Illumination device and display device

Abstract

To provide a lighting device and a display device with improved light extraction efficiency.SOLUTION: The illumination device includes a first light guide plate having a cross-sectional shape of a first trapezoidal shape in which a lower side is shorter than an upper side, a second light guide plate having a cross-sectional shape of a second trapezoidal shape in which the lower side is longer than the upper side, and a plurality of light source elements, light emitted from the plurality of light source elements is incident on the first light guide plate from a first surface, is totally reflected by a second surface and is incident on the second light guide plate, and the light incident on the second light guide plate is totally reflected by a fourth surface.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a lighting device and a display device. [Background technology]

[0002] 2. Description of the Related Art In the field of laser backlights, which use elements that emit laser light as a light source, backlights that can uniformize the in-plane luminance distribution have been developed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-126811 Summary of the Invention [Problem to be solved by the invention]

[0004] The present embodiment provides a lighting device with improved light extraction efficiency, and a display device with improved brightness by including such a lighting device. [Means for solving the problem]

[0005] An illumination device according to an embodiment includes: a first light guide plate having a first trapezoidal cross section whose bottom side is shorter than its top side; a second light guide plate provided on the first light guide plate and having a second trapezoidal cross section whose bottom side is longer than its top side; a first surface provided on the first light guide plate; a second surface that is disposed on the opposite side of the first surface and that is a hypotenuse of the first trapezoidal shape; a third surface provided on the second light guide plate; a fourth surface that is disposed opposite to the third surface and is a hypotenuse of the second trapezoidal shape; a plurality of light source elements provided to face the third side of the second light guide plate; Equipped with Light emitted from the plurality of light source elements enters the first light guide plate from the first surface, is totally reflected by the second surface, and enters the second light guide plate, and the light that has entered the second light guide plate is totally reflected by the fourth surface. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view showing an example of the appearance of a display device according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing a schematic configuration of a display device provided in the display device according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a schematic configuration of a display device. [Figure 4] FIG. 4 is a plan view illustrating light mixing. [Figure 5] FIG. 5 is a cross-sectional view showing another example of a schematic configuration of a display device. [Figure 6] FIG. 6 is a partially enlarged view of the lighting device shown in FIG. [Figure 7] FIG. 7 is a partially enlarged view of the lighting device shown in FIG. [Figure 8] FIG. 8 is a partially enlarged view of the lighting device shown in FIG. [Figure 9] FIG. 9 is a diagram showing the relationship between the angle Aa and the ratio (d1 / d0) of the thickness d1 to the thickness d0. [Figure 10] FIG. 10 is a diagram showing the relationship between the angle Aa and the ratio (ka / d0) of the thickness d1 to the distance ka. [Figure 11] FIG. 11 is a diagram showing an example in which the angle Aa is 61.75° (Aa=61.75°). [Figure 12] FIG. 12 is a diagram showing an example in which the angle Aa is 68° (Aa=68°). DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily conceive while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0008] The embodiments described in this specification are not general but are embodiments that describe the same or corresponding special technical features of the present invention. Hereinafter, a display device according to an embodiment will be described in detail with reference to the drawings.

[0009] In this embodiment, the first direction X, the second direction Y, and the third direction Z are perpendicular to one another, but may intersect at an angle other than 90 degrees. The direction toward the tip of the arrow of the third direction Z is defined as up or upward, and the direction opposite to the direction toward the tip of the arrow of the third direction Z is defined as down or downward. The first direction X, the second direction Y, and the third direction Z may also be referred to as the X direction, the Y direction, and the Z direction, respectively.

[0010] Furthermore, when the terms "second member above the first member" and "second member below the first member" are used, the second member may be in contact with the first member or may be located apart from the first member. In the latter case, a third member may be interposed between the first and second members. On the other hand, when the terms "second member above the first member" and "second member below the first member" are used, the second member is in contact with the first member.

[0011] Furthermore, it is assumed that an observation position for observing the display device is located at the tip of the arrow in the third direction Z, and viewing from this observation position toward the XY plane defined by the first direction X and the second direction Y is called planar view. Viewing a cross section of the display device in the XZ plane defined by the first direction X and the third direction Z, or in the YZ plane defined by the second direction Y and the third direction Z, is called cross-sectional view.

[0012] [Embodiment] 1 is a perspective view showing an example of the appearance of a display device according to an embodiment. In the embodiment, the display device includes a head mounted display (HMD) that is worn on a user's head when in use. Such a display device is used to provide, for example, virtual reality (VR) to a user wearing the display device on their head.

[0013] As shown in Fig. 1, the display device DSP includes a display panel PNLh for the left eye and a display panel PNLm for the right eye. The display panels PNLh and PNLm are sometimes referred to as the first display panel and the second display panel, respectively. The display panels PNLh and PNLm are each independent display panels.

[0014] The display panels PNLh and PNLm are arranged so as to be located in front of the left and right eyes of the user USR when the user USR wears the display device DSP on his / her head. In the embodiment, the display panels PNLh and PNLm are liquid crystal display panels having a liquid crystal layer.

[0015] 2 is a perspective view showing a schematic configuration of a display device provided in the display device according to the embodiment, in which the configuration of the display panel PNLh will be mainly described.

[0016] 2 includes a first substrate SUB1 and a second substrate SUB2 facing the first substrate SUB1. The display panel PNLh also has a display area DA for displaying an image. The display panel PNLh further includes a plurality of pixels PX arranged in a matrix in the display area DA, for example.

[0017] The display panel PNLh also includes a drive IC chip IC1 that drives the display panel PNLh and a flexible circuit board FPC1 that transmits control signals to the display panel PNLh. The flexible circuit board FPC1 is connected to a control module (host computer) that controls the operation of the display device DSP.

[0018] 2, the first substrate SUB1 and the second substrate SUB2 each have a long side along the first direction X and a short side along the second direction Y. The first substrate SUB1 and the second substrate SUB2 each have an octagonal shape in plan view. This shape can also be said to be a rectangle with the corners cut out. The display panel PNLh has an octagonal shape in plan view.

[0019] However, the shape of the display panel PNLh is not limited to this and may be any polygonal shape. The shape of the display panel may be any shape that prevents the display panel from hitting the nose of the user USR, as will be described later, and may be any shape that has a notched corner close to the nose of the user USR.

[0020] 2, the shape of the display panel PNLh has been described. The display panel PNLm has a shape that is line-symmetrical to the display panel PNLh with respect to the second direction Y. The configuration of the display panel PNLm is the same as that of the display panel PNLh, except for the point that it has a shape that is line-symmetrical to the display panel PNLh with respect to the second direction Y.

[0021] An illumination device ILDh is provided below the display panel PNLh. In the example shown in Fig. 2, only the light guide plate LGh of the illumination device ILDh is shown. The light guide plate LGh has a rectangular shape extending along the first direction X and the second direction Y.

[0022] Fig. 3 is a cross-sectional view showing an example of a schematic configuration of a display device. The display device DSP shown in Fig. 3 includes an illumination device ILDh and a display panel PNLh. The illumination device ILDh includes a reflector REFh, a light-output light-guide plate LGP having a light-output structure LPR for emitting light LT traveling within the light-guide plate from a surface LUS that is the upper surface of the light-output light-guide plate LGP, a mixing light-guide plate LGM for mixing laser light, an optical sheet OSHh, and a light source element LS1h. The reflector REFh, the light-output light-guide plate LGP, the mixing light-guide plate LGM, and the optical sheet OSHh are stacked in this order.

[0023] The light output light guide plate LGP and the mixed light guide plate LGM constitute the light guide plate LGh shown in Fig. 2. A display panel PNLh is provided on the illumination device ILDh.

[0024] 3, of the surfaces of the mixed light guide plate LGM, the first surface on the left side of the page that faces the light source element LS1h is designated as surface GVU1h, and the second surface that reflects light on the right side of the page is designated as surface GVU2h. Of the surfaces of the output light guide plate LGP, the third surface on the left side of the page is designated as surface GVL1h, and the fourth surface that reflects light on the right side of the page is designated as surface GVL2h.

[0025] When viewed in cross section, the first surface GVU1h and the second surface GVU2h are also referred to as the first side and the second side, respectively. When viewed in cross section, the third surface GVL1h and the fourth surface GVL2h are also referred to as the third side and the fourth side. The surfaces GVU2h and GVL2h are inclined obliquely with respect to the YZ plane.

[0026] The light output light guide plate LGP has a trapezoidal cross section in which the bottom side is shorter than the top side. A surface GVL1h, which is the left side of the trapezoid, extends along the third direction Z. A surface GVL2h, which is the right side of the trapezoid, extends at an angle with respect to the third direction Z.

[0027] The bottom surface of the light output light guide plate LGP is referred to as surface LBS, and the top surface is referred to as surface LUS. Surface LBS faces the reflector REFh. Surface LUS faces the mixed light guide plate LGM. Surface LBS is provided with a plurality of light output structures LPR (hereinafter also referred to as convex portions, protrusions, grooves, or prisms). As will be described in detail later, light LT reflected by the plurality of light output structures LPR is emitted upward. The thickness (distance along the third direction Z) of the light output light guide plate LGP is referred to as thickness d0.

[0028] The mixed light guide plate LGM has a trapezoidal cross section with the bottom side longer than the top side. A surface GVU1h, which is the left side of the trapezoid, extends along the third direction Z. A surface GVU2h, which is the right side of the trapezoid, extends at an angle with respect to the third direction Z. The thickness of the mixed light guide plate LGM is defined as d1. The thickness d1 is thinner than the thickness d0 (d1 <d0)。

[0029] The lower surface of the hybrid light guide plate LGM is called the surface UBS, and the upper surface is called the surface UUS. The surface UBS faces the surface LUS of the output light guide plate LGP. The surface UUS faces the optical sheet OPSh.

[0030] The mixed light guide plate LGM and the output light guide plate LGP may be made of a transparent material having the same refractive index. The refractive index of the transparent material is preferably close to the refractive index of air. Examples of such transparent materials include glass and light-transmitting organic resins. More specifically, examples of light-transmitting organic resins include acrylic resins.

[0031] The light source element LS1h is provided facing the surface GVU1h of the mixed light guide plate LGM. The light LT emitted from the light source element LS1h enters the mixed light guide plate LGM from the surface GVU1h of the mixed light guide plate LGM.

[0032] The light source element LS1h uses a laser light source (laser diode) such as a semiconductor laser that emits laser light. The laser light may be diffused light that spreads from the irradiation direction as the center, or may be polarized laser light.

[0033] The surface GVU2h that is the second side and the surface GVL2h that is the fourth side are inclined obliquely with respect to the Y axis.

[0034] The angle of the surface GVL2h relative to the second direction Y is defined as angle Aa. The angle of the surface GVU2h relative to the second direction Y is defined as angle Ab.

[0035] A plurality of convex portions (also called prisms) are provided on the main surfaces of the reflector REFh and the optical sheet OSHh. The optical sheet OSHh includes, for example, a prism sheet, a diffusion plate, and the like.

[0036] As described above, light LT emitted from light source element LS1h is incident on surface GVU1h of hybrid light guide plate LGM. The incident light LT propagates from surface GVU1h to surface GVU2h. When light LT reaches surface GVU2h, the light that satisfies the conditions for total reflection is reflected downward and enters light output light guide plate LGP.

[0037] Of the light incident on the light-guiding plate LGP, the light that satisfies the conditions for total reflection at the surface GVL2h reaches the surface LBS. The light LT is repeatedly reflected between the surfaces LBS and LUS and propagates in the direction opposite to the first direction X.

[0038] When propagating light LT is incident on a light output structure LPR provided on the surface LBS, which is the lower surface of the light output light guide plate LGP, the light LT is reflected by the light output structure LPR and lifted upward. The light LT that has been lifted upward exits the light output light guide plate LGP, passes through the mixed light guide plate LGM, and is incident on the optical sheet OSHh. The light LT that has entered the optical sheet OSHh is emitted upward in a direction parallel to the third direction Z by the convex portions provided on the optical sheet OSHh. The light LT enters the display panel PNLh from the optical sheet OSHh.

[0039] Fig. 4 is a plan view illustrating light mixing. In the illumination device ILDh shown in Fig. 4, only the light source element LS1h and the mixing light guide plate LGM are shown.

[0040] Light LT emitted from the light source element LS1h enters the mixed light guide plate LGM from the surface GVU1h. The light LT propagates through the inside of the mixed light guide plate LGM with a light line width WLL (length along the second direction Y). If the light source element LS1h is a laser light source (laser diode), the laser light has a high degree of linearity, so the light line width WLL is short near the surface GVU1h. Therefore, the light LT emitted from multiple light source elements LS1h does not mix with each other. As a result, bright regions RAh and dark regions RKh are generated in the mixed light guide plate LGM.

[0041] While the light LT propagates from the surface GVU1h to the surface GVU2h, the light beam width WLL increases. In the vicinity of the surface GVU2h, the light LT emitted from the multiple light source elements LS1h mixes together, becoming light LT with uniform brightness.

[0042] From the above, the width (length along the second direction Y) of the bright region RAh is narrower as it approaches the light source element LS1h. The width of the bright region RAh becomes wider as it moves away from the light source element LS1h.

[0043] As described above, the light LT having uniform brightness is reflected downward by the surface GVU2h and enters the light output light guide plate LGP from the surface LUS, which is the upper surface of the light output light guide plate LGP.

[0044] Fig. 5 is a cross-sectional view showing another example of the schematic configuration of a display device. The mixed light guide plate LGM shown in Fig. 5 is obtained by placing the mixed light guide plate LGM shown in Fig. 3 upside down. The light output light guide plate LGP shown in Fig. 5 has a trapezoidal cross section along the X axis, and the length of the surface LBS, which is the bottom surface facing the mixed light guide plate LGM, in the X axis direction is longer than the length of the surface LUS, which is the top surface, in the first direction X. In Fig. 5, the reflector REFh, mixed light guide plate LGM, light output light guide plate LGP, and optical sheet OPSh are layered in this order.

[0045] Regarding the illumination device ILDh shown in Fig. 5, the same points as those of the illumination device ILDh shown in Fig. 3 will be omitted and the description of Fig. 3 will be cited. Differences between the illumination device ILDh shown in Fig. 5 and the illumination device ILDh shown in Fig. 3 will be described below.

[0046] A plurality of light output structural bodies UPR are provided on a surface LBS, which is the lower surface of the light output guide plate LGP. Light reflected by the plurality of light output structural bodies UPR is emitted upward.

[0047] The thickness of the mixed light guide plate LGM is defined as thickness d11. The thickness of the output light guide plate LGP is defined as thickness d10. The thickness d10 is thicker than the thickness d11 (d10>d11).

[0048] The light source element LS1h is provided facing the surface GVU1h of the mixed light guide plate LGM. The light LT emitted from the light source element LS1h enters the mixed light guide plate LGM from the surface GVU1h of the mixed light guide plate LGM.

[0049] Light LT that enters the mixed light guide plate LGM propagates from surface GVU1h to surface GVU2h. When light LT reaches surface GVU2h, it is totally reflected at surface GVU2h and reflected upward, before entering the mixed light guide plate LGM. Surface GVU2h is tilted so that the light from the light source element satisfies the total reflection condition.

[0050] The light incident on the output light guide plate LGP is totally reflected by the surface GVL2h and reaches the surface LUS. The light LT is repeatedly reflected between the surface LUS and the surface LBS and propagates in the direction opposite to the first direction X.

[0051] When propagating light LT is incident on the light output structure UPR provided on the surface LBS, the light LT is reflected by the light output structure UPR and lifted upward. The light LT that has been lifted upward exits the light output light guide plate LGP and enters the optical sheet OSHh. The light LT that has entered the optical sheet OSHh is emitted upward in a direction parallel to the third direction Z by the convex portions provided on the optical sheet OSHh. The light LT enters the display panel PNLh from the optical sheet OSHh.

[0052] In the lighting device ILDh shown in FIG. 5, light LT having uniform brightness is incident on the optical sheet OSHh from the surface LUS, which is the upper surface of the light-emitting light guide plate LGP, so there is little light loss and light can be efficiently supplied to the display panel.

[0053] Regarding the above-mentioned illumination device ILDh and display device DSP, a configuration for extracting the light LT emitted from the light source element LS1h most efficiently will be described.

[0054] 3, the surface GVU2h of the mixed light guide plate LGM and the surface GVL2h of the output light guide plate LGP must satisfy the total reflection condition to reflect the light LT. If the surface GVU2h of the mixed light guide plate LGM and the surface GVL2h of the output light guide plate LGP do not satisfy the total reflection condition, the light LT may not be totally reflected and may not propagate from the mixed light guide plate LGM to the output light guide plate LGP, or may even be emitted to the outside from the light guide plate LGh. This may reduce the brightness of the light extracted upward from the lighting device ILDh, thereby reducing the extraction efficiency.

[0055] Fig. 6 is a partially enlarged view of the lighting device shown in Fig. 3. As described above, the angle of the surface GVL2h with respect to the first direction X is defined as angle Aa. The angle of the surface GVU2h with respect to the first direction X is defined as angle Ab.

[0056] The difference in distance between the surfaces LUS and LBS along the first direction X is defined as distance ka. The difference in distance between the surfaces UUS and UBS along the first direction X is defined as distance kb. It can also be said that distance ka is the width of the surface GVL2h, and distance kb is the width of the surface GVU2h.

[0057] Of the light LT emitted from the light source element, the chief ray is designated as LM and the diffused light is designated as LD. The diffused light LD is tilted at an angle dA from the chief ray LM. The chief ray LM travels along the first direction X from the surface GVU1h to the surface GVU2h.

[0058] The angle between the principal ray LM that is reflected by the surface GVU2h and reaches the surface GVL2h and the surface GVL2h is defined as angle Ac. Find the conditions under which the principal ray LM in the mixed light guide plate LGM becomes angle A0 after entering the output light guide plate LGP. In (Equation 1), π is 180° (π = 180°).

[0059] Ac=π-Ab-(Aa+Ab)=π-Aa-2Ab (Formula 1)

[0060] If the angle of the chief ray LM reflected by the surface GVL2h with respect to the first direction X is defined as angle A0, then Equation 2 holds true.

[0061] Ac=Aa-A0 (Formula 2)

[0062] Since the right-hand side of equation 1 is equal to the right-hand side of equation 2, equation 3 holds.

[0063] π-Aa-2Ab=Aa-A0 (Equation 3)

[0064] Transforming (Equation 3) yields Equation 4.

[0065] Aa+Ab=(A0+π) / 2 (Equation 4)

[0066] Consider the conditions under which all light rays (light LT), including not only the chief ray LM but also the diffused light LD, are incident on the light output light guide plate LGP. More specifically, the conditions under which the light ray at angle (A0+dA) is reflected by both the surface GVU2h and the surface GVL2h in the light output light guide plate LGP are expressed by Equation 5, which will be described later.

[0067] As shown in Figure 6, it is assumed that the diffused light LD is reflected by the surface GVU2h and then reaches the surface LBS without being reflected by the surface GVL2h. In this case, the diffused light LD is incident on the boundary between the surface LBS and the surface GVL2h. The angle formed by the diffused light LD and the surface GVL2h is defined as angle Ad.

[0068] Ad=Aa-(A0+dA) (Equation 5)

[0069] From the thickness d0 of the light output light guide plate LGP, the length ka of the surface GVL2h in the X-axis direction, and the angle Aa, the following equation (6) is established. Transforming equation (6), the following equation (7) is established.

[0070] tanAa=d0 / ka (Equation 6) ka=d0 / tanAa (Equation 7)

[0071] Equation 8 holds based on the angle Ad of the diffused light LD, the thickness d1 of the mixed light guide plate LGM, and the distance kb along the first direction X between the edge of the surface UUS, which is the upper surface of the mixed light guide plate LGM, and the edge of the surface LBS, which is the lower surface of the output light guide plate LGP. Equation 9 holds based on Equation 8 and Equation 5.

[0072] tan(Aa+Ad)=(d1+d0) / kb (Equation 8) kb=(d1+d0) / tan(Aa+Ad)=(d1+d0) / tan[2Aa-(A0+dA)] (Equation 9)

[0073] (Equation 10) is established from (Equation 7) and (Equation 9).

[0074] ka-kb=d1 / tanAb=d1 / tan[(A0+π) / 2-Aa] (Equation 10)

[0075] From the above, (Equation 11) holds. By transforming (Equation 11), (Equation 12), (Equation 13), (Equation 14), and (Equation 15) are obtained.

[0076]

number

[0077]

number

[0078]

number

[0079] [Number]

[0080] [Number]

[0081] From the above, the relationship between the thickness d0 of the light-emitting light guide plate LGP and the thickness d1 of the hybrid light guide plate LGM is expressed as (Equation 15).

[0082] Actually, if the thickness d1 of the hybrid light guide plate LGM is thinner than (Equation 15), the light LT will enter the light-emitting light guide plate LGP. Therefore, it is preferable that the thickness d1 satisfies (Equation 16).

[0083] [Number]

[0084] Figure 7 is a partially enlarged view of the lighting device shown in Figure 3. In Figure 7, it is assumed that the hybrid light guide plate LGM and the light-emitting light guide plate LGP are formed of the same material. That is, the hybrid light guide plate LGM and the light-emitting light guide plate LGP have the same refractive index. When the light LT is totally reflected by the hybrid light guide plate LGM and the light-emitting light guide plate LGP, the total reflection angle is defined as angle F.

[0085] The condition for the light LT at angle (A₀ - dA) to be totally reflected by the surface GVL2h is obtained. The angle formed by the diffused light LD reaching the surface GVL2h of the light-emitting light guide plate LGP and the surface GVL2h is defined as angle Ae. This condition is expressed by (Equation 17).

[0086] Ae = Aa - (A₀ - dA) < F (Equation 17)

[0087] When (Equation 17) is transformed, (Equation 18) is obtained. <00​​​​​The diffused light LD is incident from the surface GVU1h of the mixed light guide plate LGM, undergoes total reflection at the boundary between the surface UUS and the surface GVU2h, and is incident on the light extraction light guide plate LGP. Let the angle between the diffused light LD and the surface GVU2h be the angle Af. The condition for the diffused light LD to undergo total reflection at the surface GVU2h is expressed by (Equation 19).

[0090] Ab + dA < F (Equation 19)

[0091] (Equation 19) and (Equation 4) yield (Equation 20).

[0092] [(A0 + π) / 2] - Aa < F - dA (Equation 20)

[0093] (From Equation 20), (Equation 21) is obtained.

[0094] Aa > [(A0 + π) / 2] + dA - F (Equation 21)

[0095] Figure 8 is a partially enlarged view of the lighting device shown in Figure 3. In Figure 8, the mixed light guide plate LGM and the light extraction light guide plate LGP are light guide plates that satisfy (Equation 22).

[0096] Aa + Ad > π / 2 (Equation 22)

[0097] Consider the condition where the light LT with an angle (A0 + dA) satisfying 33° (A0 + dA = 33°) is reflected by both the surface GVU2h and the surface GVL2h. When the angle (A0 + dA) exceeds 33°, the total reflection condition is not satisfied. That is, the condition for the maximum angle at which the light LT can undergo total reflection is that the angle (A0 + dA) is 33° (A0 + dA = 33°).

[0098] When (Equation 22) holds, the angle Ad is expressed by (Equation 23).

[0099] Ad = Aa - (A0 + dA) (Equation 23)

[0100] The angle Aa and the angle Ab are respectively expressed by (Equation 24), (Equation 25), and (Equation 26).

[0101] Aa=d0 / tanAa (Equation 24)

[0102]

number

[0103] From (Equation 24) and (Equation 25), (Equation 26) is obtained.

[0104]

number

[0105] From (Equation 24) to (Equation 26), (Equation 27) is obtained.

[0106]

number

[0107] This is the same as (Equation 27) and (Equation 15). That is, the thickness d1 has the same condition in Figures 6 and 8. That is, when (Aa + Ad) ≦ π / 2 (see Figure 6) and (Aa + Ad) > π / 2 (see Figure 8), the thickness d1 is expressed by the same equation.

[0108] The relationship between the thickness d0 of the light output light guide plate LGP, the thickness d1 of the mixed light guide plate LGM, the angle dA which is the diffusion angle, the angle Aa which is the angle of the surface GVL2h of the light output light guide plate LGP, and the distance ka which is the width of the surface GVL2h, obtained from (Equation 16), (Equation 18), and (Equation 21), is described below.

[0109] 9 is a diagram showing the relationship between the angle Aa and the ratio (d1 / d0) of the thickness d1 to the thickness d0. In FIG. 9, the line CDa corresponds to (Equation 18). The line CDb corresponds to (Equation 21).

[0110] FIG. 10 is a diagram showing the relationship between the angle Aa and the ratio (ka / d0) of the thickness d1 to the distance ka.

[0111] 9 and 10, the angle dA, which is the diffusion angle, is preferably 6.5° or more and 10° or less. When the angle dA is 6.5° (dA=6.5°), the angle Aa can be in the range of 61.75° or more and 68° (61.75°≦Aa≦68°). When the angle dA is 10° (dA=10°), the angle Aa can be in the range of 64.5° or more and 65.3° or less (64.5°≦Aa≦65.3°).

[0112] 11 is a diagram showing an example in which the angle Aa is 61.75° (Aa=61.75°). In this case, the angle A0 is 26.5° (A0=26.5°), and the light LT, for which the sum of the angle A0 and the angle dA is 33° (A0+dA=33°), satisfies the total reflection condition.

[0113] Since angle Aa is 61.75°, according to (Equation 4), angle Ab is 41.5° (Ab=41.5°). Angle dA, which is the diffusion angle of diffused light LD, is set to 6.5° (dA=6.5°). In other words, the lighting device ILDh is equipped with a light source element LS1h that emits light LT whose diffusion angle dA is 6.5°.

[0114] Using equation (15), we obtain d1=0.49d0, which means that the thickness d1 of the mixed light guide plate LGM is 0.49 times the thickness d0 of the output light guide plate LGP.

[0115] Fig. 12 is a diagram showing an example in which the angle Aa is 68° (Aa = 68°). As in Fig. 11, the angle A0 is 26.5° (A0 = 26.5°), and the light LT in which the sum of the angle A0 and the angle dA is 33° (A0 + dA = 33°) satisfies the total reflection condition.

[0116] Since angle Aa is 61.8°, angle Ab is 35.25° from (Equation 4) (Ab=35.25°). Angle dA, which is the diffusion angle of diffused light LD, is 6.5° (dA=6.5°), similar to FIG. 11.

[0117] Using equation (15), we obtain d1=0.54d0, which means that the thickness d1 of the mixed light guide plate LGM is 0.54 times the thickness d0 of the output light guide plate LGP.

[0118] As described above, the suitable thicknesses d1 and d0 can be obtained from the angles Aa, dA, and A0. Furthermore, once the thickness d1 is obtained, the suitable distances ka and kb can be obtained.

[0119] In this disclosure, the light output light guide plate LGP and the mixed light guide plate LGM are also referred to as the first light guide plate and the second light guide plate, respectively. The surfaces GVL1h and GVL2h of the light output light guide plate LGP are also referred to as the first surface and the second surface, respectively. The surfaces GVU1h and GVU2h of the mixed light guide plate LGM are also referred to as the third surface and the fourth surface, respectively.

[0120] In this disclosure, the surfaces LBS and LUS of the light output light guide plate LGP are also referred to as the first and second main surfaces, respectively. The surfaces UBS and UUS of the mixed light guide plate LGM are also referred to as the third and fourth main surfaces, respectively. The thickness d0 of the light output light guide plate LGP and the thickness d1 of the mixed light guide plate LGM are also referred to as the first thickness and the second thickness, respectively.

[0121] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0122] A0...angle, Aa...angle, Ab...angle, Ac...angle, Ad...angle, Ae...angle, Af...angle, DSP...display device, GVL2h...surface, GVU2h...surface, ILDh...lighting device, LD...diffused light, LGLh...light guide plate, LGM...mixed light guide plate, LM...chief ray, LS1h...light source element, LT...light, dA...angle, ka...distance, kb...distance.

Claims

1. a first light guide plate having a first trapezoidal cross section whose lower side is shorter than its upper side; a second light guide plate provided on the first light guide plate and having a second trapezoidal cross section whose lower side is longer than its upper side; a first surface provided on the first light guide plate; a second surface that is disposed on the opposite side to the first surface and that is a hypotenuse of the first trapezoidal shape; a third surface provided on the second light guide plate; a fourth surface that is disposed on the opposite side to the third surface and that is a hypotenuse of the second trapezoidal shape; a plurality of light source elements provided opposite to the third surface of the second light guide plate; Equipped with the light emitted from the plurality of light source elements is incident on the first light guide plate from the first surface, is totally reflected by the second surface, and is incident on the second light guide plate, and the light incident on the second light guide plate is totally reflected by the fourth surface.

2. The lighting device according to claim 1 , wherein the second thickness of the second light guide plate is smaller than the first thickness of the first light guide plate.

3. The lighting device according to claim 1 , wherein the first light guide plate has a plurality of convex portions on a first main surface that is a bottom side of the first trapezoidal shape.

4. The lighting device according to claim 1 , wherein the plurality of light source elements are laser light source elements.

5. The lighting device according to claim 1 ; a display panel provided on the lighting device; A display device comprising:

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