CHI, Chul Goo (#907, Sanbon D.O. Plus 1142-2 Sanbon-dong,Gunpo-si, Gyeonggi-do 435-040, KR)
JEONG, O Yong (#281-302, Hyundai Seongwoo 3-cha Apt.Sanghyeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-130, KR)
LEE, Seong Hoon (# Daewoo Prugio Apt, Gisan-ri Taean-eup, Hwaseong-si, Gyeonggi-do 445-972, 102-1002, KR)
KIM, Jae Han (MAS Group, 5th Floor R & D Center,of Cheil Industries Inc.,Gocheon-dong, Uiwang-si, Gyeonggi-do 437-711, KR)
JOO, Sung Hyun (#A-503, Samdeok Apt. 969-3 Hogye-3 dong,Dongan-gu, Anyang-si, Gyeonggi-do 431-849, KR)
CHI, Chul Goo (#907, Sanbon D.O. Plus 1142-2 Sanbon-dong,Gunpo-si, Gyeonggi-do 435-040, KR)
JEONG, O Yong (#281-302, Hyundai Seongwoo 3-cha Apt.Sanghyeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-130, KR)
LEE, Seong Hoon (# Daewoo Prugio Apt, Gisan-ri Taean-eup, Hwaseong-si, Gyeonggi-do 445-972, 102-1002, KR)
KIM, Jae Han (MAS Group, 5th Floor R & D Center,of Cheil Industries Inc.,Gocheon-dong, Uiwang-si, Gyeonggi-do 437-711, KR)
| [CLAIMS]
[Claim 1] A light guide panel for an LCD backlight unit, comprising a main body having a lateral side for receiving incident light, a front side for emitting light, and a rear side, wherein the front side is formed with asymmetric front prisms having a triangular cross-section, one inclined side of each asymmetric front prism being processed to have a smooth specular surface, and the other inclined side being processed to have a rough diffusion surface.
[Claim 2] A light guide panel for a liquid crystal display, comprising a main body having a lateral side for receiving incident light, a front side for emitting light, and a rear side, wherein the front side is formed with asymmetric front prisms having a trapezoidal cross-section, one inclined side of each asymmetric front prism being processed to have a smooth specular surface, and the other inclined side being processed to have a rough diffusion surface.
[Claim 3] The light guide panel according to claim 1 or 2, wherein the asymmetric front prisms are disposed to have the specular surfaces facing a center of the light guide panel.
[Claim 4] The light guide panel according to claim 1 or 2, wherein the asymmetric front prisms are disposed to have the diffusion surfaces facing a center of the light guide panel.
[Claim 5] The light guide panel according to claim 1, wherein the asymmetric front prism has a cross-section of an isosceles triangular shape.
[Claim 6] The light guide panel according to claim 2, wherein the asymmetric front prism has a cross-section of an isosceles trapezoidal shape.
[Claim 7] The light guide panel according to claim 1 or 5, wherein the asymmetric front prism has a vertex angle in the range of 40~140 degrees. [Claim 8] The light guide panel according to claim 2 or 6, wherein the asymmetric front prism has an angle in the range of 20-70 degrees defined between each inclined side and a vertical line.
[Claim 9] The light guide panel according to claim 1 or 2, wherein the asymmetric front prisms are separated a predetermined distance from one another to have a separation plane therebetween.
[Claim 10] The light guide panel according to claim 2, wherein a ratio of a short side (a) to a long side (b) of the asymmetric front prism is 0.5 or less. |
[DESCRIPTION]
[Invention Title]
LIGHT GUIDE PANEL COMPRISING ASYMMETRIC FRONT PRISM FOR LCD
[Technical Field]
The present invention relates to a light guide panel for a backlight unit of a liquid crystal display (LCD), and more particularly to a light guide panel for an LCD backlight unit that has asymmetric front prisms and enables adjustment of viewing angle and brightness at a specific position by controlling a cross-sectional shape of the front prisms of the light guide panel.
[Background Art]
In general, liquid crystal display (LCD) refers to a device that displays numerals or images through application of an electric field to liquid crystals, which are an intermediate phase material between a liquid and a solid, and which are arranged between two glass substrates acting as electrodes.
Since the LCD is not an emissive device, it must have a backlight unit as a light source for emitting light. Then, images and the like are displayed on a liquid crystal panel which has the liquid crystals arranged in a predetermined pattern and adjust a transmittance amount of light emitted from the backlight unit. Fig. 1 is an exploded perspective view of a conventional LCD backlight unit.
According to a position of a light source for emitting light, a backlight unit
10 of the liquid crystal display can be classified into a direct type backlight unit in which the light source is located directly at the rear of an LCD panel 100, and an edge type backlight unit in which the light source is located at a lateral side of the LCD panel 100. Fig. 1 shows an edge type backlight unit 10.
Referring to Fig. 1, the conventional LCD backlight unit includes a light
source 105, a light guide panel 110, a reflection plate 115, a diffusion sheet 120, prism sheets 125, and a protector sheet 130.
The light source 105 serves to emanate light initially in the liquid crystal display. Although various types of light source can be used, the LCD generally employs a cold cathode fluorescence lamp (CCFL) that undergoes very low power consumption and emits very bright white light.
The light guide panel 110 is located at one side of the light source 105 below the LCD panel 100 and serves to project light in front of the light guide panel after converting spot light of the light source 105 into plane light. The reflection plate 115 is located at the rear of the light guide panel 110 and serves to reflect light emitted from the light source 105 towards the LCD panel 100 positioned in front of the reflection plate.
The diffusion sheet 120 is located at an upper side of the light guide panel 110 and serves to provide uniform light that has passed through the light guide panel 110.
The prism sheets 125 serve to improve brightness by refracting and collecting light that tends to undergo a rapid decrease in brightness due to diffusion in both directions, i.e., horizontal and vertical directions while passing through the diffusion sheet 120. The protector sheet 130 is disposed on the prism sheet, and serves to protect the prism sheets 125 from damage such as scratches and to prevent the Moire phenomenon that occurs when using prism sheets 125 stacked in two layers in the horizontal and vertical directions.
Although not shown in Fig. 1, the backlight unit 10 further includes a mold frame or housing, which serves to secure respective components of the backlight unit 10 so as to allow the backlight unit 10 to be prepared as an integral component, and a back cover or lamp cover, which serves to protect and support the backlight unit 10 while maintaining the strength of the backlight unit 10.
Figs. 2 and 3 are enlarged cross-sectional views of the light guide panel 110,
illustrating progress of light emitted from the light source 105 and passing through the light guide panel 110.
As shown in Fig. 2, the light source 105 is generally disposed near one edge of the backlight unit 10 (for LCD TV, right behind the LCD panel). Thus, light emitted from the light source 105 is not uniformly transmitted throughout the overall surface of the backlight unit, and the edges of the backlight unit tend to be brighter than other parts. The light guide panel 110 is employed to prevent such problems. The light guide panel 110 is generally made of a transparent acryl resin, which ensures a high strength of the light guide panel. Thus, the light guide panel 110 is not likely to be broken or deformed and has a light weight and a high transmittance.
The light guide panel 110 serves to guide light emitted from the light source
105 to advance uniformly in front of the light guide panel. In actuality, however, when light is emitted from the light source disposed near the light guide panel with the backlight unit 10 disassembled, it can be observed that the light guide panel does not exhibit uniform brightness, and that light is concentrated at opposite ends of the light guide panel. This is because the light guide panel 110 leads the light from the light source 105 in opposite directions.
Thus, as shown in Fig. 3, special treatment is performed on the rear side of the light guide panel 110 to induce scattered reflection therefrom so that the overall light guide panel 110 transmits light uniformly. Specifically, prominences and depressions 113 each having a predetermined shape designed in consideration of the distance from the light source 105 are formed on the rear side. With such a pattern treatment of forming the prominences and depressions 113, plane light having higher brightness and uniformity can be obtained on the LCD panel. The LCD can be classified into a twisted nematic (TN) type and an in-plane switching (IPS) type depending on the arrangement of liquid crystals. The TN type LCD provides an inferior viewing angle to the IPS type LCD. However, since it has excellent transmittance, the TN type LCD is suitable for an LCD that requires front visibility. On the other hand, although the IPS type LCD provides an
excellent viewing angle compared to the TN type LCD, it has lower transmittance, which deteriorates overall brightness.
There is often a need for improving the brightness of an LCD at a specific angle or at a specific position depending on operation surroundings, kinds of LCD panel related to liquid crystals arrangement, and other external factors.
Conventionally, a dual brightness enhancement film (DBEF) and a diffusive reflective polarization film (DRPF) have been used to improve brightness or viewing angle. However, these films lead to an increase in total thickness of the backlight unit along with an increase in manufacturing cost, thereby lowering competitiveness of LCD products incorporating such films.
The brightness uniformity- vie wing angle dependency item of the TCO '03 standard regulates that degrees of brightness uniformity with respect to horizontal and vertical views of a general visual display unit should be managed to fall within a specified range. Fig. 4 shows measurement locations defined in the TCO '03 standard for characteristics evaluation of a general visual display unit.
Figs. 5 and 6 show the TCO '03 standard with respect to brightness uniformity-viewing angle dependency, in which degrees of brightness uniformity with respect to horizontal and vertical views are respectively defined as L H and Ly, and are regulated to have a value of 1.7 or less. The TCO '03 standard is a severe obstacle to development of TN mode liquid crystal displays (LCDs) having a relatively large restriction in viewing angle of a display, and components or techniques for controlling a viewing angle at a specific location and angle in a backlight unit for LCDs have been developed.
Accordingly, there is a need for techniques to improve brightness and viewing angle of LCD without using films.
[Disclosure] [Technical Problem]
The present invention has been made in view of the above problems, and an
aspect of the present invention is to provide a light guide panel for an LCD backlight unit that not only enables adjustment in visibility at a specific location and in viewing angle at a specific angle, but also satisfies the TCO '03 standard.
[Technical Solution]
In accordance with an aspect of the present invention, a light guide panel for an LCD backlight unit includes a main body having a lateral side for receiving incident light, a front side for emitting light, and a rear side, wherein the front side is formed with an asymmetric front prism having a triangular cross-section, one inclined side of the front prism being processed to have a smooth specular surface, and the other inclined side being processed to have a rough diffusion surface.
[Advantageous Effects]
According to the present invention, a light guide panel for an LCD backlight unit optimizes distribution of viewing angles corresponding to requirements of a display, thereby enabling efficient use of a light source of the backlight unit. In addition, the light guide panel is formed to have a slim thickness with low manufacturing costs, and satisfies, in particular, optical characteristics under the TCO '03 standard while ensuring high brightness and good viewing angle characteristics, by eliminating DBEF and DRPF that have been used for the conventional light guide panel.
[Description of Drawings]
Fig. 1 is an exploded perspective view of a conventional LCD backlight unit;
Figs. 2 and 3 are enlarged cross-sectional views of the light guide panel, illustrating progress of light emitted from a light source and passing through the light guide panel;
Fig. 4 shows measurement locations defined in the TCO'03 standard for characteristics evaluation of a general visual display unit;
Figs. 5 and 6 show the TCO'03 standard with respect to brightness uniformity-viewing angle dependency; Fig. 7 is a perspective view of a light guide panel for an LCD backlight unit according to one embodiment of the present invention;
Fig. 8 is a side section view of the light guide panel for the LCD backlight unit according to the embodiment of the present invention;
Fig. 9 is a side section view of a light guide panel for an LCD backlight unit according to another embodiment of the present invention;
Fig. 10 is a side section view of a light guide panel for an LCD backlight unit according to a further embodiment of the present invention; and
Figs. 11 to 14 are cross-sectional views of various examples of asymmetric front prisms.
[Best Mode]
In accordance with an aspect of the present invention, a light guide panel for an LCD backlight unit includes a main body having a lateral side for receiving incident light, a front side for emitting light, and a rear side, wherein the front side is formed with an asymmetric front prism having a triangular cross-section, one inclined side of the front prism being processed to have a smooth specular surface, and the other inclined side being processed to have a rough diffusion surface.
In accordance with another aspect of the present invention, a light guide panel for an LCD backlight unit includes a main body having a lateral side for receiving incident light, a front side for emitting light, and a rear side, wherein the front side is formed with an asymmetric front prism having a trapezoidal cross- section, one inclined side of the front prism being processed to have a smooth specular surface, and the other inclined side being processed to have a rough diffusion surface.
[Mode for Invention]
Fig. 7 is a perspective view of a light guide panel for an LCD backlight unit according to one embodiment of the present invention.
Referring to Fig. 7, a light guide panel 30 for an LCD backlight unit according to one embodiment of the present invention is generally made of a transparent acrylic material that has high strength. Thus, the light guide panel 30 is not likely to be broken or deformed, has a light weight, and exhibits high transmittance of visible light. The light guide panel 30 includes a main body 300, asymmetric front prisms 310, and rear prisms 320. The main body 300 includes a lateral side 301 for receiving incident light, a front side 303 that is connected to the lateral side 301 and faces an LCD panel (not shown), and a rear side 305 that is connected to the lateral side 301 and faces the front side 303.
The term "lateral side 301" means a side of an object, but is defined herein as a surface through which light emitted from a light source 306 enters the light guide panel. In Fig. 7, the lateral side 301 corresponds to two opposite sides adjacent to the light source 306.
The rear prisms 320 of a predetermined shape are formed on the rear side 305 and have a longitudinal direction perpendicular to an incident direction of light (Q direction) from the light source 306. That is, when the rear prisms 320 are disposed perpendicular to the incident direction (Q) of light emitted from the light source 306, they can cause effective diffraction, refraction, and diffusion of light. An aggregate of rear prisms 320 may constitute a predetermined dot pattern or stripe pattern. The front side 303 is formed with the asymmetric front prisms 310 that have a predetermined cross-sectional shape and serve to cause uniform diffraction, refraction, and diffusion of light emitted through the main body 300.
The asymmetric front prisms 310 are formed at regular intervals over the
front side 303, and have a longitudinal direction disposed parallel to the incident direction of light from the light source, i.e., Q direction, in Fig. 7.
Unlike conventional front prisms, each of the asymmetric front prisms 310 has one inclined side processed to have a rough diffusion surface 307 and the other inclined side processed to have a smooth specular surface 308 (although the term
"specular surface" generally means a mirror plane or a smooth plane, the "specular surface" of the asymmetric front prism means the latter herein).
Herein, the specular surface 308 preferably has an Ra value of 0.2 μm or less, which is a surface roughness corresponding to abrasive finishing under Korean Standards (KS), and the diffusion surface 307 preferably has an Ra value of 6.3 μm or more, which is a surface roughness corresponding to normal finishing under KS.
In this embodiment, the specular surface 308 and the diffusion surface 307 are respectively suggested to have Ra values of 0.2 μm and 6.3 μm with reference to the regulation of surface roughness under KS. In this regard, experimental testing of the present invention showed that, when both the specular surface 308 and the diffusion surface 307 had an Ra value of about 0.2 μm, L H of the TCO'03 standard was about 1.9. Further, when the diffusion surface 307 had an Ra value of about 5 μm, L H value of the TCO'03 standard was about 1.7, and when the diffusion surface 307 had an Ra value of about 10 μm, L H value of the TCO '03 standard was about 1.4. That is, in the case of an Ra value of about 5 μm or less for the diffusion surface 307, although the light guide panel does not exhibit significantly improved effects in view of brightness uniformity-viewing angle dependency of the
TCO'03 standard, this light guide panel also satisfies the TCO'03 standard.
However, in order to obtain further improved effects, it is desirable that the diffusion surface 307 have as high an Ra value as possible.
Fig. 8 is a side section view of the light guide panel for the LCD backlight unit according to the embodiment of the present invention.
Referring to Fig, 8, the asymmetric front prisms 310 are disposed on the front side such that the specular surfaces 308 of the front prisms 310 face right and
left sides 301 of the light guide panel and the diffusion surfaces of the front prisms 310 face the center of the light guide panel. This arrangement is conceived to improve viewing angle characteristics and to satisfy the TCO '03 standard through enhancement in side visibility. In other words, the right and left inclined sides of the asymmetric front prisms 310 have different optical surface characteristics such that the specular surfaces 308 of the front prisms 310 can provide optical functions of general prisms and the diffusion surfaces 307 can provide a diffusion function as well as the optical functions of general prisms. Hence, when the asymmetric front prisms 310 cause diffraction, refraction and diffusion of light emitted from the main body 300 in a direction inclined to an LCD panel (not shown) facing the light guide panel 30, the configuration of the asymmetric front prisms 310 can further improve uniformity of light reaching the LCD panel (not shown).
In Fig. 8, the asymmetric front prisms 310 have a vertical cross-section of an asymmetric triangular shape, with the specular surfaces 308 disposed to face the right and left sides of the light guide panel 30 in opposite directions. Although this configuration of the asymmetric front prisms 310 is provided to satisfy the most suitable viewing distribution under the TCO'03 standard, it can be modified to have the diffusion surfaces 307 disposed to face the right and left sides of the light guide panel 30.
Fig. 9 is a side section view of a light guide panel for an LCD backlight unit according to another embodiment of the present invention.
Compared to the embodiment of Fig. 8, the specular surfaces 308 of Fig. 9 are disposed to face the center of the light guide panel. Such a disposition of the specular surfaces 308 improves visibility from the front side of a display. In other words, improvement in visibility of the lateral side or improvement in visibility of the front side can be selected by arranging the specular surfaces as shown in Fig. 8 or Fig. 9 depending on the kind of display.
Fig. 10 is a side section view of a light guide panel for an LCD backlight
unit according to a further embodiment of the present invention.
Referring to Fig. 10, a separation space is defined between the prisms to form a separation plane 315, by which light can be directed perpendicular to the LCD panel (not shown) to further improve the uniformity of light reaching the LCD unit (not shown).
As described above, the vertical cross-section of the asymmetric front prisms 310 has the asymmetric triangular shape in the embodiments of Figs. 7 to 10. However, it should be noted that the present invention is not limited to this configuration. For example, the vertical cross-section of the asymmetric front prisms 310 may have a trapezoidal shape, or a reverse groove shape that has a pointed vertex and a predetermined radius of curvature at each side.
Figs. 11 to 14 are cross-sectional views of various examples of asymmetric front prisms.
Referring to Figs. 11 and 12, the asymmetric front prisms 310 have a triangular shape and a prism angle (θl + θ2 ) in the range of 40~140 degrees. For the asymmetric front prism of Fig. 11, θl and θ2 are different values, and for the asymmetric front prism of Fig. 12, θl and θ2 arc the same value.
Referring to Figs. 13 and 14, the asymmetric front prisms 310 have a trapezoidal shape and a prism angle (θl + θ2 ) in the range of 20~70 degrees. For the asymmetric front prism of Fig. 13, θl and θ2 are different values, and for the asymmetric front prism of Fig. 14, θl and θ2 are the same value.
As described above, the asymmetric front prisms 310 can be modified in various shapes.
On the other hand, when the asymmetric front prisms 310 have the trapezoidal shape as shown in Figs. 13 and 14, a ratio of the short side to the long side parallel to each other is preferably 0.5 or less. If the ratio of the short side to the long side of the trapezoidal shape is greater than 0.5, an area ratio of a planar surface to the overall shape becomes excessively increased, causing brightness deterioration.