Patent Publication Number: US-8111353-B2

Title: Lens array sheet, light source and liquid crystal display device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens array sheet, a light source and a liquid crystal display device. 
     2. Description of the Related Art 
     Recently, a liquid crystal panel such as liquid crystal display device has been gradually enlarged. Although the liquid crystal panel may be enlarged, it is not allowed to degrade the image quality of the panel and it is demanded that high definition image quality of the panel can be achieved even for a large-scale screen. In order to achieve the high definition image quality for the large-scale screen, for example, it is strongly demanded that brightness of the screen can be maintained or improved, or viewing angle can be widened. In accordance with these demands, some techniques have been proposed to arrange a micro array lens in the liquid crystal panel and improve the brightness and the viewing angle of the liquid crystal panel. Arranging the micro array lens makes it possible to enhance front face brightness and/or widen the viewing angle. 
     On the contrary, there is an issue to be solved, because moire fringes may appear and visibility may become lower due to the fact that the liquid crystal panel includes an array of regular pixels (i.e., picture elements). The moire fringes are a fringe pattern which is produced by overlapping a plurality of regular repetitive patterns and visually observed by a deviation of periods between the plurality of regular repetitive patterns. The moire fringes in the liquid crystal panel are produced as each pixel in the liquid crystal panel forms a regular repetitive pattern and other members and the like has a similar regular repetitive structure. 
     Japanese Patent Application Laid-Open No. 2000-206529 discloses moire fringes as mentioned above and a method of reducing such moire fringes. 
     An optical sheet having a structured pattern of a regular pitch may be used as a launching member for guiding light from a backlight to a liquid crystal panel. In this case, overlapping of pixels forming the regular pitch of the liquid crystal panel and the structured pattern of the optical sheet overlaps light and dark lattices and causes moire fringes to be produced. A liquid crystal display device disclosed in JP-A No. 2000-206529 is arranged to reduce the moire fringes by configuring an array pitch of pixels and the pitch of the structured pattern of the optical sheet so as to minimize a pitch distance of the moire fringes. In other words, the liquid crystal display device is arranged to reduce effects of the moire fringes on the image quality by minimizing the pitch distance of the moire fringes and thus decreasing the pitch distance to a level not more than resolution of human eye. 
     SUMMARY OF THE INVENTION 
     Though the liquid crystal display device described in JP-A No. 2000-206529 may reduce the effects of the moire fringes on visibility and the like, actually the moire fringes may appear. Moreover, it is difficult to adjust the array pitch of the pixels, since there is a need for modifying a design of the liquid crystal panel itself and a manufacturing line of the liquid crystal panel. Thus, a technique has been developed to suppress moire fringes per se from being produced. 
     JP-A No. 2000-284268 and JP-A No. 2007-256575 disclose some techniques to suppress moire fringes per se from being produced. JP-A No. 2000-284268 and JP-A No. 2007-256575 propose transparent liquid crystal display devices, respectively, in which each of the transparent liquid crystal display devices includes a backlight unit using a brightness control member having a lens array structure containing repetitive lens unit. Each of the liquid crystal display devices includes a liquid crystal panel and a light source unit for emitting light from a back side of (immediately below) the liquid crystal panel. The light source unit also includes a light source, a lens array layer for guiding the light from the light source to the liquid crystal panel, and a light shielding section having an opening arranged close to a focal plane of the lens array layer (i.e., a back surface opposite to a surface on which a lens array is formed). With this arrangement, as described in JP-A No. 2000-284268 and JP-A No. 2007-256575, the moire fringes are suppressed from being produced by converting the light from the light source into parallel light to reduce a structured pattern of an optical sheet. 
     It is difficult, however, to sufficiently suppress the moire fringes from being produced using the lens array layer as described above. In other words, since the lens array layer per se also has a regular structured pattern and the regular structured pattern has effects on the parallel light, it is difficult to convert the light from the light source into perfectly parallel light. 
     Therefore, the present invention has been made in view of the above-mentioned issues, and it is desirable to provide a new and improved lens array sheet, light source and liquid crystal display device in which it is possible to suppress degradation of the image quality and reduce effects of moire fringes on the image quality. 
     According to an embodiment of the present invention, in order to solve the above-mentioned issues, there is provided a lens array sheet including a lens layer having a lens surface on which a plurality of lenses are formed in an array, a light reflection layer arranged at an opposite side to the lens surface of the lens layer and having an opening within a light focusing region in the lenses to transmit light, for reflecting light at a site other than the opening, and a light diffusion layer arranged between the lens layer and the light reflection layer, for diffusing light, which passes through the opening and is directed toward the lens layer. 
     With this arrangement, light emitted from a side of the light reflection layer to the lens array sheet is in part reflected at the light reflection layer. In addition, a part of the light emitted to the light focusing region in the plurality of lenses passes through the opening. The light having passed through the opening is diffused by the light diffusion layer before the light reaches the lens layer. Then, the diffused light reaches the lens layer and converted into generally parallel light by means of the plurality of lenses. It is noted that the light to be converted into the generally parallel light is diffused. As a result, after conversion into the generally parallel light by means of the lenses, the light turns out to be the generally parallel light, while brightness change of the light between dark and light intensity due to an array pattern of the plurality of lenses in the lens layer is reduced. 
     The light diffusion layer may also include a plurality of light diffusion portions arranged within the light focusing region in the lenses, for diffusing the light passing through the opening and directing toward the lens layer and transparent portions arranged between the light diffusion portions, for transmitting the light. 
     Each of the light diffusion portion may also have a shape such that a width of the shape gradually widens as the width approaches to the lens layer. 
     The lens array sheet may also include a transparent layer arranged between the light diffusion layer and the light reflection layer, for transmitting the light. 
     The lens array sheet may also include a transparent layer arranged between the lens layer and the light diffusion layer, for transmitting the light. 
     A haze of the light diffusion layer may be equal to or less than 20%. 
     The light reflection layer may be a scatter and reflection layer for scattering light in order to reflect the light. 
     The light reflection layer may not be formed at least around the lens array sheet. 
     A lenticular lens may also be formed on the lens surface of the lens layer in which the lenticular lens includes a plurality of convex cylindrical lenses arranged in parallel to each other and at a predetermined distance. 
     According to another embodiment of the present invention, in order to solve the above-mentioned issues, there is provided an optical sheet including a lens array sheet having a lens surface on which a plurality of lenses are formed in an array, and a light diffusion plate arranged at an opposite side to the lens surface of the lens array sheet, for diffusing light directing toward to the lens array sheet, wherein the lens array sheet includes a lens layer having the lens surface, and a light reflection layer arranged at an opposite side to the lens surface of the lens layer and having an opening within a light focusing region in the lenses to transmit light from the light diffusion plate, for reflecting light at a site other than the opening, and a light diffusion layer arranged between the lens layer and the light reflection layer, for diffusing the light passing through the opening and directing toward the lens layer. 
     The optical sheet may also include a polarization splitting film arranged at a lens surface side of the lens array sheet, for polarization splitting light. 
     The optical sheet may also include a light diffusion sheet arranged at least one of between the polarization splitting film and the lens array sheet and between the lens array sheet and the light diffusion plate, for diffusing light. 
     Furthermore, according to another embodiment of the present invention, in order to solve the above-mentioned issues, there is provided a light source including a lens array sheet having a lens surface on which a plurality of lenses are formed in an array, and a backlight arranged at an opposite side to the lens surface of the lens array sheet, for emitting light on the lens array sheet, wherein the lens array sheet includes a lens layer having the lens surface, a light reflection layer arranged at an opposite side to the lens surface of the lens layer and having an opening within a light focusing region in the lenses to transmit the light emitted from the backlight, for reflecting light at a site other than the opening, and a light diffusion layer arranged between the lens layer and the light reflection layer, for diffusing the light passing through the opening and directing toward the lens layer. 
     Furthermore, according to another embodiment of the present invention, in order to solve the above-mentioned issues, there is provided a liquid crystal display device including a lens array sheet arranged between a liquid crystal panel and a backlight emitting light on the liquid crystal panel and having, at a side of the liquid crystal panel, a lens surface on which a plurality of lenses are formed in an array, wherein the lens array sheet includes a lens layer having the lens surface, a light reflection layer arranged at an opposite side to the lens surface of the lens layer and having an opening within a light focusing region in the lenses to transmit the light emitted from the backlight, for reflecting light at a site other than the opening, and a light diffusion layer arranged between the lens layer and the light reflection layer, for diffusing the light passing through the opening and directing toward the lens layer. 
     According to the embodiments of the present invention described above, effects of moire fringes on the image quality can be reduced while suppressing the image quality being degraded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory diagram for explaining a configuration of a lens array sheet according to a first embodiment of the present invention; 
         FIG. 2  is an explanatory diagram for explaining a configuration of the lens array sheet according to the embodiment; 
         FIG. 3  is an explanatory diagram for explaining a configuration of a lens array sheet according to a second embodiment of the present invention; 
         FIG. 4  is an explanatory diagram for explaining a configuration of a lens array sheet according to a third embodiment of the present invention; 
         FIG. 5  is an explanatory diagram for explaining a configuration of a lens array sheet according to a fourth embodiment of the present invention; 
         FIG. 6  is an explanatory diagram for explaining a configuration of a lens array sheet according to a fifth embodiment of the present invention; 
         FIG. 7  is an explanatory diagram for explaining a configuration of a lens array sheet according to a sixth embodiment of the present invention; 
         FIG. 8  is an explanatory diagram for explaining a configuration of the lens array sheet according to the embodiment; 
         FIG. 9  is an explanatory diagram for explaining a configuration of a lens array sheet according to a seventh embodiment of the present invention; 
         FIG. 10  is an explanatory diagram for explaining a configuration of a lens array sheet according to an eighth embodiment of the present invention; 
         FIG. 11  is an explanatory diagram for explaining a configuration of a lens array sheet according to a ninth embodiment of the present invention; 
         FIG. 12  is an explanatory diagram for explaining a configuration of the lens array sheet according to the embodiment; 
         FIG. 13  is an explanatory diagram for explaining a configuration of a lens array sheet according to a tenth embodiment of the present invention; 
         FIG. 14  is an explanatory diagram for explaining a configuration of a liquid crystal display device according to an eleventh embodiment of the present invention; and 
         FIG. 15  is an explanatory diagram for explaining a configuration of a liquid crystal display device according to a twelfth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the appended drawings. Note that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted. 
     First, a lens array sheet according to each of embodiments of the present invention will now be described. Then, an optical sheet, a light source, and a liquid crystal display device using these lens array sheets will be described. 
     The lens array sheet according to each of the embodiments of the present invention includes a layer or a site for diffusing light, for example, to reduce effects of moire fringes on the image quality while suppressing the image quality from being degraded. In addition, the embodiments of the present invention may be classified into two groups depending on a shape or an arrangement position of a light diffusion layer or site, other structures and the like. Consequently, embodiments (i.e., a first embodiment to a sixth embodiment) concerning one group of the present invention will be first described and other embodiments (i.e., a seventh embodiment to a tenth embodiment) of the present invention will be then described. It is noted that since those embodiments have many common elements, repeated explanation of the same contents in subsequent embodiments will be conveniently omitted and the differences between the embodiments will be described. 
     Lens Array Sheet  101  According to First Embodiment 
     Referring to  FIG. 1  and  FIG. 2 , a configuration of a lens array sheet according to the first embodiment of the present invention will now be described.  FIG. 1  and  FIG. 2  illustrate the configuration of the lens array sheet according to this embodiment. In  FIG. 1  and  FIG. 2 , schematic sectional shape and configuration of the lens array sheet according to this embodiment are shown, respectively. It is noted that the sectional shape of a right-side end portion of the lens array sheet  101  is shown and a part of the lens array sheet  101  located at a left side of a line A-A is omitted in  FIG. 1 . 
     &lt;Configuration of Lens Array Sheet  101 &gt; 
     As shown in  FIG. 1 , the lens array sheet  101  according to this embodiment includes a three-layered structure formed in one piece. That is to say, the lens array sheet  101  includes a lens layer  10 , a light diffusion layer  20 A, and a light reflection layer  30 . 
     The lens layer  10  has a lens surface  11  on which a plurality of individual lenses (hereinafter, also referred to as “lenses”) U are formed in an array. A surface opposite to the lens surface  11  of the lens array sheet  101  has a generally flat shape. Hereinafter, this surface is also referred to as a “flat surface”. 
     In terms of the lens layer  10 , for example, one lens array sheet is configured such that the lenses U are formed in a one-dimension array within the lens surface  11  and another lens array sheet is configured such that the lenses U are formed in a two-dimension array within the lens surface  11 . On one hand, the lens array sheet in the form of the one-dimension array includes, for example, a lenticular lens array sheet on which convex cylindrical lenses are arranged in one direction in an array within the lens surface  11  and the like. On the other, the lens array sheet in the form of the two-dimension array includes, for example, a lens array sheet on which the lenses U are arranged in a two-dimension array within the lens surface  11  and the like, wherein each of the lenses U has a circular, rectangular, hexagonal, or polygonal shape or the like and is formed of a dome-shaped curved surface. 
     The plurality of lenses U, which are formed on the lens surface  11  of the lens layer  10 , are regularly arranged with a predetermined distance (pitch) either in one direction in case of the one-dimensional array or in two directions in case of the two-dimensional array. 
     Each of the lenses U has a focal point F on the side of the flat surface. By arranging a light source at the focal point F and emitting light to the lens U, this light is converted into parallel light directing along a normal direction of the lens surface  11  by means of the lens U. In  FIG. 1 , an optical path P denotes the light to be converted into the parallel light. As to the focal point F and the optical P, it can be said that each of the lenses U focuses the parallel light on the focal point F in case where the parallel light is emitted from the upper part of this drawing. A region through which the light being focused on the focal point F passes is herein referred to as a “light focusing region G”. A region other than the light focusing region G is also herein referred to as a “non-light focusing region N”. Furthermore, surfaces in parallel with the lens array sheet  101  in the light focusing region and the non-light focusing region are referred to as a “light focusing surface region” and a “no-light focusing surface region”, respectively. 
     The lens layer  10  may be made of a material such as glass and plastic material, but the present invention is not limited to such an example. Examples of the plastic material include, for example, homopolymer or copolymer of acrylic ester or methacrylic ester such as methyl polymethacrylate and methyl polyacrylate, and a resin material of polyester, polycarbonate, polystyrene and the like such as polyethylene terephthalate and polybutylene terephthalate. 
     The light diffusion layer  20 A is laminated on the flat surface of the lens layer  10  and formed integrally with the lens layer  10 . In short, the light diffusion layer  20 A is arranged between the lens layer  10  and the light reflection layer  30 . Thus, the light diffusion layer  20 A diffuses light, which passes through the light diffusion layer  20 A. A part of the light diffusion layer  20 A is herein referred to as a “light diffusion portion  21 ”. To achieve such light diffusion layer  20 A diffusing the light, for example, a layer can be used that disperses a diffusion agent in a light transparent resin and utilizes a light scattering effect due to the difference in refractive index between the diffusion agent and the light transparent resin. 
     On one hand, for example, it is possible to use beads or filler, or hollow beads mainly containing acryl resin, polystyrene, polyethylene, urea resin, urethane resin, organic silicone resin, calcium carbonate, titanium oxide, silica and the like as the diffusion agent. Desirably, an average particle size of the diffusion agent is, for example, in the range of about 1 to 50 μm so that the diffusion agent is easy to use. In addition, a combination of two or more kinds of diffusion agents may be used having different types and particle sizes. 
     On the other, for example, it is possible to use polyester resin, acrylic resin, polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyethylene resin, polypropylene resin, polyurethane resin, polyamide resin, polyvinyl acetate resin, polyvinyl alcohol resin, epoxy resin, cellulose resin, silicone resin, polyimide resin, polysulfone resin, polyarylate resin and the like as the light transparent resin. 
     In addition, preferably, a material having refractive index lower than that of the lens layer  10  may be used as the light transparent resin among the above-mentioned materials. Using such material enables a light beam to be directed more closely to a normal direction of the sheet due to the difference in the refractive index, as the light is incident from the light diffusion layer  20 A to the lens layer  10 . Therefore, the lens U in the lens layer  10  can work just as designed to develop lens effects (including an effect of changing an optical path and the like). 
     In addition, preferably, the light diffusion layer  20 A has a haze of not more than 20%. In case of the haze being above 20%, since a light diffusion effect of the haze on the light diffusion layer  20 A becomes stronger and an amount of light passing through the lens array sheet  101  decreases, front face brightness may probably goes down. Furthermore, in case of the haze being above 20%, it may be difficult to achieve a light focusing effect via the lens layer  10 . In addition, a haze value of the light diffusion layer  20 A may be adjusted by selecting materials of the diffusion agent and the light transparent resin, respectively, and adjusting the average particle size of the diffusion agent. 
     The light reflection layer  30  is laminated on a surface opposite to a surface that contacts with the lens layer  10  of the light diffusion layer  20 A, and formed integrally with the light diffusion layer  20 A. In short, the light reflection layer  30  is arranged at a side of the surface opposite to the lens surface  11  of the lens layer  10 . Then, the light reflection layer  30  reflects light at the light reflection portion  31 . In this case, the light reflection portion  31  may be formed as a scattering reflection layer, for example, that reflects light by scattering the light. Although, such light reflection portion  31  that reflects the light may be, for example, made of a metal material such as aluminum, silver, zinc, and the like, various materials may be used as the material of the light reflection portion  31 , the present invention is not limited to such an example. 
     The light reflection layer  30  has an opening  32  through which light passes. In short, light emitted from the lower part of this drawing passes through the opening  32  and reaches the light diffusion layer  20 A. The light diffusion layer  20 A then diffuses light that passes through the opening  32  and directs toward the lens layer  10 . 
     The opening  32  is formed within the light focusing region of the lens U at a location corresponding to a top site of the lens U. In this case, desirably, the opening  32  is not formed in the non-light focusing region. That is to say, for example, in the case where light is emitted by arranging a light source at a focal point F, the opening  32  is configured such that it transmits at least a part of one light passing through the light focusing region G of each of the lenses U and does not transmit the other light including light that passes through the non-light focusing region N. As shown in  FIG. 1 , the opening  32  transmits all of lights that run through the light focusing region, but a size of the opening  32  according to this embodiment is not limited to such an example. For example, the size of the opening  32  may be such that it does not transmit the light that passes through the non-light focusing region N or such that it transmits the part of the light that passes through the light focusing region G. If the size of the opening  32  is sufficiently large so as to reach the non-focusing region N, then a light component that can be rarely sufficiently restricted is increased. In this case, a light component that is not converted into parallel light by the lens U (i.e., light that is not emitted along a normal direction of the sheet) increase. To the contrary, if the size of the opening  32  is made small even within the light focusing region G, a light component, which is restricted to the focal point F in a more uniform way, is incident on the lens U and light emitted from the lens layer  10  more and more approximates parallel light. In this case, however, a variation of an amount of an emitted light may probably increase. Therefore, shapes and sizes of the lens U and the opening  32 , respectively, are desirably determined based on performance requested for the lens array sheet  101  (i.e., conversion efficiency, an amount of light to be transmitted (front face brightness) and the like), a size of the lens array sheet  101  or a positional relation between the lens array sheet  101  and the light source and the like. Thus, sectional shapes of the lens U and the opening  32 , respectively, may be any shape such as square, circle, ellipse, rectangular, diamond, polygon or the like. Furthermore, the sectional shapes of the lens U and the opening  32 , respectively, may be, for example, formed in a band shape that is continuously extended along one direction (such lens is referred to as a lenticular lens). In other words, the shape of the opening  32  may be formed in a shape corresponding to a light focusing surface of the lens U. 
     Since the light reflection layer  30  has this opening  32 , the light reflection layer  30  can mainly transmit light, which is to be converted into generally parallel light by the lens U, that is to say, which approximately passes through the focal point F and reflect many other lights that would not be converted into the generally parallel light. Therefore, since the lens array sheet  101  has the light reflection layer  30 , the lens array sheet  101  can enhance an effect of the lens layer  10  and convert the light into the generally parallel light. 
     In addition, the light reflection layer  30  (light reflection portion  31 ) that reflects light is, desirably, not formed at an end, that is to say, at a periphery E of the lens array sheet  101 . In other words, it can be said that the light reflection layer  30  has another opening at the periphery E of the lens array sheet  101 . An amount of light passing through the periphery E of the lens array sheet  101  is expected to be less than that of light passing through a center of the lens array sheet  101 . Therefore, the light reflection layer  30  does not reflect the light passing through the periphery E so that it can suppress a reduction of the amount of the light in the periphery E. In addition, the light focusing effect that converts the light into the generally parallel light by the lens layer  10  is weakened by suppressing the light reflection layer  30  from being formed on the periphery E. As a result, a production of moire fringes would also be restricted in the periphery E. In addition to the light reflection layer  30 , the lens U of the lens layer  10  may be omitted from the periphery E of the lens sheet array  101 . 
     &lt;Example of Dimensions for Lens Array Sheet  101 &gt; 
     Hereinbefore, a configuration of the lens array sheet  101  according to this embodiment have been described. Referring to  FIG. 2 , exemplary dimensions of each of configurations in this lens array sheet  101  will now be described. 
     In  FIG. 2 , a lens layer  10 , a light diffusion layer  20 A and a light reflection layer  30  corresponding to one lens U are shown. A width of a single lens is denoted by L, a distance from a flat surface of the lens layer  10  to a focal point F is denoted by S, a thickness of the light diffusion layer  20 A is d, and a width of a light reflection portion  31  corresponding to the single lens U is denoted by Wr. The width Wr of the light reflection portion  31  then can be set to satisfy the following condition (Formula 1). 
                   Wr   ≥     {             L   ×   d       2   ×   S           …           in   ⁢           ⁢   case   ⁢           ⁢   S     ≥   d               L   ⁡     (     1   -     d     2   ×   S         )           …           in   ⁢           ⁢   case   ⁢           ⁢   S     ≤   d                     (     Formula   ⁢           ⁢   1     )               
(Example of Method for Forming Lens Array Sheet  101 )
 
     Hereinafter, an example of a method for forming a lens array sheet  101  according to this embodiment will be described. The method for forming the lens array sheet as described herein is merely one example, but is riot intended to limit the present invention. Naturally, the lens array sheet  101  may be formed using various other methods. In addition, an example in which a lenticular lens array is used as the lens layer  10  is described, different lenses U having other shapes can also be formed. 
     First, the lens layer  10  is formed. 
     The method for forming the lens layer  10  may be any methods including, for example, a method using a mold having a shape corresponding to the lens U, a method for transferring a shape of an nickel stamper having a shape corresponding to the lens U by a heating press process, a method for applying an ultraviolet curing resin or an electron curing resin on a transparent substrate etc., embossing the resin by an embossing roll of a shape corresponding to the lens U, and thereafter curing the resin using ultraviolet ray or electron ray, and a method for forming a lens by forming a photoresist pattern with a pitch of the lens U by photolithography and heating and melting the photoresist, and the like. 
     Next, the light diffusion layer  20 A is laminated on a flat surface opposite to the lens surface  11  of the lens layer  10 . In short, the light diffusion layer  20 A is formed integrally with the lens layer  10  by either applying a material of the light diffusion layer  20 A on the lens surface  11  and curing the material or laminating cured layers. 
     Thereafter, the light reflection layer  30  having the light reflection portion  31  and the opening  32  is also laminated on the light diffusion layer  20 A. A method for forming the light reflection layer  30  includes, for example, laminating an ultraviolet curing resin film on the light diffusion layer  20 A to form an adhesive ultraviolet curing resin layer. Then, a parallel ultraviolet light is emitted to the lens surface  11 . As a result, the ultraviolet curing resin layer in a light focusing region G to which the parallel light is emitted is cured. A transfer sheet, on which a metal material forming the light reflection layer has been applied, is then pressurized such that the metal material is opposite to the ultraviolet curing resin layer. After that, by peeling the transfer sheet, the metal material (light reflection portion  31 ) is attached to a non-light focusing region N using an adhesive of the ultraviolet curing resin layer in a non-curing part. The non-curing part of the ultraviolet curing resin layer is then exposed to a ultraviolet light so that the non-curing part can be cured. During this time, the ultraviolet light may be radiated, for example, from an opposite side of the lens surface  11 . Consequently, the light reflection layer  30  having the opening  32  in the light focusing region G is formed integrally at a back side of the light diffusion layer  20 A (a surface opposite to the lens layer  10 ). 
     The method for forming the lens array sheet  101  is described by way of example only, as described above, and is not indented to limit the present invention. In addition, forming the light reflection layer  30  is herein described in terms of using the ultraviolet curing resin, but the light reflection layer  30  can be formed by various ways such as a photolithography method, a metal evaporation method, a metal printing method, a transfer method, a sputtering method, an ion plating method, a method for laminating predetermined shaped metals, and the like. 
     (Example of Advantages of Lens Array Sheet  101 ) 
     The configuration of the lens array sheet  101  according to the first embodiment of the present invention have been described as above. With this lens array sheet  101 , for example, when the light source is arranged at the side of the light reflection layer  30  and the light is emitted from the light source, light incident on the lens layer  10  is restricted to the focal point F. Thus, the lens array sheet  101  enables the generally parallel light to be emitted from a direction of the lens surface  11  of the lens layer  10 . In this case, the emitted generally parallel light includes light diffused by the light diffusion layer  20 A. Therefore, the lens array sheet  101  can reduce light having a similar pattern as a regular pattern of the lens U or a pattern of the light reflection layer  30  and included in the generally parallel light (i.e., the lens array sheet  101  can reduce a pattern of brightness uniformity, a directional pattern or the like). As a result, even if; for example, a liquid crystal panel is arranged in front of the lens array sheet  101 , the lens array sheet  101  can reduce a regular light pattern, which produces moire fringes with a regular structured pattern of the liquid crystal panel, and can suppress the moire fringes from being produced. 
     Advantages of the lens array sheet, such as suppression of the moire fringes and the like, will be described in detail with reference to an example in which the lens array sheet  101  is used for a liquid crystal display device. 
     A usual liquid crystal display device has a liquid crystal panel and a light source emitting light to the liquid crystal panel. In addition, it is desirable that the light is restricted to a direction towards a front surface of the liquid crystal display device in order to improve visibility of the liquid crystal display device. As mentioned above, the lens array sheet  101  according to this embodiment can irradiate the light, which is restricted to the focal point F by the light reflection layer  30 , on the lens layer  10  so that the generally parallel light can be emitted from the lens layer  10 . Thus, the lens array sheet  101  can improve the visibility of the liquid crystal display device. 
     In this case, the liquid crystal display device has regularly arranged pixels. Thus, moire fringes can be produced when an arrangement pitch of the pixels and the structured pattern of the lens array sheet overlap. In this case, if a light focusing effect of the lens of the lens array sheet were uniformly achieved, then production of the moire fringes would be rather facilitated. However, the lens array sheet  101  according to this embodiment has the light diffusion layer  20 A between the light reflection layer  30  and the lens layer  10 . This light diffusion layer  20 A diffuses light incident on the lens layer  10 . In this manner, since the diffused light is incident on the lens layer  10 , the light focusing effect of the lens decreases and the moire fringes are suppressed from being produced. 
     However, if the light focusing effect of the lens (a bright improving effect, a light distribution effect or the like) is too much suppressed, then a component of the generally parallel light, which is emitted from the lens array sheet, may decrease, an amount of the light, which may be emitted to a front surface of the liquid crystal display device, and visibility of the liquid crystal may be degraded. To the contrary, in the lens array sheet  101  according to this embodiment, the light diffusion layer  20 A diffuses light directing toward the lens layer  10  after the light has been restricted to the focal point F by the light reflection layer  30  and immediately before the light is incident on the lens layer  10 . Therefore, the light incident on the lens layer  10  would not be significantly diffused. Consequently, the lens array sheet  101  can maintain the light focusing effect of the lens to the extent that the visibility is not degraded while suppressing the moire fringes from being produced. 
     In addition, it is also conceivable that a light diffusion plate is arranged outside the lens array sheet  101  in order to diffuse light if it is solely intended to cancel parallel light and suppress moire fringes from being produced. In this case, with regard to an arrangement position of the light diffusion plate being arranged outside the lens array sheet, it is conceivable that the light diffusion plate may be arranged on a side of the lens surface  11  of the lens layer  10  or on a side of the light reflection layer  30 . However, if sufficiently many diffusion plates, which diffuse light, to suppress the moire fringes from being produced is arranged out side the lens array sheet  101 , a number of interfaces between layers increase. As a result, due to reflection on the interfaces between the layers, an amount of light, which follows an unexpected optical path, significantly increase so as to suppress effects such as a light focusing effect of the lens etc., a brightness improving effect, a light distribution effect or the like, and light use efficiency would be reduced. In addition, if these effects are reduced, it becomes difficult to determine a correlation between design factors and the effects, and thereby complicate the design of the lens array sheet itself. Consequently, it would be difficult to provide an optimal structure. To the contrary, in case of the lens array sheet  101  according to this embodiment, the optical path will not be extremely complicated by providing the light diffusion layer  20 A between the lens layer  10  and the light reflection layer  30 . Therefore, it is possible to appropriately suppress the moire fringes from being produced without encountering the above-mentioned issues. 
     Differently from this embodiment, in case where the light diffusion plate for diffusing the light is arranged outside on the side of the lens array sheet  101 , it leads to an increase of manufacturing cost as a number of members increase by one. In addition, in case where, for example, the light diffusion plate is arranged out side of the lens surface  11  of the lens layer  10 , a generally parallel light component will decrease. Therefore, the visibility of the liquid crystal display device probably degrade. However, the lens array sheet  101  according to this embodiment has the light diffusion layer  20 A between the lens layer  10  and the light reflection layer  30 , thereby avoiding the above-mentioned issues. 
     In addition, in case where the light diffusion plate is arranged outside on the of the light reflection layer  30 , the light widely scattered by the light diffusion plate passes through an opening  32 , which is different from a desired opening  32 , or be incident on a lens U, which is different from a lens U corresponding to the opening  32  through which the light passes. As a result, the effect that the light is restricted to the focal point F by the light reflection layer  30  will be weakened and some effects such as a light focusing effect of the lens layer  10  will be also weakened. From this point of view, a position, at which the light is diffused, is preferably located near (in particular, immediately in front of) the lens layer  10  as illustrated in this embodiment. According to the light diffusion layer  20 A of this embodiment, it is possible to diffuse light, while suppressing the light from being incident on a lens U, which is different from a lens U corresponding to an opening  32  through which the light passes. 
     An example of the advantages of the lens array sheet  101  according to this embodiment as herein described is also true for other embodiments as described hereinafter. Therefore, for an explanation of the other embodiments described below, in addition to the advantages of the lens array sheet  101  according to this embodiment, further advantages of it will now be explained. 
     Hereinbefore, the lens array sheet  101  according to the first embodiment of the present invention has been described. In addition, in the context of this lens array sheet  101 , it has been described that a haze value of the light diffusion layer  20 A may be adjusted by selecting a material of the light diffusion layer  20 A and the like. However, an available material of the light diffusion layer  20 A may be limited depending on, for example, cost of the material, unavailability of the material, convenience of the design, and the like. When a thick of the light diffusion layer  20 A becomes very thick, diffusion property of the light diffusion layer  20 A becomes too high to control the light. That is to say, light rather than light directing toward a desired direction would be incident on the lens U. In these cases, other embodiments, in which the haze value and the diffusion property are, in particular, controlled usefully and appropriately and other advantages are achieved, will now be described with reference to  FIG. 3 . 
     Lens Array Sheet  102  According to Second Embodiment 
       FIG. 3  is an explanatory diagram for explaining a configuration of a lens array sheet  102  according to a second embodiment of the present invention. 
     (Configuration of Lens Array Sheet  102 ) 
     As shown in  FIG. 3 , the lens array sheet  102  according to this embodiment includes a transparent layer  40  in addition to configurations included in the lens array sheet  101  according to the first embodiment. 
     The transparent layer  40  is arranged between a light diffusion layer  20 A and a light reflection layer  30  and formed integrally with the light diffusion layer  20 A and the light reflection layer  30 . In addition, the transparent layer  40  transmits light between the light diffusion layer  20 A and the light reflection layer  30 . A part of the transparent layer  40  is herein also referred to as a “transparent portion  41 ”. Though the transparent portion  41  is shown such that it is arranged between the light diffusion layer  20 A and the light reflection  30  with reference to this embodiment, the transparent portion  41  may be arranged, for example, between a lens layer  10  and the light diffusion layer  20 A. 
     The transparent layer  40  may be made of a material such as glass and plastic material as is the case with the lens layer  10 , but the present invention is not limited to such an example. 
     (Example of Method for Forming Lens Array Sheet  102 ) 
     Such transparent layer  40  may be formed, for example, by laminating the transparent layer  40  on the light diffusion layer  20 A before forming the light reflection layer  30  in the lens array sheet  101  according to the first embodiment. Of course, the method for forming the lens array sheet is not intended to limit the present invention. 
     (Example of Advantages of Lens Array Sheet  102 ) 
     Hereinbefore, a configuration of the lens array sheet  102  and the like according to the second embodiment of the present invention have been described. This lens array sheet  102  has an advantage in that it enables a haze value of the light diffusion layer  20 A to be adjusted without changing a total thickness of the lens array sheet  102  by adjusting a thickness of the light diffusion layer  20 A in addition to the advantages achieved by the lens array sheet  101  according to the first embodiment. The lens array sheet  102  also makes it possible to make use of effects, such as a reflection effect, a diffusion effect and the like, which utilize a further added interface between the light diffusion layer  20 A and the transparent layer  40 . 
     Referring to  FIG. 4 , a third embodiment making use of such interface will now be described. 
     Lens Array Sheet  103  According to Third Embodiment 
       FIG. 4  is an explanatory diagram for explaining a configuration of a lens array sheet according to a third embodiment of the present invention. 
     (Configuration of Lens Array Sheet  103 ) 
     A lens array sheet  103  according to this embodiment includes a light diffusion layer  20 B in place of the light diffusion layer  20 A included in the lens array sheet  101  according to the first embodiment. The light diffusion layer  20 B has a light diffusion portion  21  similar to a part of the light diffusion layer  20 A according to the first embodiment and a transparent portion  41  similar to a part of the transparent layer  40  according to the second embodiment. 
     In one hand, the light diffusion portion  21  is arranged in a light focusing region G of a lens U and diffuses light passing through an opening  32  of a light reflection layer  30  and directing toward a lens layer  10 . On the other, the transparent portion  41  is arranged between light diffusion portions  21  and transmits the light. 
     (Example of Method for Forming Lens Array Sheet  103 ) 
     Such light diffusion layer  20 B may be formed, for example, by forming the light diffusion layer  21  and forming the transparent portion  41  between the light diffusion portions  21  before forming the light reflection layer  30  in the lens array sheet  101  according to the first embodiment. In addition, the light diffusion portion  21  may be either formed by removing a part of the light diffusion layer  20 A using a photolithography or sputtering method, or formed by using other printing method, transfer method or the like. Alternatively, it is possible to firstly form the light diffusion layer  20 B and then form the lens layer  10  and the light reflection layer  30 . Of course, the method for forming the lens array sheet is not intended to limit the present invention. 
     (Example of Advantages of Lens Array Sheet  103 ) 
     Hereinbefore, a configuration of the lens array sheet  103  and the like according to the third embodiment of the present invention has been described. This lens array sheet  103  has an advantage in that it enables a haze value of the light diffusion layer  20 B to be adjusted without changing a total thickness of the lens array sheet  103  by adjusting a width of the light diffusion portion  21  in addition to the advantage achieved by the lens array sheet  101  according to the first embodiment. In addition, the lens array sheet  103  forms two interfaces between light focusing regions of one lens U and the other lens U, as the lens array sheet  103  has the transparent portion  41  between one and the other lenses U. These interfaces enable a part of light which is reflected from one of the light diffusion portions  21  and directs to a lens U other than a lens U corresponding to the one of the light diffusion portions  21 , to be reflected toward the lens U corresponding to the one of them. Therefore, the lens array sheet  103  enables a light use efficiency to be improved and also enables a light focusing effect of the lens layer  10  to be improved. 
     In addition, it is possible to combine the lens array sheet  103  according to this embodiment with a configuration of the lens array sheet  102  according to the second embodiment of the second embodiment. For this purpose, a fourth embodiment and a fifth embodiment of the present invention will be now described, which combine those lens array sheet as described above, respectively. 
     Lens Array Sheets  104  and  105  According to Fourth and Fifth Embodiments 
       FIG. 5  is an explanatory diagram for explaining a configuration of a lens array sheet according to a fourth embodiment of the present invention.  FIG. 6  is an explanatory diagram for explaining a configuration of a lens array sheet according to a fifth embodiment of the present invention. 
     (Configuration of Lens Array Sheets  104  and  105 ) 
     On one hand, a lens array sheet  104  according to the fourth embodiment has a transparent layer  40  between a lens layer  10  and a light diffusion layer  20 B, as shown in  FIG. 5 . On the other, as shown in  FIG. 6 , a lens array sheet  105  has a transparent layer  40  between a light diffusion layer  20 B and a light reflection layer  30 . 
     (Example of Method for Forming Lens Array Sheets  104  and  105 ) 
     Such lens array sheets  104  and  105  can be formed by combining a method for forming a lens array sheet  102  according to the second embodiment and a method for forming a lens array sheet  103  according to the third embodiment. Of course, the method for forming the lens array sheets  104  and  105  is not intended to limit the present invention. 
     (Example of Advantages of Lens Array Sheets  104  and  105 ) 
     Hereinbefore, a configuration of the lens array sheet  104  and  105  and the like according to the fourth and fifth embodiments of the present invention, respectively, have been described. These lens array sheets  104  and  105  can have advantages resulting from a combination of the advantages achieved by the lens array sheet  102  according to the second embodiment and the lens array sheet  103  according to the third embodiment, respectively. In particular, in case of the lens array sheet  105  according to the fifth embodiment, the light diffusion portion  21  diffuses light immediately before the light is incident on the lens layer  10 . Therefore, it becomes less likely that light passing through an opening  32  may penetrate into a lens U other than a lens U corresponding the opening  32 , and the light diffusion portion  21  also enables a light use efficiency to be improved. 
     In the above mentioned third, fourth and fifth embodiments, it is shown that a light diffusion portion  21  is not a single layer, but has a transparent portion  41  inserted between layers of the light diffusion portion  21 , and a shape of the light diffusion portion  21  (i.e., a shape of the transparent portion  41 ) is not particularly limited. However, by changing the shape of the light diffusion portion  21 , a further advantage can be achieved. Then, referring to  FIGS. 7 and 8 , a sixth embodiment will now be explained in which the sixth embodiment is based on the third embodiment and is modified such that a shape of the light diffusion portion  21  is changed. Of course, the fourth embodiment and the fifth embodiment other than the third embodiment may be similarly modified. 
     Lens Array Sheet  106  According to Sixth Embodiment 
       FIG. 7  is an explanatory diagram for explaining a configuration of a lens array sheet according to a sixth embodiment of the present invention. 
     (Configuration of Lens Array Sheet  106 ) 
     A lens array sheet  106  according to this embodiment has a light diffusion layer  20 C in place of a light diffusion layer  20 B included in a lens array sheet  103  according to the third embodiment as shown in  FIG. 7 . In addition, the light diffusion layer  20 C has a light diffusion portion  22  and a transparent portion  42 . 
     The light diffusion portion  22  may be formed as in the case of the light diffusion portion  21 , as described above, except for its shape and correspondingly the transparent portion  42  may be formed as in the case of the transparent portion  41 , as described above, except for its shape. 
     The light diffusion portion  22  is arranged in a light focusing region G of a lens U and has a shape (a width in a direction of a plane in a lens array sheet  106 ) gradually widening toward a lens layer  10 . In other words, the light diffusion portion  22  has a shape following the light focusing region G in the light focusing region of individual lenses U. In short, for example, the light diffusion portion  22  may be formed in a truncated cone shape when a section of the lens U is circular and formed in a polygonal frustum shape when the section of the lens U is polygonal. In addition, the light diffusion portion  22  diffuses light passing through an opening  32  of a light reflection layer  30  and directing toward the lens layer  10 . Furthermore, the transparent portion  42  is arranged between light diffusion portions  21  and transmits light. 
     (Example of Dimensions of Lens Array Sheet  106 ) 
     Hereinbefore, a configuration of the lens array sheet  106  according to this embodiment have been described. 
     Referring to  FIG. 8 , an example of dimensions of individual configurations in the lens array sheet and the like will now be described. 
       FIG. 8  illustrates a lens layer  10 , a light diffusion layer  20 C and a light reflection layer  30  corresponding to a single lens U. A width of a single lens is denoted by L, a distance from a flat surface of the lens layer  10  to a focal point F is denoted by S, and a width of a light reflection portion  31  corresponding to the single lens U is denoted by Wr. In addition, a depth from the lens layer  10  in the light diffusion layer  20 C is denoted di, and a width of the light diffusion portion  22  at the depth di is denoted by Wi. Then, the width Wi of the light diffusion portion  22  can be set to satisfy the following condition (Formula 2). 
                   Wi   ≤     {           L   ⁡     (     1   -     di   S       )           …           in   ⁢           ⁢   case   ⁢           ⁢   S     ≥   di               L   -     2   ⁢   Wr           …           in   ⁢           ⁢   case   ⁢           ⁢   S     ≤   di                     (     Formula   ⁢           ⁢   2     )               
(Example of Method for Forming Lens Array Sheet  106 )
 
     Such light diffusion layer  20 C may be formed, for example, as follows. First, an ultraviolet curing resin having light diffusion property is applied on a flat surface of a lens layer  10  and then an ultraviolet light is emitted from a lens surface  11  of the lens layer  10  in which the ultraviolet light has a diameter from a center of a lens U, which is equal to or smaller than a diameter of the lens U. As a result, the ultraviolet curing resin is cured as shown in  FIG. 7  and  FIG. 8 . Thereafter, a light diffusion portion  22  is formed by removing a portion that has not been cured. Subsequently, the light diffusion layer  20 C is formed by forming a transparent portion  42  between light diffusion portions  22 . In addition, this light diffusion layer  20 C may be formed by removing a part of a light diffusion layer  20 A according to the first embodiment using a photolithography or sputtering method. Of course, the present invention is not limited by the method for forming the lens array sheet. 
     (Example of Advantages of Lens Array Sheet  106 ) 
     Hereinbefore, a configuration of the lens array sheet  106  and the like according to the sixth embodiments of the present invention have been described. This lens array sheet  106  can have an advantage that a shape of an interface between a light diffusion portion  22  and a transparent portion  42  has a shape following a light focusing region G in addition to the advantages achieved by the lens array sheet  103  according to the third embodiment. Therefore, a part of light diffused by the light diffusion portion  22  can be reflected by the difference in the refractive index at the interface and an amount of light directing toward a corresponding lens U can be increased. In other words, the lens array sheet  106  according to the sixth embodiment enables in effect the light to be guided toward the lens U by the interface between the light diffusion portion  22  and the transparent portion  42 . Consequently, the lens array sheet  106  also enables a light use efficiency to be improved. 
     Hereinbefore, the embodiments (the first embodiment to the sixth embodiment) classified into one group of the present invention have been described. In the above mentioned first to sixth embodiments, it is shown that light diffusion layers  20 A,  20 B and  20 C, and a light reflection layer  30  forms individual layers. However, a lens array sheet can be formed by embedding light reflection portions  31  of the light reflection layer  30  in the light diffusion layers  20 A,  20 B and  20 C, respectively. In other embodiments (a seventh embodiment to a tenth embodiment) classified into the other group of the present invention, a light reflection portion is embedded in a light diffusion layer. Since the light diffusion layer is embedded with the light reflection portion in this manner, the light diffusion layer enables a light use efficiency to be improved. We will describe hereinafter seventh, eighth, ninth, and tenth embodiments in detail. Referring to  FIG. 9 , a lens array sheet according to the seventh embodiment will now be described. 
     Lens Array Sheet  201  According to Seventh Embodiment 
       FIG. 9  is an explanatory diagram for explaining a configuration of a lens array sheet according to the seventh embodiment of the present invention. 
     (Configuration of Lens Array Sheet  201 ) 
     As shown in  FIG. 9 , a lens array sheet  201  according to this embodiment has a light diffusion layer  50 A in place of a light diffusion layer  20 A and a light reflection layer  30  included in a lens array sheet  101  according to the first embodiment. In addition, the light diffusion layer  50 A has a light diffusion portion  21  and a light reflection portion  51 . On one hand, as shown in  FIG. 9 , a light diffusion portion  21  according to this embodiment has a layered shape that is different from that of a light diffusion portion  21  forming a light diffusion layer  20 A according to the first embodiment, and is denoted by the same reference as that in the first embodiment. On the other, thought the light reflection portion  51  according to this embodiment is denoted by a different reference from that in the first embodiment due to the fact that the light reflection portion  51  is formed by embedding it in the light diffusion layer  50 A, the light reflection portion  51  may be in principle formed in the same manner as light reflection portions  31  and  32  according to the first to sixth embodiments. 
     The light diffusion portion  21  is laminated on a flat surface of a lens layer  10  and formed integrally with the lens layer  10 . Then, the light diffusion layer  50 A diffuses light passing through it. 
     The light reflection portion  51  is embedded in the light diffusion portion  21  at least within a part of a non-light focusing region N of a lens U. In short, the light reflection portion  51  is embedded in a plane in parallel with a lens array sheet  201  such that the light reflection portion  51  covers a light focusing region. In addition, the light reflection portion  51  reflects light passing through the non-light focusing region N and directing toward the lens layer  10 . 
     (Example of Method for Forming Lens Array Sheet  201 ) 
     Such light diffusion layer  50 A may be formed, for example, as follows. For example, first, a light diffusion portion  21  is formed on a flat surface of the lens layer  10  as a flat layered structure and a recess is formed on a back side of the light diffusion portion  21  by a lithography method or a sputtering method. The light diffusion layer  50 A is then formed by applying a light reflection portion  51  on the recess. Alternatively, the light diffusion layer  50 A may be formed, for example, by evenly forming a part of the light diffusion portion  21  on the flat surface of the lens layer  10 , further laminating the light diffusion portion  21  having a recess of a predetermined pattern on the part of the light diffusion portion  21 , and thereafter applying the light reflection portion  51  on the recess. Of course, the present invention is not limited by the method for forming the lens array sheet. 
     (Example of Advantages of Lens Array Sheet  201 ) 
     Hereinbefore, a configuration of the lens array sheet  201  and the like according to the seventh embodiment of the present invention have been described. This lens array sheet  201  can have an advantage that it enables a reflectance of the light reflection portion  51  to be improved, and a light use efficiency to be also improved by adjusting a thickness of the light reflection portion  51  in addition to the advantages achieved by the lens array sheet  101  according to the first embodiment. The light reflection portion  51  may serve to restrict light, which is incident on the lens layer  10 , to light passing through a focal point F as in the case of the light reflection layer  30  and the like according to the first embodiment. However, though a metal material is used, for example, for the light reflection layer  30 , the light reflection layer  30  enables absorption or transmission of light to be generated and a reflectance is not equal to 100%. When the reflectance is low, light actually reflected by the lens layer  10  would be reduced due to the absorption or transmission of the light at the light reflection portion  51 . To the contrary, the light reflection portion  51  enables the reflectance to be improved by thickening a thickness of the light reflection portion  51 . In this manner, when the thickness of the light reflection portion  31  in the first embodiment and the like is thickened, a thickness of the lens array sheet  201  by itself would be thickened. However, the thickness of the light reflection portion  51  can be easily thickened without increasing the thickness of the light reflection portion  51  by itself, when the light reflection portion  51  is embedded in the light diffusion layer  50 A. In addition, it is desirable that a depth by which this light reflection portion  51  is embedded in the light diffusion layer  50 A, that is to say, the thickness of the light reflection portion  51  is configured such that reflection efficiency reaches equal to or more than 70%. Furthermore, it is desirable that this thickness is configured such that a reflectance becomes equal to or more than 80%, more preferably equal to or more than 90%. In addition, it is desirable that this thickness is configured depending on a material of the light reflection portion and the like, because the thickness varies depending on its material and the like. 
     The lens array sheet  106  according to the sixth embodiment enables light to be guided toward a lens U using an interface between a light diffusion portion  22  and a transparent portion  42  by arranging the transparent portion  42  between light diffusion portions  22 . The lens array sheet  201  according to this embodiment enables light to be guided toward a lens U using a light reflection portion  51 , which has a higher efficiency than the interface, by embedding the light reflection portion  51  in the light diffusion portion  21 . Therefore, embodiments will later be described that modifies a shape of the light reflection portion  51  in order to improve such light guidance effect. First, for the purpose of describing such embodiments, eighth and ninth embodiments of the present invention will be described with reference to  FIGS. 10 ,  11  and  12 . 
     Lens Array Sheets  202  and  203  According to Eighth and Ninth Embodiments 
       FIG. 10  is an explanatory diagram for explaining a configuration of a lens array sheet according to an eighth embodiment of the present invention.  FIG. 11  and  FIG. 12  illustrate a configuration of a lens array sheet according to a ninth embodiment of the present invention. 
     (Configuration of Lens Array Sheets  202  and  203 ) 
     As shown in  FIGS. 10 and 11 , each of lens array sheets  202  and  203  has light diffusion layers  50 B and  50 C in place of a light diffusion layer  50 A included in a lens array sheet  202  according to the seventh embodiment. In addition, these light diffusion layers  50 B and  50 C have light reflection portions  52  and  53 , respectively, in place of a light reflection portion  51 . 
     The light reflection portions  52  and  53  are embedded in a light diffusion portion  21  at least within a part of a non-light focusing region N of a lens U as in the case of the light reflection portion  51 . In short, the light reflection portions  52  and  53  are also embedded in a plane in parallel with the lens array sheets  202  and  203  such that the light reflection portions cover a light focusing region. In addition, the light reflection portions  52  and  53  also reflect light passing through the non-light focusing region N and directing toward a lens layer  10 . 
     In addition, each of the light reflection portions  52  and  53  has a shape (a width in a direction of a plane in each of lens array sheets  202  and  203 ) gradually narrowing toward the lens layer  10 . In other words, each of the light reflection portions  52  and  53  has a shape following the non-light focusing region N of individual lenses U. Furthermore, the light reflection portions  52  and  53  serve to riot only reflect light passing through the non-light focusing region N and directing toward the lens layer  10 , but also reflect and return light, which is diffused at a light diffusion portion  21  and departs from a light focusing region G, to the light focusing region G. 
     (Example of Dimensions of Lens Array Sheet  203 ) 
     Hereinbefore, a configuration of the lens array sheets  202  and  203  have been described. 
     Referring to  FIG. 12 , an example of dimensions of individual configurations in the lens array sheet  203  and the like will now be described as an example of a lens array sheet in which gradually narrowing light reflection portions  52  and  53  are embedded. 
       FIG. 12  illustrates a lens layer  10  and a light diffusion layer  50 C corresponding to a single lens U. A width of a single lens is denoted by L and a distance from a flat surface of the lens layer  10  to a focal point F is denoted by S. In addition, a depth from the lens layer  10  in the light diffusion layer  50 C is denoted di, a width of the light diffusion layer  50 C at the depth di is denoted by Wj, and a depth at which a light reflection portion  53  is embedded in the light diffusion layer  50 C is denoted by f. Then, the width Wj of the light reflection portion  53  can be set to satisfy the following condition (Formula 3). 
     
       
         
           
             
               
                 
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     As described above, a reflectance of the light reflection portion  53  depends on the depth f at which the light reflection portion  53  is embedded in the light diffusion layer  50 C. Therefore, it is desirable that this depth f is configured such that the reflectance in the light reflection portion  53  becomes equal to or more than 70%. Furthermore, it is desirable that the depth f is configured such that the reflectance reaches equal to or more than 80%, more preferably, 90%. 
     (Example of Method for Forming Lens Array Sheets  202  and  203 ) 
     Such light diffusion layers  50 B and  50 C may be formed, for example, as in the case of a light diffusion layer  50 A as follows. In short, for example, a light diffusion portion  21  is initially formed in a flat layered shape on a flat surface of a lens layer  10  and a recess is then formed on a back side of the light diffusion portion  21  using a photolithography method or a sputtering method. In addition, the light diffusion layers  50 B and  50 C are formed by applying a light reflection portion  52  or  53  on the recess. Alternatively, the light diffusion layers  50 B and  50 C may be formed by forming a part of the light diffusion layer  21  on the flat surface of the lens layer  10 , further laminating the light diffusion layer  21  having a recess of a predetermined pattern on the part of the light diffusion portion  21 , and thereafter applying the light reflection portion  52  or  53  on the recess. 
     Furthermore, the light diffusion layer  50 C may be formed, for example, using an ultraviolet curing resin. In this case, for example, a layered light diffusion portion  21  is initially formed, and a material that can be cured by heat and ultraviolet light is applied across the light diffusion portion  21 . A lens array sheet is then arranged on the other side of the light diffusion portion  21  with a pitch similar to that of the lens layer  10 , where a lens having a shorter focal distance than that of a lens U is arranged on the lens array sheet. This lens array sheet is then irradiated by light so as to be cured. Thereafter, the lens array sheet is removed, the lens layer  10  is bonded, and uncured ultraviolet curing resin is removed, so that a light reflection portion  53  is applied on a portion from which the lens array sheet has been removed. As a result, it is possible to form the light diffusion layer  50 C. Of course, the present invention is not limited by the method for forming the lens array sheet. 
     (Example of Advantages of Lens Array Sheets  202  and  203 ) 
     Hereinbefore, a configuration of the lens array sheets  202  and  203  and the like according to the eighth and ninth embodiments of the present invention have been described. These lens array sheets  202  and  203  can have an advantage that a shape of each of the light reflection portions  52  and  53  has a shape following a non-light focusing region N in addition to the advantages achieved by the lens array sheet  103  according to the seventh embodiment. Therefore, a part of light diffused by the light diffusion portion  21  can be reflected by the light reflection portions  52  and  53 , and an amount of light directing toward a corresponding lens U can be increased. In other words, the lens array sheets  202  and  203  according to the eighth and ninth embodiments, respectively, enable in effect the light to be guided toward the lens U by the light reflection portions  52  and  53 . Consequently, the lens array sheets  202  and  203  also enable a light use efficiency to be improved. 
     The lens array sheets  202  and  203  according to the eighth and ninth embodiments, respectively, are shown such that each of the light reflection portions  52  and  53  has a width gradually narrowing toward the lens layer  10 . In other words, it is shown that each of the light reflection portions  52  and  53  has a shape following the non-light focusing region N, and the light diffusion portion  21  has a shape following a light focusing region G. However, the shape of each of the light reflection portions  52  and  53  is not limited to this example, but may be further modified. Therefore, referring to  FIG. 13 , a tenth embodiment of the present invention will now be described in that a light reflection portion has a different shape. 
     Lens Array Sheet  204  According to Tenth Embodiment 
       FIG. 13  is an explanatory diagram for explaining a configuration of a lens array sheet according to a tenth embodiment of the present invention. 
     (Configuration of Lens Array Sheet  204 ) 
     As shown in  FIG. 13 , a lens array sheet  204  has light diffusion layers  50 D in place of a light diffusion layer  50 A included in a lens array sheet  201  according to the seventh embodiment. In addition, this light diffusion layer  50 D has a light reflection portion  54  in place of a light reflection portion  51 . 
     The light reflection portion  54  is embedded in a light diffusion portion  21  at least within a part of a non-light focusing region N of a lens U as is the case of the light reflection portion  51 . In short, the light reflection portion  54  is also embedded in a plane in parallel with the lens array sheet  204  such that the light reflection portion covers a light focusing region. In addition, the light reflection portion  54  also reflects light passing through the non-light focusing region N and directing toward a lens layer  10 . 
     In addition, the light reflection portion  54  has a shape (a width in a direction of a plane in the lens array sheet  204 ) gradually widening toward the lens layer  10 . Furthermore, the light reflection portion  54  serves to not only reflect light passing through the non-light focusing region N and directing toward the lens layer  10 , but also reflect and return light, which is diffused at a light diffusion portion  21  and departs from a light focusing region G, to the light focusing region G. 
     (Example of Method for Forming Lens Array Sheet  204 ) 
     Such light diffusion layer  50 D may be formed, for example, using a photolithography method or a sputtering method. In this case, for example, a portion in which a light reflection portion  54  is to be embedded is previously formed. In short, a layered light diffusion portion  21  is provided and a recess is formed from a direction, in which a lens layer  10  is arranged, by the photolithography method or the sputtering method. The light reflection portion  54  is then formed in the recess, and subsequently the layered diffusion portion  21  is further laminated on the reflection portion. In addition, the lens layer  10  is bonded to the laminated layered light diffusion portion  21  to complete the lens array sheet  204 . 
     Furthermore, the light diffusion layer  50 D may be formed using an ultraviolet curing resin as in the case of the eighth and ninth embodiments. In this case, a lens layer  10  is initially formed and a layered light diffusion portion  21  is formed on a flat surface of the lens layer  10 . An ultraviolet curing resin is then applied on the layered light diffusion portion  21  and subsequently a lens layer similar to the lens layer  10  is arranged at an opposite side to the lens layer  10 . In addition, a part of the ultraviolet curing resin is irradiated and cured with ultraviolet light from a side of this newly arranged lens layer. Thereafter, the lens layer and the remaining uncured ultraviolet curing resin are removed. Since a recess is formed at a position from which the ultraviolet curing resin has been removed, a light reflection portion  53  is then applied on the recess. As a result, the lens array sheet is completed. Of course, the present invention is not limited by the method for forming the lens array sheet. 
     (Example of Advantages of Lens Array Sheet  204 ) 
     Hereinbefore, a configuration of the lens array sheet  204  and the like according to the tenth embodiment of the present invention have been described. The lens array sheets  204  can have an advantage that a width of the light reflection portion  54  is gradually widened toward the lens layer  10  in addition to the advantages achieved by the lens array sheet  103  according to the seventh embodiment. For example, a part of light passing between one light reflection portion  54  and a neighbor light reflection portion  54  (i.e., a part of light passing through “an opening”) is diffused by the light reflection portion  54  and directs toward a lens U different from a lens U corresponding to the opening. In this case, the light reflection portion  54  has a shape such that an incident angle of light directing toward a direction of other lenses increases. Therefore, it is possible to reflect the light directing toward the direction of the other lenses to a light focusing region G of the primarily corresponding lens U and efficiently suppress crosstalk that is incident on the other lenses. Consequently, the lens array sheet enables a light use efficiency and conversion efficiency to generally parallel light by the lens layer  10  to be improved. 
     Hereinbefore, the lens array sheets according to various embodiments of the present invention have been described. 
     A lens array sheet incorporated a liquid display device and the like will now be described. For this purpose, lens array sheets according to the first to tenth embodiments are generally referred to as a “lens array sheet  300 ”. Any of the lens array sheets according to the first to tenth embodiments is operable to reduce moire fringes while maintaining the image quality, as described above. 
     Liquid Crystal Display Device  400  According to Eleventh Embodiment 
       FIG. 14  is an explanatory diagram for explaining a configuration of a liquid crystal display device according to an eleventh embodiment of the present invention. 
     A liquid crystal display device  400  according to this embodiment has a liquid crystal panel  403  and a light source  401 . 
     The liquid crystal panel  403  has a plurality of pixels, which are regularly arranged, and enables a predetermined image or video to be displayed by controlling transmission and blocking of light emitted from the light source  401  for each of the pixels. To this end, liquid crystal molecules are arranged in each of the pixels in the liquid crystal panel  403 . In addition, a particular polarizing filter is arranged in front and in the rear of the liquid crystal molecules. Orientation of the liquid crystal molecules is changed by controlling a voltage applied to the liquid crystal molecules. As a result, transmission and blocking of the light is controlled by the polarizing filter and the orientation of the liquid crystal molecules. 
     The light source  401  is arranged at a back side of the liquid crystal panel and emits light to the liquid crystal panel  403 . To this end, the light source  401  has a backlight  405  and an optical sheet  402 . 
     The backlight  405  emits light (e.g., white light) to the optical sheet. The back light  405  includes, for example, but not limiting to, a discharge lamp such as a cold cathode fluorescent lamp (CCFL), an electroluminescence (EL) lamp such as a light emitting diode (LED) and the like. 
     The optical sheet  402  has a lens array sheet  300  and a light diffusion plate  404 . 
     The light diffusion plate  404  is arranged in front of the backlight  405  and reduces unevenness in light intensity by diffusing light emitted from the backlight  405 . In short, the light diffusion plate  404  cancels an image of a lamp and the like constituting the backlight  405 , and equalizes light intensity. This diffusion plate  404  may be, for example, formed of a material similar to that of light diffusion portions  21  and  22  in the first to tenth embodiments as described above. 
     The lens array sheet  300  is arranged in front of the light diffusion plate  404  and just the same as the lens array sheet according to any of the first to tenth embodiments in that the lens array sheet  300  increases a component of generally parallel light in the light radiated from the light diffusion plate  404 . Therefore, the lens array sheet  300  initially restricts the diffused light, which is incident from the light diffusion plate  404 , to a focal point of a lens by means of a light reflection portion and the like, and increases the component of the parallel light by means of a lens layer. In short, the lens array sheet  300  increases the component of the light directing toward a front direction (normal direction) of the liquid crystal display device  400 . In addition, the lens array sheet  300  supplies light to the liquid crystal panel  403 . Therefore, the lens array sheet  300  enables brightness, an optical viewing angle, contrast ratio of the liquid crystal display device  400 , and the like to be improved and thereby improving the image quality. 
     In this case, the lens array sheet  300  diffuses the light restricted by the light diffusion portion and the like and directing toward the lens layer. Therefore, the light emitted from the lens array sheet  300  is such that the component of the generally parallel light has been increased, the light has been adequately diffused, and a light and dark pattern as well as a directional pattern due to a lens pitch of the lens layer and a structured pattern of the light reflection portion and the like are reduced. As a result, a light pattern that interferes with the structured pattern of the pixels in the liquid crystal panel  403  and produce moire fringes is reduced by the lens array sheet  300 . Consequently, the lens array sheet  300  is operable to improve the image quality, as described above, and suppress the moire fringes from being produced. 
     Hereinbefore, the liquid crystal display device  400  according to the eleventh embodiment of the present invention has been described. 
     Referring to  FIG. 15 , a liquid crystal display device according to a twelfth embodiment of the present invention will now be described. 
     Liquid Crystal Display Device  400  According to Twelfth Embodiment 
       FIG. 15  is an explanatory diagram for explaining a configuration of the liquid crystal display device according to the twelfth embodiment of the present invention. 
     As shown in  FIG. 15 , the liquid crystal display device  500  according to the twelfth embodiment has a polarization splitting film  503  and a light diffusion film  504  in addition to the configurations incorporated in the liquid crystal display device  400  according to the eleventh embodiment. In  FIG. 15 , since a light source  501  and an optical sheet  502  have the polarization splitting film  503  and the light diffusion film  504 , the light source  501  and the optical sheet  502  are designated by different references from those of the light source  401  and the optical sheet  402  in the liquid crystal display device  400  according to the eleventh embodiment. 
     The polarization splitting film  503  is arranged at a back side of a liquid crystal panel  403  and is a brightness improving film that improves brightness of the liquid crystal display device  500 . For example, a film having a reflected polarization may be used for the polarization splitting film  503 . A reflected polarization film transmits only light having a vibration direction in parallel with one axis in a plane, and reflects other light. Such reflected polarization film may include, for example, a brightness enhancement film such as DBEF (trade name) series and DRPF-H (trade name) series manufactured by 3M, Inc. Alternatively, a circular polarized light film may be used in place of such linear polarized light film. The circular polarized light film may include, for example, a film having a cholesteric circular polarizer such as Nipocs (trade name) manufactured by Nitto Denko Corporation. 
     The light diffusion film  504  is arranged between the polarization splitting film  503  and the lens array sheet  300 , and diffuses light emitted from the lens array sheet  300 . In addition, the light diffusion film  504  also diffuses light reflected from the polarization splitting film  503 . Such light diffusion film  504  may be, for example, formed of a material similar to that of the light diffusion portions  21  and  22  in the first to tenth embodiments. 
     As the liquid crystal display device  500  is provided with these polarization splitting film  503  and light diffusion film  504 , the liquid crystal display device  500  is also operable to improve its brightness. This brightness improving mechanism will be now described as follows. At first, light having its parallel light component, which is increased by the lens array sheet  300 , is diffused by the light diffusion film  504  and is incident on the polarization splitting film  503 . The polarization splitting film  503  then transmits light in a vibration direction in parallel with one axis and reflects other light. The light reflected by the polarization splitting film  503  is again incident on the light diffusion film  504 . The light, which is again incident on the light diffusion film  504 , is again diffused and a part of the diffused light is again incident on the polarization splitting film  503 . The polarization splitting film  503  transmits once again a light in the vibration direction in parallel with the one axis and reflects the other light. In a usual liquid crystal display device, a use efficiency of front face brightness to light irradiated by a backlight reaches about 40%. However, by repeatedly transmitting and reflecting the light by the polarization splitting film  503 , polarized light can be irradiated to the liquid crystal panel  403 . As a result, the liquid crystal display device  500  according to this embodiment enables a light use efficiency to be improved, for example, to an extent equal to or more than 50%. 
     Of course, an arrangement position of the light diffusion film  504  is not limited to a position between the polarization splitting film  503  and the lens array sheet  300 , but may be a position between the lens array sheet  300  and the light diffusion plate  404 . In addition, since the lens array sheet  300  according to each of the various embodiments of the present invention has the light diffusion portion  21  and  22  and the like, the lens array sheet  300  is operable to serve as the light diffusion film  504 . In this case, the light diffusion film  504  may be dispensed with. 
     Hereinbefore, the lens array sheet and the liquid crystal display device according to each of the embodiments of the present invention have been described. Examples of the lens array sheet and the liquid crystal display device will now be described. 
     Example 
     First, lens array sheets  101  to  105  according to the first to fifth embodiments, respectively, and lens array sheets  201  to  204  according to the seventh to tenth embodiments, respectively, were created. In this case, a lens layer and a transparent portion contained in each of the lens array sheets were formed of an acrylic resin and a light diffusion portion is formed of an acrylic resin having silica dispersed therein. In addition, a light reflection layer was formed of a urethane resin mixed with a white pigment. A shape of each of configurations was configured such that a haze value of each of light diffusion layers was equal to 20%. 
     A liquid crystal display device  400  according to the eleventh embodiment, as shown in  FIG. 14 , was then created for each of the lens array sheets. In this case, a backlight  405  and a light diffusion plate  404  were implemented by a backlight and a light diffusion plate of KDL-40X5000 (trade name) contained in a liquid crystal television manufactured by Sony Corporation and available in the market. 
     Thus, formed liquid crystal display device was subject to visual observation in order to detect whether there were any moire fringes, and front face brightness of each of the liquid crystal display devices was also measured by “CS-1000 (trade name)” manufactured by Konica Minolta Sensing, Inc. 
     Furthermore, liquid crystal display devices similar to the above-mentioned one, except for a lens array sheet, were provided as comparative examples. As Comparative Example 1, a liquid crystal display device having no lens array sheets was provided. As Comparative Example 2, a liquid crystal display device was provided that had a lens array sheet including a transparent layer in place of a light diffusion layer  20 A in a lens array sheet  101  according to the first embodiment as shown in  FIG. 1 . As Comparative Example 3, a liquid crystal display device was provided that had a lens array sheet including a transparent portion in place of a light diffusion portion  21  in a lens array sheet  201  according to the seventh embodiment as shown in  FIG. 9 . These comparative examples were also subject to the same visual observation and measurement as those of the examples. 
     Table 1 shows results of the observation and the measurement. 
     As can be seen in Table 1, moire fringes were produced in Comparative Examples 2 and 3 where the liquid crystal display devices had no light diffusion portions  21  and the like, whereas moire fringes were suppressed from being produced in the liquid crystal display device in each of the embodiments of the present invention. It is supposed that no moire fringes were produced in the liquid crystal display device in Comparative Example 1, because no light and dark patterns interfering with a structured pattern of a liquid crystal panel were generated due to the fact that the liquid crystal display device had no lens array sheets. However, in the liquid crystal display device in Comparative Example 1, since it had no lens array sheets, the front face brightness was decreased. 
     In addition, it can be seen that the front face brightness in the liquid crystal display device of each of the embodiments was much improved than that of Comparative Example 1 where the liquid crystal display device had no lens array sheets. In particular, in the second to fifth embodiments, the front face brightness was further improved due to transparency achieved by transparent portions  41  and  42  and the like, and an effect of guiding light toward a lens U by an interface of each of the transparent portions. Furthermore, in the seventh to tenth embodiments, the front face brightness was further improved, because light reflection portions  51  to  54  were embedded in light diffusion layers  50 A to  50 B and light was further effectively guided to the lens U by means of the light reflection portion  51 . 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 FRONT FACE 
               
               
                 LENS SHEET 
                 PRODUCTION 
                 BRIGHTNESS 
               
               
                 EMBODIMENTS 
                 OF MOIRE 
                 (cd/m 2 ) 
               
               
                   
               
             
            
               
                 FIRST EMBODIMENT 
                 NO 
                 518 
               
               
                 SECOND EMBODIMENT 
                 NO 
                 527 
               
               
                 THIRD EMBODIMENT 
                 NO 
                 520 
               
               
                 FORTH EMBODIMENT 
                 NO 
                 529 
               
               
                 FIFTH EMBODIMENT 
                 NO 
                 531 
               
               
                 SEVENTH EMBODIMENT 
                 NO 
                 533 
               
               
                 EIGHTH EMBODIMENT 
                 NO 
                 551 
               
               
                 NINTH EMBODIMENT 
                 NO 
                 541 
               
               
                 TENTH EMBODIMENT 
                 NO 
                 536 
               
               
                 COMPARATIVE EXAMPLE 1 
                 NO 
                 505 
               
               
                 COMPARATIVE EXAMPLE 2 
                 YES 
                 535 
               
               
                 COMPARATIVE EXAMPLE 3 
                 YES 
                 571 
               
               
                   
               
            
           
         
       
     
     Subsequently, a haze value of a light diffusion layer included in the lens array sheet according to each of the embodiments was measured. In short, five different lens array sheets were created that had the same structure as that of the lens array sheet  101  according to the first embodiment, but had light diffusion layer  20 A of different haze values, respectively. Liquid crystal display devices were then formed in similar manner as described above using individual lens array sheets. In addition, the haze value of each of the lens array sheet was measured using a haze meter HR-100 (trade name) manufactured by MURAKAMI COLOR RESEARCH LABORATORY. The liquid crystal display devices including respective lens array sheets having the different haze values were also subject to the visual observation in order to detect whether there were any moire fringes and front face brightness of each of the liquid crystal display devices was also measured. 
     Table 2 shows results of the observation and the measurement. 
     As can be seen in Table 2, no moire fringes were produced, but the front face brightness was reduced in the liquid crystal display devices having the haze value more than 20%. Therefore, the light diffusion layer included in the lens array sheet according to each of the embodiments is preferably formed such that the haze value is decreased equal to or less than 20% because decrease of the front face brightness is maintained comparatively low at that haze value. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 FRONT FACE 
               
               
                 HAZE VALUE OF LIGHT 
                 PRODUCTION 
                 BRIGHTNESS 
               
               
                 DIFFUSION LAYER 
                 OF MOIRE 
                 (cd/m 2 ) 
               
               
                   
               
             
            
               
                  9% 
                 NO 
                 527 
               
               
                 20% 
                 NO 
                 518 
               
               
                 31% 
                 NO 
                 470 
               
               
                 42% 
                 NO 
                 450 
               
               
                 49% 
                 NO 
                 421 
               
               
                 COMPARATIVE EXAMPLE 2 
                 YES 
                 535 
               
               
                   
               
            
           
         
       
     
     Furthermore, a liquid crystal display device  500  according to the twelfth embodiment, as shown in  FIG. 15 , was formed and the liquid crystal display device was also subject to the observation in order to detect whether there were any the moire fringes. In this case, a brightness improving film, DBEF (trade name) series manufactured by 3M, Inc. was used as a polarization splitting film  503 . As a result, production of the moire fringes was not observed in the liquid crystal display device  500 . Therefore, the liquid crystal display device  500  also enables the moire fringes to be suppressed from being produced with or without the polarization splitting film  503 . 
     The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-105980 filed in the Japan Patent Office on Apr. 15, 2008, the entire content of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.