PATENT DOCUMENT

Publication Number: US-9857521-B2
Application Number: US-201514881065-A
Country: US
Kind Code: B2

Title: Liquid crystal display with backlight color compensation structures

Abstract:
A display may have an array of pixels that display images for a user. The backlight unit may have a light-guide layer. An array of light-emitting diodes may emit light into an edge of the light-guide layer. The light guide layer may overlap a backlight reflector. The backlight reflector may include a backlight reflector panel formed from a stack of dielectric layers on a rectangular substrate. The backlight reflector may also include a strip of backlight reflector tape having an edge that is overlapped by an edge portion of the backlight reflector panel. Color compensating features such as printed colored ink patterns may be formed on the backlight reflector to adjust the color of backlight illumination in portions of the backlight unit adjacent to the light-emitting diodes.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 display layers forming an array of pixels; and 
 backlight structures that provide backlight illumination for the pixels, wherein the backlight structures include a backlight reflector having color compensating features that enhance color uniformity for the backlight illumination, wherein the backlight reflector comprises a first layer and a second layer, and wherein the backlight structures include a light guide layer with an edge portion interposed between the first layer and the second layer. 
 
     
     
       2. The display defined in  claim 1  wherein the first layer of the backlight reflector comprises a strip of backlight reflector tape and wherein the color compensating features are formed at least partly on the backlight reflector tape. 
     
     
       3. The display defined in  claim 2  wherein the color compensating features comprise colored ink features. 
     
     
       4. The display defined in  claim 3  wherein the color compensating features comprise printed ink dots. 
     
     
       5. The display defined in  claim 4  wherein the printed ink dots have a density that varies as a function of distance across the backlight reflector tape. 
     
     
       6. The display defined in  claim 2  wherein the color compensating features comprise a strip of printed colored ink on the backlight reflector tape. 
     
     
       7. The display defined in  claim 6  wherein the strip of printed colored ink comprises a yellow strip of printed ink. 
     
     
       8. The display defined in  claim 7  wherein the backlight reflector further comprises a backlight reflector panel having an edge that overlaps an edge portion of the backlight reflector tape, wherein the display further comprises a flexible printed circuit on which the light-emitting diodes are mounted, wherein the backlight reflector tape has an edge that overlaps the flexible printed circuit, and wherein the light-emitting diodes emit light into the light guide layer. 
     
     
       9. The display defined in  claim 1  wherein the first layer comprises a reflector tape, wherein the second layer comprises a top reflector, and wherein the color compensating features include colored ink on the top reflector. 
     
     
       10. A display, comprising:
 display layers forming an array of pixels; and 
 backlight structures that provide backlight illumination for the pixels, wherein the backlight structures include a backlight reflector having a surface, wherein color compensating features that enhance color uniformity for the backlight illumination are formed on the surface of the backlight reflector, and wherein the color compensating features include thermochromic ink. 
 
     
     
       11. The display defined in  claim 1  wherein the first layer of the backlight reflector includes a backlight reflector tape formed from a white plastic layer, wherein the backlight reflector also includes a rectangular backlight reflector panel having a stack of dielectric layers, and wherein the color compensating features comprise colored ink that covers a portion of the backlight reflector tape and that covers a portion of the backlight reflector panel. 
     
     
       12. A display, comprising:
 liquid crystal display layers having an array of pixels; and 
 backlight structures that provide backlight illumination for the array of pixels, wherein the backlight structures include a backlight reflector, a light-guide layer that overlaps the backlight reflector, and an array of light-emitting diodes emitting light into an edge of the light-guide layer, wherein the backlight structures include colored ink on the backlight reflector that compensates for variations in color of the backlight illumination across the backlight structures, wherein the backlight reflector has a first portion and a second portion, wherein the colored ink is formed on at least the first portion, wherein the first portion of the backlight reflector comprises a strip of white tape, wherein the second portion comprises a backlight reflector panel having a stack of dielectric layers with at least first and second indices of refraction, and wherein an edge portion of the backlight reflector panel overlaps an edge portion of the strip of white tape. 
 
     
     
       13. The display defined in  claim 12  further comprising a clear coating that covers the colored ink. 
     
     
       14. The display defined in  claim 12  wherein the colored ink includes first and second colored ink layers of different colors. 
     
     
       15. The display defined in  claim 10 , wherein all of the surface of the backlight reflector is covered with the thermochromic ink.

Description:
This application claims the benefit of provisional patent application No. 62/150,066 filed on Apr. 20, 2015, 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, tablet computers, and laptop computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. 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 pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. A liquid crystal display may have an array of color filter elements to provide the display with the ability to display color images. 
     The pixels in the liquid crystal display can be backlight using a backlight unit. The backlight unit may include a light guide layer. The light guide layer may be formed from a transparent material such as a transparent polymer. An array of light-emitting diodes may emit light into the edge of the light guide layer. The light that is emitted into the edge of the light guide layer may be distributed throughout the light guide layer in accordance with the principle of total internal reflection. 
     The light guide layer may be provided with light scattering features that scatter the light that is traveling within the interior of the light guide layer. Light that is scattered outwards from the light guide layer through the pixels of the liquid crystal display can serve as backlight for the display. 
     Image quality in a backlight liquid crystal display may be adversely affected by variations in backlight color. If care is not taken, portions of a display may have an unwanted color cast. As an example, portions of a display adjacent to the array of light-emitting diodes in the backlight unit may have an undesired bluish cast. 
     If would therefore be desirable to be able to provide displays such as backlit liquid crystal displays with enhanced color uniformity. 
     SUMMARY 
     A display may have an array of pixels that display images for a user. The array of pixels may be formed from liquid crystal display layers. The array of pixels may be provided with backlight illumination by a backlight unit. The backlight unit may have a light-guide layer. An array of light-emitting diodes may emit light into an edge of the light-guide layer. 
     The light guide layer may overlap backlight reflector. The backlight reflector may include a rectangular backlight panel formed from a stack of reflective dielectric layers on a substrate. The backlight reflector may also include a strip of backlight reflector tape having an edge that is overlapped by an edge portion of the backlight reflector panel. 
     The light-emitting diodes may be mounted on a flexible printed circuit. The strip of backlight reflector tape may be attached to the flexible printed circuit. Color compensating features such as printed colored ink patterns may be formed on the backlight reflector. For example, printed color ink may be formed on the backlight reflector tape or portions of the backlight reflector panel. The printed colored ink may be formed in the shape of strip of colored ink or a pattern of colored ink dots. The ink may by yellow or may have other colors that help compensate for undesired backlight color variations. If desired, the ink may be thermochromic. The presence of the ink serves to selectively adjust the color of the backlight illumination in portions of the backlight unit adjacent to the light-emitting diodes, thereby maximizing color uniformity. 
    
    
     
       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 graph in which a color parameter for a display has been plotted as a function of distance from a light-emitting diode array in a backlight for a non-color-compensated display and for a color-compensated display in accordance with an embodiment. 
         FIG. 7  is a perspective view of an edge portion of a backlight unit having a reflector with a color-compensating layer in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative backlight unit of the type shown in  FIG. 7  in accordance with an embodiment. 
         FIG. 9  is a top view of an edge portion of a backlight unit with a strip-shaped color-compensating layer in accordance with an embodiment. 
         FIG. 10  is a top view of an edge portion of a backlight unit with a color compensating layer having a graduated density in accordance with an embodiment. 
         FIG. 11  is a top view of a portion of a backlight unit with a blanket color compensating layer in accordance with an embodiment. 
         FIG. 12  is a top view of an edge portion of a backlight unit having a spatially varying color compensating layer in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of a portion of an illustrative backlight reflector showing how the reflector may have a printed color compensating ink layer in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a portion of an illustrative backlight reflector showing how the reflector may have color compensating features formed from multiple layers of ink in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a portion of an illustrative backlight reflector showing how color compensating features may be covered with a transparent protective layer in accordance with an embodiment. 
         FIG. 16  is a graph showing how the color of light reflected from a color compensating layer may vary as a function of temperature of the layer in accordance with an embodiment. 
         FIG. 17  is a graph showing how the color of a backlight reflector can vary as a function of position due to the incorporation of a color compensating structure in accordance with an embodiment. 
         FIG. 18  is a graph showing how the density of ink dots or other color compensating features can vary as a function of position in a backlight reflector 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 . 
       FIG. 1  shows how electronic device  10  may have 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 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 display such as a computer display or may be a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27  or stand  27  may be omitted (e.g., to mount 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 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 pixels formed from liquid crystal display (LCD) components. 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. 
     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  58  and  56  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 in the upper or lower portion of display  14  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). 
     Backlight structures  42  may include a light guide layer such as light guide layer  78 . Light guide layer  78  may be formed from a transparent material such as clear glass or plastic (e.g., molded plastic that forms a light guide plate, a thin flexible plastic film, etc.). 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. 
     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 layer  78  due to the principal of total internal reflection. Light guide layer  78  may include light-scattering features such as pits or bumps or other light-scattering structures. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide layer  78 . Light source  72  may be located at the left of light guide layer  78  as shown in  FIG. 5  or may be located along the right edge of layer  78  and/or other edges of layer  78 . 
     Light  74  that scatters upwards in direction Z from light guide layer  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of plastic covered with a dielectric minor thin-film coating. Reflective tape (e.g., white plastic tape or tape formed from other reflective materials) may be incorporated into the backlight reflector for display  14 . For example, backlight structures  42  may include a strip of tape that runs along the edge of reflector  80  that is adjacent to light-emitting diodes  72 . 
     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, compensation films for enhancing off-axis viewing, and brightness enhancement films (also 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 layer  78  and reflector  80 . For example, if light guide layer  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. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., polarizer layers). 
     Light  74  from light-emitting diodes  72  may be white light that is converted into desired colors (e.g., red, blue, green, etc.) by color filter elements in color filter layer  56 . Due to a variety of non-ideal effects, there is a potential that light  74  (and therefore scattered light  44 ) will have a different color near diodes  72  than at locations further into light-guide layer  78 . These non-ideal effects include temperature gradients (e.g., elevated temperatures near to diodes  72  that induce birefringence variations in layer  52  that can cause the light  44  from backlight structures  42  to be bluish at locations near diodes  72 , angular dependence of the output color of light  74  from diodes  72  that can lead to yellower light being emitted at larger angles relative to axis Y of  FIG. 5  than the light being emitted at smaller angles relative to axis Y, wavelength-dependent absorption of the material of light guide layer  78  such as absorption that causes yellow light to travel further into layer  78  than blue light so that light  74  is bluer near diodes  72  than at locations farter into layer  78 , non-uniformity in layer  52  such as non-uniformities in thickness that may be most pronounced near the edges of structures  42  and that can impact the spectrum of light  44  that is transmitted through layers  46 , etc.). These non-ideal effects can lead to visible color casts on a display. For example, the edge of a display next to the light-emitting diodes of the backlight unit may tend to be bluer than desired. 
     To compensate for undesired color variations in backlight  44 , display  14  may be provided with color variation compensation structures (sometimes referred to as color compensating structures, color compensating features, color compensation structures, color variation compensating features, etc.). The color compensating structures may be formed from printed colored ink or other structures that can impart desired colors to backlight  44 . As an example, the backlight reflector in structures  42  may be provided with a yellow strip adjacent to light-emitting diodes  72 . The presence of the yellow strip in this portion of backlight  42  may help adjust the color of light  44  in the vicinity of light-emitting diodes  72  (e.g., the yellow strip may help convert a strip of overly blue light  44  into light  44  of the same color as the light  44  that is emitted elsewhere in structures  42 ). 
       FIG. 6  is a graph in which the color of light  44  (shown as representative color parameter C) has been plotted as a function of distance Y from light-emitting diodes  72 . Parameter C may be a color coordinate associated with light  44 , may represent the ratio of yellow light to blue light in light  44 , may be a color temperature value, or may be any other parameter that is representative of the color of light  44  from structures  42 . Line  90  shows how color C may vary as a function of distance Y from light-emitting diodes  72  in a backlight unit without color compensating features. Line  92  corresponds to a display such as display  14  in which a backlight reflector with color compensating features has been incorporated into structures  42 . As shown by line  90 , the color of backlight  44  may vary significantly near diodes  72  (i.e., in region R) in the absence of color compensating features (e.g., light  44  may be overly blue in region R, as represented by the decrease in curve  90  in region R). When a strip of yellow material is included on the backlight reflector or when other color compensating features are incorporated into structures  42  in region R, the light that is reflected upwards as backlight  44  will tend to be yellower in region R. When the density and color of the yellow material or other color compensating structure in region R has been configured satisfactorily, the amount of color correction that is imposed on backlight  44  in region R will be sufficient to balance out the tendency of the backlight  44  in this region to acquire a blue cast or other undesired color cast. As illustrated by line  92 , for example, the color compensating structures may ensure that backlight  44  has a uniform color over all values of distance Y from light-emitting diodes  72  (i.e., the yellow material in region R will counteract the bluish nature of light  44  in region R and will therefore result in light of uniform color C across all of backlight unit  42  and display  14 ). 
     In general, color compensating structures may be incorporated into any suitable portion of display  14  (e.g., in layers  46 , between layers  46  and backlight structures  42 , or within structures  42 . With one suitable arrangement, which may sometimes be described herein as an example, reflective structures in backlight structures  42  may be provided with colored portions (e.g., colored ink formed from a polymer containing colored dyes or pigments) or other colored material. Configuration in which these colored portions are formed from colored ink may sometimes be described herein as an example. In general, any suitable materials and/or structures may be used to make color modifications to light  44  that is being emitted from backlight structures  42  and is passing through layers  46  of display  14 . The use of color compensating features formed from printed colored ink is merely illustrative. 
     Colored ink may be deposited on a backlight reflector (e.g., a portion of a reflective rectangular backlight panel formed from a polymer film or other substrate and/or one or more strip-shaped reflective tapes) or other portion of backlight structures  42  using ink-jet printing, screen printing, pad printing, other types of printing, painting, spraying, evaporation or other physical vapor deposition techniques, or other fabrication techniques. Configurations in which colored ink is applied to layers of material in backlight structures  42  using printing are sometimes described herein as an example. 
       FIG. 7  is a perspective view of a portion of backlight structures  42  in an illustrative configuration in which color compensating features have been formed from a strip of yellow ink printed on a backlight reflector tape. As shown in  FIG. 7 , backlight structures  42  may include structures mounted in a chassis such as plastic chassis  96 . These structures may include a backlight reflector such as reflector  80 . Reflector  80  may include a rectangular layer of reflector material that forms reflector  80 - 2  (i.e., a rectangular reflector panel that covers most of the area of display  14 ). Reflector  80 - 2  may be formed from a stack of repeating (alternating) high-index-of-refraction and low-index-of-refraction dielectric layers or other structures for creating a high reflectively broadband reflective structure (e.g., a reflector with more than 99% reflectivity). Reflector  80 - 1  may be formed from reflective tape (e.g., white plastic tape or other reflective tape). Reflector  80 - 1  may have adhesive (e.g., pressure sensitive adhesive or other adhesive). For example, reflector  80 - 1  may have a layer of adhesive in region  100  to attach reflector  80 - 1  to flexible printed circuit  98 . 
     Flexible printed circuit  98  may be formed from a layer of polyimide or a flexible sheet of other polymer materials. A portion of the exposed upper surface of flexible printed circuit  98  may be covered with a layer of adhesive such as adhesive  102 . Adhesive  102  may have the shape of an elongated strip that runs along the edge of display  14  adjacent to light-emitting diodes  72  and may be used to help secure the edge of light guide layer  78  to flexible printed circuit  98  and thereby hold layer  78  in place within backlight unit  42 . 
     Metal traces in flexible printed circuit  98  may be coupled to a source of current. Light-emitting diodes such as light-emitting diode  72  of  FIG. 7  may be soldered to the metal traces of flexible printed circuit  98  (i.e., solder pads formed from the metal traces). There may be, for example, an array of 1-10, more than 2, less than 10, or other suitable number of light-emitting diodes  72  along the edge of display  14 . Light-emitting diodes  72  may be formed along one edge of display  14  or may be formed on opposing edges of display  14  (e.g., on the left and right edges of display  14  or on the top and bottom edges of display  14 ). During operation, the source of current in device  10  can apply current to light-emitting diodes  72  to control the amount of light  74  that is produced by light-emitting diodes  72 . Portion  96 ′ may, if desired, overlap light-emitting diodes  72 . A portion of the backlight reflector structures in unit  42  (i.e., a top reflector) may overlap light guide layer  78  under portion  96 ′. 
     To compensate for undesired color variations in backlight  44 , portions of backlight structures  42  may be provided with color compensating features. In the example of  FIG. 7 , color compensating features have been provided in the form of a strip of colored ink (e.g., yellow ink or ink of other colors) in region  100  of reflective tape  80 - 1 . This is merely illustrative. Colored ink may be provided on other areas of backlight reflector  80  (e.g., on only part of reflector  80 - 1 , on all of reflector  80 - 1 , on only part of reflector  80 - 2 , on all of reflector  80 - 2 , on all of reflector  80 - 1  and part of reflector  80 - 2 , on part of reflector  80 - 1  and part of reflector  80 - 1 , on a top reflector under region  96 ′, etc.). 
     An edge portion of backlight reflector layer  80 - 2  may overlap an edge portion of backlight reflector layer (tape)  80 - 1  in region  94 . As shown in the cross-sectional side view of backlight structures  42  of  FIG. 8 , the edge of light-guide layer  78  may overlap the edge of reflector layer  80 - 2  in an assembled backlight unit. Upper backlight reflector  106  may be interposed between the edge of light-guide layer  78  and overhanging chassis portion  96 ′. Pressure sensitive adhesive  104  or other adhesive may be used to attach reflective tape  80 - 1  of backlight reflector  80  to flexible printed circuit  98 . Backlight reflector panel  80 - 2  may overlap tape  80 - 1  in region  94  (i.e., the edge of tape  80 - 1  may be placed between reflector  80 - 2  and chassis  96 ). 
     The peripheral edge of backlight structures  42  (i.e., a rectangular ring surrounding the four edges of light-guide layer  78 ) may form an inactive area IA for display  14 . Inactive area IA is a portion of display  14  in which backlight  44  is not illuminating display layers  46  and in which the pixels of display layers  46  are not present. The inactive area IA of display  14  may surround an active area AA. Active area AA may have a rectangular shape that contains an array of pixels (i.e., rows and columns of pixels). To ensure uniform color for display  14  in active area AA, color compensating features may be incorporated onto backlight structures  42  in inactive area IA and/or in active area AA. For example, color compensating features may be formed in areas such as area  100  on the edge of tape  80 - 1  closest to light-emitting diodes  72 , in area  108  (e.g., a strip-shaped region of tape  80 - 1  between area  100  and area  94 ), in area  94  (e.g., where reflector  80 - 2  overlaps tape  80 - 1 ), in area  110  immediately adjacent to area  94 , elsewhere on reflector  80 - 2  (see, e.g., area  112 ), and/or on all or part of area  114  on the lower surface of top reflective tape  106  (e.g., a white plastic tape attached to chassis portion  96 ′ with adhesive and/or attached to light-guide layer  78 ). By incorporating colored ink or other color compensating features into these areas of backlight structures  42 , excessively blue backlight  44  can be eliminated or at least reduced along the edge of backlight structure  42  adjacent to light-emitting diodes  72 . Color deviations in other areas of display  14  can also be reduced in this way. 
       FIGS. 9, 10, 11, and 12  are top views of an edge portion of backlight unit  42  that show illustrative patterns that may be used for the color compensating features in backlight unit  42 . In the example of  FIG. 9 , color compensating structures  116  include a strip of printed colored ink or other color compensating material in region  100 . Structures  116  may have an elongated rectangular shape that runs along the edge of reflector  80  adjacent to light-emitting diodes  72 . 
     In the example of  FIG. 10 , color compensating structures  116  include a pattern of dots (circular dots, rectangular dots, dots of other shapes, etc.) with a density gradient. In the  FIG. 10  example, the density of dots in structures  116  decreases with increasing distance from light-emitting diodes along lateral dimension Y. Other color compensating structures with varying density across the surface of reflector  80  may be used, if desired. 
     In the example of  FIG. 11 , all of reflector  80  has been covered with a layer of color compensating structures  116 . In this type of arrangement color compensating structures  116  may be formed from a layer of material such as a thermochromic ink that changes color as a function of temperature. When light-emitting diodes  72  heat the edge of reflector  80 , the color of structures  116  will change along the heated edge of reflector  80  (e.g., to a yellow color), thereby compensating for color deviations along the edge of display  14 . 
     As shown in the illustrative arrangement of  FIG. 12 , color compensating structures  116  may be formed in a pattern that varies in density in lateral dimension X (parallel to the edge of display  14  and running along the array of light-emitting diodes  72  that supplies light to the edge of light-guide layer  78 ) as well as lateral dimension Y. There are two clusters of color compensating structures  116  in this example: cluster  116 - 1 , which is concentrated in front of a first of light-emitting diodes  72 , and cluster  116 - 2 , which is concentrated in front of a second of light-emitting diodes  72 . This is merely illustrative. There may be any suitable number of clusters of color compensating dots or other structures  116  on reflector  80  (e.g., one cluster for each light-emitting diode  72 , etc.). 
     The cross-sectional side view of  FIG. 13  shows how color compensating structures  116  may be formed from a printed ink layer that has been patterned onto the surface of reflector  80  (e.g., reflector  80 - 1  and/or reflector  80 - 2  and/or, if desired, top reflector  106 ). Structures  116  may be patterned to form a series of dots or discrete areas of other shapes or may be patterned to cover larger sections of reflector  80  (e.g., strip-shaped bands that run along the edge of display  14 , blanket films, etc.), as described in connection with  FIGS. 9, 10, 11, and 12 . 
     If desired, multiple layers of printed ink may be used in forming structures  116 . For example, a first layer of ink  116 B may be covered (in full or in part) with additional layers of ink such as second layer  116 A. Layers  116 A and  116 B may have the same color (e.g., yellow) or may have different colors (e.g., one of layers  116 A and  116 B may be yellow and the other red, etc.). The use of multiple layers of material when forming structures  116  may allow the optical properties of structures  116  such as reflectively, light scattering, and reflection spectrum (color), to be optimized to maximize color uniformity in backlight  44 . 
       FIG. 15  is a cross-sectional side view of color compensating structures  116  in a configuration in which a transparent protective film such as transparent layer  120  has been placed on top of structures  116 . Layer  120  may be formed from a clear polymer (e.g., a cured adhesive), from a transparent inorganic layer (e.g., silicon oxide, etc.), or may be formed from other protective films that overlap color compensating structures  116 . The presence of coating layer  120  helps to protect structures  116  from damage due to rubbing from structures in display  14  such as light-guide layer  98 . 
     The ink or other material that is used for forming structures  116  may be yellow pigmented ink (e.g., polymer with yellow pigment), yellow dyed ink (e.g., polymer with yellow dye), polymer that includes dye, pigment, or other additives that impart other colors to structures  116 , or other colored structures. If desired, ink  116  may be formed from a thermochromic ink layer such as a cholesterol liquid crystal layer. The color of the light that is reflected from thermochromic ink may change as a function of applied temperature, as illustrated by curve  112  of  FIG. 16  in which reflected color C has been plotted as a function of temperature T for an illustrative thermochromic material. Because the temperature of backlight  80  increases in response to the heat being produced from light-emitting diodes  72 , the reflected color of a thermochromic material forming structures  116  will change as a function of distance from light-emitting diodes  72 . As a result, the color compensation strength of structures  116  can be configured to be strongest (i.e., structures  116  can be most yellow) near to light-emitting diodes  72 , where light  44  tends to be undesirably blue. 
     If desired, the color of color compensating structures  116  may be changed in a continuous or semi-continuous fashion as a function of lateral distance across the surface of the backlight reflector (e.g., backlight reflector layer  80  and/or upper reflector  106 ). As shown by curve  124  in  FIG. 17 , for example, the color C of structures  116  may change as a function of distance Y from light-emitting diodes  72 . As illustrated by curve  126  in  FIG. 18 , the density D of dots or other color-producing attribute in structures  116  may be altered as a function of distance Y (e.g., to make backlight reflector  80  yellowest near light-emitting diodes  72  and increasingly less yellow at increasing distances Y from light-emitting diodes). Other patterns of structures  116  may be used, if desired (e.g., patterns in which the density D of dots or other structures  116  is altered in both the X and Y lateral dimensions, etc.). The configuration of  FIG. 18  is merely illustrative. 
     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: 20151012
Publication Date: 20180102
Grant Date: 20180102
Priority Date: 20150420
Inventors: PU CHUAN
LU SHIN-YING
YOU CHENHUA
WANG SHENG MIN
QI JUN
YIN VICTOR H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0011", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0061", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/004", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0051", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0065", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133609", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133609", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0061", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0011", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0051", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0061", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0051", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/004", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0065", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133609", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57128805