Backlight unit for a backlight display

Abstract

The backlight unit includes an array of light emitting diodes, at least two optical films positioned above the array of light emitting diodes, and a pair of brightness enhancement films positioned above the at least two optical films. A majority of the optical films are light splitting optical films having a plurality of light splitting microstructures on at least one surface thereof.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 898,693, filed September 11, 2019; U.S. Provisional Patent Application Serial No. 62 / 929,309, filed November 1, 2019; and U.S. Provisional Patent Application Serial No. 63 / 023,618, filed May 12, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to a backlight unit for a backlight display, and particularly to a backlight display having a light-emitting diode (LED) light source. Background Technology

[0004] In the pursuit of improved image quality, liquid crystal displays (LCDs) are increasingly using backlight unit architectures, such as... Figure 1 The diagram schematically shows an array 110 comprising individual short-wavelength (blue) LEDs 112. Figure 2A and 2B The illustration shows a typical intensity distribution of light emitted from a single LED according to angle, as measured by a goniometer. As shown, the LED light source approximates a Lambertian light source, with its emission being substantially symmetrical with respect to the lowest point, where the light intensity is highest.

[0005] Back Figure 1 A series of films can be used to scatter or diffuse the light emitted from the blue LED 112, allowing the backlight unit 100 to deliver more uniform light to an LCD panel (not shown) containing liquid crystal located above the backlight unit 100. As shown, the backlight unit 100 typically includes a diffuser film 120, which may be a volumetric diffuser or a circular diffuser; a color conversion layer 130 that uses, for example, quantum dots or phosphor materials to convert some of the blue light emitted by the LED 110 into green and red light; a diffuser film 140, which may be a volumetric diffuser or a circular diffuser produced by a randomly textured surface, configured to scatter or diffuse the light leaving the color conversion layer 130; and two brightness enhancement films (BEFs) 150, 160, typically two prism films rotated approximately 90 degrees relative to each other. Additional films may be included in the backlight unit 100 to improve the overall uniformity and brightness of the light delivered to the LCD panel. In some backlight units, white LEDs may be used without a color conversion layer.

[0006] When LED 112 is arranged in an array, such as Figure 3The array 110 shown is intended to conceal the individual LEDs 112 and present a bright and uniform light to the LCD panel. As mentioned above, one way to achieve this goal is to include one or more diffusers, such as a diffuser film 120, in the backlight unit 100 to diffuse, scatter, or blur the light beam emitted by the LEDs 112. Figure 4 This schematic illustration shows the diffusion of light emitted by a single LED 112, where darker gray shading represents brighter light than lighter gray shading. This diffusion also reduces the average energy of the light.

[0007] Furthermore, electronic devices, including LCDs, are becoming increasingly thinner. Consequently, the backlight units of such displays are also becoming thinner, posing another challenge to effectively managing the light emitted by the LEDs 112. For example, when the diffuser film 120 is placed above the array 110 of the LEDs 112, as... Figure 5A As schematically illustrated, the individual light spots emitted by the LEDs are diffused, causing lower-intensity light from adjacent LEDs 112 to begin overlapping to create areas of higher intensity light. Increasing the thickness of the diffuser film 120, which might be undesirable for a thinner backlight unit 100, could result in the individual light spots being more widely dispersed and providing better light uniformity, but still leaving brighter and darker areas, as shown in... Figure 5B As illustrated in the diagram.

[0008] It is desirable to have a backlight unit 100 for an LCD display, which has an array 110 of blue LEDs 112 and a thin profile, but still delivers bright and uniform light to the LCD panel while effectively concealing the individual LEDs 112. Summary of the Invention

[0009] According to an embodiment of the present invention, a backlight unit is provided, the backlight unit comprising a light-emitting diode array, at least two optical films located above the light-emitting diode array, and a pair of brightness enhancement films located above the at least two optical films. Most of the at least two optical films are beam-splitting optical films having multiple beam-splitting microstructures on at least one surface.

[0010] In an embodiment, all of the at least two optical films have the plurality of spectral microstructures on at least one of their surfaces.

[0011] In one embodiment, the backlight unit includes a color conversion layer located above the light-emitting diode array and below the pair of brightness enhancement films. In another embodiment, the color conversion layer is located above at least one beam-splitting optical film. In yet another embodiment, the color conversion layer has at least one surface comprising a plurality of beam-splitting microstructures.

[0012] In one embodiment, the backlight unit includes at least one additional beam-splitting optical film located above the color conversion layer and below the pair of brightness enhancement films.

[0013] In one embodiment, the at least two optical films include a first beam-splitting optical film, which includes a plurality of first parallel linear prisms extending along a first direction on its first side and a plurality of first elliptical cylindrical structures extending along a second direction on its second side. The second direction is substantially orthogonal to the first direction. The first side faces the light-emitting diode array. In another embodiment, the at least two optical films include a second beam-splitting optical film located above the first beam-splitting optical film. The second beam-splitting optical film includes a plurality of second parallel linear prisms extending substantially along the first direction on its first side and a plurality of second elliptical cylindrical structures extending along the second direction on its second side. The first side of the second beam-splitting optical film faces the second side of the first beam-splitting optical film.

[0014] In one embodiment, the at least two optical films include a third beam-splitting optical film located above the second beam-splitting optical film. The third beam-splitting optical film includes a plurality of third parallel linear prisms extending substantially along a second direction on its first side. In another embodiment, the third beam splitter also includes a plurality of microstructures on its second side. In yet another embodiment, the second side of the third beam-splitting optical film faces the second side of the second beam-splitting optical film.

[0015] In one embodiment, at least one of the optical films is a first beam-splitting optical film, comprising a plurality of first parallel linear prisms extending along a first direction on a first side and a plurality of second parallel linear prisms extending along the first direction on a second side. In another embodiment, at least one of the optical films is a second beam-splitting optical film, comprising a plurality of first parallel linear prisms extending along a first direction on a first side and a plurality of second parallel linear prisms extending along the first direction on a second side. In yet another embodiment, at least one of the optical films is a second beam-splitting optical film, comprising a plurality of first parallel linear prisms extending along a second direction substantially orthogonal to the first direction on a first side and a plurality of second parallel linear prisms extending along the second direction on a second side.

[0016] In an embodiment, at least one of the optical films is a first beam-splitting optical film, which includes a plurality of first parallel linear prisms extending along a first direction on a first side thereon and a plurality of second parallel linear prisms extending along a second direction substantially orthogonal to the first direction on a second side thereon.

[0017] In this embodiment, two of the optical films are beam-splitting optical films. Each beam-splitting optical film includes a plurality of microstructures on its first side and a plurality of parallel linear prisms extending along a first direction on its second side. Each microstructure has a pyramidal shape.

[0018] In this embodiment, three of the optical films are beam-splitting optical films. Each beam-splitting optical film includes a plurality of microstructures on its first side and a plurality of parallel linear prisms extending along a first direction on its second side. Each microstructure has a pyramidal shape.

[0019] According to one aspect of the present invention, a backlight unit is provided, the backlight unit including a light-emitting diode array and a lower optical film stack located above the light-emitting diode array and configured to receive light emitted by the light-emitting diode array. The lower optical film stack includes a first beam-splitting optical film, the first beam-splitting optical film including a plurality of first beam-splitting microstructures on its first side facing the light-emitting diode array, the plurality of first beam-splitting microstructures being constructed and arranged to separate light received from the light-emitting diode array. The lower optical film stack includes a second beam-splitting optical film located above the first beam-splitting optical film. The second beam-splitting optical film includes a plurality of second beam-splitting microstructures on its first side facing the first beam-splitting optical film, the plurality of second beam-splitting microstructures being constructed and arranged to separate light received from the first beam-splitting optical film. The backlight unit includes a color conversion layer located above the lower optical film stack and configured to receive light from the lower optical film stack, an upper optical film stack located above the color conversion layer and configured to receive light from the color conversion layer, and a pair of brightness enhancement films located above the upper optical film stack and configured to receive light from the upper optical film stack.

[0020] In one embodiment, the plurality of first beam-splitting microstructures include a plurality of first parallel linear prisms, and the plurality of second beam-splitting microstructures include a plurality of second parallel linear prisms orthogonally oriented to the plurality of first parallel linear prisms.

[0021] In an embodiment, the first beam-splitting optical film further includes a plurality of first random rough microstructures on its second side, and the second beam-splitting optical film further includes a plurality of second random rough microstructures on its second side.

[0022] In one embodiment, the lower optical film stack further includes a third optical film located above the second beam-splitting optical film. In another embodiment, the third optical film includes a plurality of microstructures facing the second beam-splitting optical film. In yet another embodiment, each of the plurality of microstructures of the third optical film typically has a pyramidal shape.

[0023] In one embodiment, the upper optical film stack includes a third beam-splitting optical film located above the color conversion layer. In another embodiment, the upper optical film stack further includes a fourth beam-splitting optical film located above the third beam-splitting optical film.

[0024] In one embodiment, the color conversion layer has at least one surface that includes a plurality of spectral microstructures.

[0025] These and other aspects, features, and characteristics of the invention, as well as the methods of operation and function of the related elements of the structure, and the economy of combination and manufacture of the components, will become more apparent upon consideration of the following description with reference to the accompanying drawings and the appended claims, all of which form part of this specification. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to be construed as limiting the invention. As used in the specification and claims, the singular forms “a,” “an,” and “the” include plural indicators unless the context clearly specifies otherwise. Attached Figure Description

[0026] The components in the following figures are shown to emphasize the general principles of this disclosure and are not necessarily drawn to scale, although at least one figure may be drawn to scale. For consistency and clarity, reference numerals for corresponding components are repeated in all figures where necessary.

[0027] Figure 1 This is a schematic diagram of a typical backlight unit including an LED array for an LCD display;

[0028] Figure 2A It is a three-dimensional graph showing the distribution of light output from the LED as a function of angle, as measured by a goniometer;

[0029] Figure 2B yes Figure 2A The measured light distribution is represented in two dimensions;

[0030] Figure 3 yes Figure 1 A top view of a portion of the LED array of the backlight unit;

[0031] Figure 4 This is a top-view schematic diagram showing the distribution of light emitted from a single LED after it passes through a diffuser film;

[0032] Figure 5A After the light emitted by the LED passes through the diffuser film Figure 3 A top view of the LED array;

[0033] Figure 5B The light emitted by the LED passes through a thickness greater than that used for Figure 5A After the diffuse membrane Figure 3 A schematic diagram of an LED array;

[0034] Figure 6 This is a schematic diagram of a backlight unit for an LCD display according to an embodiment of the present invention;

[0035] Figure 7 This is according to an embodiment of the present invention. Figure 6 A schematic diagram of the lower optical film stack of the backlight unit;

[0036] Figure 8 This is according to an embodiment of the present invention. Figure 7 A schematic diagram of two beam-splitting optical films stacked at the bottom of the optical film;

[0037] Figure 9 It is as measured by a goniometer from having Figure 2A The light output from the LED source has a light distribution that allows light to pass through... Figure 8 A three-dimensional diagram of the distribution after the two spectroscopic optical films;

[0038] Figure 10 It is as measured by a goniometer from having Figure 2A The light output from the LED source has a light distribution that allows light to pass through... Figure 8 Two with more than have Figure 9 A three-dimensional diagram of the light distribution after the distribution of the two beam-splitting optical films with the higher refractive index.

[0039] Figure 11 yes Figure 10 Measurement of light distribution and from having Figure 2A A two-dimensional graph showing the measured distribution of light output from an LED source after it passes through a circular diffuser;

[0040] Figure 12A The light output from a single LED passes through... Figure 8 A top-view schematic diagram of the distribution behind the two beam-splitting optical films;

[0041] Figure 12B The light emitted by the LED passes through Figure 8 After the spectroscopic optical film Figure 6 A top view of a portion of the LED array;

[0042] Figure 13 It is as measured by a goniometer from having Figure 2A The light output from the LED source has a light distribution that allows light to pass through a light source with ... Figure 10 A three-dimensional diagram of the light distribution after two beam-splitting optical films and a circular diffuser that provides moderate diffusion;

[0043] Figure 14 It is as measured by a goniometer from having Figure 10 The light output from the LED source has a light distribution that allows light to pass through a light source with ... Figure 2A A three-dimensional diagram of the light distribution after two beam-splitting optical films and a volume diffuser that provides very high diffusion.

[0044] Figure 15 yes Figure 10 , 13 Two-dimensional plots of the measured light distribution of 14;

[0045] Figure 16 This is according to an embodiment of the present invention. Figure 7 A schematic diagram of the third optical film stacked on the lower optical film;

[0046] Figure 17 It is as measured by a goniometer from having Figure 2A The light output from the LED source has a light distribution that allows light to pass through a light source with ... Figure 10 Two beam-splitting optical films and light distribution Figure 16 A three-dimensional diagram of the distribution after the third optical film;

[0047] Figure 18 This is the output graph from the modeling program, which shows the intensity of light from an LED light source as a function of two-dimensional position after the light passes through two beam-splitting optical films with high refractive indices and a volume diffuser;

[0048] Figure 19 This is an output graph from the modeling program, showing the light from an LED light source passing through two beam-splitting optical films with high refractive indices and Figure 16 The intensity of the third optical film as a function of two-dimensional position; and

[0049] Figure 20 This is an output graph from the modeling program, showing the light from an LED light source passing through two beam-splitting optical films with high refractive indices and Figure 16 Another embodiment of the third optical film then shows the intensity as a function of two-dimensional position;

[0050] Figure 21A This is a schematic diagram of the first side of the beam-splitting optical film according to an embodiment of the present invention;

[0051] Figure 21B yes Figure 21A A magnified photomicrograph of a portion of the second side of the spectroscopic optical film;

[0052] Figure 22A It is as measured by a goniometer from having Figure 2A The light output from the LED source has a light distribution that allows light to pass through... Figure 21A and 21B A two-dimensional diagram of the distribution after a single beam-splitting optical film is shown.

[0053] Figure 22B It is as measured by a goniometer from having Figure 2A A two-dimensional diagram showing the distribution of light output from an LED source after passing through a single beam-splitting optical film according to an embodiment of the present invention;

[0054] Figure 22CIt is as measured by a goniometer from having Figure 2A A two-dimensional diagram showing the distribution of light output from an LED source after passing through a single beam-splitting optical film according to an embodiment of the present invention;

[0055] Figure 23 This is a schematic diagram of a beam-splitting optical film according to an embodiment of the present invention;

[0056] Figure 24 This is a schematic diagram of a beam-splitting optical film according to an embodiment of the present invention; and

[0057] Figure 25 This is a schematic diagram of a beam-splitting optical film according to an embodiment of the present invention. Detailed Implementation

[0058] Figure 6 A portion of a backlight unit 600 according to an embodiment of the present invention is schematically illustrated. As shown, the backlight unit 600 includes: an array 610 of LEDs 612, which may be the same blue emitting LEDs 112 as described above; a lower optical film stack 620; a color conversion layer 630 above the lower optical film stack 620; an upper optical film stack 640 above the color conversion layer 630, which may include one or more diffuse films; a first brightness enhancement film (“BEF”) 650 above the upper optical film stack 640; and a second brightness enhancement film (“BEF”) 660 above the first BEF 650. The first BEF 650 and the second BEF 660 may have substantially the same structure, but rotated 90° relative to each other, as is known in the art. The color conversion layer 630 may include, for example, a phosphor or quantum dot and is configured to change the wavelength of a portion of the light emitted from the LEDs 612, such as changing from blue wavelengths to red and green wavelengths, as is known in the art.

[0059] Figure 7 yes Figure 6 A more detailed schematic diagram of the lower optical film stack 620 is shown. As illustrated, the lower optical film stack 620, which serves as the optical film located between the LED 612 and the color conversion layer 630, includes a first beam-splitting optical film 622, a second beam-splitting optical film 624, and an optional third optical film 626. The third optical film 626 may be, for example, a volumetric diffuser film or another beam-splitting optical film, as described in further detail below. Additional optical films may be used in the lower optical film stack 620. The illustrated embodiment is not intended to be limiting in any way.

[0060] As defined herein, an "optical film" is a polymer film. As defined herein, a "spectrally splitting optical film" is a polymer film comprising a plurality of spectroscopic microlenses or microstructures on at least one surface. As defined herein, a "spectrally splitting microstructure" is a microstructure in which a collimated beam is split into two or more beams having a lower relative intensity on the axis when the collimated beam is guided onto the microstructure along the axis.

[0061] For example, the beam-splitting microstructure can be in the form of a prism and split the incident beam into two beams, the angle between which depends on the prism angle and the refractive index of the prism material. In one embodiment, a prism with a 90-degree angle and a refractive index of 1.5 can split an incident coaxial beam into two beams with approximately ±25 degrees. In another embodiment, the beam-splitting microstructure can be in the form of a triangular pyramid and split the incident coaxial beam into three beams. In yet another embodiment, the beam-splitting microstructure can be in the form of a square pyramid and split the incident coaxial beam into four beams. Finally, in another embodiment, the beam-splitting microstructure can be in the form of a cone and split the incident coaxial beam into a conical ring.

[0062] Many techniques known in the art can be used to create such spectral microstructures. For example, in embodiments, the shape of the spectral microstructure can be cast onto a substrate using a suitable master mold and a thermosetting or ultraviolet (UV) curable polymer, or the shape can be imprinted into a thermoplastic substrate by compression molding or other molding processes, or the shape can be produced simultaneously with the substrate using extrusion-imprinting or injection molding. The microstructure can also be produced by replicating a master mold. For example, optical films can be manufactured by replicating a master containing a desired shape, as described in U.S. Patent No. 7,190,387B2, entitled "Systems and Methods for Fabricating Optical Microstructures Using a Cylindrical Platform and a Rastered Radiation Beam," assigned to the assignee of this invention; U.S. Patent No. 7,867,695B2, entitled "Methods for Mastering Microstructures Through a Substrate Using Negative Photoresist," assigned to the assignee of this invention; and / or U.S. Patent No. 7,192,692B2, entitled "Methods for Fabricating Microstructures by Imaging a RadiationSensitive Layer Sandwiched Between Outer Layers," assigned to the assignee of this invention. The disclosures of all these patents are incorporated herein by reference as if fully set forth herein. 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 microstructures.

[0063] In embodiments, laser holography, known in the art, can be used to generate holographic patterns that create desired microstructures in photosensitive materials. In embodiments, projection or contact lithography, such as that used for semiconductors, displays, circuit boards, and other common techniques known in the art, can be used to expose microstructures to photosensitive materials. In embodiments, laser ablation using masks or using focused and modulated laser beams can be used to generate microstructures including markings in materials. In embodiments, micromachining (also known as diamond machining), known in the art, can be used to generate desired microstructures from solid materials. In embodiments, additive manufacturing (also known as 3D printing), known in the art, can be used to generate desired microstructures in solid materials.

[0064] Figure 8An embodiment of the first beam-splitting optical film 810 and the second beam-splitting optical film 820 is schematically illustrated, which can be used as... Figure 7 A first beam-splitting optical film 622 and a second beam-splitting optical film 624 are provided. The first beam-splitting optical film 810 is configured to receive individual beams emitted by the LED array 610 and split each beam into two beams. The second beam-splitting optical film 820 is configured to receive beams from the first beam-splitting optical film 810 and split each beam into two beams, resulting in the individual beams received by the first beam-splitting optical film 810 being split into four beams upon exiting the second beam-splitting optical film 820. Figure 8 As shown, the first beam-splitting optical film 810 includes a plurality of beam-splitting microstructures 812 in the form of parallel linear prisms, the beam-splitting microstructures 812 extending across the downward-facing side of the first beam-splitting optical film 810 (and toward the LED array, not shown). The first beam-splitting optical film 810 also includes a plurality of random rough microstructures 814 on the opposite side of the parallel linear prisms 812. Similarly, the second beam-splitting optical film 820 includes a plurality of beam-splitting microstructures 822 in the form of parallel linear prisms, the beam-splitting microstructures 822 extending across the downward-facing side of the second beam-splitting optical film 820 and toward one side of the first beam-splitting optical film 810, and a plurality of random rough microstructures 824 on the opposite side of the parallel linear prisms 822.

[0065] The first beam-splitting optical film 810 and the second beam-splitting optical film 820 are oriented relative to each other such that a plurality of beam-splitting microstructures 812 of the first beam-splitting optical film 810 are oriented at 90° relative to a plurality of beam-splitting microstructures 822 of the second beam-splitting optical film 820. This allows the original beam of light from a single LED (see...) Figure 2A It is split into four beams, as measured by a goniometer and... Figure 9 As shown in the diagram. By increasing the refractive index of multiple beam-splitting microstructures 812, 822, the original beam from a single LED can be split into four beams and further propagated, as measured by a goniometer and... Figure 10 As shown in the image.

[0066] Figure 11 yes Figure 10 The measured light distribution (denoted by 1100) and from having Figure 2A The figure shows a two-dimensional diagram of the measured distribution of light output from the LED source after passing through a circular diffuser (denoted by 1110). As shown, the pair of beam-splitting optical films 810, 820 splits the light received from the LED and propagates the light wider than a circular diffuser (i.e., away from the lowest point of 0°), and also suppresses on-axis (i.e., lowest point) light compared to a circular diffuser. By suppressing on-axis light by reflecting it back towards the LED, this helps to hide the LED so that it is not visible above the pair of beam-splitting optical films 810, 820.

[0067] With Figure 4 Compared to the effect of the circular diffuser schematically illustrated in the diagram on the light emitted by a single LED 112, Figure 12A The diagram schematically illustrates the effect of two beam-splitting optical films 810 and 820 on the light emitted by a single LED 612. Figure 5A and Figure 5B A comparative analysis of the effects of the circular diffuser on the array 110 of LEDs 112, as illustrated in the schematic diagram. Figure 12B The diagram schematically illustrates the effect of two beam-splitting optical films 810, 820 on the light emitted by the array 610 of LEDs 612. As illustrated, the light output by the two beam-splitting optical films 810, 820 is generally brighter and more uniform than the light output by the circular diffuser.

[0068] To further enhance the uniformity of the light output from the pair of beam-splitting optical films 810 and 820, a circular diffuser providing moderate diffusion was placed above the pair of beam-splitting optical films 810 and 820, which have a high refractive index (output as shown). Figure 10 (As shown in the image), and the light passing through the three stacked membranes was measured using a goniometric photometer. The results are in Figure 13 As shown in the figure, and indicating that after the light is split into four by the pair of beam-splitting optical films 810, 820, Gaussian diffusion appears to suppress most of the desired diffusion of the light generated by the pair of beam-splitting optical films 810, 820.

[0069] A volume diffuser providing very high diffusion was placed above the pair of beam-splitting optical films 810 and 820, which have high refractive indices, and the light passing through the stack of three films was measured using a goniometric photometer. The results were... Figure 14 As shown in the figure, and indicating that the increased diffusion after the light is split into four by the pair of beam-splitting optical films 810, 820 appears to further suppress the desired diffusion of the light generated by the pair of beam-splitting optical films 810, 820.

[0070] Figure 15 yes Figure 10 , 13 Two-dimensional plots of the measured light distribution of 14. More specifically, Figure 15 The illustration shows a comparison of the two-dimensional light intensity distribution after leaving the pair of beam-splitting optical films 810, 820 (denoted by 1100) with a higher refractive index, after leaving a circular diffuser film providing moderate diffuse (denoted by 1500), and after leaving a volume diffuser providing very high diffuse (denoted by 1510), and indicates that the increased diffuse reduces the desired diffusion provided by the pair of beam-splitting optical films 810, 820.

[0071] Similar effects to those of circular and volumetric diffusers have also been observed in the color conversion layer 630. Specifically, it has been found that phosphor films can also suppress some desired diffusion of light generated by two or more beam-splitting optical films 810, 820. Therefore, in addition to the lower film stack 620, it may be desirable to use the pair of beam-splitting optical films 810, 820 (and in some embodiments, a single beam-splitting optical film) and / or add beam-splitting microstructures to one or both surfaces of the color conversion layer 630 above the color conversion layer 630 in the upper optical film stack 640.

[0072] Figure 16 An optical film 1600 according to an embodiment of the present invention is schematically illustrated, which can be used as a third optical film 626 in a lower optical film stack 620. As shown, the optical film 1600 includes a plurality of microstructures 1610 in the form of a four-sided pyramid on one side. The optical film 1600 is placed on top of the pair of beam-splitting optical films 810, 820 having a higher refractive index, with the plurality of microstructures 1610 facing the pair of beam-splitting optical films 810, 820, and light passing through the three film stacks 810, 820, 1600 is measured using a goniometer. The results are shown in... Figure 17 The diagram illustrates and indicates that after light is split into four by the pair of beam-splitting optical films 810, 820, the optical film 1600, having a plurality of microstructures 1610 in the form of a square pyramid, increases the uniformity of light propagation in both directions provided by the beam-splitting optical films 810, 820, which is desirable. In an embodiment, the pair of beam-splitting optical films 810, 820 can be replaced by an optical film 1600 having a plurality of microstructures 1610 in the form of a square pyramid.

[0073] To further investigate the effect of optical film stacking according to an embodiment of the present invention, Synopsis' LightTools lighting design software was used to model the effects of various stacks of the three optical films 622, 624, and 626 in the lower optical film stack 620 on a point spread function (“PSF”), which is the intensity of light as a function of the position (in xy coordinates) above the third optical film 626. Figure 18 The illustration shows the modeling results using the pair of spectroscopic optical films 810, 820 and a third film in the form of a volumetric diffuser providing very high diffusion. Figure 14 Similar to measurements taken with a goniometer, Figure 18 The diagram illustrates a relatively narrow point spread function (PSF).

[0074] Figure 19 The illustration shows the results using the pair of spectroscopic optical films 810, 820 and a third optical film 1600 having multiple microstructures 1610. (Compared to...) Figure 17 Similar to measurements taken with a goniometer, Figure 19 The diagram illustrates the relationship with Figure 18 Compared to the volume diffuser results, the high-angle diffusion is maintained by multiple microstructures 1610 (quadrangular pyramids).

[0075] Figure 20 The illustration shows the modeling results when using two cross-prism films with high refractive indices similar to the aforementioned pair of beam-splitting optical films 810, 820, but without multiple random rough structures 814, 824, and a third optical film 1600 with multiple microstructures 1610. As defined herein, "high refractive index" refers to, for example, a refractive index greater than 1.65, such as 1.7. As shown, compared to the pair of beam-splitting optical films 810, 820 with random rough microstructures 814, 824, the cross-prism film with prisms on one side but without random rough microstructures provides less uniformity compared to larger single points (…). Figure 19 This leads to four differences ( Figure 20 ).

[0076] Example

[0077] To test the effects of different film combinations in the backlight unit 600, a series of optical film combinations were used in the lower optical film stack 620 and the upper optical film stack 640, with the same color conversion layer 630 (phosphor film) between the lower optical film stack 620 and the upper optical film stack 640. The films used in the lower optical film stack 620 and the upper optical film stack 640 are a pair of beam-splitting optical films, each with multiple microstructures, and a pair of diffuser-type films in the form of volume diffusers. Four different combinations were used, as summarized in Table I below.

[0078] Table I: Summary of Optical Film Stacking - Examples 1-4

[0079]

[0080] Each of Examples 1-4 was placed on a lamp plate comprising a micro-LED array with a spacing of 1.6 mm. When the pair of cross-beam splitting optical films (i.e., oriented 90° relative to each other) were used for the upper optical film stack, the pair of cross-beam splitting optical films, as units, were rotated approximately 20° clockwise relative to the micro-LED array. The total thickness of each stack, the relative average energy emanating from the stack, and the range / average energy of each stack were measured. The results are summarized in Table II below.

[0081] Table II: Summary of Test Results—Example 1-4

[0082]

[0083]

[0084] A higher relative average energy indicates brighter light exiting the backlight unit 600, which is desirable, and a lower range / average energy indicates more uniform light exiting the backlight unit 600, which is also desirable. Test results show that backlight units 600 (Examples 3 and 4) including two cross-beam splitting optical films in the upper optical film stack 640 have significantly higher average energy exiting the stack and significantly lower range / average energy compared to backlight units 600 (Examples 1 and 2) which include two volumetric diffusers in the upper stack. Example 4, which has two cross-beam splitting optical films in both the lower optical film stack 620 and the upper optical film stack 640, has the smallest thickness, the highest average energy, and the lowest range / average energy, which is desirable.

[0085] Additional samples were fabricated to investigate other combinations of the lower film stack 620 used in the backlight unit 600, and different spacings of the array 610 of light-emitting diodes 612. For Example 5, a stack of three beam-splitting optical films is used for the lower optical film stack 620. Figure 21A and 21B The beam-splitting optical film 2100, with a structure shown and a total thickness of approximately 0.11 mm, serves as the first beam-splitting optical film 622. As shown, the beam-splitting optical film 2100 includes a first side 2110 (see Figure 2110). Figure 21A Multiple parallel linear prisms 2112 extending along the first direction FD on the ) and on the second side 2120 of the beam-splitting optical film 2100 (see Figure 21B The prism 2112 is provided with a plurality of elliptical cylindrical microstructures 2122 having an extension of 1° by 60° and extending in a second direction SD substantially orthogonal to the first direction FD. The prism 2112 is made of a material having a refractive index of approximately 1.7. For the second beam-splitting optical film 624 of Example 5, the same beam-splitting optical film 2100 is used, but the total thickness is approximately 0.2 mm. Figure 8 Compared to the orientation shown, the multiple parallel linear prisms 2112 for each membrane are substantially parallel to each other in the first direction FD and are oriented to face the array 610 of the LED 612. Figure 22A The illustration shows light with a Lambertian distribution emitted from LED 612 passing through multiple parallel linear prisms facing LED 612. Figure 21A and 21B A two-dimensional plot of the distribution of the 2100-layer spectrophotometer. Lighter colors indicate higher light intensity.

[0086] Example 5 also includes a third beam-splitting optical film as a third optical film 626, which includes a plurality of random conical microstructures on a first side facing the second beam-splitting optical film 624 and a plurality of parallel linear prisms on a second side of the third beam-splitting optical film 626 opposite to the first side. The prisms are made of a material with a refractive index of 1.7, and the thickness of the third beam-splitting optical film 626 is 0.2 mm.

[0087] For Example 6, four beam-splitting optical films are used for the lower optical film stack 620. In this embodiment, the first beam-splitting optical film 622 has multiple linear prisms on the bottom side of the array 610 facing the LEDs 612, and multiple circular beam-splitting microstructures on the top side of the first beam-splitting optical film 622. In this embodiment, the first beam-splitting optical film 622 has a thickness of 0.17 mm, and the prisms are made of a material with a refractive index of approximately 1.7. Figure 22B The illustration shows a two-dimensional diagram of the distribution of light with a Lambertian distribution emitted from LED 612 after passing through the first beam-splitting optical film of this embodiment, which has multiple parallel linear prisms facing LED 612. Lighter colors indicate higher light intensity.

[0088] In this embodiment, the second beam-splitting optical film 624 has multiple parallel linear prisms on the bottom side of the array 610 facing the LED 612 and multiple random conical microstructures on the top side of the second beam-splitting optical film 624. The thickness of the second beam-splitting optical film 624 in this embodiment is 0.12 mm, and the prisms are made of a material with a refractive index of approximately 1.7. Figure 22C The illustration shows a two-dimensional diagram of the distribution of light with a Lambertian distribution emitted from LED 612 after passing through a second beam-splitting optical film in this embodiment, which has multiple parallel linear prisms facing LED 612. Lighter colors indicate higher light intensity.

[0089] The second beam-splitting optical film 624 is oriented relative to the first beam-splitting optical film 622 such that the plurality of parallel linear prisms of the second beam-splitting optical film 624 are substantially orthogonal to the plurality of parallel linear prisms of the first beam-splitting optical film 622, similar to... Figure 8 As shown in the image.

[0090] The third beam-splitting optical film 626 of Example 6 has multiple circular beam-splitting microstructures on its bottom side facing the second beam-splitting optical film 624 and multiple parallel linear prisms on its top side. The film thickness is 0.11 mm and the prisms are made of a material with a refractive index of approximately 1.7. The multiple parallel linear prisms of the third beam-splitting optical film are oriented parallel to the multiple parallel linear prisms of the second beam-splitting optical film 624. The fourth beam-splitting optical film is the same as the third beam-splitting optical film 626, but has multiple parallel linear prisms oriented substantially orthogonally to the multiple parallel linear prisms of the third beam-splitting optical film 626.

[0091] Examples 5 and 6 also include a 0.12 mm thick phosphor film for the color conversion layer 630 and located above the third beam-splitting optical film 626, and a pair of intersecting brightness enhancement films 650, 660, each with a thickness of 0.1 mm, located above the color conversion layer 630. No upper optical film stack 640 is used between the color conversion layer 630 and the pair of brightness enhancement films 650, 660. A summary of the beam-splitting optical films used in Examples 5 and 6 is provided in Table III below.

[0092] Table III: Summary of Lower Optical Film Stacking—Examples 5 and 6

[0093]

[0094] Each of Examples 5 and 6 was placed on a lamp board comprising a micro-LED array with a 2.4 mm pitch. The total thickness of each stack (including the color conversion layer and the brightness enhancement film), the relative average energy emanating from the stack, and the range / average energy of each stack were measured. The results are summarized in Table IV below.

[0095] Table IV: Summary of Test Results—Examples 5 and 6

[0096]

[0097] The test results of Examples 5 and 6 show that, compared with the backlight unit 600 (Example 5) which includes four beam-splitting optical films in the lower optical film stack 620, the backlight unit 600 (Example 5) which includes three beam-splitting optical films in the lower optical film stack 620 has a larger average energy (greater brightness) and a lower range / average energy (greater uniformity) away from the stack, even if the two lower optical film stacks have the same thickness.

[0098] Test results indicate that it may be advantageous to use two or more beam-splitting optical films in the lower optical film stack 620, which have an elliptical lens structure on their top surface and parallel linear prisms on their bottom surface, wherein the parallel linear prisms of the two films are oriented substantially in the same direction, i.e., within 30 degrees or ideally within 15 degrees. While the aforementioned elliptical lens structure has a 1° x 60° extension, other shapes can also be used. For example, according to embodiments of the invention, an elliptical lens structure with a 1° x 40° or 1° x 90° extension can be used.

[0099] Figure 23 An embodiment of the beam-splitting optical film 2300 is schematically illustrated, which can be used as... Figure 6 and Figure 7The lower optical film stack 620 shown contains one or more beam-splitting optical films 622, 624. As shown, the beam-splitting optical film 2300 includes a plurality of parallel linear prisms 2312 extending along a first direction FD on a first side 2310 of the beam-splitting optical film 2300, and a plurality of parallel linear prisms 2322 also extending along the first direction FD on a second side 2320 of the beam-splitting optical film 2300. In an embodiment, when two of the beam-splitting optical films 2300 serve as the first and second beam-splitting optical films 622, 624 of the lower optical film stack 620, all the parallel linear prisms 2312, 2322 of the two films 2300 can be aligned in substantially the same direction, for example, in the first direction FD.

[0100] In an embodiment, when the two beam-splitting optical films 622 and 624 in the beam-splitting optical film 2300 serve as the first and second beam-splitting optical films 620, one of the two beam-splitting optical films 2300 can be oriented such that a plurality of linear prisms 2312 and 2322 of one film are substantially orthogonally aligned with a plurality of linear prisms 2312 and 2322 of the other film. For example, one film 2300 may align its plurality of linear prisms 2312 and 2322 in a first direction FD, while the other film may align its plurality of linear prisms 2312 and 2322 in a second direction SD that is substantially orthogonal to the first direction FD.

[0101] In an embodiment, when two of the beam-splitting optical films 2300 serve as the first and second beam-splitting optical films 622 and 624 of the lower optical film stack 620, one of the two beam-splitting optical films 2300 can be oriented such that its plurality of linear prisms 2312 and 2322 are aligned in the first direction FD, while the plurality of linear prisms 2312 and 2322 of the other film are aligned in any direction relative to the first direction FD, for example, in the direction between the first direction FD and the second direction SD.

[0102] Figure 24 An embodiment of the beam-splitting optical film 2400 is schematically illustrated, which can be used as... Figure 6 and Figure 7The lower optical film stack 620 shown contains one or more beam-splitting optical films 622, 624. As shown, the beam-splitting optical film 2400 includes a plurality of parallel linear prisms 2412 extending along a first direction FD on a first side 2410 of the beam-splitting optical film 2400, and a plurality of parallel linear prisms 2422 extending along a second direction SD substantially orthogonal to the first direction FD on a second side 2420 of the beam-splitting optical film 2400. In an embodiment, when two of the beam-splitting optical films 2400 serve as the first and second beam-splitting optical films 622, 624 of the lower optical film stack 620, all the parallel linear prisms 2412 on the first side 2410 of the film 2400 can be aligned in substantially the same direction, for example, along the first direction FD.

[0103] In an embodiment, when two of the beam-splitting optical films 2400 serve as the first and second beam-splitting optical films 622 and 624 of the lower optical film stack 620, one of the two beam-splitting optical films 2400 can be oriented such that a plurality of linear prisms 2412 on its first side 2410 are substantially orthogonal to the plurality of linear prisms 2412 on the first side 2410 of the other film 2400, such that the plurality of linear prisms 2412 of one film are aligned in a first direction FD, while the plurality of linear prisms 2412 of the other film are aligned in a second direction SD which is substantially orthogonal to the first direction FD.

[0104] In an embodiment, when two of the beam-splitting optical films 2400 serve as the first and second beam-splitting optical films 622 and 624 of the lower optical film stack 620, one of the two beam-splitting optical films 2400 can be oriented such that a plurality of linear prisms 2412 on its first side 2410 are aligned in a first direction FD, while the other film aligns the plurality of linear prisms 2412 on its first side 2410 in any direction relative to the first direction, such as in the direction between the first direction FD and the second direction SD.

[0105] Figure 25 An embodiment of the beam-splitting optical film 2500 is schematically illustrated, which can be used as... Figure 6 and Figure 7 The lower optical film stack 620 shown contains one or more beam-splitting optical films 622, 624. As shown, the beam-splitting optical film 2500 includes the above-mentioned components on its first side 2510. Figure 16The description includes a plurality of quadrilateral pyramids 1610 and a plurality of parallel linear prisms 2522 extending on the second side 2520 of the beam-splitting optical film 2500 in a first direction FD. In an embodiment, when two of the beam-splitting optical films 622, 624 in the beam-splitting optical film 2500 serve as the first and second beam-splitting optical films 622, 624 of the lower optical film stack 620, all the parallel linear prisms 2522 on the second side 2520 of the film 2500 can be aligned in substantially the same direction, for example, in the first direction FD.

[0106] In an embodiment, when two of the beam-splitting optical films 2500 serve as the first and second beam-splitting optical films 622 and 624 of the lower optical film stack 620, one of the two beam-splitting optical films 2500 can be oriented such that a plurality of linear prisms 2522 on its second side 2520 are substantially orthogonal to the plurality of linear prisms 2522 on the second side 2520 of the other film 2500, such that the plurality of linear prisms 2522 of one film are aligned in a first direction FD, while the plurality of linear prisms 2522 of the other film are aligned in a second direction SD which is substantially orthogonal to the first direction FD.

[0107] In an embodiment, Figure 6 and Figure 7 The third optical film 626 of the lower optical film stack 620 can also be Figure 25 The beam-splitting optical film 2500, wherein multiple linear prisms 2522 are aligned in the first direction FD or the second direction SD.

[0108] The embodiments described herein represent many possible implementations and examples and are not intended to necessarily limit this disclosure to any particular embodiment. Rather, various modifications can be made to these embodiments, and different combinations of the various embodiments described herein can be used as part of the invention, even if not explicitly described, as will be understood by those skilled in the art. For example, beam-splitting and diffuse optical films may include microstructures and different combinations of microstructures different from those depicted in the figures, such as those disclosed, for example, in International Patent Application Publication No. WO2019 / 152382, the entire contents of which are incorporated herein by reference.

[0109] Furthermore, the upper optical film stack 640 may include the same film combination as the lower optical film stack 620 or may include different film combinations. In an embodiment, most of the films of the backlight unit 600 located below the brightness enhancement films 650, 660 may have microstructures configured to split the incident light beam into two or more beams. In an embodiment, all or almost all of the optical films in the backlight unit 600 may have microstructures configured to split the incident light beam into two or more beams on at least one surface. The resulting brightness and uniformity of the light exiting the lower optical film stack 620 can be adjusted by using different combinations of prisms and microstructures on various optical films in the lower optical film stack 620.

[0110] The illustrations and the above embodiments are not intended to be limiting in any way, and any such modifications to the embodiments described herein are intended to be included within the spirit and scope of this disclosure and protected by the appended claims.

Claims

1. A backlight unit, comprising: LED array; The lower optical film stack is located above the light-emitting diode array; The color conversion layer is located above the lower optical film stack; An upper optical film stack located above the color conversion layer, wherein the upper optical film stack includes a pair of intersecting beam-splitting optical films, one of the intersecting beam-splitting optical films being oriented at 90° relative to the other of the intersecting beam-splitting optical films; and A pair of brightness enhancement films located above the upper optical film stack, The majority of the lower optical film stack is a beam-splitting optical film having a plurality of beam-splitting microstructures on at least one surface, and wherein the beam-splitting microstructures are configured such that when a collimated beam is guided to the microstructure on the axis, the collimated beam is split into two or more beams having a lower relative intensity on the axis.

2. The backlight unit according to claim 1, wherein the lower optical film stack has all of the plurality of beam-splitting microstructures on at least one surface.

3. The backlight unit according to claim 1, wherein the color conversion layer is located above at least one beam-splitting optical film.

4. The backlight unit according to claim 1, wherein the color conversion layer has at least one surface comprising a plurality of spectral microstructures.

5. The backlight unit according to claim 1, wherein the lower optical film stack includes a first beam-splitting optical film, the first beam-splitting optical film including a plurality of first parallel linear prisms extending along a first direction on a first side thereon and a plurality of first elliptical cylindrical structures extending along a second direction on a second side thereon, the second direction being substantially orthogonal to the first direction, wherein the first side faces the light-emitting diode array.

6. The backlight unit of claim 5, wherein the lower optical film stack includes a second beam-splitting optical film located above the first beam-splitting optical film, the second beam-splitting optical film including a plurality of second parallel linear prisms extending substantially along a first direction on its first side and a plurality of second elliptical cylindrical structures extending along a second direction on its second side, wherein the first side of the second beam-splitting optical film faces the second side of the first beam-splitting optical film.

7. The backlight unit of claim 6, wherein the lower optical film stack includes a third beam-splitting optical film located above the second beam-splitting optical film, the third beam-splitting optical film including a plurality of third parallel linear prisms extending substantially along a second direction on its first side.

8. The backlight unit according to claim 7, wherein the third beam-splitting optical film further comprises a plurality of microstructures on its second side.

9. The backlight unit according to claim 8, wherein the second side of the third beam-splitting optical film faces the second side of the second beam-splitting optical film.

10. The backlight unit of claim 1, wherein at least one of the lower optical film stacks is a first beam-splitting optical film, the first beam-splitting optical film comprising a plurality of first parallel linear prisms extending along a first direction on a first side thereon and a plurality of second parallel linear prisms extending along the first direction on a second side thereon.

11. The backlight unit of claim 10, wherein at least one of the lower optical film stacks is a second beam-splitting optical film, the second beam-splitting optical film comprising a plurality of first parallel linear prisms extending along the first direction on a first side thereon and a plurality of second parallel linear prisms extending along the first direction on a second side thereon.

12. The backlight unit of claim 10, wherein at least one of the lower optical film stacks is a second beam-splitting optical film, the second beam-splitting optical film comprising a plurality of first parallel linear prisms extending on a first side along a second direction substantially orthogonal to the first direction, and a plurality of second parallel linear prisms extending on a second side along the second direction.

13. The backlight unit of claim 1, wherein at least one of the lower optical film stacks is a first beam-splitting optical film, the first beam-splitting optical film comprising a plurality of first parallel linear prisms extending along a first direction on a first side thereon and a plurality of second parallel linear prisms extending along a second direction substantially orthogonal to the first direction on a second side thereon.

14. The backlight unit of claim 1, wherein two of the lower optical film stacks are beam-splitting optical films, each beam-splitting optical film comprising a plurality of microstructures on its first side and a plurality of parallel linear prisms extending along a first direction on its second side, wherein each microstructure has a square pyramidal shape.

15. The backlight unit of claim 1, wherein three of the lower optical film stacks are beam-splitting optical films, each beam-splitting optical film comprising a plurality of microstructures on its first side and a plurality of parallel linear prisms extending along a first direction on its second side, wherein each microstructure has a square pyramidal shape.

16. A backlight unit, comprising: LED array; A lower optical film stack located above the light-emitting diode array and configured to receive light emitted by the light-emitting diode array, the lower optical film stack comprising... A first beam-splitting optical film includes a plurality of first beam-splitting microstructures on a first side of itself facing the light-emitting diode array, the plurality of first beam-splitting microstructures being configured and arranged to separate light received from the light-emitting diode array. A second beam-splitting optical film is located above the first beam-splitting optical film and includes a plurality of second beam-splitting microstructures on its first side facing the first beam-splitting optical film. These plurality of second beam-splitting microstructures are configured and arranged to separate light received from the first beam-splitting optical film. The first and second beam-splitting microstructures are configured such that when a collimated beam is guided to the microstructures on the axis, the collimated beam is split into two or more beams with regions having lower relative intensities on the axis. A color conversion layer located above the lower optical film stack and configured to receive light from the lower optical film stack; An upper optical film stack located above the color conversion layer and configured to receive light from the color conversion layer, wherein the upper optical film stack includes a pair of intersecting beam-splitting optical films, one of the intersecting beam-splitting optical films being oriented at 90° relative to the other of the intersecting beam-splitting optical films; and A pair of brightness enhancement films located above the upper optical film stack and configured to receive light from the upper optical film stack.

17. The backlight unit of claim 16, wherein the plurality of first beam-splitting microstructures comprises a plurality of first parallel linear prisms, and the plurality of second beam-splitting microstructures comprises a plurality of second parallel linear prisms orthogonal to the orientation of the plurality of first parallel linear prisms.

18. The backlight unit of claim 17, wherein the first beam-splitting optical film further comprises a plurality of first random rough microstructures on its second side, and the second beam-splitting optical film further comprises a plurality of second random rough microstructures on its second side.

19. The backlight unit of claim 16, wherein the lower optical film stack further comprises a third optical film located above the second beam-splitting optical film.

20. The backlight unit of claim 19, wherein the third optical film comprises a plurality of microstructures facing the second beam-splitting optical film.

21. The backlight unit of claim 20, wherein each of the plurality of microstructures of the third optical film has a quadrangular pyramid shape.

22. The backlight unit of claim 16, wherein the color conversion layer has at least one surface comprising a plurality of spectral microstructures.

Images