Patent Application
20080231780
This invention relates to diffuser sheets, and display assemblies incorporating such diffuser sheets.
A backlight illuminates a liquid crystal (LC) based display panel to provide light distribution over the entire plane of the LC display (LCD) panel. Typical direct-lit LCD backlights consist of individual fluorescent lamps placed in a reflecting cavity to directly shine light upwards towards and through the LCD panel.
A typical direct-lit LCD backlight has a diffuser sheet to hide the individual lamps. The diffuser sheet is typically filled with light-scattering particles, has a transmission of only about 55% and a haze of over 99% to drastically scatter the light so that the individual lamps cannot be seen. On top of the diffuser sheet is a “bottom diffuser” that is typically a plastic film coated with spheres and a binder, which aids in hiding the bulbs, but also turns or collimates the light somewhat in the direction of the viewer. Often a prism film is arranged on the diffuser sheet, where the prism film has prisms running in a horizontal direction (direction parallel to the orientation of the lamps) to collimate the light strongly in the vertical direction (direction in the plane of the prism film and perpendicular to the horizontal direction). Typical applications for direct-lit backlights are in televisions, where it is acceptable to collimate the light vertically since viewers typically do not view from above or below the screen, while it is typical to not collimate horizontally since it is common to view the screen from side angles.
One aspect of some embodiments of the present invention is to provide an optical diffuser sheet, and optical display assembly incorporating the sheet, that provides enough light-scattering to hide the individual light sources of a light provider from a viewer and provides relatively uniform diffuse light. Another aspect of some embodiments of the present invention is to provide an optical diffuser sheet, and optical display assembly incorporating the sheet, that directs light preferentially towards the viewer on-axis. Another aspect of the present invention provides an optical plate with a relatively thin optical diffuser film and supporting substrate or relatively thin optical diffuser film and frame.
According to one embodiment of the invention there is provided an optical plate. The optical plate comprises: a supporting substrate; and an optical diffuser film having a density of light scattering particles to provide light diffusion and having a surface facing the supporting substrate, wherein a first portion of the surface facing the supporting substrate contacts the supporting substrate and there exists a gap between a second portion of the surface facing the supporting substrate and the supporting substrate, wherein the ratio of the area of the first portion to the second portion is less than 10%.
According to another embodiment of the invention there is provided an optical display assembly. The optical display assembly comprises: a light provider comprising a plurality of light sources; and an optical plate comprising: a supporting substrate; and an optical diffuser film having a density of light scattering particles to provide light diffusion of light from the light provider and having a surface facing the supporting substrate, wherein a first portion of the surface facing the supporting substrate contacts the supporting substrate and there exists a gap between a second portion of the surface facing the supporting substrate and the supporting substrate, wherein the ratio of the area of the first portion to the second portion is less than 10%.
According to another embodiment of the invention there is provided an optical plate. The optical plate comprises: a supporting substrate; an optical diffuser film having a density of light scattering particles to provide light diffusion and having a surface facing the supporting substrate and a gap between the optical diffuser film and supporting substrate, the surface having a total area above the supporting substrate; and a plurality of pillar structures between and contacting both the optical diffuser film and the supporting substrate, the plurality of pillar structures contacting the optical diffuser film over a first area of the surface facing the supporting substrate, wherein the ratio of the first area to the total area is less than 10%.
According to another embodiment of the invention there is provided an optical display assembly. The optical display assembly comprises: a light provider comprising a plurality of light sources; and an optical plate comprising: a supporting substrate; an optical diffuser film having a density of light scattering particles to provide light diffusion of light from the light provider and having a surface facing the supporting substrate and a gap between the diffuser film and supporting substrate, the surface having a total area above the supporting substrate; and a plurality of pillar structures between and contacting both the optical diffuser film and the supporting substrate, the plurality of pillar structures contacting the optical diffuser film over a first area of the surface facing the supporting substrate, wherein the ratio of the first area to the total area is less than 10%.
According to another embodiment of the invention there is provided an optical assembly. The optical assembly comprises: a light provider comprising a plurality of light sources; an optical diffuser film over the light provider and arranged to receive light from the light provider, wherein a gap exists between the light provider and the optical diffuser film, the optical diffuser film having a density of light scattering particles to provide light diffusion.
According to another embodiment of the invention there is provided a method of forming an optical plate. The method comprises: spray coating an optical diffuser film on a supporting substrate, the optical diffuser film having a density of light scattering particles to provide light diffusion and having a surface facing the supporting substrate, wherein a first portion of the surface facing the supporting substrate contacts the supporting substrate and there exists a gap between a second portion of the surface facing the supporting substrate and the supporting substrate, wherein the ratio of the area of the first portion to the second portion is less than 10%.
The light provider 12 includes a reflector 30, and a number of light sources 32. The light sources may be, for example, lamps such as cold cathode florescent lamps (CCFLs). The light sources are oriented parallel to each other and along a horizontal direction from left-to-right as shown in
Prism film 20 has a number of prism structures generally parallel to each other and oriented along the horizontal direction. The prism film 20, may be, for example, composed of poly(ethylene terephthalate) having a texture coating with an array of prisms.
The diffuser films 16 and 18 have a density of light scattering particles to provide light diffusion and/or a rough surface to provide light diffusion. The diffuser films may be, for example, made of polycarbonate with 2 micron diameter particles composed of hydrolyzed poly(alkyl trialkoxysilanes) available under the trade name TOSPEARL™ from GE Silicones.
The horizontal view luminance as a function of horizontal zenith angle θh provides an indication of the directional nature of the light from the optical display assembly, and thus the light directing properties for a horizontal view of the optical components in the optical display assembly. For example, if the horizontal view luminance as a function of horizontal zenith angle θh exhibits a narrow peak around a zero degree zenith (on axis), then the light for the horizontal view is well collimated. In a similar fashion, the vertical view luminance as a function of vertical zenith angle θv provides an indication of the light directing properties for a vertical view of the optical components in the optical display assembly.
where Li(on) is the luminance directly above one of the lamps, and Lj(off) is the luminance directly above a midpoint between lamp j and lamp j+1, and n is the number of lamps.
Returning to
If the diffuser sheet is incorporated in a display assembly with other optical components having a regular structure, such as a prism film with regularly spaced prism structures, interference Moiré effects may results. These Moiré effects may be reduced by randomizing the idealized structure of the optical structures 40. Reducing Moiré effects by randomizing an idealized structure of an optical structure is disclosed, for example, in U.S. Pat. No. 6,862,141 to Eugene Olczak, issued on Mar. 1, 2005, which discloses modulating an idealized prism structure of an optical substrate from a nominal linear path in a lateral direction (direction perpendicular to the height) by applying a nonrandom, random (or pseudo random) amplitude and period texture. The disclosure of U.S. Pat. No. 6,862,141 is incorporated herein by reference in its entirety.
In general the height, pitch and wavelengths may be in a range between 100 nanometers and 10 millimeters. The cross section of each structure may be concave, convex, sinusoidal, or triangular (prismatic), for example. The cross section might also be a piecewise assembly of these geometries or any other useful shape including diffractive micro structures and nano structures. The size of the diffuser sheet and/or the display in which the diffuser sheet is used may be in the range of one millimeter by one millimeter to several meters by several meters. The thickness may vary between 12 microns and 25 millimeters. Each and every parameter may be held constant or varied as described above. Additionally the parameters may be designed to incorporate desirable ratios between parameters (for example the relative pitch of one structure to another or the relative pitch of one structure to the LCD pixel pitch).
The random modulation in a direction perpendicular to the lateral direction, such as shown in
Table 1 illustrates examples of diffuser sheets according to embodiments of the invention along with two comparative examples DS and DS2. The values were calculated using an optical model validated through experimental results. The optical model is based on a geometric ray-tracing program that uses a Monte Carlo geometric ray tracing technique. Error bars on the result represent one standard deviation of the Monte Carlo error. The parameter values used by the optical model are for a typical 26″ direct-lit BLM. The optical model assumes that the bulbs and the reflector in the BLM absorb 6% of the light rays intersecting them and isotropically reflects the remaining 94%. The input parameters for the detector system include the spot size of 2 mm at the top of the film stack. The detector is located at 55 mm distance from the top of the film stack. For on-bulb measurements, the detector is positioned directly over top of the bulb when at zero degrees zenith. For the off-bulb measurements the detector is position between the bulbs. The rays (i.e. photons) fired by the Monte Carlo geometric ray tracing software program each have one unit of dimensionless energy. The software program figures out how much of the energy is absorbed and finally how much energy is emitted and in what direction. The dimensionless ray energy from the model is multiplied by a coefficient that converts it to luminance units of cd/m2. The calculation results from the models were validated against experimental measurements.
DS and DS2 are volumetric scattering diffuser sheets made of 2 mm thick polycarbonate. All diffuser sheets are 2 mm in thickness. Particle concentration is in parts per hundred (pph). The particles have a 2 micron diameter and are composed of hydrolyzed poly(alkyl trialkoxysilanes) available under the trade name TOSPEARL™ from GE Silicones. The based material for all the sheets is polycarbonate.
The bottom texture is the side of the diffuser sheet facing the light sources. The top texture is the side of the diffuser sheet facing the viewer (or detector). The three textures, labeled Texture A, Texture B, and Texture C are shown in
STDP-A, STDP-B, and STDP-C, are diffuser sheets with one smooth side, and one textured side. The textured side for diffuser sheets STDP-A, STDP-B, and STDP-C have texture A, texture B and texture C, respectively, as those textures are shown in
Table 1 shows the reduction in absorption of the diffuser sheet for the single sided textures STDP-A, STDP-B and STDP-C (˜7%) as compared to a smooth surface diffuser sheet with a greater concentration of particles (˜9%). Table 1 also shows the reduction in absorption of the diffuser sheet for the double sided textures DTDP-A, DTDP-B (˜2%) as compared to a smooth surface diffuser sheet with a greater concentration of particles (˜9%).
Moreover, while the smooth diffuser plate with lower particle concentration, DS2, has an absorption less than ˜9%, it exhibits a significant loss in bulb hiding power for the smooth texture and at the equivalent of 0.125 pph particles as compared to the single texture diffuser sheets (texture A, B or C) with 0.125 pph particles.
In addition to the optical display assembly illustrated in
In some cases it may be desirable to tune the diffuser sheet, diffuser films or other components to provide an intentional transformation of the degree of polarization or polarization state to aid in more efficient polarization recycling or other display performance enhancements.
The performance of optical display assemblies including the diffuser sheet was calculated using the validated optical model.
The results of the calculation are shown in
The optical diffuser sheets 14 in FIGS. 20 and 22-25 do not have any light scattering particles, and are textured polycarbonate films.
Table 2 lists the luminance, and full width half maxima (FWHM) of both the horizontal view luminance and vertical view luminance of the arrangements of FIGS. 20 and 22-25, where
The results are shown in Table 2. The luminance shown is the on-axis luminance. Also shown in Table 2 is the full width half maxima for both the horizontal view and the vertical view.
The film stack description in Table 3 lists the components of the assembly in order from the component just above the CCFL light sources 32 to the component at the top of the stack. STDP-A, STDP-B, STDP-C, are diffuser sheets with one smooth side, and one textured side. The textured side for diffuser sheets STDP-A, STDP-B, STDP-C have texture A, texture B and texture C, respectively, as those textures are shown in
The luminance shown in Table 3 is the on-axis luminance. Also shown in Table 3 is the full width half maxima for both the horizontal view and the vertical view, and the bulb hiding power. As can be seen from the results in Table 3, the diffuser sheets provide good hiding power, and light collimation for the vertical view, as well as good on-axis luminance.
As described above, the diffuser sheet can be used with diffuser films and/or prismatic films to provide various output distributions of light. These embodiments can increase the total output of light by more than 10%. On-axis luminance may be increased by 10-100%, depending on the specific combinations of microstructures and films. This enables a variety of designs to meet specific light-output requirements of a given display model, all of which are much brighter than conventional designs.
The light management film stacks for direct-lit display backlighting described above offer improved luminous efficiency. An important component is a low-absorption diffuser sheet, which can be used with diffuser films, prismatic films, or combinations thereof, that offers hiding power comparable to conventional diffuser sheets but higher on-axis luminance, improved luminance over wider view angles, improved total light throughput, and in some embodiments fewer optical components.
Small amounts of light-scattering particles could be added to the diffuser sheet to improve hiding power, depending on the design objectives for a specific backlight.
According to another embodiment of the invention, an optical plate is provided, where the necessary hiding power is achieved by increasing the concentration of scattering particles in a relatively thin low-absorptive diffuser, and where an optical gap exists between the film and an underlying supporting substrate or between the film and a light provider with a supporting frame. The optical gap reduces optical coupling between the diffuser film and supporting substrate or light provider. Reducing the optical coupling between the diffuser film and supporting substrate reduces the effective pathlength of light that travels through the substrate with a corresponding reduction in the amount of light being absorbed by the supporting substrate.
The optical diffuser film 114 may be formed on a supporting substrate 112 by any appropriate method. For example, the optical diffuser film 114 may be formed by extruding a film composed of an optically clear thermoplastic or glass with scattering particles. The extrusion process can use rollers to apply a rough texture on the diffuser film 114 to minimize the contact when the diffuser film 114 is placed on top of the supporting substrate 112. Alternative ways to form the diffuser film 114 include solvent casting, compression molding, spray coating a thin base film with particles and a carrier medium, UV curing a coating composed of particles and a carrier medium cast on a thin base film. The supporting substrate 112 can be formed using an extrusion sheet line, injection molding, or a compression molding process. The optical diffuser film 114 can be placed on top of the supporting substrate 112.
Furthmore, the optical diffuser film 114 can be physically attached to the supporting substrate 112 by any appropriate method. For example, an adhesive can be sprayed at point locations on either the supporting substrate 112 or the optical diffuser film 114 followed by laminating the optical diffuser film 114 to the supporting substrate. By controlling the size of the sprayed point dimensions and the number and location of spray points, one can control the contact area, binding strength, and visual quality. This can be accomplished using current ink jet technology. Furthermore, one can select an adhesive that has a refractive index and absorption coefficient so that it matches the either optical diffuser film or supporting substrate. Scattering particles may be added to the adhesive prior to spraying to introduce scattering within the adhesive.
In embodiments where pillars are disposed between the optical diffuser film 114 and the supporting substrate 112, one method of attachment would require that pillars be generated on the optical diffuser film 114 and/or the supporting substrate 112 so that they stick out of the plane of the film or substrate. The pillars could be generated using a film or sheet extrusion process by using a roller tooled with pillar cavities. The pillars could also be generated by an embossing process that uses a tool with the pillar cavities. The shape, size, depth, location, and frequency of the pillar cavities could be controlled in the tool. The supporting substrate 112 or the optical diffuser film 114 could then be laminated together by melt adhesion at the tips of the pillars. The adhesion process would lead to contact points only at the locations of the pillars thus controlling the contact area. The pillars could be made to include scattering particles by generating the pillars on the optical diffuser film 114 or could be made to be clear by generating the pillars on the supporting substrate 112.
The optical diffuser film 114 may be formed of, for example, polycarbonate with scattering particles. The scattering particles may be, for example, 2 micron diameter hydrolyzed poly(alkyl trialkoxysilanes) available under the trade name TOSPEARL™ from GE Silicones. The optical diffuser film may be made using other optically clear materials filled with other types and sizes of scattering particles. Preferably, the optical diffuser film 114 is made of a material having a low yellowness index and no absorbing dyes. Preferably, the optical diffuser film 114 has a relatively small thickness. Table 4 compares calculated optical properties of diffuser films having various thicknesses and scattering particle concentrations. The total number of scattering particles is the same for each of the four sample diffuser films in Table 4, but as the thickness of the sample film decreases, the concentration of the scattering particles is increased in a corresponding amount. The diffuser films are of optical quality polycarbonate with scattering particles composed of 2 micron TOSPEARL™ particles.
The decreased absorption in the thinner diffuser films is due to the scattered light traveling a shorter distance through the polycarbonate thus leading to a lower amount being absorbed by the polycarbonate. The increase in the concentration of the scattering particles with a thinner diffuser film maintains transmission haze and thus the hiding power of the plate. As can be seen from Table 4, the thinnest film of 0.125 mm provided a transmission haze as high as the other three films, while at the same time having the lowest total absorption.
The luminance of three samples in various configurations was also determined to compare the optical properties of a relatively thick diffuser film sample, relatively thin diffuser film sample, and relatively thin diffuser film supported by a clear supporting substrate. Sample A was a 1.4 mm thick polycarbonate diffuser film with 0.5% by weight TOSPEARL™. Sample B was a relatively thin diffuser film of 0.46 mm thick polycarbonate with 4% by weight TOSPEARL™. Sample C had two parts, a first part with a thin diffuser film made of 0.46 mm thick polycarbonate with 4% by weight TOSPEARL™, and a second part of an optically clear substrate made of 1.57 mm thick quartz glass supporting the first part. The 1.4 mm thick and 0.46 mm thick polycarbonate diffuser films were made by a compression molding process. The luminance measurements were made using a Microvision detector with the samples in a Westinghouse 19″ direct lit backlight module as a light source. For sample C, the quartz glass was arranged on the bottom closest to the light source with the thin diffuser film on top closest to the detector.
Measurements were taken on the three samples in five different configurations. Configuration #1 was the sample by itself. Configurations #2, #3, and #4 were with the sample and one, two, and three micro lens diffuser films, respectively, on top of the sample. Configuration #5 was the sample with one micro lens diffuser film and one straight 90-degree prism film on top closest to the detector.
Table 5 below illustrates the luminance for samples A to C in each of the five configurations #1 to #5. The measurements show an improvement in luminance for sample B and sample C over the thicker diffuser film sample A. The % gain in the luminance for sample B and sample C relative to the thicker diffuser film sample A increases with the number of light collimating micro lens diffuser films in the film stack. The configuration with the prism film, which strongly collimates light, shows the greatest gain in the luminance for samples B and C relative to the thicker diffuser film sample A. For example, samples B and C in configuration #5 have a respective. 18.4% and 13.5% gain in luminance relative to sample A for configuration #5.
Referring again to
Referring again to
In order to reduce the optical coupling between the optical diffuser film 114 and the supporting substrate 112, and to reduce the amount of high angle light traveling through the relatively thick supporting substrate layer, it is preferable that the ratio of the area of the first portion to the second portion is less than 10%. More preferably the ratio of the area of the first portion to the second portion is less than 3%. Most preferably the ratio of the area of the first portion to the second portion is less than 1%.
It is also preferable that the optical plate 100 have a low absorption and absolute hiding power. Preferably the optical plate 100 when illuminated is characterized by an absorption of less than 10% and an absolute hiding power of less than 10%. More preferably the optical plate 100 when illuminated is characterized by an absorption of less than 7% and an absolute hiding power of less than 7%. Most preferably the optical plate 100 when illuminated is characterized by an absorption of less than 4% and an absolute hiding power of less than 4%.
The particular thicknesses of the supporting substrate 112 and optical diffuser film 114 will depend on the application, although in general the supporting substrate 112 is relatively thick as compared to the optical diffuser film 114. Preferably the thickness of the optical diffuser film 114 is less than 1 mm, more preferably less than 0.3 mm. As an example, the thickness of the optical diffuser film 114 and the supporting substrate 112 may be about 0.25 mm and about 1.75 mm, respectively. The thickness of the supporting substrate 112 should be sufficient to provide mechanical support and stiffness for the particular application, such as for large area displays. Preferably, the thickness of the supporting substrate 112 is between 0.5 to 10 mm, and more preferably between 1 and 2 mm.
The thickness of the optical gap 116 should be sufficient for its optical functionality. Preferably the thickness of the optical gap 116 is greater than 1 micron, and more preferably between 10 and 50 microns.
The absorption of the plate 100 depends on the composition and shape of the pillar structures.
The pillar structures 118a through 118d have the following compositions and shape. Pillar structure 118a is made of polycarbonate with TOSPEARL™ scattering particles and has a truncated cone shape. Pillar structure 118b is made of polycarbonate with TOSPEARL™ scattering particles and has a cylindrical shape. Pillar structure 118c is made of polycarbonate without scattering particles and has a truncated cone shape. Pillar structure 118d is made of polycarbonate without scattering particles and has a cylindrical shape.
As can be seen from the graph of
The optical diffuser film 114 is attached to a top portion of the frame 126. In this regard, the optical assembly 120 may include a plurality of anchoring pins 122 arranged to attach the optical diffuser film 114 to the top portion of the frame 126, such as by being inserted into holes 124 in the optical diffuser film 114.
Preferably, the optical diffuser film 114 has a relatively low thermal coefficient of expansion in this embodiment. For example, the thermal coefficient of expansion may be less than 6.0×10−7 K−1. The low thermal coefficient of expansion of the optical diffuser film 114 helps prevent buckling and sagging due to expansion/contraction of the film due to temperature changes.
In the embodiment of
The total thickness of the structures in the embodiments of
The optical properties, including absorption, hiding power, transmission, and haze, of various optical plates with relatively thin optical diffuser films was calculated, and compared with the properties of a thicker diffuser film, the two comparative examples DS and DS2. The results are shown in Table 6. The values in Table 6 were calculated using the validated optical model as discussed with respect to Table 1.
DS and DS2 are volumetric scattering diffuser sheets made of 2 mm thick polycarbonate as discussed above with respect to Table 1. Particle concentration is in parts per hundred (pph). The particles have a 2 micron diameter and are composed of TOSPEARL™ particles. Examples 34 through 41 were optical plates with an optical diffuser film separated by a gap of 10 microns from a supporting substrate.
The optical diffuser films of the optical plates were of polycarbonate and contained the particles, while the supporting substrates and plate texture layers were of polycarbonate without scattering particles. The designation “a” for optical plate indicates that the supporting substrate faces the light source, while the designation “b” indicates that optical diffuser film of the optical plates faces the light source. Thus, for samples 34 and 35, the supporting substrate faces the light source, while for samples 36-41, the optical diffuser film of the optical plates faces the light source. The Bottom Texture refers to the texture of the closest surface of the plate facing the light source, while the Top Texture refers to the surface of the plate furthest away from the light source. Textures B and D are sinusoidal wave and hemispherical, respectively, as discussed above.
The sample plates 34-41 have thicknesses for the optical diffuser films, supporting substrates and plate texture layer, if applicable, as follows: DPL-1: 1.75 mm thick supporting substrate and 0.25 mm thick optical diffuser film; DPL-2: 1.00 mm thick supporting substrate and 0.25 mm thick optical diffuser film; DPL-3: 1.75 mm thick supporting substrate and 0.25 mm thick optical diffuser film; and DPL-5: 1.75 mm thick supporting substrate and 0.25 mm thick optical diffuser film. The DPL-4 and DPL-6 samples also included a plate texture layer (See
The calculated optical properties in table 6 show that reducing the thickness of the clear supporting substrate from 1.75 mm down to 1.0 mm leads to less absorption for respective optical plate DPL-1a relative to DPL-2a and DPL-1b relative to DPL-2b. The calculation results in table 6 also show that there is reduced absorption if the optical diffuser film of the optical plates faces the light source instead of the supporting substrate. This is demonstrated by the reduction in absorption for optical plate DPL-1b relative to DPL-1a and for optical plate DPL-2b relative to DPL-2a. The isolation of the texture from the supporting substrate DPL-6b as illustrated in
The optical plate of the embodiments of
The display assembly 150 may also include a liquid crystal 152, and a film stack 154 between the liquid crystal 152 and the optical plate 100. The composition of the film stack will depend on the application, but in general may include one or more optical films such as light collimating diffuser films, prism films, light recycling polarizers, or lenticular films.
The performance of various optical display assemblies including an optical plate and optical stack was calculated using the validated optical mode. The results are shown in Table 7 with samples 1 and 34-41 for comparison.
The optical plates and orientation of the optical plates for DPL-1a, DPL-2a, DPL-1b, DPL-2b, DPL-3b DPL-4b, DPL-5b, and DPL-6b, are described above with respect to Table 6. For the samples with optical stacks, i.e., samples 43-62, the stacks were arranged above the optical plate (or diffuser sheets for samples 42, 49, and 57) on a side of the optical plate opposite from the light source. The description in Table 7 lists the order of the optical components from bottom to top above the optical plate. For example, for sample 67 the components are arranged with the diffuser plate at the bottom, then the light collimating diffuser film BD, and then the prism film Prism. BD is a light collimating diffuser film composed of 0.125 mm thick poly(ethylene terephthalate) with micro lens texture on a side facing viewer (detector), i.e., on a side away from the light provider. Prism is a horizontally oriented (prisms are parallel to the CCFL light sources) prism film composed of 0.125 mm thick poly(ethylene terephthalate) having a texture coating with an array of straight prisms having a 50 micron pitch and 25 micron height.
The calculated optical performances in table 7 show that reducing the thickness of the clear supporting substrate from 1.75 mm down to 1.0 mm in the optical plate leads to increase luminance for respective optical plate DPL-1a relative to DPL-2a and DPL-1b relative to DPL-2b in various display assemblies including the optical plate by itself and the optical plate with one microlens diffuser film; with two microlens diffuser film; and finally with one microlens diffuser film and one prism film. The calculation results in table 7 also show that there is increased luminance if the optical diffuser film of the optical plates faces the light source instead of the supporting substrate. This is demonstrated by the increase in luminance for optical plate DPL-1b relative to DPL-1a and for DPL-2b relative to DPL-2a. The isolation of the texture from the clear supporting substrate DPL-6b as illustrated in
The performance of various optical display assemblies including an optical plate and optical stack was also measured using a 19 inch Westinghouse backlight module and a light detector. The Westinghouse backlight has a 25.3 mm bulb spacing between its CCFL bulbs. The distance between the bottom of the sample and the bulbs was 21.1 mm. The samples were arranged between the Westinghouse backlight and the sample. The arrangement of the samples is give in Table 8.
Samples 63-67 and 92-93 included a relatively thick diffuser film made of optical grade polycarbonate as a comparison sample. The relatively thin diffuser films in samples 68-91 and 94-95 were also made of optical grade polycarbonate. The particles for all of the diffuser films were of TOSPEARL™ particles. All of the films and sheets in samples in listed in table 8 were made on an extrusion film and sheet line respectively. The transmission and transmission haze of the optical plates or diffuser films without an overlying film stack was measured and the results are shown in Table 9. As can be seen, the samples with a relatively thin diffuser film, samples 68, 73, 78, and 83, have a good transmission, while at the same time maintaining a relatively large transmission haze.
The results of the luminance measurements for the samples with an overlying film stack are shown in Table 10. The luminance gain is relative to the comparison samples with a relatively thick diffuser film, i.e. samples 64-67 and 92-93, where samples having the same stack are compared. As can be seen, the results in Table 10 show a positive luminance gain for all of the samples with a relatively thin diffuser film as compared to the thicker diffuser film. The gain increases as the number of collimating films (microlens diffuser films) is increased. The gain is greatest for those samples with a prism film.
While the invention has been described with reference to several embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
This application is a continuation-in-part application of U.S. application Ser. No. 11/723,891 filed on Mar. 22, 2007.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11723891 | Mar 2007 | US |
| Child | 11976961 | US |
