Abstract:
A flexible light guide film having a light-adjusting structure in the form of a lenticular-like microstructure on the bottom side of the light guide film. The light guide film has a substrate layer supporting a layer light-adjusting structure, which is in the form of an array of longitudinal lenticular lenses laterally arranged in parallel. A prismatic-like microstructure may be provided on the top light emitting side of the light guide film. The light guide film is fabricated by a process involving coating/embossing of a roll of sheet material, in a roll-to-roll continuous process. Advantages includes significantly reducing the thickness of the light guide film, and the roll-to-roll fabrication process provides for more precise replication of the microstructures on the master mold or drum onto the surface of the light guide film, which in turn reduces the failure rate and manufacturing cost.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority of U.S. Provisional Application Ser. No. 61/352,339 filed on Jun. 7, 2010. The present application is a continuation-in-part of U.S. patent application Ser. No. 13/073,859 filed on Mar. 28, 2011. 
     All publications noted in the present application are incorporated by reference herein as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to light guides, particularly to light guides for use in flat panel displays, and more particularly to light guides for use in liquid crystal display panels. 
     2. Description of Related Art 
     In a liquid crystal display (LCD) panel, the liquid crystal (LC) layer does not emit light inherently, as compared to, for example, an electro-luminescent material layer in a plasma display panel. The LC layer or panel functions as a modulator of light transmitted through the LC layer. In a backlit LCD panel, a backlight module serves as a planar light source, which is an important element of the LCD panel, and is critical for enhancing the brightness of the LCD panel. The backlight module includes a light guide plate, for guiding light from a planar array of light sources (e.g., a planar array of LEDs), or a linear light source (e.g., a cold cathode fluorescence (CCF) tube, or a row of LEDs). Backlight modules having the latter linear light source are referred in the art as edge-lid backlight modules. 
     Heretofore, conventional light guide plates incorporated in edge-lit backlight modules utilize total internal reflection to direct light from a light source positioned at an edge surface of the light guide plate to a light emitting major planar surface facing towards the LC panel. The light from the light source is guided to propagate through the light guide plate to an opposite edge surface of the light guide plate, so that light can be emitted from the entire planar surface towards the LC panel. In the past, the other major planar surface of the light guide plate (e.g., the bottom surface) opposite to the light emitting planar surface is provided with a structure that facilitates reflection of light towards the top planar surface. For example, in some prior art light guide plates, a reflective layer may be provided at the bottom surface, reflecting light back into the light guide plate. In other prior art light guide plates, the bottom surface of the light guide plate opposite to the light-exit surface is textured with light-reflecting or light-scattering surface dots. Light beams encountering these dots are diffused and/or reflected towards the light emitting surface of the light guide. More particularly, the light-reflecting or light-scattering dots formed or embedded on the bottom surface of the abovementioned conventional light guide plate are capable of changing the direction of propagation of light beams so as to spread light from the linear light source across the planar light emitting surface, thereby forming a planar light source emitting light from a plane. The diffused and reflecting surface of the light-reflecting or light-scattering dots are generally matte as a result of the fabrication process. Accordingly, a great deal of energy is required by the point or linear light source to produce planar light output of acceptable brightness, resulting in waste of electrical power consumption. 
     Another technique using a V-cut light guide plate has been developed in the field of backlight modules. The V-cut light guide plate is made mainly by directly micro-fabricating prisms on a light guide plate, and is usually used in a backlight module in combination with a reverse prism sheet. As shown in  FIG. 1 , the prior art backlight module mainly includes a reverse prism sheet  3 , a V-cut light guide plate  2  having a tapering thickness, and a reflective film  1  under the reverse prism sheet, and a diffusion film  4  above the reverse prism sheet. The LC panel (not shown) is placed on top of the diffusion film  4 . A linear light source/reflector  5  is positioned at the thicker edge of the light guide plate  2 . Compared to the earlier conventional backlight modules, the brightness of the backlight module having a V-cut light guide plate can be enhanced by nearly 30%. Therefore, overall power consumption for a particular output brightness can be saved by about one third using such improved backlight module, which is a considerable improvement on energy-saving performance. 
     Light guide plates used in backlight module are typically made by injection molding. In general, molten polymethyl methacrylate (PMMA) material is filled into a mold cavity having the desired mold structure and a holding pressure is maintained. After the material is allowed to cool down and harden to conform to the configuration of the mold cavity. However, when it comes to V-cut light guide plate, a high failure rate is present as a result of difficulties associated with making the mold cavity and the nature of the above-described injection molding process. The replica of the mold master having V-cut structures made by CNC precision-machining are often mal-manufactured and/or result in defects. Therefore, the manufacturing of V-cut light guide plate becomes more difficult and thereby less cost effective. 
     Furthermore, the problems with prior art light guide plates are exacerbated by the tightened requirements of lighter-weight, thinner-profile and more flexible structure for LCD devices, which are gradually becoming the mainstream in recent years. Due to the limitations of injection molding, it is not easy to obtain thin and flexible light guide plates manufactured by this method. In particular, when it comes to large LCD panels sizes, the failure rate is even higher. 
     There remains a need for a back light plate having a structure that is thin and flexible, and efficient in planar light output and easy to manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention provides a thin light guide film having a structure that is relatively easy to manufacture with high yield rate. In one aspect of the present invention, the light guide film is flexible. More particularly, the present invention provides a flexible light guide film having a light-adjusting structure in the form of a lenticular-like microstructure on the bottom side of the light guide film (i.e., the side facing away from the liquid crystal panel). 
     In one embodiment, the light guide film comprises a substrate layer supporting a layer light-adjusting structure. In a further embodiment, the light-adjusting structure comprises an array of longitudinal lenticular lenses laterally arranged in parallel. The light guide film may further comprise a prismatic-like microstructure on the top light emitting side of the light guide film (i.e., the side facing the liquid crystal panel). The light guide film can be fabricated by a process involving coating/embossing of a roll of sheet material (single-sided or double-sided depending on whether both sides of the light guide film are to be structured), in a roll-to-roll continuous process. The sheet material may be clear or transparent, may be coated with beads, and/or particles built-in on the light emitting surface. According to the present invention, the thickness of the light guide can be significantly reduced. In addition, the roll-to-roll process provides for more precise replication of the microstructures on the master mold or drum onto the surface of the light guide film, which in turn reduces the failure rate and manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates the structure of a prior art backlight module. 
         FIG. 2  schematically illustrates the structure of a LCD, which incorporates the light guide plate in accordance with one embodiment of the present invention. 
         FIG. 3  is a schematic sectional view comparing the surface profiles of a prism and a lenticular lens. 
         FIG. 4  is a perspective view illustrating a light guide film in accordance with another embodiment of the present invention. 
         FIG. 5  is a perspective view illustrating a light guide film in accordance with yet another embodiment of the present invention. 
         FIG. 6A  is a bottom view of a light guide film in accordance with a further embodiment of the present invention; and  FIG. 6B  is a perspective view illustrating the light guide film in  FIG. 6A . 
         FIG. 7  is a schematic sectional view of a light guide film to illustrate the structural parameters. 
         FIG. 8  illustrates an electronic device comprising an LCD panel that incorporates the inventive light guide film of the present invention, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description is of the best presently contemplated mode of carrying out the invention. This invention has been described herein in reference to various embodiments and drawings. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. It will be appreciated by those skilled in the art that variations and improvements may be accomplished in view of these teachings without deviating from the scope and spirit of the invention. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 2  schematically illustrates the structure of a backlight LCD device, which incorporates the light guide plate in accordance with one embodiment of the present invention. The backlight LCD  10 , in accordance with one embodiment of the present invention, comprises a liquid crystal (LC) display module  12 , a planar light source in the form of a backlight module  14 , and a number of optical films interposed between the LC module  12  and the backlight module  14 . The LC module  12  comprises liquid crystals sandwiched between two transparent substrates, and control circuitry defining a two-dimensional array of pixels. The backlight module  14  provides planar light distribution, which is of the edge-lit type, in which a linear light source  16  (e.g., a row of discrete LEDs or a longitudinal cold cathode fluorescent lamp tube) is provided at an edge of a light guide film  18  in accordance with the present invention. A reflector  17  is provided to direct light from the linear light source  16  through the edge of the light guide film  18  into the light guide film  18 . The LC module  12  modulates incident backlight through the module in accordance with image data. While the present invention is described in reference to LC module as a light modulator, the light guide film of the present invention can well be applied to be used with other types of modulation device that modules incident light through the device. 
     In particular, the present invention is directed to a novel structure of a thin and flexible light guide film having a light-adjusting structure to change the light path. In one embodiment, a first optical layer composed of a flexible transparent material supports a second optical layer formed on the lower side of the first optical layer and having a light-adjusting structure, wherein the first and second optical layers have same or different refractive indices. In accordance with the embodiment of the present invention illustrated in  FIG. 2 , the thin and flexible light guide film  18  has a clear or transparent, flexible substrate layer  19  supporting a clear or transparent layer of light-adjusting structure  20  generally comprising an array of laterally arranged rows of lenticular lenses  21 . The light guide film  18  is structured with the light-adjusting structure  20  defined at the bottom major planar surface facing away from the LC module  12 , to distribute and direct light through the flat, smooth top major planar surface facing towards the LC module  12 . A reflective sheet  22  may be provided to facilitate trapping any light escaping through the underside of the light guide film  18  and redirecting light back towards the light guide film  18 . 
     In the illustrated embodiment, there are two structured microprism substrates  26  and  28  that are arranged with the longitudinal prism structures generally orthogonal or at a slightly less than orthogonal angle between the two substrates. The microprism substrates  26  and  28  are structured to enhance luminance or brightness, redirecting light closer to a perpendicular viewing axis. A diffuser sheet  27  is provided between the light guide film  18  and the lower microprism substrate  28 . Alternatively or in addition, one or both of the microprism substrates  26  and  28  may incorporate diffusing structures at the respective bottom surfaces facing the light guide film  18  to provide both light-collimation and light-diffusing functions, which may obviate the need for separate diffuser sheet(s), thereby further reducing the overall thickness of the LCD  10 . Reference is made to co-pending U.S. patent application Ser. No. 13/073,859 filed on Mar. 28, 2011, which has been published as U.S. Patent Publication No. 2001/0234580, and which is fully incorporated by reference herein, as if fully set forth herein. 
     The light entering the LC module  12  through the combination of optical films illustrated in  FIG. 2  is uniform spatially over the planar area of the LC module  12  and has relatively strong normal light intensity. 
     In the context of the present invention, the inventive optical substrate may be adopted in display devices having display panels that may be flat or curved, and rigid or flexible, which comprise an array of display pixels. Planar light source refers to a light source that provides illumination to cover an area of the array of display pixels. Accordingly, for display panels having a curved image plane of display pixels (such panels may be rigid or flexible), the backlight would cover the array of display pixels in the curved plane, to effectively provide illumination coverage to the curved image plane. 
     The structure of the lenticular structured surface is described in greater detail below. For ease of reference, the following orthogonal x, y, z coordinate system will be adopted in explaining the various directions. For the embodiment shown in  FIG. 2 , the x-axis is in the direction across the lenticular lenses  21 , also referred to as the lateral or transverse direction of the lenticular lenses  21 . The y-axis is orthogonal to the x-axis, generally in the plane of the light guide film  18 , in a longitudinal axis or direction of the lenticular lenses  21 . The longitudinal direction of a lenticular lens  21  leads from one end to another end of the lenticular lens  21 . The lenticular lenses  21  generally lie in the x-y plane. For a rectangular piece of light guide film  18 , the x and y-axes would be along the orthogonal edges of the light guide film  18 . The z-axis is orthogonal to the x and y-axes. The edge showing the ends of the laterally arranged rows of lenticular lenses  21  lies in the x-z plane, as shown in  FIG. 2 , which also represents a sectional view in the x-z plane. References to cross sections of the lenticular lenses  21  would be sections taken in x-z planes, at various locations along the y-axis. Further, references to a horizontal direction would be in an x-y plane, and references to a vertical direction would be along the z-direction. 
     In the illustrated embodiment, the lenticular structured surface comprises a shallow-curved lens structure (e.g., a convex or concave lens structure, or a combination of convex and concave). In the embodiment illustrated in  FIG. 2 , the lenticular structured surface includes parallel rows of convex lenticular lenses  21 , each extending in the y-direction continuously between two opposing edges of the light guide film  18 . The lenticular lenses may be concave lenses in another embodiment not shown. In this illustrated embodiment, the curved surfaces of adjacent lenticular lenses  21  are spaced apart (i.e., do not intersect), defining parallel spaces or grooves  24  having longitudinal flat bottoms between lenticular lenses  21 . In other embodiment not shown, the curved surfaces of adjacent lenticular lenses may intersect. For the lenticular lenses  21 , the x-axis is in the direction across the valleys  24  and lenses  21 , also referred to as the lateral or transverse direction of the lenticular structured surface. The y-axis represents the longitudinal axis or direction of the lenticular lenses  21  and grooves  24 . The longitudinal direction of lenticular lenses  21  would be in reference to the general direction in which the convex lens section proceed from one end to another end of the lenticular lenses  21 . The edge shown in  FIG. 2  shows the ends of the laterally arranged rows of lenticular lenses  21  lies in the x-y plane, which also represents a sectional view in the x-z plane. 
     Referring also to  FIG. 7 , which schematic illustrates a cross-sectional view in the x-z plane to illustrate the general structural parameters of a light guide film. Refer to  FIG. 7 , light guide film  500  includes a substrate layer  510  and a plurality of lenticular lenses  520  having convex curved surfaces  524  formed on bottom surface of the substrate layer  510 . The surface  524  of each of the lenticular lenses  520  corresponds substantially to a section of the surface of a circular cylinders  522  having a radius “r” with center “O” in cross-section, which surface section corresponds to a subtended angle θ, and a subtended arc between point “a” and “b” in cross-section. In the sectional view shown in  FIG. 7 , the lens  520  corresponds to a segment of the circle  522 , which is bounded by the chord a-b and the arc a-b. As shown in  FIG. 7 , adjacent arcuate surfaces  524  of lenticular lenses  520  do not contact one another to form a contiguous or continuous lens surface. (As will be further discussed below, in the embodiment illustrated in  FIGS. 6A and 6B , the arcuate surfaces of some of the lenticular lenses may intersect each other. The surface  524  of each lens  520  “bottoms” onto the top of the substrate layer  510 , with a flat spacing between adjacent lenses  520 . In this illustrated embodiment, the lens width d 1  is the same for the discontinuous lenses  520 . The spacing pitch d 2  is constant within a particular area, but different for different areas. 
     In a preferred embodiment, the angle θ of lenticular structure is in the range of 5 degrees to 90 degrees, more preferably in the range of 10 degrees to 45 degrees. The height d 3  of the lenticular lens structure (measured from the top of the base layer  510 , or if the base layer is integral to the lenticular lens structure, measured from the valley between adjacent non-intersecting or non-overlapping lenticular lenses) is identical (or may be variable in other embodiments not shown), preferably in the range of 0.5 μm to 100 μm, preferably in the range of 1 μm to 60 μm, more preferably in the range of 1 μm to 45 μm. The curvature of the lenticular lenses is the same. The distance between centers O of adjacent lenses (i.e., d 1 +d 2 )=5 μm to 1000 μm. 
     In the illustrated embodiment in  FIG. 2 , the lenticular lenses  21  each has same sectional profile in the y-z plane. References to cross sections of lenticular lenses  21  would be sections taken in y-z planes, at various locations along the x-axis. Further, references to a horizontal direction would be in an x-y plane, and references to a vertical direction would be along the z-direction. In this embodiment, the curvature and height of the lenticular lenses  21  are respectively the same for all the lenticular lenses, and the distance pitch between two discontinuous lenticular lenses  21  of the structured lenticular surface is the same. In this embodiment, the surface of each lens  21  bottoms onto the top of the substrate layer  19 . While  FIG. 2  illustrates isolated or separated lenticular lenses  21  attached to the substrate layer  19 , it is understood that the layer of lenticular lenses  21  may include lenticular lenses  21  that are spaced apart but interconnected laterally (e.g., by a thin web of the same material; see, e.g.,  FIG. 4 ). The overall structure of such layer of lenticular lenses  21  resembles a layer of lenticular lenses  21  supported on a thin base layer of a desired height to maintain integrity of adhesion to the substrate layer  19 . 
     In this embodiment, the sectional profile of the lenticular lenses  21  conforms to a segment of a circle (i.e., the lenticular lenses  21  conform to surface of part of a cylinder). It is well within the scope of the present invention to adopt lenticular surfaces that conform to cylinders of different cross-sections other than a circle (e.g., an ellipse or other cross-sections of regular or irregular geometries). 
     In the illustrated embodiment in  FIG. 2 , the light guide film  18  comprises two separate layers, including the flexible substrate layer  19 , and the layer of light-adjusting structure  20 . The structured layer  20  is adhered to the substrate layer  19  to form the overall light guide film  18 . It can be appreciated that the light guide film  18  may be formed from a single integrated physical layer of material, instead of two separate physical layers, without departing from the scope and spirit of the present invention. The light guide film  18  may be a unitary or monolithic body, including a base portion bearing the surface structures of the lenticular lenses  21 . 
     The lenticular structure provides improved guidance of light towards the top light output surface of the light guide film  18 , so as to increase the luminance of the LC module  12 . Following the light path L illustrated in  FIG. 2 , when light emitted from a light source  16  is projected into the substrate layer  19 , the light enters the layer of lenticular lenses  21  from the substrate layer  19 , such that a first refraction occurs. When the light passes through the layer of lenticular lenses  21 , the lenticular lenses  21  change the light path. Then, the light passes through the substrate layer  19  towards the upper surface of the substrate layer  19  (which is also the upper surface of the light guide film  18 . Finally, the light is emitting through the upper surface of the light guide film  18 . Overall, a uniform planar surface light source is defined by the light guide film  18 . 
     It can be appreciated that in the thin and flexible light guide film  18  of the present invention, the light traveling path L can be controlled by controlling the refractive index difference between the substrate layer  19  and the layer of lenticular lenses  21 , and controlling the refraction and total reflection caused by the light-adjusting structure of the layer of lenticular lenses  21 . As compared to those conventional V-cut light guide plates described in the Background section above, the present invention simplifies the design of the light-adjusting structured surface, as the lenticular lenses have relatively low requirements for precision processing technology, and therefore the yield of the light guide film  18  can be improved. 
     The form of the light-adjusting structure of the light guide film  18  may be a regular or irregular lenticular-like structure. The improved effect of the light-adjusting structure of the light guide film  18  as compared to a prismatic structure of the conventional light guide plate  2  ( FIG. 1 ) can be better explained in reference to  FIG. 3 . As shown in  FIG. 3 , the upper inverted triangular represents the sectional profile of a conventional prismatic structure of the light guide plate  2  shown in  FIG. 1 . The lower lens represents the sectional profile of the lenticular lens  21  of the light guide film  18 . The dotted line segments T P  and T L  represent the slopes at various surface segments of the lower surface of the respective sectional profiles. As can be seen from  FIG. 3 , because the slope T P  of the prismatic structure  2  is constant, the level of breaking TIR (total internal reflection) and redirecting light is hard for design and manufacture. On the contrary, for the lenticular lens  21 , the slopes T L  of the tangents vary at various locations across the convex lens surface of the lens  21 . This level of breaking TIR makes design and manufacture much easier. The freedom of design greatly increase by considering the effect of tangent varying on breaking of TIR, and the tangent vary can be adjusted by changing the shape and/or size of the lenticular lenses. For example, the breaking level of total internal reflection may be modulated by: (a) distance between two adjacent lenses  21 ; and/or (b) radius of curvature of the lenses  21 . Using lenticular-like structure as light-adjusting structure in the present invention, more flexibility in design would be available. 
     In the illustrated embodiment, the layer of lenticular lenses  21  and the substrate layer  19  may be made of the same or different material. The layer of lenticular lenses  21  and the substrate layer  19  may be formed using an optically transparent material, preferably a polymerizable resin, such an ultraviolet or visible radiation-curable resin, such as UV curable adhesive. The light guide film  18  can be fabricated by a process involving coating/embossing of a roll of sheet material (single-sided or double-sided depending on whether both sides of the light guide film are to be structured), in a roll-to-roll continuous process. Generally, the structured lenticular surface is formed by applying a coatable composition comprising a polymerizable and crosslinkable resin onto a master mold or master drum and undergoing a hardening process. The lenticular structures may be formed on a separate base film layer by die assemblies, press rolling machines, mold pressing assemblies or other equivalent apparatuses. The base film of the layer  20  of lenticular lenses  21  is combined with the flexible substrate layer  19 , by simply stacking or applying adhesives such as pressure sensitive adhesive (PSA) to the layers to form a structure of the light guide film  18 . It is apparent that many techniques and combinations of manufacture methods may be applied to obtain the combination of the structured lenticular surface and the substrate layer, or equivalent thereof. It is also contemplated that the light guide film  18  can first be formed in a thin format, and then further combined with another significantly thicker substrate (e.g., using above described assembly process), to obtain a light guide plate of a thicker format, without departing from the scope and spirit of the present invention. 
     As noted above, most conventional V-cut light guide plates are formed by injection molding, so the refractive index of the prismatic structure on the underside facing away from the LC module is the same as that of the base substrate, and the prisms should be further designed (for example, in terms of the angle, the width, or the depth) so as to control the reflection direction of light in order to achieve the effect of guiding the direction of the light path. In contrast, for the thin and flexible light guide film of the present invention, the layer of light-adjusting structure  20  is formed on the substrate layer  19  by a coating method, such that the layers can have different refractive indices, thereby the light path can be controlled to achieve the desired effect of guiding the direction of the light towards the light emitting surface of the light guide film towards the LC module  12 . According to one embodiment of the present invention, the absolute value of the difference in the refractive indices of the two layers is in the range from 0.001 to 0.6 (either layer can have a higher refractive index than the other). 
     In another embodiment, the substrate layer  19  and the layer of lenticular lenses  21  can be integrally-formed by molding, pressing, embossing, calendaring or extrusion onto a thicker transparent film substrate. Further discussions of processes for forming a substrate having structured surfaces may be referenced to U.S. Pat. No. 7,618,164, which is incorporated by reference herein. 
     The flexible transparent material suitable for the substrate layer  19  of the thin and flexible light guide film  18  can be made of various types of material known to those having ordinary skill in the art, such as plastics, which may include, for example but not limited to, polyester resins, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyacrylate resins, such as polymethyl methacrylate (PMMA); polyimide resins; polyolefin resins, such as polyethylene (PE) and polypropylene (PP); polycycloolefin resins; polycarbonate resins; polyurethane resins; polyvinyl resins, such as polyvinyl alcohol (PVA), or polyvinyl chloride (PVC); triacetate cellulose (TAC); or a mixture thereof. In one embodiment, the preferred substrate is polymethyl methacrylate (PMMA). Likewise, the layer of lenticular lenses  21  can be made of similar materials as the substrate layer  19 , such as acrylic resins or any other transparent material known to one skill in the art, which is suitable for adhering to the substrate layer  19 . 
     The thickness of the substrate layer  19  is constant throughout (i.e., the opposing surfaces of the substrate layer  19  are parallel), which may be in the range from 100 um to 800 um, more preferably from 125 um to 600 um. In another embodiment not shown, the substrate layer  19  may be tapered, e.g., with thickness thinning from the light input edge to the opposing edge. The thickness of the layer of lenticular lenses  21  of the light guide film  18  (or the height of the lenticular lenses  21 ) may be between 0.5 um and 100 um, preferably between 1 um and 60 um, and more preferably between 1 um and 45 um. 
     In the embodiment in  FIG. 2  (and referring also to  FIG. 7 ), the vertical height d 3  of the lenticular lenses  21  (crown height of the lenses measured from the top of the substrate layer  19 , or if the substrate layer  19  is integral to the lenticular lenses  21 , measured from the valley between non-intersecting adjacent lenticular lenses  21 ) is identical, preferably in the range of 0.5 μm to 100 μm, preferably in the range of 1 μm to 60 μm, and more preferably in the range of 1 μm to 45 μm. The curvature of the lenticular lenses is the same. Spacing d 1  (between edges of adjacent lenticular lenses) is the same=0 μm to 1000 μm; width d 2  (distance between edges at the sides of the convex surface) is the same for all the lenticular lenses=0 μm to 1000 μm. The center spacing between adjacent lenticular lenses (i.e., d 1 +d 2 )=3 μm to 1200 μm. If there is a thin base film (web) integral to the lenticular lenses  21  in the layer  20  to facilitate maintaining integrity of the adhesion (see base film  42  in  FIG. 4 ), the thickness of the film (or bottom thickness) may range between 5 to 800 micrometers. 
     The present inventive concept may be extended to include light-adjusting structure comprising lenticular lenses that are coated with beads, and/or particles built-in on the lenticular surfaces. 
       FIG. 4  and  FIG. 5  are other embodiments of light guide films of the present invention which combines prism and lenticular-like structures on two sides of a substrate. 
     In the embodiment of  FIG. 4 , the light guide film  48  has a structure that combines prismatic and lenticular structures on opposing sides of the substrate layer  49 . Specifically, the light guide film  48  has a structured lenticular surface  40  and a structured prismatic surface  44 . The lenticular lenses  41  are similar in structure to the lenticular lenses  21  in the previous embodiment, except that the layer  40  of lenticular lenses  41  comprises a thin base film  42  integral to the convex lenses. The spacing d 1 , width d 2  and crown height d 3  of the lenticular lenses  41  can remain constant, or can vary by keeping two of the parameters (d 1 , d 2 , d 3 ) constant and varying one parameter across the light guide film, or keeping one of the parameters constant and varying the other two parameters across the light guide film. 
     In this illustrated embodiment, the structured prismatic surface  44  is a light output surface that enhances brightness along an orthogonal view axis (i.e., improves light collimation) and the structured lenticular surface  40  is the light-adjusting surface of the light guide film  48  for internal reflections as in the previous embodiment. As illustrated in  FIG. 4 , the prismatic surface  44  includes parallel rows of contiguous or continuous longitudinal prisms  45 , extending between two opposing edges of the substrate layer  49 . The rows of longitudinal prisms  45  are arranged in parallel laterally (side-by-side), defining parallel peaks  46  and valleys  47 . The sectional profile of the peak  46  is symmetrical about vertical (viewed in the y-z plane). The peak vertex angle may be right angled, and the peaks are of constant or similar height and/or the valleys are of constant or similar depth, across the plane of the prismatic surface  44 . The distance or pitch between adjacent peaks/valleys is constant in the illustrated embodiment of  FIG. 4 . In the illustrated embodiment, the structured prismatic surface  44  and the structured lenticular surface  40  are generally parallel to each other in the overall light guide film structure (i.e., do not form an overall substrate structure that is generally tapered like a light guide plate in a backlight module). In another embodiment, the height or the prisms may vary in the longitudinal and/or lateral directions, across the plane of the light guide film. Laterally adjacent prisms may be disjoined (i.e., spacing present between adjacent prisms). In  FIG. 4 , the longitudinal axis (in the y-direction) of the lenticular lenses  41  is orthogonal to the longitudinal axis (in the x-direction) of the prisms  45 . 
     The double-sided light guide film  48  of  FIG. 4  can be manufactured involving similar processes described above for the previous embodiment. The light guide film  48  can be fabricated by a process involving coating/embossing both sides of a roll of sheet material, in a roll-to-roll continuous process. Either or both of the lenticular structure surface  40  and the prismatic surface  44  can be formed as separate layers to the substrate layer  49 , or integral to the substrate layer  49 . In the illustrated embodiment in  FIG. 4 , the light guide film  48  comprises three separate layers, including the prismatic surface layer  44 , the flexible substrate layer  49 , and the layer of structured lenticular surface  40 . The prismatic surface layer  44  and the structured lenticular layer  40  are adhered to the substrate layer  49  to form the overall light guide film  48 . It can be appreciated that the light guide film  48  may be formed from a single integrated physical layer of material, instead of three separate physical layers, without departing from the scope and spirit of the present invention. The light guide film  48  may be a unitary or monolithic body, including a base portion bearing the surface structures of the prisms  45  and the lenticular lenses  41 . 
     In the embodiment of  FIG. 5 , like the embodiment of  FIG. 4 , the light guide film  58  has a structure that combines prismatic and lenticular structures on opposing sides of the substrate layer  59 . Specifically, the light guide film  58  has a structured lenticular surface  50  and a structured prismatic surface  54 . In this embodiment, the layer  50  of lenticular lenses  51  comprises a thin base film  52  integral to the convex lenses  51 . The structure of the lenticular lenses is similar to the earlier embodiment, except that the spacing d 2  between edges of two discontinuous adjacent lenticular lenses  51  of the structured lenticular layer  50  is variable or different across the section in the x-direction. The width d 2  of the lenticular lenses are same and constant. The height of the lenticular lenses  51  (measured from the top of the base film  52 ) is identical. 
     The prismatic surface  54  includes parallel rows of contiguous or continuous longitudinal prisms  55  similar to the structure of the prismatic surface  45 . The double-sided light guide film  58  of  FIG. 5  can be manufactured involving similar processes described above for the previous embodiments. In  FIG. 5 , the longitudinal axis (in the y-direction) of the lenticular lenses  51  is orthogonal to the longitudinal axis (in the x-direction) of the prisms  55 . 
     In other embodiments not shown, instead of or in addition to having prismatic surface ( 44 ,  54  in the previous embodiments), the light emitting surface of the light guide film may be coated with beads and/or particles built-in, e.g., on the substrate layer, or the prismatic surfaces if provided. 
     In other embodiments not illustrated, the vertical height of the structures of the lenticular lenses may be variable. Further, the radius of curvature of different lenticular lenses may also vary and/or different lenticular surfaces may conform to cylinders of different cross-sections other than a circle (e.g., an ellipse or other cross-sections of regular or irregular geometries) and further of varying sizes. Longitudinal lenticular structures having a uniform cross-section defining different convex curve surface profiles are also contemplated (e.g., same profile or different profiles for different lenticular lenses). 
     Experimental Results: 
     Experiments were carried out to determine the effect of dimensional variations in the lenticular lenses on the uniformity of light brightness distribution of the light guide film of the present invention. 
     Referring to the further embodiment of  FIGS. 6A and 6B , the light guide film  180  studied has a diagonal size of about 10.1 inches and is formed by using a transparent material such as acrylic resin.  FIG. 6A  is a schematic planar view of the bottom surface of the light guide film  180 .  FIG. 6B  is a schematic perspective view of the circle region  6 B of the light guide film  180 . A light source  150  is near one side of the light guide film  180 . In the present embodiment, the bottom surface of the light guide film  180  has fourteen defined areas which have, for example, a width of about 10 cm, from area A to area N. A plurality of lenticular lens patterns  205  are disposed on the bottom surface  190  (not facing the LC module) of the light guide film  180  such that the lenticular patterns  205  are approximately parallel to the light source  150 , and arranged to have constant spacing d 1  within each of areas A to N (i.e., with each area, the spacing between adjacent lenticular lenses is same and constant, but the spacings for the different areas are different). In this embodiment, the width d 2  and height d 3  of the lenticular lenses are same and constant, and at least some of the lenticular lenses do not intersect each other (e.g., in the area closer to area A). In the embodiment illustrated in  FIGS. 6A and 6B , the arcuate surfaces of some of the lenticular lenses may overlap or meet each other (e.g., in areas closer to area N). 
     Table 1 shows the initial design dimensions of the light guide film  180 . As shown in Table 1, variables d 2 , d 3  and R are maintained constant, and d 1  is varied in different areas A to N. The uniformity of light output from such light guide film design is not ideal; e.g., based on the “13-point” test adopted by the industry, uniformity in brightness distribution is about 30% only. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 AREA 
               
             
          
           
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
                 J 
                 K 
                 L 
                 M 
                 N 
               
               
                   
                   
               
             
          
           
               
                 d1 + d2(μm) 
                 503 
                 490 
                 469 
                 441 
                 406 
                 324 
                 287 
                 240 
                 208 
                 178 
                 151 
                 125 
                 117 
                 105 
               
               
                 d2(μm) 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
                 69.5 
               
               
                 d3(μm) 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
               
               
                 R(μm) 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
               
               
                   
               
             
          
         
       
     
     It has been found that by increasing the radius of curvature (R) (d 2  value also increased corresponding to an increase in R), and keeping the R value constant in all 14 predefined areas A to N, better brightness uniformity across the light guide film from light diffusion by internal reflection can be achieved (e.g., to 75%). By further fixing the (d 1 +d 2 ) value and the depth d 3  of the lenticular lenses, the design of the light guide film is further optimized, with an increase in brightness uniformity from 30% to 40%. 
     To achieve more freedom of design, the combination of the variables may be modulated. By fixing (d 1 +d 2 ) and R values, parameters d 2  and d 3  are further adjusted and brightness uniformity at 40% to 68% can be achieved. A relationship may be developed for optimizing d 1 +d 2  value and d 3  value: the brightness uniformity may be further increased (e.g., to over 75%) by using such optimized relationship). 
     By using the structure of the light guide film described above, the brightness is more uniformly distributed over the LCD display area. Furthermore, referring back to  FIG. 2 , a reflecting member such as reflector sheet  22 , can be incorporated into the backlight module  14  by wrapping or surrounding the light guide film  18 . The reflecting sheet  22  facilitates collection of escaping light from the light guide film  18 , and reflect such light back into the light guide film  18 . By such a light recycling function, further maximization of the brightness of the backlight module  14  can be achieved. 
     In accordance with the present invention, the light guide film (e.g.,  18  in  FIG. 2 ) comprises a structure lenticular light-adjusting surface, which improves distribution of light output across the plane of the light guide film, when applied in an LCD for example. An inventive LCD incorporating the inventive optical substrate in accordance with the present invention may be deployed in an electronic device. 
     The optical substrates in accordance with the present invention may be used with LCDs to be deployed for displays, for example, for televisions, notebook computers, monitors, portable devices such as cell phones, digital cameras, PDAs and the like, to make the displays brighter. 
     As shown in  FIG. 8 , an electronic  110  (which may be one of a PDA, mobile phone, television, display monitor, portable computer, refrigerator, etc.) comprises the inventive backlight LCD  10  in accordance with one embodiment of the present invention. The LCD  10  comprises the inventive light guide film described above. The electronic device  110  may further include within a suitable housing, a user input interface such as keys and buttons (schematically represented by the block  116 ), image data control electronics, such as a controller (schematically represented by block  112 ) for managing image data flow to the LCD  10 , electronics specific to the electronic device  110 , which may include a processor, A/D converters, memory devices, data storage devices, etc. (schematically collectively represented by block  118 ), and a power source such as a power supply, battery or jack for external power source (schematically represented by block  114 ), which components are well known in the art. 
     While the present invention has been described in connection with LCD devices, the light guide film may be applied to other applications. The inventive light guide may be in the form of a film, sheet, plate, and the like, which may be flexible or rigid, having a lenticular structured surface, and may in addition have an opposing prismatic structured surface. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed structures and processes of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.