the ridge line of the prism intersects the other downward prism sheet 16. Here, the extending direction of the multiple prisms of the second prism sheet 17 is arranged so as to be orthogonal to the light incident surface 12 c of the light guide plate 12. The extending direction of the multiple prisms of the other downward prism sheet 16 is arranged in parallel with the light incident surface 12 c of the light guide plate 12.

Then, as shown in FIG. 4B, the angle between the surface connecting the ridge lines 161 and the inclined surface 162 of the downward prism sheet 16 (16C) is 41 ° ± 0.5 °, and connects the ridge lines 161. The angle formed by the surface and the inclined surface 163 is set to 39 ° ± 0.5 °. The pitch of the ridge lines 161 of the prism is 0.07 mm, and the height (depth) of the prism is 0.0349 mm.
On the other hand, in the second downward prism sheet 17, the angle formed between the surface connecting each ridge line 171 and the inclined surface 172 is 39 ° ± 0.5 °, and the angle formed between the surface connecting each ridge line 171 and the inclined surface 173 is 39 °. It is set to ° ± 0.5 °. The pitch of the prism ridges 171 is 0.07 mm, and the height (depth) of the prism is 0.0349 mm. In addition, the code | symbol 174 of FIG.4 (b) has shown the trough part of the prism.

  And according to the 2nd Embodiment of this invention, the emitted light from the output surface of the light-guide plate 12 is made into the direction orthogonal to the direction where the ridgeline 171 of the prism extends by the 2nd downward prism sheet 17. 4 (c) and 4 (d) together with the deflection action of each of the multiple prisms extending in the direction intersecting with the prisms of the second downward prism sheet of the other downward prism sheet. As you can see, the four peaks appear. 4C indicates the luminance distribution in the direction parallel to the light incident surface 12c of the light guide plate 12, and reference numeral V indicates the luminance distribution in the direction orthogonal to the light incident surface 12c of the light guide plate 12. Show. In FIG. 4D, four portions (four peaks) showing luminance peaks appear, and the ridgelines 161 of the downward prism sheet 16 (16C) are connected. Because of the difference between the angle 41 ° ± 0.5 ° formed by the surface and the inclined surface 162 and the angle 39 ° ± 0.5 ° formed by the surface connecting the ridge lines 161 and the inclined surface 163, two peaks far from the light source side are It can be seen that it is brighter than the two peaks near the light source.

Next, a planar illumination device according to the third embodiment of the present invention will be described with reference to FIG. Here, the same or corresponding parts as those of the first and second embodiments of the present invention are denoted by the same reference numerals, and detailed description thereof is omitted.
The planar illumination device 10 (10C) according to the third embodiment of the present invention includes upward prism sheets 18 and 19 and downward prisms from the exit surface 12a of the light guide plate 12, as shown in FIG. The sheets 16 (16D) are arranged in this order. In addition, two upward prism sheets 18 and 19 are laminated so that the ridge lines of the prisms intersect each other.

Then, as shown in FIG. 5B, the prism angle (ridge angle) and valley angle of the prism of the downward prism sheet 16 (16D) are both 60 °, and are inclined with respect to the plane connecting the ridge lines 161. The angle formed with the surface 162 is set to 60 ° ± 0.5 °, and the angle formed between the surface connecting the ridge lines 161 and the inclined surface 163 is also set to 60 ° ± 0.5 °. The pitch of the ridge lines 161 of the prism is 0.07 mm, and the height (depth) of the prism is 0.0345 mm. Further, the extending direction of the multiple prisms of the downward prism sheet 16 (16 </ b> D) is arranged so as to be orthogonal to the light incident surface 12 c of the light guide plate 12.
Note that the extending direction of the multiple prisms of the upward prism sheets 18 and 19 is arranged to be orthogonal to the light incident surface 12c of the light guide plate 12 with respect to the upward prism sheet 18, and the upward prism sheet 19 is guided. The light plate 12 is arranged in parallel with the light incident surface 12c.

  According to the third embodiment of the present invention having the above-described configuration, the outgoing light from the outgoing surface 12a of the light guide plate 12 is first caused by the multiple prisms of the upward prism sheets 18 and 19 intersecting each other. Sequentially diffused. Further, it is deflected by each of the multiple prisms of the downward prism sheet 16 (16D). As a result, as shown in FIGS. 5C and 5D, the high luminance range is narrow in the direction in which the prism ridge 161 of the downward prism sheet 16 extends, and the direction in which the prism ridge of the downward prism sheet extends. It will appear widely in the direction perpendicular to.

In addition, in FIG.5 (c), the line graph shown by code | symbol 16D shows the luminance distribution of the planar illuminating device 10 (10D) which concerns on the 3rd Embodiment of this invention. Further, in FIG. 5C, as a comparative example, the first and second prism sheets 103 and 104 are excluded from the planar illumination device 100 shown in FIG. There is no ordinary planar illumination device (circled number 1), and the first and second prism sheets 103 and 104 are removed from the planar illumination device 100, and the diffusion film 105 (see FIG. 6) is different from usual. And the second prism sheet 104 of the planar illumination device 100 in the same manner as the first prism sheet 103 with the prism facing downward. The luminance distribution of the planar illumination device (circled number 3) is shown.
Then, as shown in FIG. 5D, with the light source side (the light incident surface 12c of the light guide plate 12) placed in front, the left and right light emission luminance distributions are 50% to 50%, so that the light guide plate 12 The high luminance range is widened in a direction parallel to the light incident surface 12c.

The features of the present invention are as described above. According to the first and second embodiments of the present invention, when the light emitted from the light exit surface of the light guide plate is deflected by the downward prism sheet, the display surface is displayed. Because it is deflected in a manner that compensates for the luminance deviation due to the light transmittance deviation of the liquid crystal display, and the light transmittance deviation of the display surface of the liquid crystal display device is corrected by the downward prism sheet, the transmittance is omnidirectional It is possible to provide a display device in which is averaged.
In addition, according to the third embodiment of the present invention, it is possible to provide a display device in which the transmittance is further averaged in all directions by combining with a liquid crystal panel in which the transmittance is not biased in all directions. Is possible.
In the embodiment of the present invention, the light incident surface 12c of the light guide plate 12 has one side configuration, that is, the case where the light source is disposed only on one side of the light guide plate. It will be understood that the same effect can be obtained even when the light incident surface 12c has a two-sided configuration, that is, the light source is disposed with the surface facing the light incident surface 12c as the light incident surface. Let's go.

  10, 10A, 10B, 10C, 10D: planar illumination device, 12: light guide plate, 12a: exit surface, 12c: light incident surface, 16, 16A, 16B, 16C, 16D: downward prism sheet, 162, 163: inclined surface

Claims (5)

A downward prism sheet and an upward prism sheet, each including a light guide plate and a light source disposed on one side end face of the light guide plate, and a plurality of prisms arranged in parallel on the light exit surface side of the light guide plate, The prisms are stacked so that the ridge lines of the prisms intersect with each other, and the inclination angles of the pair of inclined surfaces constituting each prism of the downward prism sheet are configured so that the inclined surfaces facing each other are different. A planar lighting device. The planar illumination device according to claim 1, wherein a cross-sectional shape of the multiple prisms of the downward prism sheet is the same throughout the downward prism sheet. The inclination angle of the pair of inclined surfaces constituting each prism of the downward prism sheet is formed in a manner that complements the luminance unevenness caused by the uneven light transmittance of the display surface of the liquid crystal display device used in combination. The planar illumination device according to claim 1, wherein the planar illumination device is provided. The extending direction of the multiple prisms of the downward prism sheet is disposed so as to be orthogonal to a light incident surface on which the light source of the light guide plate is disposed. The surface illumination device described. 5. The planar illumination device according to claim 1, wherein the downward prism sheet and the upward prism sheet are arranged in this order from the exit surface of the light guide plate. 6.