PATENT DOCUMENT

Publication Number: US-9535206-B2
Application Number: US-201414494555-A
Country: US
Kind Code: B2

Title: Display with structures for reducing blue edge effects

Abstract:
Display backlight structures may provide backlight illumination that passes through display layers in the display. Light-emitting diodes may emit blue light into an edge of a light guide plate. Optical films may overlap the light guide plate. The optical films may include a quantum dot enhancement film. A peripheral strip of yellow reflector or other light control structures may be incorporated into the backlight structures to reduce blue edge effects. The light control structures may have features with a spatially varying density, may be formed from quantum dot enhancement film, or may be formed form other structures. The light control structures may be formed on the surfaces of the optical films, on a reflective layer under the light guide plate, or on a surface of a mold frame or other structure that lies in a plane parallel to the plane of the light guide plate.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 display layers including a layer of liquid crystal material; and 
 backlight structures that supply backlight that passes through the display layers, wherein the backlight structures include:
 a rectangular light guide plate having edges; 
 a reflective layer under the rectangular light guide plate; 
 an array of blue light-emitting diodes that emit blue light into at least one edge of the light guide plate; 
 a quantum dot enhancement film on top of the light guide plate that converts the blue light into red and green light, wherein the red and green light and some of the blue light form the backlight that passes through the display layers; and 
 a light control structure that reduces blue edge effects in the display, wherein the light control structure comprises a reflector in a peripheral region of the backlight structures, wherein the reflector is a yellow reflector that absorbs some of the blue light, and wherein the yellow reflector has a spatially varying density of yellow material. 
 
 
     
     
       2. The display defined in  claim 1  wherein the spatially varying density of yellow material is formed by a spatially varying density of yellow dots. 
     
     
       3. The display defined in  claim 1  wherein the quantum dot enhancement film has opposing inner and outer surfaces and wherein the reflector is formed on a peripheral portion of the outer surface. 
     
     
       4. The display defined in  claim 3 , the backlight structures further comprising:
 at least one optical film over the outer surface of the quantum dot enhancement film, wherein the quantum dot enhancement film is interposed between the at least one optical film and the rectangular light guide plate, wherein the reflector is formed on the peripheral portion of the outer surface of the quantum dot enhancement film without overlapping the at least one optical film, and wherein the quantum dot enhancement film is interposed between the reflector and the rectangular light guide plate. 
 
     
     
       5. A display, comprising:
 display layers including a layer of liquid crystal material; and 
 backlight structures that supply backlight that passes through the display layers, wherein the backlight structures include:
 a rectangular light guide plate having edges; 
 a reflective layer under the rectangular light guide plate; 
 an array of blue light-emitting diodes that emit blue light into at least one edge of the light guide plate; 
 a quantum dot enhancement film on top of the light guide plate that converts the blue light into red and green light, wherein the red and green light and some of the blue light form the backlight that passes through the display layers; and 
 a light control structure that reduces blue edge effects in the display, wherein the light control structure comprises a reflector in a peripheral region of the backlight structures, wherein the quantum dot enhancement film has opposing inner and outer surfaces, and wherein the reflector is formed on a peripheral portion of the inner surface. 
 
 
     
     
       6. The display defined in  claim 5  wherein the reflector comprises a yellow reflector. 
     
     
       7. The display defined in  claim 1  wherein the backlight structures further comprise a support structure overlapping a peripheral edge portion of the quantum dot enhancement film and wherein the reflector is formed on a surface of the support structure. 
     
     
       8. The display defined in  claim 7  wherein the support structure is a mold frame. 
     
     
       9. The display defined in  claim 1  wherein the backlight structures further comprise at least one optical film over the quantum dot enhancement film and wherein the reflector is formed on the optical film. 
     
     
       10. The display defined in  claim 9  wherein the optical film comprises a prism film. 
     
     
       11. A display, comprising:
 display layers including a layer of liquid crystal material; and 
 backlight structures that supply backlight that passes through the display layers, wherein the backlight structures include:
 a rectangular light guide plate having edges; 
 a reflective layer under the rectangular light guide plate; 
 an array of blue light-emitting diodes that emit blue light into at least one edge of the light guide plate; 
 a quantum dot enhancement film on top of the light guide plate that converts the blue light into red and green light, wherein the red and green light and some of the blue light form the backlight that passes through the display layers; and 
 a light control structure that reduces blue edge effects in the display, wherein the light control structure comprises a reflector in a peripheral region of the backlight structures, wherein the backlight structures further comprise at least one optical film over the quantum dot enhancement film, wherein the reflector is formed on the optical film, wherein the optical film has an outer surface and an opposing inner surface, and wherein the reflector is formed on the inner surface. 
 
 
     
     
       12. The display defined in  claim 9  further comprising an additional optical film interposed between the reflector and the quantum dot enhancement film. 
     
     
       13. The display defined in  claim 12  wherein at least one of the optical film and the additional optical film comprises a prism film. 
     
     
       14. A display, comprising:
 display layers including a layer of liquid crystal material; and 
 backlight structures that supply backlight that passes through the display layers, wherein the backlight structures include:
 a rectangular light guide plate having edges; 
 a reflective layer under the rectangular light guide plate; 
 an array of blue light-emitting diodes that emit blue light into at least one edge of the light guide plate; 
 a quantum dot enhancement film on top of the light guide plate that converts the blue light into red and green light, wherein the red and green light and some of the blue light form the backlight that passes through the display layers; and 
 a light control structure that reduces blue edge effects in the display, wherein the light control structure comprises a reflector in a peripheral region of the backlight structures, and wherein the reflector is formed on a surface of the reflective layer and is interposed between the reflective layer and the light guide plate. 
 
 
     
     
       15. The display defined in  claim 14  wherein the reflector comprises a yellow reflector and wherein the reflective layer comprises a sheet of white plastic. 
     
     
       16. The display defined in  claim 15  wherein the array of blue light-emitting diodes emit the blue light into a given one of the edges of the light-guide plate and wherein a portion of the quantum dot enhancement film extends over the give edge of the light guide plate towards the light-emitting diodes. 
     
     
       17. The display defined in  claim 14 , the backlight structures further comprising:
 an additional light control structure that reduces blue edge effects in the display, wherein the additional light control structure comprises an additional reflector in the peripheral region of the backlight structures, wherein the additional reflector is formed on a surface of the quantum dot enhancement film, and wherein the quantum dot enhancement film is interposed between the additional reflector and the rectangular light guide plate. 
 
     
     
       18. The display defined in  claim 5 , wherein the reflector is interposed between the quantum dot enhancement film and the rectangular light guide plate. 
     
     
       19. The display defined in  claim 11 , wherein the quantum dot enhancement film is interposed between the optical film and the rectangular light guide plate, and wherein the reflector is interposed between the quantum dot enhancement film and the optical film.

Description:
This application claims the benefit of provisional patent application No. 62/009,504, filed Jun. 9, 2014, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers may have displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. Display pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a display pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the display pixel. 
     Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. A thin-film transistor layer contains an array of the thin-film transistors that are used in controlling electric fields in the liquid crystal layer. A color filter layer contains an array of color filter elements such as red, blue, and green elements. The color filter layer provides the display with the ability to display color images. In some displays the color filter elements are formed on the thin-film transistor layer. 
     A backlight unit is used to provide illumination for the display. The backlight unit includes light-emitting diodes that supply light to the edge of a light guide plate. The light guide plate laterally distributes light from the light-emitting diodes across the display. Scattering features in the light guide plate cause the light in the light guide plate to scatter outwardly through the layers of the display. 
     In color displays, the backlight illumination is white light that includes red, green, and blue components. In some displays, the light-emitting diodes that are used to provide light to the edge of the light-guide plate emit blue light. A quantum dot enhancement film is provided in the backlight to convert some of the blue light into red and green light. 
     Backlight units that include blue light-emitting diodes and quantum dot enhancement film can be subject to undesired blue edge effects where the peripheral edge of the backlight produces more blue light than red and green light. A display that is illuminated with this type of backlight unit will have an undesired blue color cast along its edges. The blue color cast can adversely affect the quality of images displayed on a display. 
     It would therefore be desirable to be able to provide improved backlights for displays such as liquid crystal displays. 
     SUMMARY 
     A display may have a color filter layer and a thin-film transistor layer. A liquid crystal layer may be located between the color filter layer and the thin-film transistor layer. Backlight structures may provide backlight illumination that passes through display layers in the display such as the color filter layer, thin-film transistor layer, and liquid crystal layer. 
     The backlight structures may have a light guide plate. Light-emitting diodes may emit blue light into an edge of the light guide plate. Optical films may overlap the light guide plate. The optical films may include a quantum dot enhancement film that converts some of the blue light into red and green light. 
     A strip of yellow reflector or other light control structures may be incorporated into the backlight structures to reduce blue edge effects. The material in the yellow reflector or other light control structures (e.g., yellow reflective material, quantum dot material, phosphorescent material, etc.) may absorb excess blue light at the edges of the display and may reflect or otherwise emit corresponding yellow(er) light (e.g., light that is less blue due to blue absorption by the light control structures and that may have red and green components). The light control structures may have features with a spatially varying density to reduce backlight illumination hot spots or dark areas. For example, a yellow reflector may have yellow dots with a density that decreases at increasing distances away from the edge of the light guide plate. If desired, the light control structures may be formed from peripheral strips of quantum dot enhancement film or other materials to enhance blue light conversion to red and green light near the edge of the display. 
     The light control structures may be formed on the surfaces of the optical films, on a reflective layer under the light guide plate, or on a surface of a mold frame or other structure that lies in a plane parallel to the plane of the light guide plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative light guide plate and array of light-emitting diodes for a backlight unit in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a portion of a display showing how the display may have a backlight unit with light-emitting diodes arranged along the edge of a light-guide plate that has been covered with optical films such as a quantum dot enhancement film in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of an illustrative quantum dot enhancement film in accordance with an embodiment. 
         FIG. 9  is a graph showing how reflective structures in a backlight may be provided with different spectral profiles in accordance with an embodiment. 
         FIG. 10  is a diagram showing how a reflective structure may be formed with reflective dots with a graded density or other spatially varying reflecting surfaces in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of a portion of a display in which a reflective structure has been interposed under a peripheral portion of an optical film in a backlight to help reduce blue edge effects in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of a portion of a display in which a reflective structure has been formed above a peripheral portion of an optical film in a backlight to help reduce blue edge effects in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of a portion of a display in which a reflective structure has been formed under a peripheral structure such as a mold frame that overlaps the edge of an optical film in a backlight to help reduce blue edge effects in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a portion of a display in which reflective structures have been formed above a peripheral portion of an optical film and below a light-guide plate in a backlight to help reduce blue edge effects in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a portion of a display in which layers in a backlight unit have been laterally extended to help reduce blue edge effects in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of a portion of a display in which a reflective structure has been formed on the underside of an optical film in a stack of optical films that overlap a light guide plate in a backlight to help reduce blue edge effects in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
     Illustrative electronic device  10  of  FIG. 1  has the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a computer display, a computer that has been integrated into a computer display, or a display for other electronic equipment. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  30  or stand  30  may be omitted (e.g., stand  30  can be omitted when mounting device  10  on a wall). Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include display pixels formed from liquid crystal display (LCD) components or other suitable image pixel structures. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter 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  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display 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 housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). 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 thin-film transistors and associated electrodes (display 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, lower layer  58  may be a color filter layer and upper layer  56  may be a thin-film transistor layer. Another illustrative configuration involves forming color filter elements and thin-film transistor circuits with associated pixel electrodes on a common substrate. This common substrate may be the upper substrate or may be the lower substrate and may be used in conjunction with an opposing glass or plastic layer (e.g., a layer with or without any color filter elements, thin-film transistors, etc.) to contain liquid crystal layer  52 . Illustrative configurations for display  14  in which layer  56  is a color filter layer and layer  58  is a thin-film transistor layer are sometimes described herein as an example. 
     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). 
     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. If desired, light sources such as light source  72  may be located along multiple edges 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 or humps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide 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 upwards direction by a reflective film such as reflector  80 . Reflector  80  may be formed from a reflective material such as a reflective layer of white plastic or other reflective materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include one or more diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots and one or more prism films (also sometimes referred to as turning films or brightness enhancement films) for collimating backlight  44 . If desired, optical films  70  may include a quantum dot enhancement film. Compensation films for enhancing off-axis viewing may be included in optical films  70  or may be incorporated into other portions of display  14  (e.g., polarizer layers). 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. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     A top view of an illustrative rectangular light guide plate is shown in  FIG. 6 . As shown in  FIG. 6 , light-emitting diodes  72  may be arranged in an array along edge  76  of light-guide plate  78 . Light-guide plate  78  may also have other peripheral edges such as edges  76 ′. If desired, light-emitting diodes  72  may provide light  74  for two or more peripheral edges of light guide plate  78 . The configuration of  FIG. 6  is shown as an example. 
     A cross-sectional side view of illustrative backlight structures for display  14  is shown in  FIG. 7 . As shown in  FIG. 7 , backlight structures  42  may include optical films  70 , light guide plate  78 , and reflector (reflective layer)  80 . Vertically extending edge reflector structures such as edge reflector  80 ′ may be formed from white plastic, colored material, or other reflective material. 
     Optical films  70 , light guide plate  78 , and reflective layer  80  may be mounted in a chassis structure and/or may be mounted directly in housing  12 . In the example of  FIG. 7 , films  70 , light guide plate  78 , and reflective layer  80  have been mounted in structure  102 . Structure  104  may run around the peripheral edges of backlight structures  42 . For example, structure  104  may extend along each of the four edges of a rectangular light guide plate. Portions of structure  104  may overlap portions of films  70 , light guide plate  78  and/or reflective layer  80 . Structures  104  and  102  may be formed as parts of an integral plastic or metal structure or may be separate structures. For example, structures  102  and  104  may be chassis structures in a backlight unit. If desired, structure  102  may be a metal chassis (sometimes referred to as an M-chassis) and structure  104  may be a plastic chassis (sometimes referred to as a P-chassis or mold frame). Structures  102  and  104  may also be formed from other materials such as glass, ceramic, fiber-based composites, other materials, or combinations of these materials, plastic(s), metal(s), and/or other suitable backlight structure supporting members. Structures  102  and  104  may be mounted in additional structures such as structure  100  (e.g., part of housing  12 , metal, glass, plastic, ceramic, fiber-based composite material, other materials, or combinations of these materials). Configurations in which structure  102  is a chassis structure and structure  104  is a mold frame are sometimes described herein as an example. In general, structures such a structures  100 ,  102 , and  104  and/or additional support structures for backlight structures  42  may be formed from plastic, metal, other materials, combinations of these materials, a single integral part, two separate parts, or three or more separate parts. The configuration of  FIG. 7  is merely illustrative. 
     Light-emitting diodes such as diode  72  may emit blue (B) light  74  into edge  76  of light guide plate  78 . Blue light  74  may be conveyed throughout light guide plate  78  due to the principal of total internal reflection. One of films  70  (e.g., the innermost film  70  in  FIG. 7 ) may be a quantum dot enhancement film. The quantum dot film may be a single-layer of quantum dot material or may include two or more sublayers (e.g., the quantum dot film may be formed from a stack of quantum dot films each with a different type of quantum dots and therefore a correspondingly different fluorescence spectrum). The films above the quantum dot enhancement film may be, for example, one, two, or more than two prism films, and one or more optional diffuser layers (as examples). Configurations in which films  70  include a lowermost layer that is a quantum dot enhancement film and two overlapping prism film layers are sometimes described herein as an example. Other configurations for backlight structures  42  and films  70  may be used, if desired. 
     The quantum dot enhancement film (i.e., the lowermost optical film in stack  70 ), may be formed from a polymer or other material that contains quantum dots. The quantum dots may be formed from semiconductor particles such as CdSe particles. When blue light travels through the quantum dot enhancement film, the quantum dots in the quantum dot enhancement film absorb some of the blue light and luminesce at red and green wavelengths. As a result, blue light B is converted into red, green, and blue light (R, G, B) for backlight  44 . The red, green, and blue color peaks in the spectrum of backlight  44  may be relatively narrow and may be spectrally aligned with the filter pass bands of the color filter elements in color filter layer  56 . The use of the quantum dot enhancement film may therefore be used to help ensure that display  14  has the ability to efficiently reproduce colors with a wide color gamut. 
     Backlight units such as backlight unit  42  of  FIG. 7  that incorporate quantum dot enhancement films may be prone to undesired blue color casts along their edges. The blue color cast along the edge of a backlight results from emission of excessive blue light relative to red and green light from the quantum dot film. The blue color cast may appear along edge portions of backlight structures  42  such as edges  106 , whereas central region  108  may exhibit appropriately balanced amounts of blue, green, and red light. Blue edges may be caused by light leakage of blue light B along edges  106 , ingress of oxygen and/or moisture into the edge of the quantum dot enhancement film in layers  70  that degrades the quantum dots and therefore decreases blue to red and blue to green light conversion efficiencies, preferential leakage of red and green light relative to blue light along light guide plate edges  76  and  76 ′ due to imperfect edge surfaces (i.e., surface roughness along edge surfaces  76  and  76 ′), and reduced blue light recycling (reduced passes of blue light) through the quantum dot enhancement film along edges  106  relative to central portion  108 . 
     Blue edge effects can be reduced or eliminated by incorporating light control structures into backlight structures  42  that block light and/or that reflect light. The light control structures may include reflective layers, reflective coatings, reflective portions of a mold frame or other backlight unit support structure, additional quantum dot enhancement film layers, and other structures. The light control structures may exhibit wavelength-dependent reflectivity. For example, a light control structure for backlight structures  42  may be formed from yellow structures such as peripheral strips of yellow plastic to absorb blue light. Light control structures with other spectral responses may also be used. 
     In some situations, light control structures such as reflective layers may have spatially uniform optical properties. For example, reflectance may be constant across the width of a reflector layer. In other situations, the light control structures may have gradually varying optical properties. For example, the spectrum of reflected light and/or the amount of reflected light from a light control structure may vary as a function of distance across the surface of the light control structure. Reflectors or other structures that have spatially varying reflectivities may be used to smooth transitions within backlight structures  42  (e.g., to minimize hotspots or dark spots within backlight  44 ). 
     Optical films  70  may include a quantum dot enhancement film formed from one or more sublayers of quantum dot film material. The light control structures that are incorporated into backlight unit  42  may also include quantum dot structures such as quantum dot enhancement film. A cross-sectional side view of an illustrative quantum dot enhancement film is shown in  FIG. 8 . As shown in  FIG. 8 , quantum dot enhancement film  110  may be formed from multiple layers of material. Quantum dot enhancement film  110  may, for example, include one or more polymer carrier layers such as upper polymer layer  112  and lower polymer layer  122 . Layers  112  and  122  may be substrate layers formed from materials such as polyethyleneterephthalate (PET), other polyesters, or other flexible polymer layers. Polymer resin  116  may be sandwiched between polymer layers  112  and  122 . Quantum dots  118  may be embedded within polymer  116 . Quantum dots  118  may be formed from semiconductor particles (e.g., particles of cadmium selenide or other semiconductors) or other materials. To prevent degradation of quantum dots  118  from environmental exposure (e.g., moisture and/or oxygen), moisture barrier layers such as moisture barrier layers  114  and  120  may be incorporated into quantum dot enhancement film  110 . For example, moisture barrier  114  may be interposed between polymer layer  112  and quantum dot polymer layer  116  and moisture barrier  120  may be interposed between polymer layer  122  and quantum dot polymer layer  116 . Moisture barrier films  114  and  120  may be formed from multiple layers of moisture blocking materials (e.g., layers of inorganic material). 
       FIG. 9  is a graph of illustrative reflection spectrums that may be exhibited by light control structures in backlight unit  42  (e.g., reflective materials). In the graph of  FIG. 9 , reflectivity R has been plotted as a function of wavelength over a visible wavelength range extending from 380 nm (violet) to 780 nm (red). Curve  124  corresponds to a material such as silver or other metal that is highly reflective and does not exhibit significant spectral variations across the visible spectrum. Curve  126  corresponds to another material that is relatively wavelength insensitive such as gray plastic. Curve  128  corresponds to a material that reflects red and green light more than blue light. This type of material will have a yellow appearance and is therefore sometimes referred to as a yellow reflector or yellow reflective material. Examples of yellow reflectors include yellow plastic layers, layers of plastic that have been coated with yellow paint (e.g., yellow dye or pigment in a liquid polymer binder), and molded yellow plastic that has been injection molded into a mold frame or other plastic part using one of two shots in a two shot molding process. Curve  130  is similar to curve  128  but exhibits less blue light reflectivity (i.e., curve  130  corresponds to a light control structure that has been coated with more yellow material that the structure associated with curve  128 ). 
       FIG. 10  is a diagram showing how a light control structure such as a yellow reflector or other reflector may have a pattern of dots or other surface treatment (pattern, coating depth, paint color, substrate color and/or texture, etc.) that varies as a function of lateral distance X across the surface of the light control structure. In graph  132 , curve  134  represents the density D of the surface treatment that has been applied to illustrative reflector  136 . 
     In the example of  FIG. 10 , reflector  136  has been coated with dots  138  on substrate  140 . Reflector substrate  140  may be a layer of grey plastic, white plastic, or other substrate. Dots  138  may be yellow dots formed from yellow paint or other material. Dots  138  may be formed using ink-jet printing, screen printing, pad printing, or other deposition and patterning techniques. The density D of dots  138  decreases as a function of increasing distance X across the surface of reflector  136 . As a result, reflector  136  will exhibit a reflectivity that is both spectrally varying (e.g., blue light will be reflected less than red and green light) and spatially varying (i.e., the wavelength selectivity of reflector  136  will be greater at low values of X where yellow dot density D is highest and will be lower at high values of X where yellow dot density D is lowest). The use of spatially graded reflectors and other light control structures that reflect light differently as a function of distance X across their width may be used to avoid hotspots and dark spots in backlight  44 . 
     Light control structures for reducing blue edge effects may be incorporated above or below light guide plate  78  and/or may be incorporated into other portions of backlight structures  42 . In the example of  FIG. 11 , light control structure  142  has been formed on lower (inner) surface  144  of optical film layer  70 - 1 . Optical films  70  may include layers such as layer  70 - 1 ,  70 - 2 , and  70 - 3 . Light control structure  142  may be formed as a coating on surface  144  of layer  70 - 1  in a peripheral portion of layer  70 - 1  running along the edges of the light guide plate or may be formed by attaching a strip-shaped plastic layer or other substrate for structure  142  to peripheral portions of surface  144  using adhesive. Layer  70 - 1  may be a quantum dot enhancement film. Layers  70 - 2  and  70 - 3  may be prism films (and/or additional layers such as diffuser layers, etc.). Light control structure  142  may be a yellow reflector, may be a spatially varying (graded density) yellow reflector, may have a reflectivity that is spatially invariant, may have a reflectivity that is graded, may have a non-yellow color, or may have other spectral properties and/or spatial variations. The presence of light control structure  142  may help reduce blue light at edge  106 . For example, a yellow reflective surface of light control structure  142  may absorb blue light relative to red and green light around the periphery of backlight structures  42 , so that edge  106  of backlight structures  42  emits backlight that is less blue. The use of a graded reflector (i.e., a reflector having a reflectivity that decreases as distance along dimension −X is increased) may help avoid creating hotspots or dark spots in light  44 . 
     In the example of  FIG. 12 , light control structure  142  has been formed on outer (upper) surface  146  of layer  70 - 1  (e.g., on the top layer of a quantum dot enhancement film) in a strip extending along one or more peripheral edge regions of backlight structures  42 . Light control structure  142  may be formed from yellow paint or other coating material that is deposited and patterned on surface  146 , may be formed from yellow plastic or plastic with yellow paint that has been mounted on surface  146 , or may be formed from other structures. Light control structure  142  may be graded. For example, light control structure  142  may have a pattern of yellow dots that decreases in density at increasing distances into structures  42  from each edge  76 ′ of light guide plate  78 . 
     Another illustrative arrangement for mounting light control structures  142  in backlight structures  42  is shown in  FIG. 13 . In the example of  FIG. 13 , mold frame  104  has a lower surface such as surface  148  that overlaps the edge of light guide plate  78  and that lies in a plane that is parallel to the plane of light guide plate  78 . Light control structure  142  can be formed on surface  148 . Light control structure  142  may be formed from yellow paint or other yellow coating layer on surface  148 , may be formed from a plastic substrate (e.g., a strip-shaped yellow plastic sheet or a strip of plastic that has been coated with yellow paint) that is mounted on surface  148 , or may be formed from other reflective structures. 
     If desired, mold frame  104  may be formed from multiple shots of injection molded plastic. In this scenario, light control structure  142  may be formed as one of the shots of plastic (see, e.g., plastic shot  142 ′ in  FIG. 13 ). The shot of plastic used in forming structure  142  may be, for example, yellow plastic. Light control structure  142  of  FIG. 13  may be mounted above layer  70 - 1  (e.g., a quantum dot enhancement film). Layers  70 - 2  and  70 - 3  (e.g., prism films and/or additional films) may have outer edges that are laterally adjacent to structures  104 . 
     If desired, additional light control structures such as light control structure  142 ″ may be incorporated into the edge of backlight structures  42  to reduce blue edge effects. Additional light control structure  142 ″ may be formed on outer surface  150  of layer  70 - 3 . Light control structure  142 ″ may be yellow paint or other yellow coating on surface  150 , may be formed from a yellow reflector mounted to surface  150  that is formed from a yellow plastic substrate or a plastic substrate coated with yellow paint, or may be other reflective layer(s). 
     Light control structures  142  and/or  142 ″ may be spatially invariant or may be graded (e.g., structures  142  and/or  142 ″ may have yellow dot densities or other reflective properties that vary as a function of position across their width). 
     As shown in  FIG. 14 , light control structures  142 ″′ may be formed on reflector  80  under a peripheral portion of light guide plate  78 . Light control structures  142 ″′ may be formed from yellow paint or other yellow coating layer on surface  152  of reflector  80 , may be formed from a yellow plastic strip or yellow-coated plastic strip that is mounted to peripheral portion of surface  152 , or may be formed from other reflective structures on surface  152 . Light control structures  142 ″ may be provided in a backlight unit such as backlight unit  42  of  FIG. 14  that also includes light control structure  142  on surface  146  of layer  70 - 1  (e.g., the surface of a quantum dot enhancement film) or that includes light control structures such as light control structure  142  or  142 ′ of  FIG. 13  or light control structure  142  of  FIG. 11 . 
     Light control structures  142  may be formed in a strip that runs along some or all of the peripheral edges of backlight unit  42  (e.g., a strip in a peripheral region that extends along edges  76 ′ and, if desired edge  76  of light guide plate  78 , etc.). In some configurations, one or more of the light control structures in backlight structures  42  may be formed from quantum dot enhancement film. For example, light control structures  142 ″′ of  FIG. 14  and/or a light control structure interposed between structures  142  and layer  70 - 1  of  FIG. 14  may be formed from quantum dot enhancement film. The incorporation of additional quantum dot enhancement film at the edges of backlight structures  42  enhances the conversion of blue light B into red light R and green light G for backlight  44  and helps to reduce blue edge effects. 
       FIG. 15  is a cross-sectional side view of a portion of backlight structures  42  in an illustrative configuration in which layer  70 - 1  and light control structure  142  (e.g., a peripheral reflector such as a yellow reflector, etc.) have been extended past edge  76  of light guide plate  78  towards light-emitting diode  72  and in which reflector  80  has been extended past edge  76  towards light-emitting diode  72 . This arrangement tends to enhance the conversion of blue light to red and green light (e.g., due to the presence of additional quantum dot enhancement film portion  70 - 1 ′ extending over edge  76  of light guide plate  78  towards the array of light-emitting diodes  72 ) and thereby helps to reduce blue edge effects. If desired, vertically extending reflectors in backlight structures  42  such as reflector  80 ′ of  FIG. 7  may be formed from yellow material to help further reduce blue edge effects. 
       FIG. 16  is a cross-sectional side view of a portion of a display in which a light control structure has been formed on an optical film in a stack of optical films that overlap light guide plate  78  in backlight  42  to help reduce blue edge effects. Optical films  70  may include layers such as layers  70 - 1 ,  70 - 2 , and  70 - 3 . Light control structure  142  may be formed on the upper and/or lower surface of one, two, or three or more of layers  70 - 1 ,  70 - 2 , and  70 - 3 . The optical film in layers  70  on which light control structure  142  is formed may be the uppermost of two layers  70 , may be the uppermost of three layers  70  (as shown in  FIG. 16 ) or may be any other layer in layers  70 . 
     In the example of  FIG. 16 , light control structure  142  has been formed on lower (inner) surface  160  of optical film layer  70 - 3 . Light control structure  142  may be formed as a coating on surface  160  of layer  70 - 3  in a peripheral portion of layer  70 - 3  running along the edges of light guide plate  78  or may be formed by attaching a strip-shaped plastic layer or other substrate for structure  142  to peripheral portions of surface  160  using adhesive. 
     Layers  70 - 1 ,  70 - 2 , and  70 - 3  of optical films  70  of  FIG. 16  may be prism films, diffuser layers, compensation films, quantum dot enhancement film, or other suitable optical films. For example, layer  70 - 1  may be a quantum dot enhancement film and layers  70 - 2  and  70 - 3  may be prism films or layer  70 - 1  may be a quantum dot enhancement film and layers  70 - 2  and  70 - 3  may include a prism film and a diffuser film. 
     Light control structure  142  of  FIG. 16  may be a yellow reflector, may be a spatially varying (graded density) yellow reflector, may have a reflectivity that is spatially invariant, may have a reflectivity that is graded, may have a non-yellow color, or may have other spectral properties and/or spatial variations. The presence of light control structure  142  may help reduce blue light at the edges of display  14 . For example, a yellow reflective surface of light control structure  142  may absorb blue light relative to red and green light around the periphery of backlight structures  42 , so that the edge of backlight structures  42  emits backlight that is less blue. The use of a graded reflector may help avoid creating hotspots or dark spots in light  44 . 
     In general, the light control structures that are incorporated into backlight  42  such as light control structure  142  of  FIG. 11 , light control structure  142  of  FIG. 12 , light control structures such as light control structures  142 ,  142 ′, and  142 ″ of  FIG. 13 , light control structures  142  and  142 ″′ of  FIG. 14 , light control structure  142  of  FIG. 15 , light control structure  142  of  FIG. 16 , and/or other suitable light control structures in backlight  42  may be formed from yellow reflectors or reflectors characterized by other reflection spectrums. If desired, other structures in backlight  42  may be used to reduce blue edge effects. For example, edge reflectors in backlight  42  (e.g., edge reflector  80 ′ of  FIGS. 7 and 13 , which runs vertically, perpendicular to the plane of light guide plate  78 ) may be formed from yellow reflectors or reflectors characterized by other reflection spectrums to reduce blue edge effects. Quantum dot enhancement film may be used in forming some or all of light control structure  142  of  FIG. 11 , light control structure  142  of  FIG. 12 , light control structures such as light control structures  142 ,  142 ′, and  142 ″ of  FIG. 13 , light control structures  142  and  142 ″′ of  FIG. 14 , light control structure  142  of  FIG. 15 , light control structure  142  of  FIG. 16 , and/or other suitable light control structures in backlight  42 , and/or edge reflectors  80 ′, and/or a portion or all of the area of reflective layer  80 . The quantum dot enhancement film may include one or more sublayers of quantum dot material. Self-emitting structures and/or material that emits light when stimulated by applied light (e.g., yellow light-emitting diodes, light-emitting diodes of other colors, or other light sources, phosphorescent materials, etc.) can also be used in forming some or all of light control structure  142  of  FIG. 11 , light control structure  142  of  FIG. 12 , light control structures such as light control structures  142 ,  142 ′, and  142 ″ of  FIG. 13 , light control structures  142  and  142 ″′ of  FIG. 14 , light control structure  142  of  FIG. 15 , light control structure  142  of  FIG. 16 , and/or other suitable light control structures in backlight  42 , and/or edge reflectors  80 ′, and/or a portion or all of the area of reflective layer  80 . 
     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: 20140923
Publication Date: 20170103
Grant Date: 20170103
Priority Date: 20140609
Inventors: YOU CHENHUA
QI JUN
WANG SHENG MIN
YIN VICTOR H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133617", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133617", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133617", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54769437