Tiled assemblies for a high dynamic range display panel

Techniques are provided for a high dynamic range panel that includes an array of light sources (202,203) illuminating a corresponding array of light guides (204, 206). A light source (202) of the array illuminates a first light guide (204). The light source directly underlies, such as in a cavity (208), a second light guide (206) that is adjacent to the first light guide. The light source (202) does not extend below a bottom side (214) of either the first light guide or the second light guide to reduce thickness of the panel. The light source (202) and the first light guide (204) can be integrated as a tile assembly. Alternatively, the light source (202) and the second light guide (206) can be an integrated tile assembly. In a specific embodiment, the light source emits a blue or ultraviolet light, which is converted by quantum dots to a different color.

TECHNOLOGY

The present invention relates generally to display techniques for high dynamic range images, and in particular, to compact displays for local dimming.

BACKGROUND

Dynamic range is the ratio of intensity of the highest luminance parts of an image scene and the lowest luminance parts of a scene. For example, the image projected by a video projection system may have a maximum dynamic range of 300:1.

The human visual system is capable of recognizing features in scenes which have very high dynamic ranges. For example, a person can look into the shadows of an unlit garage on a brightly sunlit day and see details of objects in the shadows even though the luminance in adjacent sunlit areas may be thousands of times greater than the luminance in the shadow parts of the scene. To create a realistic rendering of such a scene can require a display having a dynamic range in excess of 1000:1. The term “high dynamic range” (HDR) means dynamic ranges of at least 800:1.

Conventional display technology, using direct-lit local dimming (as an example, described by U.S. Pat. No. 8,277,056, “Locally Dimmed Display,” incorporated herein for all purposes), is capable of rendering images in a manner that faithfully reproduces high dynamic ranges. This is accomplished by independent modulation of light sources, as well as modulation by one or more liquid crystal panels, for improved contrast. However, a direct-lit panel100cannot do so in a form factor sufficiently thin for many applications (e.g., a cellular telephone display). As shown inFIG. 1A, the width102of a direct-lit panel stacks the light sources, liquid crystal panel, and intervening optics (such as, a diffusion layer).

As an alternative to direct-lit panels, edge-lit technology (as an example, described in U.S. Pat. No. 8,446,351, “Edge Lit LED based Locally Dimmed Display,” incorporated herein for all purposes) is employed with mixed results. As shown inFIG. 1B, an edge-lit panel150is thinner by not stacking a light source, and width152driven by the liquid crystal panel, light guide, and any intervening optics (not shown). That said, edge-lit panel150suffers from noticeably reduced HDR performance because light source modulation is row dependent and light intensity decreases along the length of the light guide (e.g., non-uniformity as a function of distance from the light source).

Accordingly, a need exists for a compact (e.g., thin) local dimming display capable of reproducing a wide range of light intensities.

SUMMARY OF THE DESCRIPTION

Techniques are provided for a high dynamic range panel that includes an array of light sources illuminating a corresponding array of light guides. A light source of the array illuminates a first light guide. The light source directly underlies, such as in a cavity, a second light guide that is adjacent to the first light guide. The light source does not extend below a bottom side of either the first light guide or the second light guide to reduce thickness of the panel.

In an embodiment of the invention, an apparatus includes a first light source to illuminate a first light guide with blue or ultraviolet light. The first light source is within a cavity formed by at least the first light guide and a second light guide. A second light source illuminates the second light guide with the blue or ultraviolet light. The second light guide is adjacent to the first light guide. The first light guide includes a sloped surface generating a broad spectrum light (e.g., white light) from the blue or ultraviolet light. The first light source does not extend beyond the cavity.

As another embodiment of the present invention, an apparatus includes an array of light sources respectively illuminating an array of light guides. A first light source of the array of light sources directly underlies a first light guide illuminated by a second light source in the array. The first light source does not extend below a bottom side of the first light guide. The first light guide includes a multi-faceted reflective layer that directs light to a different direction.

As yet another embodiment of the present invention, an apparatus includes a first light source to illuminate in a first direction a first light guide with a first light. The first light guide directs the first light to a second direction different from the first direction. A second light source illuminates in the first direction a second light guide with a second light. The second light guide directs the second light to the second direction. The second light guide is adjacent to the first light guide. The first light source underlies in the second direction the second light guide. The first and second light guides each include a multi-faceted reflective layer to direct light to the second direction. The first light source does not extend below a bottom side of the second light guide.

DESCRIPTION OF EXAMPLE POSSIBLE EMBODIMENTS

Example possible embodiments, which relate to HDR displays used for televisions, computer displays, tablets, PDAs, mobile cellular telephones, advertising displays or the like, are described herein. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are not described in exhaustive detail, in order to avoid unnecessarily occluding, obscuring, or obfuscating the present invention.

FIG. 2illustrates an exemplary HDR panel200according to an embodiment of the present invention. HDR panel200is a two dimensional array of pixel elements (e.g., 960×640; 113×640; 1920×1080; 4096×2160; 3840×2160), each pixel element includes at least a light source optically coupled to a light guide (i.e., an optical waveguide, such as optical fiber) in this example. Each light source is independently controllable for fine local dimming, or a subset of these light sources can be controlled in concert for coarse local dimming. Further, the spatial resolution of HDR panel200need not be the same, 1:1, as other optical elements, such as a liquid crystal panel (not shown). For example, the spatial resolution of HDR panel200can be 1:2, 1:4, 1:8 or less of the liquid crystal panel. In other words, a single light source of the backlight can be used to reproduce multiple pixels in an area of a display.

For improved compactness of panel200, light sources are disposed within cavities underlying adjacent light guides. For example, light source202illuminates light guide204, but it is placed in a cavity208of adjacent light guide206. Light guide206is meanwhile illuminated by light source203. Cavity208is an arbitrarily shaped void, hollow, opening, or the like sufficiently large to hold, completely or partially, light source202. In a specific embodiment, a cavity is form fitting to partially encapsulate a light source (e.g., cavity closely follows, at least in part, the contours of the light source). For simplicity, surface210of light guide206defines size and shape of cavity208. Further details relating to surface210are described more fully below in connection withFIGS. 3A-3E.

In one embodiment, light source202is physically mounted to light guide204. This can be accomplished by a form factor housing both light source202and light guide204. Alternatively light source202can be housed with adjacent light guide203. These structures containing one light guide and a one or more light sources (e.g., one white LED, three LED sources for red green blue, or the like), referred hereinafter as a “tile assembly,” provide benefits beyond compactness, such as a modular design.

Light guides (e.g.,204,206) can be glass, polymer, semiconductor, plastic, or the like whether as slab, planar, rib, strip, segmented, or fiber structure. Light guides204,206direct electromagnetic waves in the optical spectrum (e.g., light with a wavelength between about 380 to 800 nanometers) or a subset of the optical spectrum. Light guide204guides at least the desired wavelength(s) associated with light source202.

Since light source202provides lateral illumination of light guide204, light guide204is configured to reflect light in an outwards direction through a display's optical stack and ultimately to a viewer. In an implementation of the present invention, a surface of a light guide, such as surface210of light guide206, is reflective. A reflective layer can be deposited (including by chemical vapor deposition), applied or affixed to, or under, to light guide206at surface210. The reflective layer provides a specular reflection surface or diffuse reflection surface, depending on desirability. Example materials for the reflective layer include one or more of: metals (e.g., aluminum, gold, silver, copper, brass, mercury, nickel or the like), polished metals, paint (e.g., white paint, glossy paint, matte paint), optically reflective silicone, water, and plastic. The reflected light from light guide206can be further processed by subsequent elements in the optical stack. InFIG. 2, an optional layer212, overlaid on one or more light guides, can diffuse the light for improved uniformity or alter the point spread function for less or more contribution to adjacent pixels.

Light source202can be a light-emitting diode (LED), organic light-emitting diode (OLED), active matrix organic LED, light-emitting electrochemical cell, field-induced electroluminescent polymer, cold cathode lamp, cold cathode fluorescent lamp, laser, phosphor coated LED, quantum dot coated LED, incandescent bulb, or any suitable source of electromagnetic waves of an appropriate wavelength, preferably thinner than the light guides. A combination of light sources of differing technologies can be employed in panel200. In other words, light sources202and203can both be LEDs, but they need not be the same (e.g., as a specific embodiment, light source202can be an OLED, and light source203can be quantum dot coated LED).

In an embodiment of the present invention, light sources202,203produce a broad spectrum light (e.g., white light) to illuminate light guides204,206. Color can be imparted to the light exiting light guides204,206by several techniques. For example, subsequent color filters in the optical path can be used to produce each of the primary colors, such as red, green and blue. Specifically, a liquid crystal panel (not shown inFIG. 2) with subpixel color filters can be used.

A matrix array of quantum dot subpixel areas in the optical stack above a light guide can also convert light respectively to individual primary colors, e.g., red, blue, green and/or yellow. When light sources202,203produce blue and/or ultraviolet light, surface210can optionally be a layer of quantum dots (i.e., semiconductor nanocrystals, when under excitation, emit light dependent on its size and shape) to generate broad spectrum light later imparted with color by filtering. Alternatively, the layer of quantum dots can be within, above, or below surface210. As another embodiment, the light guides can reflect blue or ultraviolet light to the subsequent optical stack, which can include a quantum dot layer of a matrix of red light generating, green light generating, and blue light generating areas of quantum dots. If the appropriate blue light is directly generated by light sources202,203, then the blue light generating area can be replaced with either a transparent filter or no filter at all (e.g., a cut-out to pass light, without alteration).

As described above, light sources (e.g., light source202) is positioned, partially or wholly, within a cavity208formed by an adjacent light guide (e.g., light guide206). Light source202is at least partially within cavity208, preferably primarily within cavity208, and most preferably completely within cavity208. For a thinner tile assembly, a light source should not extend below the lowest (bottom) side214, relative to an optical stack of a display device, of either its corresponding light guide or its adjacent light guide. Similarly, the light source should not extend above the highest (top) side216of either its corresponding light guide or its adjacent light guide To the extent the light source extends above or below the light guides, thickness of the tile assembly is enlarged.

FIGS. 3A, 3B, 3C, 3D, and 3Eillustrate simplified cross-sectional views of exemplary HDR panels, according to embodiments of the present invention.FIG. 3Ashows a linear surface304. The slant angle of linear surface304can range from about 1° to about 89°, preferably about 10° to about 70°, and more preferably about 30° to about 60°. In another embodiment, surface304can vary non-linearly. The desired point spread function (PSF, a measure of the degree of spreading of a point object) of the reflected light, as well as sizing of cavity306, will influence acceptable slant angles. In a preferred embodiment, cavity306is sufficiently ample to house light source308, whether light source308is integrated as a tile assembly with light guide310or as a standalone light source device. Such an arrangement reduces thickness302, compared to stacking an entire thickness of a light guide plus height of a light source.

Referring toFIGS. 3B and 3C, light guides include multi-faceted, convex or concave, reflection surfaces325and326, although reflection surfaces can be smoothed to avoid sharp angles. The angle and number of facets (e.g., two, three, four, five, six, seven or more facets) influence the PSF of the reflected light. In some instances, PSF that spread beyond one pixel area it is preferable. This increased PSF size reduces blocking artifacts associated with abrupt illumination changes at pixel boundaries.FIG. 3Dshows an undulating surface327, which can be any waveform, such as sinusoidal, square, triangle, sawtooth or the like, or combinations of the foregoing. The waveform can be either uniform or non-uniform in frequency or amplitude. For example, about a proximal start of surface327can have a higher frequency than about the distal end of surface327. It should be appreciated, based on the teachings herein, that surfaces325,326, and327can vary with height, depth, and/or length (in all three dimensions). In other words, one side of a reflective surface (e.g., left side) can differ from its opposite side (e.g., right side) or its center. In an embodiment of the present invention, a reflecting surface in three dimensions can vary with azimuth, elevation, or both.

As depicted in the figures, the proximal start328,329of reflection surfaces325and326is disposed away by a length330from illuminating light sources. Length330can substantially range from about 0% to about 99% of the length of the entire light guide, but preferably 35% to 85%. Likewise, the distal end of reflection surfaces325and326need not abut the end of the light guide, nor coincide with a top surface (e.g.,331) of the light guide—in other words, surfaces325,326can be less than thickness302. These considerations can also apply to reflective surface304ofFIG. 3A.

InFIGS. 3B and 3C, instead of a single light source (e.g., white, blue or UV LED) for each light guide, primary light sources are arranged as a group330. Group330is collectively housed, partially or wholly, in cavity306. In other words, the primary light sources share a single light guide per group. It should be understood that in each of the embodiments described by this specification, a single light source and a group of primary light sources are interchangeable, depending on the desired architecture of a display device.

FIG. 3Eillustrates a simplified cross-sectional view of exemplary HDR panels, according to another embodiment of the present invention. In this example, a group330of primary light sources illuminates two opposite facing light guides350and352. Fewer light sources are needed, thus saving on bill of materials (BoM) cost, but reducing resolution for local dimming control. This implementation can earn further BoM savings by using group330to illuminate four or more light guides organized radially about group330. In this scenario, an “expanded tile assembly,” as a single module, can include group330and its plurality of illuminated light guides.

FIGS. 4A, 4B and 4Cillustrates exemplary groups400,450,475of primary light sources, according to an embodiment of the present invention. Groups400,450and475can be applied to the embodiments described above in connection withFIGS. 2 and 3A-3D. Groups400and450are illustrated to show three primary light sources402,404, and406; however, there can be two, four, 5 or more primaries in an HDR panel. For example, an HDR panel can implement any one of RGB, RGB+yellow, RGB+white, or RGB+yellow+cyan.

For a three dimensional (3D) rendering panel utilizing spectral separation, group475includes six primary light sources. A viewer wears spectrally sensitive glasses such that different components of the illuminated light are directed to the viewers' left and right eyes. As an example, a first red primary is perceived in a viewer's left eye, but a second red primary (spectrally different from the first) is filtered by the left eye lenses of the 3D glasses. For the right eye, the second red primary is perceptible, but not the first. Accordingly, group475includes two sets of primaries that do not overlap spectrally. Additional details about 3D spectral separation as used for cinema projection are described in U.S. Pat. No. 7,784,938, which is hereby incorporated herein by reference for all purposes.

FIG. 5illustrates a tile assembly500for subpixel resolution, according to an embodiment of the present invention. A plurality of light sources (e.g.,502,504, and506or more) emanating a display's primary colors are coupled to respective light guides (e.g.,508,510, and512). For example, light source502can be a red LED, light source504can be a green LED, and light source506can be a blue LED. The light output from light guides508,510, and512provide subpixel color modulation by the backlight, as well as further modulation by a liquid crystal display (not shown). This tile assembly avoids the use of color filters in the optical stack and quantum dots. It should be appreciated that the resulting spatial resolution of the HDR panel comprising an array of tile assemblies500can be less than, equal to, or greater than other optical components, such as the liquid crystal panel.

FIGS. 6A-6Dillustrate an exemplary HDR display, according to embodiments of the present invention. The structures depicted inFIGS. 6A-6Dcan be applied to one or more of the embodiments described above forFIGS. 2, 3A-3D, 4A-4C, and 5, as would be readily apparent by a person skilled in the art benefiting from the teachings of this specification. It will also be apparent that one or more of the depicted layers inFIGS. 6A-6Dare optional. For example, if the tile assembly602includes quantum dots, then quantum dot layer606can be omitted.

FIG. 7illustrates an exemplary HDR display with a compact design, according to an embodiment of the present invention. Light sources (such as white LEDs, RGB LED groups, etc.) are mounted along the edges of an LCD display. The light sources are tiled as closely as possible in two dimensions along the edge of the display, essentially creating a low-resolution backlight.

The light is directed to the desired location behind the LCD display. First, the light sources emit light into a planar light guide. The light is transmitted along the light guide either by total internal reflection (TIR) or by reflective boundaries. Eventually, light is reflected upwards through a diffuser and LCD. As illustrated inFIG. 7, the light sources transmit light at 90 degrees to the light guide to allow for the light guides to be very thin (order of um). The light is reflected along the light guides using an angled reflector or TIR. Alternatively, the LEDs could emit light directly into the light guide.

The backlight optics can be tiled or continuous across the display, with light being emitted along both top and bottom, or left and right edges. Instead of reflecting the light upwards towards the LCD as described above forFIG. 7, a top surface of the light guide could be diffused if using TIR, or the reflector could be terminated to eject light from the light guide in the desired location.

Color Wavelengths

This specification often refers to colors, such as blue, ultraviolet, red, green, etc. Without limiting the generality of the teachings herein, light colors can be within about the following ranges for one or more embodiments of the invention:(i) blue—450 to 490 nanometers (nm);(ii) red—635 to 700 nm;(iii) green—490 to 560 nm;(iv) ultraviolet—10 nm to 400 nm (with near UV, 300 to 400 nm);(v) white—a combination of visible light of different wavelengths perceived by the human visual system as having no specific color (e.g., average noon sunlight; CIE (International Commission on Illumination) standard illuminant D65), visible light generally ranging from 380 nm to 800 nm.

EQUIVALENTS, EXTENSIONS, ALTERNATIVES AND MISCELLANEOUS

ADDITIONAL REFERENCES

The following references, in addition to any reference cited above, are incorporated by reference herein for all purposes:(i) International Publication No. WO 2006/064500, Device and method for optical resizing;(ii) US Patent Publication No. 2007/0086712 Device and method for optical resizing and backlighting;(iii) US Patent Publication No. 2008/0205078 Illumination tiles and related methods;(iv) US Patent Publication No. 2008/0205080 Tiled illumination assembly and related methods;(v) U.S. Pat. No. 7,311,431, Light-emitting apparatus having a plurality of adjacent, overlapping light-guide plates;(vi) U.S. Pat. No. 6,768,525, Color isolated backlight for an LCD; and(vii) European Patent Application Publication No. 509096 Image display device and method of producing the same.