WO2016043988A1

WO2016043988A1 - Micro-perforated hole reflectors in light guide plates

Info

Publication number: WO2016043988A1
Application number: PCT/US2015/048473
Authority: WO
Inventors: Jacques Gollier; Kristopher Allen WIELAND
Original assignee: Corning Incorporated
Priority date: 2014-09-15
Filing date: 2015-09-04
Publication date: 2016-03-24
Also published as: TW201614293A

Abstract

Described herein are articles and methods for improving illumination and light propagation in transparent materials. In particular, the articles and methods described are useful in the design of light guide plates used in electronics devices, such as televisions and monitors. Light guiding is done via the incorporation of series of holes in the light guide to control and direct light within the structure.

Description

MICRO-PERFORATED HOLE REFLECTORS IN LIGHT GUIDE PLATES

[0001] This application claims the priority to U.S. Provisional Application 62/050313 filed September 15, 2014 the content of which is incorporated herein by reference in its entirety.

Field

[0002] Described herein are articles and methods for improving illumination and light propagation in transparent materials. In particular, the articles and methods described herein are useful in the design of light guide plates used in electronics devices, such as televisions and monitors.

Technical Background

[0003] Modern edge-lit liquid crystal displays (LCDs) typically use a light guide plate (LGP) to distribute the light behind the LCD array in an even intensity across the entire surface of the panel. In such displays, the LED light is coupled into the LGP from at least one edge of the LGP (the coupling edge) and light is extracted as it propagates by diffusing structures, typically white paint or surface scattering components, on the LGP. The edge- lit LGP present significant advantages over direct illumination, where a square array of LEDs is used to directly illuminate the panel, because the panel can be made extremely thin. However, one advantage direct illumination has over edge-lit displays is that every single LED of the array can be driven separately so that dimmer areas into images can be illuminated with less light by dimming some of the LED's. This is referred to as "local dimming" which provides savings in energy consumption and also improves image contrast, especially in the black regions of a picture. While local dimming has also been introduced into edge-lit LGPs, the efficiency is relatively low and the improvement in image contrast is less effective since the light emitted by individual LED's rapidly expands into the LGP as light propagates, providing less discrimination between the pixels. Simply put, the current methods of local dimming fail to satisfy the needs of the manufacturers and customers in the display industry.

Summary

[0004] A first aspect comprises an article comprising a light transmittive substrate that has two approximately parallel major surfaces; at least one light element coupled to the substrate and introducing light into the substrate; and a series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned in such a way as to act as a light guide for light from the coupled light element. In some embodiments, the holes have a diameter from about 200 nm to about 200 μιη. In some embodiments, the holes have a diameter from about 500 nm to about 100 μιη. In other embodiments, the series of holes comprises two or more structure lines. In still other embodiments, the holes comprising each structure line are on or scattered in an ordered or random fashion around a demarcation line.

[0005] In embodiments of the first aspect, the holes have a face that is defined by the shape of the hole on one or both of the approximately parallel major surfaces of the light transmittive substrate and a cross section defined by the shape of the hole when viewed orthogonal to the approximately parallel major surfaces of the light transmittive substrate. In some such embodiments, the face of the hole is approximately circular. In some embodiments, the cross section of the hole is cylindrical, cone-shaped, or waisted.

[0006] Embodiments of the first aspect may further comprise one or more light extraction features. In such embodiments, the one or more light extraction features may comprise one or more of spherical holes, laser formed waveguides, internal damage spots, internal structures with indices of refraction different than the glass sheet, surface modifications, bumps, pits, or nanoparticles or quantum dots.

[0007] Another embodiment further comprises a second light element coupled to the substrate and introducing light into the substrate, wherein the second light element is coupled orthogonally to the first light element; and a second series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned in such a way as to act as a light guide for light from the second coupled light element.

[0008] Another embodiment comprises a backlight unit comprising any of the articles above or alternatively, a display comprising any of the articles above.

[0009] A second aspect comprises a lightguide plate comprising a light transmittive substrate that has two approximately parallel major surfaces; at least one light element coupled to the substrate and introducing light into the substrate; and a series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned around the periphery of the edges of the substrate no coupled to the light element and wherein the holes are aligned in such a way as to act as a light guide for light for the coupled light element. Embodiments of this aspect comprise backlight units or displays that comprise the aspect. [0010] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as in the appended drawings.

[0011] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework for understanding.

Brief Description of the Drawings

[0012] The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification.

[0013] FIG. 1 is a simulation of the non-collimated expansion of light from a LED as it travels through a waveguide.

[0014] FIG. 2 is a simulation of the non-collimated light from an LED in a waveguide, where the light is guided by a prism array that has been laminated to the light guide on one of the major planes.

[0015] FIG. 3 shows the effect of a hole simulated as a cylinder of air inside the glass substrate. The ray simulation shows that the hole act like light scattering center which angularly re-distribute the light in the plane of the LGP.

[0016] FIG. 4A shows cross-sections of the holes that may be incorporated into the LGP. Fig. 4B shows additional features that may be incorporated with embodiments.

[0017] FIG. 5 is a simulation of a light guide where a light "channel" is created by lines of micro-holes 510 and 511 in the waveguide (orthogonal to the major planes). As can be seen, light emitted by a single LED remains confined. Two lines of two rows (520 and 521) of holes were created, where the lines were 50 mm apart and the rows were 1 mm apart. The holes were 60 μιη in diameter and placed 125 μιη apart (center-to-center (also referred to as "pitch")).

[0018] FIG. 6 is another simulation of a light guide where a light "channel" is created by lines of micro-holes in the waveguide where two sets of lines are running orthogonal to each other (610 and 620) and intersect at square 630.

[0019] FIG. 7A is a diagram showing the experimental setup for the picture of FIG. 7B. FIG. 7A and FIG. 7B show light from an LED being coupled into a glass light guide plate having two single lines (50 mm apart) of 1 μιη holes drilled orthogonally into the plate and spaced 5 μηι apart center-to-center. At 600 mm from the LED, the back of the light guide plate was painted with a white ink to allow for light extraction.

[0020] Fig. 8 shows an alternative embodiment where the holes in the LGP are drilled along the periphery of three sides of the LGP - the side nearest the edge-lit LED side not having holes - to scatter the light within the LGP and act as substitutes for diffusing reflectors.

[0021] Fig. 9 shows an alternative embodiment where the holes are placed randomly about a line of demarcation (910) rather than in a more exact line (920). Such an embodiment may avoid issues of weakening the LGP or creating visible light lines in the LGP.

Detailed Description

[0022] Before the present materials, articles, and/or methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific compounds, synthetic methods, or uses as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0023] In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings:

[0024] Throughout this specification, unless the context requires otherwise, the word "comprise," or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. Where comprise, or variations thereof, appears the terms "consists essentially of or "consists of may be substituted.

[0025] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a pharmaceutical carrier" includes mixtures of two or more such carriers, and the like.

[0026] "Optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0027] Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes 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.

[0028] As noted previously, edge-lit LCD backlights offer significant advantages in making displays thinner. However, they have traditionally suffered from issues of image contract and energy usage because local dimming has been unavailable or less effective than in directly illuminated LCD displays. An example of an edge-lit LGP with a single LED is shown in FIG. 1. As can be seen in the figure, light from the LED rapidly expands over 400 mm to light most of the far side of the LGP - in fact, spreading to a width greater than the length. Therefore, in the case of an edge-lit display, simply individually manipulating the light output of the LEDs will not give same the local dimming effect shown in direct-lit displays.

[0029] FIG. 2 again shows a single LED coupled to a LGP. However, in this case, the light propagation is confined through the use of prism arrays that are laminated to one or both of the top and bottom surfaces of the LGP. As can be seen, the light remains more confined, having a width of about 150 mm at 400 mm distance, but still shows significant divergence. Also, such an approach may be somewhat expensive for glass light guides since this will require to laminate large size films on the LGP and lamination is a relatively expensive process.

[0030] A first aspect described herein relates to alternative designs and technologies that provide improved local dimming in edge-lit displays. A number of technologies have been developed to drill high precision micro-holes into glass. Hole diameters range from a 1 μιη when glass is only laser exposed to over 100 μιη when the glass is both laser exposed and etched. FIG. 3 shows the effect of a hole, simulated as a cylinder of air, inside a glass waveguide where the blue lines simulate light impinging on the cylinder. Fig. 3 shows that the holes act like light scattering centers and angularly redistribute the light in the plane of the LGP. The major advantage of cylindrical geometry is that the angular scattering function is highly nonsymmetric as opposed, for instance, to a spherical configuration - meaning that light is only scattered in the plane of the LGP and the scattering centers do not add additional scattering components in the direction of the LGP thickness (i.e., scattering light out of the glass plane as a spherical scattering center would). The consequence is that, although light gets scattered at very high angle (in the plane of the LGP), it is still guided in the LGP. In other words, holes do not significantly extract light. [0031] While it is advantageous that the cylindrical holes do not add a light extraction element, it is possible to and advantageous to use other shaped holes. FIG. 4A, while not limiting, shows example cross-sections of alternative hole designs that are contemplated. For example, 410 is a cylindrical hole, while 420 shows a tapering cylinder, 430 is a hour glass, or waisted-type cylinder, and 440 provides an exponentially decaying-type structure. The different types of hole structures may be used alone or in combination. The advantages of non-cylindrical structures is that they may be useful in targeted scattering of the light out of the LGP at certain angles or at certain locations, especially when used in combination with cylindrical scattering holes. Further, it is contemplated that the hole structures can be used in combination with other scattering features used in LGP and backlights, such as those examples shown in FIG. 4B - spherical holes, laser formed waveguides, internal damage spots, or other internal structures with indices of refraction different than the glass sheet (450), surface modifications, such as bumps (460) or pits (470), or nanoparticles or quantum dots (480), either in the glass or on one or more surfaces.

[0032] Since the holes act as strong scattering centers, they act and can be used as reflectors inside glass. In other words, if a region of the LGP has a high enough hole density, light will not penetrate past that region, but instead will be backscattered. This allows for controlling and confining the in some regions of the LGP and provides for a local dimming function. According to optical modeling and experiments, the minimum condition for obtaining reflectivity is:

N*D > 0.2

where N is the amount of holes per meter in the direction of light propagation; and

D is the hole diameter

[0033] FIG. 5 shows a simulation of a light guide where a light channel is created by lines of micro-holes. As can be seen, light emitted by a single LED (501) remains confined to the 50 mm center section by lines 510 and 511. Each of 510 and 511 comprise two rows of holes, rows 520 and 521, 1 mm apart, that are made up of 60 μιη holes spaced 125 μιη apart, center-to-center. While shown as being the same size, holes can optionally have different diameters and densities which can change as a function of proximity to the LED or due to other parameters known to one of skill in the art.

[0034] This concept can also be extended to two dimensional "light channels" in the case where the display has LED's on more than one edge. For example, as shown in the simulation shown in FIG. 6, the local dimming can be done in two dimensions orthogonal to each other. Lines 620 show the scattering holes in the horizontal direction, while lines 610 highlight the scattering holes in the vertical. LEDs (601 and 602) are placed inside lines 610 and 620, respectively, and square 630 is the overlap of the two LEDs on the substrate. While the simulation shows that the intersection has improved light intensity, this configuration can suffer from the fact that light from the LEDs 601 and 602 ends up orthogonally crossing lines of holes (640 and 650, respectively) also causes some backscattering towards the light sources and leakage of light out of the light guide (seen as the relatively high intensity of light traveling between the LEDs). However, by controlling the size, shape, and spacing of the holes, this scattering can be minimized.

[0035] Another aspect described herein, shown in FIG. 8, is the use of holes in the LGP that are drilled along the periphery of three sides of the LGP (shown as dotted lines in FIG. 8) - the side nearest the edge-lit LED side not having holes - to scatter the light within the LGP and act as substitutes for diffusing reflectors. Light guide designs often consist in using a transparent light guiding sheet illuminated from one side. In order to optimize lighting efficiency a diffusing paper like diffusing tape is often attached to the 3 other edges of the LGP to minimize light leakage from those edges. However, those reflectors are usually of relatively poor efficiency since they are generally Lambertian-like diffusers and will scatter a significant amount of light out of the light guide. By drilling holes at the periphery of the LGP instead of using diffusing reflectors, light is back scattered inside the LGP but will stay entirely guide inside the LGP.

[0036] Another aspect contemplates optimizing hole placement. Optimization may be related to any number of criteria that are important in the LGP, backlight unit, or the display itself. For example, the holes may be placed to optimize light guiding, LGP strength, light extraction, color shift, etc. For example, as shown in FIG. 9, placing the holes in a line (920) may pose an issue for LGP strength and potentially lead to cracking of the substrate upon stress or repeated thermal cycles. Plus, a line of holes will encourage any crack formed to propagate meaning that this can generate reliability issues. Secondly, since the holes may not be perfect cylinders, they can partly scatter the light in the direction perpendicular to the light guide which can create light lines or other artifacts in the image. An alternative design is shown in 910 where the holes are placed around the line. To get enough reflectivity, one needs to have a high enough hole density. As used herein, lines 930 are termed "demarcation lines," and describe the center or average line formed by the linear or scattered holes that form a waveguide. Alternatively, a "structure line," as used herein, is described by the line shape defined by the dotted lines 940 and 941 and is a description of the rough "line" of holes that form a waveguide feature.

Examples

[0037] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the materials, articles, and methods described and claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Only reasonable and routine experimentation will be required to optimize such process conditions.

[0038] FIG. 7A is a schematic diagram showing the experimental setup shown FIG. 7B. FIG. 7A and FIG. 7B show light from an LED being coupled into a glass light guide plate having two single lines (50 mm apart) of 1 μιη holes drilled orthogonally into the plate and spaced 5 μιη apart center-to-center. At 600 mm from the LED, the back of the light guide plate was painted with a white ink to allow for light extraction. As shown in FIG. 7B, the white paint clearly shows the intensity increase in the center section where the LED is being guided by the cylindrical holes. The effectiveness of the holes could be increased by optimizing the hole size, spacing and placing multiple rows of holes along each line.

[0039] Although the embodiments herein have been described with reference to particular aspects and features, it is to be understood that these embodiments are merely illustrative of desired principles and applications. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the appended claims.

Claims

What is claimed is:

1. An article comprising:

a light transmittive substrate that has two approximately parallel major surfaces; at least one light element coupled to the substrate and introducing light into the substrate; and

a series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned in such a way as to act as a light guide for light from the coupled light element.

2. The article of claim 1, wherein the holes have a diameter from about 200 nm to about 200 μιη.

3. The article of claim 2, wherein the holes have a diameter from about 500 nm to about 100 μιη.

4. The article of any of claims 1-3, wherein the series of holes comprises two or more structure lines.

5. The article of claim 4, wherein the holes comprising each structure line are on or scattered in an ordered or random fashion around a demarcation line.

6. The article of any of claims 1-5, wherein the holes have a face that is defined by the shape of the hole on one or both of the approximately parallel major surfaces of the light transmittive substrate and a cross section defined by the shape of the hole when viewed orthogonal to the approximately parallel major surfaces of the light transmittive substrate.

7. The article of claim 6, wherein the face of the hole is approximately circular.

8. The article of claim 7, wherein the cross section of the hole is cylindrical, cone- shaped, or waisted.

9. The article of any of claims 1-8, further comprising one or more light extraction features.

10. The article of claim 9, wherein the one or more light extraction features comprise one or more of spherical holes, laser formed waveguides, internal damage spots, internal structures with indices of refraction different than the glass sheet, surface modifications, bumps, pits, or nanoparticles or quantum dots.

11. The article of any of claims 1-10, further comprising a second light element coupled to the substrate and introducing light into the substrate, wherein the second light element is coupled orthogonally to the first light element; and

a second series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned in such a way as to act as a light guide for light from the second coupled light element.

12. A backlight unit comprising the article of any of claims 1-11.

13. A display comprising the backlight of claim 12.

14. A lightguide plate comprising:

a series of holes in the substrate that are approximately orthogonal to the parallel major surfaces and are aligned around the periphery of the edges of the substrate no coupled to the light element and wherein the holes are aligned in such a way as to act as a light guide for light for the coupled light element.

15. A backlight unit comprising the lightguide plate of claim 14.

16. A display comprising the backlight of claim 15.