Light guide plate and backlight unit having the same

In accordance with one or more embodiments of the present disclosure, a light guide plate includes a first light incident surface receiving a first external light, a second light incident surface receiving a second external light and opposite to the first light incident surface, a light exit surface connecting the first and second light incident surfaces to output the first and second external lights, a reflective surface reflecting the first and second external lights in opposition to the light exit surface, and optical path changing portions each of which having a first inclined surface and a second inclined surface. The optical path changing portions are provided on the reflective surface with a predetermined interval and recessed toward the light exit surface to reflect the first and second external lights to the light exit surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 2008-57978, filed on Jun. 19, 2008, the contents of which are herein incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates generally to a light guide plate and a backlight unit having the same and more particularly, for example, to a light guide plate having improved optical characteristics and a backlight unit having the light guide plate.

2. Related Art

Generally, liquid crystal display (LCD) devices are utilized for convenience and efficient characteristics, such as slimness, light weight, and low power consumption. The LCD includes a LCD panel that displays an image, a backlight unit that supplies a light to the LCD panel, and a driving circuit that applies a driving signal to the LCD panel.

The backlight unit may be classified as a direct illumination type backlight unit or as an edge illumination type backlight unit according to a position of a light source for the backlight unit. In the direct illumination type backlight unit, a plurality of light sources are provided below the LCD panel to directly supply a light to the LCD panel. In the edge illumination type backlight unit, a light source is provided adjacent to a side surface of the LCD panel to supply a light to the LCD panel by using a light guide plate.

Moreover, in the edge illumination type backlight unit, the light sources may be provided at both sides of the light guide plate to supply more light to the LCD panel. In this instance, the light guide plate may have a structure capable of uniformly supplying the light over the entire surface of the LCD panel.

SUMMARY

An exemplary embodiment of the present disclosure provides a light guide plate including a protrusion having asymmetric inclined surfaces. Another exemplary embodiment of the present disclosure provides a backlight unit including a light guide plate.

In an exemplary embodiment of the present disclosure, a light guide plate includes a first light incident surface, a second light incident surface, a light exit surface, a reflective surface, and a plurality of optical path changing portions. Each of the optical path changing portions includes a first inclined surface and a second inclined surface. The first light incident surface receives a first external light. The second light incident surface receives a second external light. The second light incident surface is opposite to the first light incident surface. The light exit surface connects the first light incident surface to the second light incident surface to output the first and second external lights. The reflective surface reflects the first and second external lights in opposition to the light exit surface.

In various implementations, the optical path changing portions are provided on the reflective surface with a predetermined interval and recessed toward the light exit surface to reflect the first and second external lights to the light exit surface. A width of the first inclined surface is increased as a distance from the first light incident surface increases for corresponding ones of the first inclined surfaces. A width of the second inclined surface is increased as a distance from the second light incident surface increases for corresponding ones of the second inclined surfaces. The second inclined surface is connected to the first inclined surface. The optical path changing portions are provided symmetrically to each other about a first reference line extending from a center of the light exit surface perpendicularly to the light exit surface.

In an exemplary embodiment, a first distance between an end of the first inclined surface connected to the reflective surface and the light exit surface is increased in a direction opposite to the first light incident surface. A second distance between an end of the second inclined surface connected to the reflective surface and the light exit surface is increased in a direction opposite to the second light incident surface. In this case, the first inclined surface is inclined at a first angle with respect to the light exit surface, the second inclined surface is inclined at a second angle with respect to the light exit surface, and the first angle is different from the second angle.

In another exemplary embodiment, a first distance between an end of the first inclined surface connected to the reflective surface and the light exit surface is decreased in a direction of the first light incident surface and the second light incident surface on a basis of the first reference line, and a second distance between an end of the second inclined surface connected to the reflective surface and the light exit surface is decreased in a direction of the first light incident surface and the second light incident surface on a basis of the first reference line. The first inclined surface is inclined at a first angle with respect to the light exit surface, the second inclined surface is inclined at a second angle with respect to the light exit surface, and the first angle is equal to the second angle.

In still another exemplary embodiment, a first distance between an end of the first inclined surface connected to the reflective surface and the light exit surface is increased in a direction of the first reference line in a first region between the first light incident surface and the first reference line, the first distance is constant in a second region between the first reference line and the second light incident surface, a second distance between an end of the second inclined surface connected to the reflective surface and the light exit surface is increased in a direction of the first reference line in the second region, the second distance being constant in the first region. The first inclined surface is inclined at a first angle with respect to the light exit surface, the second inclined surface is inclined at a second angle with respect to the light exit surface, and the first angle is different from the second angle. The first inclined surface is curved. In this case, a tangential line making contact with the first inclined surface forms an angle of about 24 degrees to about 65 degrees with respect to a second reference line parallel to the light exit surface.

In still another exemplary embodiment of the present disclosure, a backlight unit includes a first light source, a second light source, and a light guide plate. The first light source generates a first light. The second light source generates a second light. The light guide plate guides and emits the first and second lights. The light guide plate includes a first light incident surface, a second light incident surface, a light exit surface, a reflective surface, and a plurality of optical path changing portions. The first light incident surface receives the first light. The second light incident surface receives the second light. The second light incident surface is opposite to the first light incident surface. The light exit surface connects the first light incident surface to the second light incident surface to output the first and second lights. The reflective surface reflects the first and second external lights towards the light exit surface. The optical path changing portions are provided on the reflective surface with a predetermined interval and recessed toward the light exit surface to reflect the first and second lights to the light exit surface. In this case, each of the optical path changing portions includes a first inclined surface and a second inclined surface. A width of the first inclined surface is increased as a distance from the first light incident surface increases for corresponding ones of the first inclined surfaces. A width of the second inclined surface is increased as a distance from the second light incident surface increases for corresponding ones of the second inclined surfaces. The second inclined surface is connected to the first inclined surface.

In still another exemplary embodiment of the present disclosure, a backlight unit includes a first light source, a second light source, and a light guide plate. The first light source generates a first light. The second light source generates a second light. The light guide plate guides and emits the first and second lights. The light guide plate includes a first light incident surface, a second light incident surface, a light exit surface, and a reflective surface. The first light incident surface receives the first light. The second light incident surface receives the second light. The second light incident surface is opposite to the first light incident surface. The light exit surface connects the first light incident surface with the second light incident surface. The light exit surface has a concave-convex shape extending between the first and second light incident surfaces. A width of the light exit surface increases as a distance from the first light incident surface increases for corresponding ones of the first inclined surfaces. The reflective surface connects the first light incident surface with the second light incident surface in opposition to the light exit surface. The reflective surface has a convex-concave shape extending between the first and second light incident surfaces. A width of the reflective surface increases as a distance from the second light incident surface increases for corresponding ones of the second inclined surfaces. A reflective sheet may be provided below the light guide plate to reflect at least one of the first and second lights emitted from the reflective surface.

According to the above, the light guide plate includes the optical path changing portions to uniformly output lights incident from two light sources. The backlight unit includes the light guide plate having the optical path changing portions to output the lights incident from the two light sources in different directions. Accordingly, the lights having the same brightness may be supplied to users positioned in different directions.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of a light guide plate and a backlight unit having the same will be described with reference to accompanying drawings. Objects to be solved by the invention, means to solve the objects, and effects thereof will be readily understood to those skilled in the art through embodiments described with reference to accompanying drawings. It is understood that the present invention should not be limited to the following exemplary embodiments but various changes and modifications may be made by one ordinary skilled in the art within the spirit and scope of the present invention. Meanwhile, elements shown in the drawings may be simplified or magnified for the purpose of clear explanation. In addition, the same reference numerals are used to designate the same elements throughout the drawings.

FIG. 1is a perspective view showing a backlight unit according to a first exemplary embodiment of the present disclosure. Referring toFIG. 1, a backlight unit5includes first light sources10, second light sources20, a light guide plate30, a reflective sheet55, a diffusion sheet60, and a prism sheet70.

The first light sources10are provided at one side of the light guide plate30. The first light sources10generate first lights15(refer toFIG. 2A) to supply the first lights15to the light guide plate30. In the present exemplary embodiment, each of the first light source10may include a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a light emitting diode (LED).

The second light sources20are provided at the other side of the light guide plate30while facing the first light sources10. The second light sources20generate second lights25(refer toFIG. 2B) to supply the second lights to the light guide plate30. In the present exemplary embodiment, the second light source20may include the CCFL, the EEFL, or the LED.

The light guide plate30is interposed between the first light sources10and the second light sources20. The light guide plate30may include at least one of acryl, poly methyl meta acrylate (PMMA), polycarbonate (PC), and polymethacrylstyrene (MS). The light guide plate30guides the first lights15and the second lights25to output the first lights15and the second lights25through an upper surface thereof. The light guide plate30includes a first light incident surface31, a second light incident surface33, a light exit surface35, and a reflective surface37.

The first light incident surface31is the side surface of the light guide plate30, to which faces the first light sources10. The first lights15emitted from the first light sources10are incident onto the first light incident surface31.

The second light incident surface33is the other surface of the light guide plate30which faces the second light sources20in opposition to the first light incident surface31. The second lights25emitted from the second light sources20are incident onto the second light incident surface33.

The light exit surface35connects an upper portion of the first light incident surface31to an upper portion of the second light incident surface33. The light exit surface35has substantially planar shape. The light exit surface35outputs the first and second lights15and25.

The reflective surface37is provided in opposition to the light exit surface35, and connects a lower portion of the first light incident surface31to a lower portion of the second light incident surface33. The reflective surface37reflects the first and second lights15and25. The reflective surface37includes plural optical path changing portions40reflecting the first and second lights15and25to the light exit surface35.

The optical path changing portions40are provided on the reflective surface37in parallel to the first light incident surface31and the second light incident surface33. The details of the optical path changing portions40will be given later with reference toFIGS. 2A to 4.

The reflective sheet55is provided below the light guide plate30, and includes a material having a higher reflective index. For example, the reflective sheet55may be formed by coating the material, such as aluminum (Al), or silver (Ag), having the higher reflective index on a base material. The reflective sheet55reflects a light, which is emitted downward from the light guide plate30, toward the light guide plate30to reduce light loss.

The diffusion sheet60is above the light guide plate30. The diffusion sheet60diffuses and emits a light supplied from the light guide plate30. The prism sheet70is provided above the diffusion sheet60. The prism sheet70enhances the brightness of the light supplied through the diffusion sheet60by using a prism75formed on an upper surface thereof. In this case, the prism75may extend perpendicularly to the first light incident surface31and the second light incident surface33.

Hereinafter, various light guide plates according to exemplary embodiments will be described in detail with reference toFIGS. 2A to 11.FIGS. 2A to 2Care sectional views showing the backlight unit5according to the first exemplary embodiment of the present disclosure, andFIG. 3is a partially enlarged view showing the optical path changing portion shown inFIG. 2A.FIG. 4is a sectional view showing an angle of the optical path changing portion shown inFIG. 1. InFIGS. 2A to 2C, the same reference numerals denote the same elements inFIG. 1, and thus the detailed description of the same elements will be omitted.

Referring toFIGS. 2A to 2C,3, and4, the backlight unit5includes the first light sources10, the second light source20, and the light guide plate30. The light guide plate30includes the first light incident surface31, the second light incident surface33, the light exit surface35, the reflective sheet37, and the optical path changing portions40.

The optical path changing portions40are provided on the reflective sheet37with a predetermined interval. For the convenience of explanation, one of the optical path changing portions40will be representatively described.

The optical path changing portion40may be recessed from the reflective surface37toward the light exit surface35. For example, the optical path changing portion40may have a prism shape. The optical path changing portion40includes a first inclined surface41reflecting the first light15in a first light exit direction and a second inclined surface45connected with the first inclined surface41to reflect the second light25in a second light exit direction.

The first inclined surface41is formed on the reflective surface37such that the first light15is uniformly output through the light exit surface35. The width of the first inclined surface41is increased as the first inclined surface41is away from the first light incident surface31(i.e., the width of the first inclined surface41increases as the distance from the first light incident surface31increases for corresponding ones of the first inclined surface41). For example, the first inclined surface41adjacent to the first light incident surface31is narrower than the first inclined surface41adjacent to the second light incident surface33. Accordingly, an area capable of reflecting the first light15is increased as the first inclined surface41is away from the first light incident surface31.

The second inclined surface45is formed on the reflective surface37such that the second light25is uniformly output through the light exit surface35. The width of the second inclined surface45is increased as the second inclined surface45is away from the second light incident surface33(i.e., the width of the second inclined surface45increases as the distance from the second light incident surface33increases for corresponding ones of the second inclined surface45). For example, the second inclined surface45adjacent to the second light incident surface33is narrower than the second inclined surface45adjacent to the first light incident surface31. An area of the second inclined surface45capable of reflecting the second light25is increased as the second inclined surface45is away from the second light incident surface33.

The first light15and the second light25are uniformly output throughout the whole area of the light exit surface35. After the first light15and the second light25are incident through the first light incident surface31and the second light incident surface33, the first light15and the second light25exit through the light exit surface35in a uniform direction. Accordingly, the first light15and the second light25may be effectively recognized by users located in different directions. In addition, the first light15and the second light25may be used to represent a three-dimensional image.

The optical path changing portions40may be arranged symmetrically to each other about a first reference line I-I′ extending in a direction perpendicular to the light exit surface35and positioned at the central portion of the light exit surface35. However, the optical path changing portions40are not limited thereto.

The light guide plate30may include a reflective film39coated on a rear surface of the reflective surface37and the optical path changing portion40. The reflective film39includes aluminum (Al) and silver (Ag).

Each of the first and second inclined surfaces41and45includes a first end42and a second end46, which are connected to the reflective surface37. The first end42and the second end46are spaced apart from the light exit surface35by a first distance H1and a second distance H2, respectively. The first distance H1and the second distance H2may have different values. However, if the optical path changing portions40are positioned on the first reference line I-I′, the first distance H1is equal to the second distance H2.

The first inclined surface41and the second inclined surface45are inclined at a first angle θ1and a second angle θ2with respect to a first virtual line A and a second virtual line B extending in parallel to the light exit surface35, respectively. In this case, the first angle θ1may be different from the second angle θ2except when the optical path changing portion40is positioned on the first reference line I-I′.

The first inclined surface41and the second inclined surface45are inclined at a predetermined angle to adjust light exit angles of the first light15and the second light25. For the convenience of the explanation, the first inclined surface41shown inFIG. 4will be representatively described.

The first inclined surface41may be inclined at a third angle θ3to a fourth angle θ4with respect to the first virtual line A extending in parallel to the light exit surface35. For example, the first inclined surface41may be inclined at about 24 degrees to about 45 degrees. If the first inclined surface41is inclined at about 45 degrees, the first light15incident onto the first inclined surface41is reflected perpendicularly to the light exit surface35. In addition, if the first inclined surface41is inclined at about 24 degrees, the first light15reflected from the first inclined surface41exits while being inclined at a predetermined angle with respect to the light exit surface35.

If the first inclined surface41is inclined at a fifth angle θ5less than about 24 degrees, the first light15is reflected from the light exit surface35, so that the first light15does not exit to an exterior. In addition, if the first inclined surface41is inclined at a predetermined angle exceeding about 45 degrees, the first light15exits in a direction similar to the light exit direction of the second light25.

The third angle θ3may be changed according to a refractive index of a material forming the light guide plate30. In other words, the minimum angle of the first inclined surface41, which reflects the first light15such that the first light15exits, may be changed according to the refractive index of the material. For example, if the light guide plate30includes polycarbonate (PC), the first inclined surface41may be inclined at the third angle θ3of about 25.5 degrees. In addition, if the light guide plate30includes methacrylstyrene (MS), the first inclined surface41may be inclined at the third angle θ3in the range of about 24 degrees to about 25.5 degrees. If the light guide plate30includes polymethyl methacrylate (PMMA), the first inclined surface41may be inclined at the third angle θ3of about 24 degrees.

FIG. 5is a sectional view showing a backlight unit according to a second exemplary embodiment of the present disclosure.FIG. 6is a partially enlarged view showing an optical path changing portion shown inFIG. 5.

Referring toFIGS. 5 and 6, the backlight unit includes first light sources10, second light sources20, and a light guide plate30. The light guide plate30includes a first light incident surface31, a second light incident surface33, a light exit surface35, a reflective surface37, and a plurality of optical path changing portions40. In the present exemplary embodiment, elements that have been described with reference toFIGS. 2A to 4will be omitted to avoid redundancy, and one of the optical path changing portions40will be representatively described.

The optical path changing portion40is recessed from the reflective surface37. The optical path changing portion40includes a first inclined surface41and a second inclined surface45connected to the reflective surface37. The optical path changing portions40may be provided symmetrically to each other about a first reference line I-I′ corresponding to the central portion of the light exit surface35.

The first inclined surface41includes a first end42connected to the reflective surface37, and the second inclined surface45includes a second end46connected to the reflective surface37. A first distance H1from the first end42to the light exit surface35is gradually reduced in the direction of the first light incident surface31and the second light incident surface33on the basis of the first reference line I-I′. In addition, a second distance H2from the second end46to the light exit surface35is also gradually reduced in the direction of the first light incident surface31and the second light incident surface33on the basis of the first reference line I-I′.

The first inclined surface41and the second inclined surface45are inclined at a first angle θ1and a second angle θ2with respect to a first virtual line A and a second virtual line B extending from the reflective surface37in parallel to the first inclined surface41and the second inclined surface45, respectively. The first angle θ1may be equal to the second angle θ2. The reflective surface37connected to the first inclined surface41and the second inclined surface45may be substantially parallel to the light exit surface35.

FIG. 7is a sectional surface showing a backlight unit according to a third exemplary embodiment of the present disclosure, andFIG. 8is a partially enlarged view showing an optical path changing portion shown inFIG. 7. Referring toFIGS. 7 and 8, the backlight unit includes first light sources10, second light sources20, and a light guide plate30. The light guide plate30includes a first light incident surface31, a second light incident surface33, a light exit surface35, a reflective surface37, and a plurality of optical path changing portions40. In the present exemplary embodiment, elements that have been described with reference toFIGS. 2A to 4will be omitted to avoid redundancy, and one of the optical path changing portions40will be representatively described.

The optical path changing portion40is recessed from a second reference line II-II′ toward the light exit surface35, which extend in parallel to the light exit surface35corresponding to ends of the first light incident surface31and the second light incident surface33. The reflective surface37connects the optical path changing portions40to each other, and has a contact point with the second reference line II-II′. For example, the optical path changing portion40may be formed by partially recessing the reflective surface37of the light guide plate30having a predetermined thickness.

The optical path changing portion40includes a first inclined surface41and a second inclined surface45connected to the reflective surface37. The optical path changing portions40may be provided symmetrically to each other about a first reference line I-I′ corresponding to the central portion of the light exit surface35.

The first inclined surface41includes a first end42connected to the reflective surface37, and the second inclined surface45includes a second end46connected to the reflective surface37. A first distance H1between the first end42and the light exit surface35is increased in a direction of the first reference line I-I′ in the region between the first reference line I-I′ and the first light incident surface31. The first distance H1is constant with respect to the first inclined surface41of the optical path changing portion40located in the region between the first reference line I-I′ and the second light incident surface33. A second distance H2between the second end46and the light exit surface35is increased in the direction of the first reference line I-I′ in the region between the first reference line I-I′ and the second light incident surface33. The second distance H2is constant with respect to the second inclined surface45of the optical path changing portion40located between the first reference line I-I′ and the first light incident surface31. Although the first distance H1and the second distance H2shown inFIG. 8are obtained based on the optical path changing portion40located between the first light incident surface31and the first reference line I-I′, the present disclosure is not limited thereto.

FIG. 9is a sectional view showing a backlight unit according to a fourth exemplary embodiment of the present disclosure.FIGS. 10A and 10Bare partially enlarged views showing an optical path changing portion shown inFIG. 9.

Referring toFIGS. 9,10A, and10B, the backlight unit includes first light sources10, second light sources20, and a light guide plate30. The light guide plate30includes a first light incident surface31, a second light incident surface33, a light exit surface35, a reflective surface37, and a plurality of optical path changing portions40. In the present exemplary embodiment, elements that have been described with reference toFIGS. 2A to 4will be omitted to avoid redundancy, and one optical path changing portions40will be representatively described.

The optical path changing portion40includes a first inclined surface41and a second inclined surface45connected to the reflective surface37. The first inclined surface41is curved, and the width of the first inclined surface41is increased as the first inclined surface41is away from the first light incident surface31. The second inclined surface45is a flat surface, and the width of the second inclined surface45is increased as the second inclined surface45is away from the second light incident surface33. Each of the first inclined surface41and the second inclined surface45includes a first end42and a second end46connected to the reflective surface37, respectively. In addition, the first inclined surface41and the second inclined surface45are connected to a third end48.

The first inclined surface41may reflect a first light15, which is incident onto one point, at a predetermined angle. For example, the curved first inclined surface41may reflect the first light15incident onto one point through a plurality of optical paths. To this end, the first inclined surface41is curved such that the first light15may be reflected at predetermined angles with respect to a third extension line C and a fourth extension line D, in which the third extension line C extends from the first end42in parallel to the light exit surface35, and the fourth extension line D extends from the third end48in parallel to the light exit surface35. For example, the first inclined surface41may be formed such that a first tangential line E in contact with the first end42is inclined at an angle of about 65 degrees or less with respect to the third extension line C. In addition, the first inclined surface41may be formed such that a second tangential line F in contact with the third end48is inclined at an angle of 24 degrees or more with respect to the fourth extension line D. That is, the first inclined surface41may be curved such that a tangential line may be formed within the range of an angle of about 24 degrees to about 65 degrees.

The second inclined surface45may reflect the second light25, which is incident onto one point, at a single angle. For example, the second inclined surface45having a flat surface may reflect the second light25incident onto one point through a single path. The second inclined surface45may be inclined at an angle of about 24 degrees to about 65 degrees.

Accordingly, the optical path changing portion40may supply light at different viewing angles by using the first inclined surface41and the second inclined surface45. For example, the first inclined surface41reflects the first light15in a relatively wide angle range to provide a wide viewing angle, and the second inclined surface45reflects the second light25in a relatively narrow angle range to provide a narrow viewing angle.

FIG. 11is a sectional view showing a backlight unit according to a fifth exemplary embodiment of the present disclosure. Referring toFIG. 11, the backlight unit includes first light sources10, second light sources20, a light guide plate30, and a reflective sheet55. The light guide plate30includes a first light incident surface31, a second light incident surface33, a light exit surface35, and a reflective surface37. In the present exemplary embodiment, elements that have been described with reference toFIG. 1will be omitted to avoid redundancy.

In one embodiment, the reflective surface37includes a third inclined surface38reflecting a first light15to form a concave-convex shape. The width of the third inclined surface38is increased as the third inclined surface38is away from the first light incident surface31. The third inclined surface38reflects the first light15to the light exit surface35. The first light15is refracted on the light exit surface35and exits through the light exit surface35. (I.e., the reflective surface37having a plurality of third inclined surfaces38that reflect the first light15, wherein a width of the third inclined surface38increases as a distance from the first incident light surface31increases for corresponding ones of the third inclined surfaces38.)

In one embodiment, the light exit surface35includes a fourth inclined surface36reflecting a second light25to form a concave-convex shape. As the fourth inclined surface36is away from the second light incident surface33, the width of the fourth inclined surface36is increased. The fourth inclined surface36reflects the second light25to the reflective surface37. The second light25exits from the reflective surface37and is reflected by the reflective sheet55. (I.e., the light exit surface35comprises a plurality of fourth inclined surfaces36that reflect the second light25, wherein a width of the fourth inclined surface36decreases as a distance from the first incident light surface31increases for corresponding ones of the fourth inclined surfaces36.)

The reflective sheet55is provided below the light guide plate30. The reflective sheet55reflects the second light25supplied from the reflective surface37to the light exit surface35. The second light25is refracted on the light exit surface35and exits from the light exit surface35.

Hereinafter, a light guide characteristic and a light radiation characteristic of the backlight unit according to one or more embodiments of the present disclosure will be described with reference toFIGS. 12A to 13.FIGS. 12A to 12Care graphs showing the light guide characteristic of the backlight unit including the light guide plate shown inFIG. 5, andFIG. 13is a graph showing the light radiation characteristic of the backlight unit including the light guide plate shown inFIG. 5.

FIGS. 12A to 13are graphs showing the light guide characteristic and the light radiation characteristic of the backlight unit, which are measured through simulation using the light guide plate, the first and second light sources provided at both sides of the light guide plate, and the reflective sheet provided below the light guide plate. The light guide plate has a length of 100 mm and a width of 50 mm. In addition, 100 optical path changing portions are provided on the light guide plate with an interval of 1 mm. In this case, the thickness of the light guide plate is not taken into consideration.

A horizontal axis shown inFIGS. 12A to 12Crepresents the length of the light guide plate, and a vertical axis represents the brightness of a light exiting from the light guide plate. The unit of the length is millimeter, and the unit of the brightness is nit. In addition, “0” on the horizontal axis represents the center of the light guide plate in a longitudinal direction, positive values on the horizontal axis represent a left side with respect to the center of the light guide plate, and negative values on the horizontal axis represent a right side with respect to the center of the light guide plate.

FIG. 12Ashows a brightness characteristic76of the first light output when the first light source provided at the left side of the light guide plate supplies the first light to the light guide plate. The brightness characteristic76of the first light shows that the first light is uniformly output even through the first light is distanced from the first light source.

FIG. 12Bshows a brightness characteristic77of the second light output when the second light source provided at the right side of the light guide plate supplies the second light to the light guide plate. The brightness characteristic77of the second light shows that the second light is uniformly output even through the second light is distanced from the second light source.

FIG. 12Cshows a brightness characteristic78of the first and second lights output when the first and second light sources provided at the left and right sides of the light guide plate supply the first and second lights to the light guide plate, respectively. The brightness characteristic78of the first and second lights represents that the first and second lights are uniformly output from the light guide plate.

As shown inFIG. 13, a horizontal axis represents an exit angle of the first and second lights output from the light guide plate, and a vertical axis represents the brightness of a light output from the light guide plate. In this case, the unit of the exit angle is a degree, and the unit of the brightness is nit. In addition, “0” on the horizontal axis represents that the first and second lights are vertically output from the light exit surface. Positive and negative values on the horizontal axis represent exit angles of the first and second lights based on the light exit surface.

FIG. 13shows third and fourth brightness characteristics81and83measured when the first and second lights, which are reflected from the optical path changing portion of the light guide plate, exit through the light exit surface. The optical path changing portion includes the first inclined surface reflecting the first light and the second inclined surface reflecting the second light, in which the first inclined surface and the second inclined surface are inclined at an angle of about 40 degrees with respect to the reflective surface of the light guide plate. The third brightness characteristic81shows a superior value at about −30 degrees, and the fourth brightness characteristic83shows a superior value at about 30 degrees. In other words,FIG. 13shows that the first and second lights exit in different directions.

Accordingly, the light guide plate may be adapted to effectively supply the first and second lights to users positioned in different directions. Moreover, the light guide plate may be employed in a display device that displays a three-dimensional image.

Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications may be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.