Patent ID: 12189150

It should be understood that the subject matter of certain Figures of this disclosure may not necessarily be drawn to scale, and that the Figures present non-exclusive examples of the light control films and optical systems disclosed herein.

DETAILED DESCRIPTION

The disclosure describes light control films (LCFs) and optical systems that include the same. An optical system, such as a display assembly, may be brighter at an on-axis position (i.e., the direction of the display normal) and less bright at off-axis positions (e.g., a direction at some angle greater than zero relative to the display normal). In some optical system applications, it may be desirable to control the horizontal light output distribution and reduce off-axis illumination in the vertical direction to provide a display that is as bright or nearly as bright to viewers at an on-axis position and a range of off-axis positions in the horizontal direction with low off-axis light in the vertical direction. For example, it may be desirable to control the horizontal light output distribution in automotive display applications where an instrument display may be in front of the driver (e.g., on-axis with respect to a driver and off-axis with respect to a front seat passenger) or a console display midway between the driver and the front seat passenger (e.g., off-axis with respect to both driver and front seat passenger) to provide a display that is as bright or nearly as bright to the driver and the front seat passenger and reduces off-axis light in the vertical direction.

In some optical system applications, LCFs may be used to control the light output distribution. The described LCFs and optical systems may include a turning film (e.g., prism-like turning structures) and a lenticular diffuser (e.g., curved diffusing structures) to regulate optical output distributions and enhance brightness characteristics. For example, the described LCFs may spread the output distribution in the horizontal direction to enhance display brightness characteristics in on-axis positions and off-axis positions. As compared to LCFs without a turning film and lenticular diffuser, the disclosed LCFs with a turning film and lenticular diffuser may improve control of the display output distribution and enhance display brightness in the horizontal direction while reducing off-axis light in the vertical direction. Thus, the disclosure provides example LCFs and optical systems having horizontal output distributions that enhance display brightness in the horizontal direction, and reduce off-axis light in the vertical direction, relative to the display surface.

The turning films and lenticular diffusers described herein each may include a plurality of microstructures (e.g., prisms). In some examples, the plurality of microstructures of the turning film may include at least two faces that are configured to collimate, refract, and/or reflect light. In some examples, the plurality of microstructures of the lenticular diffuser may include multifaceted prisms that are configured to reflect and/or refract light. For example,FIG.1is a conceptual and schematic lateral cross-sectional view of an example optical system10. In the example ofFIG.1, optical system10may include backlight light guide12, turning film14, substrate30, lenticular diffuser34, and liquid crystal display (LCD)50. In some examples, a LCF of optical system10may include turning film14and lenticular diffuser34.

For illustration purposes,FIG.1shows microstructures of turning film14, as well as for lenticular diffuser34. In practice, however, a cross-sectional view of optical system10would typically show the microstructures of only turning film14or only lenticular diffuser34because the grooves in turning film14are typically substantially perpendicular to the grooves in lenticular diffuser34. In some examples, lenticular diffuser34may be configured to receive light from turning film14collimated in a first plane (e.g., light ray56) and preferentially reflect and/or refract the collimated light toward a second plane orthogonal to the first plane (e.g., light ray58). For example, lenticular diffuser34may receive the collimated light output from a turning film type lightguide, or a wedge or pseudo-wedge lightguide, or the like. In some examples, lenticular diffuser34may be configured to spread the collimated light from turning film14in a plane horizontal to a display surface. For example, the described LCF including turning film14and lenticular diffuser34may have features that operate by refracting and/or reflecting light.

In some examples, lenticular diffuser34may define substantially smooth surface38(e.g., non-structured) and structured surface40. In some examples, structured surface40may include a plurality of microstructures44each having multifaceted face48and rounded tip46. In some examples, microstructures44may define grooves42having a substantially flat land area33. In some examples, microstructures44may be optically coupled to turning film14(i.e., no air or other significant gap between lenticular diffuser34and turning film14that may allow for significant reflection of the surface of adjacent layers).

In some examples, substantially smooth surface38may define display axis52extending substantially perpendicular to substantially smooth surface38. In some examples, substantially smooth surface38need not be completely smooth, and may qualify as a substantially smooth surface if the surface does not contain microstructures (e.g., non-structured surface). For example, an anti-wetout or anti-glare beaded coating may be included or incorporated on the surface of substantially smooth surface38, and such a surface may still be considered substantially smooth. In other words, the term smooth is not used in the sense that the surface is non-rough or perfectly planar, but instead is used to indicate that the surface is non-structured.

In some examples, structured surface40may include prismatic microstructures44. In other examples, structured surface40may include more than one microstructures44, e.g., a curved-faced or straight-faced microstructure, an arcuate microstructure, an angular microstructure, and/or multifaceted microstructure. In some examples, each of microstructures44may be linear microstructures, i.e., microstructures44may extend along a plane perpendicular to display axis52with substantially the same (e.g., the same or nearly the same) cross-sectional shape (e.g., as shown in the cross-sectional view ofFIG.1and extending along a plane into/out of the page). In other examples, microstructures44may be linear microstructures extending along a plane parallel to the page (not shown inFIG.1).

In some examples, each of microstructures44may be a prism with a multifaceted face48and rounded tip46. In some examples, microstructures44may have flat land area33between prisms. In some examples, multifaceted face48may be configured to preferentially reflect and/or refract light in the horizontal direction, e.g., toward a plane substantially perpendicular to the display axis. For example, as illustrated inFIG.3, lenticular microstructure440has multifaceted faces480having a linear base section481and linear tip section482connected by polynomial blend section483. In some examples, multifaceted face480may be shaped with control parameters to cover the space of desired width and uniformity of output light distributions. In some examples, the cross section of each microstructure may extend substantially parallel to the display axis from substantially smooth surface to vertex.

Lenticular diffuser34may be any suitable thickness and may be made from any suitable material. In some examples, microstructures44of lenticular diffuser34will be formed from a polymeric material, such as polycarbonate, polyethylene terephthalate, polyethylene naphthalate, poly (methyl methacrylate) and copolymers and blends of the same. Other appropriate materials include acrylics, polystyrenes, methyl styrenes, acrylates, polypropylenes, polyvinyl chlorides, and the like. In some examples, lenticular diffuser34may be optically transparent or have low haze and high clarity to avoid undesirably scattering incident light. In some examples, the material forming microstructures44of lenticular diffuser34may have a sufficiently high index of refraction, such as about 1.45 to about 1.75, to facilitate reflection and/or refraction over a sufficiently broad range of angles. In some examples, to achieve a desired high refractive index, particularly suitable materials are UV-curable composites containing Zr particles, as described in U.S. Pat. No. 7,833,662. In some examples the material, dimensions, or both of lenticular diffuser34may be selected to produce a flexible film.

Microstructures44may be any appropriate size. The pitch of microstructures45may be measured from the endpoint of flat land33of two consecutive grooves44. The overall arrangement of microstructures44on smooth surface38may have any suitable pitch between adjacent microstructures. In some examples, microstructures44may be on the millimeter or micrometer scale, for example, pitch of microstructures44may be between about 10 micrometers and 200 micrometers, or about 14 micrometers to about 80 micrometers. The pitch or size of microstructures44may increase, decrease, both increase and decrease, or remain constant for all or portions of structured surface40of lenticular diffuser34. In some examples, microstructures44may all be substantially the same (e.g., the same or nearly the same) or may include a combination of microstructures that are different shapes or sizes.

Microstructures44and more generally, the structured surface40may be formed through any suitable process, such as a microreplication process. For example, smooth surface38may be formed through cutting (fly cutting, thread cutting, diamond turning, or the like), or pressing a compliant but curable or hardenable material against a suitable tool with a surface defining the negative of the desired structure. For example, microstructures44may be formed to have a “linear-blend-linear” as illustrated inFIG.3.FIG.3shows microstructure440which has linear end sections481a/481b, blend section483, pitch (P), base length (B), blend section length (b), base angles (θ1and θ2), flat land width (w), fill fraction (B/P), blend fraction (b/B), aspect ratio (h/B). Blend section483spans the region between linear base section481aand481b. Blend section483has the shape of a segment of an ellipse or 2nd, 4thor 6thorder polynomial.

Microstructures44or440may be formed with a prism design tool that may include, for example, the following parameters: ellipticity of the elliptical section of the blend section, base angles, fill fraction, blend fraction and delta-n. Delta-n is the index of refraction difference at the lenticular-shaped surface of the microstructure.

In some examples, prism design tool parameters may be varied to provide a structured surface40with desired light output distribution, e.g., a suitably wide and smooth output light distribution. In some examples, the microstructure forming process may be automated with a multi-parameter search and an optimization metric such as, for example, establishing a full-width, half maximum or a half-width, half maximum and varying the second derivative of luminance versus polar view angle to achieve a desired light output distribution. Other processes for forming lenticular diffuser34may also be possible including, for example, casting and curing with an electroplated, laser cut, or etched tool, using photolithography such as two-photon mastering of a tool in conjunction with a cast and cure process, or even direct machining or an additive three-dimensional printing process. The material may be subsequently hardened or cured (e.g., through exposure to light such as ultraviolet light), leaving structured surface40with the desired microstructures44.

In some examples, structured surface40may define a plurality of substantially parallel grooves42. In some examples, each of grooves42may be linear grooves, i.e., grooves42may extend along a plane that is substantially perpendicular to display axis52with substantially the same (e.g., the same or nearly the same) cross-sectional shape (e.g., as shown in the cross-sectional view ofFIG.1, and extending along a plane into/out of the page). In other examples, grooves4may be linear grooves extending along a plane parallel to the page (not shown inFIG.1). In some examples, grooves42may be any suitable thickness.

In some examples, grooves42may be totally filled with material such that lenticular diffuser34may include substantially smooth surface36. In some examples, grooves42may be filled partially with material such that the material in grooves42is adjacent to at least a portion of structured surface40. In some examples, the material in grooves42may be any suitable material. For example, the material in grooves42may be a low refractive index material, air, an optical adhesive, silicones, fluorinated polymers and copolymers, nano-void air entrained ultra-low index material, or the like. In other examples, the material in grooves42may include more than one material, e.g., air and an optical adhesive, or the like.

In some examples, the material in grooves42may have a refractive index less than the refractive index of the material of microstructures44. In some examples, the material filling grooves42may have a sufficiently low index of refraction, such as between about 1.3 and about 1.55, to facilitate total internal reflection over a sufficiently broad range of angles. In some examples, the difference between the refractive index of the material forming microstructures44and the refractive index of the material filling grooves42may be between 0.05 and 0.6, or between about 0.1 and 0.3, or between about 0.15 and 0.25.

The horizontal output distribution of optical system10may be described as luminance as a function of as view angle. Luminance as a function of as view angle may be described as having a half width at half maximum (HWHM), i.e., the view angle position on either side of the on-axis position at which the luminance is one-half of the maximum luminance (e.g., luminance at the on-axis position). In some examples, lenticular diffuser34may be configured to provide a greater than about ±40 degrees HWHM from an input light beam less than about ±30 degrees HWHM. For example, the shape, size, and pitch of microstructures44may be selected to provide a greater than about ±40 degrees HWHM from an input light beam less than about ±30 degrees HWHM. In other examples, lenticular diffuser34may be configured to provide a greater than about ±50 degrees HWHM from an input light beam less than about ±20 degrees HWHM. For example, the shape, size, and pitch of microstructures44may be selected to provide a greater than about ±50 degrees HWHM from an input light beam less than about ±20 degrees HWHM.

Luminance as a function of as view angle may also be described as having a half width at 80% maximum (HW80), i.e., the view angle position on either side of the on-axis position at which the luminance is 80% of the maximum luminance (e.g., luminance at the on-axis position). In some examples, lenticular diffuser34may be configured to provide a greater than about ±35 degrees HW80 from an input light beam less than about ±30 degrees HWHM. For example, the shape, size, and pitch of microstructures44may be selected to provide a greater than about ±35 degrees HW80 from an input light beam less than about ±30 degrees HWHM. In other examples, lenticular diffuser34may be configured to provide a greater than about ±40 degrees HW80 from an input light beam less than about ±20 degrees HWHM. For example, the shape, size, and pitch of microstructures44may be selected to provide a greater than about ±40 degrees HW80 from an input light beam less than about ±20 degrees HWHM.

In some examples, turning film14may include substantially smooth surface16(e.g., non-structured) and structured surface18. In some examples, substantially smooth surface18may define display axis52extending substantially perpendicular to substantially smooth surface16. In some examples, structured surface18may include a plurality of microstructures19each having first side24and second side28that intersect at vertex26. In other examples, structured surface18may include more than two surfaces, e.g., a multifaceted microstructure. In some examples, microstructures19of structured surface18may define grooves22. In some examples, grooves22may be substantially parallel. In some examples, turning film14may be optically coupled to backlight light guide12. In some examples, turning film14may output light substantially collimated in a first plane.

In some examples, turning film14may be configured to receive substantially collimated light from backlight light guide12(e.g., light ray54) and output light substantially collimated in a first plane (e.g., light ray56). For example, turning film14may receive the substantially collimated light output from a turning film type lightguide, or a wedge or pseudo-wedge lightguide, or the like.

In some examples, substantially smooth surface16need not be completely smooth in all embodiments, and may qualify as a substantially smooth surface as long as the surface does not contain microstructures (e.g., non-structured surface). For example, an anti-wetout or anti-glare beaded coating may be included or incorporated on the surface of substantially smooth surface16, and such a surface may still be considered substantially smooth. In other words, the term smooth is not used in the sense that the surface is non-rough or perfectly planar, but instead is used to indicate that the surface is non-structured.

In some examples, structured surface18may include prismatic microstructures19. In other examples, structured surface18may include more than one microstructures19, e.g., an angular microstructure, a multifaceted microstructure, or the like. In some examples, each of microstructures19may be linear microstructures, i.e., microstructures19may extend along a plane perpendicular to display axis52with substantially the same (e.g., the same or nearly the same) cross-sectional shape (e.g., as shown in the cross-sectional view ofFIG.1, and extending in an axis into/out of the page). In other examples, microstructures44may be linear microstructures extending in a plane parallel to the page (not shown inFIG.1).

In some examples, each of microstructures19may have a first side24and a second side28. In some examples, first side24and second side28may be similar. For example, each of first side24and second side28may have a single, straight facet, curved facet or the like. In other examples, first side24and second side28may be dissimilar. For example, each of first side24and second side28may have a different number of facets, or may be multifaceted, or the like. In other examples, first side24or second side28may be curved or arcuate to form a suitable light output distribution from the substantially collimated input distribution. In that sense, first side24may preferentially reflect light in a first direction and second side28may preferentially reflect light in a second direction. The overall arrangement of microstructures19on structured surface18may have any suitable pitch and may or may not have land (flat areas; not shown) between adjacent microstructures. In some examples, microstructures18may be directly adjacent to one another such that a microstructure creates a shadowing effect on an adjacent microstructure.

Microstructures19may be any appropriate size. In some examples, microstructures19may be on the millimeter or micrometer scale, e.g., pitch of microstructures19between about 10 and about 200 micrometers or between about 10 and about 100 micrometers. The pitch or size of asymmetric microstructures19may increase, decrease, both increase and decrease, or remain constant for all or portions of structured surface18of turning film14. In some examples, microstructures19may all be substantially the same (e.g., the same or nearly the same) or may include a combination of microstructures that are different shapes or sizes.

Turning film14may be any suitable thickness and may be made from any suitable material. In some examples, microstructures19of turning film14may be formed from a polymeric material, such as polycarbonate, polyethylene terephthalate, polyethylene naphthalate, poly (methyl methacrylate) and copolymers and blends of the same. Other appropriate materials include acrylics, polystyrenes, methyl styrenes, acrylates, polypropylenes, polyvinyl chlorides, and the like. In some examples, turning film14may be optically transparent or have low haze and high clarity to avoid undesirably scattering incident light. In some examples, the material forming microstructures19of turning film14may have a sufficiently high index of refraction, such as between about 1.5 and about 1.75, to facilitate total internal reflection at a sufficiently broad range of angles. In some examples the material, dimensions, or both of turning film14may be selected to produce a flexible film. In some examples, useful materials for the microstructures of turning film14are those described in U.S. Pat. No. 9,360,592.

Microstructures19, and more generally, the structured surface18may be formed through any suitable process, such as a microreplication process. For example, structured surface18may be formed through cutting (fly cutting, thread cutting, diamond turning, or the like), or pressing a compliant but curable or hardenable material against a suitable tool with a surface defining the negative of the desired structure. The material may be subsequently hardened or cured (for example, through exposure to light such as ultraviolet light), leaving structured surface18with the desired microstructures19. Other processes for forming turning film14may also be possible including, for example, casting and curing with an electroplated, laser cut, or etched tool, using photolithography such as two-photon mastering of a tool in conjunction with a cast and cure process, or even direct machining or an additive three-dimensional printing process.

In some examples, backlight light guide12may include one or more of any suitable light sources or combinations of light sources (not shown). In some examples, the light source may include one or more light emitting diodes (LEDs). In some examples, the light source may each include a singular light source or may include a plurality of light sources (e.g., a bank or series of light sources). In some examples, the light source may include cold cathode fluorescent lights (CCFLs) or incandescent light sources. The light sources and any corresponding injection, collimation, or other optics may be selected to provide any suitable wavelength or combination of wavelengths, polarizations, point spread distributions, and degrees of collimation.

In some examples, backlight light guide12may be configured to output substantially collimated light, e.g., substantially collimated light output may include a light output having a full-width half maximum (FWHM) of less than about 40 degrees. For example, backlight light guide12may include a turning film lightguide including a wedge lightguide to extract light by gradual frustration of total internal reflection such that light may be output from backlight light guide12along display axis52in the down-guide direction at high angles. As another example, backlight light guide12may include a pseudo-wedge including a flat lightguide having shallow sloped extractor shapes to weakly frustrate total internal reflection such that the extracted light may be collimated at high angles from backlight light guide12substantially parallel display axis52in the down-guide direction. In such examples, the density and area fraction of such extractors (i.e., surface area of extractors to total surface area of the backlight light guide) may be arranged to uniformly emit light and substantially extract light from the backlight light guide14along its length. Additionally, in such examples, backlight light guide12may include lenticular and/or prismatic grooves or structures on one side along the light propagation direction to scatter the propagating light, break up source image artifacts, or substantially collimate the light in the cross-guide direction (i.e., the light may be substantially collimated in both the down-guide and cross-guide directions).

In some examples, substrate30may be disposed between turning film14and lenticular diffuser34. In some examples, optical system10may not include substrate30, e.g., turning film14may be directly adjacent and optically coupled to lenticular diffuser34. In some examples, substrate30may be an optical adhesive, polyethylene terephthalate, polycarbonate, or the like. In some examples, turning film14and lenticular diffuser34may be disposed on and optically coupled to opposite sides of substrate30. In other examples, turning film14and lenticular diffuser34may be disposed on and optically coupled to two separate substrates, where the two substrates are laminated together or otherwise optically coupled.

In some examples, liquid crystal display (LCD)50may be disposed adjacent lenticular diffuser34. In some examples, LCD50may be disposed adjacent and optically coupled to lenticular diffuser34. In some examples, other layers (not shown) may be disposed between LCD50and lenticular diffuser34, each layer being optically coupled to each adjacent layer. Other layers may include, for example, an optical adhesive, polyethylene terephthalate, polycarbonate, or the like.

In some examples, optical system10,11may be mounted in a vehicle. For example, a vehicle display system may include backlight light guide12, turning film14, lenticular diffuser34and LCD50. In other examples, a vehicle display system may include turning film14and lenticular diffuser34.

FIGS.2A and2Bare conceptual and schematic lateral cross-sectional views of an example optical system20in the YZ plane (FIG.2A) and the XZ plane (FIG.2B). Optical system20ofFIGS.2A and2Bmay be substantially the same as optical system10ofFIG.1and incorporates the description of elements above with respect toFIG.1. In the examples ofFIGS.2A and2B, optical system20may include backlight light guide12, turning film14, substrate30, lenticular diffuser34and liquid crystal display (LCD)50.

As shown inFIGS.2A and2B, optical system20may be disposed in the XY plane with the X-axis representing the horizontal axis relative to optical system20surface, the Y-axis representing the vertical axis relative to optical system20surface, and the Z-axis representing the display normal. As shown inFIG.2A, grooves22of turning film14may be disposed substantially perpendicular to the YZ plane (i.e., substantially parallel to the X-axis). As shown inFIG.2B, grooves42of lenticular diffuser34may be disposed substantially perpendicular to the XZ plane (i.e., substantially parallel to the Y-axis). In some examples, grooves22of turning film14may be substantially perpendicular to grooves42of lenticular diffuser34.

In some examples, turning film14may output light collimated in the YZ plane. In some examples, lenticular diffuser34reflect or refract collimated light from turning film14away from the Z-axis toward the X-axis plane. In some examples, the position of grooves42of lenticular diffuser34relative to grooves22of turning film14may spread light in the horizontal direction relative to a display surface.

Example LCFs and optical systems that include the same according to the disclosure provide will be illustrated by the following non-limiting examples.

Examples

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

In general, the hybrid lenticulars shown in the following examples are high aspect ratio, multi-faceted shapes designed to produce display systems having viewing output which simultaneously satisfies (1) wide in viewing angle, (2) flat display intensity across the viewing range and (3) sharp cut-offs on either side of the viewing angle range. The example outputs from differing lenticular structures are calculated with baseline assumptions for the other elements of the display system in order to define spreader structures most suitable to produce wide, flat and sharply defined viewing ranges. These are commonly referred to as “top-hat” profiles because of their characteristic shape.

Model Assumptions

The non-sequential optical ray-tracing package used for this study is functionally equivalent to commercial package available from LightTools, Pasadena, CA using standard methods of reverse-ray tracing and Monte-Carlo splitting as are common in the industry. The particular optical system of this invention is shown inFIG.4A. It is a turning film system in which the turning-film had prisms238toward the light-guide assembly and a set of orthogonal refractive spreader features240on a second substrate271and facing the first substrate239. The exact nature of the turning film has not been found to be particularly important to the performance of the spreader, but for these examples the model uses a turning prism with an input face angle of 65.0 deg, a base angle of 66.15, a tip angle of 50.19, a base fraction of 0.1525, a tip fraction of 0.03422, and a curvature factor of 1.419. The turning prisms are assumed to have a real refractive index of refraction 1.565 and an imaginary part of 9.104E-7 at 550 nm wavelength. The first substrate239is assumed to have a refractive index of 1.61, and absorption coefficient of 0.0191 per mm, and thickness of 127 microns.

The spreader features are formed directly on the second substrate271(shown inFIG.4B) of index 1.61 and absorption coefficient 0.0191 l/mm and a thickness of 50.8 microns. This second substrate with the spreader features can be attached directly to the first substrate via an adhesive directly applied the structured side of the spreader element. This for the case where model presumes that adhesive fills the structure, the adhesive is presumed to have optical index of refraction of 1.486 and thickness 25.4 microns plus the depth of the spreader element. The depth of the spreader elements in these cases are in the range 40 to 60 microns (suitable for a 44.4 micron pitch spreader).

As an alternative case, the spreader structure can be modelled as being filled with a material of a different index and the adhesive attached to this fill layer (for example). In this case, the fill material, either the adhesive or another fill material, forms the low index part of the spreader. The spreader feature240is assumed to have a higher refractive index than the fill material for example index of 1.681 and an absorption coefficient of 0.0104 per mm is used in some of the examples. The other side of the second substrate is bonded to the rear polarizer of the display with an adhesive241of index 1.486 and a thickness of 25.4 microns.

In both adhesive filled and alternative filled cases, either adhesive or alternative fill material is presumed to fully fill the spreader features.

The simplified model of the display module242is described as follows. It assumes a transmission of the rear polarizer in pass state of 0.95 and in the block state of 0.001, and an internal module back reflection of 0.001, a material index of 1.5, and scattering resulting from a surface deviation of 9 degrees at the exiting air boundary. The actual slope distribution of this 9 degree deviation would be similar to that of a partial sphere surface deviation. The display module242was exemplary only and could have been omitted or could have had other values.

With respect toFIG.4A, system performance can depend on the output distribution from the light-guide assembly234and this can vary depending on the design of the various components of that assembly. In practice vertical angular output (and hence turning film design goals) can vary significantly with source distribution, while horizontal angular profile (and hence spreader design) is usually far less sensitive. Such a light-guide assembly for example can be made up of a variety of components including one or more sources237, a suitable light-guide with output coupling means235, and a back-reflector236. For the purposes of this discussion we consider output distribution201of the light-guide assembly234. Output distribution201is shown inFIG.5. The down-guide cross-section of this output distribution is shown inFIG.6. The cross-guide cross-section is shown inFIG.7. The modeling, here, assumes a light-guide assembly with the chosen distribution and a reflectance optical property (looking back into the assembly) of 0.965 specular and 0.02 lambertian. These values and distributions are for example purposes only, and the following design approach can be used with other reflectance values and other light distributions.

In particular, the distribution201was derived from a measurement of a physical sample (obtained from an actual Dell XPS laptop) using a RiGO photogoniometer system (Technoteam, Germany). The RiGO system was used to measure both spatial and angular luminance data which was, subsequently, converted into a suitable light source for modelled example comparisons of spreader structures.

Modelled Results

Modelling output are provided for each of the examples described with common system assumptions in order to make comparison plots. The coordinate systems used in the conoscopic plots inFIG.5has the down-guide direction toward the 90 degree azimuthal angle and the source edge (for example LED edge) is toward the 270 degree azimuthal angle. For the luminance cross-section plots (FIG.6, for example), the down-guide direction is plus and the source edge is minus. When used in an actual vehicle display system, the cabin coordinate system typically has + up and − down and may or may not match the directions shown in the luminance cross-section plots. In fact, for the turning film generated top-hat distributions, these typically have a sharper cutoff on the minus side of the distribution, which implies that the minus direction in our down-guide luminance distributions is preferably toward the plus direction in cabin coordinates (i.e. up). For the horizontal cross-section plots, the + direction is generally to the right side of the display if down guide is considered up. In fact, most of the following horizontal cross-section plots are quite symmetric, so direction is not so important. For comparisons, the plots for examples typically include a reference curve which has a flat top of +/−40 degrees angular viewing width and a transition zone that is 30 degrees wide. The embedded refractive structures for spreading function described in these examples here can function well with design viewing able width up to 40 degree width.

Another constraint for manufacturable spreader structures pertains to the aspect ratio of the structure and the maximum angle required for the structure. If the aspect ratio and/or angles are too high, both tooling and film become difficult to manufacture. The structure discussed here is a simple, relatively low-aspect ratio (in the range of 0.8:1 to 1.5:1) lenticular element with two linear sections and a suitable blend region between these sections. We show that for some illumination angle targets in the range of +/−30-45 degrees it's possible to choose the parameters to get horizontal light distributions that have flat tops along with reasonably sharp cutoff slopes. Results also show that these structures have both lower aspect ratios and lower max slopes than previously known spreader structures.

General Refractive Lenticular Spreader

The shapes for these illustrative spreader structures are composed of linear segments on either edge of an elliptical blend section with ellipticities above 1.5; the section of the elliptical function were chosen, generally, to match desired angles at the base of the structure. When encompassed into the overall system model, the lenticular surface is oriented with the convex shape facing the light-guide and the high index side furthest away from the light-guide.

The design parameters for each example are in the table below.

Example and Comparative Examples

TABLE 1Overview of Example and Comparative example structuresBaseBlendStruc-AngleEllipti-FillBlendAspecttureFillExample(deg)cityFractionFractionRatioindexIndexCE1701100%100%0.351.7151.484CE2702100%100%0.511.7151.484CE3704100%100%0.621.7151.484CE4802100%100%0.711.7151.484CE580390%100%0.901.7151.484Example 1802.5100%100%0.821.7151.484Example 2803100%100%0.901.7151.484Example 380390%90%1.101.7151.484Example 484390%93%1.301.6811.486

Comparative examples CE1-CE5 are all modelled without linear segments at the base of the refractive structure (i.e. blend fraction is 100%). The refractive structure for these comparative examples presumes a first structured layer with an index of refraction of 1.7151 and are filled with a material having an index of refraction of 1.4837, these material types being representative of available materials.

Example 1 is designed with a maximum base angle of 80 degrees, a blend ellipticity of 2.5, 100% fill factor (i.e. no intervening flat portions), 100% blend fraction (i.e. no linear base portion) resulting in a refractive structure aspect ratio of 0.82. Example 1 further presumes a first structured layer with an index of refraction of 1.7151, and are filled with a material having an index of refraction of 1.4837.

Example 2 is designed with a maximum base angle of 80 degrees, a blend ellipticity of 3.0, 100% fill factor (i.e. no intervening flat portions), 100% blend fraction (i.e. no linear base portion) resulting in a refractive structure aspect ratio of 0.90. Example 2 further presumes a first structured layer with an index of refraction of 1.7151, and are filled with a material having an index of refraction of 1.4837.

Example 3 is designed with a maximum base angle of 80 degrees, a blend ellipticity of 3.0, 90% fill factor (i.e. 10% intervening flat portions), 90% blend fraction (i.e. 10% of structured is linear base portion) resulting in a refractive structure aspect ratio of 1.10. Example 3 further presumes a first structured layer with an index of refraction of 1. and are filled with a material having an index of refraction of 1.4837. The design profile for example 3 is shown inFIG.8.

Example 4 is designed with a maximum base angle of 84 degrees, a blend ellipticity of 3.0, 90% fill factor (i.e. 10% intervening flat portions), 93% blend fraction (i.e. 7% of structured is linear base portion) resulting in a refractive structure aspect ratio of 1.30. Example 4 further presumes a first structured layer with an index of refraction of 1.681, and are filled with a material having an index of refraction of 1.486. The design profile for example 4 shown inFIG.9.

Model Output Results

The modeled output for the comparative examples and examples shows design progression to functional ranges that provide desired flat-top output while maintaining structures with manufacturable aspect ratio and maximum slope. Comparative example CE1 demonstrates that the simple circular lenticular (Ellipticity 1.0) of CE1 does not work well because it does not give a flat top in the viewed luminance profile versus viewing angle (seeFIG.10). Other comparative examples with 70 maximum/base angle show that while it is possible to get a fairly flat top using an ellipticity of greater than 2.0, the edges still roll off too gradually (seeFIGS.11and12). By increasing the base angle to 80 degrees, the result provides wider angular viewing range at the expense of more gradual roll-off (seeFIGS.13and14).

Output plots for examples 1-4 are shown inFIGS.15-19, respectively, and show best top-hat shape. Examples 1 and 2 show that model structures with 100% fill factor (i.e. all structure and no intervening flat areas) that give good calculated performance, however, these tend to be difficult to fabricate. The primary driver for the fill fraction of <0.95 is to provide manufacturable structure. Examples 3 and 4 show how adding linear sections on the base of the structures gives preferred shaper edges at a wider view angle.

The effect of changing the linear section angles and for the different refractive index materials is shown in comparison ofFIGS.19and20, respectively.FIG.19shows calculated luminance profiles for range of angles 80 to 88 degrees for structure material of refractive index equal to 1.715.FIG.20shows calculated luminance profiles for range of angles 80 to 88 degrees for structure material of refractive index equal to 1.681. The higher material index allows for higher difference in index of refraction (Δn) between structure and filling material and, therefore, demonstrates wider top hat widths.

The complete disclosures of the publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.