Patent Application
20140146562
The present invention relates to an illumination device and a display device; in particular, the present invention relates to an illumination device loaded with a light guide member for guiding light, and a display device provided with the illumination device.
Liquid crystal display devices (display devices) loaded with a non-luminous liquid crystal display panel (display panel) normally include a backlight unit (illumination device). The backlight unit supplies light to the liquid crystal display panel.
The backlight unit may in some instances include a light guide plate (light guide member). For example, edge-lit (side-lit) backlight units include a light guide plate. In an edge-lit backlight unit, typically a light source such as a light-emitting diode (LED) is arranged at a side surface of the light guide plate. Light that is emitted from the light source is incident on the light guide plate from the side surface of the light guide plate, and the incident light is guided in the interior of the light guide plate and released to the liquid crystal display panel side.
The backlight unit 520 includes a light guide plate 521 for guiding light, an LED serving as a light source (not shown), an optical sheet group 522 made of a plurality of optical sheets, and a reflective sheet 523. The backlight unit 520 also includes a frame-shaped resin mold frame (accommodation member) 525 for accommodating the light guide plate 521 and the like. The reflective sheet 523 is affixed to the rear surface of the resin mold frame 525 with a double-sided tape 530. The light guide plate 521, the optical sheet group 522, and the liquid crystal display panel 510 are arranged inside the resin mold frame 525.
The resin mold frame 525 has a first stepped part 525a and a second stepped part 525b. The first stepped part 525a supports the optical sheet group 522, and the second stepped part supports the liquid crystal display panel 510. The optical sheet group 522 and the liquid crystal display panel 510 are fixed to the resin mold frame 525 by the double-sided tape 531.
As is illustrated in
Here, a region S101 of the resin mold frame 525 contributes to light blocking and fixation of the light guide plate 521, a region S102 contributes to light blocking and fixation of the optical sheet group 522, and a region S103 contributes to light blocking and fixation of the liquid crystal display panel 510.
With such a liquid crystal display device, the stepped resin mold frame 525 is used in order to prevent the leakage of light (see the arrows in
Moreover, in the conventional backlight unit 520, a plurality of optical sheets are used, resulting in a greater thickness of the backlight unit 520. It is therefore difficult to achieve reduced thickness. The steps of assembly are also more complicated because there are many optical sheets.
In order to solve the aforementioned problems, a first objective of the present invention is to provide an illumination device and display device making it possible to achieve a narrower frame width. Another objective of the present invention is to provide an illumination device and display device making it possible to achieve a reduced size and reduced thickness. Yet another objective of the present invention is to provide an illumination device and display device making it possible to facilitate the steps of assembly.
In order to achieve the objectives described above, an illumination device of the present invention comprises a light source, a light guide member for guiding light coming from the light source, and an accommodation member for accommodating the light source and the light guide member. The light guide member comprises a light guide onto which the light coming from the light source is incident, and a low-refractive-index layer provided on a rear surface of the light guide. The refractive index of the low-refractive-index layer is lower than the refractive index of the light guide. A plurality of first reflective parts for gradually reducing the angle of incidence of the light coming from the light source with respect to the rear surface of the light guide are provided to a front surface of the light guide or the rear surface thereof. A plurality of second reflective parts for reflecting forward the light coming from the light source are provided to the rear surface of the light guide member. The accommodation member comprises walls surrounding the light source and the light guide member. The width of an upper side of the walls and the width of a lower side thereof are equal (substantially equal).
In the illumination device, the light coming from the light source is guided while being repeatedly reflected between a portion on the front surface side of the light guide and the rear surface, and the angle of incidence of the light with respect to the rear surface of the light guide is gradually reduced. The light coming from the light source is incident on the low-refractive-index layer in a case where the angle of incidence of the light with respect to the rear surface of the light guide is less than a critical angle between the light guide and the low-refractive-index layer. For this reason, the light that is incident on the low-refractive-index layer has a smaller angle of spreading of light, and also the angle of spreading of light that is reflected at the interface between the rear surface of the light guide member and an air layer is smaller. This makes it possible to reduce the angle of spreading of the light emitted from the light guide member, and therefore makes it possible to improve the light-condensing properties. In addition, the brightness can also be improved.
It is further possible to improve the light-condensing properties and brightness without providing a plurality of optical sheets, such as condensing lenses, on the light guide member. There is accordingly no need to provide optical sheets. For this reason, it is possible to reduce the thickness and lower the costs of production of the illumination device. Also, there is no loss of light on passing through the optical sheets (for example, there is no light loss caused by multiple reflections between sheets), and thus it is possible to improve the efficiency of utilization of light.
The light coming from the light source is guided while being repeatedly reflected between the portion on the front surface side of the light guide and the rear surface, and as the distance from the light source increases, the angle of incidence of the light with respect to the rear surface of the light guide decreases. For this reason, as the distance from the light source increases, the light coming from the light source is more readily incident on the low-refractive-index layer. For this reason, it is possible to have a uniform amount of light incident on the low-refractive-index layer at a portion close to the light source, where there is a large amount of light (light flux), and a portion far away from the light source, where there is less light (light flux). As a result, the light can be uniformly emitted from the light guide member. In addition, uniform brightness can also be obtained.
The second reflective parts also make it possible to uniformly reflect the light. This makes it possible to suppress the occurrence of dot unevenness, and also makes it possible to obtain more uniform brightness. Here, it is preferable for the second reflective parts to be provided to substantially the entire rear surface of the light guide member (to a portion corresponding to at least the entire light emission region). The light can be more uniformly emitted from the entire (substantially the entire) light emission region of the light guide member.
The plurality of second reflective parts have the function of reflecting the light coming from the light source. The light that is incident on the low-refractive-index layer from the light guide is emitted from the rear surface of the light guide member, and the occurrence of loss of light can be suppressed. Because the second reflective parts reflect the light, absorption of the light at the second reflective parts is suppressed. This makes it possible to further improve the efficiency of utilization of light.
Thus, the illumination quality can be improved without providing optical sheets (an optical sheet group). For this reason, there is no need to provide to the accommodation member a stepped part for supporting and fixing the optical sheets (optical sheet group). The width of the walls of the accommodation member can be reduced by a commensurate amount. With this configuration, it is also possible to suppress the leakage of light in the lateral direction. Accordingly, there is no need to provide a region for light-blocking to the walls of the accommodation member. It is possible to eliminate the region for supporting the optical sheets and the region for light-blocking in the accommodation member. This makes it possible to cause the width of the walls of the accommodation member to be equal (substantially equal) at the lower side and upper side. As a result, the width of the walls of the accommodation member can be reduced and the frame width can be narrowed. In a case where, for example, a display device comprises the illumination device, it is possible to reduce the scale of the equipment while also increasing the display region. In addition, the design performance and freedom of design can be improved. Furthermore, because there is no need to provide the optical sheets (optical sheet group), the steps for assembling (assembly) can be simplified.
Preferably, the accommodation member is formed in a frame shape. In such a case, more preferably, the cross-section of the walls of the accommodation member is a quadrangular (substantially quadrangular) shape. This makes it possible to readily obtain a smaller, thinner illumination device of a successfully narrowed frame width.
Preferably, the height of the walls of the accommodation member is equal (substantially equal) to the thickness of the light guide member. This makes it possible to effectively reduce the thickness of the illumination device.
Preferably, the accommodation member is constituted of a light-blocking resin material. This makes it possible to effectively suppress the leakage of light in the lateral direction, and also makes it easy to narrow the frame width. The accommodation member may be constituted of a material other than a light-blocking resin material, however.
The illumination device may be further provided with a diffusion sheet that is overlapped by the light guide member. The light that is emitted from the light guide member is scattered on passing through the diffusion sheet. Accordingly, it is possible to obscure any unevenness in brightness. With the diffusion sheet, warping or displacement of the sheet or the like causes less of an impact on the properties than would another optical sheet such as a prism sheet. For this reason, it is still possible to facilitate the steps of assembling (assembly) with a configuration provided with a diffusion sheet.
In such a case, preferably, the diffusion sheet has protrusions that protrude outward as seen in plan view, and the walls of the accommodation member have notches into which the protrusions of the diffusion sheet are fitted. It is possible to support the diffusion sheet without increasing the width of the walls of the accommodation member. Accordingly, it is still easy to narrow the frame width with a configuration provided with a diffusion sheet.
Preferably, the diffusion sheet is of the size equal (substantially equal) to that of the light guide member.
In a case where the accommodation member is formed in a frame shape, the illumination device may be further provided with a reflective sheet that is disposed on the rear surface side of the light guide member. Preferably, the frame-shaped accommodation member has an opening in the middle, and the reflective sheet is arranged so as to cover the opening of the accommodation member.
A display device of the present invention is provided with the above-described illumination device, and a display panel for receiving the light coming from the illumination device. Accordingly, it is easy to obtain a smaller, thinner display device that has excellent display quality and a successfully narrowed frame width.
As described above, according to the present invention, it is easy to obtain an illumination device and display device making it possible to achieve a narrower frame width. It is also easy to obtain an illumination device and display device making it possible to reduce the size and reduce the thickness. It is moreover easy to obtain an illumination device and display device making it possible to facilitate the steps of assembly.
Embodiments embodying the present invention shall be described below on the basis of the accompanying drawings. The embodiments describe examples in which the present invention has been applied to a liquid crystal display device being used as a display unit of a portable machine such as a portable terminal.
A backlight unit of a first embodiment of the present invention and a liquid crystal display device provided with the backlight unit shall be described on the basis of
A liquid crystal display device 1 of the first embodiment, as illustrated in
The liquid crystal display panel 10 comprises an active matrix substrate 11, and an opposing substrate 12 that opposes the active matrix substrate 11. The active matrix substrate 11 comprises switching elements such as, for example, thin film transistors (TFTs). The active matrix substrate 11 and the opposing substrate 12 are pasted together with a sealant (not shown). A liquid crystal (not shown) is injected into a gap between the active matrix substrate 11 and the opposing substrate 12. Polarizing films 13 are attached onto a light-receiving surface side of the active matrix substrate 11 and an emission surface side of the opposing substrate 12.
The liquid crystal display panel 10 uses changes in transmittance caused by the inclination of the liquid crystal molecules to display an image.
The backlight unit 20 of the first embodiment is an edge-lit backlight unit. As illustrated in
In the backlight unit 20, as illustrated in
The light guide plate 22 is composed of one planar member. As illustrated in
The refractive index n1 of the light guide 23 is preferably 1.42 or higher, more preferably 1.59 to 1.65. On the other hand, the refractive index n2 of the low-refractive-index layer 24 is preferably less than 1.42, more preferably 1.10 to 1.35. The relationship between the refractive index n1 of the light guide 23 and the refractive index n2 of the low-refractive-index layer 24 is n2<n1. The relationship between the refractive index n1 of the light guide 23 and the refractive index n2 of the low-refractive-index layer 24 is preferably n1/n2>1.18.
The light guide 23 is constituted of, for example, a transparent resin material such as an acrylic or polycarbonate. When the light guide 23 is constituted of an acrylic or the like, the refractive index of the light guide 23 can be set to about 1.49. When the light guide 23 is constituted of a polycarbonate or the like, the refractive index of the light guide 23 can be set to about 1.59. In a case where the light guide 23 is constituted of an acrylic, the translucency can be better than when the light guide 23 is constituted of a polycarbonate.
The light guide 23 is formed so as to be a rectangular parallelepiped (substantially rectangular parallelepiped). That is to say, a light emission surface 23b (an upper surface) and a rear surface 23c (a lower surface) are parallel (substantially parallel). The light incidence surface 23a of the light guide 23 is arranged so as to be parallel (substantially parallel) with the light emission surface of the LEDs 21. The light incidence surface 23a is a side surface of the light guide 23.
The X direction is the width direction of the light guide plate 22, i.e., the lateral direction of the light guide 23. A Y direction is the length direction of the light guide plate 22, i.e., the longitudinal direction of the light guide 23. The Y direction is orthogonal to the X direction. A Z direction is the thickness direction of the light guide 23 (light guide plate 22). The Z direction is orthogonal to the X direction and to the Y direction.
The low-refractive-index layer 24, as illustrated in
As examples, a fluorine-based acrylate, a resin containing nanosized hollow particles such as an inorganic filler, or the like is used for the low-refractive-index layer 24. When the low-refractive-index layer 24 is constituted of a fluorine-based acrylate or the like, the refractive index of the low-refractive-index layer 24 can be set to about 1.35. When the low-refractive-index layer 24 is constituted of a resin containing nanosized hollow particles such as an inorganic filler or the like, the refractive index of the low-refractive-index layer 24 can be set to 1.30 or lower.
The prism layer 25 is formed on the lower surface (rear surface) of the low-refractive-index layer 24 without an air layer or the like interposed therebetween. That is to say, the light guide 23 and the prism layer 25 sandwich the low-refractive-index layer 24. The relationship between the refractive index n3 of the prism layer 25 and the refractive index n2 of the low-refractive-index layer 24 is n3≧n2.
In the first embodiment, a plurality of prisms 23e are formed on the light emission surface 23b of the light guide 23. The prisms 23e gradually reduces the angle of incidence of the light coming from the LEDs 21 with respect to the rear surface 23c of the light guide 23.
More specifically, as illustrated in
The flat parts 23d are formed so as to be in the same plane as the light emission surface 23b, and are formed so as to be parallel (substantially parallel) to the rear surface 23c. As illustrated in
The convex prisms 23e are formed of inclined surfaces 23f and perpendicular surfaces 23g. The inclined surfaces 23f are inclined with respect to the flat parts 23d (the light emission surface 23b), and the perpendicular surfaces 23g are perpendicular (substantially perpendicular) to the flat parts 23d (the light emission surface 23b). The inclined surfaces 23f are formed so that the inclined surfaces 23f that are increasingly far away from the LEDs 21 are increasingly close to the rear surface 23c, as illustrated in
As will be described below, the light that is emitted from the LEDs 21 is repeatedly reflected between the inclined surfaces 23f (the prisms 23e) and the rear surface 23c of the light guide 23. As a result, the angle of incidence with respect to the rear surface 23c of the light guide 23 gradually decreases. An angle of incline α1 of the inclined surfaces 23f with respect to the flat parts 23d (see
The inclined surfaces 23f (prisms 23e) have a predetermined width W12 in the Y direction. The width W12 is preferably 0.25 mm or less, more preferably 0.01 to 0.10 mm. The inclined surfaces 23f (prisms 23e) are arranged at a predetermined pitch P1 (=W11±W12) in the Y direction.
The width W11, the angle of incline α1, the width W12, and the pitch P1 may be constant irrespective of the distance from the LEDs 21.
As illustrated in
The flat parts 23h are formed so as to be in the same plane as the light emission surface 23b. The flat parts 23h have a predetermined width W13 in the X direction. The width W13 is preferably 200 μm or less.
The concave prisms 23i are formed of pairs of inclined surfaces 23j that are inclined with respect to the flat parts 23h (the light emission surface 23b). That is to say, the concave prisms 23i are formed so that the cross-section thereof has a triangular shape. An angle of incline α2 of the pairs of inclined surfaces 23j (angle of incline with respect to the flat parts 23h) is preferably about 30° to 89°.
The pairs of inclined surfaces 23j (prisms 23i) have a predetermined width W14 in the X direction. The width W14 is preferably about 0.1 mm or less, more preferably about 0.010 mm (10 μm) to about 0.020 mm (20 μm).
The prisms 23i are arranged at a predetermined pitch P2 (=W13+W14) in the X direction. Preferably, the following relationship holds: P2<W14×2(W13/W14<1). That is to say, the width W13 is preferably less than the width W14.
Preferably, the prisms 23i are formed at the same shape, the same size, and the same pitch irrespective of the positions of formation in the plane of the light guide 23. That is to say, preferably, the width W13, the angle of incline α2, the width W14, and the pitch P2 are each formed so as to be constant.
Thus, in the first embodiment, the prisms 23i are formed on the same plane as the prisms 23e so as to overlap with the prisms 23e (the prisms 23e and the prisms 23i are formed on the light emission surface 23b of the light guide 23). The prisms 23i have the function of diffusing the light in the lateral direction (the direction intersecting the direction of incidence of light, i.e., the X direction). Preferably, the ratio of surface area occupied by the prisms 23i with respect to the prisms 23e is 50% or greater.
As illustrated in
The concave prisms 25b, as illustrated in
In the first embodiment, the inclined surfaces 25c are formed so as to be flat, not curved. The inclined surfaces 25c are formed so that the inclined surfaces 25c that are increasingly far away from the LEDs 21 (see
The inclined surfaces 25c (prisms 25b) have a predetermined width W15 in the Y direction. The width W15 is about 0.1 mm or less, preferably about 0.010 mm to about 0.025 mm.
The inclined surfaces 25c (prisms 25b) are arranged at a pitch P3, the same as the width W15, in the Y direction. That is to say, the plurality of prisms 25b are formed continuously without a gap in the Y direction, and no flat parts are provided between each of the prisms 25b.
The prisms 25b may be formed at the same shape, the same size, and the same pitch on substantially the entire rear surface 25a of the prism layer 25 (at least a portion corresponding to the entire light emission region 22a) irrespective of the positions of formation in the plane of the prism layer 25. It is possible to suppress any difference in the properties of condensing of light in the plane of the prism layer 25. This makes it possible to obtain uniform brightness of the liquid crystal display panel 10 (see
As described below, the prisms 25b have the function of totally reflecting forward (to the upper surface) the light coming from the LEDs 21 at the interface between the light guide plate 22 and an air layer.
The frame 30 is a resin molded frame and is constituted of, for example, a PET resin. The frame 30 is formed so as to have a frame shape, as illustrated in
As illustrated in
A reflective sheet 40 is formed of a reflective sheet constituted of a dielectric multilayer mirror, a reflective sheet coated with silver, or a reflective sheet composed of a white PET resin. The configuration of the reflective sheet 40 is not particularly limited to the above configuration. The reflective sheet 40 is arranged on the rear surface side of the light guide plate 22 and prevents the loss of light, causing light that has leaked from the rear surface of the light guide plate 22 to be reflected so as to return to the light guide plate 22.
As illustrated in
In the first embodiment, no stepped part is formed on the walls 32 of the frame 30. As described above, there is no condensing lens or other optical sheet (for example, a prism sheet or the like) arranged in the backlight unit 20. Therefore, no stepped part for supporting and fixing optical sheets (an optical sheet group) is formed on the frame 30. For this reason, the backlight unit 20 does not include the region of the width W1 illustrated in
Leakage of light in the lateral direction (see
As such, as shown in
As illustrated in
Thus, the reflective sheet 40 is fixed to the lower surface 32b of the frame 30, and the liquid crystal display panel 10 is fixed to the upper surface 32a of the frame 30. For this reason, preferably, a surface area S1 of the upper surface 32a and a surface area S2 of the lower surface 32b are equal (substantially equal) (see
As illustrated in
In the backlight unit 20 of the first embodiment, the height T1 of the frame 30 (height T1 of the walls 32) is equal (substantially equal) to the thickness T2 of the light guide plate 22 (see
Next, the optical paths of the light emitted from the LEDs 21 of the backlight unit 20 of the first embodiment shall be described, with reference to
The light emitted from the LEDs 21 has the highest intensity in the front direction (Y direction) of the LEDs 21, and has a spread of ±90° in the X direction and Z direction in relation to the front direction. The light emitted from the LEDs 21, as illustrated in
Out of the light that is incident on the light incidence surface 23a, light Q1 that travels toward the light emission surface 23b travels at an angle of incidence equal to or greater than θ2 (=90°−θ1−α1) toward the inclined surfaces 23f of the prisms 23e, and the majority thereof is totally reflected to the rear surface 23c side at the prisms 23e (the interface between the light emission surface 23b of the light guide 23 and the air layer).
Light Q2 that is totally reflected at the prisms 23e travels at an angle of incidence equal to or greater than θ3 (=90°−θ1−α1×2) toward the rear surface 23c (low-refractive-index layer 24). Here, out of the light Q2 that travels toward the rear surface 23c, only light of an angle of incidence less than the critical angle between the light guide 23 and the low-refractive-index layer 24 is incident on the low-refractive-index layer 24. On the other hand, out of the light Q2 that travels toward the rear surface 23c, light of an angle of incidence equal to or greater than the critical angle between the light guide 23 and the low-refractive-index layer 24 is totally reflected to the light emission surface 23b side at the rear surface 23c (the interface between the light guide 23 and the low-refractive-index layer 24).
Light Q3 that is totally reflected at the rear surface 23c travels at an angle of incidence equal to or greater than θ4 (=90°−θ1−α1×3) toward the inclined surfaces 23f, and is totally reflected to the rear surface 23c side at the prisms 23e.
Light Q4 that is totally reflected at the prisms 23e travels at an angle of incidence equal to or greater than θ5 (=90°−θ1−α1×4) toward the rear surface 23c (low-refractive-index layer 24). Here, out of the light Q4 that travels toward the rear surface 23c, only light of an angle of incidence less than the critical angle between the light guide 23 and the low-refractive-index layer 24 is incident on the low-refractive-index layer 24. On the other hand, out of the light Q4 that travels toward the rear surface 23c, light of an angle of incidence equal to or greater than the critical angle between the light guide 23 and the low-refractive-index layer 24 is totally reflected to the light emission surface 23b side at the rear surface 23c.
Thus, the repeated reflection of the light emitted from the LEDs 21 between the prisms 23e (light emission surface 23b) and the rear surface 23c causes the light to be guided and incident onto the low-refractive-index layer 24 so that the angle of incidence with respect to the rear surface 23c gradually decreases.
The light that is emitted from the LEDs 21 is repeatedly reflected between the prisms 23e and the rear surface 23c, thereby causing the angle of incidence with respect to the rear surface 23c to be reduced by about α1×2 at a time. For this reason, the spread angle, in the Y direction, of the light incident on the low-refractive-index layer 24 is about α1×2 or less.
Out of the light that is incident on the light incidence surface 23a, light Q5 that travels toward the rear surface 23c is likewise incident on the low-refractive-index layer 24 by being repeatedly reflected between the rear surface 23c and the prisms 23e (light emission surface 23b).
That is to say, as illustrated in
Thereafter, as illustrated in
The refractive index n1 of the light guide 23 is 1.42 or greater (for example, about 1.59 to about 1.65), and the refractive index of the air layer is about 1. Accordingly, the critical angle between the light guide 23 and the air layer is smaller than the critical angle between the light guide 23 and the low-refractive-index layer 24. For this reason, there exists substantially no light that is emitted from the light emission surface 23b without having passed through the prisms 25b.
Thus, in the first embodiment, uniformity and condensing of light are realized with the light guide plate 22 alone. For this reason, as illustrated in
Next, the reason for which spreading of the light emitted from the light guide plate 22 in the X direction is suppressed shall be described in greater detail, with reference to
The light emitted from the LEDs 21 has a spread of ±90° in the X direction and Z direction in relation to the front direction (Y direction) of the LEDs 21. The light emitted from the LEDs 21 is refracted upon becoming incident on the light incidence surface 23a, where, as illustrated in
Here, the following formula (1) holds true when, inside the light guide 23, the light is present in ranges of the angle θ in the X direction and the Z direction in relation to the Y direction.
θ≦θ1=arcsin (1/n1) (1)
Only light of a region satisfying the following formula (2), where φ is the critical angle between the light guide 23 and the low-refractive-index layer 24, is able to be incident on the low-refractive-index layer 24.
π/2−θ<φ=arcsin(n2/n1) (2)
A depiction of this region is the region T1 (the shaded region) in
The angle of incidence of the light on the low-refractive-index layer 24 is π/2−θC, where θC is the component of spread in the Z direction of the light that is incident on the light guide 23. The condition for light to be incident on the low-refractive-index layer 24 is π/2−θC<φ, and because 0<π/2−θC<90, the following formula (3) is obtained.
cos(π/2−θC)=sin θC>cos φ (3)
From
sin2 θA=sin2 θ−sin2 θC (4)
Here, because sin θ≦sin θ1 and cos φ<sin θC≦sin θ1 in the light of formulae (1) and (3), the following formula (5) is obtained using the formula (4).
0≦sin2 θA<sin2 θ−cos2 φ (5)
When, for example, n1=1.59 and n2=1.35, the range available for θA is 0≦θA<19.95, and the spread of light in the X direction can be suppressed. The effect of suppressing the spread of light in the X direction slightly weakened by the prisms 23i, but because the width W13 of the flat parts 23h in the X direction is the size equal to or less than the width W14 of the prisms 23i in the X direction, increasing the angle of incline (reducing the apex angle) of the prisms 23i makes it possible to maintain the majority of the effect of suppressing the spread of light in the X direction.
The impact of the flat parts 23h and the prisms 23i shall now be further described. In
For this reason, a disproportionate spread of light in the Z direction and X direction inside the light guide 23 can be suppressed. That is to say, the prisms 23i cause the spread of light in the Z direction and X direction to change inside the light guide 23 at all times, enabling the Z direction and X direction components to be rendered equivalent.
This causes the light of the region T1 (see
In the first embodiment, as described above, the plurality of prisms 23e are provided to the light emission surface 23b. The light coming from the LEDs 21 is guided while being repeatedly reflected between the light emission surface 23b and the rear surface 23c. The angle of incidence of the light with respect to the rear surface 23c gradually decreases. Then, the light coming from the LEDs 21 is incident on the low-refractive-index layer 24 in a case where the angle of incidence of light with respect to the rear surface 23c is less than the critical angle between the light guide 23 and the low-refractive-index layer 24.
For this reason, the angle of spread in the Y direction of the light incident on the low-refractive-index layer 24 is reduced, and the angle of spread in the Y direction of light that is reflected at the interface between the rear surface 25a of the prism layer 25 and the air layer is also reduced. That is to say, the light condensing properties can be improved and the brightness of the liquid crystal display panel 10 can be improved. As a result, there is no need to arrange a plurality of optical sheets (condensing lenses or the like) on the light guide plate 22, making it possible to reduce the thickness of the backlight unit 20 and possible to suppress an increasing in the cost of production.
Because there is no need to provide a plurality of optical sheets, no light is lost in passing through any optical sheets (for example, there is no light loss caused by multiple reflections between sheets). The efficiency of utilization of light is accordingly improved.
Moving increasingly away from the LEDs 21, the angle of incidence with respect to the rear surface 23c of the light guide 23 is reduced and the light coming from the LEDs 21 is more readily incident on the low-refractive-index layer 24. This makes it possible for there to be a uniform amount of light incident on the low-refractive-index layer 24 at a portion close to the LEDs 21, where there is a large amount of light (light flux), and a portion far away from the LEDs 21, where there is less light (light flux). As a result, light can be uniformly emitted from the entire light emission region 22a of the light guide plate 22, and the brightness of the liquid crystal display panel 10 can be rendered uniform.
The plurality of prisms 25b, which reflect forward the light coming from the LEDs 21, are fowled on substantially the entire rear surface 25a (at least on a portion corresponding to the entire light emission region 22a) of the prism layer 25, in the light emission region 22a of the light guide plate 22. Therefore, the plurality of prisms 25b make it possible to uniformly reflect the light in the entire (substantially the entire) light emission region 22a. This makes it possible to more uniformly emit the light from the entire light emission region 22a of the light guide plate 22, and therefore makes it possible to suppress the occurrence of dot unevenness and also possible to render the brightness of the liquid crystal display panel 10 more uniform.
The plurality of the prisms 25b have the function of totally reflecting the light coming from the LEDs 21. Emission, from the rear surface 25a of the prism layer 25, of light that is incident on the low-refractive-index layer 24 (prism layer 25) from the light guide 23 can be suppressed. The occurrence of loss of light can be suppressed, and the efficiency of utilization of light can be further improved.
The utilization of this light guide plate 22 makes it possible to improve the illumination quality of the backlight unit 20 without having to provide prism sheets or other optical sheets (an optical sheet group). Therefore, no stepped part for supporting and fixing the optical sheets (optical sheet group) need be provided to the frame 30. The width W of the walls 32 of the frame 30 can be reduced by a commensurate amount. Leakage of light in the lateral direction can also be suppressed, and thus there is no need to provide a region for blocking light (a region corresponding to the width W3 in
With the liquid crystal display device 1 comprising the backlight unit 20 of such description, it is possible to reduce the scale of equipment while also increasing the display region. In addition, the design performance and freedom of design can be improved. Furthermore, with the backlight unit 20, the optical sheets (optical sheet group) is obviated, and the steps for assembling (assembly of) the backlight can be simplified.
When the frame 30 is constituted of a light-blocking resin material, the leakage of light in the lateral direction can be effectively suppressed, and the frame width can be more readily narrowed. Here, in a case where the frame is constituted of a light-blocking resin, the brightness near the frame is reduced on the display surface (light-emitting surface) in a conventional configuration. For this reason, the uniformity of the backlighting light is reduced. In the first embodiment, however, a sheetless backlight is used, and a decrease in brightness near the frame 30 can be effectively reduced. For this reason, having the frame 30 be constituted of a light-blocking resin makes it possible to more effectively suppress the leakage of light in the lateral direction.
The light emission surface 23b and the rear surface 23c are parallel (substantially parallel) with one another. The low-refractive-index layer 24 is easier to form on the rear surface 23c of the light guide 23 in comparison to a case where a wedge-shaped light guide of which the rear surface is inclined with respect to the light emission surface were to be used.
The prisms 23e comprise the inclined surfaces 23f that are inclined with respect to the light emission surface 23b. The angle of incidence of the light coming from the LEDs 21 with respect to the rear surface 23c of the light guide 23 can be easily made to gradually decrease.
In case where the angle of incline of the inclined surfaces 23f with respect to the light emission surface 23b is set to 5° or less (0.1° to 3°), the light is repeatedly reflected between the prisms 23e and the rear surface 23c, and the angle of incidence of the light with respect to the rear surface 23c is reduced in increments of 10° or less (0.2° to 6°). Accordingly, it is even easier to cause the angle of incidence of the light with respect to the rear surface 23c to gradually decrease.
The flat parts 23d are formed between prisms 23e that are adjacent to each other in the Y direction. Accordingly, dispersing of light emitted from the light guide 23 can be suppressed.
The plurality of prisms 25b are formed continuously, without any gap in the Y direction. The plurality of prisms 25b make it possible for the light to be more uniformly reflected. Accordingly, the light can be more uniformly emitted from the entire light emission region 22a of the light guide plate 22. This makes it possible to cause the brightness of the liquid crystal display panel 10 to be more uniform.
Forming the plurality of prisms 25b with the same shape and same size enables the plurality of prisms 25b to more uniformly reflect the light, and thus makes it possible to cause the light to be more uniformly emitted from the entire light emission region 22a of the light guide plate 22.
The plurality of prisms 23i for diffusing the light coming from the LEDs 21 in the X direction are formed on the light emission surface 23b (the light emission region 22a). The light can be properly diffused in the X direction inside the light guide 23. The brightness of the front portion of the LEDs 21 in the liquid crystal display panel 10 and the brightness of portions other than the front portion of the LEDs 21 in the liquid crystal display panel 10 can both be rendered uniform. That is to say, the brightness of the liquid crystal display panel 10 can be rendered more uniform. The prisms 23i make it possible to suppress the occurrence of linear unevenness and make it possible to effectively suppress uneven brightness.
The light having a large angle of incidence with respect to the rear surface 23c as seen from the light incidence surface 23a side is reflected by the prisms 23i. Accordingly, the angle of incidence with respect to the rear surface 23c can be reduced. This makes it possible to suppress spreading, in the X direction, of the light that is incident on the low-refractive-index layer 24, and makes it possible to suppress spreading, in the X direction, of light that is emitted from the light guide plate 22. As a result, it is possible to improve the light-condensing properties for the light in the X direction, and also to further improve the brightness of the liquid crystal display panel 10.
The prisms 23i are formed of the pairs of inclined surfaces 23j. The light coming from the LEDs 21 is diffused to both sides in the X direction by the pairs of inclined surfaces 23j. Accordingly, the brightness of the liquid crystal display panel 10 can be rendered more uniform.
The case where the LEDs 21 are used as light sources is susceptible to a difference between the brightness of the front portion of the LEDs 21 in the liquid crystal display panel 10 and the brightness of portions other than the front portion of the LEDs 21 in the liquid crystal display panel 10. It is particularly effective to provide the plurality of prisms 23i, which diffuse the light coming from the LEDs 21 in the X direction.
Being provided with the backlight unit 20 of such description makes it easy to obtain the small, thin liquid crystal display device 1 having excellent display quality and a successfully narrowed frame width.
The backlight unit of the second embodiment of the present invention shall now be described, with reference to
In the second embodiment, the backlight unit 20 is further provided with a diffusion sheet (diffusion plate) 60, as illustrated in
As illustrated in
The notch depth of the notches 33 of the frame 30 is the same (substantially the same) as the thickness of the diffusion sheet 60. As illustrated in
The adhesive layer 51 for fixing the liquid crystal display panel 10 (see
In the backlight unit 20 of the second embodiment, as illustrated in
With the diffusion sheet 60, warping or displacement of the sheet or the like causes less of an impact on the properties than would another optical sheet such as a prism sheet. Accordingly, even in the case where the backlight unit 20 comprises the diffusion sheet 60, it is possible to facilitate the steps for assembling (assembly).
The diffusion sheet 60 has the outwardly protruding protrusions 61 and the walls 32 of the frame 32 have the notches 33 into which the protrusions 61 are fitted. Accordingly, the frame 30 can be supported by the diffusion sheet 60 without increasing the width of the walls 32 of the frame 30. It is easy to narrow the frame width even in the case where the backlight unit 20 comprises the diffusion sheet 60.
Other configurations and effects of the second embodiment are similar to those of the first embodiment.
The backlight unit of the third embodiment of the present invention shall now be described, with reference to
In the third embodiment, the light guide plate 22 is constituted of the light guide 23 and the low-refractive-index layer 24, as illustrated in
Further, in the third embodiment, the prisms 23e of the light guide 23 are concave prisms, as illustrated in
In the third embodiment, too, similarly with respect to the first embodiment, the illumination quality of the backlight unit 20 can be improved without providing prism sheets or other optical sheets (an optical sheet group). For this reason, similarly with respect to the first embodiment, the leakage of light in the lateral direction can be effectively suppressed. As such, in a case configured in this manner, it is still easy to narrow the frame width, reduce size, and reduce thickness, and possible to facilitate the steps for assembling (assembly of) the backlight.
Other configurations and effects of the third embodiment are similar to those of the first and second embodiments.
The embodiments disclosed herein are in all respects provided by way of example and should not be construed as being restrictive. The scope of the present invention is indicated by the claims, not by the descriptions of the embodiments above, and further includes all modifications made within a meaning and scope equivalent to the claims.
In the first through third embodiments, the liquid crystal display device 1 is an example of the “display device” of the present invention, and the liquid crystal display panel 10 is one example of the “display panel” of the present invention. The backlight unit 20 is one example of the “illumination device” of the present invention.
For example, the illumination device of the present invention may be applied to an illumination device other than a backlight unit. For example, the illumination device of the present invention may be applied to general illumination such as indoor illumination or outdoor lighting.
The display panel and display device of the present invention may be a display panel and display device other than a liquid crystal display panel and liquid crystal display device.
In the first through third embodiments, the display device is a liquid crystal display device used as a display unit of a portable machine such as a portable terminal. However, the display device may be a display device used as a display unit of a machine other than a portable machine.
In the first through third embodiments, a frame-shaped frame having no bottom is used. However, the accommodation member for accommodating the light guide plate, light source, and the like may also be a configuration (frame configuration) that has a bottom. For example, the accommodation member for accommodating the light guide plate, the light source, and the like may be a box-shaped (substantially box-shaped) member. In such a case, the reflective sheet is arranged on the bottom of the accommodation member.
In each of the embodiments, the reflective member need not be arranged on the rear surface side of the light guide plate.
In the first through third embodiments, double-sided tape is used as one example of the adhesive layer. However, the adhesive layer need not be double-sided tape. For example, the adhesive layer may be an adhesive or the like.
In the first through third embodiments, the cross-section of the prisms (prisms 23i) for diffusing the light in the lateral direction has a triangular shape. However, the prisms 23i do not need to have a triangularly-shaped cross-section. The shape of the prisms 23i is not particularly limited, provided that the prisms 23i have inclined surfaces with which light can be reflected and the angle of light-guiding can be changed. For example, the cross-section of the prisms 23i may be arcuate, as illustrated in
In the first through third embodiments, the light emission surface (front surface) of the light guide has formed thereon prisms (the prisms 23e) for gradually reducing the angle of incidence of the light coming from the LEDs with respect to the rear surface of the light guide, and prisms (the prisms 23i) for diffusing the light in the lateral direction. However, these prisms may be formed elsewhere other than the light emission surface (front surface) of the light guide. For example, as illustrated in
In each of the embodiments, each of the prisms (prisms 23e, prisms 23i) formed on the light guide may be formed on one side of the light guide (either the front surface or the rear surface) or may be formed on both sides of the light guide (the front surface and the rear surface).
In each of the embodiments, a material of a different refractive index may be interposed between the light guide (refractive index n1) and the low-refractive-index layer (refractive index n2). In such a case, the relationship between the refractive index (n1) of the light guide, the refractive index (n2) of the low-refractive-index layer, and the refractive index (n5) of the interposed layer is preferably n2<n5≦n1.
In each of the embodiments, the prisms (prisms 23i) for diffusing the light in the lateral direction are formed so as to be concave. However, these prisms may be formed to a shape other than concave. For example, as illustrated in
In each of the embodiments, the prisms (prisms 23i) for diffusing the light in the lateral direction are formed so as to extend in the direction perpendicular (substantially perpendicular) to the light incidence surface. However, the shape of the prisms may be another shape that has a similar function to the above description.
In each of the embodiments, LEDs are used as the light source. However, light-emitting elements other than LEDs may be used as the light source, or a light source other than light-emitting elements (for example, a cold-cathode fluorescent lamp (CCFL) or the like) may be used as the light source. The light source should be arranged on at least one side of the backlight unit (light guide). The number of light sources (for example, LEDs) should be one or more.
In each of the embodiments, the values for the angles, widths, and the like are illustrative examples, and may be other values. The number of LEDs and the like may also be modified as appropriate.
In the first embodiment, the height of the frame and the thickness of the light guide plate are equal (substantially equal). However, the height of the frame and the thickness of the light guide plate may be different. For example, the height of the frame may be greater than the thickness of the light guide plate. In such a case, the distance between the light guide plate and the liquid crystal display panel is ensured.
In the second embodiment, the size of the diffusion sheet is equal (substantially equal) to the size of the light guide plate. However, the size of the diffusion sheet may be different from the size of the light guide plate. However, it is preferable for the size of the diffusion sheet to be equal (substantially equal) to the size of the light guide plate.
In the second embodiment, the diffusion sheet has the protrusions, and the frame has the notches. However, the diffusion sheet need not have the protrusions. With the configuration illustrated in the second embodiment, however, the diffusion sheet can be fixed to the frame without increasing the frame width of the frame. The configuration illustrated in the second embodiment is therefore preferable. In the second embodiment, the number, shape, and the like of the protrusions of the diffusion sheet may be modified as appropriate.
In the second embodiment, the shape of the notches of the frame may be another shape. For example, the shape of the notches 33 of the frame 30 may be a shape such as is illustrated in
Embodiments obtained by combining as appropriate the features disclosed above are also encompassed by the technical scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-154478 | Jul 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/065106 | 6/13/2012 | WO | 00 | 1/10/2014 |
