KR102396019B1 - Backlight Unit And Liquid Crystal Display Device Using The Same - Google Patents

Abstract

The present invention is to maintain an optimal optical distance between the light guide plate and the light source by further disposing a support part on the rear surface of the light guide plate in a backlight unit including a lower cover, a light guide plate, and a light source to face the side where the light source is not disposed in the lower cover. A backlight unit and a liquid crystal display including the same are provided. Accordingly, it is possible to maintain an optimal optical distance between the light guide plate and the light source without light splashing or dark portions.

Description

Backlight Unit And Liquid Crystal Display Device Using The Same

The present invention relates to a backlight unit capable of preventing light splashing by maintaining a constant optical distance between a side light type light source and a light guide plate, and a liquid crystal display using the same.

In line with the recent information age, the display field has also developed rapidly, and in response to this, as a flat panel display device (FPD) with the advantages of thinness, light weight, and low power consumption, liquid crystal display device: LCD), plasma display panel device (PDP), electroluminescence display device (ELD), field emission display device (FED), etc. It is rapidly replacing the ray tube (CRT) and is in the spotlight.

Among them, the liquid crystal display is excellent for displaying moving images and is most actively used in notebooks, monitors, and TVs due to its high contrast ratio. will demand

Accordingly, a backlight unit including a light source is provided on the rear surface of the liquid crystal panel to irradiate light toward the front surface of the liquid crystal panel, and an image of identifiable luminance is realized only through this.

On the other hand, a general backlight unit is divided into a side light type and a direct type type according to the arrangement structure of the light source. The side light type has a structure in which one or a pair of light sources are disposed on one side of a light guide plate Or, it has a structure in which two or two pairs of light sources are disposed on both sides of the light guide plate, and the direct type has a structure in which several light sources are disposed under the optical sheet.

Here, the side light type is easier to manufacture than the direct type, and has the advantage of being thin and light in weight and low power consumption compared to the direct type.

1 is a diagram schematically illustrating the structure of a backlight unit of a side light type in a conventional liquid crystal display device. As shown, the conventional backlight unit 1 for a liquid crystal display includes a light source and a plurality of optical members.

The light source 20 includes a plurality of point light sources, for example, a light emitting diode (LED) 21 and a printed circuit board 22 to which the light emitting diode 21 is bonded, and the optical member is a light emitting diode. The light guide plate 30 facing the light emitting surface of 21, the diffusion and prism sheet 70 for condensing and diffusing the light that is guided by the light guide plate 30 and exits upward, and the light exits to the rear surface of the light guide plate 30 and a reflector 60 that reflects the light in the direction of the light guide plate 30 again.

The above-described backlight unit 1 is modularized by being combined with a liquid crystal panel by various mechanical structures. In the case of a liquid crystal display module applied to a product, in order to prevent damage to internal components due to flow, in particular, the light guide plate 30 is stably fixed This is required, and since the light efficiency of the light emitted from the light source 20 depends on the distance between the light source 20 and the light incident surface of the light guide plate 30 , the light incident surfaces of the light source 20 and the light guide plate 30 are aligned with each other. (aligned) to maintain the optimal optical distance is required.

To this end, as shown in FIG. 2A , a separate fixing member is inserted between the light guide plate 30 and the lower cover 10 to be fixed in the mechanical structure. Accordingly, the recessed portions 31 for inserting the above-described fixing members are formed on both sides of the light guide plate 30 .

In addition, an intaglio portion (not shown) corresponding to the depression 31 is also formed on the reflective plate 60 disposed on the lower surface of the light guide plate 30 .

Referring to FIG. 2A , in the light guide plate 30 of the conventional backlight unit, the depressions 31 in the form of a predetermined depth are formed on both sides where the light source 20 is not located, and on the lower cover 10 . A fixing member 40 is formed at a position corresponding to the depression 31 . Accordingly, the light guide plate 30 takes a shape caught by the fixing member 40 , and when the light guide plate 30 is fixed with the fixing member 40 , even if the backlight unit shakes after assembly, the light guide plate 30 does not move. It is stably supported and the light guide plate 30 and the light source 20 can maintain a constant optimal optical distance d.

However, in the case of this structure, some of the light propagating inside the light guide plate 30 enters in the direction of the depression 31 , and cannot continue forward due to the shape of the depression 31 and is reflected inwardly. In the vicinity, light is focused in a specific direction. Accordingly, a light splashing phenomenon occurs in which the screen for some areas is brighter than other areas. As the bezel is thinner, the portion where the fixing member 40 is positioned is exposed closer to the screen display unit (Active Area), and the area where the light splashing phenomenon is visually recognized becomes wider.

In order to solve such a light splashing phenomenon and to maintain the distance between the light source 20 and the light guide plate 30 as an optimal optical distance, as shown in FIG. 3 , instead of inserting the fixing member 40, between the point light sources A light guide plate guide 50 may be installed on the

3 is a diagram schematically illustrating a backlight unit using the conventional light guide plate guide 50 . Referring to FIG. 3 , the light source 20 of the conventional backlight unit includes a light guide plate guide 50 protruding toward the light guide plate 30 between the point light sources, for example, light emitting diodes 21 . The light guide plate guide 50 maintains the optimal optical distance d, and even if there is shaking after assembly, the light guide plate 30 is stably supported without flow.

However, in this case, since the light guide plate guide 50 is positioned between the light emitting diodes 21 , the light emitted from the light emitting diodes 21 positioned on the left and right of the light guide plate guide 50 is transmitted to the light guide plate guide 50 . of the light guide plate 30 in the vertical direction is less likely to be coupled, thereby generating a dark portion.

Such light scattering or the occurrence of dark areas is a major cause of image quality degradation.

The present invention is to solve the above-mentioned light scattering problem and dark part generation problem. A first object is to maintain a constant gap between a light guide plate and a light source, and a second object is to reduce a bezel at the same time.

In order to achieve the object as described above, the backlight unit and the liquid crystal display including the same according to the present invention are disposed on a lower cover, a light guide plate, a light source, and a rear surface of the light guide plate to face one side of the lower cover on which the light source is not located. Includes support.

Specifically, the support part is provided with a hole or groove, and the fixing part is disposed on one side of the lower cover to correspond to the position of the support part. In addition, the fixing part is provided with a protrusion fitted into a hole or groove of the support part. That is, the protrusion of the fixing part may be fitted into the hole or groove of the support part to stably fix the light guide plate.

Alternatively, a protrusion protruding toward the outside of the lower cover is provided on the support part, and a hole or groove is provided on one side of the lower cover to be coupled with the protrusion part of the support part. Accordingly, the protrusion of the support part may be fitted into the hole or groove of the lower cover to stably fix the light guide plate.

According to the backlight unit of the present invention and a liquid crystal display including the same, the light guide plate and the light source can maintain an optimal optical distance while solving the problem of light splashing and the occurrence of dark areas, thereby improving image quality.

At the same time, since the fixing member does not exist, the bezel part existing to cover the fixing member can be deleted, so that the bezel can be reduced.

1 is a cross-sectional view of a conventional side light type backlight unit.
2A is a plan view of a backlight unit in which a light guide plate is fixed using a conventional fixing member.
FIG. 2B is a cross-sectional view taken along line a-a' of FIG. 2A.
3 is a plan view of a backlight unit in which a light guide plate is fixed using a conventional light guide plate guide.
4 is a plan view of a backlight unit according to a first embodiment of the present invention.
FIG. 5A is an enlarged plan view of FIG. 4A .
5B is a cross-sectional view taken along the line b-b' of FIG. 4 .
6 is a perspective view of a support part according to a first embodiment of the present invention.
7 is a perspective view of a fixing part according to a first embodiment of the present invention.
8 is a cross-sectional view according to a second embodiment of the present invention.
9 is a perspective view of a support part according to a second embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative and the present invention is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on the top', 'on the bottom', 'on the back', 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

Each feature of the various embodiments of the present invention can be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be independently implemented with respect to each other or implemented together in a related relationship. may be

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.

4 to 7 are views according to a first embodiment of the present invention.

Referring to FIG. 4 , the backlight unit according to the present invention includes a lower cover 100 , a light source 200 mounted on the lower cover 100 , a light guide plate 300 , and a support portion 400 attached to the rear surface of the light guide plate 300 . may include

The lower cover 100 may receive and seat the backlight unit, and may include a bottom surface that is in close contact with the rear surface of the backlight unit, and a side of which an edge is vertically bent upward.

The light source 200 may include a plurality of light emitting diodes 201 emitting light and a printed circuit board 202 on which the plurality of light emitting diodes 201 are mounted at regular intervals. The printed circuit board 202 may be a flexible printed circuit board, and the surface on which the light emitting diode 201 is not mounted, that is, the rear surface may be fixed to the sidewall of the lower cover 100 . Here, the printed circuit board 202 may be fixed to the lower cover 100 by a method such as screw coupling or using an adhesive means such as a double-sided tape.

The plurality of light emitting diodes 201 may be arranged along the light incident surface of the light guide plate 300 . The light emitting diode 201 may include a light emitting diode chip that emits all of red, green, and blue light or white light. In addition, the light emitting diode 201 may be composed of a plurality of light emitting diode chips each emitting red, green and blue light, and may emit white light by mixing colors by turning them on at once.

The light guide plate 300 is accommodated on the lower cover 100, and the light incident surface may be arranged to be spaced apart from the center of the light emitting diode 201 of the light source 200 and aligned to maintain an optimal optical distance d. there is. The light emitted from the light emitting diode 201 is incident on the light incident surface of the light guide plate 300, and the light guide plate 300 advances the incident light to the inside and transmits the light through total reflection several times in the direction of the liquid crystal panel (not shown). can be allowed to diverge. The light guide plate 300 may further include a pattern having a specific shape in order to supply a uniform surface light source to the liquid crystal panel (not shown). For example, on the rear surface of the light guide plate 300 , various patterns such as ovals, polygons, and holograms may be configured to guide incident light to the upper surface of the light guide plate 300 . Such a pattern may be formed by a printing method or an injection method.

Meanwhile, referring to FIGS. 5A to 7 , in order to maintain a structure in which the light incident surface of the light guide plate 300 and the center of the light emitting diode 201 are arranged at regular intervals, that is, spaced apart by the optimal optical distance d. One or more support parts 400 are respectively located on the lower portions of two opposite sides of the light guide plate 300 except for the light incident surface.

The upper surface 401 of the support 400 is attached to the rear surface of the light guide plate 300 and there is a hole 402 in the lower portion, which is located on the lower cover 100 to prevent the support 400 from flowing. It is fitted with the protrusion 501 of the fixing part 500 . However, the hole 402 may be in the form of a groove, and is not limited as long as it can be combined with the protrusion 501 of the fixing part 500 .

Here, the "hole" may have a structure in which the upper and lower surfaces are completely perforated, and the "groove" may have a structure in which the upper and lower surfaces are not completely perforated.

Accordingly, the light guide plate 300 may be fixed at a position where the light incident surface of the light guide plate 300 and the light source 200 are spaced apart by an optimal optical distance d.

The light guide plate 300 and the upper surface 401 of the support part 400 may be attached to each other using an adhesive member. The adhesive member is a material that is cured by light or heat, and may include at least one material selected from among materials having adhesive properties, such as acryl-based, rubber-based, and silicone-based materials. The adhesive member is applied to the upper surface 401 and cured after a preset time elapses, cured by applying heat at a preset temperature, or cured by irradiating ultraviolet rays.

UV may be used for rapid curing, and for this purpose, a photocurable oligomer resin may be used as the adhesive member. Examples of the photocurable oligomer component include urethane-modified (meth)acrylate, carbonate group-introduced urethane-modified (meth)acrylate, and silicone-introduced urethane-modified (meth)acrylate.

Since the part in which the hole 402 of the support part 400 exists only needs to be coupled with the protrusion 501 of the fixing part 500, the width and length of the support part 400 are the width of the upper surface 401 of the support part 400 as shown. and may be shorter than the length. In this case, the upper surface 401 supporting the light guide plate has a certain width or more to stably support the light guide plate, but the portion where the hole 402 is present is shortened in width and length to reduce the weight of the support portion 400 . This may lead to weight reduction of the display.

The support 400 may be made of at least one selected from the group consisting of plastic or resin, for example, polycarbonate, polystyrene, and acrylic. Preferably, it may be made of polycarbonate to enable injection molding. Specifically, the support part 400 of the present invention may form the support part shape by injecting the support part material into the mold of the present invention support part shape and curing it.

A reflective plate 600 may be positioned on the rear surface of the light guide plate 300 . The reflector 600 may improve the luminance of light by reflecting the light passing through the rear surface of the light guide plate 300 in an upper direction of the light guide plate 300 again. The reflective plate 600 may be made of a metal material having a high reflectance. In particular, a groove 403 is provided on a side surface of the support unit 400 in contact with the reflective plate 600 , so that some side surfaces of the reflective plate 600 may be fitted into the groove 403 . Accordingly, the reflecting plate 600 may be positioned on the rear surface of the light guide plate 300 , among the regions where the support part 400 does not exist, as wide as possible.

Since the reflective plate 600 cannot be positioned on the rear surface of the light guide plate 300 on which the support 400 is located, a reflective member (not shown) capable of giving a reflective effect to the upper surface 401 of the support 400 may be attached. can The reflective member may be a film using silver (Ag) or white PET with high reflectance, but is not limited as long as it can give a reflective effect.

A fixing part 500 is provided on the lower cover 100 to correspond to a place where the support part 400 is located. The fixed part 500 may be formed in an 'L' shape in which the horizontal part 502 and the vertical part 503 exist, and is vertical to the horizontal part 502 in the 'L'-shaped fixing part 500 . The part 503 is fixed to the bottom surface and the side surface of the lower cover 100 with an adhesive or the like, and protrudes from the vertical part 503 to the horizontal part 502 in parallel to the side surface of the lower cover 200 . The formed protrusion 501 is present and is fitted with the hole 402 of the support 400 .

The fixing unit 500 may be made of at least one selected from the group consisting of plastic or resin, for example, polycarbonate, polystyrene, and acrylic. Preferably, it may be made of polycarbonate to enable injection molding. Specifically, the fixing part 500 of the present invention may form the fixing part shape by injecting the support material into the mold having the shape of the support part of the present invention and curing it.

According to the first embodiment of the present invention, while maintaining the optimal optical distance between the light guide plate 300 and the light source 200, there is no need to form a engraving such as a depression (31 in FIG. 2A) on the light guide plate itself. There is no light scattering caused by In addition, since a reflective member (not shown) capable of giving a reflective effect is attached to the upper surface 401 of the support part 400 , the dark part is not visually recognized. As described above, according to the first embodiment of the present invention, the light scattering and the occurrence of dark parts are improved, so that there is no need to cover the part corresponding to the part where the support part 400 is located on the panel, so that the support part 400 is located. Part of the bezel can also be reduced.

8 to 9 are views according to a second embodiment of the present invention.

8 is a schematic cross-sectional view of a backlight unit according to a second embodiment of the present invention, according to the first embodiment, except that the shape of the support part 400 is different and the fixing part 500 does not exist. It is similar to the backlight unit. Accordingly, the same reference numerals are assigned to the same components, and only different components will be described below.

Referring to FIG. 8 , in order to maintain a structure in which the light incident surface of the light guide plate 300 and the center of the light emitting diode 201 are spaced apart by an optimal optical distance and aligned, two opposite sides of the light guide plate 300 excluding the light incident surface At least one support part 400 is positioned at the lower side of the side, respectively.

The upper surface 410 of the support 400 may be attached to the rear surface of the light guide plate 300 using an adhesive member. In addition, there is a protrusion 420 protruding in the lateral direction of the lower cover 100 at the lower portion of the support 400 to prevent the support 400 and the light guide plate 300 to which the support 400 is attached from flowing. It is coupled with the hole 110 existing on the side of the lower cover 100 so as to be there. However, the hole 110 may be in the form of a groove, and is not limited as long as it can be combined with the protrusion 420 of the support part 400 .

Here, the "hole" may have a structure in which the upper and lower surfaces are completely perforated, and the "groove" may have a structure in which the upper and lower surfaces are not completely perforated.

The protrusion 420 of the support 400 and the hole 110 of the lower cover 100 may be coupled using an adhesive member.

Alternatively, as shown in FIG. 8 , the protrusion 420 of the support 400 has a recess 440 provided at a portion in contact with the hole 110 of the lower cover 100 , and the hole of the lower cover 100 . The convex part 120 is provided at the part in contact with the concave part 440 in 110, so that the protrusion 420 of the support part 400 can be stably fitted into the hole 110 of the lower cover 100. there is.

Alternatively, although not shown, the protrusion 420 of the support part 400 is provided with a convex part at a portion in contact with the hole 110 of the lower cover 100, and the convex part and the hole 110 of the lower cover 100 have the convex part and the convex part. A concave portion is provided at the abutting portion, so that the protrusion 420 of the support 400 may be stably fitted into the hole 110 of the lower cover 100 .

The concave portion 440 of the protruding portion 420 may be formed in various shapes. The concave portion 440 is formed in a shape corresponding to the convex portion 120 of the lower cover 100 to be coupled to the concave portion 440 . It is preferable to be formed in a shape that can prevent flow.

The protrusion 420 of the support 400 may be provided in the shape of a single pillar, or may have a shape in which a plurality of pillars are provided with a predetermined interval, but is not limited thereto. In this embodiment, the protrusion 420 in which two pillars are formed with a predetermined interval on one side of the lower end of the support unit 400 will be described as an example.

When the protrusion 420 is provided in the shape of two pillars, the side surface of the lower cover 100 is positioned between the pillar and the pillar, so that the area of the hole 110 formed on the side of the lower cover 100 is equal to the area of the protrusion 420 . It becomes smaller than the case where it is provided in a single column shape. Therefore, when the protrusion 420 is provided in the shape of two pillars, the side surface of the lower cover 100 may more firmly fix the protrusion 420 .

The lower surface of the support part 400 may be in the form of being placed on the lower cover 100 , but in this case, the lower surface of the support part 400 and the lower cover 100 are physically coupled using an adhesive member, etc. Not desirable. When the support part 400 and the lower cover 100 are physically fixed, the light guide plate 300, the support part 400, and the lower cover 100 are all integrated, and in this case, the light guide plate 300 contracts or expands. This is because separation between the light guide plate 300 and the support part 400 may occur. Therefore, even when the light guide plate 300 contracts or expands, the support part 400 is spaced apart from the lower cover 100 at a predetermined distance as shown in FIG. 8 so that the light guide plate 300 and the support part 400 are not separated. It is preferable that there is a form.

Although not shown, when the side of the lower cover 100 is very thin, the end of the protrusion 420 of the support part 400 may protrude to the outside of the side of the lower cover 100 . In this case, a tape may be used to cover the outside of the side of the lower cover 100 or cover it with the side of the case top (not shown).

A groove 430 is provided on a side surface of the support 400 in contact with the reflective plate 600 , so that some side surfaces of the reflective plate 600 may be fitted into the groove 430 . Accordingly, the reflecting plate 600 may be positioned on the rear surface of the light guide plate 300 , among the regions where the support part 400 does not exist, as wide as possible.

Since the reflective plate 600 cannot be positioned on the rear surface of the light guide plate 300 on which the support 400 is located, a reflective member (not shown) capable of giving a reflective effect to the upper surface 410 of the support 400 may be attached. can The reflective member may be a film using silver (Ag) or white PET with high reflectance, but is not limited as long as it can give a reflective effect.

According to the second embodiment of the present invention, while the light guide plate 300 and the light source 200 maintain an optimal optical distance, there is no need to form a engraving such as a depression (31 in FIG. 2A ) on the light guide plate itself. There is no light scattering caused by In addition, since a structure (not shown) capable of giving a reflective effect is attached to the upper surface 401 of the support part 400 , the dark part is not visually recognized. As described above, according to the first embodiment of the present invention, the light scattering and the occurrence of dark parts are improved, so that there is no need to cover the part corresponding to the part where the support part 400 is located on the panel, so that the support part 400 is located. Part of the bezel can also be reduced.

In addition, since there is no need to provide a separate fixing part 500 and the lower cover 100 is used, slimming and weight reduction of the display device can be achieved. In addition, since a separate configuration other than the support 400 is not required, there is an advantage in terms of cost.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made within the scope without departing from the technical spirit of the present invention. . Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: lower cover 200: light source
300: light guide plate 400: support
401: upper surface 402: hole
403: groove 410: upper surface
420: protrusion 430: groove
500: fixing part 501: protrusion
502: horizontal part 503: vertical part
600: reflector

Claims (13)

lower cover;
a light guide plate accommodated in the lower cover;
a light source disposed on at least one side of the lower cover and spaced apart from each other by a predetermined interval along a light incident surface of the light guide plate; and
a support portion disposed on a rear surface of the light guide plate facing the lower cover to face the other side of the lower cover on which the light source is not disposed;
The support portion is provided with a first hole or groove,
The backlight unit further comprising: a fixing part disposed on the other side of the lower cover and provided with a protrusion protruding toward the inner side of the lower cover to fit into the first hole or groove. The method of claim 1,
The support part is a backlight unit attached to the rear surface of the light guide plate using an adhesive member. delete lower cover;
a light guide plate accommodated in the lower cover;
a light source disposed on at least one side of the lower cover and spaced apart from each other by a predetermined interval along a light incident surface of the light guide plate; and
a support portion disposed on a rear surface of the light guide plate facing the lower cover to face the other side of the lower cover on which the light source is not disposed;
The support part is provided with a protrusion protruding toward the outside of the lower cover,
The backlight unit further comprising a second hole or groove positioned on the other side of the lower cover into which the protrusion is fitted. 5. The method of claim 1 or 4,
The backlight unit further comprising a reflective plate positioned below the light guide plate. 6. The method of claim 5,
The support part has a third groove on a side surface in contact with the reflection plate, and the backlight unit is positioned so that the reflection plate is fitted into the third groove. 5. The method of claim 1 or 4,
A backlight unit having a reflective member having reflective performance on an upper surface of the support. 8. The method of claim 7,
The reflective member is a backlight unit made of Ag or PET. The method of claim 1,
The light source is located on both sides in the horizontal direction of the lower cover, the support portion is located on the rear surface of both sides in the vertical direction of the light guide plate, and the fixing portion is located on both sides in the vertical direction of the lower cover at least one backlight unit. 5. The method of claim 4,
The second hole or groove has a convex part, and the support part has a concave part at an end of the protrusion part, and the convex part and the concave part are fixed by being fitted. 5. The method of claim 4,
The second hole or groove includes a concave portion, and the support portion includes a convex portion at an end of the protruding portion, and the convex portion and the concave portion are fitted and fixed thereto. 5. The method of claim 4,
The light source is located on both sides of the lower cover in a horizontal direction, the support portion is located on the rear surface of both sides in the vertical direction of the light guide plate, and the second hole or groove is at least one provided on the other side of the lower cover. The backlight unit according to any one of claims 1, 2, 4, and 9 to 12;
an optical sheet positioned on the upper surface of the light guide plate; and
and a liquid crystal panel positioned on an upper surface of the optical sheet.

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