WO2011080997A1 - Surface light source apparatus and liquid crystal display device - Google Patents

Abstract

Disclosed is a surface light source apparatus provided with a light guide plate (3) that serves as a plane of incidence (3a) in which light enters a portion of the surface of a side edge thereof, and a light source (2) that is disposed along the plane of incidence (3a) and that emits light toward said plane of incidence (3a). Reflecting members (4, 5), which have reflecting surfaces (4a, 5a) that guide the light emitted from the light source (2) toward the plane of incidence (3a), are provided in a manner so as to control the spread of said light in the direction of thickness of the light guide plate (3) (the Z-direction), and the entire surface of each reflecting surface (4a, 5a) or a portion thereof near the light guide plate (3) is a specular surface. In cases in which a portion of each reflecting surface (4a, 5a) near the light guide plate (3) is a specular surface, the remaining portion (4b, 5b) of each reflecting surface is a diffuse reflecting surface.

Description

Surface light source device and liquid crystal display device

The present invention relates to a surface light source device that illuminates an object to be illuminated, and a liquid crystal display device including the surface light source device.

As a backlight used in a liquid crystal display device, a side-ride type backlight in which light from a light source is introduced from a side end surface of a light guide plate and is emitted from an output surface of the light guide plate is known. Sidelight type backlights have the advantage that they can be made thinner than direct type backlights.

In such a sidelight type backlight, the use of a thinner light guide plate such as a film light guide plate is being studied in order to meet the demand for further thinning of the apparatus. On the other hand, although the light source is similarly reduced in size (thinned), it is not possible to cope with the thinness of a film light guide plate.

As techniques for meeting such demands, techniques described in Patent Document 1, Patent Document 2, and Patent Document 3 are known. In the technique described in Patent Document 1, a light guide is disposed between a light source and a light guide plate so that light from the light source is guided to the light guide plate. A diffusion element is provided on the inner wall of the light guide in Patent Document 1. In the technique described in Patent Document 2, a reflection layer is disposed between the light source and the light guide plate so that light from the light source is guided to the light guide plate. The reflective layer described in Patent Document 2 is white or silver. In the technique described in Patent Document 3, the light distribution of the light source is an elliptical light distribution in which the thickness direction of the light guide plate is narrow and the direction orthogonal to the thickness direction (the direction along the light incident surface of the light guide plate) is wide. Thus, the light is guided to the light incident surface of the light guide plate.

JP 2006-324169 A JP 2008-65997 A JP 2002-43630 A

However, in the techniques described in Patent Document 1 and Patent Document 2 described above, it is possible to increase the light use efficiency as compared with a configuration in which a light guide or a reflective layer is not provided, but it is still sufficient. There is room for improvement. Moreover, in the technique described in Patent Document 3 described above, it is possible to increase the light use efficiency as compared with the case where the light distribution of the light source is not adjusted. There is room. In the specification of the present application, the light utilization efficiency refers to the ratio of the total luminous flux entering the light guide plate when the total luminous flux emitted from the light source is 100%.

The present invention has been made in view of such a point, and an object thereof is to provide a surface light source device capable of improving light utilization efficiency and a liquid crystal display device including the same.

As a result of earnest research, the inventors of the present application have provided a reflecting member that restricts the divergence of the light emitted from the light source and guides it to the side end surface of the light guide plate, and specularly reflects all or part of the reflecting surface of the reflecting member. It has been found that the light utilization efficiency can be improved by using the surface, and the present invention has been completed.

That is, the surface light source device according to the first aspect of the present invention is provided with a light guide plate in which a part of its side end surface is an incident surface on which light is incident, along the incident surface, and directed toward the incident surface. A surface light source device including a light source that emits light, and a reflection surface that guides the light to the incident surface so as to limit the divergence of the light emitted from the light source in the thickness direction of the light guide plate. A reflection light source device is provided, and the reflection surface is a surface light source device having a regular reflection surface.

In the surface light source device according to the first aspect of the present invention, the reflectance of the regular reflection surface can be set to be 96% or more.

In the surface light source device according to the first aspect of the present invention, the reflection member includes a first reflection member having a first reflection surface and a second reflection surface that are spaced apart in the thickness direction of the light guide plate. The first reflecting surface and the second reflecting surface are arranged so as to form an angle of 5 to 70 °, preferably 15 ° to 60 °, more preferably 25 ° to 35. Placed at °. The separation distance between the light source and the incident surface can be set within a range of 0 to 20 mm.

In the surface light source device according to the first aspect of the present invention, the reflecting member has a third reflecting member disposed between the first reflecting member and the second reflecting member, and the third reflecting member is The reflective surface may include a third reflective surface facing the first reflective surface and a fourth reflective surface facing the second reflective surface.

In the surface light source device according to the first aspect of the present invention, the light source is configured by arranging a plurality of point light sources along the incident surface, and the light distribution characteristic of each point light source is determined by the thickness of the light guide plate. The half-value angle in the direction can be set to θ ≦ 120 °, where θ is θ. In addition, in this specification, a half value angle shall mean a half value full angle.

In the surface light source device according to the first aspect of the present invention, a part of the reflection surface on the light source side is a diffuse reflection surface made of a material having a property of diffusing and reflecting light, or an uneven structure for diffusing and reflecting light. It can be set as the diffuse reflection surface which consists of.

Further, as a result of earnest research, the inventors of the present application have provided a reflection member that restricts the divergence of light emitted from the light source and guides it to the side end surface of the light guide plate, and in relation to this, the light distribution characteristics of the light source are improved. It has been found that the light utilization efficiency can be improved by the optimization, and the present invention has been completed.

That is, the surface light source device according to the second aspect of the present invention includes a light guide plate in which a part of the side end surface is an incident surface on which light is incident, an array along the incident surface, and the light source plate facing the incident surface. A surface light source device including a light source having a plurality of point light sources for emitting light, the light being incident on the light source so as to limit a divergence of light emitted from the light source in a thickness direction of the light guide plate. A reflecting member having a reflecting surface that leads to the surface is provided, and the half-value angle of the light distribution characteristic in the thickness direction of the light guide plate of each point light source constituting the light source is set to θ ≦ 35 °. In addition, in this specification, a half value angle shall mean a half value full angle.

In the surface light source device according to the second aspect of the present invention, the half-value angle of the light distribution characteristic in the arrangement direction of the respective point light sources constituting the light source can be set to φ / θ> 1.

In the surface light source device according to the second aspect of the present invention, the half-value angle in the arrangement direction of the point light sources constituting the light source is φ, the arrangement pitch of the point light sources is p, the width of the point light sources (in the arrangement direction) Dimension) is a, and the distance between the point light source and the incident surface is d,
The relationship φ> tan ⁻¹ ((a + p) / 2d) can be satisfied.

In the surface light source device according to the second aspect of the present invention, when the thickness of the light guide plate is smaller than the thickness of each point light source constituting the light source (the dimension corresponding to the thickness direction of the light guide plate), It can be particularly preferably used.

A liquid crystal display device according to a third aspect of the present invention includes a liquid crystal panel and the surface light source device according to the first aspect or the second aspect of the present invention.

According to the surface light source device according to the first aspect or the second aspect of the present invention, the light utilization efficiency can be improved as compared with the conventional case, and the device can be reduced in thickness, cost, and power saving. it can.

According to the liquid crystal display device according to the third aspect of the present invention, since the surface light source device according to the first aspect or the second aspect of the present invention is provided, the device is thinned, the cost is reduced, and the power is saved. Can be achieved.

It is a top view of the surface light source device of the embodiment of the present invention. It is a side view which shows the principal part of the surface light source device of embodiment of this invention. It is a top view which shows the principal part of the surface light source device of embodiment of this invention. It is a top view which shows the principal part of the surface light source device which changed a part of embodiment of this invention. It is a side view which shows the principal part (Example 5-1) of the surface light source device which changed a part of embodiment of this invention. It is a side view which shows the principal part (Example 5-2) of the surface light source device which changed a part of embodiment of this invention. It is a side view which shows the principal part (Example 5-3) of the surface light source device which changed a part of embodiment of this invention. It is a figure which shows the relationship between the reflectance of the reflective surface of a reflection member as a simulation result in embodiment of this invention, and light utilization efficiency. It is a figure which shows the relationship between the half value full angle as a simulation result at the time of making the reflective surface of the reflective member in the Example of this invention into a regular reflective surface, and light utilization efficiency. It is a figure which shows the relationship between the full width at half maximum as a simulation result at the time of making the reflective surface of the reflective member in the Example of this invention into a diffuse reflective surface, and light utilization efficiency.

Hereinafter, a surface light source device according to an embodiment of the present invention will be described with reference to the drawings. In the following, the thickness direction of the rectangular light guide plate in plan view described later is the Z direction, and the direction along one side of the rectangular light guide plate is the X direction and the X direction in a plane perpendicular to the Z direction. A description will be given using an XYZ orthonormal coordinate system in which the orthogonal direction is the Y direction.

This surface light source device is particularly suitable for use in a backlight that illuminates a liquid crystal panel of a liquid crystal display device as an object to be illuminated. However, the object to be illuminated is not limited to such a liquid crystal panel, and can also be used as illumination for a signboard arranged at a storefront or the like, illumination for a show window, or any other illumination. Below, the case where it uses as a backlight of a liquid crystal display device is demonstrated to an example.

As shown in FIGS. 1 to 3, a surface light source device 1 of this embodiment includes a light source 2, a light guide plate (film light guide plate) 3 made of a rectangular plate-like film that guides light from the light source 2, and It has.

As the light source 2, in this embodiment, LEDs (Light Emitting Diodes) 2a as a plurality of point light sources are arranged along the Y direction at a predetermined arrangement pitch. In this embodiment, each LED 2a is mounted on an elongated rectangular substrate 2b arranged such that its longitudinal direction is along the longitudinal direction (Y direction) of the incident surface 3a. As the LED 2a, a blue-yellow pseudo white light emitting diode, a three-color (RGB) white light emitting diode, or the like can be used. However, the point light source is not limited to such an LED 2a, and for example, a semiconductor laser or the like may be used. In addition, the light source 2 is not limited to one in which such point light sources are arranged, and a linear light source such as a cold cathode fluorescent lamp (CCFL) may be used.

Each LED 2a is arranged such that its axis (direction of the principal ray of emitted light) is oriented substantially in the + X direction. Here, the axis of the light source 2 (LED 2a) is preferably arranged so as to pass through the incident surface 3a of the light guide plate 3. As the LED 2a, a bullet-type LED can be used, and the width (dimension in the Y direction) of the light emitting portion is a and the thickness (dimension in the Z direction) is b. For example, a LED set to a = b = 3 mm Can be used. However, the width a and the thickness b of the LED 2a do not need to be the same, and when the cross section is set to be oval or oval according to the light distribution characteristics imparted to the LED 2a, they have dimensions different from each other. Can be used.

A general high dome type LED has a Lambertian light distribution and emits a relatively large divergent light having a half-value angle (full-width at half maximum) of about 120 °. As the LED 2a used in this embodiment, an LED having such a general light distribution can be used. However, from the viewpoint of increasing the light utilization efficiency, it is preferable to use one in which at least the half-value angle θ in the Z direction is set to 120 ° or less. The half-value angle θ is more preferably set to 40 ° or less, and further preferably set to 35 ° or less, and is as close to parallel light as possible (hereinafter simply referred to as parallel light) as much as possible. preferable. The half-value angle φ in the Y direction may be the same as the half-value angle θ in the Z direction, but it is preferable to use a larger value than that. An appropriate number or value is selected as the number or arrangement pitch of each LED 2a in relation to the dimension in the Y direction of the light guide plate 3, the maximum light emission amount of the LED 2a, the half-value angle φ in the Y direction, and the like.

The separation distance (dimension in the X direction) d between the light source 2 and the incident surface 3a of the light guide plate 3 is preferably set within a range of 0 to 20 mm. However, when the separation distance d is 0, that is, when the light source 2 is in contact with or close to the incident surface 3a, the influence of the heat generated by the light source 2 on the light guide plate 3 may not be ignored. It is preferable that they are separated to such an extent that there is no influence.

It should be noted that an LED in which the half-value angle θ in the Y direction is set to a value larger than the preferable range as described above, or an LED set in the preferable range as described above is used, and is adjacent to the + X direction of the LED. By providing an optical element such as a lens (between the LED 2a and the incident surface 3a of the light guide plate 3), the light may be converted into divergent light or parallel light in a preferable range as described above. In the present specification, a point light source includes an optical element such as a lens adjacent to the LED.

The light guide plate 3 is made of a transparent resin. The transparent resin is not particularly limited, but propylene-ethylene copolymer, polystyrene, (meth) acrylic acid ester-aromatic vinyl compound copolymer, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer. , Polycarbonate, methacrylic resin, and resin having an alicyclic structure. The light guide plate 3 may be made of glass.

Among these, resins having an alicyclic structure, methacrylic resins, and (meth) acrylic acid ester-aromatic vinyl compound copolymer resins can be preferably used, and resins having an alicyclic structure are particularly preferably used. Can be used. Resin with alicyclic structure has good flowability of molten resin, so in injection molding, mold cavity can be filled with low injection pressure, and weld line is less likely to occur. The thickness unevenness at the time of molding is small, and shape formation after molding is easy. Further, since the hygroscopic property is extremely low, the dimensional stability is excellent, the light guide plate is not warped, and the specific gravity is small, so that the light guide plate can be reduced in weight. Moreover, as resin which has an alicyclic structure, the polymer resin which has an alicyclic structure in a principal chain or a side chain can be mentioned. A polymer resin having an alicyclic structure in the main chain can be particularly preferably used because it has good mechanical strength and heat resistance. The alicyclic structure is preferably a saturated cyclic hydrocarbon structure, and the carbon number thereof is preferably 4 to 30, more preferably 5 to 20, and still more preferably 5 to 15. . The ratio of the repeating unit having an alicyclic structure in the polymer resin having an alicyclic structure is preferably 50% by weight or more, more preferably 70% by weight or more, and 90% by weight or more. More preferably.

Examples of the resin having an alicyclic structure include a ring-opening polymer or a ring-opening copolymer of a norbornene monomer or a hydrogenated product thereof, an addition polymer or an addition copolymer of a norbornene monomer, or Those hydrogenated products, polymers of monocyclic olefin monomers or their hydrogenated products, polymers of cyclic conjugated diene monomers or their hydrogenated products, vinyl alicyclic hydrocarbon monomers Or a hydrogenated product thereof, a polymer of a vinyl aromatic hydrocarbon monomer, or a hydrogenated product of an unsaturated bond part containing an aromatic ring of the copolymer. Among these, hydrogenated products of norbornene-based monomer polymers and hydrogenated products of unsaturated bonds including aromatic rings of vinyl aromatic hydrocarbon-based monomer polymers have mechanical strength and heat resistance. Since it is excellent in property, it can be used especially suitably. The methacrylic resin is excellent in transparency, tough and hardly cracked, so that it can be suitably used. Examples of the methacrylic resin include a methacrylic resin molding material containing 80% or more of a methyl methacrylate polymer defined in JIS K6717. Among the methacrylic resins specified in this standard, methacrylic resins having a specified classification code of 100 to 120 having a Vicat softening point temperature of 96 to 100 ° C. and a melt flow rate of 8 to 16 have suitable fluidity and strength. Can be used.

An antioxidant can be added to the molding material used in the present embodiment in order to prevent oxidative degradation and thermal degradation during molding. Moreover, in order to improve the light resistance etc. of a molded article, a light resistance stabilizer can be added. Examples of the antioxidant include a phenolic antioxidant, a phosphorus antioxidant, and a sulfur antioxidant. These antioxidants can be used individually by 1 type, or can be used in combination of 2 or more type. Among these, phenolic antioxidants, particularly alkyl-substituted antioxidants can be suitably used. The addition amount of the antioxidant is preferably 0.01 to 2 parts by weight, and more preferably 0.02 to 1 part by weight with respect to 100 parts by weight of the resin component.

Examples of the light resistance stabilizer include hindered amine light resistance stabilizer (HALS) and benzoate light resistance stabilizer. These light-resistant stabilizers can be used alone or in combination of two or more. Among these, hindered amine light resistance stabilizers can be particularly preferably used. The addition amount of the light-resistant stabilizer is preferably 0.01 to 2 parts by weight, more preferably 0.02 to 1 part by weight, with respect to 100 parts by weight of the resin component. More preferably, it is 5 parts by weight.

Further additives may be added to the molding material as necessary. Other additives include, for example, stabilizers such as heat stabilizers, ultraviolet absorbers and near infrared absorbers; resin modifiers such as lubricants and plasticizers; colorants such as dyes and pigments; antistatic agents, light Examples include a diffusing agent.

By the way, the light guide plate 3 made of resin undergoes dimensional changes (elongation and warpage) due to moisture absorption, and particularly when the size of the light guide plate 3 is large (for example, 40 inches), the light source 12 and the incident end 14 are caused by the dimensional change. The relative positional relationship with the light changes, and the light use efficiency decreases. Therefore, the water absorption rate of the light guide plate 3 is preferably set to 0.25% or less, more preferably 0.1% or less, and even more preferably 0.05% or less. In this embodiment, the water absorption is set to 0.01%. The water absorption rate in the specification of the present application is in a desiccator after drying a test piece having a disk shape of 50 mm in diameter or a square of 50 mm on a side at 50 ° C. for 24 hours in accordance with JIS K7209 A method. It can be calculated from the weight increase when it is allowed to cool and then immersed in 23 ° C. water for 24 hours.

The light guide plate 3 is made of a rectangular plate, and the dimensions in the X direction and the Y direction are set according to the size of the effective surface of the liquid crystal panel of the liquid crystal display device in which the light guide plate 3 is used. The thickness (dimension in the Z direction) h of the light guide plate 3 can be set to a value smaller than the thickness (dimension in the Z direction) b of the light source 2 and can be set to, for example, h = 1.0 mm. Here, since the thickness h of the light guide plate 3 can be easily manufactured and handled, it is preferably 0.02 mm or more, more preferably 0.1 mm or more, and reduction in thickness and weight can be realized. It is preferably 5 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. As the light guide plate 3, one having a refractive index of, for example, 1.533 (critical angle 40.7 °) can be used.

The light guide plate 3 is opposed to the back surface 3b that reflects light propagating through the light guide plate 3, and emits light that is propagated through the light guide plate 3 without being reflected or reflected by the back surface 3b. And an exit surface 3c. In this embodiment, the back surface 3b and the exit surface 3c (the respective average surfaces when the back surface 3b and the exit surface 3c are uneven) are substantially parallel to the XY plane.

In this embodiment, the back surface 3b of the light guide plate 3 is a reflective surface composed of a uniform plane. The back surface 3b can be configured by depositing a reflective metal on the back surface of the resin plate constituting the light guide plate 3 or by closely arranging a white scattering plate (white reflecting plate). Note that the back surface 3b is directed to the XY plane so that the thickness (dimension in the Z direction) with respect to the exit surface 3c gradually decreases from the side closer to the incident surface 3a to the side farther (toward the + X direction). It is good also as an inclined surface inclined.

Further, the back surface 3b may be provided with unevenness such as a row in order to emit light propagating through the light guide plate 3 with high efficiency and make the emitted light uniform. As a row in this case, for example, the longitudinal direction is set along the Y direction of the back surface 3b, and a row (a prism row) formed by arranging a plurality of triangular stripes in the X direction. ) Can be used. Similarly, the longitudinal direction may be set along the X direction of the back surface 3b, and a strip (prism strip) formed by arranging a plurality of triangular strips in the Y direction may be used. In addition, the apex angle of the row, the inclination angle of the pair of slopes constituting the row with respect to the XY plane, the pitch of the row arrangement, the height, etc. may be different from each other. Furthermore, adjacent strips may not have the same shape, and the shape of the strip is not limited to a triangular cross section, and may be another polygonal shape or a curved shape such as a semicircular arc or an elliptical arc. These may be mixed. Furthermore, the row is not limited to those formed uniformly over the Y direction of the back surface 3b, but may be formed in the middle or divided in the middle. Further, it may be slightly oblique with respect to the Y direction. The back surface 3b may be an irregular rough surface (a surface on which minute irregularities are randomly formed). Further, it may be formed in a dot shape, or may be formed by arranging a plurality of projections or depressions having the same or different shapes in an array or discretely. In this case, a spherical shape, a conical shape, a polygonal pyramid shape, or the like can be adopted as the shape of the protrusion or the depression. Alternatively, the shape may be formed by printing with white ink or metal vapor deposition.

In addition, from the viewpoint of preventing the surface from being scratched, a convex structure is preferable regardless of whether it is linear or dotted. In this case, the height of the protrusion is preferably 1 μm or more from the same viewpoint, and more preferably 5 μm or more.

The light exit surface 3c of the light guide plate 3 is a surface that emits light propagating through the light guide plate 3, and is a uniform flat surface in this embodiment. In order to emit light propagating through the light guide plate 3 with high efficiency and to make the emitted light uniform, unevenness such as a row may be arranged. As a row in this case, for example, the longitudinal direction is set along the Y direction of the exit surface 3c, and a row (prism strip) formed by arranging a plurality of triangular cross-sections in the X direction. Column). Similarly, the longitudinal direction may be set along the X direction of the exit surface 3c, and a strip (prism strip) formed by arranging a plurality of triangular strips in the Y direction may be used. . The apex angle of the row and the inclination angle of the pair of slopes constituting the row with respect to the XY plane, the pitch of the row arrangement, the height, etc. may be different from each other. Furthermore, adjacent strips may not have the same shape, and the shape of the strip is not limited to a triangular cross section, and may be another polygonal shape or a curved shape such as a semicircular arc or an elliptical arc. These may be mixed. Furthermore, the row is not limited to one that is uniformly formed over the Y direction of the exit surface 3c, but may be one that is divided in the middle and formed in an array or discretely. Further, it may be slightly oblique with respect to the Y direction. The emission surface 3c may be an irregular rough surface (a surface on which minute irregularities are randomly formed). Further, it may be formed in a dot shape, or may be formed by arranging a plurality of projections or depressions having the same or different shapes in an array or discretely. In this case, a spherical shape, a conical shape, a polygonal pyramid shape, or the like can be adopted as the shape of the protrusion or the depression. Alternatively, the shape may be formed by printing with white ink (screen printing or ink jet printing), metal deposition, or the like.

In addition, from the viewpoint of preventing the surface from being scratched, a convex structure is preferable regardless of whether it is linear or dotted. In this case, the height of the protrusion is preferably 1 μm or more from the same viewpoint, and more preferably 5 μm or more.

In the manufacture of the light guide plate 3 of the present embodiment, there is no particular limitation on the method for forming the specific protrusion shape on the surface. For example, when forming a prism row, it can be formed on the surface of a flat light guide plate, or the prism row can be formed simultaneously with the formation of the light guide plate. The method for forming the prism array on the surface of the flat light guide plate is not particularly limited. For example, the method can be performed by cutting using a tool capable of forming a linear prism having a desired shape, or a photo-curing resin. Can be applied and cured in a state where a mold having a desired shape is transferred. When the light guide plate is produced by extrusion molding and the prism rows are formed at the same time, the shape of the prism rows can be extrude using a deformed die having a desired prism row shape, or the prism rows can be formed by embossing after extrusion. It can also be formed. When the light guide plate is produced by casting and the prism rows are formed at the same time, a casting mold capable of forming a desired prism row shape can be used. When the light guide plate is manufactured by injection molding and the prism rows are formed at the same time, a mold capable of forming a desired prism row shape can be used. Die shape transfer to photo-curing resin, extrusion process using odd-shaped die, embossing, casting, or injection molding, the mold used to form the prism row was a tool that can form the desired linear prism It can be obtained by cutting a metal member of a mold or electroforming on a member having a desired shape.

On the exit surface 3c side of the light guide plate 3, a light diffusing sheet is sandwiched between air layers so that illumination light (light emitted from the exit surface 3c) by the surface light source device 1 is uniform and uniform. It is preferable that an optical sheet such as a prism sheet is disposed so as to increase the luminance. As an optical sheet, a transparent resin, a plate-like body in which a light diffusing agent or other additives are added to a transparent resin, or a plate-like body formed with a pattern such as a plurality of protrusions or rows on one or both surfaces, etc. Can be used.

As a reflecting member that guides the light emitted from the light source 2 to the incident surface 3a of the light guide plate 3 so as to limit the divergence of the light in the thickness direction (Z direction) of the light guide plate 3, a reflective surface (first reflective surface) ) A reflecting plate (first reflecting member) 4 having 4a and a reflecting plate (second reflecting member) 5 having a reflecting surface (second reflecting surface) 5a are provided. In this embodiment, the pair of reflecting plates 4 and 5 are separated from each other in the thickness direction (Z direction) of the light guide plate 3 so that the reflecting surfaces 4a and 5a face each other, Are arranged symmetrically to each other.

In FIG. 2, the upper reflecting plate 4 has a right edge (+ X direction side edge) on an upper side (+ Z direction side) of the light incident surface 3a of the light guide plate 3 and a left edge (−X direction side edge). It can be arranged so that the edge) is connected to or located near the upper side (the side on the + Z direction side) of the substrate 2b on which the LED 2a is mounted. Similarly, the lower reflector 5 has a right edge (+ X direction side edge) on a lower side (−Z direction side) of the light incident surface 3a of the light guide plate 3 and a left edge (−X direction side). Can be arranged so as to be connected to or located near the lower side (side on the −Z direction side) of the substrate 2b on which the LED 2a is mounted.

By the way, the light guide plate 3 made of resin undergoes a dimensional change (elongation or warpage) due to moisture absorption, and particularly when the size of the light guide plate 3 is large (for example, 40 inches), the light source 2a and the incident surface 3a are caused by the dimensional change. As a result, the light utilization efficiency decreases. Therefore, the water absorption rate of the light guide plate 3 is preferably set to 0.25% or less, more preferably 0.1% or less, and even more preferably 0.05% or less. In this embodiment, the water absorption is set to 0.01%. In addition, the water absorption rate in the present specification is a desiccant after drying a test piece having a disk shape of 50 mm in diameter or a square of 50 mm on a side at 50 ° C. for 24 hours in accordance with JIS K7209 A method. It can be determined from the increase in weight when allowed to cool in a plate and immersed in water at 23 ° C. for 24 hours.

The angle between the reflecting plates 4 and 5 (reflecting surfaces 4a and 5a) is preferably 90 ° or less, more preferably 70 ° or less, further preferably 60 ° or less, and 40 °. It is particularly preferred that In this embodiment, the angle between the reflecting plates 4 and 5 (reflecting surfaces 4a and 5a) with respect to the XY plane is set to 15 °, so that the angle between them is set to 30 °. However, the angles of the reflecting plates 4 and 5 (reflecting surfaces 4a and 5a) with respect to the XY plane may be different from each other. That is, the angle of the reflecting surface 4a of the reflecting plate 4 with respect to the XY plane may be α, the angle of the reflecting surface 5a of the reflecting plate 5 with respect to the XY plane may be β, and α ≠ β (see FIG. 5). The angles α and β are each preferably 35 ° or less, and more preferably 10 ° or less. As an example, when the angle (α + β) between the reflecting plates 4 and 5 (reflecting surfaces 4a and 5a) is 30 °, α = 22.5 ° and β = 7.5 °. In this case, the angle α or the angle β may be set to approximately 0 ° (that is, the reflecting surface 4a or the reflecting surface 5a is substantially parallel to the XY plane) (see FIG. 6). In FIG. 6, α = 30 ° and β = 0 ° are set. When the inclination of the reflecting plate 4 (reflecting surface 4a) or the reflecting plate 5 (reflecting surface 5a) with respect to the XY plane is reduced (when the angle α or the angle β is reduced), the light guide plate 3 is guided when the light guide plate 3 is installed in the backlight. Since the distance between the back surface 3b of the optical plate 3 and the backlight frame is reduced, it is possible to suppress the deflection and misalignment of the light guide plate 3 during transportation and use, and facilitate assembly work. In this way, when the angle α and the angle β are different, the axis of the light source 2 (LED 2a) (the direction of the principal ray of the emitted light) is the direction of the incident surface 3a of the light guide plate 3 as shown in FIG. The inclination of the axis of the light source 2 (LED 2a) with respect to the incident surface 3a (YZ plane) of the light guide plate 3 may be changed according to the ratio of the angle α and the angle β. For example, in FIG. 7, when α = 30 ° and β = 0 °, the angle between the axis of the light source 2 (LED 2a) and the normal of the incident surface 3a is set as γ, and γ = 15 ° is set. Can do.

The reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 are regular reflecting surfaces (mirror surfaces) over the entire surface. The reflecting plates 4 and 5 can be manufactured, for example, by mirror-finishing one surface (surface to be the reflecting surfaces 4a and 5a) of a silver plate (silver sheet). The reflectance can be increased by reducing the surface roughness of the reflecting surface. The reflectivity of the reflecting surfaces 4a and 5a is preferably 96% or more. By using the entire reflecting surfaces 4a and 5a as regular reflecting surfaces, the light utilization efficiency can be improved as compared with the case where the entire reflecting surfaces are diffuse reflecting surfaces.

However, only the portions 4b and 5b on the light source 2 side of the reflection surfaces 4a and 5a can be diffuse reflection surfaces made of a material having a property of diffusing and reflecting light (Lambert scattering). An example of such a material that diffusely reflects light is barium sulfate. In this case, the part which should become a regular reflection surface of the reflectors 4 and 5 is mirror-finished, and the material which diffuses and reflects such light is coated on the remaining part ( parts 4b and 5b which should become a diffuse reflection surface). Can be manufactured.

Alternatively, only the portions 4b and 5b on the light source 2 side of the reflection surfaces 4a and 5a can be diffused reflection surfaces made of a concavo-convex structure that diffusely reflects light. In this case, the reflecting plates 4 and 5 are mirror-finished on the portions to be the regular reflection surfaces of the reflection surfaces 4a and 5a, and such light is applied to the remaining portions ( portions 4b and 5b to be the diffuse reflection surfaces). Can be produced by providing a concavo-convex structure that diffusely reflects the light.

An example of the concavo-convex structure is a row formed by arranging a plurality of strips having a triangular cross section. In this case, the strips constituting the strip are arranged on the plate surfaces of the reflection plates 4 and 5 such that the longitudinal direction thereof is substantially the Y direction. The cross-sectional shape of each strip is not limited to a triangular shape, and may be a polygonal shape, an arc shape, or other curved shape. Note that the diffuse reflection surface having such a concavo-convex structure may be formed by arranging a plurality of protrusions in an array or discretely instead of in a row. As the shape of the protrusion in this case, a spherical shape, a conical shape, a polygonal pyramid shape or the like can be adopted. The diffuse reflection surface having the concavo-convex structure may be an irregular rough surface (a surface on which minute undulations are randomly formed).

As a ratio of the regular reflection surface constituting a part of the reflection surfaces 4a and 5a on the light guide plate 3 side and the diffuse reflection surface constituting the other part ( parts 4b and 5b on the light source 2 side), the reflection surface Of all the regions 4a and 5a, 2/3 or more can be regular reflection surfaces, and the remaining 1/3 can be diffuse reflection surfaces. When the angle between the reflecting plates is 60 °, it can be within 1/3, and when it is 15 °, it can be within 1/12.

In this way, a part of the reflection surfaces 4a and 5a on the light guide plate 3 side is a regular reflection surface and the other portions ( parts 4b and 5b on the light source 2 side) are diffuse reflection surfaces. Most of the above-mentioned light distribution light is reflected into the light guide plate 3 from the incident surface 3a by being reflected by the reflecting surfaces 4a and 5a at an appropriate angle, for example, once or twice. A part (for example, light reflected about three times or more) returns to the light source 2 side and is considered to be a loss. Therefore, by making the reflection surfaces 4a, 5a part 4b, 5b on the light source 2 side as a diffuse reflection surface, the light returning to the light source 2 side is diffusely reflected, so that part of the return light is reflected. It becomes possible to return to the light guide plate 3 side, and the light utilization efficiency can be improved. Further, it is considered that the light incident efficiency is increased because part of the light is directed toward the incident surface 3a side by the diffuse reflection.

Next, a modified example of the configuration described above will be described with reference to FIG. In the configuration of FIG. 4, the reflecting member includes a reflecting plate (third reflecting member) 6 in addition to the reflecting plates 4 and 5 described above. The reflection plate 6 is provided between the reflection plate 4 and the reflection plate 5, and one of the reflection surfaces 6 a faces the reflection surface 4 a of the reflection plate 4 with a predetermined first angle, and the other reflection surface 6 b. Is arranged so as to be parallel to the XY plane in a state of facing the reflecting surface 5a of the reflecting plate 5 at a predetermined second angle. Here, the first angle and the second angle coincide with each other, and are set to half of the angle formed by the reflecting surface 4a and the reflecting surface 5a. However, the first angle and the second angle do not necessarily coincide with each other, and the reflecting plate 6 may be inclined with respect to the XY plane.

The reflection surfaces 6a and 6b of the reflection plate 6 are regular reflection surfaces, respectively, as in the case of the reflection surfaces 4a and 5a. The reflection plate 6 can be manufactured, for example, by mirror-finishing both surfaces of a silver plate (silver sheet). In the case where the diffuse reflection surfaces 4b and 5b are provided on a part of the reflection plates 4 and 5 on the light source 2 side, the corresponding portions of the reflection plate 6 can be formed as similar diffusion reflection surfaces. By adding such a reflector 6, it is possible to further improve the light utilization efficiency.

The light distribution in the Y direction and the light distribution in the Z direction of each LED 2a is as follows. The half value angle in the Y direction of the LED 2a is φ (see FIG. 3), and the half value angle in the Z direction of the LED 2a is θ (see FIG. 2).
φ / θ> 1
This relationship is preferably satisfied, more preferably φ / θ ≧ 2, and further preferably φ / θ ≧ 3. From the viewpoint of improving the light utilization efficiency, it is preferable to reduce the half-value angle θ in the Z direction of the LED 2a as described above. However, if the half-value angle φ in the Y direction is also reduced, the emission surface of the light guide plate 3 This is because in 3c, so-called eyeballs (locally bright portions) or the like may occur, resulting in uneven brightness. The upper limit of φ / θ is a range in which light distribution is not unnecessarily performed, but can be set to 100 or less, for example.

Further, as shown in FIG. 3, the light distribution in the Y direction of each LED 2 a is p, the arrangement pitch in the Y direction of the LEDs 2 a, the width (dimension in the Y direction) of the LEDs 2 a, and the LED 2 a and the light guide plate 3. Assuming that the distance from the incident surface 3a (space in the X direction) is d,
φ> tan ⁻¹ ((a + p) / 2d)
It is preferable to satisfy the relationship. This is because, by setting the relationship as described above, the light emitted from the adjacent LEDs 2a overlap each other in the Y direction, so that uneven brightness on the emission surface 3c of the light guide plate 3 can be suppressed. Note that the minimum value of the array pitch p is limited to a size that does not interfere with each other in relation to the width a of the LEDs 2a.

The surface light source device 1 configured as described above can constitute a surface light source device that illuminates the entire area of the liquid crystal panel as the object to be illuminated. In addition, the surface light source device 1 configured as described above is configured as a single unit, and a plurality of units are appropriately arranged to configure a surface light source device that illuminates the entire area of the liquid crystal panel as the object to be illuminated. You can also.

In the liquid crystal display device, the surface light source device 1 described above is provided on a back surface side of a liquid crystal panel in which an alignment film, a transparent electrode, a color filter, a glass plate, a polarizing plate, and the like are appropriately stacked with a liquid crystal layer interposed therebetween. Each is configured to be fixed to a housing or the like so as to be arranged in a positional relationship.

Next, examples of the present invention will be described. For the surface light source device 1 described above, an optical model is created using a software optical simulator, and light usage efficiency (%) or light is emitted from the light exit surface 3c of the light guide plate 3 while appropriately setting and changing specifications. The intensity distribution of the emitted light is calculated. As an optical simulator, lighting design analysis software LightTools (developer: ORA) was used.

The performance of the surface light source device 1 is evaluated based on the calculated light use efficiency. Further, based on the calculated light intensity distribution, luminance unevenness on the exit surface 3c is evaluated. The brightness unevenness is assumed to be a defective “x” when a so-called eyeball (locally bright part) is expected to occur when actually viewed from the calculated light intensity distribution, and no eyeball is expected to occur. The case is evaluated as good “◯”, and the case that is intermediate between these is evaluated as slightly good “Δ”.

Example 1-1
The configuration shown in FIG. 2 was used. The light distribution (half-value angle θ in the Z direction) of the LED 2a is 30 °, the LED height (dimension in the Z direction on the side where the LED 2a is disposed on the reflectors 4 and 5) b is 3 mm, and the separation distance (the LED 2a and the light guide plate 3 (Dimension in the X direction between the incident surface 3a) and d was 3 mm. The reflection surfaces (reflection surfaces 4a and 5a) were regular reflection surfaces over the entire surface, and the reflectance was 96%. As the light guide plate material (material of the light guide plate 3), norbornene resin (ZEONOR 1060R (trade name, manufactured by Nippon Zeon Co., Ltd.), refractive index 1.533) was used. The thickness of the light guide plate (dimension in the Z direction of the light guide plate 3) h was 0.2 mm. As a result of the simulation, the light utilization efficiency (%) was 75% as shown in Table 1.

Example 1-2
The configuration shown in FIG. 2 is the same as Example 1-1 except that a part (one third) of the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 on the light source 2 side is a diffuse reflecting surface. . The reflectance of the portions (regular reflection surfaces) other than the diffuse reflection surfaces of the reflection surfaces 4a and 5a was 96%. As a result of the simulation, the light utilization efficiency (%) was 77% as shown in Table 1.

(Example 1-3)
Using the configuration of three reflecting plates shown in FIG. 4 (a configuration in which an intermediate reflecting plate 6 is added), the reflecting surfaces 6a and 6b of the reflecting plate 6 are formed as regular reflecting surfaces (reflectance 96%) over the entire surface. Except for this, it was the same as Example 1-1. As a result of the simulation, the light utilization efficiency (%) was 79% as shown in Table 1.

(Conclusion 1)
As is clear from Example 1-1, the light utilization efficiency can be greatly improved by making the reflecting surfaces 4a and 5a regular reflection surfaces.

As is clear from the comparison between Example 1-1 and Example 1-2, only a part of the reflection surfaces 4a and 5a on the light source 2 side is used as a diffuse reflection surface, but the light utilization is slight. Efficiency can be further improved.

As is clear from the comparison between Example 1-1 and Example 1-3, the light utilization efficiency is further improved by adding the reflector 6 in the middle of the reflecting surfaces 4a and 5a. be able to.

Example 2-1
The configuration shown in FIG. 2 was used. The light distribution (half-value angle θ in the Z direction) of the LED 2a is 40 °, the LED height (dimension in the Z direction on the side where the LED 2a of the reflecting plates 4 and 5 is disposed) b is 4 mm, and the separation distance (the LED 2a and the light guide plate 3 (Dimension in the X direction between the incident surface 3a) and d was set to 9.3 mm. The reflection surfaces (reflection surfaces 4a and 5a) are regular reflection surfaces over the entire surface, and the reflectance is 98%. As the light guide plate material (material of the light guide plate 3), norbornene resin (ZEONOR 1060R (trade name, manufactured by Nippon Zeon Co., Ltd.), refractive index 1.533) was used. The thickness of the light guide plate (dimension in the Z direction of the light guide plate 3) h was 1 mm. As a result of the simulation, the light utilization efficiency (%) was 69% as shown in Table 1.

(Example 2-2)
The same as Example 2-1, except that the reflectivity of the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 was set to 97%. As a result of the simulation, the light utilization efficiency (%) was 60% as shown in Table 2.

(Example 2-3)
The same as Example 2-1, except that the reflectivity of the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 was set to 96%. As a result of the simulation, the light utilization efficiency (%) was 55% as shown in Table 2.

(Example 2-4)
The same as Example 2-1, except that the reflectivity of the reflection surfaces 4a and 5a of the reflection plates 4 and 5 was set to 95%. As a result of the simulation, the light utilization efficiency (%) was 50% as shown in Table 2.

(Example 2-5)
The same as Example 2-1, except that the reflectance of the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 was set to 94%. As a result of the simulation, the light utilization efficiency (%) was 49% as shown in Table 2.

(Example 2-6)
The same as Example 2-1, except that the reflectance of the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 was set to 93%. As a result of the simulation, the light utilization efficiency (%) was 47% as shown in Table 2.

(Conclusion 2)
FIG. 8 shows a graph of the results of Examples 2-1 to 2-6, in which the horizontal axis represents the reflectance (regular reflectance) (%) and the vertical axis represents the light utilization efficiency (%). From the figure, as the reflectivity increases from 93%, the light utilization efficiency increases with a relatively small slope, and as the inflection point is around 96%, with a relatively large slope as it increases from 96%. You can see that it is rising. Therefore, by setting the reflectance to a value of 96% or higher, high light utilization efficiency can be realized.

Example 3-1
The light guide plate was the same as Example 2-1, except that acrylic resin (PMMA: polymethyl methacrylate resin, refractive index 1.49) was used. As a result of the simulation, the light utilization efficiency (%) was 69% as shown in Table 3.

(Example 3-2)
The same as Example 2-2, except that acrylic resin (PMMA: polymethyl methacrylate resin, refractive index 1.49) was used as the light guide plate material. As a result of the simulation, the light utilization efficiency (%) was 60% as shown in Table 3.

Example 3-3
Example 3 was the same as Example 2-3 except that acrylic resin (PMMA: polymethyl methacrylate resin, refractive index 1.49) was used as the light guide plate material. As a result of the simulation, the light utilization efficiency (%) was 55% as shown in Table 3.

(Example 3-4)
Example 2-4 was the same as Example 2-4 except that acrylic resin (PMMA: polymethyl methacrylate resin, refractive index 1.49) was used as the light guide plate material. As a result of the simulation, the light utilization efficiency (%) was 50% as shown in Table 3.

(Example 3-5)
The same as Example 2-5, except that acrylic resin (PMMA: polymethyl methacrylate resin, refractive index 1.49) was used as the light guide plate material. As a result of the simulation, the light utilization efficiency (%) was 49% as shown in Table 3.

(Conclusion 3)
From the results of Example 3-1 to Example 3-5, the same conclusion as the above conclusion 2 was obtained.

Example 4-1
The configuration shown in FIG. 2 was used. The light distribution (half-value angle θ in the Z direction) of the LED 2a is 30 °, the LED height (dimension in the Z direction on the side where the LED 2a is disposed on the reflectors 4 and 5) b is 3 mm, and the separation distance (the LED 2a and the light guide plate 3 (Dimension in the X direction between the incident surface 3a) and d was 14 mm. The reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 15 ° (the angle of the reflection surface 4a with respect to the XY plane is α, the angle of the reflection surface 5a with respect to the XY plane is β, α = β = 7.5 °). The reflection surfaces (reflection surfaces 4a and 5a) were regular reflection surfaces over the entire surface, and the reflectance was 96%. As the light guide plate material (material of the light guide plate 3), norbornene resin (ZEONOR 1060R (trade name, manufactured by Nippon Zeon Co., Ltd.), refractive index 1.533) was used. The thickness of the light guide plate (dimension in the Z direction of the light guide plate 3) h was 1 mm. As a result of the simulation, the light utilization efficiency (%) was 56% as shown in Table 4.

(Example 4-2)
The separation distance (dimension in the X direction between the LED 2a and the incident surface 3a of the light guide plate 3) d is 9 mm, and the reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 25 ° (X− of the reflection surface 4a). Except for α = β = 12.5 °, where α is the angle with respect to the Y plane and β is the angle of the reflecting surface 5a with respect to the XY plane, the same as Example 4-1. As a result of the simulation, the light utilization efficiency (%) was 61% as shown in Table 4.

(Example 4-3)
The separation distance (dimension in the X direction between the LED 2a and the incident surface 3a of the light guide plate 3) d is 7.4 mm, and the reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 30 ° (of the reflection surface 4a). Except for α = β = 15 °, where α is the angle with respect to the XY plane, and β is the angle of the reflecting surface 5a with respect to the XY plane, the same as Example 4-1. As a result of the simulation, the light utilization efficiency (%) was 68% as shown in Table 4.

(Example 4-4)
The reflection surface angle (angle formed between the reflection surfaces 4a and 5a) is 35 ° (the angle of the reflection surface 4a with respect to the XY plane is α, the angle of the reflection surface 5a with respect to the XY plane is β, α = β = 17.5 °), except that it was the same as Example 4-3. As a result of the simulation, the light utilization efficiency (%) was 61% as shown in Table 4.

(Example 4-5)
The reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 40 ° (the angle of the reflection surface 4a with respect to the XY plane is α, the angle of the reflection surface 5a with respect to the XY plane is β, α = β = 20 °) except that the angle was 20 °. As a result of the simulation, the light utilization efficiency (%) was 59% as shown in Table 4.

(Example 4-6)
The reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 60 ° (the angle of the reflection surface 4a with respect to the XY plane is α, the angle of the reflection surface 5a with respect to the XY plane is β, α = β = 30 °), but the same as Example 4-3. As a result of the simulation, the light utilization efficiency (%) was 58% as shown in Table 4.

(Comparative Example 4-1)
The reflection surface angle (angle formed by the reflection surfaces 4a and 5a) is 90 ° (the angle of the reflection surface 4a with respect to the XY plane is α, the angle of the reflection surface 5a with respect to the XY plane is β, α = β = 45 °), but the same as Example 4-3. As a result of the simulation, the light utilization efficiency (%) was 45% as shown in Table 4.

(Conclusion 4)
From the results of Example 4-1 to Example 4-3, the light utilization efficiency is improved as the separation dimension d between the LED 2a and the incident surface 3a of the light guide plate 3 is reduced in the range of 14 mm to 7.4 mm. I understand that

Further, from the results of Examples 4-1 to 4-6, the angle between the reflecting surfaces 4a and 5a is preferably in the range of 15 to 60 °, more preferably in the range of 25 to 35 °, and 30 It can be seen that the degree of ° is most preferable.

Example 5-1
5 except that the angle of the reflecting surface 4a with respect to the XY plane is α = 22.5 ° and the angle of the reflecting surface 5a with respect to the XY plane is β = 7.5 °. Same as Example 4-3. Note that the angle (γ) between the axis of the light source 2 (LED 2a) (the direction of the principal ray of the emitted light) and the normal direction of the incident surface 3a of the light guide plate 3 is 0 as in Example 4-3. ° (ie, parallel). The separation distance d (see FIG. 5) was 7.4 mm. As a result of the simulation, the light utilization efficiency (%) was 66% as shown in Table 5.

(Example 5-2)
Example 4-3, except that the configuration shown in FIG. 6 was used and the angle of the reflecting surface 4a with respect to the XY plane was α = 30 ° and the angle of the reflecting surface 5a with respect to the XY plane was β = 0 °. And the same. Note that the angle (γ) between the axis of the light source 2 (LED 2a) (the direction of the principal ray of the emitted light) and the normal direction of the incident surface 3a of the light guide plate 3 is 0 as in Example 4-3. ° (ie, parallel). The separation distance d (see FIG. 6) was 7.4 mm. As a result of the simulation, the light utilization efficiency (%) was 63% as shown in Table 5.

(Example 5-3)
Using the configuration shown in FIG. 7, the angle between the axis of the light source 2 (LED 2a) (the direction of the principal ray of the emitted light) and the normal direction of the incident surface 3a of the light guide plate 3 is γ = 15 °. Except for this, it was the same as Example 5-2. The separation distance d (see FIG. 7) was 7.4 mm. As a result of the simulation, the light utilization efficiency (%) was 65% as shown in Table 5.

(Conclusion 5)
From the results of Example 4-3, Example 5-1, and Example 5-2, the light equivalent to the case where the inclination angle is large by reducing the inclination angle (β) of the reflecting plate 5a with respect to the XY plane is small. It can be seen that the light guide plate 3 can be bent and misaligned while maintaining the utilization efficiency, and can be easily assembled. Further, from the results of Example 5-2 and Example 5-3, the axis of the light source 2 (LED 2a) is aligned with the direction of the incident surface 3a of the light guide plate 3 according to the angle of the reflecting surfaces 4a and 5a with respect to the XY plane. It can be seen that the light utilization efficiency is increased by changing the inclination with respect to the incident surface 3a (YZ plane) so as to be directed toward.

Example 6-1
The configurations shown in FIGS. 1 to 3 were used, and the light distribution (half-value angle θ in the Z direction and half-value angle φ in the Y direction) of the LED 2a was 0 ° (ie, parallel light). As the reflection member, the reflection surfaces 4a and 5a of the reflection plates 4 and 5 were used as regular reflection surfaces (reflectance 96%) over the entire surface. The LED height (dimension in the Z direction of the LED 2a) b was 3 mm, the height of the substrate 2b was 5.0 mm, and the thickness of the light guide plate (dimension in the Z direction of the light guide plate 3) h was 1 mm. The distance d (space in the X direction) d between the LED 2a and the incident surface 3a of the light guide plate 3 was 7.4 mm. The pitch in the arrangement direction of the LEDs 2a was 7.5 mm. The angle formed by the reflecting surface 4a of the reflecting plate 4 and the reflecting surface 5a of the reflecting plate 5 is 30 ° (the angles of the reflecting surfaces 4a and 5a with respect to the XY plane are 15 °, respectively). Norbornene resin (ZEONOR 1060R (trade name, manufactured by Nippon Zeon Co., Ltd.)), refractive index 1.533, critical angle 40.7 degrees) was used. As a result of the simulation, the light utilization efficiency (%) was 97% as shown in Table 6.

(Example 6-2)
Example 2 was the same as Example 6-1 except that the light distribution (half-value angle θ in the Z direction and half-value angle φ in the Y direction) of the LED 2a was 15 °. As a result of the simulation, the light utilization efficiency (%) was 77% as shown in Table 6.

(Example 6-3)
The light distribution of the LED 2a (half-value angle θ in the Z direction and half-value angle φ in the Y direction) was set to 30 °, respectively, and was the same as Example 6-1. As a result of the simulation, the light utilization efficiency (%) was 68% as shown in Table 6.

(Example 6-4)
The light distribution of LED 2a (half-value angle θ in the Z direction and half-value angle φ in the Y direction) was set to 15 °. As the reflecting member, the reflecting surfaces 4a and 5a of the reflecting plates 4 and 5 were used as regular reflecting surfaces (reflectance 96%) over the entire surface. The LED height (dimension in the Z direction of the LED 2a) b was 1 mm, the height of the substrate 2b was 1.7 mm, and the thickness of the light guide plate (dimension in the Z direction of the light guide plate 3) h was 0.2 mm. The distance d (space in the X direction) d between the LED 2a and the incident surface 3a of the light guide plate 3 was 7.4 mm. The pitch in the arrangement direction of the LEDs 2a was 7.5 mm. The angle formed by the reflecting surface 4a of the reflecting plate 4 and the reflecting surface 5a of the reflecting plate 5 is 30 ° (the angles of the reflecting surfaces 4a and 5a with respect to the XY plane are 15 °, respectively). , Norbornene resin (ZEONOR 1060R (trade name, manufactured by Nippon Zeon Co., Ltd.), refractive index 1.533, critical angle 40.7 degrees) was used. As a result of the simulation, the light utilization efficiency (%) was 61% as shown in Table 6.

(Comparative Example 6-1)
The light distribution (the half-value angle θ in the Z direction and the half-value angle φ in the Y direction) of the LED 2a was set to 45 °, respectively, and was the same as Example 6-1. As a result of the simulation, the light utilization efficiency (%) was 59% as shown in Table 6.

(Comparative Example 6-2)
The light distribution (the half-value angle θ in the Z direction and the half-value angle φ in the Y direction) of the LED 2a was the same as that in Example 6-1 except that each was set to 60 °. As a result of the simulation, the light utilization efficiency (%) was 58% as shown in Table 6.

(Comparative Example 6-3)
The same as Example 6-1 except that the light distribution (half-value angle θ in the Z direction and half-value angle φ in the Y direction) of the LED 2a was 90 °. As a result of the simulation, the light utilization efficiency (%) was 55% as shown in Table 6.

(Comparative Example 6-4)
The same as Example 6-1 except that the light distribution (half-value angle θ in the Z direction and half-value angle φ in the Y direction) of the LED 2a was 120 ° (Lambertian). As a result of the simulation, the light utilization efficiency (%) was 53% as shown in Table 6.

(Conclusion 6)
Regarding the results of Examples 6-1 to 6-3 and Comparative Examples 6-1 to 6-4, the horizontal axis represents the full width at half maximum (°), and the vertical axis represents the light use efficiency (%). A graph is shown in FIG. From the figure, as the half-value angle decreases from 120 °, the light utilization efficiency increases with a relatively small slope, and around 35 ° as an inflection point, with a relatively large slope as it further decreases from 35 °. You can see that it is rising. Accordingly, high light utilization efficiency can be realized by setting the half-value angle to a value of 35 ° or less.

Example 7-1
The reflective member was the same as Example 6-1 except that the reflective surfaces 4a and 5a of the reflective plates 4 and 5 were diffused reflective surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 72% as shown in Table 7.

(Example 7-2)
The reflective member was the same as Example 6-2 except that the reflective surfaces 4a and 5a of the reflective plates 4 and 5 were diffused reflective surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 63% as shown in Table 7.

(Example 7-3)
The reflective member was the same as Example 6-3 except that the reflective surfaces 4a and 5a of the reflective plates 4 and 5 were diffused reflective surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 57% as shown in Table 7.

(Comparative Example 7-1)
The reflection member was the same as Comparative Example 6-1, except that the reflection surfaces 4a and 5a of the reflection plates 4 and 5 were diffuse reflection surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 53% as shown in Table 7.

(Comparative Example 7-2)
The reflection member was the same as Comparative Example 6-2 except that the reflection surfaces 4a and 5a of the reflection plates 4 and 5 were diffuse reflection surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 52% as shown in Table 7.

(Comparative Example 7-3)
The reflection member was the same as Comparative Example 6-3 except that the reflection surfaces 4a and 5a of the reflection plates 4 and 5 were diffuse reflection surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 51% as shown in Table 7.

(Comparative Example 7-4)
The reflection member was the same as Comparative Example 6-4 except that the reflection surfaces 4a and 5a of the reflection plates 4 and 5 were diffuse reflection surfaces over the entire surface. As a result of the simulation, the light utilization efficiency (%) was 50% as shown in Table 7.

(Conclusion 7)
Regarding the results of Examples 7-1 to 7-3 and Comparative Examples 7-1 to 7-4, the horizontal axis represents the full width at half maximum (°), and the vertical axis represents the light use efficiency (%). A graph is shown in FIG. From the figure, as the half-value angle decreases from 120 °, the light utilization efficiency increases with a relatively small slope, and around 35 ° as an inflection point, with a relatively large slope as it further decreases from 35 °. You can see that it is rising. Accordingly, high light utilization efficiency can be realized by setting the half-value angle to a value of 35 ° or less.

9 and 10 that the reflection surfaces 4a and 5a of the reflection member have higher light utilization efficiency than the diffuse reflection surface. Therefore, it is preferable to use regular reflection surfaces as the reflection surfaces 4a and 5a.

Example 8-1
The light distribution of the LED 2a was the same as Example 6-1 except that the half-value angle θ in the Z direction was 15 ° and the half-value angle φ in the Y direction was 45 ° (ie, φ / θ = 3). The width (dimension in the Y direction) a of the LED 2a was set to 3.0 mm, and the arrangement pitch p was set to 7.5 mm. As a result of the simulation, as shown in Table 8, the luminance unevenness was good “◯”.

(Example 8-2)
The light distribution of the LED 2a was the same as Example 6-1 except that the half-value angle θ in the Z direction was 15 ° and the half-value angle φ in the Y direction was 30 ° (ie, φ / θ = 2). As a result of the simulation, as shown in Table 8, the luminance unevenness was slightly good “Δ”.

(Comparative Example 8-1)
The light distribution of the LED 2a was the same as that in Example 6-1 except that the half-value angle θ in the Z direction was 15 ° and the half-value angle φ in the Y direction was 15 ° (ie, φ / θ = 1). As a result of the simulation, as shown in Table 8, the luminance unevenness was defective “x”.

(Conclusion 8)
From the results of Example 8-1 to Example 8-2 and Comparative Example 8-1, the ratio (φ / θ) between the half-value angle θ in the Z direction and the half-value angle φ in the Y direction of the LED 2a is greater than 1. In addition, it is further preferable that the luminance unevenness is determined to be good and (φ / θ) is 3 or more, and it can be seen that more uniform light can be emitted.

The embodiment described above is described for easy understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the embodiment described above is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Claims (12)

1. A surface light source device comprising: a light guide plate having a part of the side end surface as an incident surface on which light is incident; and a light source that is provided along the incident surface and emits light toward the incident surface.
   In order to limit the divergence of the light emitted from the light source in the thickness direction of the light guide plate, a reflective member having a reflective surface for guiding the light to the incident surface is provided.
   The reflective surface includes a first reflective member having a first reflective surface and a second reflective member having a second reflective surface, which are disposed apart from each other in the thickness direction of the light guide plate.
   The surface light source device, wherein the first reflection surface and the second reflection surface are arranged so as to form an angle of 5 ° to 70 ° with each other and have a regular reflection surface.
2. 2. The surface light source device according to claim 1, wherein the reflectance of the regular reflection surface is set to be 96% or more.
3. 3. The surface light source device according to claim 1, wherein a separation distance between the light source and the incident surface is set within a range of 0 to 20 mm.
4. The reflective member has a third reflective member disposed between the first reflective member and the second reflective member,
   The third reflecting member according to any one of claims 1 to 3, wherein the third reflecting member has a third reflecting surface facing the first reflecting surface and a fourth reflecting surface facing the second reflecting surface as the reflecting surface. The surface light source device described.
5. The light source is configured by arranging a plurality of point light sources along the incident surface,
   The light distribution characteristic of each point light source is set to θ as the half-value angle in the thickness direction of the light guide plate.
   5. The surface light source device according to claim 1, wherein θ ≦ 120 ° is set.
6. The surface light source device according to any one of claims 1 to 5, wherein a part of the reflection surface on the light source side is a diffuse reflection surface made of a material having a property of diffusing and reflecting light.
7. The surface light source device according to any one of claims 1 to 5, wherein a part of the reflection surface on the light source side is a diffuse reflection surface having a concavo-convex structure that diffuses and reflects light.
8. A surface provided with a light guide plate in which a part of the side end surface is an incident surface on which light is incident, and a light source having a plurality of point light sources arranged along the incident surface and emitting light toward the incident surface A light source device,
   In order to limit the divergence of the light emitted from the light source in the thickness direction of the light guide plate, a reflective member having a reflective surface for guiding the light to the incident surface is provided.
   The half-value angle of the light distribution characteristic in the thickness direction of the light guide plate of each point light source constituting the light source is θ,
   A surface light source device set to θ ≦ 35 °.
9. The half-value angle of the light distribution characteristic in the arrangement direction of each point light source constituting the light source is φ,
   The surface light source device according to claim 8, wherein φ / θ> 1 is set.
10. The half-value angle in the arrangement direction of each point light source constituting the light source is φ, the arrangement pitch of the point light sources is p, the width of the point light source is a, and the distance between the point light source and the incident surface is d,
    The surface light source device according to claim 8, satisfying a relationship of φ> tan ⁻¹ ((a + p) / 2d).
11. 11. The surface light source device according to claim 8, wherein a thickness of the incident surface of the light guide plate is smaller than a height of each point light source constituting the light source.
12. A liquid crystal display device comprising a liquid crystal panel and the surface light source device according to any one of claims 1 to 11.

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