Light guide panel, surface light source apparatus including light guide panel, and flat panel display including surface light source apparatus

A light guide panel includes: a light guide layer having a light incident surface; a polarization separation layer configured to select a desired polarization among light emitted from the light guide layer and to emit light having the polarization; and a light homogenization layer including a plurality of fibers and a supporting medium of the fibers, the light homogenization layer configured to diffuse and scatter light incident on the light guide layer into the light guide layer. The polarization separation layer includes: a plurality of first fibers having birefringence; and a first supporting medium that is isotropic and configured to support the first fibers. The refractive index of the first supporting medium corresponds to at least one of two different refractive indices of the first fibers. The light homogenization layer includes: a plurality of second fibers having birefringence; and a second supporting medium that is isotropic and configured to support the second fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2011-0140649, filed on Jun. 24, 2011, and Korean Patent Application No. 10-2012-0005277, filed Jan. 17, 2012, the disclosure of each of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to display apparatuses and more particularly, to light guide panels, surface light source apparatuses including the light guide panels, and/or flat panel displays including the surface light source apparatuses.

2. Description of the Related Art

Liquid crystal displays used in personal computers (PCs), computer monitors, liquid crystal display (LCD) TVs, mobile communication terminals, or the like are light-receiving displays that do not emit light by themselves but display images by selectively transmitting light irradiated from the outside. Thus, a backlight is included on a rear surface of the liquid crystal displays as a surface light source apparatus.

In the liquid crystal displays, light emitted from the surface light source apparatus transmits through a liquid crystal layer arranged between a pair of polarization plates that have transmission axes at right angles to each other. An image is displayed as the light that transmits through the liquid crystal layer is electrically turned on or off.

An absorption-type polarization plate is used as the polarization plates. In the absorption-type polarization plate, an iodine-colored uniaxially oriented polyvinyl alcohol film is used as a polarizer. A protection film such as triacetyl cellulose film or the like, and a coating layer formed of an acrylic resin, or a phase difference film such as norbornene or polycarbonate is formed on one or both sides of the polarizer.

The absorption-type polarization plate transmits only light in a direction of a transmission axis of the polarization plate and absorbs the other components of light. Thus, in principle, light usage efficiency thereof (light transmittance) does not exceed 50%. Moreover, considering that reflectivity of an inner surface of the absorption-type polarization plate is 4%, the light usage efficiency of the absorption-type polarization plate is 46% at the greatest. Thus, to achieve low power consumption by liquid crystal displays, an efficient use of the backlight and an improvement in luminance are desirable.

As one of the methods for solving the above-described problem, a reflective polarization plate that uses optical reflection and interference is known. The reflective polarization plate reflects a desired polarization component light and transmits polarization of the opposite property to the desired polarization component light.

An axis of the reflective polarization plate is adjusted such that only polarization in a transmission axis direction is transmitted so that the light transmitted through the reflective polarization plate remains the same as linear polarization, and at the same time, the absorbed polarization is reflected for reuse in the absorption-type polarization plate. Thus, light usage efficiency of light emitted from the backlight may be improved.

An example of the reflective polarization plate is a dual brightness enhancement film (DBEF) including refractive index isotropic layers and refractive index anisotropic layers that are alternately stacked. However, a DBEF requires polymer films of several hundreds of stacked layers in total in order to provide polarization over a visible region. Thus, precise control is needed and this increases manufacturing costs.

To improve light usage efficiency and polarization separation power more cost-effectively, a technique of using a polarization sensitive scattering element (PSSE) is being researched. For example, Prior Art 1 (Japanese Patent Publication No. Hei 11-502036) discloses a method in which a polarization component in a direction perpendicular to a transmission axis is scattered to the backside by using a PSSE, and a polarization state of a corresponding backside scattering component is converted by using a ing s of stacked lay

In addition, Prior Art 2 (Japanese Patent Publication No. 2009-047802) discloses a reflective polarization plate in which a birefringent body formed of fibers having birefringence is used as a PSSE. In the reflective polarization plate, a layer in which a refractive index in a cross-sectional direction of the birefringent body (ordinary ray refractive index) corresponds to a refractive index of a supporting medium (polarization layer A) and a layer (polarization layer B) in which a refractive index in a length direction of the birefringent body (ordinary ray refractive index) corresponds to a refractive index of a supporting medium are alternately stacked such that arrangement directions of the birefringent bodies cross each other. Accordingly, polarization separation with respect to light that is obliquely incident or diffused light is improved.

In addition, Prior Art 3 (Japanese Patent Publication No. 2006-517720) discloses a method of improving polarization separation efficiency by scattering only one component of polarization and emitting the same to the outside by integrating an isotropic resin layer, in which birefringence fibers are buried as a PSSE, into a light guide panel.

To reduce power consumption of the surface light source apparatuses, LEDs having a long life span and power consumption reduction effect are frequently used as a backlight.

SUMMARY

At least one example embodiment including light guide panels for improving polarization separation efficiency and preventing luminance spots even when a discontinuous light source is disposed on a cross-section of the light guide panels is provided.

At least one example embodiment including surface light source apparatuses including the light guide panels is provided.

At least one example embodiment including flat panel displays including the surface light source apparatuses as a light source apparatus is provided.

According to an example embodiment, a light guide panel includes: a light guide layer including a light incident surface; a polarization separation layer configured to select a desired polarization among light emitted from the light guide layer and to emit light having the polarization; and a light homogenization layer including a plurality of first fibers and a first supporting medium of the first fibers, the light homogenization layer configured to diffuse and scatter light incident on the light guide layer into the light guide layer.

The polarization separation layer may include: a plurality of second fibers having birefringence; and a second supporting medium that is isotropic and configured to support the second fibers.

A refractive index of the second supporting medium may correspond to at least one of two different refractive indices of the second fibers.

The plurality of first fibers have birefringence and the first supporting medium is isotropic and configured to support the first fibers.

A refractive index of the first supporting medium may be different from at least one of the two different refractive indices of the first fibers.

A surface roughness Rz of an outer circumferential surface of the second fibers may be from about 0.1 μm to about 10 μm.

The second fibers may have a polygonal cross-section in a radius direction.

One of the light guide layer, the polarization separation layer, and the light homogenization layer may be between the remaining two layers.

The light guide panel may further include: a phase difference plate configured to convert a polarization direction of light in the light guide layer; and a reflection plate on a surface except the light incident surface and a light emitting surface of the light guide layer, the reflection plate configured to reflect light emitted from the light guide layer back into the light guide layer.

The polarization separation layer and the light homogenization layer may be stacked on the light emitting surface of the light guide layer. The polarization separation layer and the light homogenization layer may be integrated into a single layer. In the single layer, the first fibers and the second fibers may alternate, and a third supporting medium may include the first and second supporting media that supports the first and second fibers.

The first fibers and the second fibers may be different materials.

The light guide layer may be a same material as at least one of the first and second supporting media.

A density of the second fibers may be higher away from the light incident surface.

A density of the first fibers may vary according to arrangement positions.

Some of the plurality of first and second fibers may include discontinuous portions.

Portions of the plurality of first and second fibers may be overlapped.

According to another example embodiment, a surface light source apparatus including: a light source unit including a plurality of light sources spaced apart from one another; and a light guide panel configured to emit light having a polarization component of light incident from the light source unit, wherein the light guide panel is one described above.

A density of the first fibers may be higher between the plurality of light sources.

The plurality of light sources may be on two opposite sides of the light guide panel.

According to another example embodiment, a flat panel display includes: a light source apparatus; and a liquid crystal panel configured to display an image by using light supplied from the light source apparatus, wherein the light source apparatus is the surface light source apparatus described above.

According to some example embodiments, light is scattered and diffused at various angles in an in-plane direction via a light homogenization layer in which first fibers extended vertically to an incident surface are arranged. Thus, even when a discontinuous light source is used, uniform luminance may be obtained.

By using a polarization separation layer in which second fibers extended parallel to an incident surface are arranged, only desired polarization components may be selectively emitted with a high polarization separation efficiency.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this specification, thicknesses of layers or regions illustrated in the drawings are exaggerated for clarity of description. In addition, measurement ratios in the drawings are exaggerated for convenience of description and may vary from actual ratios. In this regard, the example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

When a (e.g., layer, region, or plate) is referred to as being herein “on,” “connected to,” or “coupled to” another member, the member may be directly on, or connected or coupled to the another member or intervening member(s) between the member and the another member may be present.

A surface light source apparatus according to some example embodiments will be described.

FIG. 1is a perspective view of a surface light source apparatus1according to an example embodiment.

FIGS. 2A and 2Bare schematic views illustrating an example of a relationship between a fiber and a refractive index, andFIG. 3is a cross-sectional view illustrating a modified example of a cross-section of the fiber.

As illustrated inFIG. 1, the surface light source apparatus1is an edge light type surface light source apparatus. The surface light source apparatus1includes a light source unit10and a light guide panel20transmitting a desired polarization component among the light emitted from a plurality of light sources11of the light source unit10. In an example embodiment, light is emitted as surface emission from the surface light source apparatus1in an upward direction ofFIG. 1. Although not shown inFIG. 1, when the surface light source apparatus1is applied to a liquid crystal display, a liquid crystal unit may be arranged on a surface of the surface light source apparatus1from which light is emitted.

The light source unit10emits light to be supplied in the surface light source apparatus1and the light source unit10is on a side of the light guide panel20. The light source unit10includes a plurality of light sources11arranged at intervals. The intervals between the plurality of light sources10may be regular or irregular.

While the plurality of light sources11are arranged one-dimensionally inFIG. 1, they may also be arranged two-dimensionally. For example, the plurality of light sources11may be point light-emitting diodes (LEDs).

The light guide panel20may include a rectangular parallelepiped plate. The light guide panel20includes a light guide layer30, a polarization separation layer40stacked on the light guide layer30, a light homogenization layer50stacked on the light guide layer30, and a phase difference plate60and a reflection plate70on the light guide layer30. The polarization separation layer40and the light homogenization layer50face each other with the light guide layer30interposed therebetween. The light guide layer30allows light emitted from the light source11to be incident to an incident surface30a, which is a side surface thereof, and enter the light guide panel20. The entered light is propagated in the light guide layer30and only a desired polarization component is selectively emitted from the polarization separation layer40. The light guide layer30may be formed of a transparent material capable of transmitting incident light. The transparent material may be, for example, an optical isotropic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC). The polarization separation layer40is stacked on the light guide layer30. The polarization separation layer40derives desired polarization among the light in the light guide layer30from a light emitting surface30bof the light guide layer30, which is a principal surface of the light guide layer30on a side. The polarization separation layer40reflects polarization light that is perpendicular to this derived polarization. The polarization separation layer40may be on an outer surface of the light guide layer30but is not limited thereto.

The polarization separation layer40may include a first fiber41and a first supporting medium42that supports the first fiber41. For example, the first fiber41may extend parallel to the incident surface30aof the light guide layer30, or may extend in a direction which is inclined by about ±45° with respect to the direction parallel to the incident surface30a. The first fiber41may be provided in plural. That is, the polarization separation layer40may include a plurality of first fibers41. The light homogenization layer50is stacked on the light guide layer30. The light homogenization layer50homogenizes a light direction by diffusing light in the light guide layer30in an in-plane direction, for example, in a direction perpendicular to a light propagation direction. The light homogenization layer50includes a second fiber51and a second supporting medium52that supports the second fiber51. For example, the second fiber51may extend in a direction perpendicular to the incident surface30aof the light guide layer30, or may extend in a direction which is inclined by about ±45° with respect to the direction perpendicular to the incident surface30a.

The light homogenization layer50includes a plurality of second fibers51. The plurality of second fibers51are parallel to the incident surface30aof the light guide layer30. For example, the second fibers51are arranged in a direction perpendicular to the arrangement direction of the first fibers41of the polarization separation layer40. The first and second fibers41and51of the polarization separation layer40and the light homogenization layer50have birefringence. The first and second fibers41and51have an extraordinary ray refractive index ne and an ordinary ray refractive index no. The refractive index ne is greater than the refractive index no.

The relationship between refractive indices of the first and second fibers41and51will be described below with reference toFIGS. 2A and 2B.

As illustrated inFIGS. 2A and 2B, the first and second fibers41and51have the ordinary ray refractive index no in a cross-sectional direction that is smaller than the extraordinary ray refractive index ne in a length direction. The first and second fibers41and51may be formed of various materials having birefringence. For example, a polymer fiber that is prepared by extending a polymer may be used for a stable cross-section, excellent durability, and easy orientation characteristics.

Examples of the polymer fiber may include polyolefin fibers such as polyethylene (PE), polytetrafluoroethylene (PTFE), polypropylene (PP); polyvinyl fibers such as polyfluorinated vinylidene (PVdF), polyfluorinated vinyl (PVF), polyvinyl chloride (PVC), or polyvinyl alcohol; and acrylic fibers such as polyacrylonitrile (PAN).

The polymer fiber may be aliphatic polyamide fiber such as Nylon 6 (N6), Nylon 6,6 (N66), Nylon 4,6 (N46), or Nylon 6,10 (N610); aromatic polyamide fibers (aramid fiber) such as poly(m-phenyleneisophthalamide) (PMPIA) or poly(p-phenylene terephthalamide) (PMPTA); or polyester fibers such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or poly-),caprolactone.

The polymer fiber may be animal fibers such as silk, wool, or cobweb, or cellulose vegetable fiber such as cupra, rayon fibers, etc. The types of the first fiber41and the second fiber51may be selected to satisfy the relationship between refractive indices that will be described below, or the same or different types may be used. Various types of fibers may be used in the polarization separation layer40or the light homogenization layer50.

The first and second fibers41and51may be formed of a polymer fiber. This polymer has a great refractive index difference An between an extraordinary ray refractive index ne and an ordinary ray refractive index no. The larger the refractive index difference Δn is, the more improved polarization separation efficiency of the polarization separation layer40or light diffusion efficiency of the light homogenization layer50may be. The difference An in the refractive indices may be 0.03 or greater, and for example, 0.05 or greater or 0.1 or greater.

The extraordinary ray refractive index ne and the ordinary ray refractive index no of the polymer fiber may be controlled by adjusting a tensioning speed of a polymer, or a tensioning rate thereof, a material of the polymer, a thickness (diameter) or density of a fiber.

Table 1 below shows an extraordinary ray refractive index ne and an ordinary ray refractive index no of representative draft polymer fibers. The refractive indices of Table 1 are calculated by dipping a fiber in liquids of various refractive indices, adjusting a liquid that is invisible as fiber lines are assimilated with the liquid by using a polarization microscope, and measuring the refractive index of the adjusted liquid using Atagosa Digital Abbe Refraction System DRA1 (wavelength: 589 nm). The refractive index of the adjusted liquid may be measured with respect to each of transmission axes of polarization to measure no and ne.

Thicknesses of the first and second fibers41and51may vary. The thicknesses of the first and second fibers41and51may be controlled according to a size of a display to which they are applied. The thicknesses of the first and second fibers41and51may be controlled to have desired refractive indices. For example, the thicknesses of the first and second fibers41and51may be from about 1 μm to about 200 μm.

The intervals between the first and second fibers41and51may vary. The intervals between the first and second fibers41and51may be selected according to a size of a display and to be smaller than a pixel pitch of a liquid crystal display to which the first and second fibers41and51are applied. The intervals between the first and second fibers41and51may be regular or irregular. The first and second fibers41and51may have a single-layer structure or a multi-layer structure.

The first fibers41may be arranged with uniform or non-uniform density. For example, the first fibers41may be arranged with a density that increases away from the light sources11. For example, a density of the first fibers41in the polarization separation layer40may increase continuously or stepwise away from the light sources11. A light amount is reduced away from the light sources11. Accordingly, in an area with a small light amount and away from the light sources11, the first fibers41may be densely arranged. In an area with a large light amount near the light sources11, the first fibers41may be coarsely arranged. Accordingly, a uniform light may be emitted over the entire image plane (light-emitting surface) of the light guide panel20.

Lengths of the first and second fibers41and51may be determined according to a size of the polarization separation layer40or a size of the light homogenization layer50in which the first and second fibers41and51are arranged. The lengths of the first and second fibers41and51are not limited to being continuous in a longitudinal direction of the polarization separation layer40or the light homogenization layer50. For example, some portions of the first and second fibers41and51may be removed and discontinuous portions may be present. Some of the first and second fibers41and51may be overlapped. The first and second fibers41and51may have a circular cross-section as illustrated inFIG. 1but are not limited thereto, and may have a different cross-section. For example, as illustrated inFIG. 3, the first and second fibers41and51may have a regular or irregular polygonal cross-section such as a triangular, rectangular, or hexagonal cross-section, or a cross-section formed by combining a curved line and a straight line. “Polygonal cross-section” includes not only figures respective sides of which formed by straight lines, but also figures respective sides of which are formed by curved lines. For example, polygonal cross-sections of the first and second fibers41and51may have some curved lines on each side or on each vertex, and these cross-sections are also included in the above-described “polygonal cross-section.”

As will be described below, in the polarization separation layer40, only a desired polarization component of light is selectively scattered by the first fibers41, and emitted from the light emitting surface30b. The light is likely to scatter in a light guide direction, and thus, the amount of scattered light in a direction perpendicular to a light proceeding direction is reduced.

When a surface light source apparatus including a light guide panel according to an example embodiment is used as a backlight of a liquid crystal display, and if the first fibers41have a polygonal cross-section, various scattering angles are formed, and thus scattering of light may increase in a direction perpendicular to the light guide direction. As a result, light with a more uniform angle distribution may be obtained.

Forms of external circumferential surfaces of the first and second fibers41and51may vary. Surface roughness Rz of an outer circumferential surface of the first fibers41may be from about 0.1 μm to about 10 μm. Various light scattering angles are formed by the first fibers41, and thus, light with a more uniform angle distribution may be obtained. The e, tlight scattering angles are formed by the first fibers41, and thus, lined based on JIS B 0601-2001.

The first and second supporting media42and52support the first and second fibers41and51, respectively, and may be formed of an optically isotropic material. Accordingly, the first and second supporting media42and52may be formed of any material that has excellent adhesiveness with respect to the first and second fibers41and51and optical transparency. For example, the first and second supporting media42and52may be formed of a curable resin that is polymerable/linkable by heat or radiation.

The curable resin may be, for example, a UV-curing resin formed of a compound including, for example, an acryloyl group, a methacryloyl group, a vinyl group, an aryl group, a styryl group, a thiol group, an epoxy group, a vinyl ether group, or an oxetanyl group.

The curable resin may be a thermosetting resin formed of silicon resin, aryl ester, acrylic resin, epoxy resin, polyimide, or urethane resin.

The curable resin may be a compound of the UV-curing resin and the thermosetting resin.

The first and second supporting media42and52may be formed of an acrylic resin such as PMMA; a polyolefin resin such as PE, PP, or cycloolefin polymer (COP); a polyester resin such as PET; a polyether such as polyphenylene oxide (PPO); a vinyl resin such as polyvinyl alcohol; polystyrene, PC, polyurethane, polyamide, polyimide, or epoxy resin; a copolymer including at least two types of monomers forming these materials; or a blend of these polymers.

By mixing a plurality of resins, refractive indices (nm) of the first and second supporting media42and52may be controlled as desired.

The polarization separation layer40may be formed such that a refractive index nm1of the first supporting medium42matches an ordinary ray refractive index no1or an extraordinary ray refractive index ne1of the first fiber41.

An example embodiment in which the refractive index nm1of the first supporting medium42and the ordinary ray refractive index no1of the first fiber41match each other will be described.

In this specification, “the refractive indexes nA and nB match each other” means that the refractive indexes nA and nB match each other with a precision to the second decimal point or greater, and this may also indicate that the refractive indexes nA and nB match each other with a precision to the third decimal point or greater.

The light homogenization layer50may be formed such that a refractive index nm2of the second supporting medium52is different from at least one of an ordinary ray refractive index no2and an extraordinary ray refractive index ne2of the second fiber51.

An example embodiment in which the refractive index nm2of the second supporting medium52is different from both the ordinary ray refractive index no2and the extraordinary ray refractive index ne2of the second fiber51will be described.

A phase difference plate60is opposite to the incident surface30aof the light guide layer30, and converts a polarization direction of light propagating in the light guide layer30. The phase difference plate60may be, for example, a λ/4 plate that shifts a phase by λ/4. The phase difference plate60may be included selectively. Thus, the phase difference plate60may also be omitted.

The reflection plate70prevents light in the light guide layer30from leaking to other portions except through the light emitting surface30b. To this end, the reflection plate70is stacked on a side except the incident surface30aof the light guide layer30or on a principal surface of the light guide layer30that is opposite to the light emitting surface30b. The reflection plate70is stacked on the phase difference plate60or the light homogenization layer50. Although not shown in the drawings, the reflection plate70may also be formed on two surfaces besides the incident surface30aof the light guide layer30and the opposite surface to the incident surface30a. Also, although not shown in the drawings, the reflection plate70may be disposed between the plurality of light sources11or on or under the light sources11.

The principle of surface emission of light from a light source in the surface light source apparatus1will be described.

FIG. 4Ais a right-side cross-sectional view illustrating the surface light source apparatus1ofFIG. 1.FIG. 4Bis an expanded view ofFIG. 4Aillustrating an example of propagation of an S-polarization component incident to the polarization separation layer40.FIG. 4Cis an expanded view ofFIG. 4Aillustrating an example of propagation of a P-polarization component incident to the polarization separation layer40.

As illustrated inFIG. 4A, light is incident from the light source11on the incident surface30aof the light guide layer30. The incident light propagates through the light guide layer30by repetitive internal reflection on interfaces between the polarization separation layer40, the light homogenization layer50, and the phase difference plate60as denoted by a chain line or a long-and-short broken line. Light is reflected by the reflection plate70that is attached outside the phase difference plate60, below the light homogenization layer50, and on a side of the light guide layer30, and thus, is not leaked except through the light emitting surface30bbut is propagated further in the light guide layer30.

Light emitted from the light source11is natural light, and various polarization components are mixed in the light. Hereinafter, the chain line with black circles inFIGS. 4A through 4Cdenotes a P-polarization component that vibrates on a plane such as a ground surface. The long-and-short broken line with arrows denotes an S-polarization component that vibrates on the plane perpendicular to the ground surface. The S-polarization component is selectively emitted from the light emitting surface30bby the polarization separation layer40.

As described above, the polarization separation layer40includes the first fibers41. As illustrated inFIG. 2A, the first fibers41have an extraordinary ray refractive index ne1in a length direction and an ordinary ray refractive index no1in a cross-sectional direction. The S-polarization component vibrates on a plane that is parallel to a cross-section of the first fibers41along the length direction. Accordingly, the S-polarization component may be affected by the extraordinary ray refractive index ne1in the length direction of the first fibers41, but not by the ordinary ray refractive index no1in the cross-sectional direction.

On the other hand, as the P-polarization component vibrates on a plane parallel to the cross-section of the first fibers41, it may be affected by the ordinary ray refractive index no1of the first fibers41in the cross-sectional direction. However, the P-polarization component is not affected by the extraordinary ray refractive index ne1of the first fibers41in the length direction.

The first supporting medium42that supports the first fibers41is formed to correspond to the refractive index of the first fibers41. Accordingly, when light is incident from the first supporting medium42to the first fibers41or from the first fibers41to the first supporting medium42, a P-polarization component propagates in a material of the same refractive index. Accordingly, the P-polarization component of light proceeds straight without being affected by the refractive index. In other words, the P-polarization component of light may propagate inside the first supporting medium,42in the same manner as when the first fibers41are not included. Accordingly, the P-polarization component denoted by the chain line ofFIG. 4is not refracted by the first fibers41, and thus, is reflected under an internal total reflection condition of the first supporting medium42.

On the other hand, the first supporting medium42has a refractive index that is different from the refractive index of the first fibers41. Accordingly, when light is incident from the first supporting medium42to the first fibers41or from the first fibers41to the first supporting medium42, the S-polarization component propagates in a material of a different refractive index. Accordingly, the S-polarization component is affected by the refractive index and is refracted or reflected. The S-polarization component denoted by the long-and-short broken line ofFIG. 4is refracted or reflected by the first fibers41and a portion thereof deviates from an internal total reflection condition of the first supporting medium42and is incident on an interface at an acute angle and is emitted from the first supporting medium42.

By stacking the polarization separation layer40on the light guide layer30, only an S-polarization component may be selectively scattered and be emitted from the light emitting surface30b. As a result, a polarization component that is necessary for a liquid crystal unit may be selectively emitted.

Above is described the first supporting medium42having a refractive index nm1that corresponds to the ordinary ray refractive index no1of the first fibers41and that is different from the extraordinary ray refractive index ne1of the first fibers41.

However, the refractive index nm1of the first supporting medium42may be formed to correspond to the extraordinary ray refractive index ne1and to the ordinary ray refractive index no1of the first fibers41. In this case, only a P-polarization component may be selectively scattered to be emitted from the light emitting surface30b. However, scattering efficiency may be improved when using an S-polarization component that does not vibrate within the same plane as the light guide direction of light instead of using a P-polarization component that vibrates in the same plane of the light guide direction of light. Accordingly, the refractive index nm1of the first supporting medium42may be set to correspond to the ordinary ray refractive index no1of the first fibers41.

The principle of diffusing light in the light guide layer30in an in-plane direction by using the light homogenization layer50will be described below.FIG. 5is a bottom view of the surface light source apparatus1ofFIG. 1.

As illustrated inFIG. 5, the light sources11formed of LEDs emit light as a point light source. Thus, a light amount between adjacent light sources11may be reduced and dark portions may be generated in an area12near the light sources11. As light propagating in the light guide layer30is scattered in the in-plane direction, light direction distribution in the light guide layer30may be homogenized. Accordingly, some of the dark portions may disappear.

The light homogenization layer50includes the second fibers51as described above. The second fibers51include an extraordinary ray refractive index ne2in a length direction and an ordinary ray refractive index no2in a cross-sectional direction. The second fibers51are arranged such that a length direction thereof corresponds to a light guide direction of light. Accordingly, light incident on the second fibers51is influenced by the ordinary ray refractive index no1and the effective extraordinary ray refractive index ne2_eff.

As illustrated inFIG. 2B, when light that is guided in the length direction of the second fibers51in the light homogenization layer50is incident to the second fibers51at an incident angle θ, the effective extraordinary ray refractive index ne2—effmay be expressed as Equation (A):

In Equation (A), no2denotes the ordinary ray refractive index of the second fibers51, and ne2denotes the extraordinary ray refractive index of the second fibers51, and θ denotes an incident angle of light with respect to the second fibers51(length direction).

The P-polarization component vibrates along a plane parallel to a cross-section of the second fibers51in the length direction. Accordingly, the P-polarization component may be influenced by the effective extraordinary ray refractive index ne2_eff of the second fibers51in the length direction, but is not influenced by the ordinary ray refractive index no2along the cross-sectional direction.

On the other hand, the S-polarization component vibrates along the plane parallel to the cross-section of the second fibers51. Accordingly, the S-polarization component may be influenced by the ordinary ray refractive index no2of the second fibers51in the cross-sectional direction but is not influenced by the effective extraordinary ray refractive index ne2_eff of the second fibers51in the length direction.

When light is incident from the second supporting medium52to the second fibers51or from the second fibers51to the second supporting medium52, the P-polarization component is influenced by the effective extraordinary ray refractive index ne2_eff and is refracted or reflected, and the S-polarization component is influenced by the ordinary ray refractive index no2and is refracted or reflected. The second fibers51are arranged in the light homogenization layer50such that the length direction thereof is parallel to the light guide direction. Accordingly, an interface between the second fibers51and the second supporting medium52does not lie at a right angle to the light guide direction, and when the P-polarization component or the S-polarization component is refracted or reflected in the corresponding interface, angle distribution in the in-plane direction of light varies. In other words, light may be inclined on the right and left sides of the light guide direction. Accordingly, light propagating in the light guide layer30is scattered and diffused at various angles, thereby homogenizing the light direction distribution.

Light is refracted and extended only in a horizontal, left and right direction in the light homogenization layer50, but the angle in a vertical direction does not vary. Accordingly, both of the P- and S-polarization components do not satisfy the total internal reflection condition due to the light homogenization layer50. For example, light extends in the horizontal, left and right direction in the light homogenization layer50so as to remove only spots of an LED, and a refraction angle in the vertical direction in the polarization separation layer40varies such that only the S-polarization component may be emitted from the polarization separation layer40. Accordingly, a desired polarization component may be emitted from the light guide panel, and also light spots of the LED may be removed.

To perform the light homogenizing function, the refractive index nm2of the second supporting medium52may be different from the ordinary ray refractive index no2and the extraordinary ray refractive index net of the second fibers51.

However, the light homogenization layer50may be act more intensely as a homogenization layer of S-polarization.

The ordinary ray refractive index no2and the refractive index nm2of the second supporting medium52may have a difference of 0.03 or greater, and for example, 0.05 or greater or 0.1 or greater.

To scatter and diffuse both the S- and P-polarization components with a proper balance, the ordinary ray refractive index no2and the extraordinary ray refractive index ne2of the second supporting medium52and the refractive index nm2of the second supporting medium52may satisfy Equation (1) below:
no2<nm2<ne2(1)

In particular, the refractive index nm2of the second supporting medium52and the effective extraordinary ray refractive index ne2_eff of the second fibers51may satisfy Equation (2) below:
no2<nm2<ne2—eff(2)

The refractive index nm2of the second supporting medium52may satisfy Equation (3) below. The refractive index nm2of the second supporting medium52is smaller than the effective extraordinary ray refractive index ne2_eff of the second fibers51, and thus the P-polarization component may be scattered and diffused. Accordingly, the second supporting medium52may function as a light homogenization layer that effectively scatters and diffuses both the P- and S-polarization.

In Equation (3), no2denotes the ordinary ray refractive index of the second fibers51, and ne2denotes the extraordinary ray refractive index of the second fibers51, and nl denotes the refractive index of the light guide layer30.

Equation (3) is derived from Equation (2) and Equation (A) and Equations (B) through (F).

In Equations (B) through (F) above, no2denotes the ordinary ray refractive index of the second fibers51, ne2denotes the extraordinary ray refractive index of the second fibers51, ni denotes a refractive index of an external medium of the light guide panel20, nl denotes a refractive index of the light guide layer30, θi denotes an incent angle of light incident on the light guide layer30, θl denotes a refraction angle of light incident on the light guide layer30, θin denotes an incident angle of light incident on the light homogenization layer50, and θout denotes a refraction angle of light incident on the light homogenization layer50. The light guide panel20is usually disposed in air, and a refraction index ni of an external medium of the light guide panel20is the same as the refractive index of air(=1) and is expressed by Equation (B).

Equation (F) is derived in Equation (A) by substituting nm2as nm2=ne2_eff and modifying Equation (A) using Equations (B) through (E). Equation (3) is derived from Equation (2) and Equation (F).

If nm2=ne2_eff, an incident light component (θ≈π/2) having a maximum angle among P-polarization does not proceed linearly without being refracted or reflected by the second fibers51of the light homogenization layer50. Accordingly, the light homogenization layer50may not perform the function of light homogenization with respect to the same light component. An effective refractive index of light of the incident light component, which has an angle smaller than the maximum angle, is close to the ordinary ray refractive index no2.

When Equations (B) through (F) are all satisfied, light homogenization with respect to an incident light component incident to the second fibers51at all angles θ may be performed.

When nm2and the refractive index ne2_eff denoted by Equation (F) have a difference in refraction of 0.03 or greater, the effect of the light homogenization layer of the P-polarization component may be further improved.

As illustrated inFIG. 5, a density of the second fibers51disposed on a central line between adjacent light sources11may be greater than a density of the second fibers51disposed on an axis in a light emitting direction of the light source11in the light homogenization layer50. A light amount between adjacent light sources11may be reduced and dark portions may be likely to be generated in the area12near the light sources11. Accordingly, by densely arranging the second fibers51between the light sources11, a light homogenization effect may be further improved.

The first fibers41are arranged in the polarization separation layer40such that the length direction of the first fibers41lies at a right angle to a light guide direction. Accordingly, a cross-section of the first fibers41in a diameter direction may be substantially uniform in any position. As the first fibers41hardly vary in form in the length direction, when the P- or S-polarization component is refracted or reflected by the first fibers41, light is substantially not scattered on both sides of the light guide direction even when seen from the plane. Light is scattered in the plane according to the light guide direction. Angle distribution in the in-plane direction does not vary substantially.

Light may be scattered in the in-plane direction by the second fibers51that extend in a direction perpendicular to the incident surface30ain the light homogenization layer50. Accordingly, light may be scattered in the in-plane direction, which may not be performed by using just a PSSE of the first fibers41that extend in parallel to the incident surface30a.

If the S-polarization component is emitted only, light at a phase near to the P-polarization component remains in the light guide layer30. To also use the remaining light effectively, the phase difference plate60is disposed.

InFIG. 1, the phase difference plate60is a λ/4 plate and has a thickness changing phases of light that is incident to the phase difference plate60at right angles by 90 degrees. Light that is totally reflected internally in the light guide layer30is not incident to the phase difference plate40at a right angle, as shown inFIG. 4.

Conversely, although the S-polarization component is sometimes converted into the P-polarization component, since the S-polarization component is selectively emitted to the outside, a ratio of conversion from the P-polarization component to the S-polarization component is high. As such, the remaining light in the light guide layer30is also converted to the S-polarization component, and thus, emission efficiency of the S-polarization component may be increased and light usage efficiency may be improved as a result.

The phase difference plate40may be used according to a wavelength band. For example, a birefringence sheet formed by drawing a film formed of, for example, PC, polysulfide (PS), PMMA, polyvinyl alcohol, polyamide, polyester, etc. or a support sheet of a liquid crystal polymer orientation layer, or a multi-layer stack structure may be used as the phase difference plate40. A sheet formed by arranging the first or second fibers41or51used in the polarization separation layer40or the light homogenization layer50in a supporting medium may be used as the phase difference plate40.

FIG. 6is a side view of a surface light source apparatus1according to another example embodiment.

InFIG. 4, the light homogenization layer50is below the light guide layer30. However, the position of the light homogenization layer50may vary. The light homogenization layer50may be stacked on the light guide layer30. Thus, as in the surface light source apparatus1illustrated inFIG. 6, the light homogenization layer50may also be between the light guide layer30and the polarization separation layer40.

FIG. 7is a side view of a surface light source apparatus1according to another example embodiment.

In the surface light source apparatus1illustrated inFIG. 7, the light homogenization layer50may be on the polarization separation layer40.

FIG. 8is a side view of a surface light source apparatus1according to another example embodiment.

Referring toFIG. 4, the phase difference plate60is mounted on a side opposite to the incident surface30aof the light guide layer30. However, the phase difference plate60may be mounted on a principal surface of the light guide layer30opposite to a surface on which the polarization separation layer40is stacked. Also, the phase difference plate60may be mounted on at least one side besides the incident surface30aof the light guide layer30.

For example, like the surface light source apparatus1illustrated inFIG. 8, the phase difference plate60may be disposed on the principal surface of the light guide layer30opposite to the surface on which the polarization separation layer40is formed, for example, on a lower surface of the light guide layer30. However, when the phase difference plate60is on the principal surface or the side of the light guide layer30that is perpendicular to the light guide direction of light as illustrated inFIG. 8, the phase difference plate60is a λin plate, and may have a thickness changing a phase of light incident to the phase difference plate60by 180 degrees.

Accordingly, when light is refracted or reflected by the polarization separation layer40toward the light guide layer30, or is incident to the phase difference plate60at an acute angle, a phase of light varies by about 180 degrees, and thus the S-polarized light is maintained. Thus, the S-polarized light is reflected by the reflection plate70, returns to the light guide layer30, and is emitted from the polarization separation layer40. Thus, the S-polarized light is emitted, and light of the P-polarized light is prevented from being emitted.

As described above, light that propagates in the light guide layer30is usually not incident on the phase difference plate60at a right angle, and thus is converted from the P-polarization component to the S-polarization component by the λon phase difference plate60.

FIG. 9is a side view of a surface light source apparatus according to another example embodiment.

The surface light source apparatus illustrated inFIG. 9includes a polarization separation light homogenization layer80.

In the first through fourth example embodiments described above, the polarization separation layer40and the light homogenization layer50are separately included.

However, as illustrated inFIG. 9, the surface light source apparatus may include the polarization separation light homogenization layer80that is formed by integrating the polarization separation layer40and the light homogenization layer50.

Referring toFIG. 9, the polarization separation light homogenization layer80includes first fibers81and second fibers82, and a third supporting medium83that supports the first and second fibers81and82. The first fibers81extend parallel to the incident surface30aof the light guide layer30, and the plurality of first fibers81are arranged in a direction perpendicular to the incident surface30a. The second fibers82extend in a direction perpendicular to the incident surface30a, and the plurality of second fibers82are arranged in a direction parallel to the incident surface30a. For example, the first fibers81and the second fibers82extend and are arranged in directions at right angles to each other, and while the first and second fibers81and82are woven with each other, they are supported by the third supporting medium83.

In the polarization separation light homogenization layer80, an ordinary ray refractive index no1and an extraordinary ray refractive index ne1of the first fibers81, an ordinary ray refractive index no2and an extraordinary ray refractive index neo2of the second fibers82, and a refractive index nmatrix3of the third supporting medium83satisfy Equations (4) and (5) below:
no1=nmatrix3<nel(4)
no2<nmatrix3=ne2(5)

Accordingly, the first fibers81(warp threads) selectively scatter only an S-polarization component and emit the same through a light emitting surface that is an upper surface of the polarization separation light homogenization layer80. The second fibers82(woof) diffuse light propagating in the light guide layer30in an in-plane direction to homogenize a light direction distribution. A refractive index nmatrix3of the third supporting medium83may correspond to the ordinary ray refractive index no1of the first fibers81and may be different from the extraordinary ray refractive index ne1of the first fibers81. Thus, the P-polarization component may not be refracted by the first fibers81but proceed straight, and only the S-polarization component may be influenced by the extraordinary ray refractive index ne1of the first fibers81and a portion thereof may be emitted through the light emitting surface.

On the other hand, the refractive index nmatrix3of the third supporting medium83may be different from the ordinary ray refractive index not and the extraordinary ray refractive index ne2of the second fibers82. Accordingly, the S-polarization component may not be refracted by the second fibers82but proceed straight, and only the P-polarization component may be influenced by the extraordinary ray refractive index ne1of the second fibers82and be refracted and reflected to be diffused in the in-plane direction.

As the first and second fibers81and82, the first and second fibers41and51described above may be used, and the first supporting medium42or the second supporting medium52may be used as the third supporting medium83. However, in an example embodiment, in order to satisfy Equations (4) and (5), the first fibers81and the second fibers82may be formed of different materials.

FIG. 10is a side view of a surface light source apparatus1according to another example embodiment.

In the first through fifth embodiments (FIGS. 1 through 9), the light guide layer30is formed of a material different from the first supporting medium42and the second supporting medium52.

However, the light guide layer30may be formed of the same material as a material of at least one of the first supporting medium42and the second supporting medium52.

A light guide layer34in the surface light source apparatus1illustrated inFIG. 10corresponds to the light guide layer30of the surface light source apparatus1ofFIG. 1and is formed of the same material as the first supporting medium42. For example, the light guide layer34may be regarded as the light guide layer30and the polarization separation layer40according to the example embodiment ofFIG. 1integrated into a single layer.

Although not shown in the drawings, the light guide layer30of the surface light source apparatus1may be formed of the same material as the second supporting medium52so that the light guide layer30and the light homogenization layer50are integrated into a single layer. Although not shown in the drawings, in the surface light source apparatus1ofFIG. 1, the light guide layer30, the first supporting medium42, and the second supporting medium52may all be formed of the same material so that the light guide layer30, the polarization separation layer40, and the light homogenization layer50are integrated into a single layer.

In the surface light source apparatus ofFIG. 9, in which the polarization separation light homogenization layer80is formed by integrating the polarization separation layer40and the light homogenization layer50, the light guide layer30may be formed of the same material as the third supporting medium83to integrate the polarization separation light homogenization layer80and the light guide layer30into a single layer.

By integrating the light guide layer30with the polarization separation layer40and/or the light homogenization layer50, manufacturing may be simplified and manufacturing costs may be reduced, and both a light guide panel and a surface light source apparatus having a thin thickness may be manufactured.

The first fibers41are arranged in an upper portion of the light guide layer34ofFIG. 10. Alternatively, the first fibers41may be arranged throughout light guide layer34, or in an area different from the upper portion of the light guide layer34.

FIG. 11is a side view of a surface light source apparatus1according to another example embodiment.

In the surface light source apparatus1according to the first through sixth example embodiments, the light source unit10is on a side along a short-axis of the light guide layer30constituting the light guide panel20.

However, the surface light source apparatus1may include a plurality of light source units10. For example, as illustrated inFIG. 11, the light source units10may be disposed on both sides along the short-axis of the light guide layer30.

The surface light source apparatus1illustrated inFIG. 11corresponds to the surface light source apparatus1ofFIG. 8, except that the light source units10are on a side of the surface light source apparatus1illustrated inFIG. 11instead of the reflection plate70.

Although not shown in the drawings, in some of the above-described example embodiments t, for example, in the surface light source apparatuses1of the first, second, and fourth embodiments, the light source units10may be disposed on both sides along the short-axis of the light guide layer30. For example, the light source units10may face each other with respect to the light guide layer30.

The light source units10may be further disposed on a side besides a light-emitting surface of a long-axis of the light guide layer30.

EXPERIMENTAL EXAMPLES

Experimental examples conducted to verify the effects of the surface light source apparatuses according to some example embodiments and a comparative example are described. The technical scope is not limited to the experimental examples.

Experimental Example 1

Preparation of Light Guide Layer

(2) Formation of Polarization Separation Layer

As a first fiber, PET fibers (material: PET, no=1.5449, ne=1.7200, a surface roughness of external circumferential surface (Rz)=2 μm, cross-section: circular (diameter: 20 μm)) were arranged to a thickness of fifteen layers in one direction on an upper surface of the prepared light guide layer. As a first supporting medium designed to have a refractive index of 1.545 after curing, a UV curable resin was penetrated between the PET fibers. A mixture of 40 parts by weight of EA-F5503 available by Osaka Gas Chemicals Co., Ltd.; 58 parts by weight of MK esterA-400 available by Shin Nakamura Chemical Co., Ltd.; and 2 parts by weight of Photopolymer Initiator Irgacure available by Shiba Specialty Chemicals was used as the UV curable resin. The air between the PET fiber and the UV curable resin was removed by vacuum degassing, and then the UV curable resin was covered with a released glass plate, and a UV lamp was used to cure the UV curable resin. The glass plate was exfoliated to form a polarization separation layer on the light guide layer.

When observing a cross-section of the polarization separation layer using a laser microscope (available by Keyence Corporation VK-9600), as illustrated inFIG. 11, the polarization separation layer has a structure in which the first fibers arranged in one direction are supported by the UV curable resin.

(3) Formation of Light Homogenization Layer

As a second fiber, N610 fibers (material: Nylon 6,10, no=1.5217, ne=1.5711, cross-section: circular (diameter: 50 μm)) were arranged on a lower surface of the prepared light guide layer in three layers in a direction perpendicular to the arrangement direction of the first fibers of the polarization separation layer. As a second supporting medium designed to have a refractive index of 1.571, a UV curable resin was penetrated between the N610 fibers. A mixture of 40 parts by weight of EA-F5503 available by Osaka Gas Chemicals Co., Ltd.; 58 parts by weight of MK esterA-400 available by Shin Nakamura Chemical Co., Ltd., and 2 parts by weight of Photopolymer initiator Irgacure available by Shiba Specialty Chemicals may be used as the UV curable resin. By curing the UV curable resin in the same manner as when forming the polarization separation layer, a light homogenization layer was formed on the light guide layer.

(4) Arrangement of Light Source Unit, Phase Difference Plate, and Reflection Plate

A light source unit including nine LEDs as light sources arranged in one dimension (serial arrangement) is installed along a short-axis of the light guide layer. The side at which the light source unit is installed is set to be parallel to the length direction of the first fibers of the polarization separation layer, and perpendicularly to the length direction of the second fibers of the light homogenization layer, and the arrangement direction of the LEDs is set to be in a direction parallel to the length direction of the first fibers of the polarization separation layer. Then, a λse phase difference plate is arranged at a side of the light guide layer opposite to the side where the light source unit is installed. Also, a reflection plate is mounted on all surfaces except an upper surface of the polarization separation layer (light-emitting surface) and the side on which the light source unit is installed. Consequently, the surface light source apparatus was manufactured. The surface light source apparatus according to Experimental example 1 corresponds to the surface light source apparatus of the example embodiment illustrated inFIG. 1.

Experimental Example 2

A light homogenization layer was formed on the upper surface of the light guide layer. The surface light source apparatus was manufactured in the same manner as Experimental example1except that PET fibers (PET, no=1.5449, ne=1.7200, a surface roughness of external circumferential surface (Rz)=2 μm, cross-section: circular (diameter: 20 μm)) were used as the second fiber, and a UV curable resin designed to have a refractive index of 1.605 after curing was used as the second supporting medium. A mixture of 68 parts by weight of EA-F5503 available by Osaka Gas Chemicals Co., Ltd.; 30 parts by weight of benzylacrylate; and 2 parts by weight of Photopolymer Initiator Irgacure 184 available by Shiba Specialty Chemicals may be used as the UV curable resin.

The surface light source apparatus manufactured according to Experimental example 2 corresponds to the surface light source apparatus1illustrated inFIG. 6.

Experimental Example 3

A polarization separation layer was formed on the upper surface of a light guide layer. Except that a light homogenization layer was formed on the upper surface of the polarization separation layer, the surface light source apparatus was manufactured in the same manner as Experimental example 2.

The surface light source apparatus manufactured in Experimental example 3 corresponds to the surface light source apparatus1illustrated inFIG. 7.

Experimental Example 4

A surface light source apparatus was manufactured in the same manner as Experimental example 2 except that PET fibers (PET, no=1.5449, ne=1.7200, a surface roughness of external circumferential surface (Rz)=2 μm, cross-section: equilateral triangular (each side length: 10 um) were used as first fibers forming the polarization separation layer.

Comparative Example 1

A surface light source apparatus was manufactured in the same manner as Experimental example 1 except that a light homogenization layer was not formed.

In the surface light source apparatuses obtained in the experimental examples and Comparative example 1, a luminance of light emitted from the light emitting surface and luminance spots and a polarization of the light were measured. The luminance, the luminance spots, and the polarization were measured by using a two-dimensional colorimeter, Konica Minolta CA-2000 or Conoscope 80 available by AUTRONIC-MELCHERS GmbH in combination with a polarization plate to calculate a ratio of a desired polarization component. A luminance was measured by driving the serially-arranged nine LEDs with a constant current of 30 mA. As the luminance of emitted light, front luminance in the center of the light-emitting surface of the light guide panel was measured. Table 2 below shows the measurement result.

Referring toFIGS. 13 and 14, two-dimensional luminance distribution of light emitted from an upper surface of the light guide panel (light-emitting surface) of the surface light source apparatuses manufactured according to Experimental example 2 and Comparative example 1 measured by CA-2000 is shown. The same two-dimensional luminance distribution as that shown inFIG. 13may be obtained from the surface light source apparatuses manufactured according to Experimental examples 1, 3, and 4.

In the surface light source apparatuses of Experimental examples 1 through 4 in which the light homogenization layer is included, as illustrated inFIG. 13, stripe spots are not observed in light emitted from the upper surface of the stacked structure. Thus, as can be seen from this result, according to the surface light source apparatuses of some of the example embodiments, luminance spots are removed when an LED, which is a discontinuous light source, is used. According to the surface light source apparatuses manufactured according to the above experimental examples, high polarization separation performance may be obtained.

In the surface light source apparatus manufactured according to Comparative example 1, a ratio of polarization separation is similar to that of Experimental examples. However, as illustrated inFIG. 14, stripe spots are clearly observed in light emitted from the upper surface of the stacked structure.

In the surface light source apparatus of Experimental example 4 in which the first fibers of the polarization separation layer have an equilateral triangular cross-section, an intensity (luminance) of light emitted in a direction perpendicular to the light guide layer (light emitted from the upper surface of the stacked structure) is twice as large as that in the surface light source apparatus of Experimental example 2 in which the first fibers have a circular cross-section.

As described above, according to at least one of the example embodiments, the surface light source apparatuses have excellent polarization separation performance, and, even when a discontinuous light source such as an LED is used, stripe spots of light may be prevented.

Hereinafter, a flat panel display according to an example embodiment will be described.

The flat panel display includes a liquid crystal panel on which an image is formed and a light source apparatus that supplies light used in displaying the image to the liquid crystal panel. The light source apparatus may be a surface light source apparatus according to the example embodiments. The liquid crystal panel may be on a surface from which light of the surface light source apparatus is emitted. The liquid crystal panel may be a typical liquid crystal panel.