WO2008140176A1

WO2008140176A1 - Prism sheet and lgp using polygonal prism structure, blu and lcd with the same

Info

Publication number: WO2008140176A1
Application number: PCT/KR2008/000972
Authority: WO
Inventors: Gyoung Tae No; Sun Mi Shin; Young Rim Lee
Original assignee: Gyoung Tae No; Sun Mi Shin; Young Rim Lee
Priority date: 2007-05-11
Filing date: 2008-02-19
Publication date: 2008-11-20

Abstract

Disclosed is a prism sheet and a light guide plate having reversed prism peaks and prism peaks, respectively, based on a polygonal prism structure, as well as a backlight unit and an LCD using the same to improve both brightness and characteristics regarding the field of view.

Description

PRISM SHEET AND LGP USING POLYGONAL PRISM STRUCTURE, BLU AND LCD WITH THE SAME

Technical Field

[1] The present invention relates to the construction of an optical path modification means by using a polygonal prism structure. More particularly, the present invention relates to a prism sheet and a light guide plate having reversed prism peaks and prism peaks, respectively, based on a polygonal prism structure, as well as a backlight unit and an LCD using the same to improve both brightness and characteristics regarding the field of view. Background Art

[2] As generally known in the art, LCDs are light-receiving devices, i.e. they cannot emit light by themselves, unlike CRTs (Cathode Ray Tubes), and need a backlight device to maintain uniform brightness across the entire screen.

[3] The backlight device, as shown in FIG. 1, includes a lamp 1 as a light source, a light guide plate 2 for scattering light incident from the lamp 1 to uniformize it; a reflection sheet 3 positioned below the light guide plate 2 to reflect light incident from the lamp 1 toward the top, on which a liquid crystal panel (not shown) is positioned, to prevent the light from leaking through the bottom of the light guide plate 2 and being lost; a diffusion sheet 4 positioned on a surface of the light guide plate 2 opposite the reflection sheet 3 to increase the uniformity of light; a prism sheet 5 arranged on top of the diffusion sheet 4; and a protection sheet 6 for stabilizing the color coordinate and protecting the prism structure of the prism sheet 5.

[4] The prism sheet 5 is used to condense light diffused by the diffusion sheet 4 to obtain a predetermined level of brightness. As shown in FIG. 2, the prism sheet 5 has prism peaks 5a protruding upward from its upper surface to increase the efficiency of condensing light.

[5] Such a conventional prism sheet 5 has a problem in that, although light diffused by the diffusion sheet 4 is vertically refracted and condensed toward the top so that the user can watch high-brightness images in front of the liquid crystal panel, the brightness substantially degrades as the field of view increases. In addition, the characteristics of the prism structure cause a loss of light because light is emitted from the lateral surface.

[6] In the case of a prism sheet 5 and a light guide plate 2 having reversed prism peaks

5b, as shown in FIG. 3, the fact that the optical propagation path is limited narrows the field of view, although the brightness may be increased by reflection. The loss of light due to emission of light from the lateral surface persists.

[7] Furthermore, the use of a pattern having a predetermined shape of prism peaks to manufacture a product results in a structure susceptible to curling in environments of high temperature and humidity.

[8] In summary, the degradation of characteristics regarding the field of view and the high possibility of obtaining erroneous products adversely affect the reliability of backlight units and LCDs employing conventional prism sheets.

[9] The optical propagation path is still limited even when prism peaks are formed on the light emission surface of the light guide plate. This restricts brightness improvement. Disclosure of Invention Technical Problem

[10] Therefore, the present invention has been made in view of the above-mentioned problems occurring in conventional prism sheets, as well as backlight units and displays using them, and the present invention provides a prism sheet having polygonal reversed prism peaks on its light incident surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[11] The present invention also provides a backlight unit including a prism sheet having polygonal reversed prism peaks on its light incident surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[12] The present invention also provides an LCD including a prism sheet having polygonal reversed prism peaks on its light incident surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[13] The present invention also provides a light guide plate having polygonal prism peaks on its light emission surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[14] The present invention also provides a backlight unit including a light guide plate having polygonal prism peaks on its light emission surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[15] The present invention also provides an LCD including a light guide plate having polygonal prism peaks on its light emission surface based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view.

[16] The present invention also provides a prism sheet and a light guide plate having polygonal reversed prism peaks and polygonal prism peaks on the light incident surface and the light emission surface, respectively, based on a polygonal prism structure to improve both brightness and characteristics regarding the field of view, as well as a backlight unit and an LCD including the same. Technical Solution

[17] In accordance with an aspect of the present invention, there is provided a prism sheet for refracting light incident on a lower surface to concentrate the light toward an upper portion by using a polygonal prism structure, the prism sheet including a plurality of reversed prism peaks protruding from a reversed prism peak base region on the lower surface of the prism sheet, wherein each reversed prism peak is configured in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, and left and right sides of each reversed prism peak are bent to define first, second, and third regions of each reversed prism peak.

[18] According to another aspect of the present invention, there is provided a prism sheet for refracting light incident on a lower surface to concentrate the light toward an upper portion by using a polygonal prism structure, the prism sheet including a plurality of reversed prism peaks protruding from a reversed prism peak base region on the lower surface of the prism sheet, wherein each reversed prism peak is configured in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, and left and right sides of each reversed prism peak are bent to define first, second, and third regions of each reversed prism peak.

[19] According to another aspect of the present invention, there is provided a backlight unit having a prism sheet using a polygonal prism structure, the backlight unit including a light guide plate for diffusing, reflecting, and refracting light rays from a light source to modify a propagation direction of the light rays so that the light rays are uniformly emitted toward an upper portion; a reflection sheet for reflecting light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets.

[20] According to another aspect of the present invention, there is provided a liquid crystal display having a prism sheet using a polygonal prism structure, the liquid crystal display including a backlight unit including a light guide plate for diffusing, reflecting, and refracting light rays from a light source to modify a propagation direction of the light rays so that the light rays are uniformly emitted toward an upper portion, a reflection sheet for reflecting light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

[21] According to another aspect of the present invention, there is provided a light guide plate using a polygonal prism structure, the light guide plate including a plurality of prism peaks positioned on an emission surface, wherein each prism peak has a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, and left and right sides of each prism peak of the light guide plate are bent to define first, second, and third regions of each prism peak so that light rays from a light source are emitted toward an upper portion.

[22] According to another aspect of the present invention, there is provided a light guide plate using a polygonal prism structure, the light guide plate including a plurality of prism peaks positioned on an emission surface, wherein each prism peak has a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, and left and right sides of each prism peak of the light guide plate are bent to define first, second, and third regions of each prism peak so that light rays from a light source are emitted toward an upper portion.

[23] According to another aspect of the present invention, there is provided a backlight unit having a light guide plate using a polygonal prism structure, the backlight unit including a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak; a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets before a liquid crystal display is assembled. [24] According to another aspect of the present invention, there is provided a backlight unit having a light guide plate using a polygonal prism structure, the backlight unit including a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak; a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets before a liquid crystal display is assembled.

[25] According to another aspect of the present invention, there is provided a liquid crystal display having a light guide plate using a polygonal prism structure, the liquid crystal display including a backlight unit including a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak, a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets before the liquid crystal display is assembled; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

[26] According to another aspect of the present invention, there is provided a liquid crystal display having a light guide plate using a polygonal prism structure, the liquid crystal display including a backlight unit including a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak, a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets before the liquid crystal display is assembled; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

Advantageous Effects

[27] The inventive prism sheet and light guide plate based on a polygonal prism structure, as well as the backlight unit and LCD including the same, have the following advantages. [28] Firstly, the prism sheet has polygonal reversed prism peaks on its light incident surface to improve both brightness and characteristics regarding the view of view. [29] Particularly, the polygonal reversed prism peaks direct all light along paths that increase brightness. [30] Secondly, the second regions of reversed prism peaks of the prism sheet also emit light in a direction that improves characteristics regarding the field of view. This both guarantees a wide field of view and prevents the loss of light due to the conventional prism structure. [31] Thirdly, the first, second, and third regions of polygonal prism peaks of the light guide plate refract, diffuse, and reflect incident light in different directions so that more uniform incident light is directed to the liquid crystal panel. [32] Fourthly, the second regions of prism peaks of the light guide plate emit light in a direction that improves characteristics regarding the field of view. This both guarantees a wide field of view and prevents the loss of light due to the conventional prism structure.

Brief Description of the Drawings [33] The foregoing and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: [34] FIG. 1 shows the construction of a conventional backlight unit; [35] FIG. 2 shows the construction of a prism sheet according to the prior art;

[36] FIG. 3 shows the construction of a reversed prism sheet according to the prior art;

[37] FIGs. 4-9 show the construction of light guide plates having polygonal prism peaks according to the present invention; [38] FIGs. 10 and 11 show the detailed construction of polygonal prism peaks of a light guide plate according to the present invention; [39] FIG. 12 shows the construction of a prism sheet having polygonal reversed prism peaks according to the present invention; [40] FIG. 13 shows the path of incident light propagating through a polygonal reversed prism peak of a prism sheet according to the present invention; [41] FIGs. 14 and 15 show the detailed construction of polygonal reversed prism peaks of a prism sheet according to the present invention; [42] FIGs. 16 and 17 show the results of a simulation regarding the path of incident light propagating through a simple reversed prism peak of a prism sheet and through a polygonal reversed prism peak according to the present invention, respectively; [43] FIG. 18 shows the characteristics regarding the path of incident light propagating through polygonal reversed prism peaks of a prism sheet according to the present invention; [44] FIG. 19 shows the coupling between a prism sheet and a light guide plate having polygonal prism peaks according to the present invention; [45] FIG. 20 shows another type of coupling between a prism sheet and a light guide plate having polygonal prism peaks according to the present invention; [46] FIGs. 21-32 are photographs and graphs showing brightness distributions in relation to the field of view and the path of incident light propagating through simple reversed prism peaks, polygonal reversed prism peaks, and the pattern on the lower surface of the light guide plate; [47] FIG. 33 shows the construction of a backlight unit having polygonal reversed prism peaks according to the present invention; [48] FIG. 34 shows the construction of an LCD having polygonal reversed prism peaks according to the present invention; [49] FIG. 35 shows the construction of a backlight unit including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism pea ks according to the present invention; [50] FIG. 36 shows the construction of another backlight unit including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention; [51] FIG. 37 shows the construction of an LCD including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention; and

[52] FIG. 38 shows the construction of another LCD including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention. Mode for the Invention

[53] Hereinafter, prism sheets and light guide plates using a polygonal prism structure, as well as backlight unitsand LCDs using the same, according to exemplary embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

[54] A light guide plate having polygonal prism peaks according to the present invention will be described first.

[55] FIGs. 4-9 show the construction of light guide plates having polygonal prism peaks according to the present invention. FIGs. 10 and 11 show the detailed construction of polygonal prism peaks of a light guide plate according to the present invention.

[56] The light guide plate 40 according to the present invention is adapted to condense incident light upward by diffusing, reflecting, and refracting it. The light guide plate 40 has a plurality of polygonal prism peaks 41 protruding from the upper emission surface.

[57] Particularly, a plurality of polygonal prism peaks 41 are formed on the emission surface of the light guide plate 40 so that light incident from the light source is uniformly emitted toward the liquid crystal panel (not shown) by means of diffusion, reflection, and refraction.

[58] The cross section of each prism peak 41 of the light guide plate 40 has the shape of a heptagon, which is symmetric horizontally about a vertical line extending through its apex.

[59] Particularly, the left and right sides of each prism peak 41 of the light guide plate 40 are bent to define first, second, and third regions 42a, 42b, and 42c of the prism peak 41.

[60] Those skilled in the art can easily understand that, althoughit has been assumed in the description of the present embodiment that the cross section of each prism peak 41 of the light guide plate 40 has the shape of a heptagon symmetric horizontally about a vertical line extending through the apex, the prism peak 41 may have a heptagonal cross section that is asymmetric horizontallyabout the vertical line. In addition, the cross section is not limited to the heptagon, and may have more vertices.

[61] The first regions 42a of each prism peak 41 have one end extending upward from the lower surface of the light guide plate 40, i.e. the base region of the prism peak 41, at an angle. The second regions 42b of each prism peak 41 are bent inward from the other end of the first regions 42a so that they extend upward at an angle. [62] The third regions 42c of each prism peak 41 are bent outward from the other end of the second regions 42b so that theyextend upward at an angle. The left and right third regions 42c are joined at the apex 45 of the prism peak 41. [63] Incident light propagating through the first, second, and third regions 42a, 42b, and

42c of each prism peak 41, which are constructed as described above, is refracted, diffused, and reflected in different directions. [64] The geometric structure of the light guide plate having polygonal prism peaks according to the present invention will now be described with reference to FIGs. 10 and 11. The interior angle αbetween the first and second regions 42a and 42b of each prism peak 41 constitutes a minor angle smaller than 180°, and the interior angle β between the second and third regions 42b and 42c of the prism peak 41 constitutes a major angle larger than 180°. [65] The point of intersection between the first and second regions 42a and 42b of each prism peak 41 will be referred to as afirst vertex 43, and the point of intersection between the second and third regions 42b and 42c will be referred to as a second vertex

44. [66] The first and second vertices 43 and 44 of each prism peak 41 may be rounded to have a predetermined radius r, as shown in FIG. 11. [67] The height hi of the first vertices 43 of each prism peak 41 from its base region is larger than lμm. In addition, the difference between the height h3 of the apex and the height h2 of the second vertices 44 (i.e. h3-h2) is larger than lμm. [68] In other words, the height hi of the first vertices 43 of each prism peak 41 from the base region is in the range of l-12μm, and the height h2 of the second vertices44 from the base region is in the range of 13-23μm. [69] The height h3 of the apex of each prism peak 41 from the base region is 24μm, and the length w of the base region is 50mμ. [70] However, those skilled in the art can easily understand that the heights hi, h2, and h3 and the length w are not limited to the above-mentioned values, and may be varied to construct desired polygonal prism peaks. [71] For example, the length w may be in the range of 20-80μm. Preferably, the length w is 50μm, 25 μm, or 24μm. [72] Based on this range of values, the interior angle θ between the base region of each prism peak 41 and the second regions 42b is calculated to be 0-43.73°. [73] It can be said that, when the interior angle θ is 0°, the second regions 42b of each prism peak 41 are parallel with its base region. [74] As such, the second regions 42b of each prism peak 41 lie at apredetermined angle relative to the base region. [75] When the height h3 and the length w are varied, the interior angle θ can be modified accordingly.

[76] The interior angle δ between the base region and the first regions 42a of each prism peak 41 is 35-55°.

[77] The interior angle between the opposite third regions 42c, which are joined at the apex 45, is 80-120°, preferably 110°.

[78] The light guide plate having polygonal prism peaks according to the present invention is made of a material having a refractive index of 1.52-1.62, including polymethylmethacrylate (PMMA) and polycarbonate (PC)for injection molding. The material can be selected from substances including mono- or di-acrylate series compounds, such as urethane acrylate and epoxy acrylate, and poly olefin series compounds, such as polyester, polysiloxane, and poly ether, so that UV curing is possible.

[79] Light propagating through the first, second, and third regions 42a, 42b, and 42c of the polygonal prism peaks of the light guide plate according to an embodiment of the present invention isrefracted, diffused, and reflected in different directions so that more uniform incident light is directed toward the liquid crystal panel.

[80] The light guide plate having polygonal prism peaks according to the present invention has a reflection pattern on its lower surface. Referring to FIG. 4, the light guide plate has a circular relief pattern formed in a direction parallel with the direction of extension of the prism peaks 41 and spaced from them.

[81] Alternatively, referring to FIG. 5, the light guide plate has a prism relief pattern formed in a direction parallel with the direction of extension of the prism peaks 41 and spaced from them.

[82] Alternatively, referring to FIG. 6, the light guide plate has a prism intaglio pattern formed in a direction parallel with the direction of extension of the prism peaks 41 and spaced from them.

[83] Alternatively, referring to FIG. 7, the light guide plate has a circular relief pattern formed in a direction perpendicular to the direction of extension of the prism peaks 41 and spaced from them.

[84] Alternatively, referring to FIG. 8, the light guide plate has a prism relief pattern formed in a direction perpendicular to the direction of extension of the prism peaks 41 and spaced from them.

[85] Alternatively, referring to FIG. 9, the light guide plate has a prism intaglio pattern formed on a direction perpendicular to the direction of extension of the prism peaks 41 and spaced from them.

[86] Those skilled in the art can easily understand that the reflection pattern on the lower surface of the light guide plate is not limited to the above mentioned types, and various types of patterns (e.g. dot pattern) may be used.

[87] In addition, although it has been assumed in the above description of the light guide plate having polygonal prism peaks according to the present invention with reference to FIGs. 10 and 11 that the interior angle α between the first and second regions 42a and 42b of each prism peak 41 constitutes a minor angle smaller than 180°, and that the interior angle β between the second and third regions 42b and 42c of the prism peak 41 constitutes a major angle larger than 180°, the angles may be varied in the following manner to improve characteristics regarding the recycle of incident light.

[88] That is, the interior angle αbetween the first and second regions 42a and 42b of each prism peak 41 may constitute a minor angle smaller than 180°, and the interior angle β between the second and third regions 42b and 42c of the prism peak 41 may constitute a minor angle smaller than 180°.

[89] In this case, the height hi of the first vertices 43 of each prism peak 41 from the base region is larger than the height h2 of the second vertices 44. As a result, in addition to the central apex 45, the left and right vertices 43 act as additional apexes of the prism peak 41.

[90] Alternatively, the height hi of the first vertices 43 from the base region may vary between adjacent prism peaks 41 of the light guide plate, while the height h3 of the central apex 45 remains the same, so that the height of the prism peaks 41 is irregularly repeated.

[91] A prism sheet having polygonal reversed prism peaks according to the present invention will now be described.

[92] FIG. 12 shows the construction of a prism sheet having polygonal reversed prism peaks according to the present invention. FIG. 13 shows the path of incident light propagating through a polygonal reversed prism peak of a prism sheet according to the present invention.

[93] FIGs. 14 and 15 show the detailed construction of polygonal reversed prism peaks of a prism sheet according to the present invention.

[94] The prism sheet 61 according to the present invention is adapted to condense light, which is incident on its lower surface, upward by refracting and reflecting it. The prism sheet 61 has a plurality of reversed prism peaks 62 protruding from the lower surface.

[95] Particularly, a plurality of reversed prism peaks 62 are formed on the light incident surface of theprism sheet 61, which faces the emissionsurface of the light guide plate 40, and light incident from the light guide plate 40 is refracted and reflected so that it is uniformly emitted to the liquid crystal panel (not shown).

[96] The cross section of each reversed prism peak 62 of the prism sheet 61 has the shape of a heptagon, which is symmetric horizontally about a vertical line extending through its apex. [97] Particularly, the left and right sides of each reversed prism peak 62 of the prism sheet

61 are bent to define first, second, and third regions 62a, 62b, and 62c of the reversed prism peak 62.

[98] Those skilled in the art can easily understand that, although it has been assumed in the description of the present embodiment that the cross section of each reversed prism peak 62 of the prism sheet 61 has the shape of a heptagon symmetric horizontally about a vertical line extending through the apex, the reversed prism peak 62 may have a heptagonal cross section that is asymmetric horizontally about the vertical line. In addition, the cross section is not limited to the heptagon, and may have more vertices.

[99] The first regions 62a of each reversed prism peak 62 have one end extending downward from the lower surface of the prism sheet 61, i.e. the base region 65 of the reversed prism peak 62, at an angle. The second regions 62b of each reversed prism peak 62are bent inward from the other end of the first regions 62a so that they extend downward at an angle.

[100] The third regions 62c of each reversed prism peak 62 are bent outward from the other end of the second regions 62b so that they extend downward at an angle. The left and right third regions 62c are joined at the apex of the reversed prism peak 62.

[101] Incident light propagating through the first, second, and third regions 62a, 62b, and 62c of each reversed prism peak 62, which are constructed as described above, is refracted, reflected, and condensed in different directions.

[102] Referring to FIG. 13, when light is incident on a reversed prism peak62 of the prism sheet 61, a portion of the light is incident on the first region 62a on one side of the reversed prism peak 62, and is reflected by the base region 65 of the reversed prism peak 62. Then, the portion of light is reflected by the second region 62b and the first region 62a on the other side ofthe reversed prism peak 62 (which lie opposite the incident surface), so that theportion of light is emitted via the base region 65 to improve the brightness.

[103] In other words, the secondary reflection by the second region 62b and the first region 62a of the reversed prism peak 62, which lie opposite the incident surface, prevents the loss of light and improves the brightness.

[104] Another portion of light incident on the reversed prism peak 62 is incident on the second region 62b on one side of the reversed prism peak 62 and undergoes primary reflection. The portion of light is reflected secondarily by the base region 65, and is emitted in a direction that improves characteristics regarding the field of view.

[105] Another portion of light incident on the reversed prism peak 62 is incident on the third region 62c on one side ofthe reversed prism peak 62. The portion of light is reflected by the third region 62c on the other side of the reversed prism peak 62 (which lies opposite the incident surface), and is emitted via the base region 65 to improve the brightness.

[106] It is clear from FIG. 13, which briefly shows the path of light propagating through a reversed prism peak 62 of the prism sheet according to the present invention, that not all light is emitted by the reversed prism peak 62 in the upward direction (brightness improving direction) via the base region 65, but a portion of light is emitted by the second region 62b in a direction for improving characteristics regarding the field of view.

[107] The geometric structure of the prism sheet having polygonal reversed prism peaks according to the present invention will now be described with reference to FIGs. 14 and 15. The interior angle α between the first and second regions 62a and 62b of each reversed prism peak 62 constitutes a minor angle smaller than 180°, and the interior angle β between the second and third regions 62b and 62c of the reversed prism peak 62 constitutes a major angle larger than 180°.

[108] The point of intersection between the first and second regions 62a and 62b of each reversed prism peak 62 will be referred to as a first vertex 63, and the point of intersection between the second and third regions 62b and 62c will be referred to as a second vertex 64.

[109] The first and second vertices 63 and 64 of each reversed prism peak 62may be rounded to have a predetermined radius r, as shown in FIG. 15.

[110] The height hi of the first vertices 63 of each reversed prism peak 62 from its base region 65 is larger than lμm. In addition, the difference between the height h3 of the apex and the height h2 of the second vertices 64 (i.e. h3-h2) is larger than lμm.

[I l l] In other words, the height hi of the first vertices 63 of each reversed prism peak 62 from the base region 65 is in the range of l-12μm, and the height h2 of the second vertices 64 from the base region 65 is in the range of 13-23μm.

[112] The height h3 of the apex of each reversed prism peak 62 from thebase region 65 is 24μm, and the length w of the base region 65 is 50μm.

[113] However, those skilled in the art can easily understand that the heights hi, h2, and h3 and the length w are not limited to the above-mentioned values, and may be varied to construct desired polygonal reversed prism peaks.

[114] For example, the length w may be in the range of 20-80μm. Preferably, the length w is 50μm, 25 μm, or 24μm.

[115] Based on this range of values, the interior angle θ between the base region 65 of each reversed prism peak 62 and the second regions 62b is calculated to be 0-43.73°.

[116] It can be said that, when the interior angle θ is 0°, the second regions 62b of each reversed prism peak 62 are parallel with its base region 65.

[117] As such, the second regions 42b (labeled A in FIG. 14) of each reversed prism peak 62 lie at a predetermined angle relative to the base region 65. [118] When the height h3 and the length w are varied, the interior angle θ can be modified accordingly.

[119] The interior angle δ between the base region 65 and the first regions 62a of each reversed prism peak 62 is 40-55°.

[120] The interior angle between the opposite third regions 62c of each reversed prism peak 62, which are joined at the apex, is 50-80°, preferably 68°.

[121] The prism sheet having polygonal reversed prism peaks according to the present invention is made of a material having a refractive index of 1.52-1.62. The material can be selected from substances including mono- or di-acrylate series compounds, such as urethane acrylate and epoxy acrylate, and polyolefin series compounds, such as polyester, polysiloxane, and polyether, so that UV curing is possible.

[122] As such, the polygonal reversed prism peaks 62 of the prism sheet 61 according to an embodiment of the present invention do not emit all light in the upward direction (brightness improving direction) via the base region 65, but emit a portion of light by the second regions 62b in a direction for improving characteristics regarding the field of view.This both guarantees a wide field of view and prevents the loss of light due to the conventional prism structure.

[123] The path of light propagating through the prism sheet having polygonal reversed prism peaks accordingto the present invention, as well as refraction and reflection characteristics, will now be described.

[124] FIGs. 16 and 17 show the results of a simulation regarding the path of incident light propagating through a simple reversed prism peak of a prism sheet and through a polygonal reversed prism peak according to the present invention, respectively. FIG. 18 shows the characteristics regarding the path of incident light propagating through polygonal reversed prism peaks of a prism sheet according to the present invention.

[125] It is clear from FIG. 16 that, in the case of a prism sheet having simple reversed prism peaks, the modification of the path of light incident on the prism sheet is concentrated only in the upward direction (which improves the brightness).

[126] In contrast, in the case of a polygonal reversed prism peak accordingto the present invention shown in FIG. 17, the modification of the path of incident light does not only occur in the brightness improving direction, but also in a direction improving the field of view.

[127] The coupling structure between the above-mentioned light guide plate and the prism sheet according to the present invention, which are based on a polygonal prism structure, will now be described.

[128] Those skilled in the art can easily understand that, although the coupling structure between a prism sheet and a light guide plate according to an embodiment of the present invention will be described, a conventionalprism sheet may be coupled to a light guide plate based on a polygonal prism structure, or a prism sheet having polygonal reversed prism peaks may be coupled to a conventional light guide plate.

[129] FIG. 19 shows the coupling between a prism sheet and a light guide plate having polygonal prism peaks according to the present invention. FIG. 20 shows another type of coupling between a prism sheet and a light guide plate having polygonal prism peaks accordingto the present invention.

[130] Referring to FIG. 19, the pattern arrangement direction of the prism peaks 41 of the light guide plate 40 is parallel with that of the reversed prism peaks 62 of the prism sheet 61.

[131] Referring to FIG. 20, the pattern arrangement direction of the prism peaks 41 of the light guide plate 40 is perpendicular to that of the reversed prism peaks 62 of the prism sheet 61.

[132] FIGs. 21-32 are photographs and graphs showing brightness distributions in relation to the field of view and the path of incident light propagating through simple reversed prism peaks, polygonal reversed prism peaks, and the pattern on the lower surface of the light guide plate.

[133] FIG. 21 is a graph showing a brightness distribution when a light guide plate having a conventional dot pattern is used. It is clear from FIG. 21 that the brightness has the largest value of 1 at an observing angle of 0°, and this value is used as the reference for data.

[134] FIG. 22 compares a brightness distribution when a light guide plate having a conventional dot pattern is used with brightness distributions of a simple reversed prism sheet and a polygonal reversed prism sheet, respectively. It is clear from FIG. 22 that the simple reversed prism sheet has a brightness enhancement ratio of about 5.5, while the polygonal reversed prism sheet has a brightness enhancement ratio of about 8.

[135] FIG. 23 shows an analysis of brightness of a reversed prism sheet when a light guide plate having a prism shape on theupper surface and a dot pattern on the lower surface is used. Particularly, FIG. 23 shows a brightness comparison based on an assumption that the brightness enhancement ratio of a conventionallight guide plate is 1.

[136] It is clear from FIG. 23 that the simple reversed prism sheet has a brightness enhancement ratio of 9.7127 at an angle of 4°, while the polygonal reversed prism sheet has a brightness enhancement ratio of 12.417 at an angle of -2°.

[137] FIG. 24 shows the result of measuring brightness when a prism light guide plate having a prism shape on the upper surface and a prism pattern on the lower surface is solely used. It is clear from FIG. 24 that the prism pattern shape decreases the brightness at the center, but increases the brightness on the lateral surface.

[138] Such an increase in brightness on the lateral surface means that optimization is possible only if a reversed prism sheet is used. [139] FIG. 25 shows the brightness enhancement ratio when a light guide plate having a prism pattern on the upper and lower surfaces is used. It is clear from FIG. 25 that a sheet of a simple reversed prism structure has a brightness enhancement ratio of about 50, while a sheet ofa polygonal reversed prism structure has a brightness enhancement ratio of about 64.

[140] FIG. 26 shows a brightness comparison when a light guide plate having a prism pattern on the upper and lower surfaces is used. It is clear from FIG. 26 that the brightness of a sheet of a simple reversed prism structure is 3.5nit, while the brightness of a sheet of a polygonal reversed prism structure is 4.3nit.

[141] FIG. 27 shows a comparison in the orientation angle between a simple prism sheet and a polygonal prism sheet when a light guide plate of a dot pattern is used. In the case of the simple prism sheet, the center of the brightness distribution has shifted about 6°. In the case of the polygonal prism sheet, the brightness is highest at the center (ideal characteristics).

[142] FIGs. 28 and 29 show light emission types when a light guide plate of a dot pattern is used. In the case of a polygonal prism sheet, as shown in FIG. 28, light emission is concentrated at the center (i.e. lies at the center of the Y-axis). In the case of a simple prism sheet, light emission is not concentrated at the center (i.e. lies at a distance from the center of the Y-axis).

[143] FIG. 30 shows a comparison in the orientation angle between a simple prism sheet and a polygonal prism sheet when a light guide plate of a prism pattern is used. In the case of the simple prism sheet, the center of the brightness distribution has shifted about 9°. In the case of the polygonal prism sheet, the brightness is highest at the center (ideal characteristics).

[144] FIGs. 31 and 32 show light emission types when a light guide plate of a prism pattern is used. In the case of a polygonal prism sheet, as shown in FIG. 31, light emission is concentrated at the center (i.e. lies at the center of the Y-axis). In the case of a simple prism sheet, as shown in FIG. 32, light emission is not concentrated at the center (i.e. lies below the center of the Y-axis).

[145] Therefore, regarding the brightness distribution depending on the field of view, light rays are deflected in the (-y) directionaway from the measuring position in the case of the simple prism sheet. In addition, a considerable number of light rays are irregularly emitted to the surroundings.

[146] In contrast, in the case of the prism sheet having polygonal reversed prism peaks according to the present invention, light rays are evenly emitted in both (+y) and (-y) directions. This is favorable to the field of view, and reduces the amount of unnecessarily emitted light rays.

[147] The prism sheet accordingto an embodiment of the present invention, which has been described above, is not only applicable to a backlight for an LCD, but can also be used to increase the brightness of a backlight using an organic EL display emitting light by itself.

[148] A backlight unit and an LCD using a prism sheet having polygonal reversed prism peaks according to the present inventionwill now be described.

[149] FIG. 33 shows the construction of a backlight unit having polygonal reversed prism peaks accordingto the present invention. FIG. 34 shows theconstruction of an LCD having polygonal reversed prism peaks according to the present invention.

[150] Referring to FIG. 33, the backlight unit having polygonal reversed prism peaks accordingto the present invention includes a light guide plate 100 having an incident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 for reflecting light rays propagating vertically downward a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protruding from the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets.

[151] As mentioned above, those skilled in the art can easily understand that the reversed prism peaks may have a heptagonal cross section that is asymmetric horizontally about the vertical line. In addition, the cross section is not limited to the heptagon, and the backlight unit may include a prism sheet having reversed prism peaks with more vertices.

[152] Referring to FIG. 34, the LCD having polygonal reversed prism peaks accordingto the present invention includes a backlight unit and a liquid crystal panel 600. The backlight unit includes a light guide plate 100 having an incident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 for reflecting light rays propagating vertically downward; a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protruding from the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through theapex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets. The liquid crystal panel 600 is coupled to the backlight unit, and has liquid crystal cells arranged in an active matrix type to adjust the degree of transmission of projected light so that images are displayed by the light projected by the backlight unit.

[153] As mentionedabove, those skilled in the art can easily understand that the reversed prism peaks may have a heptagonal cross section that is asymmetric horizontally about the vertical line. In addition, the cross section is not limited to the heptagon, and a prism sheet having reversed prism peaks with more verticesmay be used for the backlight unit and the LCD.

[154] As such, the polygonal reversed prism peaks of the prism sheet, the backlight unit, and the LCD according to an embodiment of the present invention do not emit all light in the upward direction (brightness improving direction) via the base region of the reversed prism peaks, but emit a portion of light by the second regions of the reversed prism peaks in a direction for improving characteristics regarding the field of view. This both guarantees a wide field of view and prevents the loss of light due to the conventional prism structure.

[155] FIGs. 33 and 34 also show positionsA and B on the light guide plate 100, in which a light source can be installed. Particularly, the light source may be installedin position A or B on the lateral surface of the light guide plate 100.

[156] A backlight unit using a light guide plate having polygonal prism peaks on its light emission surface and a prism sheet having polygonal reversed prism peaks according to the present invention will now be described.

[157] FIG. 35 shows the construction of a backlight unit including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention. FIG. 36 shows the construction of another backlight unit including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention.

[158] Referring to FIG. 35, abacklight unit according to the present invention includes a light guide plate 100 having a plurality of prism peaks formed on its emission surface to have a heptagonal cross section symmetric horizontally about a verticalline extending through the apex, the left and right sides of each prism peak being bent to define first, second, and third regions of the prism peak, the light guide plate 100 having an incident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 positioned below the light guide plate 100 to reflect light rays propagating vertically downward; a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protruding from the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets before theLCD is assembled. The prism peaks of the light guide plate 100 and the reversed prism peaks of the prism sheet 200 are formed in the same direction.

[159] FIG. 35 shows positions A and B on the light guide plate 100, in which a light source can be installed. Particularly, the light source may be installed in position A or B on the lateral surface of the light guide plate 100.

[160] Referring to FIG. 36, another backlight unit according to the present invention includes a light guide plate 100 having a plurality of prism peaks formed on its emission surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each prism peak being bent to define first, second, and third regions of the prism peak, the light guide plate 100 having an incident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 positioned below the light guide plate 100 to reflect light rays propagating vertically downward; a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protruding from the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets before theLCD is assembled. The prism peaks of the light guide plate 100 and the reversed prism peaks of the prism sheet 200 are formed in perpendicular directions.

[161] FIG. 36 shows positions A and B on the light guide plate 100, in which a light source can be installed. Particularly, the light source may be installed in position A or B on the lateral surface of the light guide plate 100.

[162] As mentioned above, those skilled in the art can easily understand that the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet may have a heptagonal cross section that is asymmetric horizontally about the vertical line. In addition, the cross section is not limited to the heptagon, and prism peaks and reversed prism peaks having more vertices may be used to constitute the backlight unit.

[163] The diffusion sheet 300 may be a separate component as mentioned above. Alternatively, the upper surface of the prism sheet 200 may be subjected to diffusion treatment so that no separate diffusion sheet 300 is necessary to constitute the backlight unit.

[164] An LCD using a light guide plate having polygonal prism peaks on its light emission surface and a prism sheet having polygonal reversed prism peaks according to the present invention will now be described.

[165] FIG. 37 shows the construction of an LCD includinga light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention. FIG. 38 shows the construction of another LCD including a light guide plate having polygonal prism peaks and a prism sheet having polygonal reversed prism peaks according to the present invention.

[166] Referring to FIG. 37, an LCD according to the present invention includes a back- lightunit and a liquid crystal panel 600. The backlight unit includes a light guide plate 100 having a plurality of prism peaks formed on its emission surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each prism peak being bent to define first, second, and third regions of the prism peak, the light guide plate 100 having an incident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 positioned below the light guide plate 100 to reflect light rays propagating vertically downward; a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protrudingfrom the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets before theLCD is assembled. The liquid crystal panel 600 is coupled to the backlight unit, and has liquid crystal cells arranged in an active matrix type to adjust the degree of transmission of projected light so that images are displayed by the light projected by the backlight unit. The prism peaks of the light guide plate 100 and the reversed prism peaks of the prism sheet 200 are formed in the same direction.

[167] FIG. 37 shows positions A and B on the light guide plate 100, in which a light source can be installed. Particularly, the light source may be installed in position A or B on the lateral surface of the light guide plate 100.

[168] Referring to FIG. 38, another LCD according to the present invention includes a backlightunit and a liquid crystal panel 600. The backlight unit includes a light guide plate 100 having a plurality of prism peaks formed on its emission surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each prism peak being bent to define first, second, and third regions of the prism peak, the light guide plate 100 having an inc ident surface, on which light rays from a light source are incident and are diffused, reflected, and refracted to change the direction of propagation so that they are uniformly emitted upward; a reflection sheet 400 positioned below the light guide plate 100 to reflect light rays propagating vertically downward; a prism sheet 200 positioned on top of the light guide plate 100, the prism sheet 200 having reversed prism peaks protruding from the lower surface to have a heptagonal cross section symmetric horizontally about a vertical line extending through the apex, the left and right sides of each reversed prism peak being bent to define first, second, and third regions of the reversed prism peak; a diffusion sheet 300 positioned on top of the prism sheet 200 to increase the uniformity of light; and a protection sheet 500 for stabilizing the color coordinate and protecting the sheets before theLCD is assembled. The liquid crystal panel 600 is coupled to the backlight unit, and has liquid crystal cells arranged in an active matrix type to adjust the degree of transmission of projected light so that images are displayed by the light projected by the backlight unit. The prism peaks of the light guide plate 100 and the reversed prism peaks of the prism sheet 200 are formed in perpendicular directions.

[169] FIG. 38 shows positions A and B on the light guide plate 100, in which a light source can be installed. Particularly, the light source may be installedin position A or B on the lateral surface of the light guide plate 100.

[170] The diffusion sheet 300 may be a separate component as mentioned above. Alternatively, the upper surface of the prism sheet 200 may be subjected to diffusion treatment so that no separate diffusion sheet 300 is necessary to constitute the backlight unit.

[171] As mentioned above, those skilled in the art can easily understand that the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet may have a heptagonal cross section that is asymmetric horizontally about the vertical line. In addition, the cross section is not limited to the heptagon, and prism peaks and reversed prism peaks having more vertices may be used to constitute the backlight unit and the

LCD.

Industrial Applicability

[172] The inventive prism sheet and light guide plate having reversed prism peaks and prism peaks, respectively, based on a polygonal prism structure, as well as a backlight unit and an LCD using the same improve both brightness and characteristics regarding the field of view.

[173] Although several exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A prism sheet for refracting light incident on a lower surface to concentrate the light toward an upper portion by using a polygonal prism structure, the prism sheet comprising: a plurality of reversed prism peaks protruding from a reversed prism peak base region on the lower surface of the prism sheet, wherein each reversed prism peak is configured in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, and left and right sides of each reversed prism peak are bent to define first, second, and third regions of each reversed prism peak.

[2] A prism sheet for refracting light incident on a lower surface to concentrate the light toward an upper portion by using a polygonal prism structure, the prism sheet comprising: a plurality of reversed prism peaks protruding from a reversed prism peak base region on the lower surface of the prism sheet, wherein each reversed prism peak is configured in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, and left and right sides of each reversed prism peak are bent to define first, second, and third regions of each reversed prism peak.

[3] The prism sheet as claimed in claim 1 or 2, wherein light incident on an incident surface of a reversed prism peak undergoes secondary reflection by a second region of the reversed prism peak opposite the incident surface.

[4] The prism sheet as claimed in claim 1 or 2, wherein the first regions of each reversed prism peak have a first end extending downward at an angle from the reversed prism peak base region on the lower surface of the prism sheet, the second regions of each reversed prism peak have a first end bent inward from a second end of the first regions of each reversed prism peak to extend downward at an angle, and the third regions of each reversed prism peak are bent outward from a second end of the second regions of each reversed prism to extend downward at an angle so that left and right third regions of each reversed prism peak are joined at the apex of each reversed prism peak.

[5] The prism sheet as claimed in claim 1 or 2, wherein an interior angle ( α) between the first and second regions of each reversed prism peak constitutes a minor angle smaller than 180° and an interior angle (β) between the second and third regions of each reversed prism peak constitutes a major angle larger than 180°.

[6] The prism sheet as claimed in claim 1 or 2, wherein a height (hi) of first vertices from the reversed prism peak base region is larger than lμm, the first and second regions of each reversed prism peak being joined at the first vertices, and a difference (h3-h2) between a height (h3) of the apex and a height (h2) of second vertices is larger than lμm, the second and third regions of each reversed prism peak being joined at the second vertices.

[7] The prism sheet as claimed in claim 6, wherein the height (hi) of the first vertices of each reversed prism peak from the reversed prism peak base region is in a range of l-12μm, and the height (h2) of the second vertices of each reversed prism peak from the reversed prism peak base region is in a range of 13-23μm.

[8] The prism sheet as claimed in claim 6, wherein the height (h3) of the apex of each reversed prism peak from the reversed prism peak base region is 24μm.

[9] The prism sheet as claimed in claim 6, wherein the reversed prism peak base region has a length (w) of 50μm, 24μm, or 25 μm.

[10] The prism sheet as claimed in claim 1 or 2, wherein an interior angle (θ) of the second regions of each reversed prism peak relative to the reversed prism peak base region is in a range of 0-43.73°.

[11] The prism sheet as claimed in claim 1 or 2, wherein an interior angle (δ) between the reversed prism peak base region and the first regions of each reversed prism peak is 40-60°.

[12] The prism sheet as claimed in claim 1 or 2, wherein an interior angle between opposite third regions joined at the apex of each reversed prism peak is 50-80°.

[13] The prism sheet as claimed in claim 1 or 2, wherein an interior angle between opposite third regions joined at the apex of each reversed prism peak is 68°.

[14] The prism sheet as claimed in claim 1 or 2, wherein the prism sheet having polygonal reversed prism peaks is made of a material having a refractive index of

1.52-1.62.

[15] A backlight unit having a prism sheet using a polygonal prism structure, the backlight unit comprising: a light guide plate for diffusing, reflecting, and refracting light rays from a light source to modify a propagation direction of the light rays so that the light rays are uniformly emitted toward an upper portion; a reflection sheet for reflecting light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets.

[16] A liquid crystal display having a prism sheet using a polygonal prism structure, the liquid crystal display comprising: a backlight unit comprising a light guide plate for diffusing, reflecting, and refracting light rays from a light source to modify a propagation direction of the light rays so that the light rays are uniformly emitted toward an upper portion, a reflection sheet for reflecting light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

[17] A light guide plate using a polygonal prism structure, the light guide plate comprising: a plurality of prism peaks positioned on an emission surface, wherein each prism peak has a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, and left and right sides of each prism peak of the light guide plate are bent to define first, second, and third regions of each prism peak so that light rays from a light source are emitted toward an upper portion.

[18] A light guide plate using a polygonal prism structure, the light guide plate comprising: a plurality of prism peaks positioned on an emission surface, wherein each prism peak has a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, and left and right sides of each prism peak of the light guide plate are bent to define first, second, and third regions of each prism peak so that light rays from a light source are emitted toward an upper portion.

[19] The light guide plate as claimed in claim 17 or 18, wherein the first regions of each prism peak have a first end extending downward at an angle from a prism peak base region on a lower surface of the light guide plate, the second regions of each prism peak have a first end bent inward from a second end of the first regions of each prism peak to extend downward at an angle, and the third regions of each prism peak are bent outward from a second end of the second regions of the prism peak to extend downward at an angle so that left and right third regions of each prism peak are joined at the apex of each prism peak.

[20] The light guide plate as claimed in claim 19, wherein an interior angle (α) between the first and second regions of each prism peak constitutes a minor angle smaller than 180° and an interior angle (β) between the second and third regions of each prism peak constitutes a major angle larger than 180°.

[21] The light guide plate as claimed in claim 19, wherein a height (hi) of first vertices from the prism peak base region is larger than lμm, the first and second regions of each prism peak being joined at the first vertices, and a difference (h3-h2) between a height (h3) of the apex and a height (h2) of second vertices is larger than lμm, the second and third regions of each prism peak being joined at the second vertices.

[22] The light guide plate as claimed in claim 19, wherein an interior angle (θ) of the second regions of each prism peak relative to the prism peak base region is in a range of 0-43.73°.

[23] The light guide plate as claimed in claim 19, wherein an interior angle (δ) between the prism peak base region and the first regions of each prism peak is 35-60°.

[24] The light guide plate as claimed in claim 19, wherein an interior angle between opposite third regions joined at the apex of each prism peak is 80-120°.

[25] The light guide plate as claimed in claim 19, wherein an interior angle between opposite third regions joined at the apex of each prism peak is 110°.

[26] The light guide plate as claimed in claim 19, wherein the light guide plate having polygonal prism peaks is made of a material having a refractive index of 1.52-1.62.

[27] The light guide plate as claimed in claim 26, wherein the light guide plate having polygonal prism peaks is made of a material comprising polymethylmethacrylate (PMMA) and polycarbonate (PC) for injection molding, and the material is selected from substances comprising mono- or di-acrylate series compounds, such as urethane acrylate and epoxy aery late, and poly olefin series compounds, such as polyester, polysiloxane, and polyether, so that UV curing is possible.

[28] The light guide plate as claimed in claim 19, wherein an interior angle (α) between the first and second regions of each prism peak constitutes a minor angle smaller than 180° and an interior angle (β) between the second and third regions of each prism peak constitutes a minor angle smaller than 180°.

[29] The light guide plate as claimed in claim 28, wherein the height (hi) of the first vertices of each prism peak from the prism peak base region is larger than the height (h2) of the second vertices.

[30] The light guide plate as claimed in claim 28, wherein the height (hi) of the first vertices of the prism peaks from the prism peak base region is varied between adjacent prism peaks of the light guide plate while the height (h3) of central apexes of the prism peaks from the prism peak base region remains constant so that irregular heights are repeated.

[31] The light guide plate as claimed in claim 19, wherein the first and second vertices of each prism peak are rounded to a predetermined extent, the first and second regions of each prism peak being joined at the first vertices, the second and third regions of each prism peak being joined at the second vertices.

[32] A backlight unit having a light guide plate using a polygonal prism structure, the backlight unit comprising: a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak; a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets before a liquid crystal display is assembled.

[33] A backlight unit having a light guide plate using a polygonal prism structure, the backlight unit comprising: a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak; a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward; a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak; a diffusion sheet positioned on top of the prism sheet to increase uniformity of light; and a protection sheet for stabilizing color coordinates and protecting the sheets before a liquid crystal display is assembled.

[34] The backlight unit as claimed in claim 32 or 33, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are formed in an identical propagation direction.

[35] The backlight unit as claimed in claim 32 or 33, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are formed in perpendicular propagation directions.

[36] The backlight unit as claimed in claim 32 or 33, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are arranged to face each other.

[37] The backlight unit as claimed in claim 32 or 33, wherein an upper surface of the prism sheet is subjected to diffusion treatment so that the backlight unit has no separate diffusion sheet.

[38] The backlight unit as claimed in claim 32 or 33, wherein the first regions of each prism peak of the light guide plate have a first end extending downward at an angle from a prism peak base region on a lower surface of the light guide plate, the second regions of each prism peak have a first end bent inward from a second end of the first regions of each prism peak to extend downward at an angle, and the third regions of each prism peak are bent outward from a second end of the second regions of each prism peak to extend downward at an angle so that left and right third regions of each prism peak are joined at the apex of each prism peak.

[39] The backlight unit as claimed in claim 32 or 33, wherein an interior angle (α) between the first and second regions of each prism peak of the light guide plate constitutes a minor angle smaller than 180° and an interior angle (β) between the second and third regions of each prism peak constitutes a major angle larger than 180°.

[40] The backlight unit as claimed in claim 32 or 33, wherein a height (hi) of first vertices from a prism peak base region is larger than lμm, the first and second regions of each prism peak of the light guide plate being joined at the first vertices, and a difference (h3-h2) between a height (h3) of the apex and a height (h2) of second vertices is larger than lμm, the second and third regions of each prism peak of the light guide plate being joined at the second vertices.

[41] The backlight unit as claimed in claim 32 or 33, wherein an interior angle (α) between the first and second regions of each prism peak of the light guide plate constitutes a minor angle smaller than 180° and an interior angle (β) between the second and third regions of each prism peak of the light guide plate constitutes a minor angle smaller than 180°.

[42] The backlight unit as claimed in claim 41, wherein the height (hi) of the first vertices of each prism peak of the light guide plate from a prism peak base region is larger than the height (h2) of the second vertices.

[43] The backlight unit as claimed in claim 41, wherein a height (hi) of the first vertices of the prism peaks of the light guide plate from a prism peak base region is varied between adjacent prism peaks of the light guide plate while a height (h3) of central apexes of the prism peaks of the light guide plate from the prism peak base region remains constant so that irregular heights are repeated.

[44] The backlight unit as claimed in claim 32 or 33, wherein the first and second vertices of each prism peak are rounded to a predetermined extent, the first and second regions of each prism peak being joined at the first vertices, the second and third regions of each prism peak being joined at the second vertices.

[45] A liquid crystal display having a light guide plate using a polygonal prism structure, the liquid crystal display comprising: a backlight unit comprising a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak, a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section symmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets before the liquid crystal display is assembled; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

[46] A liquid crystal display having a light guide plate using a polygonal prism structure, the liquid crystal display comprising: a backlight unit comprising a light guide plate having a plurality of prism peaks on an emission surface, each prism peak having a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each prism peak of the light guide plate being bent to define first, second, and third regions of each prism peak, a reflection sheet positioned below the light guide plate to reflect light rays propagating vertically downward, a prism sheet positioned on top of the light guide plate, the prism sheet having reversed prism peaks protruding from a lower surface in a heptagonal cross section asymmetric horizontally about a vertical line extending through an apex, left and right sides of each reversed prism peak being bent to define first, second, and third regions of each reversed prism peak, a diffusion sheet positioned on top of the prism sheet to increase uniformity of light, and a protection sheet for stabilizing color coordinates and protecting the sheets before the liquid crystal display is assembled; and a liquid crystal panel coupled to the backlight unit, the liquid crystal panel having liquid crystal cells arranged in an active matrix type for adjusting an amount of transmission of projected light so that images are displayed by light projected by the backlight unit.

[47] The liquid crystal display as claimed in claim 45 or 46, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are formed in an identical propagation direction.

[48] The liquid crystal display as claimed in claim 45 or 46, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are formed in perpendicular propagation directions.

[49] The liquid crystal display as claimed in claim 45 or 46, wherein the prism peaks of the light guide plate and the reversed prism peaks of the prism sheet are arranged to face each other.

[50] The liquid crystal display as claimed in claim 45 or 46, wherein an upper surface of the prism sheet is subjected to diffusion treatment so that the backlight unit has no separate diffusion sheet.