Backlight and Display System

A backlight includes a plurality of light sources, a reflective polarizer disposed on the plurality of light sources, and an optical film disposed between the reflective polarizer and the plurality of discrete spaced apart light sources. For a substantially collimated incident light, for a visible wavelength range, and for a first incident angle of less than about 5 degrees, the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized. For the average of p-polarized and s-polarized incident lights and the visible wavelength range, the optical film has an average optical transmittance T1 for the first incident angle, and an average transmittance T2 for a second incident angle of greater than about 35 degrees, such that T1/T2≥1.5.

TECHNICAL FIELD

The present disclosure relates generally to a backlight for providing illumination to a display panel, and a display system including the display panel disposed on the backlight.

BACKGROUND

Electronic devices, such as smart phones, tablet computers, personal computers, music players, etc., often include displays. For example, the electronic devices may be provided with a liquid crystal display (LCD) panel. Liquid crystal displays typically use light-modulating properties of liquid crystals. The liquid crystals do not emit light directly and a backlight unit is used to illuminate the LCD panel to produce images in color or monochrome. Thus, the backlight unit provides illumination to the LCD panel.

SUMMARY

In a first aspect, the present disclosure provides a backlight for providing illumination to a display panel. The backlight includes a plurality of discrete spaced apart light sources arranged two-dimensionally on an optically reflective surface. The backlight further includes a reflective polarizer disposed on the plurality of discrete spaced apart light sources. The backlight further includes an optical film disposed between, and substantially co-extensive in length and width with, the reflective polarizer and the plurality of discrete spaced apart light sources. Each of the reflective polarizer and the optical film includes a plurality of polymeric layers numbering at least 10 in total. Each of the polymeric layers has an average thickness of less than about 500 nm. For a substantially collimated incident light propagating in an incident plane, for a visible wavelength range extending from about 420 nanometers (nm) to about 680 nm, and for a first incident angle of less than about 5 degrees, the plurality of polymeric layers of the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized. For the substantially collimated incident light propagating in the incident plane, for the visible wavelength range, for the first incident angle, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an average optical transmittance T1. For the substantially collimated incident light propagating in the incident plane, for the visible wavelength range, for a second incident angle of greater than about 35 degrees, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an average optical transmittance T2, T1/T2≥1.5.

In a second aspect, the present disclosure provides a display system including a display panel disposed on the backlight of the first aspect.

In a third aspect, the present disclosure provides a display system. The display system includes a plurality of discrete spaced apart light sources arranged two-dimensionally on an optically reflective surface. The display system further includes a display panel disposed on the light sources and configured to form an image. The display system further includes a reflective polarizer disposed between the display panel and the light sources. The display system further includes an optical film disposed between, and substantially co-extensive in length and width with, the reflective polarizer and the light sources. Each of the reflective polarizer and the optical film includes a plurality of polymeric layers numbering at least 10 in total. Each of the polymeric layers has an average thickness of less than about 500 nm. A visible wavelength range extends from about 420 nm to about 680 nm. An infrared wavelength range extends from about 700 nm to about 780 nm. For a substantially collimated incident light propagating in an incident plane, for a first incident angle of less than about 5 degrees, and the visible wavelength, the plurality of polymeric layers of the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized. For the substantially collimated incident light propagating in the incident plane, for the first incident angle, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an optical transmittance T1a at least one visible wavelength in the visible wavelength range and an optical transmittance T1b at at least one infrared wavelength in the infrared wavelength range. For the substantially collimated incident light propagating in the incident plane, for a second incident angle of greater than about 35 degrees, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an optical transmittance T1c at the at least one visible wavelength and an optical transmittance T1d at the at least one infrared wavelength, T1a/T1c≥1.5, T1b/T1d≤0.7.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

As used herein, the term “film” generally refers to a material with a very high ratio of length or width to thickness. A film has two major surfaces defined by a length and width. Films typically have good flexibility and can be used for a wide variety of applications, including displays. Films may also be of thickness or material composition, such that they are semi-rigid or rigid. Films described in the present disclosure may be composed of various polymeric materials. Films may be monolayer or multilayer or blend of different polymers.

As used herein, the term “optical film” generally refers to a film that can be used to produce an optical effect. Optical films are typically at least partially transmissive, reflective, antireflective, polarizing, optically clear, and/or diffusive for certain wavelengths of the electromagnetic spectrum (e.g., wavelengths in the visible, ultraviolet, or infrared regions of the electromagnetic spectrum).

As used herein, the term “layer” generally refers to a thickness of material within a film that has a relatively consistent chemical composition. Layers may be of any type of material including polymeric, cellulosic, metallic, or a blend thereof. A given polymeric layer may include a single polymer-type or a blend of polymers and may be accompanied by additives. A given layer may be combined or connected to other layers to form films. A layer may be either partially or fully continuous as compared to adjacent layers or the film. A given layer may be partially or fully coextensive with adjacent layers. A layer may contain sub-layers.

As used herein, the term “adhesive” generally refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives may include curable adhesives, heat activated adhesives, pressure sensitive adhesives, or combinations thereof.

As used herein, the term “diffuser” generally refers to any film, layer or substrates that are designed to scatter light. This light diffusion may be affected, for example, through use of a textured surface of the substrate, or through other means such as incorporation of light scattering particles within a matrix of the film. While it is noted that all optical articles can be considered to scatter light to some extent, substrates and films that are optically transparent or optically clear are not considered to be “light scattering” unless some light scattering property is imparted to these substrates or films.

As used herein, the term “specularly reflective” generally refers to a concept that can be described with reference to a term “specular reflection”. “Specular reflection” or “specularly reflected” refers to mirror-like reflection of light whereupon light from a single incident direction is reflected from a surface into a single outgoing direction, with both directions making the same angle with respect to a normal to the surface. “Specular reflectance” refers to a fraction, expressed as a percent, of incoming light intensity that is specularly reflected by the surface. Specular reflectance can be a function of the wavelength of the incident light.

As used herein, the term “diffusely reflective” generally refers to a concept that can be described with reference to the term “diffuse reflection”. Diffuse reflection or diffusely reflected refers to non-specular reflection of light whereupon light from a single incident direction is reflected from a surface into outgoing directions that do not include the specular direction. “Diffuse reflectance” refers to a fraction, expressed as a percent, of incoming light intensity that is diffusely reflected by the surface. Diffuse reflectance can be a function of a wavelength of the incident light.

The present disclosure relates generally to a backlight for providing illumination to a display panel, and a display system including the display panel disposed on the backlight.

The backlight may be used in electronic devices that include displays, such as computer monitors, televisions, mobile phones, personal digital assistants (PDAs), laptops, wearable devices and other portable devices. The backlight may also be used with displays for automotive applications. In some cases, the backlight may be incorporated in the display system.

Current display systems may typically include either direct-lit backlight units or edge-lit backlight units for providing illumination to a display panel. The edge-lit backlight units typically include light sources that emit light into an edge of a lightguide. The lightguide guides the emitted light from the light sources and directs the emitted light toward the display panel. The direct-lit backlight units typically include an array of light sources that emit light vertically toward the display panel. However, the direct-lit backlight units are generally bulky and may produce non-uniform backlight illumination.

The backlight of the present disclosure provides illumination to a display panel. The backlight includes a plurality of discrete spaced apart light sources arranged two-dimensionally on an optically reflective surface. The backlight further includes a reflective polarizer disposed on the plurality of discrete spaced apart light sources. The backlight further includes an optical film disposed between, and substantially co-extensive in length and width with, the reflective polarizer and the plurality of discrete spaced apart light sources. Each of the reflective polarizer and the optical film includes a plurality of polymeric layers numbering at least 10 in total. Each of the polymeric layers has an average thickness of less than about 500 nm. For a substantially collimated incident light propagating in an incident plane, for a visible wavelength range extending from about 420 nanometers (nm) to about 680 nm, and for a first incident angle of less than about 5 degrees, the plurality of polymeric layers of the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized. For the substantially collimated incident light propagating in the incident plane, for the visible wavelength range, for the first incident angle, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an average optical transmittance T1. For the substantially collimated incident light propagating in the incident plane, for the visible wavelength range, for a second incident angle of greater than about 35 degrees, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers of the optical film has an average optical transmittance T2, T1/T2≥1.5.

For the visible wavelength range, the optical film therefore has the average transmittance for the substantially collimated incident light propagating in the incident plane and incident at the first incident angle of less than about 5 degrees (i.e., substantially normally incident light or on-axis light) greater than the average transmittance for the substantially collimated incident light propagating in the incident plane P and incident at the second incident angle of greater than about 35 degrees (i.e., an off-axis light). Therefore, for the visible wavelength range, the optical film may have a greater reflectance for the substantially collimated incident light propagating in the incident plane and incident at the second incident angle. Thus, for the visible wavelength range, the optical film may substantially reflect the substantially collimated incident light propagating in the incident plane and incident at the second incident angle back toward the optically reflective surface of the backlight. The optical film may act as a collimating multilayer optical film (CMOF) with a greater transmittance for the on-axis light than the off-axis light.

Reflected light from the optical film may be recycled by the optically reflective surface of the backlight. The optically reflective surface may redirect the reflected light toward the optical film until the redirected light is substantially normally incident on the optical film (i.e., incident along a direction closer to an on-axis of the backlight). The optical film of the backlight of the present disclosure may therefore at least partially collimate and recycle the off-axis light generated by the plurality of discrete spaced apart light sources or the off-axis light redirected by the optically reflective surface, between the optical film and the optically reflective surface of the backlight. The increased recycling may therefore result in improved light use efficiency and increased brightness of illumination from the backlight. Further, the recycling of the off-axis light may further improve a uniformity of backlight illumination. This may further help in reducing a thickness of the backlight since the backlight exhibits good performance balance between brightness, uniformity and light use efficiency compared to other backlights with similar thickness.

FIG.1illustrates a schematic side view of a display system400according to an embodiment of the present disclosure. Specifically,FIG.1shows a sectional side view of the display system400. The display system400may be configured to display content, such as text and/or graphics.

The display system400defines mutually orthogonal x, y, and z-axes. The x and y-axes are in-plane axes of the display system400, while the z-axis is a transverse axis disposed along a thickness of the display system400. In other words, the x and y-axes are disposed along a plane of the display system400, while the z-axis is perpendicular to the plane of the display system400.

In some embodiments, the display system400may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.). In some other embodiments, the display system400may be a display that is not touch-sensitive.

The display system400includes a backlight300and a display panel10. The backlight300provides illumination to the display panel10. The display system400includes a plurality of discrete spaced apart light sources20arranged two-dimensionally on an optically reflective surface30. Specifically, the backlight300includes the plurality of discrete spaced apart light sources20arranged two-dimensionally on the optically reflective surface30. In some embodiments, the plurality of discrete spaced apart light sources20are arranged substantially along the x-axis and the y-axis. In some embodiments, “plurality of discrete spaced apart light sources20” may be interchangeably referred to as “light sources20”.

In some embodiments, the display system400includes the display panel10disposed on the backlight300. Specifically, the display system400includes the display panel10disposed on the light sources20and configured to form an image11. In some embodiments, the display panel10may selectively transmit or block light to form the image11for viewing by a user14. In some embodiments, the display panel10includes a liquid crystal display (LCD) panel. In some embodiments, the display panel10may include a plurality of individually addressable pixels (not shown). In some embodiments, the display panel may be, partly or entirely, a touch sensitive display panel configured to receive contact inputs from the user14. Accordingly, the display system400may receive touch inputs from the user14.

In some embodiments, the light sources20may include one or more light emitters that emit light. In some embodiments, at least one of the light sources20in the plurality of discrete spaced apart light sources20includes a light emitting diode (LED). In some other embodiments, at least one of the light sources20in the plurality of discrete spaced apart light sources20may include any other type of light emitters, for example, fluorescent lights, or any other suitable light emitting device. In some embodiments, the light sources20may be controlled in unison by a control circuitry (not shown) of the display system400or may be individually controlled.

In some embodiments, the light sources20may emit light of any suitable color (e.g., blue, red, green, white, etc.). In some other embodiments, the light sources20may be monochromatic or may include a number of light emitters operating at different wavelengths in order to produce a white light output. In some embodiments, the plurality of discrete spaced apart light sources20includes one or more of a blue light emitting light source, a green light emitting light source, a red light emitting light source, and a white light emitting light source. In some embodiments, each light source20in the plurality of discrete spaced apart light source20is a blue light emitting light source emitting only blue light. In some embodiments, the light sources20may be encapsulated by any suitable encapsulant. In some embodiments, the encapsulant may be air. In some embodiments, the encapsulant may also include phosphorescent materials or other color conversion materials.

In some embodiments, the backlight300includes a circuit board120including the optically reflective surface30. In some embodiments, the LEDs may be mounted on the circuit board120. Light from the light sources20may be reflected from the optically reflective surface30. Further, light reflected from the optically reflective surface30may illuminate the display panel10. In some embodiments, the backlight300may include side reflectors32surrounding at least a portion of a periphery of the backlight300. The side reflectors32may reflect light received at an edge portion of the backlight300from the optically reflective surface30.

In some embodiments, the optically reflective surface30is primarily specularly reflective having a specular optical reflectance of greater than about 70% for at least one wavelength in a visible wavelength range80(shown inFIGS.4and6) extending from about 420 nanometers (nm) to about 680 nm. In some embodiments, the optically reflective surface30has a specular optical reflectance of greater than about 80% for at least one wavelength in the visible wavelength range80. In some embodiments, the optically reflective surface30is primarily diffusely reflective having a diffuse optical reflectance of greater than about 70% for at least one wavelength in the visible wavelength range80. In some embodiments, the optically reflective surface30has the diffuse optical reflectance of greater than about 80% for at least one wavelength in the visible wavelength range80. In some embodiments, the optically reflective surface30may include a metallic surface. In some embodiments, the optically reflective surface30may include one or more elements, such as silver, aluminum, a white coating, a non-conductive coating, etc. In some embodiments, the optically reflective surface30may be useful for recycling light within the display system400. For example, the optically reflective surface30may recycle light generated by the light sources20. This may result in improved light use efficiency and increased brightness.

The display system400further includes a reflective polarizer40disposed between the display panel10and the light sources20. Specifically, the backlight300includes the reflective polarizer40disposed on the plurality of discrete spaced apart light sources20. In some embodiments, the reflective polarizer40may substantially allow light of a specific polarization to pass through while substantially blocking light of an orthogonal polarization.

FIG.2illustrates a schematic top view of the backlight300. The backlight300extends along the x-y plane with a length L substantially along the y-axis and a width W substantially along the x-axis. Various components of the display system400(shown inFIG.1) and the backlight300may be co-extensive in the length L and the width W of the backlight300.

Referring toFIGS.1and2, the display system400further includes an optical film50disposed between, and substantially co-extensive in the length L and the width W with, the reflective polarizer40and the light sources20. Specifically, the backlight300includes the optical film50disposed between, and substantially co-extensive in the length L and the width W with, the reflective polarizer40and the plurality of discrete spaced apart light sources20. The reflective polarizer40and the optical film50will be described in detail later with reference toFIGS.3and5. Each of the reflective polarizer40and the optical film50includes a plurality of polymeric layers (not shown inFIG.1) numbering at least 10 in total. In some embodiments, each of the reflective polarizer40and the optical film50includes the plurality of polymeric layers numbering at least 50, at least 100, at least 200, at least 300, at least 400, or at least 500 in total.

In some embodiments, the backlight300further includes a light converting component100disposed between the optical film50and the plurality of discrete spaced apart light sources20. In some embodiments, the light converting component100is a light converting film100substantially co-extensive in the length L and the width W with the plurality of discrete spaced apart light sources20. In some embodiments, “light converting component100” may be interchangeably used hereinafter as “light converting film100”. In some embodiments, a first bonding layer110bonds the light converting film100to the optical film50. In some embodiments, the first bonding layer110may include an optically clear adhesive layer or an epoxy layer for bonding the light converting film100to the optical film50.

In some embodiments, the light converting component100may be configured to convert light from the light sources20from one color to a different color. In some embodiments, the light converting component100is configured to convert at least a portion of the blue light emitted by the blue light emitting light sources (e.g., one or more of the light sources20) to a green light and convert at least a portion of the blue light emitted by the blue light emitting light sources to a red light. In some embodiments, the light converting component100includes one or more of phosphor, fluorescent dye, and quantum dots. For example, when the light sources20emit blue light, phosphor (e.g., a layer of phosphor material or other photoluminescent material) in the light converting component100may convert at least a portion of the blue light to the green light or at least a portion of the blue light into the red light.

In some embodiments, the backlight300further includes a first optically diffusive layer130disposed between, and substantially co-extensive in the length L and the width W with, the optical film50and the plurality of discrete spaced apart light sources20. In some embodiments, the first optically diffusive layer130is configured to scatter light. In some embodiments, the first optically diffusive layer130includes a plurality of discrete spaced apart optically diffusive portions132disposed on a first substrate131. In some embodiments, the diffusive portions132are disposed between the first substrate131and the light sources20. In some embodiments, the diffusive portions132and the light sources20are aligned to each other in a one-to-one correspondence. In some embodiments, the first optically diffusive layer130may diffuse light received from the light sources20. Specifically, light emitted by the light sources20is received by the first optically diffusive layer130and is scattered by the diffusive portions132of the first optically diffusive layer130. Thus, the first optically diffusive layer130may improve a uniformity of light emitted by the plurality of discrete spaced apart light sources20.

In some embodiments, the light converting component100and the first optically diffusive layer130are disposed between the optical film50and the light sources20. In some embodiments, a second bonding layer111bonds the light converting component100to the first optically diffusive layer130. In some embodiments, the second bonding layer111may include an optically clear adhesive layer or an epoxy layer for bonding the light converting component100to the first optically diffusive layer130. In some embodiments, the second bonding layer111is substantially similar to the first bonding layer110.

In some embodiments, the backlight300further includes a second optically diffusive layer140disposed between the reflective polarizer40and the optical film50. In some embodiments, the second optically diffusive layer140may be substantially similar to the first optically diffusive layer130. In some embodiments, the backlight300further includes a third bonding layer112bonding the second optically diffusive layer140to the optical film50. In some embodiments, the third bonding layer112may include an optical adhesive layer or an epoxy layer for bonding the second optically diffusive layer140to the optical film50. In some embodiments, the third bonding layer112may be substantially similar to the first bonding layer110and/or the second bonding layer111.

In some embodiments, the backlight300further includes at least one light redirecting film150,151disposed between the reflective polarizer40and the optical film50. In the illustrated embodiment ofFIG.1, the at least one light redirecting film150,151includes two light redirecting films150,151. In some embodiments, the at least one light redirecting film150,151redirects at least one of a recycling light and a collimating light received from the optical film50. In some embodiments, at least one of the at least one light redirecting film150,151(e.g., the light redirecting film150) includes a plurality of substantially parallel linear prisms152extending along a first direction and arranged along a different second direction. In some embodiments, the first direction may be substantially along the y-axis and the second direction may be substantially along the x-axis. In some embodiments, at least one of the at least one light redirecting film150,151may enhance a brightness of an image (e.g., the image11) formed by the display panel10. In some embodiments, the two light redirecting films150,151may be crossed prism films. Therefore, the linear prisms152of the light redirecting film150may be substantially orthogonal to the linear prisms (not shown) of the light redirecting film151.

In some embodiments, various components of the display system400and the backlight300are disposed along the z-axis. In some embodiments, the display system400may further include other light management layers. These layers may be used for spatial mixing or color mixing of light, light source hiding, and uniformity improvement. Layers that may be used for these purposes include, but are not limited to, diffuser films, diffuser plates, partially reflective layers, color-mixing lightguides or films, and non-Gaussian diffusers (diffusing systems in which a peak brightness ray of diffused light propagates in a direction that is not parallel to a direction of the peak brightness ray of input light). In some embodiments, the layers may include one or more color filter layers, polarizer layers, micro-structured layers, etc., or combinations thereof. In some embodiments, the display system400may further include a cover layer (not shown) disposed on the display panel10. The cover layer may provide protection to the various layers of the display system400.

FIG.3illustrates a schematic side view of the reflective polarizer40according to an embodiment of the present disclosure. In some embodiments, the reflective polarizer40is an Advanced Polarizing Filter (APF). However, the reflective polarizer40may be any suitable reflective polarizer. In some embodiments, the reflective polarizer40may include one or more of a multilayer polymeric reflective polarizer, a wire grid reflective polarizer, and a diffuse reflective polarizer. In some embodiments, light reflected from the reflective polarizer40may be recycled by the optically reflective surface30(shown inFIG.1).

The reflective polarizer40includes a plurality of polymeric layers60,61numbering at least 10 in total. In some embodiments, the reflective polarizer40includes the plurality of polymeric layers60,61numbering at least 50, at least 100, at least 200, at least 300, at least 400, or at least 500 in total. In the illustrated embodiment ofFIG.3, the reflective polarizer40includes the plurality of polymeric layers60,61disposed in an alternating configuration. Specifically, the polymeric layers60,61form alternating polymeric layers along the z-axis. Each of the polymeric layers60,61has an average thickness of less than about 500 nm. In some embodiments, each of the polymeric layers60,61has the average thickness of less than about 400 nm, less than about 300 nm, or less than about 200 nm. The average thickness is measured along the z-axis.

In some embodiments, one of the polymeric layers60,61includes a material with a high refractive index relative to the other. In some embodiments, at least one of the polymeric layers60,61includes a birefringent material. In some embodiments, the reflective polarizer40may further include at least one intermediate layer (not shown) disposed between the plurality of polymeric layers60,61. In some embodiments, the intermediate layer may include a material with a low refractive index.

In some embodiments, the reflective polarizer40further includes at least one skin63disposed on the plurality of polymeric layers60,61thereof. In the illustrated embodiment ofFIG.3, the reflective polarizer40includes skins63on both major surfaces of the reflective polarizer40. Specifically, the plurality of polymeric layers60,61are disposed between the skins63. The at least one skin63may protect the plurality of polymeric layers60,61, and may also provide mechanical stability to the reflective polarizer40. In some cases, the at least one skin63may act as protective boundary layer (PBL). In some embodiments, the at least one skin63has an average thickness of greater than about 500 nm. In some embodiments, the at least one skin63has the average thickness of greater than about 750 nm, or greater than about 1000 nm.

As shown inFIG.3, a substantially collimated incident light70propagating in an incident plane P is incident on a major surface41of the reflective polarizer40at a first incident angle α1 with respect to a normal NRto the major surface41. The incident plane P may substantially correspond to the x-z plane. The normal NRmay lie in the incident plane P. In some embodiments, the first incident angle α1 is less than about 5 degrees. In some embodiments, the first incident angle α1 is less than about 4 degrees, less than about 3 degrees, less than about 2 degrees, or less than about 1 degree. However, the incident light70may be incident on the reflective polarizer40at any oblique angle. In some embodiments, “substantially collimated incident light70” may be interchangeably referred to as “incident light70”.

FIG.4is an exemplary graph90depicting optical transmittance versus wavelength of the reflective polarizer40(shown inFIG.3) for different polarization states of incident light. Wavelength is expressed in nanometers (nm) in the abscissa. Wavelength includes the visible wavelength range80and an infrared wavelength range81extending from about 700 nm to about 780 nm. Optical transmittance is expressed as a transmittance percentage in the left ordinate. Reflectance is expressed as a reflectance percentage in the right ordinate. The reflectance percentage is complementary to the transmittance percentage, i.e., the reflectance percentage=(100−transmittance percentage).

The graph90includes a curve172and a curve174. The curve172depicts optical transmittance versus wavelength of the reflective polarizer40when the incident light70is p-polarized. The curve174depicts optical transmittance versus wavelength of the reflective polarizer40when the incident light70is s-polarized.

Referring toFIGS.3and4, as is apparent from the curve172, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, and for the first incident angle α1 of less than about 5 degrees, the plurality of polymeric layers60,61of the reflective polarizer40has an average optical reflectance Ravgof at least 60% when the incident light70is p-polarized. In some embodiments, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, and for the first incident angle α1 of less than about 5 degrees, the plurality of polymeric layers60,61of the reflective polarizer40has the average optical reflectance Ravgof at least 70%, at least 80%, at least 90%, or at least 95% when the incident light70is p-polarized.

As is apparent from the curve174, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, and for the first incident angle α1 of less than about 5 degrees, the plurality of polymeric layers60,61of the reflective polarizer40has an average optical transmittance Tavgof at least 60% when the incident light70is s-polarized. In some embodiments, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, and for the first incident angle α1 of less than about 5 degrees, the plurality of polymeric layers60,61of the reflective polarizer40has the average optical transmittance Tavgof at least 70%, at least 80%, at least 90%, or at least 95% when the incident light70is s-polarized.

FIG.5illustrates a schematic side view of the optical film50. The optical film50includes a plurality of polymeric layers64,65numbering at least 10 in total. In some embodiments, the optical film50includes the plurality of polymeric layers64,65numbering at least 50, at least 100, at least 200, at least 300, at least 400, or at least 500 in total. In the illustrated embodiment ofFIG.5, the optical film50includes the plurality of polymeric layers64,65disposed in an alternating configuration. Specifically, the polymeric layers64,65form alternating polymeric layers along the z-axis. Each of the polymeric layers64,65has an average thickness of less than about 500 nm. In some embodiments, each of the polymeric layers64,65has the average thickness of less than about 400 nm, less than about 300 nm, or less than about 200 nm.

In some embodiments, one of the polymeric layers64,65includes a material with a high refractive index relative to the other. In some embodiments, at least one of the polymeric layers64,65includes a birefringent material. In some embodiments, the optical film50may further include at least one intermediate layer (not shown) disposed between the plurality of polymeric layers64,65. In some embodiments, the intermediate layer may include a material with a low refractive index.

In some embodiments, the optical film50further includes at least one skin66disposed on the plurality of polymeric layers64,65thereof. In the illustrated embodiment ofFIG.5, the optical film50includes skins66on both major surfaces of the optical film50. Specifically, the plurality of polymeric layers64,65are disposed between the skins66. The at least one skin66may protect the plurality of polymeric layers64,65, and may also provide mechanical stability to the optical film50. In some cases, the at least one skin66may act as PBL. In some embodiments, the at least one skin66has an average thickness of greater than about 500 nm. In some embodiments, the at least one skin66has the average thickness of greater than about 750 nm or greater than about 1000 nm.

As shown inFIG.5, the incident light70propagating in the incident plane P may be incident on the optical film50at the first incident angle α1 of less than about 5 degrees, and a second incident angle α2 of greater than about 35 degrees, relative to a normal No to a major surface51of the optical film50. The incident plane P may substantially correspond to the x-z plane. The normal No may lie in the incident plane P. In some embodiments, the first incident angle α1 is less than about 4 degrees, less than about 3 degrees, less than about 2 degrees, or less than about 1 degree. In some embodiments, the second incident angle α2 is greater than about 40 degrees, greater than about 45 degrees, greater than about 50 degrees, or greater than about 55 degrees. In some embodiments, the incident light70propagating in the incident plane P is incident on the optical film50at a third incident angle α3 of between about 20 degrees and about 40 degrees relative to the normal No to the major surface51of the optical film50. In some embodiments, the third incident angle α3 is between about 25 degrees and about 35 degrees. In some embodiments, the incident light70propagating in the incident plane P is incident on the optical film50at a fourth incident angle α4 of greater than about 45 degrees relative to the normal No to the major surface51of the optical film50. In some embodiments, the fourth incident angle α4 is greater than about 50 degrees, or greater than about 55 degrees.

FIG.6is an exemplary graph91depicting optical transmittance versus wavelength of the optical film50(shown inFIG.5) corresponding to different incident angles. Wavelength is expressed in nanometers (nm) in the abscissa. Wavelength includes the visible wavelength range80and the infrared wavelength range81. Optical transmittance is expressed as a transmittance percentage in the left ordinate.

The graph91includes a curve182, a curve184, a curve186, a curve188, and a curve190. Referring toFIGS.5and6, the curve182depicts optical transmittance versus wavelength of the optical film50for a light incident at 0 degree relative to the normal No to the major surface51of the optical film50and for the average of p-polarized and s-polarized incident lights (i.e., light linearly polarized in the plane of incidence and perpendicular to the plane of incidence, respectively). The curve184depicts optical transmittance versus wavelength of the optical film50for a light incident at 30 degrees relative to the normal No to the major surface51of the optical film50and for the average of p-polarized and s-polarized incident lights. The curve186depicts optical transmittance versus wavelength of the optical film50for a light incident at 40 degrees relative to the normal No to the major surface51of the optical film50and for the average of p-polarized and s-polarized incident lights. The curve188depicts optical transmittance versus wavelength of the optical film50for a light incident at 50 degrees relative to the normal No to the major surface51of the optical film50and for the average of p-polarized and s-polarized incident lights. The curve190depicts optical transmittance versus wavelength of the optical film50for a light incident at 60 degrees relative to the normal No to the major surface51of the optical film50and for the average of p-polarized and s-polarized incident lights.

FIGS.7A and7Billustrate tables200and250, respectively. The table200lists exemplary values of average optical transmittance for the visible wavelength range80and for the infrared wavelength range81at different angles of light incident on the optical film50(shown inFIGS.1and5) corresponding to the graph91shown inFIG.6. The table200includes multiple column headings in a row202. The column headings in the row202includes different angles of light incident on the optical film50. A column203indicates the visible wavelength range80(about 420 nm to about 680 nm) and the infrared wavelength range81(about 700 nm to about 780 nm). The table200further incudes multiple cells corresponding to different values of the average optical transmittance for the visible wavelength range80and for the infrared wavelength range81at different angles of light incident on the optical film50.

The table200includes cells204and206indicative of values of an average optical transmittance T1 and an average optical transmittance T3 corresponding to the visible wavelength range80(about 420 nm to about 680 nm) and the infrared wavelength range81(about 700 nm to about 780 nm), respectively, and for the substantially normally incident light (angle of incidence less than about 5 degrees). Further, the table200includes a cell208indicative of a value of an average optical transmittance T4 for the infrared wavelength range81and for the light incident at 30 degrees relative to the normal No, a cell210indicative of a value of an average optical transmittance T2 for the visible wavelength range80and for the light incident at 40 degrees relative to the normal No, a cell212indicative of a value of an average optical transmittance T5 for the infrared wavelength range81and for the light incident at 50 degrees relative to the normal No.

The table250lists exemplary values for a ratio of an average optical transmittance for the substantially normally incident light (angle of incidence less than about 5 degrees) to an average optical transmittance corresponding to various angles of light incident on the optical film50. The table250includes multiple column headings in a row252. The column headings in the row252includes the visible wavelength range80(about 420 nm to about 680 nm) and the infrared wavelength range81(about 700 nm to about 780 nm). A column254indicates the ratios of the average optical transmittance for the substantially normally incident light (angle of incidence less than about 5 degrees) to the average optical transmittance corresponding to various angles of light incident on the optical film50for the visible wavelength range80and the infrared wavelength range81. The table250further incudes multiple cells corresponding to different values of the ratio of the average optical transmittance for the substantially normally incident light to the average optical transmittance corresponding to various angles of light incident on the optical film50for the visible wavelength range80and the infrared wavelength range81.

The table250includes a cell256indicative of a ratio of the average optical transmittance T1 to the average optical transmittance T2 for the visible wavelength range80, a cell258indicative of a ratio of the average optical transmittance T3 to the average optical transmittance T4 for the infrared wavelength range81, and a cell260indicative of a ratio of the average optical transmittance T3 to the average optical transmittance T5 for the infrared wavelength range81.

Referring now toFIGS.5-7Band the curve182, for the substantially collimated incident light70propagating in the incident plane P, for the first incident angle α1 (about 0 degree), and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers64,65of the optical film50has an optical transmittance T1a at at least one visible wavelength82in the visible wavelength range80and an optical transmittance T1b at at least one infrared wavelength83in the infrared wavelength range81. Further, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, for the first incident angle α1, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers64,65of the optical film50has the average optical transmittance T1. Moreover, for the average of p-polarized and s-polarized incident lights propagating in the incident plane P, and for the infrared wavelength range81, the plurality of polymeric layers64,65of the optical film50has the average optical transmittance T3 for the first incident angle α1.

Referring to the curves184,186, for the average of p-polarized and s-polarized incident lights propagating in the incident plane P, and for the infrared wavelength range81, the plurality of polymeric layers64,65of the optical film50has the average optical transmittance T4 for the third incident angle α3 of between about 20 degrees and about 40 degrees, or between about 25 degrees and about 35 degrees.

Further, referring to the curve188, for the substantially collimated incident light70propagating in the incident plane P, for the second incident angle α2 of greater than about 35 degrees, and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers64,65of the optical film50has an optical transmittance T1c at the at least one visible wavelength82and an optical transmittance T1d at the at least one infrared wavelength83in the infrared wavelength range81. Further, for the substantially collimated incident light70propagating in the incident plane P, for the visible wavelength range80, for the second incident angle α2 of greater than about 35 degrees and for the average of p-polarized and s-polarized incident lights, the plurality of polymeric layers64,65of the optical film50has the average optical transmittance T2.

Referring to the curves188,190, for the average of p-polarized and s-polarized incident lights propagating in the incident plane P, and for the infrared wavelength range81, the plurality of polymeric layers64,65of the optical film50has the average optical transmittance T5 for the fourth incident angle α4 of greater than about 45 degrees, greater than about 50 degrees, or greater than about 55 degrees.

As is apparent from the graph91, the optical transmittance T1a is greater than or equal to 1.5 times the optical transmittance T1c, i.e., T1a/T1c≥1.5. In some embodiments, T1a/T1c≥1.8, T1a/T1c≥2, T1a/T1c≥2.5, T1a/T1c≥3, T1a/T1c≥3.5, T1a/T1c≥4, T1a/T1c≥4.5, or T1a/T1c≥5. Further, the optical transmittance T1b is less than or equal to 0.7 times the optical transmittance T1d, i.e., T1b/T1d≤0.7. In some embodiments, T1b/T1d≤0.6, or T1b/T1d≤0.5.

Further, as is apparent from the graph91and the tables200and250, the average optical transmittance T1 is greater than or equal to 1.5 times the average optical transmittance T2, i.e., T1/T2≥1.5. In some embodiments, T1/T2≥1.8, T1/T2≥2, T1/T2≥2.5, T1/T2≥3, T1/T2≥3.5, T1/T2≥4, T1/T2≥4.5, or T1/T2≥5. Further, the average optical transmittance T3 is greater than or equal to the average optical transmittance T4, i.e., T3/T4≥1. In some embodiments, T3/T4≥1.1, T3/T4≥1.2, or T3/T4≥1.3. Further, the average optical transmittance T3 is less than or equal to 0.7 times the average optical transmittance T5, i.e., T3/T5≤0.7. In some embodiments, T3/T5≤0.6, or T3/T5≤0.5.

Referring now toFIGS.1,5-7B, for the visible wavelength range80, the optical film50therefore has the average transmittance T1 for the substantially collimated incident light70propagating in the incident plane P and incident at the first incident angle α1 of less than about 5 degrees (i.e., substantially normally incident light or an on-axis light). Further, for the visible wavelength range80, the optical film50has the average transmittance T2 for the substantially collimated incident light70propagating in the incident plane P and incident at the second incident angle α2 of greater than about 35 degrees (i.e., an off-axis light). The average transmittance T1 is greater than the average transmittance T2. Therefore, for the visible wavelength range80, the optical film50may have a greater reflectance for the substantially collimated incident light70propagating in the incident plane P and incident at the second incident angle α2. Thus, for the visible wavelength range80, the optical film50may substantially reflect the substantially collimated incident light70propagating in the incident plane P and incident at the second incident angle α2 back toward the optically reflective surface30of the backlight300. The optical film50may act as a collimating multilayer optical film (CMOF) with a greater transmittance for the on-axis light than the off-axis light.

Reflected light from the optical film50may be recycled by the optically reflective surface30of the backlight300. The optically reflective surface30may redirect the reflected light toward the optical film50until the redirected light is substantially normally incident on the optical film50(i.e., incident along a direction closer to an on-axis of the backlight300). The optical film50of the backlight300may therefore at least partially collimate and recycle the off-axis light generated by the plurality of discrete spaced apart light sources20or the off-axis light redirected by the optically reflective surface30, between the optical film50and the optically reflective surface30of the backlight300. The increased recycling may therefore result in improved light use efficiency and increased brightness of illumination from the backlight300. Further, the recycling of the off-axis light may further improve a uniformity of backlight illumination. This may further help in reducing a thickness of the backlight300since the backlight300exhibits good performance balance between brightness, uniformity and light use efficiency compared to other backlights with similar thickness.

Further, for the infrared wavelength range81, the optical film50has the average transmittance T3 for the substantially collimated incident light70propagating in the incident plane P and incident at the first incident angle α1 of less than about 5 degrees. For the infrared wavelength range81, the optical film50has the average transmittance T4 for the substantially collimated incident light70propagating in the incident plane P and incident at the third incident angle α3 of between about 20 degrees and about 40 degrees. For the infrared wavelength range81, the optical film50has the average transmittance T5 for the substantially collimated incident light70propagating in the incident plane P and incident at the fourth incident angle α4 of greater than about 45 degrees. The average transmittance T3 is greater than the average transmittance T4. However, the average transmittance T5 is greater than the average transmission T3. Therefore, the average transmittance of the optical film50in the infrared wavelength range81may decrease from substantially normally incidence (e.g., the first incident angle α1) to an incident angle between about 20 degrees and about 40 degrees (e.g., the third incident angle α3). However, the average transmittance of the optical film50in the infrared wavelength range81may increase with an increase in the incident angle above 45 degrees (e.g., the fourth incident angle α4). Therefore, the average transmittance of the optical film50in the infrared range81may increase or decrease in various ranges of the incident angle.

FIG.8Aillustrates a schematic top view of the plurality of discrete spaced apart light sources20disposed on the optically reflective surface30. In the illustrated embodiment ofFIG.8A, the light sources are arranged in a regular two-dimensional array of light sources20forming rows21and columns22of the light sources20. In some embodiments, the sources may be arranged in a hexagonal array or other irregular patterns. In general, each light source20from the plurality light sources20may include a single LED, a pair of LEDs, 2-10 LEDs or any number of LEDs. In the illustrated embodiment ofFIG.8A, a single LED is shown representing each light source20. Further, the light sources20are shown substantially circular in shape. However, the light sources20may have any suitable shape, for example, a square shape, a rectangle shape, an elliptical shape, a polygonal shape, etc. In some embodiments, the light sources20may have same or different sizes based on desired application attributes.

In some embodiments, each light source20may be covered by an encapsulant of different shape or an encapsulant with different dopants. In some embodiments, the encapsulant may include color conversion materials, such as phosphorescent materials or quantum dots. In some embodiments, some light sources20from the plurality of discrete spaced apart light sources20may have different properties to tune the light that is emitted from the light sources20. In some embodiments, some light sources20from the plurality of discrete spaced apart light sources20may emit red, blue, green, or white light.

In some embodiments, the circuit board120(shown inFIG.1) may include the optically reflective surface30. The light sources20may be mounted on the circuit board120by any suitable attachment mechanism (e.g., soldering) and may be arranged using any suitable arrangement based on desired application attributes.

FIG.8Billustrates a schematic side view of the light sources20and the circuit board120. In some embodiments, light emitted by the plurality of light sources20and incident on the optical film50has a minimum luminance L1 (shown inFIG.9as Lmin) and a maximum luminance L2 (shown inFIG.9as Lmax) within a cone24of emitted light centered on an optical axis B substantially orthogonal to the optically reflective surface30with a half cone angle CA of at least 40 degrees. In some embodiments, the half cone angle CA is at least 45 degrees, at least 50 degrees, at least 55 degrees, or at least 60 degrees.

FIG.9illustrates an exemplary graph92including a curve162depicting luminance versus polar angle for the plurality of light sources20after transmission through the diffuser130(shown inFIG.1) and the color conversion film100(shown inFIG.1). This result is obtained on a partial optical stack to measure the uniformity of the illumination of the backlight300(shown inFIG.1) before entering the optical film50(shown inFIG.1). Polar angle is expressed in degrees in the abscissa. Luminance is expressed in candela per square meter (cd/m2) in the left ordinate. The polar angle may correspond to a viewer observation angle or the half cone angle CA of the cone24(shown inFIG.8B) of emitted light.

As is apparent from the curve162, for the polar angles substantially in the range of about −40 degrees to about 40 degrees, the luminance is substantially constant. For the half cone angle CA of at least ±40 degrees, the luminance varies between the minimum luminance L1 and the maximum luminance L2. The minimum luminance L1 is greater than or equal to 0.5 times the maximum luminance L2, i.e., L1/L2≥0.5. In some embodiments, L1/L2≥0.55, L1/L2≥0.6, L1/L2≥0.65, L1/L2≥0.7, or L1/L2≥0.75.

FIG.10Aillustrates a schematic side view of the light sources20, the first optically diffusive layer130, and a light converting component100a. The light converting component100asubstantially encapsulates the plurality of discrete spaced apart light sources20. In some embodiments, the light converting component100amay have substantially similar optical properties as the light converting component100ofFIG.1. In some embodiments, the light converting component100amay substantially conform to the light sources20arranged on the optically reflective surface30of the circuit board120. In some embodiments, the light converting component100amay have any thickness based on desired application attributes.

FIG.10Billustrates a schematic side view of the light sources20, the first optically diffusive layer130, and a light converting component100b. In some embodiments, the light converting component100bmay have substantially similar optical properties as the light converting component100ofFIG.1. The light converting component100bincludes a plurality of discrete light converting component portions101. Each of the light converting component portions101substantially encapsulates a corresponding one of the light sources20. Thus, each of the light converting component portions101may be associated with the corresponding one of the light sources20. In some embodiments, the plurality of discrete light converting component portions101may have any thickness based on desired application attributes.

FIGS.11A and11Billustrate schematic side views of the first optically diffusive layer130according to different embodiments of the present disclosure. The first optically diffusive layer130includes the plurality of discrete spaced apart optically diffusive portions132disposed on the first substrate131. Referring toFIG.11A, at least one of the diffusive portions132is primarily a bulk diffuser133. Generally, in bulk diffusers, small particles, or spheres of a different refractive index are embedded within a primary material of the bulk diffuser. The embedded small particles or spheres act as light scattering elements. In some other embodiments, a refractive index of a material of the bulk diffuser133varies across a body of the bulk diffuser133, thus causing light passing through the material to be refracted or scattered at different points.

Referring toFIG.11B, at least one of the diffusive portions132is primarily a surface diffuser132a. Generally, surface diffusers utilize surface roughness to refract or scatter light in a number of directions. The rough surfaces of the surface diffuser132amay be exposed to air or a surrounding medium, and may cause the largest angular spread for an incident light. In some embodiments, at least two of the diffusive portions132are primarily surface diffusers132a,132band include two different surface structures. It should be understood that the shapes and configurations of the surface diffusers132a,132bas shown inFIG.11Bare exemplary and may vary as per desired application attributes.

FIG.12illustrates a schematic perspective view of the light redirecting films150,151. In some embodiments, the at least one light redirecting film150,151includes first and second prismatic films150a,151a. In some embodiments, the first prismatic film150aincludes a plurality of substantially parallel linear first prisms152aextending along the first direction and arranged along the different second direction. The second prismatic film151aincludes a plurality of substantially parallel linear second prisms153aextending along a third direction, different from the first direction, and arranged along a different fourth direction. In some embodiments, the first direction and the fourth direction may be disposed substantially along the y-axis. In some embodiments, the second direction and the third direction may be disposed substantially along the x-axis. Thus, the first and second prismatic films150a,151amay be in a crossed configuration (i.e., the second prismatic film151amay be rotated 90 degrees with respect to the first prismatic film150a). In other words, the first prims152aand the second prisms153aare arranged to be perpendicular to each other.

In some embodiments, the first and second prismatic films150a,151amay enhance a brightness of an image (e.g., the image11) emitted by the display system400by at least partially collimating and recycling light emitted by the light sources20. The first prims152aand the second prisms153amay redirect off-axis light in a direction closer to the on-axis of the display system400.

Examples

Example films for the reflective polarizer40and the optical film50were prepared in accordance with embodiments of the description.

The reflective polarizer40was prepared as follows. A single multilayer optical packet was co-extruded. The packet included 275 alternating layers of 90/10 coPEN, a polymer composed of 90% polyethylene naphthalate (PEN) and 10% polyethylene terephthalate (PET), and a low refractive index isotropic layer, which was made with a blend of polycarbonate and copolyesters (PC:coPET). The low refractive index isotropic layer had a refractive index of about 1.57 and remained substantially isotropic upon uniaxial orientation. A molar ratio of the PC:coPET was approximately 42.5 mol % polycarbonate (PC) and 57.5 mol % coPET, and the material had a glass transition temperature (Tg) of 105° C. This isotropic material was chosen such that after stretching, the refractive indices of the isotropic material in two non-stretch directions remained substantially matched with those of the birefringent material in the non-stretching direction, while in the stretching direction there was a substantial mis-match in refractive indices between birefringent and non-birefringent layers.

The 90/10 PEN and PC:coPET polymers were fed from separate extruders to a multilayer coextrusion feedblock, in which they were assembled into a packet of 275 alternating optical layers, and thicker protective boundary layers of the PC:coPET polymer on each side, resulting in a total of 277 layers. After the feedblock, skin layers were added where the polymer used for the skin layers was a second PC:coPET having a molar ratio of 50 mol % polycarbonate and 50 mol % coPET, and having a Tg of 110° C. The multilayer melt was then cast through a film die onto a chill roll, in the conventional manner for polyester films, upon which it was quenched. The cast web was then stretched in a parabolic tenter as described in U.S. Pat. No. 7,104,776 (Merrill et al.) at temperatures and draw ratios (about 6.0) similar to that described in Example 2A of US Patent Application Publication No. 2007/0047080 (Stover et al.).

During the production of the multilayered film, a linear layer profile for a single packet was targeted to best balance optical performance and manufacturing efficiency. The targeted slope was approximately 0.24 nm/layer. The film had a resulting thickness of approximately 26.5 microns as measured by a capacitance gauge.

The optical film50was prepared as follows. Optical film50was manufactured using the feedblock method described in U.S. Patent Application 61/332,401 (Attorney Docket No. 64248US002) entitled “Feedblock for Manufacturing Multilayer Polymeric Films”, filed May 7, 2010. Two packets of 275 layers, each of alternating low and high index polymer layers, were coextruded as a cast web and then stretched in a tenter on a continuous film making line. The high index material was a90/10coPEN (90% naphthalate units and 10% teraphthalate units). The low index isotropic layer was made with a blend of polycarbonate and copolyesters (PC:coPET). The low index layer had a refractive index of about 1.57 and remained substantially isotropic upon uniaxial orientation. The PC:coPET molar ratio was approximately 42.5 mol % polycarbonate and 57.5 mol % coPET, and the material had a Tg of 105° C.

The 325 alternating microlayers in each packet were arranged in a sequence of ¼ wave layer pairs to produce the transmission spectra shown inFIG.6. The overall thickness of the film was approximately 76 microns.