WO2022182522A1

WO2022182522A1 - Tiled and partially laminated liquid crystal display backlights

Info

Publication number: WO2022182522A1
Application number: PCT/US2022/015919
Authority: WO
Inventors: Kirk Richard ALLEN; Dmitri Vladislavovich Kuksenkov
Original assignee: Corning Incorporated
Priority date: 2021-02-23
Filing date: 2022-02-10
Publication date: 2022-09-01
Also published as: KR20230146660A; CN116997853A; JP2024506949A; TW202240258A

Abstract

A backlight unit for use in a display device includes a light board with a first light source and a second light source. The backlight unit also includes a light guide positioned adjacent to the light board to distribute light emitted from the first light source and the second light source. A supplemental connector is positioned at a connector location between the first light source and the second light source to bond the light guide to the light board, wherein an optical property of the light board at the connector location or of the supplemental connector is different from the optical property at adjacent locations to make the supplemental connector undetectable to a viewer of the backlight unit.

Description

TILED AND PARTIALLY LAMINATED LIQUID CRYSTAL DISPLAY BACKLIGHTS

PRIORITY CLAIM AND CROSS-RELERENCE

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63/152463 filed on Lebruary 23, 2021, the content of which is relied upon and incorporated herein by reference in its entirety.

PIELD

[0002] The disclosure relates to tiled and partially laminated liquid crystal (LCD) backlights. More particularly, the disclosure relates to backlights that may include tiled light boards and/or tiled light guides laminated to each other to produce robust backlight assemblies with improved mechanical reliability and uniform brightness.

BACKGROUND

[0003] In modern and emerging display technologies, display trends, such as trends in liquid crystal displays (LCDs), include increasing resolution, higher peak brightness and dynamic range (HDR), higher contrast, thinner set design and narrower bezels. In order to address these trends, displays can include direct-lit backlights that can include a two-dimensional array of light sources positioned directly behind the LCD panel. The two-dimensional array of light sources can include an array of light emitting diodes (LEDs). Various elements can distribute the light from the array of light sources uniformly across the display panel to meet the brightness, contrast and other requirements for the display.

[0004] In some display designs, the array of light sources can be distributed across the display using a light guide(s) that can include various elements such as a light guide plate, films, patterns, or other optical elements and layers to meet the requirements of the display. Existing designs, however, suffer from several drawbacks. Lor example, one drawback is that it can be difficult to align a light guide with the array of light sources. Another example drawback is that existing backlight designs can include materials that do not allow for thinner and/or narrow bezels. Another example drawback is that existing backlight designs can suffer from mechanical reliability problems. Still another example drawback is that existing designs can require complex and/or expensive manufacturing processes. There exists a need, therefore, for improved backlights that are easier to align light guides with light sources, have designs that allow for thinner display thickness and narrower bezels, have improved mechanical reliability, and can be manufactured using less complex and less costly processes.

SUMMARY

[0005] The present disclosure provides a backlight that can be used in a display that includes supplemental connectors positioned intermittently between a light guide plate and a light board at predetermined positions between the light sources on the light board. The optical properties of the supplemental connectors can be adjusted so that the supplemental connectors are undetectable to the viewer of the backlight unit. The additional connectors can improve the mechanical reliability of the backlight unit as well as allowing the use of tiled light plates to improve the accuracy and repeatability of properly aligning the light guide to the light board.

[0006] In one aspect, the present disclosure provides a backlight unit. In accordance with some embodiments, a backlight unit for use in a display device includes a light board with a first light source and a second light source. The backlight unit also includes a light guide positioned adjacent to the light board to distribute light emitted from the first light source and the second light source. A connector is positioned at a connector location between the first light source and the second light source to bond the light guide to the light board, wherein an optical property of the light board at the connector location or of the connector is different from the optical property at adjacent locations to make the connector undetectable to a viewer of the backlight unit.

[0007] In another aspect, the optical property can include a transparency of the connector.

[0008] In another aspect, the supplemental connector can be tinted with a gray color to reduce the transparency of the supplemental connector.

[0009] In another aspect, the supplemental connector can be tinted with a yellow color to reduce the transmission of blue light.

[0010] In another aspect, the optical property can include a reflectivity of the light board at the connector location.

[0011] In another aspect, the reflectivity of the light board at the connector location can be lower than a reflectivity of the light board adjacent to the connector location. [0012] In another aspect, the light board can include a gray color coating at the connector location to reduce the reflectivity of the light board at the connector location.

[0013] In another aspect, the light board can include a yellow color coating at the connector locations to reduce the transmission of blue light at the connector location.

[0014] In another aspect, the light guide can include a first light guide tile including a first edge and a second light guide tile including a second edge, the connector aligned with the first edge and the second edge.

[0015] In another aspect, the light board can include an array of light sources and a connector is positioned between adjacent light sources in the array of light sources.

[0016] In another aspect, the light guide can be bonded to the first light source and the second light source.

[0017] In accordance with some embodiments, a backlight unit for use in a display can include a light board comprising a plurality of light sources and a first light guide tile and a second light guide tile positioned adjacent to each other with a first edge of the first light guide tile positioned adjacent to a second edge of the second light guide tile to define a tile seam between the first light guide tile and the second light guide tile. The backlight unit can also include a connector positioned between the light board and the first light guide tile and the second light guide tile at the tile seam, wherein the connector bonds the first light guide tile and the second light guide tile to the light board.

[0018] In another aspect, a method of assembling a backlight unit is provided. In accordance with some embodiments, the method includes providing a light board comprising a first light source and a second light source and positioning a connector on the light board at a connector location between the first light source and the second light source. The method can also include applying a light guide plate to the light board to bond the light guide plate to the light board at the connector location.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Like reference numerals denote like features throughout specification and drawings.

[0020] FIG. 1 is a cross-sectional view illustrating an exemplary backlight unit.

[0021] FIG. 2 is a plan view of an exemplary light board with an array of light sources in accordance with some embodiments.

[0022] FIG. 3 is a cross-sectional view illustrating an exemplary backlight unit with a connection between a light board and a light guide plate.

[0023] FIG. 4 is a cross-sectional view illustrating an exemplary backlight unit that includes a supplemental connection between a light board and a light guide plate in accordance with some embodiments.

[0024] FIG. 5 is a cross-sectional view illustrating an exemplary backlight unit that includes a tiled light guide plate in accordance with some embodiments.

[0025] FIG. 6 is a cross-sectional view illustrating an exemplary backlight unit that includes a supplemental connection between the light board and the tiled light guide plate of FIG. 4.

[0026] FIGS. 7 is a cross-sectional view illustrating an exemplary backlight unit that includes supplemental connections between a light board and another exemplary tiled light guide plate in accordance with some embodiments.

[0027] FIG. 8 is a cross-sectional view illustrating an exemplary backlight unit of FIG. 4 that includes multiple optical layers in accordance with some embodiments.

[0028] FIG. 9 is a flow chart illustrating an exemplary method of producing a backlight unit that includes supplemental connections between a light board and a light guide plate in accordance with some embodiments.

DETAILED DESCRIPTION

[0029] This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.

[0030] For purposes of the description hereinafter, it is to be understood that the embodiments described below may assume alternative variations and embodiments. It is also to be understood that the specific articles, compositions, and/or processes described herein are exemplary and should not be considered as limiting.

[0031] In the present disclosure the singular forms “a,” “an,” and “the” include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. When values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. As used herein, “about X” (where X is a numerical value) preferably refers to ±10% of the recited value, inclusive. For example, the phrase “about 8” preferably refers to a value of 7.2 to 8.8, inclusive. Where present, all ranges are inclusive and combinable. For example, when a range of “1 to 5” is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, “2-5”, and the like. In addition, when a list of alternatives is positively provided, such listing can be interpreted to mean that any of the alternatives may be excluded, e.g., by a negative limitation in the claims. For example, when a range of “1 to 5” is recited, the recited range may be construed as including situations whereby any of 1, 2, 3, 4, or 5 are negatively excluded; thus, a recitation of “1 to 5” may be construed as “1 and 3-5, but not 2”, or simply “wherein 2 is not included.” It is intended that any component, element, attribute, or step that is positively recited herein may be explicitly excluded in the claims, whether such components, elements, attributes, or steps are listed as alternatives or whether they are recited in isolation.

[0032] The present disclosure provides a backlight unit that includes one or more supplemental connections between a light board and a light guide plate. The supplemental connections can provide increased mechanical robustness and allow for improved dimensional alignment between the light board and the light guide plate. The improved mechanical robustness can decrease the likelihood of mechanical failures of the backlight unit over existing designs and can improve the efficiency and dimensional accuracy of the backlight unit. This, in turn, can reduce costs and improve the ability of the backlight unit to provide uniform brightness in a display that incorporates the backlight unit.

[0033] In some embodiments, the light guide plate of the backlight unit can include a panel that is made of glass. Unless expressly indicated otherwise, the term “glass article” or “glass” used herein is understood to encompass any object made wholly or partly of glass. Glass articles include monolithic substrates, or laminates of glass and glass, glass and non-glass materials, glass and crystalline materials, and glass and glass-ceramics (which include an amorphous phase and a crystalline phase).

[0034] The glass article such as a glass light guide plate may be flat or curved, and is transparent or substantially transparent. As used herein, the term “transparent” is intended to denote that the article, at a thickness of approximately 1 mm, has a transmission of greater than about 85% in the visible region of the spectrum (400-700 nm). For instance, an exemplary transparent glass panel may have greater than about 85% transmittance in the visible light range, such as greater than about 90%, greater than about 95%, or greater than about 99% transmittance, including all ranges and subranges therebetween. According to various embodiments, the glass article may have a transmittance of less than about 50% in the visible region, such as less than about 45%, less than about 40%, less than about 35%, less than about 30%, less than about 25%, or less than about 20%, including all ranges and subranges therebetween. In certain embodiments, an exemplary glass panel may have a transmittance of greater than about 50% in the ultraviolet (UV) region (100-400 nm), such as greater than about 55%, greater than about 60%, greater than about 65%, greater than about 70%, greater than about 75%, greater than about 80%, greater than about 85%, greater than about 90%, greater than about 95%, or greater than about 99% transmittance, including all ranges and subranges therebetween.

[0035] Exemplary glasses can include, but are not limited to, aluminosilicate, alkali- aluminosilicate, borosilicate, alkali-borosilicate, aluminoborosilicate, alkali- aluminoborosilicate, and other suitable glasses. Non-limiting examples of available glasses suitable for use as a light guide include, for instance, IRIS™, and GORILLA^® glasses from Corning Incorporated. The glass article may be optionally strengthened. In some embodiments, the glass article may be strengthened mechanically by utilizing a mismatch of the coefficient of thermal expansion between portions of the article to create a compressive stress region and a central region exhibiting a tensile stress. In some embodiments, the glass article may be strengthened thermally by heating the glass to a temperature above the glass transition point and then rapidly quenching. In some other embodiments, the glass article may be chemically strengthening by ion exchange.

[0036] Referring to FIG. 1 , an exemplary backlight unit 100 is shown. The backlight unit 100 can be used, for example, in a liquid crystal display (LCD). Some LCDs have brightness, contrast and other requirements that can be met using a direct-lit backlight unit. Direct-lit backlight units often include a two-dimensional array of light sources. The two- dimensional array of light sources can be arranged as multiple light emitting diodes (LEDs) that are positioned on a printed circuit board (PCB). Such PCBs or light boards deliver light toward a viewer of the display and are positioned behind a panel of the display. The light that is emitted from the light board can be distributed uniformly using a light guide. In this manner, the display can be illuminated according to the various requirements for the display such as brightness, contrast, etc.

[0037] In the example shown in FIG. 1, the backlight unit 100 can include a light board 102 and a light guide 104. The light board 102 can include multiple light sources 106 positioned on a surface of the light board 102 that faces a viewer when the backlight unit 100 is used in a display. The light sources 106 can be LEDs, for example. The light sources 106 can be mounted to a mounting board 108. The mounting board 108 can be, for example, a printed circuit board (PCB) that can deliver electrical power to the light sources 106. The light board 106 can also include a back reflector 110 that is positioned on the same surface of the mounting board 108 as the light sources 106. The light guide 104 can be positioned adjacent to the light sources 106. The light guide 104 can include various features and/or layers that can distribute the light emitted from the light sources 106. The light guide 104 can distribute the light emitted from the light sources 106 so that the light is distributed uniformly across the light guide 104 so that the position of the light sources is undetectable to the human eye when the display is viewed. The light guide 104 can include, for example, a printed reflector 118 positioned opposite to the light source 106 on a surface of the light guide 104. The printed reflector 118 can reflect light that is emitted from the light source 106 so that a localized bright spot does not appear above the location of each of the light sources. The light guide 104 can also include various light extractors 120 that can be positioned on a surface of the light guide 104. The light extractors 120 can be dots, dimples or other features that can be printed, etched or otherwise deposited or formed in the light guide. The light extractors 120 can be distributed along the light guide 104 to uniformly distribute the light across the light guide.

[0038] As shown in FIG. 1, the emitted light from the light source 106 (as indicated by arrows 122) can be refracted, reflected or otherwise guided in the light guide 104 to distribute the light from the light sources 106 across the light guide 104. The light guide 104 can include a light guide plate 124 that can be a made of a suitable material to guide the light emitted from the light sources. In some examples, the light guide plate 124 can be made of a glass material. The dimensional and reliability requirements of modern displays make glass a desirable material of for the light guide plate. The thermal and mechanical characteristics of glass allow the backlight unit 100 to be designed and manufactured to be thinner and to have an increased dimensional stability over those that have light guide plates 124 made of other materials such as polymers or other suitable plastic materials. Glass light guide plates also allow the bezel of a LCD to have a smaller overall width than LCD that incorporate backlight units with light guide plates made of non-glass materials.

[0039] The backlight unit 100 shows in FIG. 1 can illustrate a portion of a backlight unit. As can be appreciated, the backlight unit 100 can be reproduced in various profiles such that the backlight unit can include multiple light sources 106. Such an example is shown in FIG. 2. In the example, the light board 200 can include a mounting board 202, such as a PCB, that can deliver electrical power to the LEDs 204. As shown, the light board 200 can include multiple LEDs 204 that can be arranged in an array with multiple rows and columns of LEDs. The light board 200 can be any suitable size that is necessary to illuminate an LCD. As shown, the light board 200 includes twenty LEDs 204. In other examples, the light board 200 can include more or less than twenty LEDs. In some displays, it is not uncommon for the light board 200 to include hundreds of LEDs. For example, the light board 200 can be used in a display having an 80 inch or larger diagonal size. In such an example, the light board 200 can include 900 or more LEDs. At each LED, the backlight unit can include the structure illustrated in FIG. 1 with a light guide disposed over the light board 200.

[0040] In designs with multiple light sources 106, the light guide plate 104 needs to be carefully positioned and secured relative to the light board 102. As can be appreciated, the reflector 118 needs to be positioned relative to the light source 106 to ensure that the management of the light in the light guide produces uniform light distribution in the light guide 104. If there is excessive mismatch between the reflector 118 and the light source 106, there can be bright spots or other non-uniformity in the backlight unit 100 that is termed Mura. To minimize Mura effects, the alignment of the light guide 104 to the light board 102 should be carefully controlled during manufacturing of the backlight unit 100. As the number of light sources 106 increases, it becomes more difficult to ensure proper alignment between the light guide 104 and the light board 102.

[0041] One possible solution to make the assembly and alignment of the light guide 104 to the light board 102 easier to control and to repeatably accomplish within suitable tolerances is to separate either or both of the light guide 104 and the light board 102 into tiles. In such example designs, rather than having a single light guide 104 that includes a single light guide plate 124 with the size of the overall display screen, the light guide 104 can be separated into separate tiles that are positioned adjacent to one another. The light guide tiles, when assembled together, can have an overall size of the overall display screen. Such designs can also include a light board 102 that is created from multiple tiled light boards assembled together. Such a tiled structure allows the individual tiles to be adjusted relative to one another to ensure proper alignment between the light guide tiles and/or the light board tiles. In various examples, the light guide 104 can be created from multiple light guide tiles that are assembled to a one-piece light board. In another example, a single light guide plate can be assembled to a light board made of multiple light board tiles. In still other examples, the light guide and the light board can each be made of multiple light guide tiles and light board tiles, respectively. Such tiled designs are further described in U.S. Appl. No. 63/017,078 filed on April 29, 2020, the contents of which is hereby incorporated herein in its entirety.

[0042] Another problem that can arise in the assembly of a direct-lit backlight unit is in the mechanical robustness and reliability of the backlight unit. In some designs, the backlight unit is required to be very thin in order to be assembled into a thin or ultra-thin backlight unit for assembly into a thin or ultra-thin LCD device. Such thin or ultra-thin backlight units can have an overall thickness t (see FIG. 1) of between about 1 mm to about 5 mm. The thickness t in the example of FIG. 1 is shown without additional optical diffusers, layers, and films such as BEFs, DBEFs. The additional thickness of these optical diffusers, layers and/or films can add an thickness of about 0.5 mm to about 3 mm to the overall thickness of a backlight unit. In such thin and/or ultra-thin designs, the light guide plate 124 and/or the mounting board 108 can have a thickness of less than about 1 mm. In other designs the light guide plate 124 and/or the mounting board 108 can have a thickness of less than about 0.5 mm.

[0043] Referring now to FIG. 2, another example backlight unit 300 is shown. The backlight unit 300 is similar in many respects to the backlight unit 100 previously described. As shown, the backlight unit 300 includes the light board 102, the light source 106 and the light guide 104. As shown in this example, the light guide 104 can be fixed relative to the light board 102 using a quantity of optically clear adhesive (OCA) 302. The OCA 302 can be applied to the light source 106 since the light source 106 can extend above the surface of the light board. In such examples, the light guide 104 is bonded to the light board at each location of the light sources 106. The OCA can be applied to a facing surface of the light source that faces the light guide 104. In addition, the OCA can be present around each light source 106 such that a footprint of the OCA can be larger than the footprint of the light source 106.

[0044] The light guide 104 and the light board 102 can be assembled to each using various suitable methods and processes. In some examples, the light guide 104 and the light board 102 are laminated to each other using an optically clear adhesive. While the light guide 104 and the light board 102 can be manufactured to have substantially planar surfaces, neither the light guide 104 nor the light board 102 is perfectly flat. The light guide 104 and the light board 102 can be flexible such that when the light guide 104 and the light board 102 are applied to each other, the light guide 104 and the light board 102 can conform to each other. In some example processes, the light guide 104 and the light board can be pressed or pulled together to conform to each other after the light guide 104 is applied to the light board 102. The light guide 104 and the light board 102 can be applied to one another by pulling a vacuum or by providing hydrostatic pressure over the surface of the light guide 104 or the light board 102. In other examples, other processes can be used.

[0045] After the light guide 104 and the light board 102 are applied to one another with the OCA positioned therebetween, the light guide 104 will be secured to the light board 102.

The strength of the bond between the light guide 104 and the light board 102 can be compromised due a variety of factors. Such bond, however, needs to be sufficient to withstand normal use of the backlight unit and during normal transportation and processing that may occur to the backlight unit when the backlight unit is assembled into a display device. The integrity of the bond between the light guide 104 and the light board 102 can be compromised, for example, due to normal stresses, vibrations and shock than occur. In addition, temperature changes and thermal expansion can also exert stresses on the bonds and compromise their integrity. Still further, the strength of the bond can be insufficient because the surface are of the bond can be very small. In some designs, the light sources can be very small. In one example, the light board 102 can include LED chips with a surface area of about 1.4 mm by 1.4 mm and the distance between the LED chips can be 38 mm. In this example, when the OCA is applied to the LED chip, the OCA footprint can have a footprint of about a 3 mm diameter disk that encapsulates the LED as shown in FIG. 3. With this footprint the amount of surface area per LED chip is about 7 mm². Even in instances where there are many LEDs per light board, the amount of bonded surface can be about 0.5% of the total area of the light guide. This amount of surface can be insufficient to robustly bond the light guide 104 to the light board 102.

[0046] In some embodiments of the present disclosure, supplemental connectors can be positioned between the light sources 106 to add supplemental bonds between the light guide 104 and the light board. One example of such a backlight unit 400 is shown in FIG. 4. In this example, a supplemental connector 410 can be positioned between the light sources 106. In this example, the supplemental connector 410 can be provide an additional bonding force between the light guide 104 and the light board 102. Any number of supplemental connectors can be positioned between the light sources 106. In the example shown, one supplemental connector 410 is positioned between the light sources 106. In other examples, more than one supplemental connector can be added between the light sources. In the example shown, the supplemental connector 410 is added in a backlight in which the top surface of each light source 106 is bonded to the light guide 104 by a layer 404 of optically clear adhesive (OCA). The supplemental connectors 410 can also be added in backlight units that include light sources that are encapsulated in OCA (see FIG. 3).

[0047] Any suitable bonding element can be used for the supplemental connector 410. The supplemental connector 410 can be an amount of optically clear adhesive (OCA), for example. The OCA can be a UV, catalytic or thermally curable OCA. In other examples, the supplemental connector 410 can be a pressure-sensitive adhesive (PSA) commonly known as a mounting tape. Such mounting tapes can be two-sided such that the mounting tape bonds to the light board 102 on one side and to the light guide 104 on the opposite side. The mounting tape can be selected to have a suitable thickness to support the light board 102 at a distance away from the light board 102 to maintain a constant gap as determined by a height of the light sources 106.

[0048] In order for the supplemental connectors 410 to not affect the uniform light distribution that is caused by the light guide and other optical films that may be positioned above the light guide 104 (not shown in FIG. 4), the supplemental connectors are at least partially transparent. Since the supplemental connectors 410 are in optical contact with the light guide plate 104, it can be expected that the supplemental connectors 410 will cause some additional light to be extracted at the connector location. Thus, if the supplemental connectors 410 are included in the backlight unit 400 without taking any additional measures, a viewer viewing the backlight unit 400 will see a bright spot at the connector location (i.e., the location at which the supplemental connector 410 is positioned in the backlight unit 400). In order to prevent this non uniformity known in the art as mura, a few measures can be taken. A first measure can be to position the supplemental connectors 410 at locations in which light extraction caused by the supplemental connector 410 will be less noticeable. Such locations can be at positions under areas of the light guide 104 that have a maximum density of light extractors 120. Other suitable locations can be at the edges of dimming zones of the light guide 104. Still other suitable locations can be at positions equally spaced between light sources 106 in the array of light sources 106 that can be included in the light board 102. In a hexagonal array, the supplemental connectors can be positioned in the middle between three light sources 106. In a rectangular array, the supplemental connectors can be positioned in the corner of a dimming zone equal distance from four light sources.

[0049] Another measure that can be taken to make the supplemental connectors 410 undetectable to viewer include changing at least one optical property of the light board at the connector location or of the supplemental connector relative to adjacent regions of the backlight unit. By positioning the supplemental connector at an advantageous connector location and changing an optical property of the light board at the connector location or of the supplemental connector, the existence of the supplemental connector 410 can be made to be undetectable to a viewer that is viewing the backlight unit when it is assembled into a display device. For the purposes of this disclosure, undetectable to a viewer means that the viewer cannot see a localized area of non-uniformity in the backlight unit without the aid of an optical detection device such as a camera, photo detector or other light sensor. [0050] Various optical properties can be changed at the connector location to make the supplemental connector 410 undetectable to a viewer. In some examples, the reflectivity of the light board 102 at the connector location can be adjusted to cause less light to be reflected. For example, the reflectivity of the back reflector 110 can be adjusted at the connector location. The reflectivity of the light board 102 can be changed, for example, by printing a suitable color (e.g., a gray color) ink on the light board 102 at the connector location(s).

[0051] In other examples, the optical property of the supplemental connector 410 can be changed to adjust the transparency of the supplemental connector 410. For example, a suitable color (e.g., a gray color) ink can be printed on the top surface of a mounting tape. In another example, a suitable color ink can be printed on the bottom surface of a mounting tape. In still another example, a suitable color pigment can be added to a bond material such as to an optically clear adhesive (OCA). Any of the foregoing or other inserts or color pigments can be added to the supplemental connector 410 to adjust the transparency of the supplemental connector 410.

As can be appreciated, experimentation can be used to determine the preferred optical property to be changed or to be adjusted to make the supplemental connector undetectable to a viewer of the backlight unit.

[0052] In one experiment, a 1.1 mm thick light guide was bonded to a light board. The test light board included 1.4 mm square LED light sources positioned about 38 mm apart in one direction and about 39 mm apart in the second direction. Test supplemental connectors were positioned equally spaced between the light sources. The test supplemental connects were constructed using layers of an optically clear adhesive (OCA) on both sides of 6 mm diameter discs of white paper. The reflectivity of the paper discs were adjusted by printing variable shades of gray on the upward facing surface of the disks using a laser printer. The test backlight unit was assembled by applying the light guide to the light board with the test supplemental connectors positioned therebetween. A typical back reflector used in backlight assemblies is approximately 97% reflective. The experimental results revealed that the test supplemental connectors can be adjusted to be undetectable when a 1% density gray is printed on the paper disks, resulting in the reflectivity deceasing to about 80%. Reflectivity for purposes of the present disclosure describes an optical property of a material or surface that describes the ability of the material or surface to reflect light that is directed at or toward the material or surface. Reflectivity can be described using a percentage that measures the amount of light that is reflected relative to the light directed at or toward the material or surface. Thus, a surface that is about 97% reflective can reflect about 97% of the light that is directed at or toward the surface. Reflectivity of the diffuse reflectance surfaces discussed in the present disclosure can be measured using any suitable technique known in the art. In the experiments described herein, the reflectivity of the diffuse reflectance surfaces were measured using a diffuse reflectance measuring device that included a spectrometer and integrating sphere.

[0053] In light of the experimental results, it has been determined that the reflectivity of the back reflector on the light board at the connector locations can be adjusted to make the supplemental connectors undetectable to a viewer. In some examples, the back reflector (i.e., a region of the light board adjacent to the connector locations) can have a reflectivity in a range of about 90% to about 98%. In order to make the supplemental connectors undetectable, the optical properties of the light board (or the back reflector) at the connector locations can be adjusted to have a reflectivity of about 50% to about 90%. In another example, the light board or the back reflector can have a reflectivity of about 90% to about 98% at the regions adjacent to the connector locations and the light board or the back reflector can have a reflectivity of about 50% to about 85%. In yet another example, the light board or the back reflector can have a reflectivity of about 90% to about 98% at the regions adjacent to the connector locations and the light board or the back reflector can have a reflectivity of about 50% to about 80%. The reflectivity can be adjusted using any suitable technique such as printing a low density gray color ink onto the light board or onto the back reflector. The low density gray color ink (or other coating) can be deposited or printed using any suitable printing method (e.g., inkjet printing, screen printing, microprinting, etc.). The term low density in the context of the low density gray color previously described can be characterized, for example, by the printing or imaging software that can be used to print the gray color onto the substrate. Such software can, for example, use a percentage to characterize the density of gray color. In the example described above, the low density gray color was a 1% density gray. In other examples and depending on the specific construction of the backlight unit, other low density gray colors can be used such a low density gray in a range of 1% to 5% density gray. In still other examples, other densities can be used.

[0054] Referring now to FIG. 5, another example backlight unit 500 is shown. In this example, the light guide 502 can include a first light guide tile 504 and a second light guide tile 506. The backlight unit 500 can include two or more light guide tiles that can be bonded to the light board 102. This type of configuration can be used to improve the ability of the light guide tiles to be adjusted relative to the light board 102 to ensure that proper alignment is maintained to reduce the likelihood of mura at the light sources 106. One challenge that can arise in the context of a tiled light guide such as that shown in FIG. 5 is the likelihood of light extraction between a first edge 508 of the first light guide tile 504 and a second edge 510 of the second light guide tile 506. The first edge 508 and the second edge 510 can define a tile gap 512 through which light can escape. The tile gap 512 can appear as a bright spot or bright line when viewed by a user.

[0055] Even in instances in which the first light guide tile 504 and the second light guide tile 506 abut one another such that the tile gap 512 can be negligible, the surfaces and edge quality of the first edge 508 and the second edge 510 can cause light to extracted of each tile.

For example, scratches, dings and other defects at the edge surfaces can make the seam between the first edge 508 and the second edge 510 to be perceptible to a viewer.

[0056] In order to reduce the likelihood of light extraction at the tile gap 512 and to make the tile gap 512 undetectable to a viewer of the backlight unit 500, one or more measures can be taken. A first example is shown in FIG. 5. As shown, the light extractors 120 that are typically printed, etched or otherwise formed on the light guide 502 can be removed or not etched, printed or otherwise formed in a seam region 514. The seam region 514 can extend away from the first edge 508 and from the second edge 510 along the first light guide tile 504 and the second light guide tile 506, respectively. The width of the seam region 514 can be determined from experimentation and can depend on the structure and size of the light guide tiles. Experimental results indicate that the seam region can have a width of about 3 mm on the top surface of each light guide tile. In other examples, the seam region 514 can have a width measured along the top surface of each light guide tile of about 0.5 mm to about 5 mm. In other examples, the seam region can have other widths.

[0057] Another measure that can be taken to make the tile gap 512 (or tile seam) undetectable to a viewer is to add a supplemental connector at the tile gap 512. An example backlight unit 600 shows a configuration in which a supplemental connector 610 is positioned between the light board 102 and the light guide 502. In the configuration shown, the supplemental connector 610 is positioned at a connector location 612 aligned with the tile gap 512. In instances in which the first light guide tile 504 abuts the second light guide tile 506, the connector location 612 can be aligned with the first edge 508 and the second edge 510.

[0058] The supplemental connector 610 can be similar to the supplemental connector 410 previously described. The supplemental connector 610 can be made of an OCA or a mounting tape, for example. The supplemental connector 610, however, can extend along the entire gap or seam between adjacent light guide tiles, such as between the first light guide tile 504 and the second light guide tile 506. As shown, the supplemental connector 610 can be positioned between light sources 106 and can be aligned with the first edge 508 and/or the second edge 510. In this position, the supplemental connector 610 can not only bond the first light guide tile 504 and the second light guide tile 506 to the light board 102 but also can cause the tile gap 512 (or the tile seam) and the supplemental connector 610 to be undetectable to a viewer of the backlight unit 600.

[0059] An optical property of the supplemental connector 610 or of the light board 102 at the connector location 612 can be made different from the optical property of the light guide adjacent to the connector location 612 to cause the supplemental connector and the tile gap or seam to be undetectable to a viewer of the backlight unit 600. In some examples, a transparency or a reflectivity of the supplemental connector 610 can be adjusted to cause the supplemental connector and the tile gap or seam to be undetectable to a viewer of the backlight unit 600. In other examples, a reflectivity of the back reflector 110 can be adjusted to cause the supplemental connector and the tile gap or seam to be undetectable to a viewer of the backlight unit 600. For example, a colored ink or other coating can be printed on the supplemental connector 610 or on the back reflector 110 at the connector location 612 to cause the supplemental connector and the tile gap or seam to be undetectable to a viewer of the backlight unit 600.

[0060] Experimental results have verified the successful implementation of the structure of the backlight unit 600 shown in FIG. 6. In one experiment, a 5 mm wide strip of polyester (PET) film was used as the supplemental connector. The supplemental connector was placed between the light board and the edges of a first light guide tile and a second light guide tile. Before an OCA was added to both sides of the PET film, a layer of yellow ink was printed on the PET film using a laser printer. The density of the yellow ink was varied during the testing. In one test, the density of the yellow ink printed on the PET film corresponded to 10% opacity as set by the image generating software. According to measurements, adding this density of yellow ink to the PET film causes the film transmission in the blue wavelength (450 nm) to decrease to about 75% while leaving the PET film mostly transparent (measuring 92% due to reflection on both surfaces) in the green wavelength (550 nm) and the red wavelength (650 nm).

[0061] Based on the experiments described above, it has been confirmed that the tile gap and/or the tile seam as well as the supplemental connector can be made to be undetectable to a viewer of the backlight unit by adjusting the transmission of the blue wavelength. In examples in which the transparency of the supplemental connector (e.g., a mounting tape) is adjusted, the transmission of the supplemental connector needs to be reduced to about 50% to 90% in the blue wavelength. In examples in which the back reflector is adjusted and the supplemental connector is maintained as substantially clear or transparent, the reflectivity of the back reflector at the connector location can be reduced 25% to 80% in the blue wavelength. In order to implement changes in the optical properties of the supplemental connector or the back reflector, various embodiments can be used. For example, a low density yellow ink can be printed on a top surface of the supplemental connector (e.g., a mounting tape). In another example, a low density yellow ink can be printed on a bottom surface of the supplemental connector (e.g., a mounting tape). In another example, a low density ink can be printed on the back reflector surface at the connector location under a clear supplemental connector (e.g., a mounting tape). In still another example, a low density yellow pigment can be added to the material of the supplemental connector to tint the supplemental connector.

[0062] In the above experiment and in the above recommended transmission changes to the supplemental connector and/or the back reflector, a light board was used that included LEDs that emit a blue light. This often the case with state-of-the-art backlight units in modern displays. The backlight units include various optical films and other layers positioned above light guide and/or the light guide tiles. A more complete backlight unit is illustrated in FIG. 7.

In this example, the backlight unit 600 previously described is shown with a bulk diffuser plate 702 and various optical layers and films 704 positioned adjacent the light guide 502. The optical layers and films 704 can include a Brightness Enhancement Film (BEF), a Dual Brightness Enhancement Film (DBEF), a reflective polarizer, diffuser films, and a quantum dot (QD) color converter layer, for example. The quantum dot (QD) color converting layer can be used to add red light and green light to the backlight output. It should be noted that the optical layers and films 704 also play a role in washing out the remaining local brightness variations that may exist in the backlight unit 600. In addition, since the LEDs in the light board 102 included LEDs that emit blue light, there is excess blue light that needs to be attenuated by the supplemental connector 610 at the edges of the first light guide tile 504 and the second light guide tile 506.

[0063] If other light boards are used that include light sources or LEDs that emit other colors of light or emit a white light, the optical property of the supplemental connector and/or of the back reflector can be adjusted to attenuate the necessary colors of light as needed to cause the supplemental connector and/or the tile gap or tile seam to be undetectable to viewer of the backlight. For example, in instances in which the light board includes light sources that emit white light and in which the quantum dot (QD) color converter layer is not present, the supplemental connector used at the edges of the first light guide tile 504 and the second light guide tile 506 can have a neutral gray color printed at the connector location to attenuate all colors by roughly the same amount as previously described with respect to the supplemental connector 410 of FIG. 4.

[0064] Another example backlight unit 800 is shown in FIG. 8. In this example, the backlight unit 800 can include a first light guide tile 802, a second light guide tile 804 and a light board 806. The backlight unit 800 is similar to the backlight units previously described. The backlight unit 800 illustrates an embodiment in which the light guide tiles 802, 804 can be bonded to the light board 806 using supplemental connectors both positioned between light sources 106 on a single light guide tile and at the edges of light guide tiles. As shown, the backlight unit 800 can include a first supplemental connector 810 and a second supplemental connector 820. The first supplemental connector 810 can be positioned between light sources 106 to add additional mechanical bonding strength to secure the second light guide tile 806 to the light board 806. The first supplemental connector 810 can be similar to the supplemental connector 410 previously described. The transparency or reflectivity of the first supplemental connector 810 or of the back reflector 110 at the first connector location 812 can be adjusted to cause the first supplemental connector 810 to be undetectable to a viewer of the backlight unit 800.

[0065] The second supplemental connector 820 can be positioned at a second connector location 822 that can extend along the edge 814 of the first light guide tile 802 and along the edge 816 of the second light guide tile 804. The second supplemental connector 820 can be similar to the supplemental connector 610 previously described. The transparency or reflectivity of the second supplemental connector 820 or of the back reflector 110 at the second connector location 822 can be adjusted to cause the second supplemental connector 820 and the tile gap or tile seam between the edges 814, 816 to be undetectable to a viewer of the backlight unit 800.

[0066] As can be appreciated, the structure of the backlight unit 800 can be reproduced in backlight units that are constructed to be used in large display units. Thus, supplemental connectors like the first supplemental connector 810 can be included between each of the light sources on a light board that includes an array of light sources as previously described. In addition, supplemental connectors like the second supplemental connector 820 can be used at the seams between each of the light guide tiles that may be used to build a large backlight unit. The second supplemental connector 820 can extend in either direction along edges of the light guides tiles.

[0067] Referring now to FIG. 9, a method 900 of assembling a backlight unit is shown. The method 900 can be used, for example, to assemble one of the backlight units previously described. For the sake of brevity, the backlight unit 800 shown in FIG. 8 is used to describe the method 900. It should be appreciated, however, that the method (or variations thereof) can be used to assemble the backlight units 400, 600 as well.

[0068] At step 902, a light board is provided. The light board can be the light board 806, for example. The light board can include multiple light sources 106 that can be arranged in an array or other pattern along the light board. The light sources 106 can project away from the mounting board of the light board 806 such that the light sources 106 can extend above the mounting board when the light board is oriented horizontally.

[0069] At step 904, supplemental connectors can be positioned between the light sources. In the example backlight unit 800, first supplemental connectors 810 can be positioned between the light sources 106. The first supplemental connectors 810 can be positioned at about an equal distance from each of the light sources 106. The first supplemental connectors 810 can be positioned on the light board 806 using an adhesive or other connection means. The first supplemental connectors 810 can have an optical property that is different from an optical property of the light board in a region adjacent to the first connector location 812. In this manner, the first supplemental connectors 810 can be undetectable by a viewer of the backlight unit when the backlight unit is used in a display device. [0070] At step 906, supplemental connectors can be positioned at edge locations. In the example backlight 800, the second supplemental connectors 820 can be positioned at a location that is aligned with the first edge 814 and/or the second edge 816 of the first light guide tile 802 and the second light guide tile 804, respectively. The second supplemental connector 820 can be a length of mounting tape, for example. The second supplemental connector 820 can have an optical property that is different from an optical property of the light board in a region adjacent to the second connector location 822. In this manner, the second supplemental connector 820 and the edges 814, 816 can be undetectable by a viewer of the backlight unit when the backlight unit is used in a display device.

[0071] At step 908, primary connectors can be applied to the light sources. In the example backlight unit 800, a mounting tape or a layer of adhesive, such as an optically clear adhesive (OCA) can be applied to surface of the light sources 106 that face the first light guide tile 802 and/or the second light guide tile 804.

[0072] At step 910, the light guide can be applied to the light board. The first light guide tile 802 and the second light guide tile 804 can be applied to the light board 806 such that force is applied at each of the locations at which the light guide tiles 802, 804 contacts either the light sources 106, the first supplemental connectors 810 and the second supplemental connectors 820. An application force can be applied, for example, by pulling a vacuum to draw the light guide tiles 802, 804 and the light board 806 together or by applying a hydrostatic pressure to the light guide tiles 802, 804 and/or to the light board 806. In other examples, the application force can be applied using other methods. As can be appreciated, when the first light guide tile 802 and/or the second light guide tile 804 is applied to the light board, the light guide tile is aligned with the light board to ensure that proper alignment is maintained between the light guide tiles 802, 804 and the light board 806.

[0073] The methods and system described herein may be at least partially embodied in the form of computer-implemented processes and apparatus for practicing those processes. The disclosed methods may also be at least partially embodied in the form of tangible, non-transient machine readable storage media encoded with computer program code. The media may include, for example, RAMs, ROMs, CD-ROMs, DVD-ROMs, BD-ROMs, hard disk drives, flash memories, or any other non-transient machine-readable storage medium, or any combination of these mediums, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the method. The methods may also be at least partially embodied in the form of a computer into which computer program code is loaded and/or executed, such that, the computer becomes an apparatus for practicing the methods. When implemented on a general-purpose processor, the computer program code segments configure the processor to create specific logic circuits. The methods may alternatively be at least partially embodied in a digital signal processor formed of application specific integrated circuits for performing the methods.

[0074] Although the subject matter has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments, which may be made by those skilled in the art.

Claims

What is claimed is:

1. A backlight unit comprising: a light board comprising a first light source and a second light source; a light guide positioned adjacent to the light board to distribute light emitted from the first light source and the second light source; and a connector positioned at a connector location between the first light source and the second light source to bond the light guide to the light board, wherein an optical property of the light board at the connector location or of the connector is different from an optical property at adjacent locations to make the connector undetectable to a viewer of the backlight unit.

2. The backlight unit of claim 1, wherein the optical property comprises a transparency of the connector.

3. The backlight unit of claim 1, wherein the connector is tinted with a gray color to reduce the transparency of the supplemental connector.

4. The backlight unit of claim 1, wherein the connector is tinted with a yellow color.

5. The backlight unit of claim 1, wherein the optical property comprises a reflectivity of the light board at the connector location.

6. The backlight unit of claim 1, wherein a reflectivity of the light board at the connector location is lower than a reflectivity of the light board adjacent to the connector location.

7. The backlight unit of claim 1, wherein the light board comprises a gray color coating at the connector location.

8. The backlight unit of claim 1, wherein the light board comprises a yellow color coating at the connector location.

9. The backlight unit of claim 1, wherein the light guide comprises a first light guide tile including a first edge and a second light guide tile including a second edge, the connector aligned with the first edge and the second edge.

10. The backlight unit of claim 1, wherein the light board comprises an array of light sources and the connector is positioned between adjacent light sources in the array of light sources.

11. The backlight unit of claim 1, wherein the light guide is bonded to the first light source and the second light source.

12. A backlight unit for use in a display, the backlight unit comprising: a light board comprising a plurality of light sources; a first light guide tile and a second light guide tile positioned adjacent to each other with a first edge of the first light guide tile positioned adjacent to a second edge of the second light guide tile to define a tile seam between the first light guide tile and the second light guide tile; and a connector positioned between the light board and the first light guide tile and the second light guide tile at the tile seam, wherein the connector bonds the first light guide tile and the second light guide tile to the light board.

13. The backlight unit of claim 12, wherein a portion of the light board at a connection location of the connector has a lower reflectivity than adjacent portions of the light board to cause the connector and the first edge and the second edge to be undetectable by a viewer of the backlight unit.

14. The backlight unit of claim 13, wherein the reflectivity of the portion of the light board at the connection location is reduced to have a reflectivity of blue light in a range of about 25% to about 80%.

15. The backlight unit of claim 12, wherein the connector is tinted to reduce the transmission of light at a connector location of the connector to cause the supplemental connector and the first edge and the second edge to be undetectable by a viewer of the backlight unit.

16. The backlight unit of claim 15, wherein a transmission of blue light having a wavelength of about 450 nm by the connector is reduced to be in a range of about 50% to about 90%.

17. A method of assembling a backlight unit comprising: positioning a connector on a light board at a connector location between a first light source and a second light source; and bonding a light guide plate to the light board at the connector location.

18. The method of claim 17, wherein the connector is tinted to reduce transmission of light at the connector location.

19. The method of claim 17, wherein a portion of the light board at the connection location has a lower reflectivity relative to adjacent portions of the light board.

20. The system of claim 17, further comprising positioning the connector to align with an edge of the light guide plate.