Illumination apparatus and film

An illumination apparatus comprises:

FIELD OF THE INVENTION

The present invention generally relates to an illumination apparatus and optical film, and more particularly relates to a light extracting film using an arrangement of features for conditioning illumination for use in display and lighting applications.

BACKGROUND OF THE INVENTION

While liquid crystal displays (LCDs) offer a compact, lightweight alternative to cathode ray tube (CRT) monitors, there are many applications for which LCDs are not satisfactory due to a low level of brightness, or more properly, luminance. The transmissive LCD that is used in known laptop computer displays is a type of backlit display, having a light-providing surface positioned behind the liquid crystal (LC) array for directing light outwards, towards the LCD. The light-providing surface itself provides illumination that is essentially Lambertian, having an essentially constant luminance over a broad range of angles.

With the goal of increasing on-axis and near-axis luminance, a number of brightness enhancement films have been proposed for redirecting a portion of this light having Lambertian distribution toward normal, relative to the display surface. There have been many proposed solutions for brightness or luminance enhancement for use with LCD displays and with other types of backlit display types.

U.S. Pat. No. 6,111,696 (Allen et al.) describes a brightness enhancement film for a display or lighting fixture. The surface of the optical film facing the illumination source is smooth and the opposite surface has a series of structures, such as triangular prisms, for redirecting the illumination angle. U.S. Pat. No. 5,629,784 (Abileah et al.) describes various embodiments in which a prism sheet is employed for enhancing brightness, contrast ratio, and color uniformity of an LCD display of the reflective type. The brightness enhancement film is arranged with its structured surface facing the source of reflected light for providing improved luminance as well as reduced ambient light effects. U.S. Pat. No. 6,356,391 (Gardiner et al.) describes a pair of optical turning films for redirecting light in an LCD display, using an array of prisms, where the prisms can have different dimensions.

U.S. Pat. No. 6,280,063 (Fong et al.) describes a brightness enhancement film with prism structures on one side of the film having blunted or rounded peaks. U.S. Pat. No. 6,277,471 (Tang) describes a brightness enhancement film having a plurality of generally triangular prism structures having curved facets. U.S. Pat. No. 5,917,664 (O'Neill et al.) describes a brightness enhancement film having “soft” cutoff angles in comparison with known film types, thereby mitigating the luminance change as viewing angle increases.

While known approaches, such as those noted above, provide some measure of brightness enhancement at low viewing angles, these approaches have certain shortcomings. Some of the solutions noted above are more effective for redistributing light over a preferred range of angles rather than for redirecting light toward the normal for best on-axis viewing. These brightness enhancement film solutions often exhibit a directional bias, working best for redirecting light in one direction. For example, a brightness enhancement film may redirect some of the light in the vertical direction to relatively high off-axis angles that is out of the desired viewing cone. In another approach, multiple orthogonally crossed sheets are overlaid in order to redirect light in different directions, typically in both the horizontal and vertical directions with respect to the display surface. Necessarily, this type of approach is somewhat of a compromise; such an approach is not optimal for light in directions diagonal to the two orthogonal axes. In addition, such known films typically use “recycling” in which the light is reflected back through the backlight module multiple times in an effort to increase brightness. However, some of the reflected light is absorbed by materials and lost in reflection during recycling.

As discussed above, brightness enhancement layers have been proposed with various types of refractive surface structures formed atop a substrate material, including arrangements employing a plurality of protruding prism shapes, both as matrices of separate prism structures and as elongated prism structures, with the apex of prisms both facing toward and facing away from the light source. For the most part, these films exhibit directional bias, with some of the light poorly directed.

Certain types of light redirecting layers rely on Total Internal Reflection (TIR) effects for redirecting light. When a light guide is employed and such features are included in contact with the light output surface of the light guide, the features are more correctly termed “light extracting” features since they enable the light to be output rather than simply redirecting existing light. If the light guide is surrounded by air, features are needed to extract the light. These layers include prism, parabolic or aspheric structures, which re-direct light using TIR. For example, U.S. Pat. No. 5,396,350 to Beeson et al., describes a backlight apparatus comprising a slab waveguide and an array of microprisms attached on one face of the slab waveguide. U.S. Pat. Nos. 5,739,931 and 5,598,281 to Zimmerman et al. describe illumination apparatus for backlighting, using arrays of microprisms and tapered optical structures. U.S. Pat. No. 5,761,355 to Kuper et al. describes arrays for use in area lighting applications, wherein guiding optical structures employ TIR to redirect light towards a preferred direction. U.S. Pat. No. 6,129,439 to Hou et al. describes an illumination apparatus in which microprisms utilize TIR for light redirection. Japanese Laid-open Patent Publication No. 8-221013 entitled “Plane Display Device And Backlight Device For The Plane Display Device” by Yano Tomoya (published 1996) describes an illumination apparatus having collimating curved facet projections for light redirection utilizing TIR. U.S. Pat. No. 6,425,675 to Onishi et al., using curved facets similar to those originally described in the Tomoya 8-221013 disclosure, describes an illumination apparatus in which a light output plate also has multiple curved facet projections with their respective tips held in tight contact with the light exit surface of a light guide member.

A number of patent disclosures, such as the Tomoya 8-221013 and '675 Onishi et al. disclosures cited above, employ films having projecting structures and specify that these structures have one or more curved surfaces. While the use of a curved surface for TIR may be useful for providing on-axis light extraction, the design of curved projections for obtaining light over a broader range of angles can be more difficult. Moreover, curved surfaces themselves can prove to be difficult to fabricate, particularly at the dimensional scale that is needed for structures of a light extracting film.

Light extracting films must be optically coupled to their corresponding light guiding component in some way. Embodiments using structures with flat light input surfaces can be optically coupled simply by physical contact with the light guide, provided that this contact is maintained. Embodiments using structures with curved light input surfaces must be held in tight contact against the light guide. In order to prevent the tips of the projections of the light output plate from being embedded in the bonding layer, the bonding agent is semi-hardened beforehand and, after the bonding layer and the tips of the projections are brought to a tight contact each other, the bonding agent is hardened completely, as noted in the Onishi et al. '675 disclosure; however, the use of a two step hardening process, as described, can increase cost and complexity of fabrication. Also described in the art is a method for stacking surface structured optical films in which the structured surface of one film is bonded to an opposing surface of second film using a layer of adhesive by penetrating the structured surface into the adhesive layer to a depth less than a feature height of the structured surface, see U.S. Pat. No. 6,846,089 and U.S. 2005/0134963 A1. This, however, does not provide for more effective light extraction from a light guide plate.

What is needed, therefore, is a light extracting film that overcomes at least the shortcomings of known films previously described and that can be fabricated at reasonable cost.

SUMMARY OF THE INVENTION

As used herein, the terms ‘a’ or ‘an’ means one or more, and the term ‘plurality’ means at least two.

The invention provides an illumination apparatus comprising:(a) at least one light source;(b) a light guide for accepting light from the at least one light source and for guiding the light using total internal reflection;(c) a light extracting film having an input surface optically coupled with the light guide and an output surface parallel to the input surface for providing light,wherein the input surface comprises a plurality of light extracting features which are optically coupled to the light guide, such features being extended in a longitudinal direction and having a cross section in the plane perpendicular to the longitudinal direction, the cross section comprising(i) a first side comprising at least two but not more than six linear segments, and(ii) a second side comprising at least two but not more than six linear segments,wherein at least one of the plurality of light extracting features has a length measured in the longitudinal direction that is less than the length of the light extracting film measured in the longitudinal direction.

This invention further provides a light extracting film as described above. Additionally, the invention provides an apparatus and film where at least some of the features have sides comprised of two or more planar segments that meet in an apex.

This invention provides a simplified and integrated light extracting film that leads to easy manufacturing and low cost. This invention also maximizes optical efficiency so as to enhance brightness as well as viewing angle. The film has improved uniform display brightness and decreased interference effects such as Moiré effects. This invention also provides a article that redistributes light over a range of viewing angles.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth, in order to provide a thorough understanding of the present teachings. However, it will be apparent to one having ordinary skill in the art that other embodiments that depart from the specific details disclosed herein are possible. Moreover, descriptions of well-known devices, methods, and materials may be omitted so as to not obscure the description of the example embodiments. Nonetheless, such devices, methods, and materials that are within the purview of one of ordinary skill in the art may be used in accordance with the example embodiments.

FIG. 1is a cross-sectional view of an illumination apparatus10having a light extracting film20optically coupled to the top surface16of a light guide12in one embodiment, typically coupled using a layer of optical adhesive36. Light sources14, typically cold-cathode fluorescent lights (CCFLs) or light-emitting diodes (LEDs) or some other emissive source, provide source illumination to light guide12, which guides light using TIR. Light extracting film20obtains this light at an optical input surface22and directs this light toward an output surface24at suitable angles for various lighting and display applications. Light extracting film20has a plurality of features26projecting from a film substrate38to form input surface22and optically coupled with light guide12to obtain and direct the light from light guide12. Referring toFIG. 2, each light extracting feature26has a first side28having two or more planar segments30a,30band a second side32similarly formed, with two or more planar segments31a,31b. Both sides28and32terminate at an apex34. In one embodiment, light extracting feature26has end faces33. In one embodiment, light extracting feature26is fabricated as a discrete structure, as shown inFIG. 2. With this type of discrete embodiment, light extracting film20has multiple light extracting features26formed onto or fastened onto film substrate38to form input surface22. In another embodiment the light extracting features26are integral to the film substrate, with no boundary between them as shown inFIG. 3. In another embodiment, light extracting film20has a plurality of linearly extended light extracting features26, distributed in rows having various spacing arrangements, as described subsequently. AsFIG. 3shows, the light extracting feature26extends in the direction of a longitudinal axis A, such that planar segments30a,30b,31a, and31bare parallel to the longitudinal axis and axis A is itself parallel to input surface22. In one embodiment at least two of light extracting features26have respective longitudinal axes substantially in parallel with each other, and generally all of the light extracting features26are parallel. The light extracting features may be the same length or they may be of different lengths. In one embodiment two or more of the light extracting features may extend the length of the light extracting film. In another embodiment the lengths of at least two of the light extracting features are at least 100 times shorter than the length of the light extracting film measured in the same direction. Preferably the light extracting film20has a thickness of about 10.0 microns to about 1.0 mm.

In alternative embodiments, the two sides28,32of the light extracting features26may not meet in an apex. For example, the apex may be replaced by a slightly rounded or chamfered tip to relieve the stresses on the apex of the cutting tool used to fabricate the mold. In another example embodiment, the tip of the light extracting features26may be widened to form a flat planar segment to improve manufacturing consistency of the light coupling region between the light extracting features26and the light guide12.

It is instructive to point out a number of advantageous characteristics of light extracting features26and light extracting film20. As the term implies, planar segments30a,30b,31a,31bare flat, without curvature (other than what would be allowed by standard tolerances, such as some small amount of unintended curvature that might result from inherent properties of the composite materials themselves). By comparison with other light extraction solutions, such as those described in the Onishi et al. '675 disclosure cited earlier, in which a cross-section of a projecting element exhibits curvature, the light extracting features26of the present invention have transverse cross sections composed only of linear segments. The light output distribution of the light extracting features is highly dependent on the surface slope, and the slopes of cross-sectional linear segments are more easily controlled to tight tolerances than are the slopes of curved cross-sectional segments. By comparison with other light extraction solutions whose cross sections have a single linear segment for each side, the multiple linear segments in the cross section of the present invention provide improved brightness and improved ability to tune the angular light output distribution as desired for display applications.

As would be appreciated by those skilled in the optical design arts, light extracting features26, optical adhesive36, and light guide12are preferably formed from materials having indices of refraction n that are substantially identical. This improves the extraction of light from light guide12and substantially prevents light at the interface from being reflected back into light guide12.

The transverse cross section ofFIG. 4Ashows more details for key features of sides28,32in one embodiment. The outmost planar segments30band31bmeet or intersect at apex34, with each of segments31band30boriented at an angle θ1relative to the plane of input surface22, which would be parallel to the horizontal dotted line h inFIG. 4A. In order to meet requirements for TIR in the ideal case, the apex angle θ3should satisfy:

θ⁢⁢3≥(sin-1(1n))×2(1)
where n is the index of refraction of the light extracting feature. That is, the relationship given as (1) above would provide TIR at any given incident angle within light guide12. However, in practice, apex angle θ3may be smaller than needed to satisfy relationship (1) and still provide very good luminance distribution. After extensive optical simulation, it is found that the luminance distribution is optimal when apex angle θ3is in the range from approximately 60 degrees to approximately 120 degrees.

Adjacent planar segments30aand31aare then disposed at a steeper angle θ2, preferably at least 7 degrees greater than angle θ1, in order to utilize TIR for extracting light into optimal viewing angles. It should be noted that the incidence angle of light increases with increased distance from the apex34. Thus, it is necessary to increase the slope of successive planar segments in order to direct light in the viewing direction.

Any additional planar segment would be at an angle that is steeper yet, preferably at least 7 degrees greater for each subsequent planar segment, with no angle at or above 90 degrees with respect to the plane of input surface22. Thus, a maximum of 6 planar segments would be used to form each side28,32. Therefore, in one embodiment, the first or second, or both sides28,32may have less than six planar segments. These angular constraints apply whether light extracting feature26is formed as a discrete feature and attached to film substrate38or is formed into the film substrate itself, such as by molding or embossing, or by machining. Sides28and32may be symmetrical, or more precisely bilaterally symmetrical, about axis N. Alternately, sides28and32may be asymmetrical, with different angles θ1and θ2used for corresponding planar segments of each side, and/or a different number of planar segments, in order to be better suited to different display applications requiring particular viewing angles, for example.FIG. 4Bshows an example cross-section of a light extracting feature26that is not symmetric. Side28comprises two planar segments30aand30b, whereas side32comprises three planar segments31a,31b, and31c. Such a light extracting feature26might be used to tailor the output angular light distribution to be different when viewed from either side of on-axis viewing direction N.

FIG. 5is a cross-sectional view of light extracting features26in an example embodiment, showing typical light trajectories through these features. Ray R1from light guide12is directed through light extracting feature26. Most of the incident light from light guide12is at an oblique angle about a principal ray, as exemplified by ray R1. This light is reflected from sides28or32by TIR. TIR (for a structure in air) is achieved when the critical angle φTIRfor incident light is exceeded as defined in equation (2) below, where n is the index of refraction of the material used for light extracting feature26:

The critical angle φTIRis measured relative to normal (that is, perpendicular) to the reflective surface. Typically, planar segments30a,30b,31a, and31bof light-extracting features26are surrounded by air, with an index of refraction of 1.0; alternatively, these may be surrounded by another material with an index of refraction chosen to be relatively small in order to allow TIR on the surfaces of light extracting features26. As shown in the example ofFIG. 5, light entering light extracting feature26at an oblique angle is directed toward a more favorable viewing direction. In one embodiment, the light extracting features26may substantially cover the entire input surface. In another embodiment, there may be a flat region40between adjacent light extracting features26. Flat region40may have varying width in the transverse direction, depending upon the pitch of light extracting features26and the angular orientations of their planar segments30a,30b,31a,31b.

In order to obtain light from light guide12, light extracting features26must be optically coupled with the surface of light guide12. Referring toFIG. 6, optical coupling is obtained using a layer of optical adhesive or other bonding agent36that has an index of refraction closely matched to the index of refraction n of light guide12and light extracting features26. Use of the layer of optical adhesive36is advantageous for optical coupling, helping to compensate for dimensional tolerance errors in fabrication of light extracting features26and providing some allowance for varying the surface area for incident light obtained from light guide12. As shown inFIG. 7, optical adhesive36can be applied to some fixed depth for optical coupling of light extracting feature26. Light extracting feature26is partially embedded in the optical adhesive36so that optical coupling occurs between light guide12and light extracting feature26. This arrangement is advantageous in manufacturing since, in practice, it can be very challenging to position microstructures on top of a soft material such as optical adhesive36with minimal embedment or without embedment at all. Embedment of light extracting features26in optical adhesive36allows a wide range of mechanical tolerance and is inherently more robust than are complex positioning/placement mechanisms that might otherwise be necessary for proper placement and optical coupling of these structures. With embedment in optical adhesive36, optical coupling occurs over an area that lies along the tilted planar segments30band31b, closest to apex34. Thus, unlike conventional solutions such as that proposed in the Beeson et al. '350 disclosure, for example, there is no need to define the light input surface as one particular facet of light extracting feature26. Instead, the level of embedment in optical adhesive36determines the effective area used for receiving light from light guide12. As a result, the optical contact area can be carefully controlled using the present invention, and precision bonding process is unnecessary, resulting in lower manufacturing costs and higher production yields. It is important to notice that the same tilted planar segments30band31bare also used to direct incident light using total internal reflection. In many cases, light reflected from the tilted planar segment30band31bis not incident on the planar segments30aand31a.

Optical adhesives have been used with earlier light extraction articles, such as that described in the '675 Onishi et al. patent, for example. However, as pointed out in the '675 Onishi et al. disclosure, the conventional approach teaches that embedment of light extracting structures in an optical adhesive is to be avoided where possible. In conventional practice, the optical adhesive is employed as a bonding agent only, without actively employing the adhesive material at the optical interface. Thus, for example, a type of surface lamination has been used to bond various types of microstructures to a light guiding plate, without embedment of the structures in the adhesive layer. The present invention, on the other hand, uses a controllable amount of embedment within the optical adhesive layer as a mechanism for achieving a needed level of optical coupling. This also helps to increase the contact area between adhesive and microstructures, resulting in an improved bond to light guide12.

As shown in the example ofFIG. 8A, apex34may lie directly against the surface of light guide12, registered against light guide12in this way, with the layer of optical adhesive36used to hold light extracting features26in place and to provide a suitably sized input aperture for light extracting features26. In one embodiment, light extracting features26are embedded within optical adhesive36to a depth of about 9 micrometers.

As shown in the side view example ofFIG. 8B, the ends41of the light extracting features26may be sloped at a slope angle37. In this case, the length L of the light extracting feature26is the length of its central portion39, where optical coupling occurs. The ends41may have different slope angles37or the ends41may be curved. The optical adhesive36may embed a portion of the sloped ends41, resulting in some optical coupling in regions35outside the region where apex34contacts the light guide12. The sloped ends41of neighboring light extracting features26may intersect.

FIGS. 9 through 11show perspective views from various angles of film20used as part of illumination apparatus10. In these and other figures of the present disclosure, the light extracting features26are shown without sloped ends41. In order to control beam divergence in the direction normal to the plane of output surface24, a bottom micro-structured layer42may be used. In a specific embodiment described herein, the bottom micro-structured layer42includes a plurality of prism-shaped elements that reduce beam angle by total internal reflection (TIR) in a direction normal to the plane of output surface24and thus more efficiently enhance brightness within a predetermined viewing angle. The bottom micro-structured layer42may form the bottom surface18of the light guide12as shown inFIG. 9, or it may be disposed next to the bottom surface18of the light guide12and optically coupled to the light guide12, for example with optical adhesive43as shown inFIG. 11. Depending on the viewing angle requirement, the apex angle of the prismatic structure on bottom micro-structured layer42is in the range of approximately 20.0 degrees to approximately 170 degrees. Illustratively, the pitch of the prismatic structure is in the range of approximately 10.0 micrometers to approximately 1.0 millimeter. In specific embodiments, the pitch is in the range of approximately 25.0 micrometers to approximately 200 micrometers.

Notably, bottom micro-structured layer42may include features that are other than prism-shaped. For example, the micro-structured layer may have features that are arcuate, semi-circular, conic, aspherical, trapezoidal, or composite of at least two shapes in cross-section. The pitch of each shape is in the range of approximately 10.0 micrometers to approximately 1.0 millimeter; and in specific embodiments the pitch is in the range of approximately 25.0 micrometers to approximately 200.0 micrometers.

In general, the features of micro-structured layer42are elongated in shape in a direction perpendicular to light accepting surface44on light guide12. The size and shape of features can be varied along this direction, and in one embodiment at least one of the microstructures has a finite length that is less than the length of the light guide along the longitudinal direction. For example, the apex angle of a prismatic shape may be approximately 90.0 degrees near light accepting surface44and approximately 140.0 degrees farther away from the light source (i.e. toward the central portion of light guide12). The features of the micro-structured layer42can be continuous or discrete, and they can be randomly disposed, staggered, or overlapped with each other. Finally, a bottom reflector that is planar or has a patterned relief may be disposed beneath light guide12or micro-structured layer42in order to further enhance brightness by reflecting back to the display light that has been reflected or recycled from display or backlight structures.

As detailed herein, light extracting features26of film20are disposed to provide an increased luminance to display and lighting surfaces. Moreover, the light provided to the display and lighting surfaces is more uniformly distributed over the surfaces. The combined effect is an increased luminance and a greater uniformity of light in display and lighting application. In addition, the ill-effects of interference patterns such as Moiré patterns are substantially mitigated through the structures of the example embodiments.

FIG. 9shows an embodiment having two light sources14.FIG. 10is a perspective view of illumination apparatus10in accordance with an example embodiment. The illumination apparatus10includes light extracting features26described previously. In addition, illumination apparatus10includes the micro-structured layer42having features that are semi-circular in cross-section in this embodiment.FIG. 11shows an embodiment having one light source14.

FIGS. 12 and 13show perspective views of light extracting film20as seen from the input side, with light guide12removed for clarity. Each light extracting feature26has a length L. Light extracting features26may be separated by lengthwise gaps G, where there would be no optical coupling with light guide12, allowing for a variable lengthwise distribution of light. In the width direction, the pitch P between light extracting features26may be substantially constant or may be varied to change the light distribution by changing the amount of optical coupling with light guide12. Adjacent light extracting features26are generally in parallel, so that longitudinal axes A and A′ are substantially in parallel with each other and also in parallel with the plane of input surface22. Consistent with the coordinate axes ofFIG. 12, the length L is along the x-axis, the pitch P along the y-axis. Notably, the z-axis is directed toward the viewer of the display (not shown). Each light extracting feature26has a cross-sectional shape in the yz-plane and the cross-sectional shape is substantially constant along the length of the feature.

As is shown in the perspective view ofFIG. 13, light extracting features26can be distributed differently over different portions of light extracting film20. In the example ofFIG. 13, a central portion46of light extracting film20has light extracting features26that are close together with respect to pitch P and have few or no gaps G. By comparison, end portions48have a number of gaps G that can be of varying dimensions and may also have larger values for pitch P. With such an arrangement, the amount of optical coupling over central portion46would be greater than the amount of optical coupling over end portion48. Thus, the capability for light coupling over central portion46would be higher than at either end portion48.

As shown inFIG. 13, light sources14are typically positioned nearest one or more edges of light guide12. As a result, in many display and lighting applications, the amount of light extracted at the regions near light sources14is greater than, for example, that extracted nearer the center of the light guide. As can be readily appreciated, this can result in brightness nonuniformities across the display or lighting surface.

In the present example embodiment ofFIG. 13, the length L of light extracting features26is selected to provide a suitable amount of optical coupling with the light guide12relative to their location on light extracting film20. As a general principle, the optical contact area in a region of light extracting film20is the area of optical coupling between light extracting features26and light guide12in the region. The optical contact ratio over a portion of light extracting film20can be expressed as the ratio of the optical contact area in that portion to the total area of the light guide12surface in the portion. With reference toFIG. 13, for example, in end portions48, near light sources14, the length of light extracting features26is relatively small and gaps are distributed. Thus, because this translates directly into a smaller optical contact ratio of light extracting features26with light guide12, the optical contact area per unit area of light extracting film20is less in end portions48than over central portion46. The lower the optical contact ratio between light extracting features26and light guide12in a certain area, the lower the amount of light (flux) that will be extracted from the light guide in this area.

In accordance with example embodiments, light from light sources14, which is normally most intense near end portions48, is purposely extracted to a lesser extent in these portions; and light in central portion46, which is normally less intense compared to end portions48, is purposely extracted to a greater extent in this portion. Overall, this fosters a more uniform extracted light distribution compared to known light-extracting structures.

As will be apparent to those skilled in the art, this same approach may also be applied to achieve desired non-uniform light distributions. In this case, the optical contact area is increased further in regions where higher than average brightness is desired and the optical contact area is decreased further in regions where lower than average brightness is desired.

This principle can be used to increase the local uniformity of light in certain regions of light extracting film20. For instance, in many display applications, there can be dark regions in the corners of the display. In this case, the light flux in the light guide varies in the x-direction, parallel to the light source. As such, for one reason or another, even though the corners translate to portions of light guide12near light sources14, there can be less light extracted from the light guide at these portions. In keeping with the example embodiments, the intensity of the light at the corners may be increased and the uniformity of the light distribution improved by increasing the optical contact area of light extracting features26in corner regions of light extracting film20. Similarly, if a region of a display or lighting device has a local brightness, the uniformity can be improved by reducing the optical contact area at the corresponding portion of light extracting film20. In the former case, the features may be made longer and in the latter the features may be made shorter in order to increase and decrease, respectively, the optical contact area in the pertinent portion of light extracting film20.

In general, the light flux in light guide12will require a given amount of optical contact area at each location on light extracting film20, where the optical contact area is calculated over a comparatively small ‘neighborhood’ of light extracting film20around each location. The neighborhood must be small enough to avoid visible non-uniformity of brightness to the viewer of the display. The neighborhood must also be small enough to support variation in brightness across light extracting film20without brightness transitions between neighborhoods that are visible to the viewer of the display. As a result, the size of the neighborhood will depend on the application, and depends on pixel size of the LCD display, diffusing power of layers to be placed between light extracting film20and the LC panel, expected distance from the display to the viewer, and other application-specific factors. The size of a neighborhood might be considerably less than the size of a small LC panel pixel or might be as large as approximately 1.0 millimeter or more in larger display applications.

In example embodiments, the first pitch P is substantially the same across light extracting film20. The first pitch P is illustratively between approximately 10.0 micrometers and approximately 300.0 micrometers depending on the type of display and is chosen in order to mitigate the ill-effects of interference patterns such as Moiré interference in lighting and display applications. Moiré patterns become visible when two periodic or partially-periodic patterns are superimposed on each other. The period of Moiré patterns is calculated as follows:

pM=(np1-mp2)-1(3)
where p1and p2are pitches of two periodic patterns and pMis the period of the resulting Moiré pattern when the two patterns are superimposed. The n and m are positive integer numbers. Generally speaking, Moiré patterns are not visible for cases when n or m is greater than or equal to 4. This means that a human eye usually cannot perceive Moiré patterns if one of the two pitches becomes smaller than one fourth of the other pitch. Depending on other details of the two periodic patterns, in many cases when one pitch p1is known, another pitch p2can be chosen such that substantially all of the resulting Moiré patterns are of sufficiently low contrast, or sufficiently high or low frequency, that they are not visible to the human eye or they can be hidden using a diffusing sheet or other means added to the display.

The diffusing sheet can be any type of diffusing sheet that provides the necessary optics to prevent the visibility of Moiré patterns, or defects in the preceding film or light guide. Typically, the diffuser is either a volume diffuser or a sheet diffuser. Alternatively, the diffusing functionality can be integrated into the light extracting film. This can be accomplished by a surface coating the on the output surface of the film. In a preferred embodiment, the light extracting features can be formed directly on to a diffusing sheet.

Known light extracting layers include a varying y-direction pitch along the y-direction of the layer, using the coordinate system ofFIG. 12. Varying the pitch provides variance in the optical contact ratio. However, the varying pitch in these known structures can cause objectionable Moiré patterns in the display. As these fringes degrade the image quality of the display or the light pattern of a lighting device, they are beneficially avoided or mitigated to the extent possible. Furthermore, varying the pitch in the y-direction can only compensate for y-direction variability in the light flux in the light guide, and cannot compensate for x-direction variability in the light flux in the light guide.

In order to prevent or at least significantly reduce Moiré fringes, in example embodiments the first pitch P is selected and maintained substantially constant across light extracting film20. This may be done by choosing the pitch P smaller than approximately 0.25 times the pitch of LC panel in the corresponding direction or by choosing pitch P in other ways such that all interference patterns are not visible to the human eye.

In other example embodiments, the first pitch P may be variable across light extracting film20in order to substantially avoid objectionable Moiré patterns. For example, the positions of the light extracting features26in the y-direction may be randomly perturbed in the y-direction while maintaining the desired optical contact ratio within each small neighborhood on light extracting film20. To substantially reduce Moiré interference, it is desirable to randomly perturb the positions of the light extracting features by at least 5% of their pitch. (As used herein, the term “random” means random or pseudo-random as generated by computer algorithms or other methods known in the art.)

With reference toFIG. 12, the second pitch D is the distance in the x-direction from the same point on two neighboring light extracting features26. The second pitch D is also selected to significantly reduce, if not prevent Moiré effects. The second pitch D is chosen with respect to the pitch of periodic structures in the LC panel or other display components in the corresponding x-direction.

In a specific embodiment, the second pitch D is substantially constant and is selected in a manner described in connection with the selection of the first pitch P. In such embodiments, the length of the light extracting features26may be varied to achieve the desired optical contact area in each neighborhood. If it is not feasible to fabricate the light extracting features26small enough to achieve the desired optical contact area in any neighborhood, then some of the light extracting features26may be omitted entirely. The light extracting features26that are omitted may be in a carefully chosen pattern (such as every other one, every third one, or in a ‘checkerboard’ pattern), or they may be omitted in a randomly chosen pattern, so long as the optical contact area in each small neighborhood is preserved. Methods known in the art may be used to determine the length of features and which features are omitted. These methods include dithering techniques such as half-toning, Floyd-Steinberg dithering, and partially-random dithering methods.

In another example embodiment, the lengths of the light extracting features26may be constant and the second pitch D varied to achieve the desired optical contact area. In this case, the x positions, and resulting pitches, of the features may be randomly perturbed to lessen Moiré effects.

In other example embodiments, the length of light extracting feature26and the second pitch D are both varied while maintaining the desired optical contact ratio within each neighborhood. For purposes of illustration, consider the area of light extracting film20divided into rows. Further suppose the desired optical contact ratio in a neighborhood requires that 60% of a row in the x-direction consist of light extracting feature26, with 40% ‘empty’ space between features. This could be achieved by light extracting features26that are 60 micrometers long and spaces that are 40 micrometers long (i.e., second pitch D of 100 micrometers), or light extracting features26that are 90 micrometers long and spaces that are 60 micrometers long (for a second pitch D of 150 micrometers), or any other combination that maintains the approximately 60:40 ratio between feature lengths and spaces. A row may have light extracting feature26and spaces therebetween of several sizes, where the average over the neighborhood achieves substantially the desired optical contact ratio. The feature positions, lengths, and spaces may follow a pattern designed to minimize Moiré interference effects; or may be chosen randomly from a range of possible values such that the desired optical contact ratio is achieved.

In still other example embodiments, first pitch P and second pitch D may both be varied across light extracting film20in ways that avoid or minimize Moiré effects. One example of placing light extracting features26in these embodiments, as will be appreciated by one skilled in the art, is analogous to the placement of backlight dots as described in Journal of the Optical Society of America A, Vol. 20, No. 2, February 2003, pp. 248-255, to Ide, et al., the disclosure of which is specifically incorporated herein by reference. With this method, the locations of light extracting features26are determined by combinations of known methods such as random placement, low-discrepancy sequences, and dynamic relaxation. Additional similar methods will be appreciated by those skilled in the art. As applied to the present embodiment, such methods result in non-periodic yet varying-pitch patterns that achieve the desired optical contact ratio within each small neighborhood of light extracting film20and simultaneously avoid or minimize Moiré patterns.

The methods used to distribute light extracting features26over the surface of light extracting film20, the choices of first and second pitches, and related methods of varying the optical contact area described above may be combined in embodiments. The method chosen will depend on the particular application domain and details.

FIG. 14illustrates the optical contact area of the light extracting features26of a light extracting film20in accordance with an example embodiment. In the present embodiment, the first pitch P in the y-direction and the second pitch D in the x-direction are both constant across light extracting film20. The lengths of the light extracting features26are increased in an upper region50to increase optical contact area, and the lengths of light extracting features26are decreased in a lower region52to decrease optical contact area. At lower region52, some features (shown as dotted line features54) have been omitted entirely to further decrease optical contact area in that region.

FIG. 15illustrates another example embodiment. In this embodiment the first pitch P in the y-direction is chosen to be constant and less than approximately one-fourth of the LC panel pixel pitch in the corresponding direction to avoid Moiré, while the second pitch D in the x-direction is varied randomly together with the feature lengths L1, L2, and gaps G to achieve the desired optical contact area in each neighborhood of light extracting film20. The optical contact area is greater in upper region50of the illustrated area of light extracting film20, and the optical contact area is comparatively smaller in lower region52. Notably, the optical contact ratio in this example embodiment varies in both the x-direction and the y-direction. In upper region50, the feature lengths L1are generally greater and gaps G between features are generally smaller. In lower region52, the feature lengths L2are generally smaller and the gaps G between features are generally larger.

Notably, the optical contact area can be tailored to extract light from the light guide12by forming the light extracting features26as discrete or discontinuous elements, having a substantially constant pitch (in the y-direction ofFIG. 12) that is selected to avoid creating a visible Moiré pattern. Moreover, as described previously, the light extracting features26are distributed so as to avoid Moiré patterns in the direction of their length (x-direction).

Light extracting film20according to the example embodiments may be fabricated using a variety of known methods, generally involving replication from a mold.FIG. 16shows a cross-section of a light extracting film20being replicated from a mold56. Mold56may be made of materials such as copper, aluminum, nickel and other standard mold materials and alloys thereof, capable of holding optical-quality surfaces and of withstanding the stresses induced by the intended molding processes. Mold cavities58(‘cavities’) in the mold are the negative shape of the light extracting features26that are formed.

In one embodiment, mold56may be planar and light extracting film20is formed by injection molding. In another embodiment, light extracting film20is formed as a film in a roll-to-roll process using a mold in roller form. Suitable forming processes will be known to those skilled in the art, including but not limited to solvent or heat embossing, UV casting, or extrusion-roll molding as disclosed in U.S. Pat. No. 6,583,936, the disclosure of which is specifically incorporated herein by reference. After the continuous film is formed in a roll-to-roll process, then the individual sections of light extracting film20may be cut from the film. If the optical contact ratio of light extracting film20only varies along the y-direction, then the roller for light extracting film20may be made with one or more continuous bands around the roller, and the individual sections may be cut from film that is molded from any circumferential position around the roller. However, if the optical contact ratio of light extracting film20varies along the x-direction as well, for example to compensate for dark corners in the light guide, then the roller will have one or more rectangular images of light extracting film20on it, and the individual sections of light extracting film20must be cut from the corresponding locations on the film. The roller might have images of one or more different light extracting film20designs for multiple applications.

A roller for molding light extracting film20may be fabricated using a gravure-type engraving process, or by a digitally controlled fast-servo diamond turning machine, or similar technology. For example, gravure-type engraving may be effected in accordance with commonly assigned U.S. patent application Ser. No. 10/859,652 entitled “Method for Making Tools for Microreplication” to Thomas Wright, et al. The disclosure of this application is specifically incorporated herein by reference. In these processes, a blank roller is mounted in a cutting machine, and the roller is turned about its axis. A cutting head moves a cutter into and out of the surface of the roller as the roller turns. The cutting edges of the cutter determine the cross section of the mold cavity. The tip of the cutter typically follows a path that is substantially contained in a plane, and in example embodiments the plane containing the cutter path is not perpendicular to the roller surface.

In the coordinate system ofFIG. 12, the turning of the roller creates the lengthwise (x) direction of the cavities. The timing of moving the cutter into the surface determines the x starting position of each cavity, and the length of time the cutter is left in the roller determines the length of that cavity. After cutting cavities at a particular axial position on the roller (corresponding to the y-direction location of the features), the cutting head is moved to a new axial position to cut additional cavities. By repeating this process across the roller, a roller may be fabricated to produce light extracting film20in a roll-to-roll replication process.

FIG. 17Aillustrates a cross-section of a single light extracting feature26in contact with light guide12.FIG. 17Bshows a cross-section of the same light extracting feature26along the line indicated17B-17B in the x-z plane of light extracting film20, again using the coordinate system ofFIG. 12. In creating a roller or mold56for light extracting film20, a cutting tool typically cannot enter or exit the roller surface instantly. As the roller turns, the cutter enters the roller surface, resulting in a sloped end on the roller cavity58and a corresponding sloped end41on light extracting feature26as well. Typical cavity and light extracting feature end slopes range from approximately 5 degrees to approximately 25 degrees measured from the uncut roller surface. The cutting tool may be able to exit the roller surface more quickly than it enters, or vice versa, resulting in different slopes on two sloped ends61,62. In some cases, when light extracting features26are spaced closely in the x-direction, the sloped ends62,63may intersect where the cutting tool does not exit the roller surface completely between cavities58. This is acceptable for light extracting film20because light extracting features26do not need to be fully interrupted, but only need to be small enough that they no longer contact or are laminated to light guide12, thus avoiding optical contact and keeping light from being extracted.

The roller cavities might be cut using single or multiple cuts to achieve the final shape on the roller.FIG. 18shows a cross-sectional view of a cutter64cutting a mold cavity58in a roller surface60in three cuts. In this example, the cutter cross-section is shaped as shown, resulting in mold cavities and light extracting features26with the same shape. During one pass on roller surface60, cutter64only plunges to the level shown in position66against roller surface60. During later passes across roller surface60, cutter64plunges to the next two positions67and68, with the final position68cutting mold cavity58to its final shape.

In the noted roller-cutting processes, diamond cutting tools are beneficial because of their ability to form an optical-quality cut surface finish and their resistance to wear, chipping, and other types of cutter damage.FIG. 19Ashows a front view of the tip70of a diamond cutter64, andFIG. 19Bshows a side view of the same cutter. The cutting edges71a,71bof diamond cutter64determine the cross-section of the mold cavities58on the roller, which in turn determines the cross-section of light extracting features26on light extracting film20. As will be known to those with skill in the art, diamond cutters64must have adequate relief angles72to allow cutter64to plunge into the turning roller without the roller material coming into contact with the non-cutting faces of the cutter64, which would result in swaging the roller material and possible substandard cut surface quality. Typical relief angles72ranges from approximately 7 degrees to approximately 25 degrees.

The light extracting features26and light extracting film20of the present invention are particularly advantageous for fabrication. As will be recognized by those skilled in the optical fabrication arts, it can be more difficult to form a surface with a curved cross-section, particularly for a microstructure that is on a film substrate. Tooling costs for fabricating surfaces with curved cross sections can be several times the cost for planar surfaces. In addition, cutters64for fabricating molds often wear most at the tip of the cutter64, which forms the apex34of the light extracting features26. Wear at the cutter tip can cause lowered surface finish quality, deformed mold cavities58, and other manufacturing errors. By embedding the tip of the light extracting features26into an adhesive36or other means to optically couple the light extracting film20to the light guide, the cosmetic or optical impact of any incorrectly-formed apexes34of light extracting features26is minimized.

The tolerances for fabricating diamond cutters64play a critical role in the performance and performance variation of light extracting film20of the present invention. The cutting edges71a,71bof the cutter64principally determine the cross-sectional shape of the mold cavities58and light features26, which in turn determines the angular light distribution from the light extracting feature26and light extracting film20. Hence variations in cutter64shape lead directly to variations in light extracting film20performance. As noted herein, the angle of cutting edge segments71a,71bcan be held to tight tolerances by typical diamond-tool fabrication methods. However, as will be appreciated by those skilled in the art, when angles θ4between cutting edge segments71a,71bbecome small, variations in the placement of each cutting edge segment71a,71bin its normal direction cause unacceptable changes in the lengths of cutting edge segments71a,71b. For example, the normal direction73for cutting edge71ais shown. Depending on the angle θ4, variation in placing cutting edge71ain its normal direction73will cause different amounts of variation in the length of cutting edge71aand71b. If cutting edge71ais displaced by an amount d1in its normal direction73, then the length of cutting edge71awill change by a distance d2, where the following equation holds:
d2=d1/tan θ4  (4)
Diamond tool fabrication methods can place cutting edges71a,71bto within approximately 0.5 micrometers in the normal direction73. In testing and optical simulations, variations of more than about 4 micrometers in the length of planar segments31a,31bcause unacceptable variations in angular light distribution. The simulation data inFIG. 20shows one example in which the length of planar segments31a,31bare varied by 4 micrometers from the optimal value. Curve101shows the luminance distribution when the length of planar segments31a,31bare as designed. Curve102shows the luminance distribution when planar segment31ais 4 micrometers shorter than optimal, and curve103shows the luminance distribution when planar segment31ais 4 micrometers longer than optimal. It will be appreciated that a significant drop in on-axis brightness occurs when the length of planar segments31a,31bis varied more than 4 micrometers from the optimal value. As a result, there is a range that the length of planar segments31a,31bshould satisfy for optimal optical performance. Solving equation (4) for θ4shows that when the angles between planar segments are lower than approximately 7 degrees, the cutting edges71a,71band planar segments31a,31bcannot be held within acceptable tolerance limits.

As another alternative, a flat mold for injection molding may be formed by a scribing process using diamond cutting tools described herein. A sleeve may also be mounted on a cylinder and engraved as described herein for fabricating a roller. Then the sleeve may be removed from the cylinder and unrolled to form the molding surface of a flat mold56. Various replication processes known in the art, such as electroforming, may be used to copy and transform the mold56surface into a usable form.

FIG. 21shows a perspective view of a diamond cutter64cutting mold cavities in the surface of a roller. Cutter64is shown at several locations in the process of cutting cavities of various sizes. At one location cutter64is in a short cavity58a. At another location cutter64is shown at the start of a longer cavity58b. Also shown are two cavities58cwhose ends65intersect such that cutter64never emerges fully from the surface until the end of the second cavity. Two cavities58aand58dare far enough apart that the cutter may exit completely between them.

In general, light extracting film20may be formed from a variety of materials. In a specific embodiment, light extracting film20is formed from an acrylic film; however, light extracting film20may be formed from any of various types of transparent materials, including, but not limited to polycarbonate, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polymethyl methacrylate (PMMA).

Suitable optical adhesives would be provided for the layer of optical adhesive36. The index of refraction of optical adhesive36preferably matches that of light extracting film20and light guide12.

FIG. 22Ais a graphical representation of the feature index (feature number in y-direction from the end of light extracting film20) versus optical contact ratio for an example embodiment. In this example the first pitch P and second pitch D are both constant across the light extracting film20. Feature length in millimeters is used as a measure of optical contact ratio, but other methods discussed herein may be used as well. Curve74shows the feature index versus length for a light extracting film20. At point76, features relatively close to an edge of light extracting film20near a light source have a relatively short length. Such features may be those disposed near end portions48as shown inFIG. 13. At point78, the features are longer, and may be features between the edge of light extracting film20and the central portion46shown inFIG. 13. At point80, the length of a feature is significantly larger. The features are farther from the edge of light extracting film20. Such features may be disposed near the central portion46of light extracting film20of the embodiment ofFIG. 13.

FIG. 22Bis a graphical representation of the spatial luminance versus distance from the center of light guide12for light extracting film20having the length variation of features set forth inFIG. 22A. As shown in a curve82, over the distance, the spatial luminance substantially maintains the same intensity level.

FIG. 23is a graphical representation of light intensity versus viewing angle. A curve84is the luminance (relative scale) versus vertical viewing angle (degrees) for light extracting film20in keeping with the example embodiments. Here the vertical direction is measured in the y-z plane shown inFIG. 13. Notably, two light sources14(for example, CCFLs) are disposed on both sides/edges of light extracting film20for light distribution. By comparison, a curve86is the luminance versus viewing angle for a known BEF.

As can be appreciated, a peak value85of the luminance is significantly greater than a peak value87of the luminance of the known BEF layer. Moreover, curve86includes side lobes88. These side lobes88represent regions of brightness and thus light leakage at the extreme viewing angles.

The width of the peak luminance is often used to characterize light redirecting and light extracting articles. In the example embodiment, the width of the peak is between points89and90and has an angular breadth (Full Width Half-Maximum (FWHM)) of approximately 35.0 degrees.

FIG. 24is a graphical representation of luminance versus viewing angle of an example backlight device utilizing a light extracting film20of an example embodiment and a comparable backlight device utilizing two crossed known BEF layers. Both backlights included a single CCFL light source103along one edge. A curve96is the luminance of the backlight for light extracting film20measured at the center of the display. A curve98is the luminance of the BEF backlight measured at the center of the display. As can be appreciated, a peak value97of the luminance of the backlight is significantly greater than a peak value99of the luminance of the known BEF layer backlight.

FIG. 25is a graphical representation of luminance versus horizontal viewing angle of an example backlight device with different apex angles of bottom prismatic shapes on micro-structured layer42ofFIG. 11. Here the horizontal direction is parallel to the x-axis inFIG. 12.FIG. 25illustrates how the horizontal viewing angle as well as the peak luminance can be adjusted by changing the apex angle of the bottom prisms. A curve106is the luminance when the apex angle is 90 degrees. A curve108is the luminance when the apex angle is 150 degrees. A third curve110is the luminance when there is no bottom prism structure. As shown, the bottom prismatic structure collects more light into smaller viewing angle so that it increases peak brightness.

The perspective view ofFIG. 26shows a display apparatus120that employs light extracting film20in one embodiment. Illumination apparatus10has light guide12optically coupled with one or more light sources14. Light extracting film20, formed according to the present invention, is optically coupled to light guide12through adhesive layer36. Other components may be provided for further conditioning of light from light extracting film20, such as a diffuser114and reflective polarizer116, for example. Reflective polarizer116transmits a portion of the light having a polarization state parallel to its transmission axis. A light gating device112modulates incident light from light extracting film20and any other intervening light conditioning components in order to form an image. Light gating device112may be any of a number of types of spatial light modulator, such as a liquid crystal (LC) spatial light modulator for example.

FIGS. 27A and 27Bshow scanning electron micrographs of the input surface22(such as shown inFIG. 1) at two locations of an example light extracting film20according to one embodiment. In this example, the two sides28,32of the light extracting features26each have two planar segments30a,30b. Each light extracting feature26is 50 micrometers wide, and the pitch P in the y direction (seeFIG. 12; shown horizontally inFIGS. 27A and 27B) is a constant 55 micrometers, leaving an approximately 5 micrometer wide flat region40(seeFIG. 5) between the light extracting features26. The pitch D in the longitudinal x direction (shown vertically inFIGS. 27A and 27B) is 250 micrometers. The light extracting features26have sloped ends41(seeFIG. 8B) that overlap with the sloped ends41of neighboring light extracting features26in the x direction.FIG. 27Ashows a location of the light extracting film20wherein the optical contact ratio is lower and the light extracting features26are approximately 150 micrometers in length.FIG. 27Bshows a location of the light extracting film20wherein the optical contact ratio is higher and the light extracting features26are approximately 220 micrometers in length.

In order to obtain light from light guide12, light extracting features26must be optically coupled with the surface of light guide12. Referring to FIG.28, optical coupling is obtained using a layer of optical adhesive or other bonding agent36that has an index of refraction closely matched to the index of refraction n of light guide12and light extracting features26. Use of the layer of optical adhesive36is advantageous for optical coupling, helping to compensate for dimensional tolerance errors in fabrication of light extracting features26and providing some allowance for varying the surface area for incident light obtained from light guide12. Light extracting feature26is partially embedded in the optical adhesive36so that optical coupling occurs between light guide12and light directing feature26. With embedment in optical adhesive36, optical coupling occurs over an area that lies along the tilted planar segments30band31b, closest to apex34. Therefore, the level of embedment in optical adhesive36determines the effective area used for receiving light from light guide12. It is important to notice that the same tilted planar segments30band31bare also used to direct incident light using total internal reflection (TIR). As shown by the ray trace, R1, light is extracted from the light guide12, and directed using TIR toward the output surface. InFIG. 28the ray R1is diffused by the diffusing substrate29. This illustrates that diffusing and light extracting film21can effectively extract and direct light from light guide12and provide diffuse light output, reducing the need for a diffuser in another location with in the backlight structure.

As shown in the example ofFIG. 29A, the light extracting features26may be formed on a diffusing substrate29. The light extracting features26would be used in any manner previously described. For example,FIG. 29Ashows apex34touching the surface of light guide12with the layer of optical adhesive36used to hold light extracting features26in place and to provide a suitably sized input aperture for light extracting features26. In an alternative embodiment shown inFIG. 29B, the light extracting features26may be formed on a film substrate38, and a diffusive coating27applied. The diffusive coating27may be applied to the substrate38prior to forming the light extracting features. In another embodiment, the diffusive coating may be coated onto a light extracting film20in order to form diffusing and light extracting film21; this light extracting film20may contain a film substrate or may be formed as a monolithic film.

A functional coating may optionally be added to light extracting film20. Functional coatings include anti-reflective, antistatic, hard coat, and other coatings known in the art. Functional coatings can serve any purpose in the integrated film including optical or physical. For example, a coating may be applied in order to reduce stress and provide dimensional stability.FIG. 29Cshows an alternative embodiment where the functional coating25is added to the diffusing and light extracting film21. Diffusing and light extracting film21ofFIG. 29Cand light extracting film20may be chosen from any embodiment of the present invention.

The perspective view ofFIG. 30shows an alternate embodiment of display apparatus120that employs diffusing and light extracting film21. As inFIG. 26, illumination apparatus10has light guide12optically coupled with one or more light sources14. Diffusing and light extracting film21, formed according to the present invention, is optically coupled to light guide12through adhesive layer36. In this preferred embodiment, the diffuser114shown inFIG. 26is not needed due to the integrated functionality of diffusing and light extracting film21. Additional components may be provided such as a reflective polarizer116. A light gating device112modulates incident light from diffusing and light extracting film21and any other intervening components in order to form an image. Light gating device112may be any of a number of types of spatial light modulator, preferably a liquid crystal (LC) spatial light modulator.

In view of this disclosure it is noted that the various methods and devices described herein can be implemented in a variety of applications. Further, the various materials, elements and parameters are included by way of example only and not in any limiting sense. In view of this disclosure, those skilled in the art can implement the present teachings in determining their own techniques and needed equipment to affect these techniques, while remaining within the scope of the appended claims.

PARTS LIST