Abstract:
A system for illuminating a reflective display or other material from a planar front device and a method of manufacture thereof. The system includes a light guide plate that conducts light from an edge light source across the face of a reflective display. Micro scattering features are formed on an outer surface of the light guide, farthest from the reflective display or material. A stepped index layer is formed on the surface of light guide plate containing the micro scattering features. The stepped index layer has an index of refraction lower than an index of refraction of the light guide plate to assist in the total internal reflection of light injected into the light guide plate. The micro scattering features, light reflecting areas, redirect luminous flux toward the display. In one embodiment, the micro scattering features are formed as white dots on the light guide plate. A black absorbing layer can be added to each white scattering dot in order to improve the apparent contrast when the front light is deactivated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Application No. 61/525,667, filed Aug. 19, 2011, which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to planar front illumination systems for the illumination of reflective materials and displays, and more particularly to a light guide plate that conducts light from an edge light source across the face of a reflective display. 
     BACKGROUND OF THE INVENTION 
     In contrast to backlit displays (e.g., a backlit transmissive Liquid Crystal Display, LCD), where light is projected through one or more filters or shutters to create an observable image, a reflective display (e.g., an electrophoretic display, EPD) relies on light reflected off of a reflective surface to generate an image. Typically, reflective displays make use of the ambient light present in the environment where the display is used. Planar front illumination systems have been used for many years to augment the ambient light so that reflective displays can be used in darker environments. Typical planar front light illumination systems are made of clear materials and are attached to the front of reflective electronic displays. Front lights provide supplemental illumination to the face of the display when the reflected ambient light is insufficient to create an observable image. 
     An ideal front light illumination system would be able to efficiently and uniformly direct the light from a supplemental light source toward the display while not emitting stray light toward the environment or user. This ideal front light illumination system passes all of the reflected light to the user without optical loss or optical artifacts. Further, such an ideal front illumination system would be unobtrusive under ambient lighting, i.e., maintaining the contrast, brightness and image quality of the underlying display. In addition, such an ideal front light is also low cost, thin, lightweight, easily manufactured, compatible with touch technologies and widely available. 
     One common type of front light illumination system includes a light guide plate constructed with numerous microscopic optical surface features. Each of these optical surface features incrementally redirects a small portion of the light inside the light guide plate using reflection or refraction. Ideally, these optical surfaces extract and distribute the luminous flux within the light guide plate uniformly over the surface of the reflective display. To achieve reflection or refraction without mirrored surfaces (which would be costly), optical engineers carefully construct the critical features and angles of the micro optical surface features to reliably and predictably reflect or refract a desired amount of light despite the often poor collimation (i.e., the wide distribution of ray angles) of the source illuminators (e.g., LEDs). The refractive and reflective feature of an optical interface is strongly dependent on the relative indices of refraction of the materials on either side of the interface. To maximize the reflective and refractive power of these micro optical features, the micro optical features are usually exposed directly to air to maximize the refractive index difference. 
       FIG. 1  shows a conventional front illumination system with microscopic optical surface features. This system comprises a reflective display  100 , a light source  101  and a light guide plate  102 . The light guide plate has optical features  103  formed on the outer facing surface of the front illumination system. The light source  101  is typically comprised of one or more cold cathode fluorescent lights (CCFLs) or one or more LEDs, suitably arranged to produce moderately collimated light  104  directed into a light injection surface of the light guide plate  102 . 
     Common additional features known in the art (not shown) include a reflective housing for the light source  101 , surface treatments on the light source  101  and the injection area of the light guide plate  102 , and films or mixing plates inserted between the light source  101  and light guide plate  102  that improve coupling efficiency, uniformity, manufacturability, optical performance and cost. Such additions are applicable to the present invention as well to achieve similar advantageous effects. 
     A substantial portion of the light  104  injected into guide plate  102  remains within the light guide plate  102  due to the well-known optical effect of total internal reflection (TIR). Light guide plate  102  has a plurality of micro optic features  103  on its outer surface that redirect a portion of the guided rays  107  downward at each micro optic feature  103 . Ideally, the injected light  104  is uniformly redirected and distributed across the entire surface of the reflective display  100 . To achieve uniformity, the density, height, angle, pitch and shape of the micro optic features  103  and the thickness or shape of the light guide plate  102  is modulated across the breadth and width of the light guide plate  102  to account for the diminished light flux as a function of distance from the light source  101 . 
     The incrementally redirected light  107  illuminates the reflective display  100  creating reflected rays  109  that can be seen by a user (the user, not shown, is above the front illumination systems as illustrated herein). 
     A typical front illumination system is usually only activated when the ambient light  108  falling on the display from external sources is insufficient for the user to perceive an image from the reflective display  100 . When ambient illumination  108  is strong enough and consequently the front illumination source is not needed, the front illumination system should be as unobtrusive as possible. Specifically, the front light system should not create unusual reflections, image artifacts or stray light paths that degrade the appearance of the underlying display  100 . 
       FIG. 2  shows a prior art back illumination system comprising a transmissive display  200 , a light source  201  and a light guide plate  202 . Light guide plate  202  has light extraction dots  203  formed on the outer surface farthest from the display  200 . The light source  200  injects light  204  into the light guide plate  202 , which is then substantially guided by total internal reflection in a lateral direction in the light guide plate  202 . The plurality of light extraction dots  203  is screen or inkjet printed etched, stamped, burned, or molded (among the many conventional methods well known in the art of backlight design) on the outer surface of the light guide plate  202  to act as scattering centers that redirect the guided light  204  in a diffuse scattering pattern  207  towards the transmissive display  200  and ultimately toward the viewer (ray  209 ). The density, color and/or sizes of the light extraction dots  203  is conventionally varied as a function of position to account for non-uniformity of the light source and to compensate for the consumption of guided light flux as a function of distance from the light source  201 . As is known in the art, additional films  208  can be placed between the back light and the transmissive display (e.g. diffusers and light redirecting films, polarizing films, etc.) to improve the optical efficiency and uniformity of the overall display. 
     The refractive and reflective feature of an optical interface between two clear materials (e.g. plastic and air) is strongly dependent on the relative indices of refraction of the materials on either side of the interface. To optimize the light guiding (via total internal reflection) and light extraction (via scattering, reflection or refraction) behaviors, the micro optical features are usually exposed directly to air to maximize the refractive index difference. 
     SUMMARY OF THE INVENTION 
     The front illumination systems of the prior art that rely on air interfaces, while improving the refracting and reflecting effects, create a number of substantial difficulties that are solved by the present invention. First, air gaps between optical elements over a wide area are difficult to mechanically construct while maintaining thinness and optical quality. If the front illumination system is integrated with a touch panel function, the front face must be sufficiently rigid so that it can maintain the air gap under worst case user finger pressure. Air gaps, due to the high relative index of refraction change, also can create substantial unwanted reflections unless costly anti-reflection coatings are used at each interface. 
     Second, if air gaps are formed on films that are subsequently laminated to a light guide plate (i.e., an embedded air gap), these air gaps are difficult to control in production as the lamination adhesive can be displaced into the air gaps or grooves, modifying the behavior of the light extraction phenomena and creating uniformity problems. An inherent tradeoff in adhesion strength versus optical quality and feature size is introduced that may not provide satisfactory solutions. Furthermore, air pressure and humidity vary widely (sometimes quickly, e.g., on an aircraft) and condensation, contamination and pressure related effects (if sealed) can create engineering, production and user difficulties. 
     Further, since the source light is usually poorly collimated, stray light leakage can be inadvertently directed toward the viewer, significantly increasing the brightness of the black level and thus degrading contrast. Such stray light leakage, even if not directed to the viewer, e.g., if exported at a highly acute angle from the front surface of the display system, can still result in poor electro-optical efficiency, which can negatively impact the battery life of mobile devices. 
     Additionally, controlling the quality of the micro optical features created in a molding process can be challenging as the light guide plate is made thinner and lighter. 
     Another concern associated with the prior art systems is that mechanical damage, e.g., scratches, may extract light from the light guide plate causing them to be especially highlighted when the front light is activated. Additional mechanical barriers between the light guide plate and the user are often required to prevent scratch highlighting, increasing thickness of the front illumination system and degrading optical performance of the display system. 
     Front light illumination system design forces a number of compromises where optical design goals, e.g. minimizing ambient reflections and image artifacts. are optimized at the expense of some other constraints, e.g., the cost of anti-reflection coatings and thickness of the system. 
     The front illumination system of the present invention addresses a number of the aforementioned limitations and forced compromises in the art, enabling a fully laminated, thin, light, economical, uniform, mechanically robust, efficient, highly transparent, low artifact, low leakage front illumination system. 
     The system of the present invention includes a light guide plate that conducts light from one or more edge light sources across the face of a reflective display. Micro scattering features are formed on an outer surface of the light guide farthest from the reflective display or material. These micro scattering features redirect luminous flux from within the light guide toward the display. In one embodiment, the micro scattering features are formed as white dots on the light guide plate. A black absorbing layer can be added to each white scattering dot in order to improve the apparent contrast when the front light is deactivated. 
     A layer having a lower index of refraction is formed on the surface of the light guide plate having the micro scattering features. This layer is also known as a stepped index layer and assists in substantially confining the injected light in the light guide plate by total internal reflection. This structural configuration provides a fully laminated front illumination system with a buried light guide layer, In addition or in the alternative, the light guide plate can be laminated to the reflective display or other material, or laminated to a top layer protective coat or touch screen, providing a fully laminated front illumination system with a buried light guide layer. 
     The planar front illumination system of the present invention can be fully laminated with no air gaps, thus maximizing the ruggedness and minimizing the internal surface reflections which can degrade optical performance. The system simplifies integration of reflective displays with touch sensors and is thin and light. The system maximizes the light directed inward toward, for example, a display while minimizing stray light in all other directions. The system generates uniform illumination over a large area while minimizing image and illumination related artifacts such as Moire, ghosting and pressure sensitivity. The system is efficiently and inexpensively produced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purposes of illustrating the present invention, there is shown in the drawings a form which is presently preferred, it being understood however, that the invention is not limited to the precise form shown by the drawing in which: 
         FIG. 1  depicts a prior art front illumination system for a reflective display with micro optic features on the front face of a light guide plate; 
         FIG. 2  illustrates a prior art back illumination system for a transmissive display utilizing a printed dot pattern light guide plate; 
         FIG. 3  illustrates a planar front illumination system of the present invention with printed dots formed on the outer face of a light guide plate; 
         FIG. 4A  shows a top view of a planar front illumination system of the present invention with printed dots formed on the outer face of a light guide plate; 
         FIG. 4B  shows a side view of a planar front illumination system of the present invention; 
         FIG. 4C  shows a bottom view of a planar front illumination system of the present invention; 
         FIG. 5  depicts a flow for a manufacturing process of the present invention using two pass printing; 
         FIG. 6  illustrates a flow for a manufacturing process of the present invention using single pass white dot printing followed by a reactive addition of a black top layer; 
         FIG. 7  depicts a flow for a manufacturing process of the present invention using single pass white dot printing followed by a self-aligned lift-off process; 
         FIG. 8  illustrates a flow for a manufacturing process of the present invention using a photomask and lift-off processing; 
         FIG. 9  depicts a flow for a manufacturing process of the present invention using a photomask and etch processing; and 
         FIG. 10  illustrates a planar front illumination system of the present invention with printed dots formed on the outer face of a light guide plate with additional lamination layers which remove all air gaps and voids. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following abbreviations are utilized in the following description, which are intended to have the meanings provided as follows: 
     CCFL—cold cathode fluorescent light 
     EPD—electrophoretic display 
     LCD—liquid crystal display 
     LGP—light guide plate 
     LED—light emitting diode 
     OCA—optically clear adhesive 
     OLED—organic light emitting diode 
     PC—polycarbonate 
     PET—polyethylene terephthalate 
     PMMA—poly methyl methacrylate 
     TIR—total internal reflection 
       FIG. 3  shows an embodiment of the present invention comprising a reflective display or material  300 , a light source  301  and a light guide plate  302 . A plurality of micro scattering features  303  are formed on the outer surface of the light guide plate  302 . In a preferred embodiment, the micro scattering features are formed as white dots. The light source  301  and light guide plate  302  are coupled as is well known in the art to achieve efficient, uniform and reproducible injection of light  304  into the light guide plate  302 . As illustrated in this  FIG. 3 , laterally propagating rays  305  are confined within the light guide plate  302  by, in part, the TIR effect from the inner surface of the light guide plate  302  at the interface to a stepped index layer  310 . The stepped index layer has an index of refraction that is lower than that of the light guide plate  302 . In a preferred embodiment, the stepped index layer  310  is a clear adhesive layer. Although air can be used as the stepped index layer, it is preferred to use some other material, such as the above described clear adhesive layer. 
     The term “stepped index” is borrowed from the fiber optic technology and is distinguished from other indexes such as “graded index” fiber which has a smooth index peak that confines a single mode in order to keep propagation speed very uniform). In a fiber structure, a cylindrical inner core of high index material is cladded with a lower index material to achieve TIR for light propagating down the length of the cylinder. In contrast to the use in fiber structures, the present invention uses its stepped index layer to confining light in only one dimension and leave the light to freely propagate freely in the other two dimensions. In a fiber, the light is confined in two dimensions and can freely propagate in only one dimension. 
     Dots  303  with a white or lightly colored scattering side facing the light guide plate  302  are formed in or on the light guide plate  302 . In a preferred embodiment, dots  303  are formed on the surface of light guide plate  302 . Dots  303  perform a light extraction function in which the laterally propagating rays  305  are diffusely scattered by the dots  303  as rays  307  and are directed toward the reflective display  300 . The reflective display  300  reflects the incoming light  307  and the incident ambient light  308  toward the viewer as rays  309 , passing through the clear areas of light guide plate  302  and through the stepped index layer  310 . 
     In one embodiment of the present invention, the density of the scattering dots  303  is preferably kept low enough so that the vast majority (e.g. &gt;95%) of the ambient light rays  308  and display reflections  309  cross unimpeded through the light guide plate  302  without encountering a scattering dot  303 . In this manner, the impact of the scattering dots  303  on the ambiently lighted display performance is minimized. 
     In a further embodiment of the present invention, the area of each scattering dot  303  is kept substantially smaller than the underlying reflective display  300  unit pixel area (not shown) so that the scattering dots  303  do not objectionably obscure the underlying pixels. In a further embodiment, the scattering dots  303  are spaced sufficiently closely together and sufficiently elevated above the display  300  image plane so that the scattered light  307  reaching the display  300  image plane is substantially spatially uniform. 
     In a further embodiment of the present invention, the scattering dots  303  are constructed so that the spatial density, size and/or reflective properties of the dots  303  are varied across the light guide plate  302  so that the uniformity of the extracted light  307  is controlled and optimized. In addition, or in the alternative, the thickness, shape or composition of the light guide plate  302  is varied to compensate for such non-uniformities. 
     In another embodiment of the present invention, the scattering dots  303  are composed of a white, lightly colored or reflective bottom material facing the light guide plate  302  and a black, darkly colored, or otherwise light absorbing top material facing the viewer (not shown in  FIG. 3 ). Such bi-color composition, dark outside, light inside, prevents the ambient illumination  308  from scattering directly back to the viewer when it falls directly on a scattering dot  303 . In this embodiment, the additional dark top of the scattering dots  303  substantially improves the perceived black level of the display  300 , thus providing a high contrast ratio substantially similar to the underlying reflective display&#39;s native contrast. 
     A large number of materials are available to the design engineer for constructing the present invention. Light guides are commonly constructed of PMMA or PC plastic, although any optically clear material, e.g., glass, with a higher index of refraction than the surrounding material, e.g., stepped index layer  310  above the light guide plate  302 , and air or vacuum below the light guide plate  302  in  FIG. 3 , and a substantially flat surface will act as a light guide. Light source  301  can assume many forms. For example a CCFL, an OLED or one or more LED lamps coupled to a light bar or mixing plate may be used as the light source  301 . One or more sides of the light guide plate  302  may have injecting surfaces with one or more light sources  301 . For simplicity, only one light source  301  is shown in the Figures but as is well known in the art, the number and positions of light sources  301 , e.g., one or more edges or corners, can be varied, given system constraints on cost, light uniformity, brightness, mechanical boundaries, form factor, etc. Additionally, other light sources  301 , e.g., incandescent lamps, lasers, vacuum fluorescent tubes, could be substituted without limiting the present invention. 
     The optical interfaces and surfaces of the components of the present invention can be coated, shaped, processed, textured or modified by the inclusion or application of specialized films so as to achieve any number of standard desirable changes in properties, e.g., to improve light confinement, improve light guide injection uniformity, reduce stray reflections, improve light source  301  to light guide plate  302  coupling efficiency, improve light guide plate  302  to reflective display interface, reduce thickness and weight, etc. Such additions and modifications are well known in the art of illumination design and are available at the discretion of the designer to achieve the desired balance between cost, performance, yield, etc. 
     There are many options available for fabricating scattering dots  303  on the light guide plate  302 . In one embodiment, the scattering dots  303  are printed using, for example, an industrial inkjet printer. Such printers can apply small, e.g., 30 to 50 microns or less, white or colored dots  303  precisely, rapidly and inexpensively directly onto the surface of the light guide  302 . Such scattering dots  303  can also be laser etched, hot stamped, molded, mechanically embossed, chemically etched or created lithographically. 
     The exact shape of the scattering dots  303  can be substantially changed within the present teachings. The reflecting areas  303  can be circular, square, rectangular or oval in shape, although other shapes are possible. In addition or in the alternative, the reflecting areas  303  can be formed as scattering lines, segments or traces. 
     In one embodiment of the present invention, the light guide plate  302  and the stepped index layer  310 , e.g., optically clear adhesive layer, can be manufactured as a unit, for later incorporation in the assembly of a completed device having a light source  301  and a display  300 . 
     In a preferred embodiment of the present invention, the light guide plate  302  is fabricated from polycarbonate with an index of refraction of approximately 1.585. In a further preferred embodiment, the stepped layer  310  is made of a low index optical adhesive with an index of refraction of between 1.32 and 1.50. In an alternative embodiment, the light guide plate  302  is fabricated from PMMA with an index of refraction of approximately 1.49 and the stepped layer  310  is made of a low index optical adhesive with an index of refraction of between 1.32 and 1.46. Those skilled in the art will recognize the wide variety of light guide materials and adhesive laminating materials that can be substituted within the general framework of the present teachings to create the conditions for sufficient confinement by TIR within the light guide plate  302 . 
     As further described below with respect to  FIG. 10 , a protective layer (not shown in  FIG. 3 ) can be formed on top of the stepped index layer  310  and can used as a substrate for integrating a fully laminated touch sensor onto the top of the display system. Such laminated touch sensors are well known in the art, e.g., projected capacitance, surface capacitance, infrared, etc., and the lamination of such a touch sensor as, or in addition to, the top protective layer does not alter or degrade the performance of the system of the present invention. 
       FIGS. 4A ,  4 B and  4 C respectively show top, side and bottom views of a representative embodiment of the present invention. The system includes a light source  401 , a light guide plate  402 , a stepped index layer  310  and a plurality of white or lightly colored scattering dots  403  formed on the surface of the light guide plate  402 . In the embodiment illustrated in  FIG. 4 , black dots  404  are formed directly on the white scattering dots  403 , substantially covering each white dot  403 . As described above, one function of the black covering  404  is to absorb direct ambient light ( 308  in  FIG. 3 ) preventing a direct reflection back to the user by the white dots  403 . The reflection of light in the light guide  402  toward the reflecting display is maximized by the white dots  403 , while the reflection of ambient light back toward the user is minimized by the black covers  404 . 
       FIG. 5  shows a representative manufacturing flow of the present invention. In this  FIG. 5 , and the flowing  FIG. 6-9 , the process is described in the flow chart on the left of the Figures and the corresponding effect of the manufacturing process on the structure is illustrated on the right. In act  500 , the process starts with a bare (blank) light guide plate substrate  502 . In act  510 , a plurality of white dots  503  is printed onto the light guide plate substrate  502 . In an optional third act  520 , a plurality of black dots  504  is printed on the surface of the light guide plate  502  substantially aligned on or with the white dots  503 . 
     A wide variety of printing methods, machinery, ink compositions, surface preparations, adhesion promoters, curing options and thermal profiles, etc. are available to the process engineer to achieve the desired balance between cost, throughput, uniformity, yield, etc. Such alternative print or deposition methods are applicable to and within the scope of the present teachings. 
     Although not shown in  FIG. 5 , a stepped index layer with an index of refraction lower than that of the light guide plate  502  is preferably applied on top of the light guide plate  502  and dots  504 . 
       FIG. 6  illustrates an alternative manufacturing process of the present invention. In act  600 , the process starts with a blank light guide plate substrate  602 . In act  610 , a plurality of white dots  603  are printed onto the light guide plate  602 . In act  620 , a black top surface  604  is reactively created on the previously printed white dots  603 . Such reactive processing can be a chemically, electrically, thermally or optically activated or mediated process that only affects the exposed area of the white printed ink dots  603 . Alternatively, an additive that binds to the surface of the ink drop  603 , e.g., a pigment dust or slurry, can be applied to achieve the desired darkened top  604 . 
     Although not shown in  FIG. 6 , a stepped index layer with an index of refraction lower than that of the light guide plate  602  is preferably applied on top of the light guide plate  602  and dots  604 . 
       FIG. 7  depicts an alternative manufacturing process of the present invention. As with the previous processes, act  700  starts with a bare light guide plate substrate  702 . In act  710  a plurality of white dots  703  are printed on the surface of the light guide  702  using one of the aforementioned printing techniques and inks. In act  720  a negative photoresist  705  is deposited on the substrate  702 . Such photoresists  705  are well known in the art, e.g., photoresist AZ5214E. In act  730 , the photoresist  705  is exposed  706  from below the light guide plate  702 , using the printed dots  703  as an exposure mask. In act  740 , the photoresist  705  is developed. In act  750 , a black layer  704  is deposited over the photoresist  705  and the printed dots  703 . In act  760  the photoresist  705  and the excess black layer  704  on the photoresist  705  is lifted off (stripped) leaving behind white dots  703  with self-aligned black deposits  704  on top of them. 
     The lift off processing is well known and those skilled in the art can substitute and insert processing steps (e.g., cleaning the substrate, pre-baking the photoresist, etc.) that do not alter the scope of the present teachings. The use of the printed dots  703  as a mask for the photoresist exposure is neither taught or suggested by the prior art. Other processing steps are well known in the art and can be adjusted to achieve a desired cost/yield optimization without loss of generality of the present invention. 
     Although not shown in  FIG. 7 , a stepped index layer with an index of refraction lower than that of the light guide plate  702  is preferably applied on top of the light guide plate  702  and dots  704 . 
       FIG. 8  illustrates a further alternative manufacturing process of the present invention. In act  800 , the process starts with a bare light guide plate substrate  802 . In act  810 , a photoresist  805  is deposited on the substrate  802 . In act  820  the photoresist  805  is exposed using a lithographic mask  809  that represents the desired dot pattern. In act  830 , the photoresist  805  is developed. In act  840 , a white  803  and a black layer  804  are sequentially deposited on the photoresist.  805  and substrate  802 . In act  850 , the photoresist  805  and the non-dot material is lifted off and cleared, leaving the white colored dots  803  with a black covering  804 . As appreciated by those skilled the art, the application of the black layer  804  is an optional process. 
     Although not shown in  FIG. 8 , a stepped index layer with an index of refraction lower than that of the light guide plate  802  is preferably applied on top of the light guide plate  802  and dots  804 . 
       FIG. 9  depicts an alternative manufacturing process of the present invention. In act  900 , the process starts with a bare light guide plate substrate  902 . In act  910 , first a white  903  then a black layer  904  is deposited on the substrate  902 . In act  920 , a photoresist  905  is deposited on the black layer  904 . In act  930 , the photoresist  905  is exposed using a lithographic mask  909  representing the desired dot pattern. In act  940  the photoresist  905  is developed. In step  950 , the black  904  and white layers  903  are etched and in act  960  the remaining photoresist  905  is stripped, leaving the white colored dots  903  with a black covering  904 . As appreciated by those skilled the art, the application of the black layer  904  is an optional process. 
     Although not shown in  FIG. 9 , a stepped index layer with an index of refraction lower than that of the light guide plate  902  is preferably applied on top of the light guide plate  902  and dots  904 . 
     The lithographic techniques as described in  FIGS. 7 ,  8  and  9  can be modified to optimize for a variety of constraints, e.g., line throughput, repeatability, cost, etc., by changing or adding processing steps or materials. 
       FIG. 10  shows a further embodiment of the present invention. This embodiment includes a reflective display or material  1050 , a light source  1051  and a light guide plate  1052 . As with the previous embodiments, a plurality of scattering dots  1053  is formed on the outer surface of the light guide plate  1052 . Low index of refraction laminating adhesive layers  1060  and  1061  form a stepped index layer that is used for substantially confining injected  1054  and propagated light  1055  by TIR  1056  within the light guide plate  1052 . An additional protective layer  1062  is optionally added to the top of the optical stack. 
     The light source  1051  and light guide plate  1052  are coupled as is well known in the art to achieve efficient, uniform and reproducible light injection  1054  into the light guide plate  1052 . Laterally propagating rays  1055  are confined within the light guide plate by TIR effect  1056 . A portion of the confined light  1055  strikes a given scattering dot  1053  which redirects a portion  1057  of the luminous flux toward the reflective display  1050 , which is then reflected back through the optical stack  1060 ,  1052 ,  1061  and  1062  out toward the viewer as rays  1059 . Ambient light  1058  incident on the display  1050  propagates substantially through the optical stack  1060 ,  1052 ,  1061  and  1062  with minimum optical losses and distortions to illuminate the display  1050  and create a viewable ray  1059  when ambient light is available. 
     In a preferred embodiment of the present invention, the light guide plate  1052  is fabricated from polycarbonate with an index of refraction of approximately 1.585. In a further preferred embodiment, the optical adhesive layers  1060  and  1061  are made of a low index optical adhesive with an index of refraction of between 1.32 and 1.50. In an alternative embodiment, the light guide plate  1052  is fabricated from PMMA with an index of refraction of approximately 1.49 and the optical adhesive layers  1060  and  1061  are made of a low index optical adhesive with an index of refraction of between 1.32 and 1.46. Those skilled in the art will recognize the wide variety of light guide materials and adhesive laminating materials that can be substituted within the general framework of the present teachings to create the conditions for sufficient confinement by TIR within the light guide plate  1052 . 
     Protective layer  1062  can be used as a substrate for integrating a fully laminated touch sensor onto the top of the display system. Such laminated touch sensors are well known in the art, e.g., projected capacitance, surface capacitance, infrared, etc., and the lamination of such a touch sensor as, or in addition to, the top protective layer  1062  does not alter or degrade the performance of the system of the present invention. 
     The system as illustrated in  FIG. 10  enables the full lamination of the front illumination system to both the display  1050  and an outer protective sheet  1062  by using micro scattering dots  1053  on the outer surface of the light guide plate  1052  as opposed to prisms, lenses or TIR mirrors as has been described in the prior art. By eliminating the micro optic features used in the prior art for light extraction from the light guide plate  1052 , the system as of  FIG. 10  can tolerate a reduced refractive index step (between light guide core and optical adhesive layers), while still acceptably confining the injected light  1054 . This allows the elimination of air gaps in the device structure and the benefits of thinness, robustness, uniformity and repeatability that ensue. 
     As described above, the white dots  1053  can additionally be coated with a dark or black pigment. An additional benefit of a two layer dot (black on white) is that any stray light entering the display from above (by stray reflections or external sources) or guided within the optical adhesive  1060  and protective sheet  1062  will encounter absorbing black dots when crossing into the light guide plate  1052  from above and thus will not refract or reflect back to the viewer as often happens with micro optical feature based light extraction systems. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and other uses will be apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the gist and scope of the disclosure.