PATENT DOCUMENT

Publication Number: US-10126480-B2
Application Number: US-201514861686-A
Country: US
Kind Code: B2

Title: Display backlight with light mixing structures

Abstract:
A display may have a backlight unit with a row of light-emitting diodes that emit light into the edge of a light guide plate. The light guide plate may have opposing upper and lower surfaces. The upper surface of the light guide plate may have ridges and the lower surface of the light guide plate may have bumps. The edge of the light guide plate may have light mixing structures. The light mixing structures may include edge surfaces that refract light at a high angle. The high angle light may then be reflected by a reflective surface so that the light propagates down the light guide plate. Some light may pass through the light mixing structures and propagate down the light guide plate without being reflected by the reflective surface. This arrangement may reduce the mixing distance of the backlight unit.

Claims:
What is claimed is: 
     
       1. A display backlight comprising:
 a row of light-emitting diodes; and 
 a light guide plate having first and second opposing surfaces connected by an edge, wherein the edge receives light from the row of light-emitting diodes, wherein the edge has a plurality of protrusions and a reflective portion, wherein a portion of the light that passes through the plurality of protrusions is subsequently reflected by the reflective portion of the edge of the light guide plate, wherein each protrusion comprises first and second surfaces, and wherein each protrusion comprises third and fourth surfaces that are interposed between the first and second surfaces and connect the first surface to the second surface. 
 
     
     
       2. The display backlight defined in  claim 1 , wherein the first and second surfaces are at a first angle relative to a planar portion of the edge of the light guide plate. 
     
     
       3. The display backlight defined in  claim 2 , wherein the third and fourth surfaces are at a second angle relative to the planar portion of the edge of the light guide plate. 
     
     
       4. The display backlight defined in  claim 3 , wherein the first angle is between 70° and 89°. 
     
     
       5. The display backlight defined in  claim 4 , wherein the second angle is between 5° and 35°. 
     
     
       6. The display backlight defined in  claim 5 , wherein the portion of the light that passes through the plurality of protrusions and is subsequently reflected by the reflective portion of the edge of the light guide plate passes through the first and second surfaces of the protrusion. 
     
     
       7. The display backlight defined in  claim 1 , wherein an additional portion of the light that passes through the plurality of protrusions is not reflected by the reflective portion of the edge of the light guide plate. 
     
     
       8. A display backlight comprising:
 a row of light-emitting diodes; 
 a light guide plate having first and second opposing surfaces connected by an edge, wherein the edge receives light from the row of light-emitting diodes, wherein the edge has at least one light mixing structure and a reflective portion, and wherein a portion of the light that passes through the at least one light mixing structure is subsequently reflected by the reflective portion of the edge of the light guide plate; and 
 a reflector that is parallel to the first and second opposing surfaces of the light guide plate and substantially perpendicular to the reflective portion of the edge of the light guide plate. 
 
     
     
       9. The display backlight defined in  claim 1 , wherein the reflective portion comprises a layer of reflective material on the edge of the light guide plate. 
     
     
       10. The display defined in  claim 1 , wherein a planar portion of the edge receives the light from the row of light-emitting diodes, and wherein the reflective portion of the edge is at an angle with respect to the planar portion of the edge. 
     
     
       11. A light guide plate comprising:
 a top surface; 
 a bottom surface; and 
 first and second opposing surfaces that connect the top and bottom surfaces, wherein the first surface has a planar portion and light mixing structures configured to distribute light, wherein the light mixing structures comprise protrusions with edge surfaces and center surfaces, wherein the edge surfaces are at a first angle with respect to the planar portion, wherein the center surfaces are at a second angle with respect to the planar portion, and wherein the first angle is greater than the second angle. 
 
     
     
       12. The light guide plate defined in  claim 11 , wherein the first angle is between 70° and 89°. 
     
     
       13. The light guide plate defined in  claim 12 , wherein the second angle is between 5° and 35°. 
     
     
       14. The light guide plate defined in  claim 11 , wherein the edge surfaces of the light mixing structures are configured to refract light towards a reflective surface. 
     
     
       15. The light guide plate defined in  claim 14 , wherein the light guide plate comprises a recess, and wherein the reflective surface at least partially defines the recess. 
     
     
       16. The light guide plate defined in  claim 11 , wherein the edge surfaces comprise first and second surfaces, and wherein the center surfaces comprise third and fourth surfaces interposed between the first and second surfaces. 
     
     
       17. The light guide plate defined in  claim 11 , wherein the top surface of the light guide plate has ridges, and wherein the bottom surface of the light guide plate has bumps. 
     
     
       18. The display backlight defined in  claim 1 , wherein the first, second, third, and fourth surfaces are planar surfaces.

Description:
This application claims the benefit of provisional patent application No. 62/204,649 filed on Aug. 13, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to displays with backlights. 
     Electronic devices such as computers and cellular telephones have displays. Some displays such as plasma displays and organic light-emitting diode displays have arrays of pixels that generate light. In displays of this type, backlighting is not necessary because the pixels themselves produce light. Other displays contain passive pixels that can alter the amount of light that is transmitted through the display to display information for a user. Passive pixels do not produce light themselves, so it is often desirable to provide backlight for a display with passive pixels. 
     In a typical backlight assembly for a display, a light guide plate is used to distribute backlight generated by a light source such as a light-emitting diode light source. Optical films such as a diffuser layer and prism films may be placed on top of the light guide plate. A reflector may be formed under the light guide plate to improve backlight efficiency. 
     A strip of light-emitting diodes may provide light to an edge of a light guide plate. Light from the strip of light-emitting diodes is initially concentrated in the vicinity of the outputs of the light-emitting diodes. The light must travel a sufficient distance into the light guide plate to mix enough to be used as backlight illumination. Backlight units that require large mixing distances may consume more volume within a display than desired. 
     It would therefore be desirable to be able to provide displays with improved backlights. 
     SUMMARY 
     A display may have an array of pixels for displaying images for a viewer. The array of pixels may be formed from display layers such as a color filter layer, a liquid crystal layer, a thin-film transistor layer, and polarizer layers. 
     A backlight unit may be used to produce backlight illumination for the display. The backlight illumination may pass through the polarizers, the thin-film transistor layer, the liquid crystal layer, and the color filter layer. The backlight unit may have a row of light-emitting diodes that emit light into a light guide plate. 
     The light guide plate may have first and second opposing surfaces connected by an edge that receives light from the row of light-emitting diodes. The edge of the light guide plate may have a light mixing structure and a reflective portion. A portion of the light emitted by the light-emitting diodes may pass through the light mixing structure and be refracted at a high angle. The portion of light may subsequently be reflected by the reflective portion of the edge. An additional portion of the light may pass through the light mixing structure and be refracted at a low angle. The additional portion of the light may not be reflected by the reflective portion. 
     The light mixing structures may include protrusions with edge surfaces and center surfaces. The edge surfaces may be positioned at a first angle with respect to a planar portion of the edge of the light guide plate. The center surfaces may be positioned at a second angle with respect to the planar portion of the edge of the light guide plate. The first angle may be greater than the second angle. The center surfaces may be interposed between the edge surfaces. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative display in an electronic device in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative display in accordance with an embodiment. 
         FIG. 4  is cross-sectional side view of an illustrative symmetrically tapered portion of a light guide plate for a display backlight in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative light guide plate with light-scattering features such as bumps on its lower surface in accordance with an embodiment. 
         FIG. 6  is graph in which bump density has been plotted as a function of position along the length of a light guide plate in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a light guide plate showing how different light rays interact with the surfaces of the light guide plate by different amounts in accordance with an embodiment. 
         FIG. 8  is a cross-sectional perspective view of a light guide plate showing how rounded ridges may extend along the upper surface of the light guide plate in accordance with an embodiment. 
         FIG. 9  is a perspective view of an illustrative light guide plate with light mixing structures along an edge in accordance with an embodiment. 
         FIG. 10  is a top view of illustrative protrusions for mixing light in accordance with an embodiment. 
         FIGS. 11A and 11B  are top views of light-emitting diodes emitting light into light guide plates showing how light is mixed with and without the protrusions of  FIG. 10  in accordance with an embodiment. 
         FIGS. 12A and 12B  are top views of illustrative light mixing structures in accordance with an embodiment. 
         FIGS. 13A and 13B  are top views of light-emitting diodes emitting light through the center surfaces and edge surfaces of the light mixing structures of  FIGS. 12A and 12B  in accordance with an embodiment. 
         FIG. 14  is a top view of a light-emitting diode emitting light through the light mixing structures of  FIGS. 12A and 12B  in accordance with an embodiment. 
         FIG. 15  is a top view of an illustrative light guide plate with recesses that provide a reflective surface in accordance with an embodiment. 
         FIG. 16  is a top view of an illustrative light guide plate with protruding portions that provide a reflective surface in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  12  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  12  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14 . 
     Device  10  may be a tablet computer, laptop computer, a desktop computer, a television, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device. 
     Display  14  for device  10  includes an array of pixels. The array of pixels may be formed from liquid crystal display (LCD) components or other suitable display structures. Configurations based on liquid crystal display structures are sometimes described herein as an example. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer, thin-film transistor layer, or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , display  14  may include a backlight unit such as backlight unit  42  (sometimes referred to as a backlight or backlight structures) for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 2 ) and passes through pixel structures in display layers  46 . This illuminates any images that are being produced by the pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in a housing in device  10  or display layers  46  may be mounted directly in an electronic device housing for device  10  (e.g., by stacking display layers  46  into a recessed portion in a metal or plastic housing). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of pixel circuits based on thin-film transistors and associated electrodes (pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). Integrated circuits such as integrated circuit  62 A and/or flexible printed circuits such as flexible printed circuit  64  may be attached to substrate  58  in ledge region  66  (as an example). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes (e.g., a series of light-emitting diodes that are arranged in a row that extends into the page in the orientation of  FIG. 2 ). The array of light-emitting diodes may be mounted to a rigid or flexible printed circuit. The printed circuit may be adhered to adjacent layers in the electronic device. In certain embodiments, the printed circuit may be adhered to portions of light guide plate  78 . 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits, bumps, grooves, or ridges that help light exit light guide plate  78  for use as backlight  44 . These features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . With one illustrative configuration, which is described herein as an example, a first surface such as the lower surface of light guide plate  78  has a pattern of bumps and an opposing second surface such as the upper surface of light guide plate  78  has a pattern of ridges (sometimes referred to as lenticules, lenticular structures, or lenticular ridges). Light source  72  may be located at the left of light guide plate  78  as shown in  FIG. 2  or may be located along the right edge of plate  78  and/or other edges of plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upward direction by reflector  80 . Reflector  80  may be formed from a reflective structure such as a substrate layer of plastic coated with a dielectric mirror formed from alternating high-index-of-refraction and low-index-of-refraction inorganic or organic layers. Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots. Optical films  70  may also include prism films (sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 2 , optical films  70  and reflector  80  may each have a matching rectangular footprint. Optical films  70  may include compensation films for enhancing off-axis viewing or compensation films may be formed within the polarizer layers of display  14  or elsewhere in display  14 . 
       FIG. 3  is a top view of a portion of display  14  showing how display  14  may have an array of pixels  90  formed within display layers  46 . Pixels  90  may have color filter elements of different colors such as red color filter elements R, green color filter elements G, and blue color filter elements B. Pixels  90  may be arranged in rows and columns and may form active area AA of display  14 . The borders of active area AA may be slightly inboard of the borders of light-guide plate  78  to ensure that there are no visible hotspots in display  14  (i.e., no areas in which the backlight illumination for display  14  is noticeably brighter than surrounding areas). For example, border  92  of active area AA may be offset by a distance  82  from lower edge  76  of light guide plate. It is generally desirable to minimize the size of distance  82  so that display  14  is as compact as possible for a given active area size. Nevertheless, distance  82  should not be too small to ensure that there is adequate light mixing. In particular, distance  82  should be sufficiently large to allow light  74  that is emitted from light-emitting diodes  72  to homogenize enough to serve as backlight illumination. Distance  82  is often as long as necessary to ensure light from light-emitting diodes  72  is sufficiently mixed. Accordingly, distance  82  may sometimes be referred to as mixing distance  82 . When light  74  is initially emitted from individual light-emitting diodes  72 , light  74  is concentrated at the exits of light-emitting diodes  72  and is absent in the spaces between light-emitting diodes  72 . After light  74  has propagated sufficiently far within light-guide plate  78  (i.e., after light  74  has traversed a sufficiently large mixing distance  82 ), light  74  will be smoothly distributed along dimension X and will no longer be concentrated near the exits of respective individual light-emitting diodes  72 . 
     To enhance the efficiency with which light  74  is coupled into edge  76  of light guide plate from light-emitting diodes  72  without overly thickening light-guide plate  78 , it may be desirable to provide light-guide plate  78  with an outwardly tapered (flared) edge. Conventional edge tapers are formed by creating a taper in the upper surface of a light guide plate adjacent to the light-emitting diodes and leaving the opposing planar lower surface of the light guide plate untouched. If care is not taken, however, this type of taper may have an angle that is too steep, raising the potential for excessive light leakage due to the loss of total internal reflection conditions in the taper region. With the illustrative taper configuration shown in the cross-sectional side view of illustrative light guide plate  78  of  FIG. 4 , excessive light losses are avoided by providing light guide plate  78  with both upper and lower taper structures  100  and  102 , respectively. Tapers  102  and  100  may be symmetrical or tapers  102  and  100  may have different shapes. In region  96 , light-guide plate  78  is planar and has planar parallel opposing upper and lower surfaces  106  and  108 , respectively. In taper region  98 , light guide plate  78  has a thickness that varies from the thickness of region  96  (T 2 ) to enlarged thickness T 1  at edge  76 , so taper structure surfaces  112  and  104  are angled at non-zero angles with respect to planar upper and lower light guide plate surfaces  106  and  108 . Thickness T 2  may be about 400 microns 300-500 microns, less than 600 microns, more than 200 microns, or other suitable thickness. The enlarged size of dimension T 1  helps light guide plate  78  receive light  74  from light-emitting diodes  72 . The taper in light guide plate  78  formed by taper structures  100  and  102  helps concentrate light  74  into region  96  of light guide plate for use in forming backlight  44 . 
     As shown in  FIG. 5 , lower surface  96  of light guide plate  78  may be provided with light scattering features such as bumps (protrusions)  114 . Bumps  114  may help redirect light  74  that is traveling within the interior of light guide plate  78  upwards in direction Z to serve as backlight  44  for display  14 . 
     As light  74  that is traveling within light guide plate  78  is directed upwards in direction Z to serve as backlight  44 , the intensity of the light  74  that remains in light guide plate  78  decreases. As a result, the intensity of light  74  is greatest at edge  76  of light guide plate  78  adjacent to light-emitting diodes  72  and decreases with increasing distance along axis Y away from edge  76 . It is generally desirable for the intensity of backlight  44  to be evenly distributed across the surface of light guide plate  78  in dimensions X and Y. To ensure that backlight  44  is not too dim at large values of Y, the density of bumps  114  can be increased as a function of increasing value of Y, as shown in  FIG. 6 . The increase in the density of bumps  114  at larger Y values offsets the decrease in the intensity of light  74  within light guide plate at larger Y values and thereby ensures that backlight  44  has a uniform intensity as a function of dimension Y. 
     Light-emitting diodes  72  emit light  74  in a cone. This cone of light includes highly angled off-axis light rays. As shown in the cross-sectional side view of light guide plate  78  of  FIG. 7 , some of the highly angled light rays such as light ray  74 - 1  lie primarily in the YZ plane. These light rays interact strongly with upper surface  106  and lower surface  108  of light guide plate and therefore tend to be heavily extracted by bumps  114  on lower surface  108 . Other highly angled light rays in the cone of emitted light  74  such as illustrative light ray  74 - 2  in  FIG. 7  lie primarily in the XY plane. These rays are angled more along dimension X than dimension Z and therefore interact with surfaces  106  and  108  less frequently than ray  74 - 1 . To ensure that light rays such as light ray  74 - 2  are adequately extracted and can serve as backlight  44 , light guide plate  78  may be provided with lenticular ridges such as ridges  130  of  FIG. 8 . Ridges  130  may be formed on upper surface  106  of light guide plate  78  (as an example). As shown in  FIG. 8 , ridges  130  may run parallel to dimension Y (i.e., the direction in which the exit faces of light-emitting diodes  72  are oriented and the direction in which light  74  is emitted into edge  76  of light guide plate  78 ). Ridges  130  may have semicircular cross-sectional shapes or may have other suitable shapes (triangular, etc.). As shown in  FIG. 8 , the presence of ridges  130  may help extract highly angled light rays such as light ray  74 - 2  that are propagating close to the XY plane to produce corresponding backlight  44 . 
       FIG. 9  is a perspective view of an illustrative light guide plate. As shown, the light guide plate may have protruding portions  94  that extend between light-emitting diodes  72 . The light-emitting diodes  72  may be positioned on a rigid or flexible printed circuit (not shown in  FIG. 9 ). Protruding portions  94  may act as a substrate for securing the printed circuit. For example, adhesive may attach the bottom surface of protruding portions  94  to a rigid or flexible printed circuit. Light-emitting diodes may be positioned on the printed circuit such that each light-emitting diode is interposed between two protruding portions  94  when the printed circuit is adhered to protruding portions  94 . Any type of adhesive may be used to attach protruding portions  94  to a rigid or flexible printed circuit (e.g., pressure sensitive adhesive, liquid cured adhesive, light cured adhesive, etc.). 
     As discussed in connection with  FIG. 3 , a given mixing distance may be necessary to ensure that light from light-emitting diodes is homogenous before entering the active area of the display. In order to reduce the size of display  14  and, accordingly, electronic device  10 , it may be desirable to reduce the length of mixing distance  82 . To reduce mixing distance  82 , edge  76  of light guide plate  78  may include light mixing structures. Edge  76  may be defined as the surface that connects the top surface of light guide plate  78  to the bottom surface of light guide plate  78 . Edge surface  76  may be substantially perpendicular to the top and bottom surfaces of light guide plate  78 . Edge surface  76  may be substantially perpendicular to optical films  70  and reflector  80 . Regions  75  of edge surface  76  (e.g., the regions in front of the light-emitting diodes) may include light mixing structures. Light mixing structures may be included on the edge of light guide plate  78  for the portions of edge  76  that are directly in front of light-emitting diodes  72 . This will ensure that light exiting light-emitting diodes  72  travels through the light mixing structures while entering light guide plate  78 . 
       FIG. 10  is a top view of an illustrative light guide plate with light mixing structures. As shown in  FIG. 10 , edge  76  of light guide plate  78  may be provided with locally raised features such as protrusions  122 . Protrusions  122  may have semicircular profiles, or may have other shapes. Angle A may be about 140-175° or other suitable value to help refract light  74  at angles in plate  78 , thereby enhancing light mixing and helping to reduce mixing distance  82  ( FIG. 3 ). Protrusions  122  may have widths (in dimension X) of about 75-125 microns or other suitable widths. Protrusions  122  may be spaced apart by about 250 microns, 200-300 microns, less than 320 microns, or more than 150 microns (as examples). Protrusions  122  may be spread evenly along edge  76  or may be clustered adjacent to respective light-emitting diodes  72 . 
       FIGS. 11A and 11B  show the light emission of a light-emitting diode with and without protrusions  122 .  FIG. 11A  shows a light-emitting diode  72  emitting light rays  74  into a light guide plate  78  with a planar edge surface  76 . In  FIG. 11A , edge  76  may lack light mixing structures such as protrusions  122 . As shown, light-emitting diode  72  emits light  74  in a cone. The cone of light in  FIG. 11A  has a width  124 .  FIG. 11B  shows a light-emitting diode  72  emitting light rays  74  into a light guide plate  78  with an edge surface  76  that has light mixing structures. In  FIG. 11B , edge  76  may include protrusions  122  as shown in  FIG. 10 . As shown, the width  126  of the cone of light in  FIG. 11B  is greater than the width  124  of the cone of light in  FIG. 11A . The protrusions assist in spreading the light. This may assist in decreasing mixing distance  82 . 
     Even with the additional light mixing caused by protrusions  122 , there may still be portions of light guide plate  78  that do not receive light  74  close to edge  76 . As previously mentioned, when light  74  is initially emitted from individual light-emitting diodes  72 , light  74  is concentrated at the exits of light-emitting diodes  72  and is absent in the spaces between light-emitting diodes  72 . For example, area  132  (positioned in between light-emitting diodes  72 ) in  FIG. 11B  may not receive any light. In order to distribute light to regions in between light-emitting diodes  72  (e.g., area  132 ), light mixing structures must generate high angled light rays. In this context, low angled rays may mean light that travels substantially in the X direction, while high angled rays may mean light that travels substantially in the Y direction. 
     High-angled light rays may reach the areas in between light-emitting diodes. However, high-angled light rays may leak out of lenticular ridges  130 , causing undesirable bright bands. High-angled light rays may also leak out of the edges of light guide plate  78 . Therefore, while some high-angled light is desirable to reduce mixing distance  82 , too much high-angled light may not be desirable. 
     As shown in  FIG. 12A , in order to reduce mixing distance  82  while ensuring there is not too much high-angled light, display  14  may be provided with light mixing structures  142 . Light mixing structures  142  may include center surfaces  144  and edge surfaces  146 . Center surfaces  144  may be interposed between edge surfaces  146 . Center surfaces  144  may connect a first edge surface to a second edge surface. A portion of light that travels through light mixing structures  142  will pass through the center surfaces while a portion will travel through the edge surfaces. The light that travels through the center surfaces may respond similarly to light travelling through protrusions  122  in  FIG. 11B . The light that travels through the edge surfaces may exit the light mixing structures at a very high angle. In this way, light mixing structures  142  produce both low angle and high angle light. 
       FIG. 12B  is a top view of a single illustrative light mixing structure  142 . As shown, the center surfaces  144  may be positioned at angle  152  with respect to the plane of planar edge  76  (shown by the dashed line). Angle  152  may be between 5° and 35°, between 10° and 30°, between 15° and 25°, more than 15°, less than 30°, or any other desired value. In one illustrative embodiment, angle  152  may be 20°. In certain embodiments, angle  152  may be 0°. In these embodiments, a single surface that is parallel to planar edge  76  may connect edge surfaces  146 . Edge surfaces  146  may be positioned at an angle  154  with respect to the plane of planar edge surface  76 . Angle  154  may be between 70° and 89°, between 75° and 85°, more than 85°, less than 85°, or any other desired value. In one illustrative embodiment, angle  154  may be 80°. 
     The height and width of light mixing structures  142  may be any desired value. Height  158  may be, for example, between 5 microns and 100 microns, between 20 microns and 50 microns, less than 5 microns, more than 100 microns, more than 1000 microns, or any other desired distance. Width  156  may be, for example, between 30 and 100 microns, between 40 and 60 microns, less than 40 microns, greater than 40 microns, greater than 500 microns, or any other desired distance. In one illustrative example, height  158  may be equal to 25 microns while width  156  may be equal to 50 microns. 
     Each light mixing structure may be separated by distance  160 , as shown in  FIG. 12A . Distance  160  may be between 30 and 100 microns, between 40 and 60 microns, less than 40 microns, greater than 40 microns, greater than 500 microns, or any other desired distance. The distance between each light mixing structure may be uniform (e.g., the same distance separates each light mixing structure). The distance between each light mixing structure may also vary. The distance between some light mixing structures may be smaller than the distance between other light mixing structures. 
     The total amount of edge  76  that is taken up by light mixing structures  142  may be referred to as the coverage of the light mixing structures. For example, if the width  156  of each light mixing structure was 40 microns, the distance  160  between each light mixing structure was 60 microns, and the light mixing structures were evenly spaced in front of each light-emitting diode, the coverage of light mixing structure  142  would be 40%. Light mixing structures  142  may have a coverage of less than 10%, between 10% and 80%, between 35% and 65%, more than 65%, more than 80%, more than 90%, 100%, or any other desired percentage. 
     Instead of protrusions, the light mixing structures shown in  FIGS. 10 and 12  may be implemented as recesses. For example, instead of triangular protrusion  122  in  FIG. 10 , the same shaped triangle may be formed as a recess. In one illustrative example, angle A of triangular protrusion  122  in  FIG. 10  may be equal to 160°. Instead a triangular recess may be formed, with angle A made equal to 200°. 
       FIGS. 13A and 13B  show how light is scattered when passing through the center surfaces and edge surfaces of light mixing structures  142 .  FIG. 13A  shows light  74  emitted from light-emitting diode  72  that passes through the center surfaces  144  of light mixing structures  142 . As shown, light  74  that passes through center surfaces  144  is emitted in a cone primarily in the Y direction similar to those shown in  FIGS. 11A and 11B .  FIG. 13B  shows light  74  emitted from light-emitting diode  72  that passes through the edge surfaces  146  of light mixing structures  142 . As shown, light  74  that passes through edge surfaces  146  is refracted at a high angle primarily in the X direction. 
     In order to prevent the undesirable effects of high angle light, light guide plate  78  may be provided with a reflective surface as shown in  FIG. 14 . As shown, light may be emitted from light-emitting diode  72  and pass through light mixing structures  142  such as those shown in  FIGS. 12A and 12B . For clarity, the light mixing structures on edge  76  of light guide plate  78  are not drawn in  FIG. 14 . A first portion of the light ( 74 -C) may pass through the center surfaces of light mixing structures  142  or the planar edge surface  76  (e.g., the planar portions of light guide plate  78  in between each light mixing structure  142 ). Light  74 -C may be emitted in a cone as previously depicted in  FIG. 13A . A second portion of the light ( 74 -E) may pass through the edge surfaces of light mixing structures  142 . Light  74 -E may be refracted at high angles and travel primarily in the X direction. Light  74 -E may then be reflected off of a reflective surface  162 . Reflective surfaces  162  may direct the high angle light in the Y direction to become low angle light. This causes light  74 -E to travel into the light guide plate. The light mixing structures  142  used in combination with reflective surfaces  162  cause light  74  to mix very quickly after being emitted from light-emitting diodes  72 . Light  74  will be smoothly distributed along dimension X and will no longer be concentrated near the exits of respective individual light-emitting diodes  72 . 
     The reflective surfaces  162  may be implemented in a variety of different ways. For example, a reflector may be formed on reflective surface  162 . Reflector  162  may be formed from a reflective structure such as a substrate layer of plastic coated with a dielectric mirror formed from alternating high-index-of-refraction and low-index-of-refraction inorganic or organic layers. Reflector  162  may be formed from a reflective material such as a layer of white plastic or other shiny materials. In addition or in combination with using a reflective material, reflective surface  162  may have no additional material and use total internal reflection to reflect the light. In certain situations, light that strikes reflective surface  162  at a high enough angle will not pass through the surface and be totally reflected. The light guide plate may be designed so that light  74 -E strikes reflective surface  162  at an angle and is reflected due to total internal reflection. In general, any material or setup may be used that reflects light  74 -E in the Y direction. 
     Reflective surface  162  may be separated from the edge of light-emitting diode  72  by distance  164 . Distance  164  may be less than 0.1 millimeters, less than 0.5 millimeters, less than 1.0 millimeters, less 1.5 millimeters, greater than 1.0 millimeters, or any other desired distance. Reflective surface  162  may be at an angle  166  with respect to the planar surface of edge  76 . Angle  166  may have any desired value (e.g., between 5° and 80°, between 30° and 60°, between 40° and 50°, less than 60°, more than 20°, etc.). 
       FIG. 15  shows an illustrative light guide plate with light mixing structures. As shown, a number of light-emitting diodes  72  may be positioned adjacent to edge  76  of light guide plate  78 . Although not drawn in  FIG. 15 , edge  76  may include light mixing structures such as light mixing structures  142  on the edge of the light guide plate in front of the light-emitting diodes. Light guide plate  78  may include recesses  168  that provide an angled surface for reflective surface  162 . Some of light  74  may pass directly through the light mixing structures down the light guide plate while some light may be refracted at a high angle before being reflected in the Y direction by the reflective surface  162 . 
     Adhesive may be positioned between light-emitting diodes  72  (e.g., area  170 ) on the printed circuit that acts as a substrate for the light-emitting diodes. The adhesive may be used to attach the light-emitting diodes&#39; printed circuit to additional layers in the display. 
     As discussed in connection with  FIG. 9 , the light guide plate may have protruding portions  94  that extend adjacent light-emitting diodes  72 . Protruding portions  94  may act as a substrate for attaching the printed circuit with light-emitting diodes  72 . For example, adhesive may attach the bottom surface of protruding portions  94  to a rigid or flexible printed circuit. Light-emitting diodes may be positioned on the printed circuit such that each light-emitting diode is interposed between two protruding portions  94  when the printed circuit is adhered to protruding portions  94 . As shown in  FIG. 16 , protruding portions  94  may be designed to provide a reflective surface  162  for the light guide plate. Reflective surface  162  may be provided with a reflective material or use total internal reflection to reflect light. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20150922
Publication Date: 20181113
Grant Date: 20181113
Priority Date: 20150813
Inventors: BROWN, MICHAEL J.
DOYLE, DAVID A.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0025", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0018", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0018", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0025", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57994645