Backlight unit

Abstract

The utility model relates to a backlight unit. The backlight unit includes a two-dimensional array of light emitting diodes (LEDs), a transparent solid material layer, a diffuser film, a brightness enhancing film, and a second diffuser film located between the diffuser film and the brightness enhancing film.

Description

[0001] The section headings used in this document are for organizational purposes only and should not be construed as limiting the subject matter described in this application in any way.

[0002] Cross - Reference to Related Applications

[0003] This application claims priority to U.S. Provisional Patent Application 63 / 503,517, filed May 22, 2023, entitled "Back Light Unit for Backlit Displays"; this application claims priority to U.S. Non - Provisional Patent Application 18 / 418,311, filed January 21, 2024, entitled "Back Light Unit for Backlit Displays"; this application also claims priority to PCT Application PCT / US24 / 29010, filed May 11, 2024, entitled "Back Light Unit for Backlit Displays". U.S. Provisional Patent Application 63 / 503,517, U.S. Non - Provisional Patent Application 18 / 418,311, and PCT Application PCT / US24 / 29010 are hereby incorporated by reference. Technical Field

[0004] This teaching generally relates to the technology of backlight units used in backlit displays. Background Art

[0005] Display technology is evolving rapidly in an effort to improve the quality of displayed images. In particular, liquid crystal displays (LCDs) are increasingly adopting backlight unit architectures to enhance image quality. There is a strong desire for improved backlight units for this and other applications. For example, mini - LEDs are becoming an important backlight technology for new high - dynamic range (HDR) LCD displays, including monitors, mobile phones, and tablets. The advantage of these displays and the associated backlight units (BLUs) is local dimming, where individual LEDs in the BLU can be turned on and off to create a higher contrast ratio required to support HDR, for example, compared to edge - lit LEDs. For example, compared to OLED displays, such systems offer local dimming, enabling richer contrast, darker blacks, lower power, ultra - high brightness, high reliability, and no burn - in. Applications of these displays include, for example, automotive displays, laptops, desktops, tablets, and professional and custom displays. Summary of the Utility Model

[0006] The object of this utility model is to provide a backlight unit.

[0007] In an embodiment of the present utility model, a backlight unit includes:

[0008] a) A two-dimensional array of light-emitting diodes (LEDs), wherein at least one LED in the two-dimensional array of LEDs emits light having an angular distribution of nominally ±90 degrees about the center of the at least one LED;

[0009] b) A layer of transparent solid material positioned with its bottom surface above the two-dimensional array of LEDs, the transparent solid material layer being configured to transform the light generated by the two-dimensional array of LEDs into light having an angular distribution of nominally less than ±90 degrees about the center of the at least one LED at the top surface of the transparent solid material layer;

[0010] c) A first diffuser film positioned above the top surface of the transparent solid material layer, the first diffuser film being configured to provide a full width at half maximum greater than 60 degrees and being configured to diffuse the light generated at the top surface of the transparent solid material layer to produce diffused light at the top surface of the first diffuser film;

[0011] d) A brightness enhancement film positioned above the top surface of the first diffuser film and including a plurality of prism microstructures on at least one surface, at least some of the prism microstructures having a vertex angle of ninety degrees; the brightness enhancement film being configured to narrow the angular optical distribution of the diffused light generated at the top surface of the first diffuser film; and

[0012] e) A second diffuser film, wherein the second diffuser film is located between the first diffuser film and the brightness enhancement film.

[0013] Preferably, the first diffuser film includes a top surface diffuser layer, a bottom surface diffuser layer, and a thin transparent material layer located between the top surface diffuser layer and the bottom surface diffuser layer.

[0014] Preferably, the two-dimensional array of LEDs includes a row pitch of 8 mm and a column pitch of 8 mm.

[0015] Preferably, the two-dimensional array of LEDs includes ten rows and eight columns.

[0016] Preferably, the two-dimensional array of LEDs includes less than or equal to fifteen rows and greater than or equal to fifteen columns.

[0017] Preferably, the two-dimensional array of LEDs includes less than or equal to ten rows and greater than or equal to ten columns.

[0018] Preferably, the transparent solid material includes a polymethyl methacrylate material.

[0019] Preferably, the transparent solid material includes a polycarbonate material.

[0020] Preferably, the transparent solid material includes a material having a refractive index of 1.75.

[0021] Preferably, the thickness of the transparent solid material layer is greater than or equal to half of the thickness measured from the top surface of the two-dimensional array of LEDs to the top surface of the backlight unit.

[0022] Preferably, the thickness of the transparent solid material layer is greater than or equal to 0.7 times the thickness measured from the top surface of the two-dimensional array of LEDs to the top surface of the backlight unit.

[0023] Preferably, the diffuser film has a full width at half maximum greater than 80 degrees.

[0024] Preferably, the diffuser film has a full width at half maximum greater than 100 degrees.

[0025] Preferably, the backlight unit includes at least one additional film positioned above the brightness enhancement film.

[0026] Preferably, the at least one additional film is configured to further shape the light from the brightness enhancement film.

[0027] Preferably, the at least one additional film is configured to redirect the light from the brightness enhancement film.

[0028] Preferably, the backlight unit includes a polarizer reflector film positioned above the brightness enhancement film.

[0029] Preferably, the backlight unit includes a second brightness enhancement film positioned above the brightness enhancement film.

[0030] Preferably, the backlight unit includes a polarizer reflector film positioned above the second brightness enhancement film.

[0031] Preferably, the backlight unit includes at least one additional film positioned above the polarizer reflector film.

[0032] Preferably, the at least one additional film is configured to further shape the light from the brightness enhancement film.

[0033] Preferably, the at least one additional film is configured to redirect the light from the brightness enhancement film.

[0034] In another embodiment of the present invention, a backlight unit includes:

[0035] a) A two-dimensional array of light-emitting diodes (LEDs), wherein the number of rows in the two-dimensional array is less than the number of columns in the two-dimensional array, and at least one LED in the two-dimensional array generates light having an angular distribution of nominally ±90 degrees about the center of the at least one LED;

[0036] b) A transparent solid material layer positioned with its bottom surface above the two-dimensional array of LEDs, the transparent solid material layer being configured to transform the light generated by the two-dimensional array of LEDs into light having an angular distribution of nominally less than ±90 degrees around the center of the at least one LED at the top surface of the transparent solid material layer;

[0037] c) A first diffuser film positioned above the top surface of the transparent solid material layer, the first diffuser film being configured to provide a full width at half maximum greater than 60 degrees and being configured to diffuse the light generated at the top surface of the transparent solid material layer to produce diffused light at the top surface of the first diffuser film;

[0038] d) A pair of cross brightness enhancement films positioned above the top surface of the first diffuser film and including a plurality of prism microstructures on at least one surface, at least some of the prism microstructures having a vertex angle of ninety degrees;

[0039] e) A polarizer reflector film positioned above the pair of cross brightness enhancement films and being configured to transmit one polarization and reflect the other polarization, thereby improving the uniformity of the light output from the backlight unit; and

[0040] f) A second diffuser film, wherein the second diffuser film is located between the first diffuser film and the pair of cross brightness enhancement films.

[0041] Preferably, the first diffuser film includes a top surface diffuser layer, a bottom surface diffuser layer, and a thin transparent material layer located between the top surface diffuser layer and the bottom surface diffuser layer.

[0042] Preferably, the backlight unit further includes a prism angle bending film positioned above the polarizer reflector film and being configured to tilt the light distribution of the output from the backlight unit.

[0043] Preferably, the backlight unit further includes an elliptical diffuser film positioned above the polarizer reflector film and being configured to broaden the light distribution of the output from the backlight unit in one direction.

[0044] Preferably, the number of rows in the two-dimensional array is less than or equal to fifteen.

[0045] The technical effect of one aspect of the present utility model is to provide a technically improved backlight unit. Description of the Drawings

[0046] The present teachings in accordance with preferred and exemplary embodiments and further advantages thereof are described more specifically in the detailed description below in conjunction with the accompanying drawings. Those skilled in the art will understand that the drawings described below are for illustrative purposes only. The drawings are not necessarily to scale; instead, emphasis is generally placed on illustrating the principles of the teachings. The drawings are not intended in any way to limit the scope of the applicant's teachings.

[0047] Figure 1A A schematic diagram illustrating an embodiment of a backlight unit architecture that includes an array of light-emitting diodes (LEDs) for a liquid crystal display (LCD) in accordance with the present teachings.

[0048] Figure 1B A schematic diagram illustrating another embodiment of a backlight unit architecture that includes an array of light-emitting diodes (LEDs) for a liquid crystal display (LCD) in accordance with the present teachings.

[0049] Figure 2A A three-dimensional graph illustrating the light distribution generated by a known LED as a function of angle as measured by a goniophotometer;

[0050] Figure 2B Illustrates in combination with Figure 2A The measured light distribution of the illumination pattern represented in two dimensions as described.

[0051] Figure 3 A schematic diagram illustrating a two-dimensional array of LEDs that can be used in an embodiment of a narrow backlight unit in accordance with the present teachings.

[0052] Figure 4A A table related to an embodiment of a diffuser layer including a single-sided coating in accordance with the present teachings.

[0053] Figure 4B A table related to an embodiment of a diffuser layer including a double-sided coating in accordance with the present teachings.

[0054] Figure 4C A table related to an embodiment including a volume diffuser layer having strong hiding or LED smoothing characteristics.

[0055] Figure 5 A graph of the measured angular intensity distribution of an embodiment of a high-hiding microstructure double-sided diffuser layer in accordance with the present teachings.

[0056] Figure 6A A schematic diagram of the layer structure of an embodiment of a backlight unit in accordance with the present teachings having a double-sided diffuser layer and an air gap.

[0057] Figure 6B Illustrates having a double-sided diffuser layer and a small air gap thickness Figure 6AVisual image of an embodiment of a backlight unit.

[0058] Figure 6C Illustrates a backlight unit with a double-sided diffuser layer and a relatively large air gap thickness Figure 6A Visual image of an embodiment of a backlight unit.

[0059] Figure 7A Schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer, a second diffuser layer, and a transparent material layer according to the present teachings.

[0060] Figure 7B Illustrates a backlight unit with a double-sided diffuser layer and a small transparent material layer thickness Figure 7A Visual image of an embodiment of a backlight unit.

[0061] Figure 7C Schematic diagram of the layer structure of an embodiment of a backlight unit according to the present teachings having a double-sided diffuser layer and a relatively large transparent material layer thickness.

[0062] Figure 7D Illustrates Figure 7C Visual image of an embodiment of a backlight unit.

[0063] Figure 7E Schematic diagram of the layer structure of an embodiment of a backlight unit according to the present teachings having a double-sided diffuser layer and an even larger transparent material layer thickness.

[0064] Figure 7F Illustrates Figure 7E Visual image of an embodiment of a backlight unit.

[0065] Figure 7G Visual image of an embodiment of a backlight unit having a double-sided diffuser layer over a 20 mm thick transparent material layer.

[0066] Figure 7H Visual image of an embodiment of a backlight unit having a double-sided diffuser layer over a 24 mm thick transparent material layer.

[0067] Figure 7I Visual image of an embodiment of a backlight unit having a double-sided diffuser layer over a 28 mm thick transparent material layer.

[0068] Figure 8A Schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer over an air gap and a pair of additional high refractive index cross brightness enhancement films and a polarizer reflector film over the double-sided diffuser layer.

[0069] Figure 8B Illustrates a backlight unit having an air gap thickness of 6 mm Figure 8AVisual image of an embodiment of a backlight unit.

[0070] Figure 8C Illustrates a visual image of an embodiment of a backlight unit having a 7 mm air gap thickness Figure 8A Visual image of an embodiment of a backlight unit.

[0071] Figure 9A Illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit according to the present teachings, the backlight unit having a double-sided diffuser layer, a second diffuser layer, a transparent material layer, a pair of high refractive index cross brightness enhancement films, and a polarizer reflector film.

[0072] Figure 9B Illustrates Figure 9A Visual image of an embodiment of a backlight unit.

[0073] Figure 9C Illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer above an air gap and a pair of additional high refractive index cross brightness enhancement films and a polarizer reflector film above the double-sided diffuser layer.

[0074] Figure 9D Illustrates Figure 9C Visual image of an embodiment of a backlight unit.

[0075] Figure 10 Illustrates a graph of the point spread function of a single LED for an embodiment of a backlight unit according to the present teachings.

[0076] Figure 11A Illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer above a transparent material layer and a pair of additional high refractive index cross brightness enhancement films above the double-sided diffuser layer.

[0077] Figure 11B Illustrates Figure 11A Visual image of an embodiment of a backlight unit.

[0078] Figure 11C Illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer located above an air gap and a pair of additional high refractive index cross brightness enhancement films above the double-sided diffuser layer.

[0079] Figure 11D Illustrates Figure 11C Visual image of an embodiment of a backlight unit.

[0080] Figure 12A Illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit having a volume diffuser layer above a transparent material layer and a pair of additional high refractive index cross brightness enhancement films above the volume diffuser layer.

[0081] Figure 12B Illustrates Figure 12A a visual image of an embodiment of a backlight unit.

[0082] Figure 12C Illustrates a schematic diagram of a layer structure of an embodiment of a backlight unit having a volume diffuser layer over an air gap and a pair of additional high refractive index cross brightness enhancement films over the volume diffuser layer.

[0083] Figure 12D Illustrates Figure 12C a visual image of an embodiment of a backlight unit.

[0084] Figure 13A Illustrates a schematic diagram of a layer structure of an embodiment of a backlight unit having a volume diffuser layer over a transparent material layer, a second volume diffuser layer, and an additional high refractive index cross brightness enhancement film and a polarizer reflector layer over the second volume diffuser layer.

[0085] Figure 13B Illustrates Figure 13A a visual image of an embodiment of a backlight unit.

[0086] Figure 13C Illustrates a schematic diagram of a layer structure of an embodiment of a backlight unit having a volume diffuser layer over an air gap and a pair of additional high refractive index cross brightness enhancement films and a polarizer reflector film over the volume diffuser layer.

[0087] Figure 13D Illustrates Figure 13C a visual image of an embodiment of a backlight unit.

[0088] Figure 14A Illustrates graphs of light intensity versus horizontal divergence angle and light intensity versus vertical divergence angle of light passing through a pair of high refractive index cross brightness enhancement films and a polarizer reflector film used in an embodiment of the present teachings generated by a known LED.

[0089] Figure 14A-1 Illustrates a three-dimensional plot of the light distribution of light passing through a pair of high refractive index cross brightness enhancement films and a polarizer reflector film used in an embodiment of the present teachings generated by a known LED and a projection of the three-dimensional plot of the light distribution.

[0090] Figure 14B Illustrates graphs of light intensity versus horizontal divergence angle and light intensity versus vertical divergence angle of light passing through a single high refractive index cross brightness enhancement film and a polarizer reflector film used in an embodiment of the present teachings generated by a known LED.

[0091] Figure 14B-1Illustrated is a three-dimensional diagram of the light distribution passing through a single high refractive index cross brightness enhancement film and a polarizer reflector film used in an embodiment of the present teachings generated by a known LED, as well as a projection of the three-dimensional diagram of the light distribution. Detailed Description

[0092] The present teachings will now be described in more detail with reference to exemplary embodiments of the present teachings shown in the accompanying drawings. Although the present teachings are described in connection with various embodiments and examples, it is not intended to limit the present teachings to such embodiments. On the contrary, as will be recognized by those skilled in the art, the present teachings cover various alternatives, modifications, and equivalents. Those of ordinary skill in the art who can obtain the teachings herein will recognize additional embodiments, modifications, and examples within the scope of the present disclosure described herein, as well as other fields of use.

[0093] References in this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present teachings. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0094] It should be understood that the various steps of the methods of the present teachings can be performed in any order and / or simultaneously, so long as the present teachings remain operable. Additionally, it should be understood that the apparatus and methods of the present teachings can include any number or all of the described embodiments, so long as the present teachings remain operable.

[0095] In the pursuit of improved image quality, various thin displays, including for example liquid crystal displays, increasingly use a backlight unit architecture. The present teachings relate to a backlight unit for a backlight display having a two-dimensional array of light emitting diode (LED) light sources. Figure 1A and 1B Shown is a schematic diagram of a backlight unit including an LED array for a liquid crystal display (LCD). Figure 1A Illustrated is a schematic diagram of an embodiment of a backlight unit architecture including an LED array for an LCD of the present teachings.

[0096] Reference Figure 1A , the backlight unit architecture 100 can include an array 110 of respective LEDs 112, which can be, for example, blue LEDs, white LEDs, and / or red-green-blue LED clusters. Any known type of LED can be used in conjunction with the present teachings. Figure 2A Illustrated is a three-dimensional diagram of the light distribution generated by a known LED as a function of angle as measured by a goniophotometer. Figure 2B Illustrated is Figure 2A the measured light distribution of the illumination pattern represented in two dimensions in connection with Figure 2A and 2BIllustrated is a typical intensity distribution of light emitted from a single LED as a function of angle as measured by a goniophotometer. As shown, the LED source is approximately a Lambertian source. By a Lambertian source, we mean a source that emits a light distribution that is substantially symmetric with respect to a nadir. This corresponds to the highest light intensity being at the nadir. In general, the light emission angle of a Lambertian source is 180 degrees, or ±90 degrees about the center.

[0097] Returning again to Figure 1A , a series of films (also referred to as layers) can be used to diffuse or scatter the light emitted from LED 112 such that the backlight unit architecture 100 can deliver more uniform light to an LCD module 180 that includes liquid crystal located above the backlight unit. Some embodiments of the backlight unit of the present teachings do not use the LCD module 180. Some embodiments of the present teachings use a different lighting module in place of the LCD module 180. In some embodiments, the backlight unit architecture 100 includes a diffuser film 120. Various known diffuser films 120 can be used. The diffuser film 120 can also be referred to as a diffuser layer or a diffuser. For example, the diffuser film 120 can be a single-sided diffuser layer, a double-sided diffuser layer, a volume diffuser layer, and / or a circular diffuser layer. For example, if LED 112 emits blue light, then a color conversion layer 130 can be used. The color conversion layer 130 can use quantum dots or phosphor materials to, for example, convert some of the blue light emitted by LED 112 into green and red light. A second diffuser film 140, for example, which can be a volume diffuser or a circular diffuser produced by a randomly textured surface, is configured to diffuse or scatter the light exiting the color conversion layer 130. There are two brightness enhancement films (BEF) 150, 160 located above the second diffuser film 140. In some embodiments, only one brightness enhancement film 150, 160 is used. In some embodiments, the two brightness enhancement films 150, 160 are two prism films that are rotated approximately 90 degrees relative to each other. These two 90-degree rotated prism films together are also referred to as a pair of cross brightness enhancement films. A polarizer reflector 170, also referred to as a DBEF, is positioned above the brightness enhancement films 150, 160. In some embodiments, additional films (not shown) can be present in the backlight unit architecture 100 that are used to improve the overall uniformity and brightness of the light delivered to the LCD panel.

[0098] In some embodiments, the DBEF 170 (reflective polarizer) film is combined with the LCD module 180 or is located below the LCD module 180 as a separate film. In some backlight units, white LEDs can be used without the color conversion layer 130. By using an array of LEDs 110, a better contrast ratio can be achieved by adjusting the brightness of each individual LED 112, which is often referred to as local dimming.

[0099] Generally, consumers prefer electronic devices including LCDs to become thinner and thinner. Therefore, the backlight unit of such a display also needs to become thinner and thinner. This poses a challenge of managing the light emitted by LEDs in an effective way to ensure uniformity and brightness in a thinner backlight unit.

[0100] Figure 1B A schematic diagram illustrating another embodiment of a backlight unit architecture 190, which includes an array of light emitting diodes (LEDs) for a liquid crystal display (LCD) of the present teachings. For example, referring to an embodiment of an LCD display with a backlight unit architecture 190 having Figure 1B When a diffuser film 120 is placed over an array 110 of LEDs 112, each light spot emitted by the LEDs is diffused such that the light with a lower intensity from adjacent LEDs 112 begins to overlap to create regions of higher intensity light between the LEDs 112. For example, if the thickness of the diffuser film 120 is increased, which may be undesirable for a thinner backlight unit, then each light spot can be further diffused and provide better light uniformity, but still may have brighter and darker regions.

[0101] In one embodiment, the LEDs 112 are blue LEDs formed in the array 110, and the backlight unit of the present teachings delivers bright and uniform light to an LCD module 180 in a thin cross-section of the layer between the array 110 and the module 180. These layers may include a pair of crossed brightness enhancement films 150, 160 placed over the diffuser film 120, and a polarizer reflector 170 placed over the pair of crossed brightness enhancement films 150, 160. When viewed from the module 180 side of the backlight unit architecture 190, this layer structure effectively hides the individual LEDs 112 and provides a thinner backlight unit cross-section than the backlight unit architecture 100 described in conjunction with Figure 1A Various layer structures of the present teachings, including different layer types, layer thicknesses, and layer positions, can be used to provide one or more display performance goals as further described herein. These performance goals include, for example, generating bright, uniform light while maintaining a desired backlight unit thickness, hiding the individual, and / or supporting a dimming operation with a better contrast ratio with the display.

[0102] The LEDs 112 can be arranged in the array 110. Figure 3FIG. illustrates a schematic view of a two-dimensional array 300 of LEDs 302 that can be used in an embodiment of the narrow backlight unit of the present teachings. The LED elements 302 of the array 300 are positioned at a nominally uniform pitch X 304 in one dimension and at a nominally uniform pitch Y 306 in a second dimension. The LED pitches X 304 and Y 306 can be the same or can be different. In some embodiments of the LED array 300 of the present teachings, the LED pitch X 304 is 8 mm and the LED pitch Y 306 is 8 mm. Other LED pitches can also be used. The pitch X 304 can also be referred to as the column pitch, and the pitch Y 306 can be referred to as the row pitch. An embodiment of the array 300 has seven rows and seven columns. The number of rows and the number of columns can also vary in various configurations. The number of rows can be the same as the number of columns, as shown in the array 300. In some embodiments, one dimension has fewer LED elements than the second dimension. For example, the narrow dimension of the backlight unit can be configured with fewer than 15 LED rows or even fewer than 10 LED rows. For example, the wider dimension can have more columns than rows.

[0103] Reference Figure 1A , FIG. 1b and Figure 3 all of, when the LEDs 112, 302 are configured in the arrays 110, 300, it is desirable to hide the individual LEDs 112, 302 and present a bright and uniform light to the LCD module 180. As described above, one way to achieve this goal is to include one or more diffuser films 120, 140 in the backlight units 100, 190 to diffuse, spread, or blur the light beams emitted by the LEDs 112, 302. In some embodiments, it is desirable to keep the backlight unit architectures 100, 190 as thin as possible and use a series of MLA films.

[0104] In some other embodiments, the thickness of the backlight unit is not a significant constraint, and the backlight unit layer thickness can be comparable to or thicker than the LED pitches 304, 306. In these embodiments, the problems can be somewhat similar to those faced by LED-based lighting. Often, a single diffuser film can be used above the LED and an air gap can be left below it. As an example, Tables 400, 430, 450 described below in conjunction with Figure 4A -C provide guidance on the relative dimensions of the air gap to the LED pitch, which is for achieving uniform light distribution in these embodiments with a thicker backlight unit dimension. These tables 400, 430, 450 relate to various commercial diffuser layers produced by Brightview Technologies, the assignee of the present application.

[0105] One feature of the backlight unit of the present teachings is the ability to create a highly uniform light output from a thin, efficient, and cost-effective LED array. Instead of using a conventional diffuser film that relies on light scattering, some embodiments of the present teachings use a microlens array or MLA diffuser film to provide improved performance. The MLA manages the optics by relying on refraction and total internal reflection rather than scattering, which offers many advantages, including better light uniformity and local dimming performance, thinner film stacks, improved efficiency, and the ability to work with color conversion films to minimize crosstalk.

[0106] The diffuser film used in embodiments of the present teachings can include surface microstructures that can be created using many techniques known in the art. For example, in some embodiments, the diffuser film of the present teachings can be manufactured by casting a polymer with a desired shape of a spectroscopic microstructure onto a substrate using a suitable master mold and a thermally curable polymer or an ultraviolet (UV) light curable polymer. The microstructure shape can also be imprinted into a thermoplastic substrate by compression molding or other molding. The shape can also be created simultaneously with the substrate using extrusion embossing or injection molding. The microstructures can be produced by replicating a master. For example, an optical film can be manufactured by replicating a master containing a desired shape, as described in U.S. Patent No. 7,190,387B2 to Rinehart et al. titled "Systems and Methods for Fabricating Optical Microstructures Using a Cylindrical Platform and a Rastered Radiation Beam"; U.S. Patent No. 7,867,695B2 to Freese et al. titled "Methods for Mastering Microstructs Through a Substrate using Negative Photoresist"; and U.S. Patent No. 7,192,692B2 to Wood et al. titled "Methods for Fabricating Microstructions by Imaging a Radiation Sensitive Layer Sandwiched Between Outer Layers", which patents are assigned to the assignee of the present utility model, the disclosures of all of which patents are incorporated herein by reference in their entirety. The master itself can be manufactured using the laser scanning techniques described in these patents and can also be replicated using the replication techniques described in these patents to provide the microstructures.

[0107] In some embodiments, projection or contact lithography, such as techniques used in semiconductors, displays, circuit boards, and other common techniques known in the art, can be used to expose microstructures into photosensitive materials. In some embodiments, either masking or laser ablation using a focused and modulated laser beam can be used to create microstructures including markers in materials. In some embodiments, micromachining (especially diamond micromachining) can be used to create desired microstructures from solid materials. In some embodiments, additive manufacturing (such as 3D printing) can be used to create desired microstructures in solid materials.

[0108] The diffuser film in some embodiments of the present teachings can also be a volume diffuser, where a certain concentration of particles is embedded in a matrix of different refractive indices.

[0109] The diffuser film can be characterized by the so-called full width at half maximum (FWHM). The FWHM is a measure of the spread of the light distribution leaving the film when illuminated by a collimated beam. The FWHM can be expressed as an angle in degrees. A diffuser with a larger FWHM is a stronger diffuser than one with a smaller FWHM. Some embodiments of the present teachings utilize diffuser films having an FWHM greater than sixty degrees.

[0110] Figure 4A Table 400 related to an embodiment of a diffuser layer including a single-sided coating according to the present teachings is illustrated. Table 400 indicates the approximate ratio of the LED pitch to the air gap between the top of the LED array and the bottom surface of the diffuser layer required to achieve a uniform spatial intensity and angular distribution. The diffusers towards the top of this table 400 have relatively weak hiding or LED smoothing and require a larger air gap to achieve smooth and uniform luminance. When it is required to firmly and smoothly hide the LED source with a smaller air gap, the diffusers towards the bottom of this table 400 are used.

[0111] Figure 4B Table 430 related to an embodiment of a diffuser layer including a double-sided coating according to the present teachings is illustrated. Table 430 indicates the approximate ratio of the LED pitch to the air gap to achieve a uniform spatial intensity and angular distribution. Some embodiments of the diffuser layer include a double-sided coating, which gives them stronger LED hiding and can provide higher efficiency than the embodiments of the diffuser layer described in combination Figure 4A The diffuser layers towards the top of this table 430 have relatively weak hiding or LED smoothing and require a larger air gap to achieve smooth and uniform luminance. When it is desired to firmly and smoothly hide the LED source with a smaller air gap, the diffuser layers towards the bottom of this table 430 are used. The increase in the diffusion intensity results in more LED hiding with a smaller air gap.

[0112] Figure 4C Table 450 related to an embodiment including a volume diffuser layer with strong hiding or LED smoothing characteristics is illustrated. Table 450 indicates the approximate ratio of LED pitch to air gap to achieve uniform spatial intensity and angular distribution. The volume diffuser film shown in Table 450 provides smooth and uniform luminance with a small air gap.

[0113] Figure 5 Graph 500 of the measured angular intensity distribution of an embodiment of the high-hiding microstructured double-sided diffuser layer of the present teachings is illustrated. By strong hiding or high hiding is meant that a uniform output is generated from multiple LEDs, and this uniform output makes it impossible to see individual LED elements at the output. A lower degree of hiding still makes the light at the output smoother and more uniform, but when viewed from the top surface or the output of the backlight unit, there is more variation in the light at the LED centers compared to the regions near the LED centers. The double-sided diffuser layer subjected to measurement is the diffuser associated with the last entry in Table 430 described in conjunction with Figure 4B its description. That is diffuser product number C-HH90, which has a distance that achieves complete LED hiding, and the ratio of LED pitch to air gap is 1:0.85.

[0114] In some embodiments of the backlight unit of the present teachings, the LEDs typically have an emission area of several hundred micrometers to greater than one millimeter. To achieve high brightness with a relatively small number of LEDs, a large emission area is necessary. Similar to known lighting applications, it is desirable for the backlight unit of the present teachings to achieve uniformity of intensity and angular distribution while maximizing brightness. In embodiments using a mini-LED array, it is also desirable to minimize the point spread function of the light from an individual LED to facilitate local dimming.

[0115] The various descriptions of the embodiments herein relate to the use of a double-sided diffuser layer. However, different diffuser layers can be used, including for example a single-sided diffuser layer, a volume diffuser layer, and a circular diffuser layer.

[0116] Figure 6AFIG. illustrates a schematic diagram of a layer structure 600 of an embodiment of a backlight unit having a double-sided diffuser layer and an air gap. A diffuser film 602 is positioned over an LED array 604 that includes individual LEDs 612 spaced apart by a pitch x 605. An air gap 606 is formed between the top of the LED array 604 and the bottom of the film 602. The air gap has a thickness d607. Light exits from the top of the LED 612 with an angular distribution characterized by an angle 608. The distribution from the LED 612 can be a Lambertian distribution into air having an angular distribution with a diffusion angle 608 equal to 180 degrees (±90 degrees). It can be seen that for a fixed angle 608 characterizing the light emitted from the LED, the greater the thickness of the air gap, the greater the size of the light distribution at the bottom surface of the diffuser film 602, and thus the film 602 requires less hiding or LED smoothing to produce a smooth and uniform luminance from the top surface of the layer structure 600.

[0117] Figure 6B FIG. illustrates an embodiment of a backlight unit having a double-sided diffuser layer and a small air gap thickness Figure 6A of a visual image 630. Specifically, Figure 6B is a visual image 630 of an ~8x8 LED array spaced 8 mm apart, where a 200 micron thick HH90 diffuser is placed 8 mm above the LEDs and there is an air gap between the LEDs and the HH90 diffuser. Thus, x = 8 mm and d = 8 mm. The reference to HH90 herein refers to a diffuser having a product number C-HH90, as Figure 4B shown in Table 430 of

[0118] Figure 6C FIG. illustrates an embodiment of a visual image 650 of a backlight unit having a double-sided diffuser layer and a larger air gap thickness Figure 6A of. Specifically, Figure 6C is a visual image 650 of an ~8x10 LED array spaced 8 mm apart, where a 200 micron thick HH90 diffuser is placed 12 mm above the LEDs (d = 12 mm) and there is an air gap between the LEDs and the HH90 diffuser. The additional smoothing of the illumination caused by the greater thickness d 607 of the air gap 606 is evident when using the same diffuser film 602. Referring to Figure 6B and 6C both, it can be seen from the Figure 6B visual image 630 that with an 8 mm air gap, there are some significant spatial non-uniformities in intensity, but for a 12 mm air gap, as in Figure 6CAs shown in the visual image 650, the intensity is very uniform. Therefore, by using a specific air gap thickness and a specific array pitch ratio between the array and the diffuser layer, embodiments of the backlight unit of the present utility model can provide the required uniformity and / or the concealment of individual LEDs.

[0119] Figure 7A FIG. illustrates a schematic diagram of the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer, a second diffuser layer, and a transparent material layer according to the present teachings. A first diffuser film 702 is positioned above an LED array 704, which includes individual LEDs spaced apart by a pitch x 705. In one embodiment, the first diffuser film 702 includes a top diffuser layer, a bottom diffuser layer, and a thin transparent material layer located between the top diffuser layer and the bottom diffuser layer. Such a thin film is sometimes referred to as a double-sided diffuser layer. In certain configurations, a second diffuser film 702' is located above the first diffuser film 702.

[0120] A layer 706 of transparent material having a thickness d 707 is positioned between the LED array 704 and the diffuser film 702. In various embodiments, the transparent material layer 706 includes one or more films that occupy the region from the top of the LED array 704 to the bottom of the diffuser film 702. The transparent material layer 706 generally has a refractive index higher than that of air. In some embodiments, the transparent material layer 706 is one or more polymethyl methacrylate (PMMA) films. Light exits the top of the LEDs in the array 704 in a Lambertian distribution, which is transformed into a narrower angular distribution characterized by an angle 708 in the transparent material layer 706. The angle 708 characterizing the angular distribution of light in the transparent material layer 706 is less than the angle 608 of the light in the air gap 606 described in conjunction with Figure 6A because the refractive index is greater than one. This transformation is described by Snell's law, as further described below. For example, a Lambertian distribution emitted from an LED into a material with a refractive index of 1.5 results in an angular distribution with an angle 708, where the angle 708 is equal to 79.2 degrees (±39.6 degrees). Generally, the transparent material layer 706 transforms the angular distribution of light emitted from the bare LEDs into an angle less than ±90 degrees about the center.

[0121] Figure 7B FIG. illustrates a visual image 710 of an embodiment of a backlight unit having a double-sided diffuser layer and a small transparent material layer thickness. Specifically, Figure 7A is a visual image 710 of an ~8x10 LED array spaced 8 mm apart, where a 200-micron-thick HH90 diffuser is placed 8 mm above the LEDs, and there are two 4-mm-thick PMMA layers between the LEDs and the HH90 diffuser. Figure 7B is a visual image 710 of an ~8x10 LED array spaced 8 mm apart, where a 200-micron-thick HH90 diffuser is placed 8 mm above the LEDs, and there are two 4-mm-thick PMMA layers between the LEDs and the HH90 diffuser.

[0122] Figure 7C FIG. shows a schematic diagram of a layer structure 720 of an embodiment of a backlight unit of the present teachings having a double-sided diffuser layer and a greater thickness of the transparent material layer. A diffuser film 722 is positioned over an LED array 724 that includes individual LEDs spaced apart by a pitch x725. A transparent material layer 726 having a thickness d727 is positioned between the LED array 724 and the diffuser film 722. Light exits from the top of the LEDs in the array 724 and has an angular distribution characterized by an angle 728.

[0123] Figure 7D FIG. shows Figure 7C a visual image 730 of an embodiment of a backlight unit. Specifically, the visual image 730 is from an ~8x10 LED array spaced 8 mm apart, with a 200-micron-thick HH90 diffuser placed 12 mm above the LEDs, and three 4-mm-thick PMMA layers between the LEDs and the HH90 diffuser. For example, compared to the visual image 710 described in connection with Figure 7B it is apparent from this visual image 730 that the illumination from each LED in the array is smoother due to the thicker transparent material layer.

[0124] Figure 7E FIG. shows a schematic diagram of a layer structure 740 of an embodiment of a backlight unit of the present teachings having a double-sided diffuser layer and an even greater thickness of the transparent material layer. Similar to the layer structures 700, 720 described in connection with Figure 7A and 7C this layer structure 740 also has a diffuser layer 742, an LED array 744 with a pitch x 745, a transparent material layer 746, and an angular distribution angle 748. Compared to the layer structures 700, 720, the thickness d747 in the layer structure 740 is greater. For the same diffuser film 742 characteristics, the thicker transparent material layer 746 results in better hiding of the individual LEDs in the array 744.

[0125] Figure 7F FIG. shows Figure 7E a visual image 750 of an embodiment of a backlight unit. Specifically, the visual image 750 is from an ~8x10 LED array spaced 8 mm apart, with a 200-micron-thick HH90 diffuser placed 16 mm above the LEDs, and four 4-mm-thick PMMA layers between the LEDs and the HH90 diffuser. The better hiding of the thicker transparent material layer is apparent.

[0126] Figure 7GIllustrated is a visual image 760 of an embodiment of a backlight unit having a double-sided diffuser layer over a 20 mm thick transparent material layer. Specifically, the visual image 760 is from an ~8x10 LED array spaced 8 mm apart, with a 200 micron thick HH90 diffuser placed 20 mm above the LEDs, and there are 5 layers of 4 mm thick PMMA between the LEDs and the HH90 diffuser. This visual image 760 also shows the illumination of some LEDs directly from the LED array without a film. With the increase in the thickness of the transparent material layer, better hiding is evident.

[0127] Figure 7H Illustrated is a visual image 770 of an embodiment of a backlight unit having a double-sided diffuser layer over a 24 mm thick transparent material layer. Specifically, the visual image 770 is from an ~8x10 LED array spaced 8 mm apart, with a 200 micron thick HH90 diffuser placed 24 mm above the LEDs, and there are 6 layers of 4 mm thick PMMA between the LEDs and the HH90 diffuser. With the increase in the thickness of the transparent material layer, better hiding is evident.

[0128] Figure 7I Illustrated is a visual image 780 of an embodiment of a backlight unit having a double-sided diffuser layer over a 28 mm thick transparent material layer. Specifically, the visual image 780 is from a visual image 780 of an ~8x10 LED array spaced 8 mm apart, with a 200 micron thick HH90 diffuser placed 28 mm above the LEDs, and there are 7 layers of 4 mm thick PMMA between the LEDs and the HH90 diffuser. With the increase in the thickness of the transparent material layer, better hiding is evident. Figure 7A The examples in -I illustrate how embodiments of the backlight unit of the present teachings provide the desired uniformity and / or hiding of individual LEDs by using a specific ratio of array spacing and a specific thickness of the transparent material layer between the array and the diffuser layer. The refractive index of the transparent layer can also be selected as a parameter to provide the desired degree of uniformity.

[0129] will be combined with Figure 6A the backlight unit embodiments described in -C and compared with the backlight unit embodiments described in Figure 7A -I. Clearly, if PMMA with a refractive index of 1.5 is used instead of an air gap, then if the air gap thickness is the same or similar to the thickness of the transparent material layer, the visual uniformity will be much worse. For example, comparing the Figure 6C visual image 650 with the Figure 7D visual image 730, it can be seen that 12 mm of air produces excellent uniformity, while 12 mm of PMMA has very poor uniformity, where the Figure 6C visual image 650 has 12 mm of air between the diffuser and the LEDs, while the Figure 7DThe visual image 730 has 12 mm of PMMA between the diffuser and the LED. In fact, for a transparent material layer including PMMA, it can be seen that a thickness of 24 to 28 mm is required to achieve excellent uniformity, as Figure 7H shown in the visual image 770 and Figure 7I evident in the visual image 780 shown in

[0130] This greater thickness requirement for the higher refractive index material in the space between the LED array and the bottom of the diffuser layer is expected because in air, the Lambertian distribution has light rays from -90 to +90 degrees, which allows the light to quickly diffuse in the lateral direction. In contrast, once the Lambertian distribution from the LED enters a transparent material layer made of, for example, PMMA, due to Snell's equation it is restricted between ±41.8 degrees, where for air, n1 = 1 and for PMMA, n2 = 1.5. For a polycarbonate material with a higher refractive index of 1.57, the light will be restricted between ±39.6 degrees. If the refractive index of the material between the LED and the diffuser is 1.75, then the light is restricted between ±34.8 degrees. For example, some polymer materials can have a high refractive index. When using PMMA or other high refractive index transparent materials between the LED and the diffuser, a large thickness can be disadvantageous due to the significant increase in thickness, weight, and material. Therefore, some embodiments of the backlight unit of the present teachings use additional layers in the layer architecture of the backlight unit, as further described below.

[0131] For example, some embodiments of the present teachings use a backlight unit architecture that includes a pair of brightness enhancement films oriented generally perpendicular to each other (e.g., using ~90 degree apex angle prisms) and a DBEF film that is a reflective polarizer. The crossed brightness enhancement films narrow the optical distribution, thereby enhancing the on-axis brightness. The DBEF film also enhances the brightness of the LCD module by transmitting only one polarization and recycling the other polarization.

[0132] Figure 8AA schematic diagram showing the layer structure 800 of an embodiment of a backlight unit, the backlight unit having a double-sided diffuser layer 802 above an air gap 806 and a pair of additional high refractive index cross brightness enhancement films 810, 812 and a polarizer reflector film 814 above the double-sided diffuser layer 802. The diffuser film 802 is positioned above an LED array 804, which includes individual LEDs spaced apart by a pitch x 805. The air gap 806 is formed between the top of the LED array 804 and the bottom of the film 802. The air gap has a thickness d 807. Light exits from the top of the LEDs in the array 804 and has an angular distribution characterized by an angle 808. A pair of brightness enhancement films 810, 812 are positioned above the diffuser film 802, and a polarizer reflector (DBEF) film 814 is positioned above the pair of brightness enhancement films 810, 812.

[0133] Figure 8B Illustrates a backlight unit having an air gap thickness of 6 mm Figure 8A The visual image 820 of an embodiment of the backlight unit. Specifically, the visual image 820 is from an ~8x10 LED array spaced 8 mm apart, where a 200 micron thick HH90 diffuser is placed 6 mm above the LEDs, with air between the LEDs and the HH90 diffuser. In this embodiment, there is a pair of additional high refractive index cross brightness enhancement films and a DBEF film above the HH90 diffuser, each film having a thickness of approximately 200 microns.

[0134] Figure 8C Illustrates a backlight unit having an air gap thickness of 7 mm Figure 8A The visual image 840 of an embodiment of the backlight unit. Specifically, the visual image 840 is from an ~8x10 LED array spaced 8 mm apart, where a 200 micron thick HH90 diffuser is placed 7 mm above the LEDs, with air between the LEDs and the HH90 diffuser. In this embodiment, there is a pair of additional high refractive index cross brightness enhancement films and a DBEF film above the HH90 diffuser, each film having a thickness of approximately 200 microns.

[0135] Comparison Figure 6A -C with Figure 8A -C illustrates the benefits of including two brightness enhancement films 810, 812 and a polarizer reflector 814 above the diffuser film 802 and the air gap 806. If additional films are used, uniform illumination can be provided through a relatively small air gap. Figure 8C The visual image 840 of shows very good uniformity achieved with an air gap of approximately 7 mm. This is compared to cases where the value is closer to 10 or 12 mm but there are no three additional films above the HH90 diffuser. For example, for Figure 6A the architecture layer structure 600 shown in without additional films above the diffuser film 602,Figure 6C The visual image 650 shows a highly uniform distribution with a 12 mm air gap.

[0136] Figure 9A FIG. shows a schematic diagram of a layer structure 900 of an embodiment of a backlight unit according to the present teachings, the backlight unit having a double-sided diffuser layer 902, a second diffuser layer 902', a transparent material layer 906, a pair of high refractive index cross brightness enhancement films 910, 912, and a polarizer reflector film 914. The first diffuser film 902 is located on one or more transparent material layers 906. The first diffuser film 902 can be a double-sided diffuser layer, including a top diffuser layer, a bottom diffuser layer, and a thin transparent material layer (structural details not shown) located between the top diffuser layer and the bottom diffuser layer. In other embodiments, the first diffuser film 902 is a single-sided diffuser layer.

[0137] In some configurations, the second diffuser layer 902' is located above the first diffuser layer 902. An LED array 904 having an element pitch of x 905 is positioned below the transparent material layer 906. The transparent material layer 906 has a thickness d 907. Each LED has an angular distribution of light characterized by an angle 908 in the transparent material layer 906. A pair of high refractive index cross brightness enhancement films 910, 912 are located above the second diffuser film 902'. The polarizing reflector film 914 is located above the double-sided diffuser layer.

[0138] Figure 9B FIG. shows Figure 9A a visual image 920 of an embodiment of a backlight unit. Specifically, the visual image 920 is from an ~8x10 LED array spaced 8 mm apart, a 200 micron thick HH90 diffuser is placed 7 mm above the LEDs, and there are 4 mm and 3 mm PMMA layers between the LEDs and the HH90 diffuser. In this embodiment, there is a pair of additional high refractive index cross BEF films 910, 912 and a DBEF film 914 above the HH90 diffuser 902, each film having a thickness of approximately 200 microns.

[0139] Figure 9C FIG. shows a schematic diagram of a layer structure 930 of an embodiment of a backlight unit, the backlight unit having a double-sided diffuser layer 932 above an air gap 936 and a pair of additional high refractive index cross brightness enhancement films 940, 942 and a polarizer reflector film 944 above the double-sided diffuser layer 932. An LED array 934 having an element pitch of x 935 is positioned below the air gap 936. The air gap 935 has a thickness d 937. Each LED has an angular distribution of light characterized by an angle 938.

[0140] Figure 9D FIG. shows Figure 9CVisual image 950 of an embodiment of a backlight unit. Specifically, visual image 950 is from an 8x10 LED array spaced 8 mm apart, with a 200-micron-thick HH90 diffuser placed 7 mm above the LEDs, and air between the LEDs and the HH90 diffuser. In this embodiment, there is a pair of additional high-refractive-index cross BEF films 940, 942 and a DBEF 944 film above the HH90 diffuser, each film having a thickness of approximately 200 microns.

[0141] Surprisingly, it can be seen that Figure 9B the uniformity shown in visual image 920 is comparable to or better than Figure 9D that of visual image 950, where Figure 9B there is a 4-mm PMMA layer and a 3-mm PMMA layer under the HH90 diffuser, while Figure 9D there is a 7-mm air gap under the HH90 diffuser. This is compared with the need for 24 - 28 mm of PMMA without the need for three additional films and seeing a similar uniformity with an air gap of the same thickness, as discussed in connection with Figure 7H and 7I .

[0142] In some embodiments, the thickness of the solid transparent material layer is greater than or equal to half of the thickness measured from the top of the two-dimensional LED array to the top of the backlight unit. Thus, for example, and referring to an embodiment that includes three films above the transparent material layer, such as Figure 9A the embodiment, the thickness d907 of the transparent material layer 906 is half of the thickness measured from the top of the array 904 to the top of the polarizer reflector 914. This thickness is the sum of the thickness d907 plus the thickness of the diffuser film 902, plus the thickness of the brightness enhancement film 910, plus the thickness of the brightness enhancement film 912, and plus the thickness of the polarizer reflector film 914. In various embodiments, this thickness is generally the thickness of the transparent material layer plus the thickness of any additional layers on top of the transparent material layer. In some embodiments, the thickness of the solid transparent material layer is greater than or equal to 0.7 times the thickness measured from the top of the two-dimensional LED array to the top of the backlight unit. In various embodiments, this thickness is the thickness of the transparent material layer plus the thickness of any additional layers on top of the transparent material layer.

[0143] Figure 10FIG. 1000 is a graph showing the point spread function of a single LED for an embodiment of a backlight unit for the present teachings. The point spread function can be considered to characterize the degree of spread of the image of a point source produced by an optical system. For the case where there is 7.5 mm of PMMA (dashed line) or air (solid line) between the LED and a film stack consisting of an HH90 diffuser, a pair of crossed BEF films, and a DBEF film, the luminance distribution as a function of position (m) is shown in FIG. 1000 when a single LED is turned on. Each profile has been normalized by the peak intensity. The case of 7.5 mm of PMMA has a peak intensity that is 67% higher than the case of the air gap. Also, correspondingly, the case of PMMA has a relatively small luminance in the tails. For the case of a solid material (PMMA in this case) in the transparent material layer between the LED and the film stack, this results in a better point spread function than the air gap. A better point spread function facilitates local dimming. The higher peak intensity and lower energy in the wings are due to the narrower light confinement in PMMA compared to the Lambertian distribution in air. In many cases, this in turn results in an overall higher average luminance. For example, in the case where the LED pitch is 8 mm and the total dimension in the narrow direction is ~90 mm, the average luminance is ~10% higher, which is highly desirable.

[0144] Figure 11A FIG. 1100 is a schematic diagram showing the layer structure of an embodiment of a backlight unit having a double-sided diffuser layer 1102 over a transparent material layer 1106 and a pair of additional high refractive index crossed brightness enhancement films 1110, 1112 over the double-sided diffuser layer 1102. An LED array 1104 having an element pitch of x 1105 is positioned below the transparent material layer 1106. The transparent material layer 1106 has a thickness d 1107. Each LED has an angular distribution of light characterized by an angle 1108.

[0145] Figure 11B FIG. shows Figure 11A the visual image 1120 of an embodiment of a backlight unit. Specifically, the visual image 1120 is from a ~8x10 LED array spaced 8 mm apart, with a 200 micron thick HH90 diffuser placed 7 mm above the LEDs and PMMA layers of 4 mm and 3 mm between the LEDs and the HH90 diffuser 1102. In this embodiment, there is a pair of additional high refractive index crossed brightness enhancement films 1110, 1112 above the HH90 diffuser 1102, each film having a thickness of approximately 200 microns.

[0146] Figure 11CFIG. illustrates a schematic diagram of a layer structure 1130 of an embodiment of a backlight unit having a double-sided diffuser layer 1132 above an air gap 1136 and a pair of additional high refractive index cross brightness enhancement films 1140, 1142 above the double-sided diffuser layer 1132. An LED array 1134 having an element pitch of x 1135 is positioned below the air gap 1136. The air gap 1136 has a thickness d 1137. Each LED has an angular distribution of light characterized by an angle 1138.

[0147] Figure 11D FIG. illustrates Figure 11C a visual image 1150 of an embodiment of a backlight unit. Specifically, the visual image 1150 is from an LED array of ~8x10 spaced 8 mm apart, with a 200 micron thick HH90 diffuser 1132 placed 7 mm above the LEDs and air between the LEDs and the HH90 diffuser 1132. In this embodiment, there is a pair of additional high refractive index cross brightness enhancement films 1140, 1142, each film having a thickness of approximately 200 microns.

[0148] Except that the DBEF has been removed, Figure 11B and 11D corresponds to Figure 8B and 8C From Figure 11B and 11D it can be observed that for both the PMMA and air gap cases, the uniformity is poor. This is because the DBEF reflects ~50% of the light, and this additional recycled light improves the uniformity. The poor uniformity without the DBEF can be compensated for by increasing the thickness of the diffuser or the hiding strength. For example, a volume diffuser has a greater hiding strength than a double-sided diffuser.

[0149] One feature of this teaching is that a diffuser with a stronger hiding strength can provide uniformity and / or dimming operation in a very thin backlight unit. For example, Figure 12A -D illustrates an embodiment of a backlight unit using a volume diffuser layer with a full thickness half-max of 105 degrees. For example, the volume diffuser layer has a higher hiding strength compared to a double-sided or single-sided diffuser layer.

[0150] Figure 12AA schematic diagram of a layer structure 1200 of an embodiment of a backlight unit is illustrated, which has a volume diffuser layer 1202 above a transparent material layer 1206 and a pair of additional high refractive index cross brightness enhancement films 1210, 1212 above the volume diffuser layer 1202. An LED array 1204 with an element pitch of x 1205 is located below the transparent material layer 1206. The transparent material layer 1206 has a thickness d 1207. Each LED has an angular distribution of light characterized by an angle 1208.

[0151] Figure 12B illustrates Figure 12A A visual image 1220 of an embodiment of a backlight unit is illustrated. Specifically, the visual image 1220 is from an LED array of ~8x10 spaced 8 mm apart, with a 200-micron-thick VH105 diffuser 1202 placed 8 mm above the LEDs, and PMMA layers of 4 mm and 4 mm between the LEDs and the VH105 diffuser 1202. In this embodiment, there is a pair of additional high refractive index cross brightness enhancement films 1210, 1212 above the VH105 diffuser 1202, each film having a thickness of approximately 200 microns.

[0152] Figure 12C A schematic diagram of a layer structure 1230 of an embodiment of a backlight unit is illustrated, which has a volume diffuser layer 1232 above an air gap 1236 and a pair of additional high refractive index cross brightness enhancement films 1240, 1242 above the volume diffuser layer. An LED array 1234 with an element pitch of x 1235 is positioned below the air gap 1236. The air gap 1236 has a thickness d 1237. Each LED has an angular distribution of light characterized by an angle 1238.

[0153] Figure 12D illustrates Figure 12C A visual image 1250 of an embodiment of a backlight unit is illustrated. Specifically, the visual image 1250 is from an LED array of ~8x10 spaced 8 mm apart, with a 200-micron-thick VH105 diffuser 1232 placed 8 mm above the LEDs, and air between the LEDs and the VH105 diffuser 1232. In this embodiment, there is a pair of additional high refractive index cross brightness enhancement films 1240, 1242, each film having a thickness of approximately 200 microns. Figure 12B The visual image 1220 with PMMA is visually brighter than Figure 12D the visual image 1250 with an air gap.

[0154] In some applications, it is desirable to use one BEF film in combination with a DBEF film instead of two crossed BEF films. This results in more diffusion of light in one direction, as combined Figure 13Aas described in the description of -D. Figure 13A FIG. is a schematic diagram of a layer structure 1300 of an embodiment of a backlight unit having a volume diffuser layer 1302 over a transparent material layer 1306, a second volume diffuser layer 1302', and an additional high refractive index cross brightness enhancement film 1310 and a polarizer reflector film 1314 over the second volume diffuser layer 1302'. An LED array 1304 having an element pitch of x 1305 is positioned below the transparent material layer 1306. The transparent material layer 1306 has a thickness d 1307. Each LED has an angular distribution of light characterized by an angle 1308.

[0155] Figure 13B FIG. illustrates Figure 13A a visual image 1320 of an embodiment of a backlight unit. Specifically, the visual image 1320 is from an LED array of ~8x10 spaced 8 mm apart, with a 200 micron thick VH105 diffuser 1302 placed 8 mm above the LEDs, and PMMA layers of 4 mm and 4 mm between the LEDs and the VH105 diffuser 1302. In this embodiment, there is an additional high refractive index cross brightness enhancement film 1310 and a DBEF film 1314 above the VH105 diffuser 1302, each film having a thickness of approximately 200 microns.

[0156] Figure 13C FIG. is a schematic diagram of a layer structure 1330 of an embodiment of a backlight unit having a volume diffuser layer 1332 over an air gap 1336 and an additional high refractive index cross brightness enhancement film 1340 and a polarizer reflector film 1344 over the volume diffuser layer 1332. An LED array 1334 having an element pitch of x 1335 is positioned below the air gap 1336. The air gap 1336 has a thickness d 1337. Each LED has an angular distribution of light characterized by an angle 1338.

[0157] Figure 13D FIG. illustrates Figure 13C a visual image 1350 of an embodiment of a backlight unit. Specifically, the visual image 1350 is from an LED array of ~8x10 spaced 8 mm apart, with a 200 micron thick VH105 diffuser 1332 placed 8 mm above the LEDs, and air between the LEDs and the VH105 diffuser 1332. In this embodiment, there is an additional high refractive index cross brightness enhancement film 1340 and a DBEF film 1344, each film having a thickness of approximately 200 microns. Comparing Figure 12A 13A-D with -D, it can be observed that when one BEF film is replaced with a DBEF film, the uniformity is only slightly worse.

[0158] Figure 14AIllustrated are graph 1400 of light intensity versus horizontal divergence angle and graph 1410 of light intensity versus vertical divergence angle of light generated by a known LED passing through a pair of high refractive index cross brightness enhancement films and a polarizer reflector film used in an embodiment of the present teachings.

[0159] Figure 14A-1 Illustrated are three-dimensional graph 1420 of the light distribution of light generated by a known LED passing through a pair of high refractive index cross brightness enhancement films and a polarizer reflector film used in an embodiment of the present teachings and a projection of three-dimensional graph 1430 of the light distribution.

[0160] Figure 14B Illustrated are graph 1450 of light intensity versus horizontal divergence angle and graph 1460 of light intensity versus vertical divergence angle of light generated by a known LED passing through a single high refractive index cross brightness enhancement film and a polarizer reflector film used in an embodiment of the present teachings.

[0161] Figure 14B-1 Illustrated are three-dimensional graph 1470 of the light distribution of light generated by a known LED passing through a single high refractive index cross brightness enhancement film and a polarizer reflector film used in an embodiment of the present teachings and a projection of three-dimensional graph 1480 of the light distribution.

[0162] A feature of the present teachings is that when the number of rows of LEDs in the narrow direction is less than 10 or 15, the increase in brightness associated with using a transparent material layer is particularly significant. In some cases, it may be desirable to tilt the optical distribution or widen the optical distribution in one direction. This can be achieved by tilting the distribution using a prism angle bending film above the crossed BEF films or widening the distribution in one direction using an elliptical diffuser, such as BVT E40-01.

[0163] In some display applications, thickness is not a major limitation, but it is desirable to use a mini-LED array to achieve higher brightness and use local dimming. One option is to use a technique similar to lighting, where an air gap is used between the LED and a strong diffuser to achieve excellent uniformity. A feature of the present teachings is the recognition that it is advantageous to use a solid transparent material having a refractive index between 1.4 and 1.7 instead of an air gap. When combined with two crossed brightness enhancement films (e.g., a prism with a vertex angle of ~90 degrees, referred to as BEF) and a DBEF film (reflective polarizer), the backlight unit has excellent uniformity, brightness, and a good point spread function for local dimming results.

[0164] In some embodiments, the backlight unit includes the following: a mini-LED array; a transparent solid material layer such as PMMA or polycarbonate; a strong diffuser (preferably having a full width at half maximum when measured with a collimated light angle of >60 degrees and even better 80 or 100 degrees); and a pair of high refractive index cross BEF films and DBEF films. In some embodiments, the solid transparent material represents at least 50% of the height from the top of the LED to the top film in the BLU, and preferably >70%. In some embodiments, there may be additional films above the cross BEF films to further shape or redirect the beam. In some embodiments, one of the BEF film or DBEF is omitted. Moreover, in some embodiments, the narrow dimension of the backlight unit may consist of fewer than 15 LED rows or even fewer than 10 LED rows.

[0165] Equivalent

[0166] While the applicant's teachings are described in conjunction with various embodiments, the applicant's teachings are not intended to be limited to such embodiments. Instead, as will be recognized by those skilled in the art, the applicant's teachings cover various alternatives, modifications, and equivalent forms that can be made without departing from the spirit and scope of the teachings.

Claims

1. A backlight unit, characterized in that: The backlight unit comprises: a) a two-dimensional array of light emitting diodes (LEDs), at least one LED in the two-dimensional array of LEDs generating light having an angular distribution of nominally ±90 degrees about a center of the at least one LED; b) a layer of transparent solid material positioned with a bottom surface over the two-dimensional array of LEDs, the transparent solid material layer configured to transform light generated by the two-dimensional array of LEDs into light having an angular distribution nominally less than ±90 degrees about a center of the at least one LED at a top surface of the transparent solid material layer; c) a first diffuser film positioned over the top surface of the transparent solid material layer, the first diffuser film being configured to provide a full width at half maximum greater than 60 degrees and configured to diffuse light generated at the top surface of the transparent solid material layer to generate diffused light at the top surface of the first diffuser film; d) a brightness enhancement film positioned over the top surface of the first diffuser film and comprising a plurality of prismatic microstructures on at least one surface, at least some of the prismatic microstructures having a vertex angle of ninety degrees; the brightness enhancement film being configured to narrow the angular optical distribution of diffused light produced at the top surface of the first diffuser film; and e) a second diffuser film, wherein the second diffuser film is located between the first diffuser film and the brightness enhancement film.

2. The backlight unit according to claim 1, wherein: The first diffuser film includes a top diffuser layer, a bottom diffuser layer, and a thin layer of transparent material between the top diffuser layer and the bottom diffuser layer.

3. The backlight unit according to claim 1, wherein: The two-dimensional array of LEDs includes a row spacing of 8 mm and a column spacing of 8 mm.

4. The backlight unit according to claim 1, wherein: The two-dimensional array of LEDs includes ten rows and eight columns.

5. The backlight unit according to claim 1, wherein: The two-dimensional array of LEDs includes less than or equal to fifteen rows and greater than or equal to fifteen columns.

6. The backlight unit according to claim 1, wherein: The two-dimensional array of LEDs includes less than or equal to ten rows and greater than or equal to ten columns.

7. The backlight unit according to claim 1, wherein: The transparent solid material includes polymethyl methacrylate material.

8. The backlight unit according to claim 1, wherein: The transparent solid material includes a polycarbonate material.

9. The backlight unit according to claim 1, wherein: Transparent solid materials include materials having a refractive index of 1.

75.

10. The backlight unit according to claim 1, wherein: The transparent solid material layer has a thickness greater than or equal to half of a thickness measured from a top surface of the two-dimensional array of LEDs to a top surface of the backlight unit.

11. The backlight unit according to claim 1, wherein: The transparent solid material layer has a thickness greater than or equal to 0.7 times the thickness measured from the top surface of the two-dimensional array of LEDs to the top surface of the backlight unit.

12. The backlight unit according to claim 1, wherein: The diffuser film includes a full width at half maximum greater than 80 degrees.

13. The backlight unit according to claim 1, wherein: The diffuser film includes a full width at half maximum greater than 100 degrees.

14. The backlight unit according to claim 1, wherein: The backlight unit includes at least one additional film positioned above the brightness enhancement film.

15. The backlight unit according to claim 14, wherein: The at least one additional film is configured to further shape light from the brightness enhancement film.

16. The backlight unit according to claim 14, wherein: The at least one additional film is configured to redirect light from the brightness enhancement film.

17. The backlight unit according to claim 1, wherein: The backlight unit includes a polarizer reflector film positioned over a brightness enhancement film.

18. The backlight unit according to claim 1, wherein: The backlight unit includes a second brightness enhancement film positioned over the brightness enhancement film.

19. The backlight unit according to claim 18, wherein: The backlight unit includes a polarizer reflector film positioned over a second brightness enhancement film.

20. The backlight unit according to claim 19, wherein: The backlight unit includes at least one additional film positioned over the polarizer reflector film.

21. The backlight unit according to claim 20, wherein: The at least one additional film is configured to further shape light from the brightness enhancement film.

22. The backlight unit according to claim 20, wherein: The at least one additional film is configured to redirect light from the brightness enhancement film.

23. A backlight unit, characterized in that: The backlight unit comprises: a) a two-dimensional array of light emitting diodes (LEDs), wherein the number of rows in the two-dimensional array is less than the number of columns in the two-dimensional array, and at least one LED in the two-dimensional array generates light having an angular distribution of nominally ±90 degrees about a center of the at least one LED; b) a layer of transparent solid material positioned with a bottom surface over the two-dimensional array of LEDs, the transparent solid material layer configured to transform light generated by the two-dimensional array of LEDs into light having an angular distribution nominally less than ±90 degrees about a center of the at least one LED at a top surface of the transparent solid material layer; c) a first diffuser film positioned over the top surface of the transparent solid material layer, the first diffuser film being configured to provide a full width at half maximum greater than 60 degrees and configured to diffuse light generated at the top surface of the transparent solid material layer to generate diffused light at the top surface of the first diffuser film; d) a pair of crossed brightness enhancement films positioned over the top surface of the first diffuser film and comprising a plurality of prismatic microstructures on at least one surface, at least some of the prismatic microstructures having a ninety degree top angle; e) a polarizer reflector film positioned over the pair of crossed brightness enhancement films, and configured to transmit one polarization and reflect another polarization, thereby improving uniformity of light output from the backlight unit; and f) a second diffuser film, wherein the second diffuser film is located between the first diffuser film and the pair of crossed brightness enhancement films.

24. The backlight unit according to claim 23, wherein: The first diffuser film includes a top diffuser layer, a bottom diffuser layer, and a thin layer of transparent material between the top diffuser layer and the bottom diffuser layer.

25. The backlight unit according to claim 23, wherein: The backlight unit also includes a prismatic angle bending film positioned over the polarizer reflector film and configured to tilt light distribution from the output of the backlight unit.

26. The backlight unit according to claim 23, wherein: The backlight unit also includes an elliptical diffuser film positioned over the polarizer reflector film and configured to broaden the light distribution of the output of the backlight unit in one direction.

27. The backlight unit according to claim 23, wherein: The number of rows in the two-dimensional array is less than or equal to fifteen.

Images