WO2018144509A1

WO2018144509A1 - Backlight unit with 2d local dimming

Info

Publication number: WO2018144509A1
Application number: PCT/US2018/016090
Authority: WO
Inventors: Xiang-Dong Mi; Steven S. Rosenblum
Original assignee: Corning Incorporated
Priority date: 2017-01-31
Filing date: 2018-01-31
Publication date: 2018-08-09
Also published as: TW201835655A

Abstract

Disclosed herein are backlight units comprising a light guide plate having an array of holes and a plurality of light extraction features, a light source positioned in at least one of the holes in the array of holes, and an optical layer positioned on a light-emitting major surface of the light guide plate, the optical layer having at least two regions with different optical properties. Display and lighting devices comprising such backlight units are further disclosed.

Description

BACKLIGHT UNIT WITH 2D LOCAL DIMMING

FIELD OF THE DISCLOSURE

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 62/452,470 filed on January 31, 2017, the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

BACKGROUND

[0002] The disclosure relates generally to backlight units and display or lighting devices comprising such backlight units, and more particularly to backlight units comprising light sources positioned in a light guide plate having an array of holes

[0003] Liquid crystal displays (LCDs) are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. LCDs can comprise a backlight unit (BLU) for producing light that can then be converted, filtered, and/or polarized to produce the desired image. BLUs may be edge-lit, e.g., comprising a light source coupled to an edge of a light guide plate (LGP), or back-lit, e.g., comprising a two-dimensional array of light sources disposed behind the LCD panel.

[0004] Direct-lit BLUs may have the advantage of improved dynamic contrast as compared to edge-lit BLUs. For example, a display with a direct-lit BLU can independently adjust the brightness of each LED to optimize the dynamic range of the brightness across the image. This is commonly known as local dimming. However, to achieve desired light uniformity and/or to avoid hot spots in direct-lit BLUs, the light source(s) may be positioned at a distance from the LGP and/or the diffuser film, thus making the overall display thickness greater than that of an edge-lit BLU. While edge-lit BLUs may be thinner, the light from each LED can spread across a large region of the LGP such that turning off individual LEDs or groups of LEDs may have only a minimal impact on the dynamic contrast ratio.

[0005] Accordingly, it would be advantageous to provide thin BLUs having improved local dimming efficiency without negatively impacting the uniformity of light emitted by the BLU. It would also be advantageous to provide backlights having a thinness similar to that of edge-lit BLUs while also providing local dimming capabilities similar to that of direct-lit BLUs. SUMMARY

[0006] The disclosure relates, in various embodiments, to backlight units comprising a light guide plate having an array of holes and a plurality of light extraction features; a light source positioned in at least one of the holes in the array of holes; and an optical layer positioned on a light-emitting major surface of the light guide plate. The optical layer can comprise a first region disposed over the at least one hole and a second region disposed over a portion of the light guide plate adjacent to the at least one hole and the first and second regions of the optical layer can have different optical properties, such as different diffuse reflectance or diffuse transmittance. Display and lighting devices comprising such backlight units are also disclosed herein.

[0007] According to various embodiments, a first diffuse reflectance of the first region of the optical layer is greater than a second diffuse reflectance of the second region of the optical layer. In other embodiments, a first diffuse transmittance of the first region of the optical layer is less than a second diffuse transmittance of the second region of the optical layer. According to further embodiments, a first intensity of light transmitted through the first region of the optical layer is within about 5% of a second intensity of light transmitted through the second region.

[0008] In certain embodiments, the light guide plate may comprise glass. The light source may be chosen, for example, from side-emitting LEDs. According to non- limiting embodiments, at least one major surface of the LGP may be patterned with a plurality of light extraction features or the LGP matrix may comprise a plurality of light extraction features. The light extraction features may include, for instance, light-scattering particles, laser-damaged sites, and/or roughened surface features. In certain embodiments, the plurality of light extraction features may comprise a gradient or grid pattern.

[0009] Additional features and advantages of the disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the methods as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0010] It is to be understood that both the foregoing general description and the following detailed description present various embodiments of the disclosure, and are intended to provide an overview or framework for understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure and together with the description serve to explain the principles and operations of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following detailed description can be further understood when read in conjunction with the following drawings.

[0012] FIG. 1 illustrates a light guide plate comprising an array of holes and light sources positioned in the holes;

[0013] FIG. 2 illustrates an exemplary optical layer according to certain embodiments of the disclosure;

[0014] FIG. 3 illustrates a cross sectional view of a light guide assembly according to various embodiments of the disclosure;

[0015] FIG. 4 is a graphical depiction of angular emission intensity distribution of an exemplary LED; and

[0016] FIG. 5 is a plot of light extraction feature density according to

embodiments of the disclosure.

DETAILED DESCRIPTION

[0017] Disclosed herein are backlight units comprising a light guide plate having an array of holes and a plurality of light extraction features; a light source positioned in at least one of the holes in the array of holes; and an optical layer positioned on a light-emitting major surface of the light guide plate. The optical layer can comprise a first region disposed over the at least one hole and a second region disposed over a portion of the light guide plate adjacent to the at least one hole and the first and second regions of the optical layer can have different optical properties, such as different diffuse reflectance or diffuse transmittance.

[0018] Devices comprising such backlights are also disclosed herein, such as display, lighting, and electronic devices, e.g., televisions, computers, phones, tablets, and other display panels, luminaires, solid-state lighting, billboards, and other architectural elements, to name a few.

[0019] Various embodiments of the disclosure will now be discussed with reference to FIGS. 1-5, which illustrate exemplary components of the backlight units disclosed herein. The following general description is intended to provide an overview of the claimed devices, and various aspects will be more specifically discussed throughout the disclosure with reference to the non-limiting depicted embodiments, these embodiments being interchangeable with one another within the context of the disclosure.

[0020] FIG. 1 illustrates an exemplary light guide plate (LGP) 100 comprising an array of holes 105. At least one light source 110 can be positioned in at least one hole in the array of holes 105. While the illustrated embodiment comprises a light source 110 in each hole, other embodiments are contemplated in which only certain holes comprise light sources. Additionally, alternative LGP configurations are intended to fall within the scope of the disclosure, including different hole locations, sizes, shapes, and/or spacing. For instance, while the depicted embodiment includes a periodic or regular array of holes having the same size, shape, and spacing, other embodiments are contemplated in which the array is irregular or non-periodic. Furthermore, each hole in the array of holes can have any size and/or shape as appropriate to accommodate a desired light source and/or light output including, but not limited to, circular holes, square holes, rectangular holes, and other polygonal or curvilinear shapes, which may be regular or irregular. The portion 115 of the LGP 100 located between the holes may similarly vary in dimension and/or shape.

[0021] The LGP 100 may have any dimensions, such as length L and width W, which can vary depending on the display or lighting application. In some embodiments, the length L can range from about 0.01 m to about 10 m, such as from about 0.1 m to about 5 m, from about 0.5 m to about 2.5 m, or from about 1 m to about 2 m, including all ranges and subranges therebetween. Similarly, the width W can range from about 0.01 m to about 10 m, such as from about 0.1 m to about 5 m, from about 0.5 m to about 2.5 m, or from about 1 m to about 2 m, including all ranges and subranges therebetween. Each hole in the array of holes 105 may also define a unit block (represented by dashed lines) having an associated unit length L₀ and unit width Wo, which can vary depending on the dimensions of the LGP 100 and the number and/or spacing of the holes 105 along the LGP 100. The length L and the width W of the LGP may, in some embodiments be substantially equal or they may be different. Similarly, the unit length Lo and the unit width Wo may be substantially equal or they may be different.

[0022] Of course, while a rectangular LGP 100 is illustrated in FIG. 1, it is to be understood that the LGP may have any regular or irregular shape as appropriate to produce a desired light distribution for a chosen application. The LGP 100 may comprise four edges as illustrated in FIG. 1, or may comprise more than four edges, e.g. a multi-sided polygon. In other embodiments, the LGP 100 may comprise less than four edges, e.g., a triangle. By way of a non-limiting example, the LGP may comprise a rectangular, square, or rhomboid sheet having four edges, although other shapes and configurations are intended to fall within the scope of the disclosure including those having one or more curvilinear portions or edges.

[0023] According to various embodiments, the LGP may comprise any transparent material used in the art for lighting and display applications. As used herein, the term "transparent" is intended to denote that the LGP has an optical transmission of greater than about 80% over a length of 500 mm in the visible region of the spectrum (~420-750nm). For instance, an exemplary transparent material may have greater than about 85%

transmittance in the visible light range over a length of 500 mm, such as greater than about 90%, greater than about 95%, or greater than about 99% transmittance, including all ranges and subranges therebetween. In certain embodiments, an exemplary transparent material may have an optical transmittance of greater than about 50% in the ultraviolet (UV) region (-100- 400nm) over a length of 500 mm, 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.

[0024] The optical properties of the LGP may be affected by the refractive index of the transparent material. According to various embodiments, the LGP may have a refractive index ranging from about 1.3 to about 1.8, such as from about 1.35 to about 1.7, from about 1.4 to about 1.65, from about 1.45 to about 1.6, or from about 1.5 to about 1.55, including all ranges and subranges therebetween. In other embodiments, the LGP may have a relatively low level of light attenuation (e.g., due to absorption and/or scattering). The light attenuation (a) of the LGP may, for example, be less than about 5 dB/m for wavelengths ranging from about 420-750 nm. For instance, a may be less than about 4 dB/m, less than about 3 dB/m, less than about 2 dB/m, less than about 1 dB/m, less than about 0.5 dB/m, less than about 0.2 dB/m, or even less, including all ranges and subranges therebetween, e.g., from about 0.2 dB/m to about 5 dB/m.

[0025] The LGP 100 may comprise polymeric materials, such as plastics, e.g., polymethyl methacrylate (PMMA), methylmethacrylate styrene (MS), polydimethylsiloxane (PDMS), or other similar materials. The LGP 100 can also comprise a glass material, such as aluminosilicate, alkali-aluminosilicate, borosilicate, alkali-borosilicate, aluminoborosilicate, alkali-aluminoborosilicate, soda lime, or other suitable glasses. Non-limiting examples of commercially available glasses suitable for use as a glass light guide include, for instance, EAGLE XG^®, Lotus™, Willow^®, Iris™, and Gorilla^® glasses from Corning Incorporated. [0026] Some non-limiting glass compositions can include between about 50 mol % to about 90 mol% Si0₂, between 0 mol% to about 20 mol% A1₂0₃, between 0 mol% to about 20 mol% B₂O₃, and between 0 mol% to about 25 mol% R_xO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1. In some embodiments, R_xO - A1₂0₃ > 0; 0 < R_xO - A1₂0₃ < 15; x = 2 and R₂0 - A1₂0₃ < 15; R₂0 - A1₂0₃ < 2; x=2 and R₂0 - A1₂0₃ - MgO > -15; 0 < (R_xO - A1₂0₃) < 25, -11 < (R₂0 - A1₂0₃) < 11, and -15 < (R₂0 - A1₂0₃ - MgO) < 11 ; and/or -1 < (R₂0 - A1₂0₃) < 2 and -6 < (R₂0 - A1₂0₃ - MgO) < 1. In some embodiments, the glass comprises less than 1 ppm each of Co, Ni, and Cr. In some embodiments, the concentration of Fe is < about 50 ppm, < about 20 ppm, or < about 10 ppm. In other embodiments, Fe + 30Cr + 35Ni < about 60 ppm, Fe + 30Cr + 35Ni < about 40 ppm, Fe + 30Cr + 35Ni < about 20 ppm, or Fe + 30Cr + 35Ni < about 10 ppm. In other embodiments, the glass comprises between about 60 mol % to about 80 mol% Si0₂, between about 0.1 mol% to about 15 mol% A1₂0₃, 0 mol% to about 12 mol% B₂0₃, and about 0.1 mol% to about 15 mol% R_xO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1.

[0027] In other embodiments, the glass composition can comprise between about 65.79 mol % to about 78.17 mol% Si0₂, between about 2.94 mol% to about 12.12 mol% A1₂0₃, between about 0 mol% to about 11.16 mol% B₂0₃, between about 0 mol% to about 2.06 mol% Li₂0, between about 3.52 mol% to about 13.25 mol% Na₂0, between about 0 mol% to about 4.83 mol% K₂0, between about 0 mol% to about 3.01 mol% ZnO, between about 0 mol% to about 8.72 mol% MgO, between about 0 mol% to about 4.24 mol% CaO, between about 0 mol% to about 6.17 mol% SrO, between about 0 mol% to about 4.3 mol% BaO, and between about 0.07 mol% to about 0.11 mol% Sn0₂.

[0028] In additional embodiments, the glass can comprise an R_X0/A1₂0₃ ratio between 0.95 and 3.23, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2. In further embodiments, the glass may comprise an R_X0/A1₂0₃ ratio between 1.18 and 5.68, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1. In yet further embodiments, the glass can comprise an R_xO - A1₂0₃ - MgO between - 4.25 and 4.0, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2. In still further embodiments, the glass may comprise between about 66 mol % to about 78 mol% Si0₂, between about 4 mol% to about 11 mol% A1₂0₃, between about 4 mol% to about 11 mol% B₂0₃, between about 0 mol% to about 2 mol% Li₂0, between about 4 mol% to about 12 mol% Na₂0, between about 0 mol% to about 2 mol% K₂0, between about 0 mol% to about 2 mol% ZnO, between about 0 mol% to about 5 mol% MgO, between about 0 mol% to about 2 mol% CaO, between about 0 mol% to about 5 mol% SrO, between about 0 mol% to about 2 mol% BaO, and between about 0 mol% to about 2 mol% Sn0₂.

[0029] In additional embodiments, the glass can comprise between about 72 mol % to about 80 mol% S1O2, between about 3 mol% to about 7 mol% AI2O3, between about 0 mol% to about 2 mol% B2O3, between about 0 mol% to about 2 mol% L12O, between about 6 mol% to about 15 mol% Na₂0, between about 0 mol% to about 2 mol% K₂0, between about 0 mol% to about 2 mol% ZnO, between about 2 mol% to about 10 mol% MgO, between about 0 mol% to about 2 mol% CaO, between about 0 mol% to about 2 mol% SrO, between about 0 mol% to about 2 mol% BaO, and between about 0 mol% to about 2 mol% Sn0₂. In certain embodiments, the glass can comprise between about 60 mol % to about 80 mol% S1O2, between about 0 mol% to about 15 mol% AI2O3, between about 0 mol% to about 15 mol% B₂O₃, and about 2 mol% to about 50 mol% R_xO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein Fe + 30Cr + 35Ni < about 60 ppm.

[0030] In some embodiments, the LGP 100 can comprise a color shift Ay less than 0.015, such as ranging from about 0.005 to about 0.015 (e.g., about 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, or 0.015). In other embodiments, the LGP can comprise a color shift less than 0.008. Color shift may be characterized by measuring variation in the x and y chromaticity coordinates along the length L using the CIE 1931 standard for color measurements. For LGPs the color shift Ay can be reported as Ay=y(L₂)- y(Li) where L2 and Li are Z positions along the panel or substrate direction away from the source launch and where L₂-Li=0.5 meters. Exemplary LGPs have Ay< 0.01, Ay< 0.005, Ay < 0.003, or Ay < 0.001. According to certain embodiments, the LGP can have a light attenuation ai (e.g., due to absorption and/or scattering losses) of less than about 4 dB/m, such as less than about 3 dB/m, less than about 2 dB/m, less than about 1 dB/m, less than about 0.5 dB/m, less than about 0.2 dB/m, or even less, e.g., ranging from about 0.2 dB/m to about 4 dB/m, for wavelengths ranging from about 420-750 nm.

[0031] The LGP 100 may, in some embodiments, comprise glass that has been chemically strengthened, e.g., ion exchanged. During the ion exchange process, ions within a glass sheet at or near the surface of the glass sheet may be exchanged for larger metal ions, for example, from a salt bath. The incorporation of the larger ions into the glass can strengthen the sheet by creating a compressive stress in a near surface region. A

corresponding tensile stress can be induced within a central region of the glass sheet to balance the compressive stress. [0032] Ion exchange may be carried out, for example, by immersing the glass in a molten salt bath for a predetermined period of time. Exemplary salt baths include, but are not limited to, K O₃, L1NO₃, NaNCh, RbNCh, and combinations thereof. The temperature of the molten salt bath and treatment time period can vary. It is within the ability of one skilled in the art to determine the time and temperature according to the desired application. By way of a non-limiting example, the temperature of the molten salt bath may range from about 400°C to about 800°C, such as from about 400°C to about 500°C, and the predetermined time period may range from about 4 to about 24 hours, such as from about 4 hours to about 10 hours, although other temperature and time combinations are envisioned. By way of a non- limiting example, the glass can be submerged in a KNO3 bath, for example, at about 450°C for about 6 hours to obtain a K-enriched layer which imparts a surface compressive stress.

[0033] Referring to FIG. 2, which depicts an exemplary optical layer 120, the optical layer may have at least two regions with different optical properties. For instance, a first region 125 may correspond to at least one hole in the array of holes 105 of the LGP 100, as illustrated in FIG. 1. A second region 130 may correspond to a portion 115 of the LGP 100 between the holes 105, as illustrated in FIG. 1. Upon assembly, as depicted in FIG. 3, the first region 125 may be disposed over at least one hole and the second region 130 may be disposed over LGP portions adjacent or between the holes. The optical layer 120 may comprise any material capable of at least partially modifying the light output from the LGP 100. In some embodiments, the optical layer 120 may comprise a diffusing film. In such instances, the first and second regions 125, 130 of the optical layer 120 may have different diffuse reflectance. In other embodiments, the optical layer 120 may adjust the amount of light transmitted by the LGP 100. For example, the first and second regions 125, 130 of the optical layer 120 may have different diffuse transmittance.

[0034] According to various embodiments, a first diffuse reflectance of the first region 125 may be about 50% or greater and a second diffuse reflectance of the second region 130 may be about 20% or less. For example, the first diffuse reflectance may be at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90%, such as ranging from about 50% to 100%, including all ranges and subranges therebetween. The second diffuse reflectance may be about 20% or less, about 15% or less, about 10% or less, or about 5% or less, such as ranging from 0% to about 20%, including all ranges and subranges therebetween. In some embodiments, the first diffuse reflectance may be at least about 2.5 times greater than the second diffuse reflectance, e.g., about 3 times greater, about 4 times greater, about 5 times greater, about 10 times greater, about 15 times greater, or about 20 times greater, such as from about 2.5 to about 20 times greater, including all ranges and subranges therebetween. Diffuse reflectance of the optical layer 120 may be measured, for example, by a UV/Vis spectrometer available from Perkin Elmer.

[0035] In additional non-limiting embodiments, a first diffuse transmittance of the first region 125 may be about 50% or less and the second diffuse transmittance of second region 130 may be about 80% or greater. For example, the first diffuse transmittance may be about 50% or less, about 40% or less, about 30% or less, about 20% or less, or about 10% or less, such as ranging from 0% to about 50%, including all ranges and subranges

therebetween. The second diffuse transmittance may be 80% or greater, about 85% or greater, about 90% or greater, or about 95% or greater, such as from about 80% to 100%, including all ranges and subranges therebetween. In some embodiments, the second diffuse transmittance may be at least about 1.5 times greater than the first diffuse transmittance, e.g., about 2 times greater, about 3 times greater, about 4 times greater, about 5 times greater, about 10 times greater, about 15 times greater, or about 20 times greater, such as from about 1.5 to about 20 times greater, including all ranges and subranges therebetween. Diffuse transmittance of the optical layer 120 may be measured, for example, by the UV/Vis spectrometer available from Perkin Elmer.

[0036] While FIG. 2 illustrates discrete first and second regions 125, 130, it is also to be understood that a gradient may exist between these two regions, e.g., a gradient of increasing diffuse reflectance from the second region to the first region, or a gradient of increasing diffuse transmittance from the first region to the second region, and so forth.

[0037] While FIG. 2 illustrates a single optical film, it is to be understood that the optical layer 120 may comprise multiple pieces, films, or layers. For example, portions of the optical layer corresponding to the first region 125 may first be positioned over the holes 105 of the LGP 100, and portions of the optical layer corresponding to the second region 130 may subsequently be placed over the remainder of the LGP, e.g., the portions 115 between the holes, or vice versa. Alternatively, portions of a first film or layer having first optical properties may be positioned over the holes 105 of the LGP 100 and a second film or layer having second optical properties may be overlaid to cover substantially all of the LGP 100, including the first region 125, or vice versa. In such an embodiment, the first region 125 of the multi-layer optical layer can have the aggregate optical properties of the first and second films while the second region 130 can have the optical properties of the second film alone, or vice versa. The optical layer 120 may thus comprise a single film or a composite film, a single layer or multiple layers, as appropriate to produce the desired optical effect. [0038] In some embodiments, the first region 125 of the optical layer is positioned over only the holes 105 of the LGP 100 and the second region 130 is positioned over only the portions 115 of the LGP 100 between the holes 105. Regardless of the optical layer configuration, it is to be understood that embodiments disclosed herein can comprise an optical layer having at least one optical property that is different in first regions

corresponding to the holes 105 of the LGP (e.g., higher diffuse reflectance and/or lower diffuse transmittance) as compared to second regions corresponding to the portions 115 between holes (e.g., lower diffuse reflectance and/or higher diffuse transmittance).

Furthermore, embodiments of BLUs disclosed herein may produce substantially uniform light, e.g., light emanating from regions corresponding to the holes of the LGP may have a luminance that is substantially equal to that of light emanating from regions between the holes of the LGP.

[0039] In various embodiments, the luminance of light measured through the first region 125 of the optical layer 120 may be substantially the same as that measured through the second region 130 of the optical layer 120. For example, a first luminance of the first region 125 may be within about 10% of a second luminance of the second region 130, such as within about 0.01 % to about 10%, within about 0.1% to about 5%, within about 1% to about 4%, or within about 2% to about 3%, including all ranges and subranges therebetween. Light intensity may be measured by any luminance meter, for example, PR650 available from Photo Research.

[0040] FIG. 3 illustrates a cross-sectional view of a non-limiting light guide assembly comprising an optical layer 120 positioned on an LGP 100 comprising an array of holes 105 (one hole illustrated). The LGP 100 may comprise a light emitting first major surface 140 and an opposing second major surface 150. The major surfaces may, in certain embodiments, be planar or substantially planar and/or parallel or substantially parallel. In certain embodiments, the LGP 100 may have a thickness t extending between the first and second major surfaces of less than or equal to about 3 mm, for example, ranging from about 0.1 mm to about 2.5 mm, from about 0.3 mm to about 2 mm, from about 0.5 mm to about 1.5 mm, or from about 0.7 mm to about 1 mm, including all ranges and subranges therebetween.

[0041] The optical layer 120 may be positioned on the light emitting surface 140 of the LGP 100. The term "positioned on" and variations thereof is intended to denote that a component or layer is located on a particular surface of a listed component, but not necessarily in direct physical contact with that surface. For instance, the optical layer 120 is depicted in FIG. 3 in direct physical contact with light emitting surface 140; however, in some embodiments, other layers or films may be present between these two components. As such, a component A positioned on a surface of component B may or may not be in direct physical contact with component B.

[0042] As shown in FIG. 3, the first region 125 of the optical layer 120

corresponds to at least one hole 105 in the LGP and the second region 130 corresponds to a portion 115 of the LGP between holes 105. The backlight unit may comprise one or more additional films or components, such as a reflective film 160 and/or at least one supplemental optical film 170. The reflective film 160 may be positioned on the opposing second major surface 150 of the LGP 100, either in direct physical contact or with other films or layers positioned therebetween, e.g., an adhesive layer. Exemplary reflective films 160 include, but are not limited to, metallic foils, such as silver, platinum, gold, copper, and the like. The supplemental optical film(s) 170 may be positioned on the light emitting first major surface 140 of the LGP 100, e.g., with the optical layer 120 between the LGP 100 and supplemental optical film(s) 170, or vice versa. Exemplary supplemental optical films 170 can include, but are not limited to, diffusing films, prismatic films, e.g., a brightness enhancing film (BEF), or reflective polarizing films, e.g., a dual brightness enhancing film (DBEF), to name a few. While not illustrated in FIG. 3, the BLUs disclosed herein may comprise or may be combined with other components typically present in display and lighting devices, such as a thin film transistor (TFT) array, a liquid crystal (LC) layer, and a color filter, to name a few exemplary components.

[0043] As illustrated in FIG. 3, a light source 110 is positioned in the hole 105. The light source 110 may, in certain embodiments, comprise a light-emitting diode with a non-Lambertian distribution. For example, a side-emitting LED may be used, which directs a significant portion of light at high angles relative to the normal of the LED. By way of a non- limiting example, a side-emitting LED may direct at least 3x of light at angles of 60° or greater relative to the normal of the LED, such as 4x, 5x, lOx, or greater, e.g., ranging from about 3x to about lOx, including all ranges and subranges therebetween. FIG. 4 presents a graphical plot of angular emission intensity distribution for an exemplary side-emitting LED. The LED emits a majority of light at higher angles (e.g., approaching 70°), which is different from the Lambertian distribution provided by typical LEDs. According to certain embodiments, the angular emission intensity distribution may be symmetrical about the normal of the LED, as illustrated in FIG. 4. The LED may, in various embodiments, emit blue, UV, or near-UV light, e.g., light having wavelengths ranging from about 100 nm to about 500 nm. [0044] The at least one light source 110 can be optically coupled to the LGP 100 via holes 105. As used herein, the term "optically coupled" is intended to denote that a light source is positioned at a surface of the LGP so as to introduce light into the LGP. A light source may be optically coupled to the LGP even though it is not in direct physical contact with the LGP.

[0045] A general direction of light emission from light source 110 is depicted in FIG. 3 by the solid arrows. Light injected into the LGP 100 may propagate within the LGP due to total internal reflection (TIR), until it strikes an interface at an angle of incidence that is less than the critical angle. Total internal reflection (TIR) is the phenomenon by which light propagating in a first material (e.g., glass, plastic, etc.) comprising a first refractive index can be totally reflected at the interface with a second material (e.g., air, etc.) comprising a second refractive index lower than the first refractive index. TIR can be explained using Snell's law:

«_j Sin(0,.) = n₂ sin(#_r)

which describes the refraction of light at an interface between two materials of differing indices of refraction. In accordance with Snell's law, «; is the refractive index of a first material, n₂ is the refractive index of a second material, Θ; is the angle of the light incident at the interface relative to a normal to the interface (incident angle), and Θ_Γ is the angle of refraction of the refracted light relative to the normal. When the angle of refraction (Θ_Γ) is 90°, e.g., sin(0_r) = 1, Snell's law can be expressed as: n_x

The incident angle Θί under these conditions may also be referred to as the critical angle Θ_ς. Light having an incident angle greater than the critical angle (Θ; > Θ_ς) will be totally internally reflected within the first material, whereas light with an incident angle equal to or less than the critical angle (Θ; < Θ_ς) will be transmitted by the first material.

[0046] In the case of an exemplary interface between air («;=1) and glass

(«2=1.5), the critical angle (Θ_ς) can be calculated as 41°. Thus, if light propagating in the glass strikes the air-glass interface at an incident angle greater than 41°, all the incident light will be reflected from the interface at an angle equal to the incident angle. If the reflected light encounters a second interface comprising an identical refractive index relationship as the first interface, the light incident on the second interface will again be reflected at a reflection angle equal to the incident angle. [0047] According to various embodiments, the first and/or second major surfaces 140, 150 of the LGP 100 may be patterned with a plurality of light extraction features. As used herein, the term "patterned" is intended to denote that the plurality of light extraction features is present on or under the surface of the LGP in any given pattern or design, which may, for example, be random or arranged, repetitive or non-repetitive, uniform or nonuniform. In other embodiments, the light extraction features may be located within the matrix of the LGP adjacent the surface, e.g., below the surface. For instance, the light extraction features may be distributed across the surface, e.g. as textural features making up a roughened or raised surface, or may be distributed within and throughout the LGP or portions thereof, e.g., as laser-damaged sites or features. Suitable methods for creating such light extraction features can include printing, such as inkjet printing, screen printing,

microprinting, and the like, texturing, mechanical roughening, etching, injection molding, coating, laser damaging, or any combination thereof. Non-limiting examples of such methods include, for instance, acid etching a surface, coating a surface with T1O₂, and laser damaging the substrate by focusing a laser on a surface or within the substrate matrix.

[0048] In various embodiments, the light extraction features optionally present on the first or second surface of the LGP may comprise light-scattering sites. According to various embodiments, the extraction features may be patterned in a suitable density so as to improve the uniformity of light intensity output across the light emitting surface of the LGP. In certain embodiments, a density of the light extraction features proximate the light source may be lower than a density of the light extraction features at a point further removed from the light source, or vice versa, as appropriate to create the desired light output distribution across the LGP.

[0049] Referring to FIG. 5, an exemplary light extraction pattern is provided for an individual unit block depicted in FIG. 1, having a unit length L₀ and a unit width Wo. The center X of the depicted unit block represents a hole in which a light source may be placed. Generally speaking, the density of light extraction features increases with distance from the hole or center X. In some embodiments, the light extraction features may be patterned to form a grid, in which the central region X and the regions Y extending orthogonally from the center are more sparsely populated with light extraction features, while the corner regions Z are more densely populated. As such, referring to FIG. 1, a representative grid could be formed by drawing lines along the length L and width W of the LGP 100 that orthogonally intersect at the center of each hole. The central regions adjacent each hole may comprise the least light extraction features, whereas the regions proximate the grid lines may be sparsely populated with light extraction features, and the regions farthest from the grid lines may be more densely populated with light extraction features. Of course, the configuration depicted in FIG. 1 is non-limiting and a different array of holes having different spacing, number, shape, etc. could be used with a different grid shape. The configuration depicted in FIG. 5 is likewise non-limiting and different light extraction feature patterns may be used as appropriate to create a desired light output distribution.

[0050] The LGP may be treated to create light extraction features according to any method known in the art, e.g., the methods disclosed in co-pending and co-owned International Patent Application Nos. PCT/US2013/063622 and PCT/US2014/070771 , each incorporated herein by reference in their entirety. For example, a surface of the LGP may be ground and/or polished to achieve the desired thickness and/or surface quality. The surface may then be optionally cleaned and/or the surface to be etched may be subjected to a process for removing contamination, such as exposing the surface to ozone. The surface to be etched may, by way of a non-limiting embodiment, be exposed to an acid bath, e.g., a mixture of glacial acetic acid (GAA) and ammonium fluoride (NH4F) in a ratio, e.g., ranging from about 1 : 1 to about 9: 1. The etching time may range, for example, from about 30 seconds to about 15 minutes, and the etching may take place at room temperature or at elevated temperature. Process parameters such as acid concentration/ratio, temperature, and/or time may affect the size, shape, and distribution of the resulting extraction features. It is within the ability of one skilled in the art to vary these parameters to achieve the desired surface extraction features.

[0051] While the light extraction feature partem may be chosen to improve uniformity of light extraction along the length and width of the LGP 100, it is possible that the regions of the LGP corresponding to the individual light sources may emit light having a higher intensity, e.g., the overall light output of the LGP may not be uniform. The optical layer 120 may thus be engineered with regions of varying optical properties to further homogenize the light output. For instance, a first region of the optical layer 120 may further diffuse the light in regions corresponding to the light source and/or limit the amount of light transmitted through the optical layer in those regions. Such a configuration may allow for closer placement of the diffuser film or other optical films with respect to the light sources in the LGP and, thus, a thinner overall BLU and resulting lighting or display device without negatively impacting the uniformity of light produced by the BLU or device.

[0052] The BLUs disclosed herein may be used in various display devices including, but not limited to televisions, computers, phones, handheld devices, billboards, or other display screens. The BLUs disclosed herein may also be used in various illuminating devices, such as luminaires or solid state lighting devices.

[0053] It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.

[0054] It is also to be understood that, as used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a light source" includes examples having two or more such light sources unless the context clearly indicates otherwise. Likewise, a

"plurality" or an "array" is intended to denote "more than one." As such, a "plurality of light scattering features" includes two or more such features, such as three or more such features, etc., and an "array of holes" includes two or more such holes, such as three or more such holes, and so on.

[0055] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, examples include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0056] The terms "substantial," "substantially," and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to denote a surface that is planar or approximately planar. Moreover, "substantially similar" is intended to denote that two values are equal or approximately equal. In some embodiments,

"substantially similar" may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0057] While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase "comprising," it is to be understood that alternative embodiments, including those that may be described using the transitional phrases

"consisting" or "consisting essentially of," are implied. Thus, for example, implied alternative embodiments to a device that comprises A+B+C include embodiments where a device consists of A+B+C and embodiments where a device consists essentially of A+B+C.

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A backlight unit comprising:

a light guide plate comprising an array of holes and a plurality of light extraction features;

a light source positioned in at least one hole in the array of holes; and

an optical layer positioned on a light-emitting major surface of the light guide plate, the optical layer comprising a first region disposed over the at least one hole and a second region disposed over a portion of the light guide plate adjacent to the at least one hole;

wherein at least one of:

a first diffuse reflectance of the first region of the optical layer is greater than a second diffuse reflectance of the second region of the optical layer; and

a first diffuse transmittance of the first region of the optical layer is less than a second diffuse transmittance of the second region of the optical layer.

2. The backlight unit of claim 1, wherein the light guide plate comprises glass.

3. The backlight unit of claim 2, wherein the glass comprises the following composition, on a mol% oxide basis:

50-90 mol% Si0₂,

0-25 mol% R_xO,

wherein x is 2 and R is chosen from Li, Na, K, Rb, Cs, and combinations thereof, or wherein x is 1 and R is chosen from Zn, Mg, Ca, Sr, Ba, and combinations thereof.

4. The backlight unit of claim 1, wherein the light guide plate comprises a color shift Ay of less than about 0.015.

5. The backlight unit of claim 1, wherein the light source is a side-emitting LED.

6. The backlight unit of claim 5, wherein the side-emitting LED comprises an angular emission intensity distribution that is symmetrical about a normal of the LED.

7. The backlight unit of claim 1, wherein the plurality of light extraction features comprises a gradient pattern.

8. The backlight unit of claim 1, wherein the plurality of light extraction features comprises a grid pattern.

9. The backlight unit of claim 1, wherein the light extraction features comprise light- scattering particles, laser-damaged sites, roughened surface features, or combinations thereof.

10. The backlight unit of claim 1, wherein the light extraction features are present on the light-emitting major surface of the light guide plate, on an opposing major surface of the light guide plate, within a matrix of the light guide plate, or combinations thereof.

11. The backlight unit of claim 1, wherein the optical layer comprises a gradient of diffuse reflectance or diffuse transmittance from the first region to the second region.

12. The backlight unit of claim 1, wherein the first diffuse reflectance is at least about 5% greater than the second diffuse reflectance.

13. The backlight unit of claim 1, wherein the first diffuse transmittance is at least about 5% less than the second diffuse transmittance.

14. The backlight unit of claim 1, wherein an intensity of light transmitted through the first region of the optical layer is within about 5% of an intensity of light transmitted through the second region of the optical layer.

15. The backlight unit of claim 1, wherein the optical layer comprises a single layer or a composite layer.

16. The backlight unit of claim 1, further comprising a reflective film on a major surface of the light guide plate opposite the light-emitting surface.

17. The backlight unit of claim 1, further comprising at least one of a diffusing film, a prismatic film, and a reflective polarizing film.

8. A display or lighting device comprising the backlight unit of claim 1.