JP2017084738A - Surface light source device, video source unit and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device which restricts emission light to the other directions so as to be easily observed on a driver seat side and on a front passenger seat side, and in which a structure for that purpose is simple.SOLUTION: A surface light source device (20) includes: a light source (26); a light guide plate (21) for guiding the light emitted from the light source; and a prism sheet (30) arranged on the light emission side of the light guide plate, and for changing the direction of the incident light and emitting the same. The prism sheet has: a sheet-like body part (31) having light permeability; and a unit prism part (32) which is arranged on the surface side on the light guide plate side out of the body part, in which a plurality of convex unit prisms (32a) extend by having a predetermined cross section in the direction along a seat surface of the body part and are arrayed in the direction different from the extending direction. The direction in which the unit prisms extend is inclined in a range of surpassing 0 degree and below 90 degrees, when the direction orthogonal to the light guide direction is defined as 0 degree.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface light source device that functions as illumination of a display device, an image source unit using the same, and a liquid crystal display device.

  A liquid crystal display device such as a liquid crystal television makes an image visible to an observer by using a surface light source device (backlight) arranged on the back side of the liquid crystal panel as illumination for a liquid crystal panel containing video information. provide.

  2. Description of the Related Art In recent years, equipment mounted on automobiles and the like for viewing by a driver and a passenger seat has been increasingly equipped with a monitor (liquid crystal display device). In addition to the navigation system and the audio equipment, monitors corresponding to the respective uses may be arranged in the rearview mirror, the A pillar, and the like.

  Since such a monitor has a limited number of observers, it is sufficient that the range of light (image) emitted from the monitor is in accordance with this, so that it can be operated in the so-called eyepoint direction, that is, from the irradiation surface that emits light. It is necessary to emit light with high luminance in the direction in which the viewpoint of the person sitting in the seat or passenger seat is located. Patent Document 1 discloses a backlight device in which the luminance in the three directions of the eye point direction and the vertical direction with respect to the irradiation surface is improved in view of such eye point characteristics. According to this, the luminance can be improved in the three directions of the driver's seat, the passenger's seat, and the front, and it has excellent luminance distribution characteristics as a vehicle-mounted monitor. For this purpose, a polarizing sheet, a diffusion sheet, a light guide plate, and a reflection sheet are provided in this order, and a prism sheet having a triangular groove base angle in the range of 40 ° to 60 ° is provided between the polarizing sheet and the diffusion sheet. Provided.

JP 2004-296343 A

  However, in the surface light source device as described in Patent Document 1, it is complicated in structure to emit light having high luminance in the eyepoint direction to each of the monitors arranged at various positions. Tended to be.

  In view of the above, the present invention has an object to provide a surface light source device that is easy to observe on the driver's seat side and the passenger's seat side, restricts light emission in other directions, and has a simple structure. . In addition, an image source unit including the surface light source device and a liquid crystal display device are provided.

  The present invention will be described below. Here, in order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated form.

  According to the first aspect of the present invention, the light source (26), the light guide plate (21) for guiding the light emitted from the light source, and the light output side of the light guide plate are arranged to change the direction of the incident light to be emitted. A prism sheet (30), and the prism sheet is disposed on the light guide plate side surface side of the main body and a plurality of convex unit prisms. (32a) includes a unit prism portion (32) extending in a direction along the sheet surface of the main body portion and arranged in a direction different from the extending direction, and the unit prism extends. The direction is the surface light source device (20) that is inclined in the range of more than 0 degree and less than 90 degrees when the direction orthogonal to the light guide direction is 0 degree.

  According to a second aspect of the present invention, in the surface light source device (20) according to the first aspect, when the viewing angle characteristic is expressed by a coordinate system expressed by an azimuth angle and an elevation angle, the highest luminance is 50%. A line connecting luminance parts is substantially elliptical.

  According to a third aspect of the present invention, in the surface light source device according to the second aspect, the substantially elliptical long axis is not parallel to the coordinate axis in the coordinate system but has an inclination.

  According to a fourth aspect of the present invention, there is provided an image source unit comprising the surface light source device (20) according to any one of the first to third aspects and a liquid crystal panel (15) disposed on the light output side of the surface light source device. (10).

  A fifth aspect of the present invention is a liquid crystal display device comprising: the video source unit (10) according to the fourth aspect; and a housing that encloses the video source unit.

  According to the present invention, the contour lines of the light emission luminance distribution are substantially elliptical, and in the substantially elliptical shape, the viewing angle is wide in the major axis direction and the viewing angle can be limited in the minor axis direction. The size of the substantially elliptical shape and the light exit direction can be achieved by simply changing the angle in the direction in which the unit prism extends, and the light exit characteristics can be changed very easily.

FIG. 3 is an exploded perspective view illustrating a video source unit 10. 2 is an exploded view showing one cross section of the video source unit 10. FIG. It is a perspective view of a light-guide plate. It is a figure showing a part in the cross section of a light-guide plate. It is the figure showing the other cross section of the light-guide plate. It is a perspective view of a prism sheet. It is a top view of a prism sheet. It is the figure which expanded a part of cross section of a prism sheet. FIG. 9A shows the influence of the form of the unit prism 32a on the elliptical luminance distribution, and FIG. 9B shows the influence of the form of the unit optical element 24a on the elliptical luminance distribution. FIG. 10A is a diagram for explaining the influence of the angle α of the reflection surface of the unit prism 32a, and FIG. 10B is another diagram for explaining the influence of the angle α of the reflection surface of the unit prism 32a. is there. It is a figure explaining the influence which the angle which the unit prism 32a extends has. It is a figure explaining a light emission characteristic. It is a figure explaining the example of application of a display apparatus.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings. However, the present invention is not limited to these forms. Moreover, in each figure shown below, the magnitude | size and shape of a member may be exaggerated and described for easy understanding, and the code | symbol which becomes repeated may be abbreviate | omitted for easiness to see.

FIG. 1 is an exploded perspective view conceptually showing an image source unit 10 included in a liquid crystal display device according to one embodiment.
The liquid crystal display device has an image source unit 10, and the white light source light emitted from the surface light source device 20 included in the image source unit 10 passes through the liquid crystal panel 15 to obtain image information, and then an observer is obtained. Provided on the side. The liquid crystal display device includes a housing (not shown) in which the video source unit 10 is built. The casing is a member that forms an outer shell of the liquid crystal display device and accommodates most of the members constituting the liquid crystal display device inside. The housing has an opening so as to support the image source unit 10, and the image source unit 10 is fitted and attached to the opening. In addition, the liquid crystal display device includes various known constituent members for functioning as a liquid crystal display device.

  The video source unit 10 includes a liquid crystal panel 15, a surface light source device 20, and a functional sheet 41. Here, in FIG. 1, the upper side of the drawing is the observer side.

  The liquid crystal panel 15 includes an upper polarizing plate 13 disposed on the viewer side, a lower polarizing plate 14 disposed on the surface light source device 20 side, and a liquid crystal disposed between the upper polarizing plate 13 and the lower polarizing plate 14. It has a layer 12. The upper polarizing plate 13 and the lower polarizing plate 14 decompose the incident light into two orthogonal polarization components (P wave and S wave), and a polarization component in one direction (direction parallel to the transmission axis) (for example, P And has a function of absorbing a polarization component (for example, S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

  The liquid crystal layer 12 can be applied with an electric field for each region where one pixel is formed. Then, the orientation of the liquid crystal layer 12 applied with an electric field changes. A polarization component (for example, P wave) in a specific direction that has passed through the lower polarizing plate 14 disposed on the surface light source device 20 side (that is, the light incident side) changes its polarization direction when passing through the liquid crystal layer 12 to which an electric field is applied. While rotating 90 °, the polarization direction is maintained when passing through the liquid crystal layer 12 to which no electric field is applied. For this reason, depending on whether or not an electric field is applied to the liquid crystal layer 12, the polarization component (P wave) in a specific direction transmitted through the lower polarizing plate 14 is further transmitted through the upper polarizing plate 13 disposed on the light output side of the lower polarizing plate 14. It is possible to control whether it is absorbed or blocked by the upper polarizing plate 13.

  In this way, the liquid crystal panel 15 is configured to be able to express an image by controlling transmission or blocking of light from the surface light source device 20 for each pixel. There are various types of liquid crystal panels, but they can be used without any particular limitation.

Next, the surface light source device 20 will be described. FIG. 2 shows a cross-sectional view in the thickness direction (vertical direction in FIG. 1) of the surface light source device 20 along the dotted line shown in FIG.
The surface light source device 20 is an illuminating device that is disposed on the side opposite to the observer side with the liquid crystal panel 15 interposed therebetween and emits planar light to the liquid crystal panel 15. As can be seen from FIGS. 1 and 2, in this embodiment, the surface light source device 20 is configured as an edge light type surface light source device, and includes a light guide plate 21, a light source 26, a prism sheet 30, and a reflection sheet 40. .

  As can be seen from FIGS. 1 and 2, the light guide plate 21 includes a base portion 22, a back prism portion 23, and an optical element portion 24. The light guide plate 21 is a plate-like member as a whole formed of a light-transmitting material, and an optical element portion 24 is formed on one plate surface side as a light output surface. The other plate surface side is a back surface, and a back surface prism portion 23 is formed.

  Various materials can be used as the material forming the base portion 22, the back prism portion 23, and the optical element portion 24. However, a material that is widely used as a material for an optical sheet to be incorporated in a display device, has excellent mechanical characteristics, optical characteristics, stability, workability, and the like and can be used at a low cost can be used. Examples thereof include polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrenes, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, polyether sulfones, and the like, And epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like).

  The base portion 22 is a portion serving as a base for the back prism portion 23 and the optical element portion 24, and has a plate shape having a predetermined thickness.

  The back prism portion 23 has a concavo-convex shape formed on the back surface side of the base portion 22 (the plate surface opposite to the light exit surface). 3 is a perspective view of the light guide plate 21 as viewed from the rear prism 23 side, and FIG. 4 is a partial cross section taken along the line IV-IV (line along the light guide direction) in FIG. expressed. As can be seen from FIGS. 2 to 4, in the present embodiment, a plurality of triangular prism-shaped unit rear surface prisms 23 a are arranged. The unit back surface prism 23a has a columnar shape in which the ridge line of the convex portion extends in the light source arrangement direction, and the plurality of unit back surface prisms 23a are arranged at a predetermined pitch in a direction orthogonal to the extending direction. That is, the direction in which the ridge portion of the unit back surface prism 23a extends is the direction in which the light source 26 is arranged, the direction in which the unit back surface prism 23a is arranged is a direction orthogonal to the direction, and the light guide direction.

  The unit back surface prism 23a of this embodiment has a triangular cut surface (so-called “main cut surface”) orthogonal to the direction in which the ridge line extends, but is not limited to this, and is not limited to this, and may be a square, pentagon, hexagon, or the like. Any shape such as a part of a curve such as a square, a circle, an ellipse, and a hyperbola (columnar lens shape) may be used.

  Next, the optical element part 24 provided on the light outgoing side surface of the base part 22 will be described. FIG. 5 shows an enlarged view of a part of a cross section of the light guide plate 21 along the light source arrangement direction. As can be seen from FIG. 5, the optical element section 24 is provided on the light output side surface of the base section 22 so that the plurality of unit optical elements 24 a are arranged along the light source arrangement direction and extend in parallel to the light guide direction.

  In this embodiment, as shown in FIG. 5, the plurality of unit optical elements 24 a are arranged without a gap in the light source arrangement direction on the light output side surface of the base 22. Therefore, the light exit surface of the light guide plate 21 is composed of the inclined surface of the unit optical element 24a. Further, each unit optical element 24a is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction thereof.

  As can be seen from FIG. 5, the cross-sectional shape of the unit optical element 24a is a shape that tapers toward the light output side. That is, the width of the unit optical element 24 a parallel to the plate surface of the light guide plate 21 decreases as the distance from the base portion 22 increases along the normal direction of the light guide plate 21.

  In the present embodiment shown in FIG. 5, the unit optical element 24a has a pentagonal outer contour in the cross section. This pentagonal shape may be a shape formed by chamfering one or more corners of a triangle. In this embodiment, the cross-sectional shape of the unit optical element 24a is symmetric with respect to the normal line. That is, the light output side surface of each unit optical element 24a is configured by a pair of bent surfaces that are symmetrically configured with the front direction as the center. The pair of folding surfaces are connected to each other to define a tip. Each folded surface has a first surface 24b that defines a tip, and a second surface 24c that is connected to the first surface 24b from the base 22 side.

  As a general configuration of the optical element portion 24, a front direction from the base portion 22 of the unit optical elements 24a of the light guide plate 30 with respect to a width Wa in the arrangement direction of the unit optical elements 24a in the cross section shown in FIG. It is preferable that the ratio (Ha / Wa) of the protrusion height Ha along the line is 0.3 or more and 0.45 or less. According to such a unit optical element 24a, an excellent light condensing function is exhibited with respect to light components along the arrangement direction (light source arrangement direction) of the unit optical elements 24a by refraction and reflection at the light exit side. And generation of side lobes can be effectively suppressed.

In addition, the “pentagonal shape” in the present specification includes not only a pentagonal shape in a strict sense but also a substantially pentagonal shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings. Interpretation will be made including such an error that a similar optical function can be expected.

  Here, as an example, the dimensions of the light guide plate 21 may be such that the width Wa of the unit optical element 24a is 10 μm or more and 500 μm or less, and the thickness of the base portion 22 is 0.2 mm to 6 mm.

  The light guide plate 21 having the above-described configuration can be manufactured by extrusion molding or by molding the unit back prism 23a and / or the unit optical element 24a on the base portion 22. In the light guide plate 21 manufactured by extrusion molding, the back prism portion 23 and / or the optical element portion 24 can be integrally formed with the base portion 22. Moreover, when manufacturing the light-guide plate 21 by shaping | molding, the back surface prism part 23 may be the same resin material as the base 22, or a different material.

  The form of the unit optical element may be a polygonal shape such as a triangle or a quadrangle, or a lens shape such as a lenticular lens, in addition to the above pentagonal cross section. Moreover, it is not restricted to the form which protruded from the base like this form, A concave element may be sufficient. An example of this is a concave lenticular lens shape. Further, the unit optical elements may be arranged without a gap or may be arranged with a gap.

  Returning to FIGS. 1 and 2, the light source 26 will be described. The light source 26 is disposed on one or both of the pair of side surfaces in the light guide direction among the two sets of side surfaces of the base portion 22 of the light guide plate 21 (FIGS. 1 and 2 are one example). The type of the light source is not particularly limited, but may be configured in various forms such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), or an incandescent lamp. In the present embodiment, the light source 26 includes a plurality of LEDs, and the output of the LEDs, that is, the lighting and extinguishing of the LEDs and / or the brightness when the LEDs are lit, is controlled by a control device (not shown). All of the plurality of LEDs may be controlled together or may be individually controllable.

  Next, the prism sheet 30 will be described. As can be seen from FIG. 1 and FIG. 2, the prism sheet 30 is provided on the surface facing the light guide plate 21, that is, on the light incident side surface, of the main body 31 formed in a sheet shape and the surface of the main body 31. Unit prism portion 32. 6 is a perspective view of the prism sheet 30 viewed from the unit prism section 32 side, FIG. 7 is a plan view of the prism sheet 30 viewed from the unit prism section 32 side, and FIG. 8 is indicated by VII-VII in FIG. Sectional drawing of the prism sheet 30 along the line was represented.

  This prism sheet 30 is combined with the configuration of the unit optical element portion 24a of the light guide plate 21 described above, and changes the traveling direction of light incident from the light incident side to be emitted from the light output side, and is substantially elliptical in a predetermined manner. A function of intensively improving the luminance so as to emit light having a uniform luminance distribution. Therefore, this function is mainly exhibited by the unit prism portion 32 of the prism sheet 30 and the optical element portion 24 of the light guide plate 21.

  As shown in FIGS. 1, 2, and 6 to 8, the main body 31 is a flat sheet-like member having a function of supporting the unit prism portion 32.

The unit prism portion 32 is arranged so that a plurality of unit prisms 32 a are arranged along the light incident side surface of the main body portion 31 as well shown in FIGS. 1, 2, and 6 to 8. More specifically, the unit prism 32a is a columnar member formed such that the ridgeline extends while maintaining the predetermined cross-sectional shape shown in FIG. 8 in the direction of the angle θ with respect to the direction orthogonal to the light guide direction. It is. Therefore, the direction in which the ridgeline extends is inclined at an angle of θ with respect to the direction orthogonal to the light guide direction. The plurality of unit prisms 32a have this inclination and are arranged in the light guide direction. As a result, it is possible to emit light having a substantially elliptical luminance distribution having high luminance at a position shifted from the center of the screen.
The specific value of θ can be adjusted to obtain a desired luminance distribution. Therefore, the range of 0 ° <θ <90 ° can be taken.

Next, the sectional shape of the unit prisms 32a in the arrangement direction will be described. FIG. 8 is an enlarged view of a part of the sectional view of the prism sheet 30 taken along line VII-VII in FIG. 6, and is a section orthogonal to the direction in which the ridgeline of the unit prism 32a extends. In FIG. 8, n _d represents the normal direction of the sheet surface of the main body 31.

As can be seen from FIG. 8, in this embodiment, the unit prism 32 a has an isosceles triangular cross section that protrudes from the main body 31 toward the light guide plate 21. That is, the width of the unit prism 32 a in the direction parallel to the sheet surface of the main body 31 decreases as the distance from the main body 31 increases along the normal direction _nd of the main body 31.

Further, in this embodiment, the outer contour of the unit prism 32a is an axis parallel to the normal direction n _d of the main body portion 31 as a symmetrical axis, has a line-symmetric cross-section is an isosceles triangle.

Here, the dimensions of the unit prism 32a are not particularly limited, but the apex angle θ ₇ (see FIG. 8) at the convex tip of the unit prism 32a in the cross section of FIG. 8 may be 80 ° or less. preferable. Thereby, in the arrangement form of the unit prisms 32a arranged to face the light output surface of the light guide plate 21, more appropriate light collecting characteristics can be obtained. A more preferable apex angle θ ₇ is 60 ° or more and 80 ° or less. Further, the base width W is preferably the same as the pitch P. The pitch P between adjacent unit prisms 32a is preferably 10 μm or more.

  In the present embodiment, the unit prism having a triangular cross section as described above has been described. However, the present invention is not limited to this, and a trapezoid in which the top of the triangle has a short upper base may be used. Further, the shape of one and / or the other of the slope may be a polygonal line or a curve. Therefore, the cross-sectional shape may be a polygon such as a quadrangle or a pentagon.

The prism sheet 30 having the above configuration is manufactured, for example, by forming the base unit prism portion 32 that becomes the main body portion 31.
Various materials can be used as the material forming the main body 31 and the unit prism portion 32. However, it is transparent and widely used as a material for an optical sheet to be incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, etc., and can be obtained at low cost, for example, polymethyl Acrylic resins such as methacrylate, styrene resins, various polycarbonate resins, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, resins such as polyacrylonitrile, resins mixed with other resins based on one or more of these resins, and epoxy An ionizing radiation curable resin obtained by curing a reactive monomer or prepolymer such as an acrylate type or a urethane acrylate type by a crosslinking reaction or a polymerization reaction by irradiation with ultraviolet rays, electron beams or the like can be suitably used.

  Here, an example in which the main body portion 31 and the unit prism portion 32 are integrated has been described. However, the main body portion 31 and the unit prism portion 32 are separated so as to form an air layer, or other functional layers. May be sandwiched.

  Returning to FIG. 1 and FIG. 2, the reflection sheet 40 of the surface light source device 20 will be described. The reflection sheet 40 is a member that reflects light emitted from the back surface of the light guide plate 21 and makes the light enter the light guide plate 21 again. Although the material which comprises the reflective sheet 40 is not specifically limited, A white film (Toray Co., Ltd. Lumirror (registered trademark) E6SR), a multilayer film reflective film (3M Japan Co., Ltd. ESR), and a silver vapor deposition film (Kyoto Nakai Corporation) Examples thereof include films having light reflectivity such as Kiraraflex (registered trademark). More preferably, a sheet made of a material having a high reflectivity such as a metal, a sheet including a thin film (for example, a metal thin film) made of a material having a high reflectivity as a surface layer, or the like that enables so-called specular reflection is applied. can do. Thereby, it becomes possible to improve the usability of light and to improve the energy utilization efficiency.

  The functional sheet 41 is a sheet having various functions used in a normal liquid crystal display device. Examples thereof include a sheet for correcting color tone, a sheet having an antiglare function, a sheet for preventing reflection, and a hard coat sheet.

  Next, the operation of the display device having the above configuration will be described with an example of the optical path. However, this optical path example is conceptually shown and does not strictly indicate the degree of reflection or refraction.

First, as shown in FIG. 2, the light emitted from the light source 26 enters the light guide plate 21 through the light incident surface of the end surface of the light guide plate 21. FIG. 2 shows an example of an optical path of light L ₂₁ and L ₂₂ incident on the light guide plate 21 from the light source 26 as an example.

As shown in FIG. 2, the light L ₂₁ and L ₂₂ incident on the light guide plate 21 are totally reflected by the difference in refractive index with air on the surface of the unit optical element portion 24 of the light guide plate 21 and the light exit surface on the opposite side. To do. Although not shown, the light emitted from the back surface is returned to the light guide plate 21 by the reflection sheet 40. Such reflection is repeated, and the light travels away from the light source 26 in the light guide direction.

However, a back prism portion 23 is formed on the back side of the base portion 22 of the light guide plate 21. For this reason, as shown in FIG. 2, the light L ₂₁ and L ₂₂ traveling in the light guide plate 21 is sequentially changed in direction by the back prism portion 23 and is incident on the light exit surface at an incident angle less than the total reflection critical angle. There is also. In this case, the light can be emitted from the light exit surface of the light guide plate 21. Lights L ₂₁ and L ₂₂ emitted from the light guide plate 21 travel toward the prism sheet 30 disposed on the light output side of the light guide plate 21.
As a result, the light traveling in the light guide plate 21 is gradually emitted from the light exit surface, and the light quantity distribution along the light guide direction of the light emitted from the unit optical element portion 24 of the light guide plate 21 is made uniform. Can do.

Here, the optical element portion 24 of the light guide plate 21 shown in the figure is composed of a plurality of unit optical elements 24a, and the sectional shape of each unit optical element 24a is a pentagon. Therefore, the unit optical element 24 a is configured to have an inclined surface with respect to the light guide direction of the light guide plate 21. Thereby, as shown in FIG. 6, the light L ₅₁ emitted from the light guide plate 21 via the unit optical element 24 a is refracted when emitted from the light guide plate 21. This refraction is a refraction that approaches the sheet surface normal line nd in the arrangement direction of the unit optical elements 24a (the angle formed by the normal line nd becomes small). By such an effect | action, the optical element part 24 can narrow down the advancing direction of the transmitted light to the front direction side about the component of the light along the direction orthogonal to the light guide direction. That is, the unit optical element section 24 exerts a condensing action on the light component along the direction orthogonal to the light guide direction.

  As described above, the emission angle of the light emitted from the light guide plate 21 is narrowed down to a narrow angle range centering on the front direction on a plane parallel to the arrangement direction of the unit optical elements 24a of the light guide plate 21.

The light emitted from the light guide plate 21 then enters the prism sheet 30. The unit prism 32a of the prism sheet 30 exerts a condensing action on the transmitted light by refraction and total reflection at the light incident surface of the unit prism 32a. However, the light whose traveling direction is changed by the prism sheet 30 is a component in a plane perpendicular to the arrangement direction of the unit prisms 32 a in the prism sheet 30, and the component condensed by the light guide plate 21. Is different. That is, as indicated by _L81 in FIG. 8, the light incident on the unit prism 32a is totally reflected at the interface based on the refractive index difference between the unit prism 32a and air. Then, the hypotenuse of the unit prisms 32a so inclined theta _7/2 relative to the seat surface normal nd, light reflection at the interface at an angle which is close to the normal nd than the incident light.

  Furthermore, in the present invention, the direction in which the unit prism 32a extends is inclined at an angle θ with respect to the direction orthogonal to the light guide direction as described above. Therefore, the direction is changed by an angle corresponding to θ when the total reflection is performed by the unit prism 32a.

The light output is controlled as follows by the light guide plate and the prism sheet as described above.
That is, first, light having a substantially elliptical luminance distribution can be obtained in a predetermined manner by the shape of the unit prism 32a of the prism sheet 30 and the shape of the unit optical element 24a of the light guide plate 21. Details are as follows. FIG. 9 shows an explanatory diagram. FIG. 9A shows the influence of the form of the unit prism 32a on the elliptical luminance distribution, and FIG. 9B shows the influence of the form of the unit optical element 24a on the elliptical luminance distribution. The light guide direction is represented by the vertical axis, and the light source arrangement direction is represented by the horizontal axis. Since the origin O represents the luminance distribution in the vertical direction of the screen, it means that light is emitted in a direction inclined from the vertical direction of the screen by moving away from the origin. Such a light emission characteristic is Ezcontrast (manufactured by ELDIM). According to this, the viewing angle characteristic is expressed in the coordinate system expressed by the azimuth angle φ and the elevation angle β, and the luminance is expressed in the Z-axis direction (for example, it can be expressed by a color distribution). be able to.

As can be seen from FIG. 9A, when the unit prism 32a is adjusted to be a unit prism 32a having a high light condensing property, the spread in the light guide direction is the light source array as shown by the solid line in FIG. 9A. Since it becomes smaller with respect to the direction, it becomes an elliptical light output characteristic having a long axis in the light source arrangement direction.
On the other hand, when the unit prism 32a is adjusted to be a unit prism 32a having a low light collecting property, the spread in the light guide direction is larger than the light source arrangement direction as shown by the dotted line in FIG. Therefore, an elliptical light output characteristic having a long axis in the light guide direction is obtained.

On the other hand, as can be seen from FIG. 9B, when the unit optical element 24a has a high light collecting property by adjusting the form of the unit optical element 24a, as shown by the solid line in FIG. Since the spread becomes smaller with respect to the light guide direction, an elliptical light output characteristic having a long axis in the light guide direction is obtained.
On the other hand, when the unit optical element 24a is adjusted to have a low light collecting property by adjusting the form of the unit optical element 24a, the spread in the light guide direction is larger than the light source arrangement direction as shown by the dotted line in FIG. Therefore, the light emission characteristic becomes an elliptical shape having a long axis in the light source arrangement direction.

  The light having the elliptic luminance distribution as described above is adjusted in the light emission position by the angle at which the unit prism 32a extends and the inclination angle of the reflection surface of the unit prism 32a. FIG. 10 and FIG. 11 are diagrams for explanation.

FIG. 10A is a diagram for explaining the influence of the reflection surface angle α (see FIG. 8) of the unit prism 32a, and FIG. 10B is the reflection surface angle α of the unit prism 32a (see FIG. 8). It is another figure explaining the influence which acts. The light guide direction is represented by the vertical axis, and the light source arrangement direction is represented by the horizontal axis. In these figures, the light source is positioned below. Since the origin O represents the luminance distribution in the vertical direction of the screen, it means that light is emitted in a direction inclined from the vertical direction of the screen by moving away from the origin.
FIG. 10A shows a case where the angle α of the reflecting surface of the unit prism 32a shown in FIG. 8 (the angle of the reflecting surface of the unit prism 32a with respect to the normal line of the base material 31) is large. Light is emitted inclining in the direction of moving away.
On the other hand, FIG. 10B shows a case where the angle α of the reflecting surface of the unit prism 32a shown in FIG. 8 (the angle of the reflecting surface of the unit prism 32a with respect to the normal line of the base material 31) is small. Light is emitted in a direction inclined to the light source arrangement side.

FIG. 11 is a diagram for explaining the influence of the angle (θ in FIGS. 6 and 7) that the unit prism 32a extends.
As can be seen from FIG. 11, when θ is increased from the state of FIG. 10A, the inclination in the emission direction changes according to θ as shown by the arrow in FIG.

By combining the shape of the unit prism 32a and the unit optical element 24a and the relationship of the arrangement described above, as shown by B in FIG. 12, a substantially elliptical luminance that emits light in a direction inclined from the front direction. It will have a distribution. A diagram indicated by B in FIG. 12 is a diagram schematically showing contour lines of the light emission luminance distribution. And it is preferable that the 50% luminance contour line shown by C in FIG. 12 (a line connecting directions in which the luminance is 50% when the peak luminance is 100%) is substantially elliptical.
In addition, it is preferable that the major axis of the ellipse is not parallel to the coordinate axis in the coordinate system but has an inclination.

Such an emission inclined from the front direction and a substantially elliptical shape can emit light in a desired direction, and further has a wide viewing angle on the major axis side of the ellipse and a viewing angle on the minor axis side of the ellipse. Is narrow. Therefore, as shown in FIG. 13, consider the front of the vehicle as viewed from the driver's seat and passenger seat of the vehicle.
On the screen of the car navigation system indicated by P, light can be emitted in the left-right direction and a slightly upwardly inclined direction, and images can be provided to the driver's seat and the passenger seat. At this time, since light having an inclination in the vertical direction is suppressed to a small extent, reflection on the windshield and emission of light in an unnecessary direction can be prevented.
Further, as indicated by Q, on the screen provided in the rearview mirror, a luminance distribution that is emitted slightly inclined downward toward the driver's seat is formed. This allows the driver to see it brightly.
As indicated by R, on the screen provided in the A pillar, the display device itself is inclined, but the light is emitted in a horizontal direction toward the passenger seat side and the driver seat side. Can do. This makes it easier to see from the driver's seat and passenger seat.

DESCRIPTION OF SYMBOLS 10 Image source unit 12 Liquid crystal layer 13, 14 Polarizing plate 15 Liquid crystal panel 20 Surface light source device 21 Light guide plate 22 Base part 23 Back surface prism part 23a Unit back surface prism 24 Optical element part 24a Unit optical element 26 Light source 30 Prism sheet 31 Main body part 32 Unit Prism unit 32a Unit prism

Claims (5)

A light source;
A light guide plate for guiding light emitted from the light source;
A prism sheet that is disposed on the light output side of the light guide plate and changes the direction of the incident light and emits the light; and
The prism sheet is
A sheet-like main body having optical transparency;
A plurality of convex unit prisms are arranged on the surface of the main body on the light guide plate side and extend in a direction along the sheet surface of the main body with a predetermined cross section, which is different from the extending direction. Unit prisms arranged in a direction,
The direction in which the unit prism extends is inclined in the range of more than 0 degree and less than 90 degrees, when the direction orthogonal to the light guide direction is 0 degree.
Surface light source device.   2. The surface light source device according to claim 1, wherein when the viewing angle characteristic is expressed in a coordinate system expressed by an azimuth angle and an elevation angle, a line connecting portions having luminances of 50% from the highest luminance is substantially elliptical. .   3. The surface light source device according to claim 2, wherein the major axis of the substantially elliptical shape is not parallel to the coordinate axis in the coordinate system but has an inclination. A surface light source device according to any one of claims 1 to 3,
A liquid crystal panel disposed on the light output side of the surface light source device. A video source unit according to claim 4;
A liquid crystal display device comprising: a housing containing the video source unit.

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