JP6844730B2 - Surface light source device, image source unit, and liquid crystal display device - Google Patents

Description

The present invention relates to a surface light source device that functions as illumination for a display device, a video source unit using the surface light source device, and a liquid crystal display device.

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

In recent years, devices installed in automobiles and the like for viewing by drivers and passengers are increasingly equipped with monitors (liquid crystal display devices). Not only navigation systems and audio equipment, but also rear-view mirrors, A-pillars, etc. may be equipped with monitors according to their respective uses.

Since the number of observers of such a monitor is limited, the range of light (image) emitted from the monitor may be adjusted to this, and the operation is performed in the so-called eye point direction, that is, from the irradiation surface that irradiates the light. It is necessary to emit high-brightness light 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 brightness is improved in the three directions of the eye point direction and the vertical direction with respect to the irradiation surface in view of such characteristics of the eye point. According to this, it is possible to improve the brightness in three directions of the driver's seat, the passenger seat, and the front, and it is said that the monitor has excellent brightness distribution characteristics as an in-vehicle monitor. As a configuration for that purpose, a polarizing sheet, a diffusion sheet, a light guide plate, and a reflective sheet are provided in this order, and a prism sheet having a base angle of a triangular groove in the range of 40 ° to 60 ° is provided between the polarizing sheet and the diffusion sheet. It is provided.

Japanese Unexamined Patent Publication No. 2004-296343

However, in a surface light source device as described in Patent Document 1, it is complicated to configure a monitor arranged at various positions to emit high-intensity light in the eye point direction. It tended to be.

Therefore, in view of the above points, it is an object of the present invention to provide a surface light source device that is easy to observe on the driver's seat side and the passenger's seat side, limits light emission in other directions, and has a simple structure for that purpose. .. Further, a video source unit including this surface light source device and a liquid crystal display device are provided.

One aspect of the present invention includes a light source, a light guide plate that guides light emitted from the light source, and a prism sheet that is arranged on the light emitting side of the light guide plate and emits light by changing the direction of the incident light. The prism sheet is arranged on a sheet-like main body having light transmission and on the surface side of the main body on the light source side, and a plurality of convex unit prisms are predetermined in a direction along the sheet surface of the main body. It has a unit prism portion that extends with a cross section and is arranged in a direction different from the extending direction, and the direction in which the unit prism extends is 0 when the direction orthogonal to the light source direction is 0 degrees. It is tilted in the range of more than degrees and less than 90 degrees, and when the viewing angle characteristics are expressed in the coordinate system expressed by the azimuth angle and elevation angle, the line connecting the parts with the highest brightness to the brightness of 50% is approximately elliptical. It is a surface light source device having a shape, and the long axis of the substantially elliptical shape is not parallel to the coordinate axes in the coordinate system but has an inclination.

An image source unit including the surface light source device and a liquid crystal panel arranged on the light emitting side of the surface light source device can be provided.

It is possible to provide a liquid crystal display device including the above-mentioned video source unit and a housing including the video source unit.

According to the present invention, the contour lines of the 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 and light emission direction of such a substantially elliptical shape can be adjusted only by changing the angle in the direction in which the unit prism extends, and the light emission characteristics can be changed very easily.

It is an exploded perspective view explaining the image source unit 10. It is an exploded view which shows one cross section of the image source unit 10. It is a perspective view of the light guide plate 21. It is a figure showing a part of the cross section of a light guide plate 21. It is a figure showing another cross section of a light guide plate 21. It is a perspective view of a prism sheet 30. It is a top view of the prism sheet 30. It is an enlarged view of a part of the cross section of a prism sheet 30. FIG. 9A is a diagram showing the influence of the morphology of the unit prism 32a on the elliptical luminance distribution, and FIG. 9B is a diagram showing the influence of the morphology of the unit optical element 24a on the elliptical luminance distribution. FIG. 10A is a diagram illustrating the effect of the angle α of the reflecting surface of the unit prism 32a, and FIG. 10B is another diagram illustrating the effect of the angle α of the reflecting 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 the light output characteristic. It is a figure explaining an example of application of a display device.

Hereinafter, the present invention will be described based on the form shown in the drawings. However, the present invention is not limited to these forms. Further, in each of the figures shown below, the size and shape of the member may be exaggerated for ease of understanding, and the repeated reference numerals may be omitted for ease of viewing.

FIG. 1 is an exploded perspective view conceptually showing the image source unit 10 included in the liquid crystal display device according to one form.
The liquid crystal display device includes the image source unit 10, and the observer obtains image information after 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. Provided to the side. The liquid crystal display device includes a housing (not shown), in which the image source unit 10 is built. The housing is a member that forms the outer shell of the liquid crystal display device and houses most of the members constituting the liquid crystal display device inside. Further, the housing has an opening capable of supporting the video source unit 10, and the video source unit 10 is fitted and attached to the opening. In addition, the liquid crystal display device is provided with various known components for functioning as the liquid crystal display device.

The image 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 paper surface is the observer side.

The liquid crystal panel 15 is an upper polarizing plate 13 arranged on the observer side, a lower polarizing plate 14 arranged on the surface light source device 20 side, and a liquid crystal arranged 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 polarizing components (P wave and S wave), and the polarizing component in one direction (direction parallel to the transmission axis) (for example, P). It has a function of transmitting a (wave) and absorbing a polarizing component (for example, an S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

In the liquid crystal layer 12, an electric field can be applied to each region forming one pixel. Then, the orientation of the liquid crystal layer 12 to which the electric field is applied changes. The polarization component (for example, P wave) in a specific direction transmitted through the lower polarizing plate 14 arranged on the surface light source device 20 side (that is, the light entry side) changes its polarization direction when passing through the liquid crystal layer 12 to which an electric field is applied. It is rotated by 90 °, while maintaining its polarization direction as it passes through the liquid crystal layer 12 to which no electric field is applied. Therefore, depending on whether or not an electric field is applied to the liquid crystal layer 12, the polarizing component (P wave) in a specific direction transmitted through the lower polarizing plate 14 further transmits through the upper polarizing plate 13 arranged on the light emitting side of the lower polarizing plate 14. It is possible to control whether or not it is absorbed by the upper polarizing plate 13 and blocked.

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

Next, the surface light source device 20 will be described. FIG. 2 shows a cross-sectional view of the surface light source device 20 along the dotted line shown in FIG. 1 in the thickness direction (vertical direction on the paper surface of FIG. 1).
The surface light source device 20 is an illumination device that is arranged 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 has a base portion 22, a back surface prism portion 23, and an optical element portion 24. The light guide plate 21 is a plate-like member as a whole made of a translucent material, and an optical element portion 24 is formed on one plate surface side to form an light emitting surface. The other plate surface side is the back surface, and the back surface prism portion 23 is formed.

Various materials can be used as the material forming the base portion 22, the back surface prism portion 23, and the optical element portion 24. However, a material that is widely used as a material for an optical sheet incorporated in a display device, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. This includes, for example, polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrenes, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, thermoplastic resins such as polyether sulfone, and the like. , Epoxy acrylate, styrene acrylate-based reactive resin (ionized radiation curable resin, etc.) and the like.

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

The back surface 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 emitting surface). FIG. 3 is a perspective view of the light guide plate 21 as viewed from the back surface prism 23 side, and FIG. 4 is a part of a cross section along the line shown by IV-IV in FIG. 3 (line along the light guide direction). expressed. As can be seen from FIGS. 2 to 4, in this embodiment, a plurality of triangular columnar unit back surface prisms 23a are arranged. The unit back surface prism 23a is a columnar shape in which the ridgeline of the convex portion extends in the light source arrangement direction, and the plurality of unit back surface prisms 23a are arranged side by side at a predetermined pitch in the direction orthogonal to the extension 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, and the direction in which the unit back surface prism 23a is arranged is the direction orthogonal to the light source direction.

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

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

In this embodiment, as shown in FIG. 5, the plurality of unit optical elements 24a are arranged without a gap in the light source arrangement direction on the surface of the base 22 on the light emitting side. Therefore, the light emitting surface of the light guide plate 21 is composed of an 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 emitting side. That is, the width of the unit optical element 24a parallel to the plate surface of the light guide plate 21 becomes smaller as it is separated from the base 22 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. Further, in the present embodiment, the cross-sectional shape of the unit optical element 24a has symmetry about the normal line. That is, the light emitting side surface of each unit optical element 24a is composed of a pair of bent surfaces symmetrically configured with respect to the front direction. The pair of bent surfaces are connected to each other to define the tip. Each bent surface has a first surface 24b that defines the tip and a second surface 24c that connects to the first surface 24b from the side of the base 22.

As an overall configuration of the optical element portion 24, the front direction of the light guide plate 30 from the base 22 of the unit optical element 24a with respect to the width Wa in the arrangement direction of the unit optical element 24a in the cross section shown in FIG. The ratio of the protruding height Ha along the above (Ha / Wa) is preferably 0.3 or more and 0.45 or less. According to such a unit optical element 24a, by refraction and reflection on the light emitting side surface, an excellent focusing function is exhibited for the light component along the arrangement direction (light source arrangement direction) of the unit optical element 24a. It is also possible to effectively suppress the occurrence of side lobes.

The term "pentagonal shape" in the present specification includes not only a pentagonal shape in a strict sense but also a substantially pentagonal shape including limits in manufacturing technology and errors during molding. Similarly, other terms used herein that specify shape and geometric conditions, such as "parallel," "orthogonal," and "symmetrical," are not bound by strict meaning. The interpretation shall include an error to the extent that a similar optical function can be expected.

Here, as an example, the dimensions of the light guide plate 21 can 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 22 is 0.2 mm to 6 mm.

The light guide plate 21 having the above configuration can be manufactured by extrusion molding or by molding the unit back surface 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 surface prism portion 23 and / or the optical element portion 24 can be integrally formed with the base portion 22. Further, when the light guide plate 21 is manufactured by molding, the back surface prism portion 23 may be made of the same resin material as the base portion 22 or may be made of a different material.

The form of the unit optical element may be a pentagon in cross section as described above, another polygon such as a triangle or a quadrangle, or a lens shape such as a lenticular lens. Further, the form is not limited to the form protruding from the base portion as in this form, and may be a concave element. This includes, for example, 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 arranged on one or both of the two sets of side surfaces of the base 22 of the light guide plate 21 in the light guide direction (FIGS. 1 and 2 are examples of one). The type of the light source is not particularly limited, but may be configured in various modes 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 a control device (not shown) controls the output of the LEDs, that is, the lighting and extinguishing of the LEDs, and / or the brightness when the LEDs are lit. The plurality of LEDs may be controlled collectively or individually.

Next, the prism sheet 30 will be described. As can be seen from FIGS. 1 and 2, the prism sheet 30 is provided on the surface of the main body 31 formed in the shape of a sheet and the surface of the main body 31 facing the light guide plate 21, that is, the side surface of the light entering light. It includes a unit prism unit 32. FIG. 6 is a perspective view of the prism sheet 30 seen from the unit prism portion 32 side, FIG. 7 is a plan view of the prism sheet 30 seen from the unit prism portion 32 side, and FIG. The cross-sectional view of the prism sheet 30 along the vertical line is shown.

In combination with the form of the unit optical element portion 24a of the light guide plate 21, the prism sheet 30 changes the traveling direction of the light incident from the incoming light side and emits it from the light emitting side, and is substantially elliptical in a predetermined embodiment. It has a function of intensively improving the brightness so as to emit light having a shape of brightness distribution. Therefore, this function is mainly exerted 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, 6 to 8, the main body portion 31 is a flat plate-shaped sheet-like member having a function of supporting the unit prism portion 32.

As is often shown in FIGS. 1, 2, 6 to 8, the unit prism portions 32 are arranged so that a plurality of unit prisms 32a are arranged along the light entrance side surface of the main body portion 31. More specifically, the unit prism 32a is a columnar member formed so that the ridge line 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. 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 brightness distribution having high brightness at a position deviated from the center of the screen.
The specific value of θ can be adjusted to obtain the desired brightness distribution. Therefore, the range of 0 ° <θ <90 ° can be taken.

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

As can be seen from FIG. 8, in the present embodiment, the unit prism 32a has an isosceles triangular cross section protruding from the main body 31 toward the light guide plate 21. That is, the width of the unit prism 32a in the direction parallel to the seat surface of the main body 31 decreases as the distance from the main body 31 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 is 80 ° or less. preferable. As a result, more appropriate light-collecting characteristics can be obtained in the arrangement form of the unit prism 32a, which is arranged so as to face the light emitting surface of the light guide plate 21. 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 the adjacent unit prisms 32a is preferably 10 μm or more.

In the present embodiment, the unit prism having a triangular cross-sectional shape has been described as described above, but the present invention is not limited to this, and the top of the triangle may be a trapezoid having a short upper base. Further, the shape of one and / or the other of the slopes may be a polygonal line or a curved line. 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 by forming, for example, the unit prism portion 32 on the base material which is the main body portion 31.
Various materials can be used as the material forming the main body portion 31 and the unit prism portion 32. However, a material that is transparent and widely used as a material for an optical sheet incorporated in a display device, has excellent mechanical properties, optical properties, stability, processability, etc., and is inexpensively available, for example, polymethyl. Acrylic resin such as methacrylate, styrene resin, various polycarbonate resins, polyester resin such as polyethylene terephthalate and polyethylene naphthalate, resin such as polyacrylonitrile, resin obtained by mixing one or more of these resins with other resins, or epoxy. An ionizing radiation curable resin obtained by curing a reactive monomer or prepolymer such as an acrylate-based or urethane acrylate-based resin by a cross-linking reaction or a polymerization reaction by irradiation with ultraviolet rays, electron beams, or the like can be preferably used.

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

Returning to FIGS. 1 and 2, the reflective sheet 40 of the surface light source device 20 will be described. The reflective sheet 40 is a member for reflecting the light emitted from the back surface of the light guide plate 21 and causing the light to enter the light guide plate 21 again. The material constituting the reflective sheet 40 is not particularly limited, but is a white film (Toray Co., Ltd. Lumirror (registered trademark) E6SR), a multilayer film reflective film (3M Japan Ltd. ESR), and a silver vapor deposition film (Kyoto Nakai Shoji). Examples of films having light reflectivity such as Kiraraflex Co., Ltd. (registered trademark). More preferably, a sheet made of a material having a high reflectance such as metal, a sheet made of a thin film made of a material having a high reflectance (for example, a metal thin film) as a surface layer, or the like that enables so-called specular reflection is applied. can do. As a result, the utilization of light can be improved, and the energy utilization efficiency can be improved.

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 a color tone, a sheet having an antiglare function, a sheet for preventing reflection, a hard coat sheet and the like.

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

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

As shown in FIG. 2, the lights 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 emitting surface on the opposite side. To do. Further, although not shown, the light emitted from the back surface is returned to the light guide plate 21 by the reflective sheet 40. By repeating such reflection, the light travels away from the light source 26 in the light guide direction.

However, the back surface prism portion 23 is formed on the back surface side of the base portion 22 of the light guide plate 21. Therefore, as shown in FIG. 2, the light L ₂₁ and L ₂₂ traveling in the light guide plate 21 are sequentially changed in direction by the back surface prism portion 23, and are incident on the light emitting 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 emitting surface of the light guide plate 21. _{The lights L 21} and L ₂₂ emitted from the light guide plate 21 head toward the prism sheet 30 arranged on the light emitting 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 emitting surface, and the light amount distribution of the light emitted from the unit optical element portion 24 of the light guide plate 21 along the light guide direction is made uniform. Can be done.

Here, the optical element portion 24 of the light guide plate 21 shown is composed of a plurality of unit optical elements 24a, and the cross-sectional shape of each unit optical element 24a is a pentagon. Therefore, the unit optical element 24a is configured to have an inclined surface with respect to the light guide direction of the light guide plate 21. As a result, as shown in FIG. 5, the light L ₅₁ emitted from the light guide plate 21 via the unit optical element 24a is refracted when emitted from the light guide plate 21. This refraction, in the arrangement direction of the unit optical elements 24a, closer to the seat surface normal n _d (the angle between the normal line n _d decreases) the refractive. By such an action, the optical element unit 24 can narrow down the traveling direction of the transmitted light to the front direction side with respect to the light component along the direction orthogonal to the light guide direction. That is, the unit optical element unit 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 within a narrow angle range centered on the front direction on the 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 on the incoming light surface of the unit prism 32a. However, the light whose traveling direction can be changed by the prism sheet 30 is an in-plane component of the prism sheet 30 that is orthogonal to the arrangement direction of the unit prisms 32a, and is a component focused by the light guide plate 21. Is different. That is, as shown by L ₈₁ in FIG. 8, the light incident on the unit prism 32a is totally reflected at the interface based on the difference in refractive index between the unit prism 32a and air. Then, the hypotenuse of the unit prisms 32a so that theta _7/2 inclined with respect to the seat surface normal n _d, light reflection at the interface at an angle which is close to the normal n _d than the incident light.

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

The light emission is controlled as follows by the light guide plate and the prism sheet as described above.
That is, first, depending on 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, light having a substantially elliptical brightness distribution can be obtained in a predetermined embodiment. The details are as follows. FIG. 9 shows a diagram for explanation. FIG. 9A shows the influence of the morphology of the unit prism 32a on the elliptical luminance distribution, and FIG. 9B shows the influence of the morphology 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. Further, since the origin O represents the brightness distribution in the vertical direction of the screen, it means that the light is emitted in the direction inclined from the vertical direction of the screen by moving away from the origin. Such light emission characteristics are expressed by Ezcontlast (manufactured by ELDIM). According to this, the viewing angle characteristics are expressed in the coordinate system represented by the azimuth angle φ and the elevation angle β, and the brightness is expressed in the Z-axis direction (for example, the color distribution can also be expressed). be able to.

As can be seen from FIG. 9A, when the form of the unit prism 32a is adjusted to obtain a unit prism 32a having high light-collecting property, the spread in the light guide direction is arranged as a light source as shown by the solid line in FIG. 9A. Since it becomes smaller with respect to the direction, it has an elliptical light emission characteristic having a long axis in the light source arrangement direction.
On the other hand, if the form of the unit prism 32a is adjusted to obtain a unit prism 32a having a low light-collecting property, the spread in the light guide direction is large with respect to the light source arrangement direction as shown by the dotted line in FIG. 9 (a). Therefore, it has an elliptical light emission characteristic having a long axis in the light guide direction.

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

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

FIG. 10A is a diagram illustrating the effect of the angle α of the reflecting surface of the unit prism 32a (see FIG. 8), and FIG. 10B is the angle α of the reflecting surface of the unit prism 32a (see FIG. 8). It is another figure explaining the effect of. The light guide direction is represented by the vertical axis, and the light source arrangement direction is represented by the horizontal axis. Further, in these figures, the light source is arranged below. Further, since the origin O represents the brightness distribution in the vertical direction of the screen, it means that the light is emitted in the 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 of the base material 31) is large, and at that time, from the light source arrangement side. Light is emitted by tilting in the direction away from it.
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 of the base material 31) is smaller. Light is emitted in a direction tilted toward the light source arrangement side.

FIG. 11 is a diagram illustrating the effect of the extension angle of the unit prism 32a (θ in FIGS. 6 and 7).
As can be seen from FIG. 11, when the 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 shapes and arrangements of the unit prism 32a and the unit optical element 24a described above, as shown in FIG. 12B, the brightness of a substantially elliptical shape that emits light in a direction inclined from the front direction. It will have a distribution. The figure shown by B in FIG. 12 is a diagram schematically showing the contour lines of the Idemitsu luminance distribution. Then, it is preferable that the 50% luminance contour line (the line connecting the directions in which the luminance becomes 50% when the peak luminance is 100%) shown by C in FIG. 12 has a substantially elliptical shape.
Further, it is preferable that the long axis of the ellipse is not parallel to the coordinate axis in the coordinate system and has an inclination.

Such an emission tilted from the front direction and a substantially elliptical shape can emit light in a desired direction, and the viewing angle is wide on the long axis side of the ellipse and the viewing angle on the short axis side of the ellipse. Has the characteristic of being narrow. Therefore, as shown in FIG. 13, consider the front surface of the vehicle as seen from the driver's seat and the passenger seat of the vehicle.
On the screen of the car navigation system shown by P, light can be emitted in a left-right direction and a slightly upwardly tilted direction, and images can be provided to the driver's seat and the passenger seat. At this time, since the light having an inclination in the vertical direction is suppressed to a small extent, it is possible to prevent the light from being reflected on the windshield and the light being emitted in an unnecessary direction.
Further, as shown by Q, the screen provided in the rear-view mirror forms a luminance distribution that is slightly downward and is emitted toward the driver's seat side. This allows the driver to see it brightly.
Then, as shown by R, on the screen provided in the A pillar, the display device itself is slanted, but light is emitted so as to have a horizontal tilt toward the passenger seat side and the driver's seat side. Can be done. This makes it easier to see from the driver's seat and the passenger seat.

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 23 Back prism 23a Unit Back prism 24 Optical element 24a Unit Optical element 26 Light source 30 Prism sheet 31 Main body 32 Unit Prism part 32a Unit prism

Claims (3)

Light source and
A light guide plate that guides the light emitted from the light source and
A prism sheet, which is arranged on the light emitting side of the light guide plate and emits light by changing the direction of the incident light, is provided.
The prism sheet is
A sheet-like body with light transmission and
A plurality of convex unit prisms arranged on the surface side of the main body portion on the light guide plate side extend with a predetermined cross section in a direction along the sheet surface of the main body portion, which is different from the extending direction. It has unit prisms arranged in the direction, and
The direction in which the unit prism extends is tilted in a range of more than 0 degrees and less than 90 degrees when the direction orthogonal to the light guide direction is 0 degrees.
When the viewing angle characteristics are expressed in a coordinate system expressed by the azimuth angle and the elevation angle, the line connecting the parts of the brightness from the highest brightness to 50% is a substantially elliptical shape, and the long axis of the substantially elliptical shape is the above. In the coordinate system, it is not parallel to the coordinate axes and has a slope.
Surface light source device. The surface light source device according to claim 1 and
A video source unit including a liquid crystal panel arranged on the light emitting side of the surface light source device. The video source unit according to claim 2 and
A liquid crystal display device including a housing including the image source unit.

Images