Display Backlight with Light Mixing Structures

A display may have a backlight unit with a row of light-emitting diodes that emit light into the edge of a light guide layer. The light guide layer may have opposing upper and lower surfaces. The upper surface of the light guide layer may have ridges and the lower surface of the light guide layer may have bumps. The edge of the light guide layer may have light mixing structures. The light mixing structures may include an alternating pattern of protrusions with different shapes. For example, triangular protrusions of a first size may be patterned with triangular protrusions of a second size. The light mixing structures may reduce the mixing distance of the backlight unit.

BACKGROUND

This relates generally to electronic devices with displays, and, more particularly, to displays with backlights.

Electronic devices such as computers and cellular telephones have displays. Some displays such as plasma displays and organic light-emitting diode displays have arrays of pixels that generate light. In displays of this type, backlighting is not necessary because the pixels themselves produce light. Other displays contain passive pixels that can alter the amount of light that is transmitted through the display to display information for a user. Passive pixels do not produce light themselves, so it is often desirable to provide backlight for a display with passive pixels.

In a typical backlight assembly for a display, a light guide layer is used to distribute backlight generated by a light source such as a light-emitting diode light source. Optical films such as a diffuser layer and prism films may be placed on top of the light guide layer. A reflector may be formed under the light guide layer to improve backlight efficiency.

A strip of light-emitting diodes may provide light to an edge of a light guide layer. Light from the strip of light-emitting diodes is initially concentrated in the vicinity of the outputs of the light-emitting diodes. The light must travel a sufficient distance into the light guide layer to mix enough to be used as backlight illumination. Backlight units that require large mixing distances may consume more volume within a display than desired.

It would therefore be desirable to be able to provide displays with improved backlights.

SUMMARY

A display may have an array of pixels for displaying images for a viewer. The array of pixels may be formed from display layers such as a color filter layer, a liquid crystal layer, a thin-film transistor layer, and polarizer layers.

A backlight unit may be used to produce backlight illumination for the display. The backlight illumination may pass through the polarizers, the thin-film transistor layer, the liquid crystal layer, and the color filter layer. The backlight unit may have a row of light-emitting diodes that emit light into a light guide layer.

The light guide layer may have first and second opposing surfaces connected by an edge that receives light from the row of light-emitting diodes. The edge of the light guide layer may have a pattern of light mixing structures configured to distribute light. The pattern may include a first plurality of light mixing structures with a first shape that alternates with a second plurality of light mixing structures with a second shape that is different than the first shape. Each light mixing structure of the first plurality of light mixing structures may be interposed between respective first and second light mixing structures of the second plurality of light mixing structures.

The light mixing structures may include triangular protrusions with varying sizes. The different shaped protrusions may mix the backlight quickly without producing a cross-hatched pattern of light.

Further features will be more apparent from the accompanying drawings and the following detailed description.

DETAILED DESCRIPTION

Input-output circuitry in device10such as input-output devices12may be used to allow data to be supplied to device10and to allow data to be provided from device10to external devices. Input-output devices12may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device10by supplying commands through input-output devices12and may receive status information and other output from device10using the output resources of input-output devices12.

Input-output devices12may include one or more displays such as display14. Display14may be a touch screen display that includes a touch sensor for gathering touch input from a user or display14may be insensitive to touch. A touch sensor for display14may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements.

Control circuitry16may be used to run software on device10such as operating system code and applications. During operation of device10, the software running on control circuitry16may display images on display14.

Device10may be a tablet computer, laptop computer, a desktop computer, a television, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device.

Display14for device10includes an array of pixels. The array of pixels may be formed from liquid crystal display (LCD) components or other suitable display structures. Configurations based on liquid crystal display structures are sometimes described herein as an example.

A display cover layer may cover the surface of display14or a display layer such as a color filter layer, thin-film transistor layer, or other portion of a display may be used as the outermost (or nearly outermost) layer in display14. 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 display14of device10is shown inFIG. 2. As shown inFIG. 2, display14may include a backlight unit such as backlight unit42(sometimes referred to as a backlight or backlight structures) for producing backlight44. During operation, backlight44travels outwards (vertically upwards in dimension Z in the orientation ofFIG. 2) and passes through pixel structures in display layers46. This illuminates any images that are being produced by the pixels for viewing by a user. For example, backlight44may illuminate images on display layers46that are being viewed by viewer48in direction50.

Display layers46may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in a housing in device10or display layers46may be mounted directly in an electronic device housing for device10(e.g., by stacking display layers46into a recessed portion in a metal or plastic housing). Display layers46may form a liquid crystal display or may be used in forming displays of other types.

In a configuration in which display layers46are used in forming a liquid crystal display, display layers46may include a liquid crystal layer such a liquid crystal layer52. Liquid crystal layer52may be sandwiched between display layers such as display layers58and56. Layers56and58may be interposed between lower polarizer layer60and upper polarizer layer54.

Layers58and56may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers56and58may 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 layers58and56(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 layers58and56and/or touch sensor electrodes may be formed on other substrates.

With one illustrative configuration, layer58may 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 layer52and thereby displaying images on display14. Layer56may be a color filter layer that includes an array of color filter elements for providing display14with the ability to display color images. If desired, layer58may be a color filter layer and layer56may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer may also be used.

During operation of display14in device10, control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display14(e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit62A or62B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit64(as an example). Integrated circuits such as integrated circuit62A and/or flexible printed circuits such as flexible printed circuit64may be attached to substrate58in ledge region66(as an example).

Backlight structures42may include a light guide layer such as light guide layer78. Light guide layer78may be formed from a transparent material such as clear glass or plastic. Light guide layer78may sometimes be referred to as a light guide plate or a light guide film. During operation of backlight structures42, a light source such as light source72may generate light74. Light source72may be, for example, an array of light-emitting diodes (e.g., a series of light-emitting diodes that are arranged in a row that extends into the page in the orientation ofFIG. 2). The array of light-emitting diodes may be mounted to a rigid or flexible printed circuit. The printed circuit may be adhered to adjacent layers in the electronic device. In certain embodiments, the printed circuit may be adhered to portions of light guide layer78.

Light74from light source72may be coupled into edge surface76of light guide layer78and may be distributed in dimensions X and Y throughout light guide layer78due to the principal of total internal reflection. Light guide layer78may include light-scattering features such as pits, bumps, grooves, or ridges that help light exit light guide layer78for use as backlight44. These features may be located on an upper surface and/or on an opposing lower surface of light guide layer78. With one illustrative configuration, which is described herein as an example, a first surface such as the lower surface of light guide layer78has a pattern of bumps and an opposing second surface such as the upper surface of light guide layer78has a pattern of ridges (sometimes referred to as lenticules, lenticular structures, or lenticular ridges). Light source72may be located at the left of light guide layer78as shown inFIG. 2or may be located along the right edge of layer78and/or other edges of layer78.

Light74that scatters upwards in direction Z from light guide layer78may serve as backlight44for display14. Light74that scatters downwards may be reflected back in the upward direction by reflector80. Reflector80may be formed from a reflective structure such as a substrate layer of plastic coated with a dielectric mirror formed from alternating high-index-of-refraction and low-index-of-refraction inorganic or organic layers. Reflector80may be formed from a reflective material such as a layer of white plastic or other shiny materials.

To enhance backlight performance for backlight structures42, backlight structures42may include optical films70. Optical films70may include diffuser layers for helping to homogenize backlight44and thereby reduce hotspots. Optical films70may also include prism films (sometimes referred to as turning films) for collimating backlight44. Optical films70may overlap the other structures in backlight unit42such as light guide layer78and reflector80. For example, if light guide layer78has a rectangular footprint in the X-Y plane ofFIG. 2, optical films70and reflector80may each have a matching rectangular footprint. Optical films70may include compensation films for enhancing off-axis viewing or compensation films may be formed within the polarizer layers of display14or elsewhere in display14.

FIG. 3is a top view of a portion of display14showing how display14may have an array of pixels90formed within display layers46. Pixels90may have color filter elements of different colors such as red color filter elements R, green color filter elements G, and blue color filter elements B. Pixels90may be arranged in rows and columns and may form active area AA of display14. The borders of active area AA may be slightly inboard of the borders of light-guide layer78to ensure that there are no visible hotspots in display14(i.e., no areas in which the backlight illumination for display14is noticeably brighter than surrounding areas). For example, border92of active area AA may be offset by a distance82from lower edge76of light guide layer. It is generally desirable to minimize the size of distance82so that display14is as compact as possible for a given active area size. Nevertheless, distance82should not be too small to ensure that there is adequate light mixing. In particular, distance82should be sufficiently large to allow light74that is emitted from light-emitting diodes72to homogenize enough to serve as backlight illumination. Distance82is often as long as necessary to ensure light from light-emitting diodes72is sufficiently mixed. Accordingly, distance82may sometimes be referred to as mixing distance82. When light74is initially emitted from individual light-emitting diodes72, light74is concentrated at the exits of light-emitting diodes72and is absent in the spaces between light-emitting diodes72. After light74has propagated sufficiently far within light-guide layer78(i.e., after light74has traversed a sufficiently large mixing distance82), light74will be smoothly distributed along dimension X and will no longer be concentrated near the exits of respective individual light-emitting diodes72.

To enhance the efficiency with which light74is coupled into edge76of light guide layer from light-emitting diodes72without overly thickening light-guide layer78, it may be desirable to provide light-guide layer78with an outwardly tapered (flared) edge. Conventional edge tapers are formed by creating a taper in the upper surface of a light guide layer adjacent to the light-emitting diodes and leaving the opposing planar lower surface of the light guide layer untouched. If care is not taken, however, this type of taper may have an angle that is too steep, raising the potential for excessive light leakage due to the loss of total internal reflection conditions in the taper region. With the illustrative taper configuration shown in the cross-sectional side view of illustrative light guide layer78ofFIG. 4, excessive light losses are avoided by providing light guide layer78with both upper and lower taper structures100and102, respectively. Tapers102and100may be symmetrical or tapers102and100may have different shapes. In region96, light-guide layer78is planar and has planar parallel opposing upper and lower surfaces106and108, respectively. In taper region98, light guide layer78has a thickness that varies from the thickness of region96(T2) to enlarged thickness T1at edge76, so taper structure surfaces112and104are angled at non-zero angles with respect to planar upper and lower light guide layer surfaces106and108. Thickness T2may be about 400 microns 300-500 microns, less than 600 microns, more than 200 microns, or other suitable thickness. The enlarged size of dimension T1helps light guide layer78receive light74from light-emitting diodes72. The taper in light guide layer78formed by taper structures100and102helps concentrate light74into region96of light guide layer for use in forming backlight44.

As shown inFIG. 5, lower surface96of light guide layer78may be provided with light scattering features such as bumps (protrusions)114. Bumps114may help redirect light74that is traveling within the interior of light guide layer78upwards in direction Z to serve as backlight44for display14.

As light74that is traveling within light guide layer78is directed upwards in direction Z to serve as backlight44, the intensity of the light74that remains in light guide layer78decreases. As a result, the intensity of light74is greatest at edge76of light guide layer78adjacent to light-emitting diodes72and decreases with increasing distance along axis Y away from edge76. It is generally desirable for the intensity of backlight44to be evenly distributed across the surface of light guide layer78in dimensions X and Y. To ensure that backlight44is not too dim at large values of Y, the density of bumps114can be increased as a function of increasing value of Y, as shown inFIG. 6. The increase in the density of bumps114at larger Y values offsets the decrease in the intensity of light74within light guide layer at larger Y values and thereby ensures that backlight44has a uniform intensity as a function of dimension Y.

Light-emitting diodes72emit light74in a cone. This cone of light includes highly angled off-axis light rays. As shown in the cross-sectional side view of light guide layer78ofFIG. 7, some of the highly angled light rays such as light ray74-1lie primarily in the YZ plane. These light rays interact strongly with upper surface106and lower surface108of light guide layer and therefore tend to be heavily extracted by bumps114on lower surface108. Other highly angled light rays in the cone of emitted light74such as illustrative light ray74-2inFIG. 7lie primarily in the XY plane. These rays are angled more along dimension X than dimension Z and therefore interact with surfaces106and108less frequently than ray74-1. To ensure that light rays such as light ray74-2are adequately extracted and can serve as backlight44, light guide layer78may be provided with lenticular ridges such as ridges130ofFIG. 8. Ridges130may be formed on upper surface106of light guide layer78(as an example). As shown inFIG. 8, ridges130may run parallel to dimension Y (i.e., the direction in which the exit faces of light-emitting diodes72are oriented and the direction in which light74is emitted into edge76of light guide layer78). Ridges130may have semicircular cross-sectional shapes or may have other suitable shapes (triangular, etc.). As shown inFIG. 8, the presence of ridges130may help extract highly angled light rays such as light ray74-2that are propagating close to the XY plane to produce corresponding backlight44.

FIG. 9is a perspective view of an illustrative light guide layer. As shown, the light guide layer may have protruding portions94that extend between light-emitting diodes72. The light-emitting diodes72may be positioned on a rigid or flexible printed circuit (not shown inFIG. 9). Protruding portions94may act as a substrate for securing the printed circuit. For example, adhesive may attach the bottom surface of protruding portions94to a rigid or flexible printed circuit. Light-emitting diodes may be positioned on the printed circuit such that each light-emitting diode is interposed between two protruding portions94when the printed circuit is adhered to protruding portions94. Any type of adhesive may be used to attach protruding portions94to a rigid or flexible printed circuit (e.g., pressure sensitive adhesive, liquid cured adhesive, light cured adhesive, etc.).

As discussed in connection withFIG. 3, a given mixing distance may be necessary to ensure that light from light-emitting diodes is homogenous before entering the active area of the display. In order to reduce the size of display14and, accordingly, electronic device10, it may be desirable to reduce the length of mixing distance82. To reduce mixing distance82, edge76of light guide layer78may include light mixing structures. Edge76may be defined as the surface that connects the top surface of light guide layer78to the bottom surface of light guide layer78. Edge surface76may be substantially perpendicular to the top and bottom surfaces of light guide layer78. Edge surface76may be substantially perpendicular to optical films70and reflector80. Regions75of edge surface76(e.g., the regions in front of the light-emitting diodes) may include light mixing structures. Light mixing structures may be included on the edge of light guide layer78for the portions of edge76that are directly in front of light-emitting diodes72. This will ensure that light exiting light-emitting diodes72travels through the light mixing structures while entering light guide layer78.

FIG. 10is a top view of an illustrative light guide layer with light mixing structures. As shown inFIG. 10, edge76of light guide layer78may be provided with locally raised features such as protrusions122. Protrusions122may have semicircular profiles, or may have other shapes. For example, each protrusion122may have a triangular shape. Angle124may be about 5-45° or another suitable value to help refract light74at angles in layer78, thereby enhancing light mixing and helping to reduce mixing distance82(FIG. 3). Protrusions122may have widths (in dimension X) of about 25-75 microns or other suitable widths. Protrusions122may be spaced apart by about 200 microns (i.e., 200 microns may separate the tip of one protrusion from the tip of an adjacent protrusion), 150-250 microns, less than 320 microns, or more than 150 microns (as examples). Protrusions122may be spread evenly along edge76or may be clustered adjacent to respective light-emitting diodes72.

Protrusions122may all be a uniform size and shape. For example, each protrusion122may have a triangular shape with identical dimensions (as shown inFIG. 10). In these embodiments, light that travels through protrusions may travel in the pattern shown inFIG. 11. As shown, light may be emitted from a light emitting diode such as light emitting diode72A. The light that passes through protrusions122may be split into two cones of light. A first cone74A may be diverted in the negative X-direction while a second cone74B may be diverted in the positive X-direction. Both cones74A and74B may also travel in the positive Y-direction.

Because the light mixing structures on edge76of light guide layer78are all identical (as shown inFIG. 10), the light from each light emitting diode72may be split into similar cones of light. The result is a cross-hatched pattern of light as shown inFIG. 11. There may be a pattern of regions such as region126where light from the cones of light overlap, producing a brighter area of light. Other regions such as region128may not be overlapped by any of the cones and therefore be a dimmer area of light. This regular pattern of bright regions in the backlight may be visible to the user of the electronic device.

InFIG. 11, the cones of light are illustrated as evenly spaced columns of light. This is merely illustrative and it should be understood that the actual cones of light would have much more spreading and exhibit a much less regular pattern. However, a simplified version of the light pattern is shown so as to not obfuscate the cross-hatched pattern formed from uniform light mixing structures such as those shown inFIG. 10.

To avoid the cross-hatched pattern of light shown inFIG. 11, edge76of light guide layer78may include light mixing structures with different shapes, as shown inFIG. 12. As shown, light guide layer78may include a first set of protrusions122A and a second set of protrusions122B. Each set of protrusions may have a different shape. The protrusions may be arranged in an alternating pattern such that each protrusion122A is only adjacent to protrusions122B and protrusions122B are only adjacent to protrusions122A. Including light mixing structures such as protrusions122A and122B may reduce mixing distance82without resulting in the cross-hatched pattern shown inFIG. 11.

The example of two sets of protrusions with different shapes is merely illustrative. If desired, there may be three sets of protrusions with different shapes, four sets of protrusions with different shapes, or more than four sets of protrusions with different shapes. The sets of protrusions may be arranged in any desired pattern. A pattern may be used where a single protrusion from each set is arranged sequentially and then this unit is repeated in an alternating pattern. However, more than one protrusion from each set may be arranged sequentially (e.g., two protrusions from the first set, two protrusions from the second set, two protrusions from the third set) and the pattern repeated. In general, any pattern of protrusions that uses protrusions with at least two different shapes may be used.

It should also be understood that the light mixing structures are not limited exclusively to protrusions. For example, recesses may be used that provide the same spreading characteristics as protrusions. In certain embodiments, prisms that spread light may be included to spread the light. Additionally, the shape of the light mixing features is not limited to triangles. Protrusions122may have a triangular shape, a semicircular shape, a semi-oval shape, or any other desired shape.

FIG. 13is a close-up view of light mixing structures with different shapes on edge76of light guide layer78. As shown, protrusion122A may be a triangle with a first shape, while protrusion122B may be a triangle with a second shape that is different than the first shape. Protrusions122A and122B may both be symmetrical triangles (e.g., isosceles triangles), or other types of triangles. The edge of light guide layer78may have a planar portion from which protrusions122A and122B extend. Protrusion122A may have a first surface132that is at an angle136with respect to the planar portion of the edge. Protrusion122A may have a second surface134that is at an angle138with respect to the planar portion of the edge. Angles136and138may be the same or may be different. Similarly, surface132and surface134may have the same lengths or different lengths. In one illustrative embodiment, angles136and138are the same and both between 25° and 40° or both between 20° and 30°. Angles136and138may both be 25°, may both be 30°, or may both be 35°. Angles136and138may be less than 30° or less than 60°. The base of protrusion122A may have a length140of between 25 microns and 75 microns, about 50 microns, less than 25 microns, more than 25 microns, or any other desired length.

Protrusion122B may have a first surface142that is at an angle146with respect to the planar portion of the edge. Protrusion122B may have a second surface144that is at an angle148with respect to the planar portion of the edge. Angles146and148may be the same or may be different. Similarly, surface142and surface144may have the same lengths or different lengths. In one illustrative embodiment, angles146and148are the same and both between 17.5° and 22.5°, both between 10° and 22.5°, both between 5° and 25°, or both between 10° and 15°. Angles146and148may both be 20° or may both be 12.5°. Angles146and148may be less than 30° or less than 60°. The base of protrusion122B may have a length150of between 25 microns and 75 microns, about 50 microns, less than 25 microns, more than 25 microns, or any other desired length.

Length150of each protrusion122B may be the same as the length140of each protrusion122A. Alternatively, length150of each protrusion122B may be different than the length140of each protrusion122A. The distance between the tips of each protrusion (distance154) may be any desired distance (e.g., between 100 and 300 microns, less than 100 microns, more than 100 microns, about 200 microns, etc.). Distance154may be the same throughout the pattern of protrusions (i.e., the distance between each protrusion is the same). Alternatively, some protrusions may be spaced closer together and some protrusions may be spaced further apart.

FIG. 14shows light guide layer processing tool160for forming protrusions such as protrusions122A and122B inFIGS. 12 and 13. Light guide layer processing tool160may include a robotically or manually controlled positioner162that is attached to bit164. Light guide layer processing tool160may use bit164to cut light guide layer78and form protrusions. Bit164may be, for example, a diamond bit.

FIG. 15shows an illustrative method for forming light mixing structures on a light guide layer. The method ofFIG. 15may be used to form light mixing structures such as the protrusions shown inFIGS. 12 and 13. At step172, a first light guide layer processing tool may be used to form a first plurality of light mixing structures with a first shape. The light guide layer processing tool may be, for example, light guide layer processing tool160inFIG. 14. At step174, a second light guide layer processing tool may be used to form a second plurality of light mixing structures with a second shape that is different than the first shape. The second light guide processing tool may be, for example, light guide layer processing tool160inFIG. 14.

In certain embodiments, the same light guide layer processing tool may be used in both steps172and174. In other embodiments, different light guide layer processing tools may be used for each step. In one embodiment, a light guide layer processing tool with a first bit164may be used in step172. After completing step172, a different bit164may be attached to positioner162. The tool may then be used in step174with the new bit. The bit for step172may be a certain size that is configured to cut light mixing structures with the first shape, while the bit for step174may be a different size that is configured to cut light mixing structures with the second shape.

In various embodiments of the invention, a display backlight may include a row of light-emitting diodes and a light guide layer. The light guide layer may have first and second opposing surfaces connected by an edge that may receive light from the row of light-emitting diodes. The edge may have a first plurality of protrusions that each have a first shape and a second plurality of protrusions that each have a second shape that is different than the first shape. The first plurality of protrusions and second plurality of protrusions may be arranged in a pattern. The first plurality of protrusions and the second plurality of protrusions may be arranged in an alternating pattern. In the alternating pattern, each protrusion of the first plurality of protrusions may be positioned adjacent to a respective protrusion of the second plurality of protrusions. The first shape may be a first triangular shape, and the second shape may be a second triangular shape.

The edge may have a planar portion. The first triangular shape may include first and second surfaces that are at a first angle relative to the planar portion of the edge, and the second triangular shape may include third and fourth surfaces that are at a second angle relative to the planar portion of the edge. The first angle may be between 17.5° and 22.5°, and the second angle may be between 25° and 40°. The first angle may be 20°. The second angle may be 30° or 35°. The first angle may be between 10° and 15°, and the second angle may be between 20° and 30°. The first angle may be 12.5°, and the second angle may be 25°. The display backlight may also include a reflector that is parallel to the first and second opposing surfaces of the light guide layer.

In various embodiments of the invention, a light guide layer may include a top surface, a bottom surface, and first and second opposing surfaces that connect the top and bottom surfaces. The first surface may have a pattern of light mixing structures configured to distribute light, and the pattern may include a first plurality of light mixing structures with a first shape that alternates with a second plurality of light mixing structures with a second shape that is different than the first shape. Each light mixing structure of the first plurality of light mixing structures may be interposed between respective first and second light mixing structures of the second plurality of light mixing structures. Each light mixing structure of the first plurality of light mixing structures may include a triangular protrusion with first and second surfaces of a first length. Each light mixing structure of the second plurality of light mixing structures may include a triangular protrusion with third and fourth surfaces of a second length that is different than the first length. The top surface of the light guide layer may have ridges, and the bottom surface of the light guide layer may have bumps.

In various embodiments of the invention, a liquid crystal display may include first and second transparent substrates, a liquid crystal layer between the first and second substrates, a light guide layer configured to pass backlight through the first and second substrates and the liquid crystal layer, and at least first and second light-emitting diodes that each emit light into the first edge of the light guide layer. The light guide layer may have first and second opposing edges. The first edge of the light guide layer may include a pattern of protrusions configured to distribute light, and the pattern may include a first plurality of protrusions with a first shape that alternates with a second plurality of protrusions with a second shape that is different than the first shape.