KR20100105927A - Backlight unit of direct light type - Google Patents

Abstract

PURPOSE: A direct-type back light unit is provided to supply the light by a plurality of light diverging unit to a liquid panel, thereby removing an optical sheet such as light diffusing plate or prism sheet. CONSTITUTION: A plurality of insertion grooves(110) or a plurality of diffraction grids is formed on lower side of the light guide plate(100). A plurality of light diverging unit(200) is arranged to the upper side of the light guide plate. The light diverging unit diverges light propagating inside the light guide plate to upper side by internal total reflection. A plurality of LED(Light Emitting Diodes)(310) is respectively arranged to the insertion groove or lower part of the diffraction lattice. A plurality of leasing members(400a) or a plurality of condensing lenses is induces light of the LED inside the light guide plate.

Description

Direct backlight unit {Backlight unit of direct light type}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit for a liquid crystal display (LCD), and more particularly, to a direct type backlight unit in which a light source such as a light emitting diode (LED) is disposed directly below a liquid crystal panel. will be.

In general, a backlight unit for a liquid crystal display device includes a direct light type in which the light source is arranged directly under the liquid crystal panel, and an edge type in which the light source is provided on the side of the light guide plate, depending on the installation mode of the light source constituting the backlight. It is divided into (Edge light type).

The direct type backlight unit is capable of large screens of liquid crystal panels, and it is possible to drive LEDs by location according to the brightness of an image. In addition, in recent years, LEDs have been used as new light sources instead of CFLs or External Electrode Fluorescence Lamps (EEFLs), which have been generally used as the light source for the purpose of energy efficiency and high image quality. It is a recent trend.

1 shows an example of a liquid crystal display device employing a general direct type backlight unit, and FIG. 2 shows a liquid crystal display device employing a conventional direct type backlight unit using an LED as a light source.

As shown in FIG. 1, a conventional liquid crystal display device includes a liquid crystal panel 20 including a liquid crystal pixel 23 that acts as a light valve by controlling light transmittance and a backlight for supplying light to the liquid crystal panel 20. It consists of the unit 10.

The backlight unit 10 reflects the light source assembly 11 portion including the CCFL 11a or the EEFL, and the light emitted from the light source from the reflector 11b located under the light source or evenly mixes the light through the light sheet. Is composed of light sheets scattered by the liquid crystal pixels 23. The light sheet is basically composed of a diffusion plate 12, a diffusion sheet 13, a light collecting sheet 14, a reflective polarizing sheet 15, and a protective film 16 and the like to properly adjust the viewing angle and brightness.

The liquid crystal panel 20 includes a rear glass substrate 22 having a TFT (Thin Film Transistor), a front glass substrate 25 having a color filter 24, a rear glass substrate 22 and a front glass substrate 25. And a plurality of liquid crystal pixels 23 to be installed, a polarizing sheet A 21 attached to the rear glass substrate 22, a polarizing sheet B 26 attached to the front glass substrate 25, and the like.

Alternatively, as shown in FIG. 2, in a direct type LCD using a white light LED or R, G, and B LEDs 11c emitting three colors of R, G, and B, the LED 11c corresponding to the light source of the backlight unit 10 may be used. In order to remove bright bright spots and to obtain light with uniform brightness across the entire backlight, the diffusion plate 12, the diffusion sheet 13, and the like are used, and the prism sheet 14a or the micro One or more lens array sheets were used. Here, R, G, and B are the abbreviations of Red, Green and Blue, respectively, and R, G, and B refer to red, green, and blue without further indication.

In particular, when the LED 11c of FIG. 2, which has been increasingly adopted for the purpose of energy saving and high image quality, is used as a light source, when the distance S between the liquid crystal panel 20 and the LED 11c becomes small, sufficient light mixing effect does not occur well. May cause spots or spots to appear on the screen. This phenomenon becomes worse as the distance between the LED 11c and the liquid crystal panel 20 gets closer by adopting a thin backlight.

On the other hand, edge backlights using a plurality of LEDs on the edge instead of direct backlights and using light guide plates are suitable for small LCDs that consume less power. Recently, edge type LED backlight is used for the backlight of large LCD TVs, but there are problems of high heat generation and local dimming technology.

The present invention is to remove the diffuser plate (diffuser plate) used in the direct backlight, and to remove the bright spots and spots that occur when placing a plurality of LEDs in a direct type effectively thin direct type that can obtain a uniform illumination Its purpose is to provide a backlight unit.

The direct type backlight unit according to the present invention includes a light guide plate having a plurality of insertion grooves or a plurality of diffraction gratings formed on a lower surface thereof; A plurality of light splitting parts disposed on an upper surface of the light guide plate to split light traveling through the light guide plate upward by total internal reflection; A plurality of LEDs respectively disposed below the insertion groove or the diffraction grating; And a plurality of photoconductors or a plurality of condenser lenses disposed between the insertion groove or the diffraction grating and the LED, and guide the light from the LED into the light guide plate.

Here, the photoconductor, the light of the LED incident to the lower guided by the total internal reflection to the upper, and the light diffusion disposed in the upper portion which is inserted into the insertion groove so that the light guided to the upper guided into the light guide plate. It may further include cotton.

In addition, the photoconductor may have an inverted cone shape and may be inserted into an upper portion of the insertion groove, and a reflective material may be coated on a surface thereof to reflect light from the LED and to enter the light guide plate.

In addition, the light splitter may be integrally formed with the light guide plate.

In addition, the light splitter may have a shape of a reverse circular truncated cone or a reverse prism.

Further, an angle formed between the side surface of the light splitter and the top surface of the light guide plate may be in a range of 45 degrees to 75 degrees.

In addition, the optical branches may have a sinusoidal grating or binary grating having a cross-sectional shape. The light splitter may be a plurality of micro lenses.

In addition, the diffraction grating may be arranged to form a plurality of concentric circles on a plane. In addition, the diffraction grating may have a sinusoidal grating or binary grating having a cross-sectional shape.

Furthermore, the LED may be an RGB LED or a white light LED having red, green, and blue LEDs.

According to the direct type backlight unit of the present invention,

First, compared to a conventional LED backlight using a spaced space between the LED and the diffusion plate and using the diffusion plate, the diffusion sheet and the light collecting sheet, it is possible to effectively dissipate heat generated in the LED while achieving a much thinner thickness.

Second, since it is a direct backlight, it is possible to apply division driving technology, achieve high contrast ratio, and reduce power consumption.

Third, since the illumination light having an appropriate viewing angle and vertical luminance illuminates the liquid crystal panel by the plurality of light splitting parts, it is possible to remove the optical sheet such as a diffuser plate or a prism sheet, which is advantageous in cost reduction.

Fourth, when inducing the light of the RGB LED into the light guide together, it is possible to achieve a sufficient color mixing to remove the color blur effect, and at the same time can achieve a high image quality by the RGB LED light.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

Hereinafter, the direct type backlight unit according to the first embodiment of the present invention will be described with reference to FIGS. 3 and 4. 3 is a cross-sectional view illustrating a direct backlight unit according to a first embodiment of the present invention, and FIG. 4 is a partially enlarged view of P shown in FIG. 3.

The direct type backlight unit includes a light guide plate 100, a light branch 200, a plurality of white light LEDs 310, and a plurality of light guides 400a. The light guide plate 100 has a plurality of insertion grooves 110 formed on the bottom surface thereof. A plurality of light splitters 200 are disposed on an upper surface of the light guide plate 100 to split light traveling through the light guide plate 100 to an upper side where the liquid crystal panel LP is located by total internal reflection. The white light LEDs 310 are disposed under the insertion groove 110, respectively. The photoconductors 400a are disposed between the insertion groove 110 and the white light LED 310 and serve to guide light emitted from the white light LED 310 into the light guide plate 100.

The photoconductor 400a has a cylindrical shape or a rod shape, and guides the light of the white light LED 310 incident to the lower side to the upper side by total internal reflection at the side of the photoguide. In addition, a light diffusion surface 410a is disposed on a surface of the light guide 400a inserted into the insertion groove 110 to allow the light guided upward to enter the light guide plate. The LED cup 350 is disposed below the white light LED 310. The photoconductor 400a, the white light LED 310, and the LED cup 350 may all be made integrally to form the LED assembly 300A.

A diffusion sheet 210 may be disposed between the liquid crystal panel LP and the light guide plate 100 to adjust the diffusion angle of the light and to improve the uniformity of the light.

Referring to FIG. 4, the light once entered into the light guide plate 100 passes through the inside of the light guide plate 100 again by total internal reflection. In this case, a plurality of light splitting parts having a shape of a reverse circular truncated cone or a reverse prism in order to branch the light traveling in the light guide plate 100 vertically upwards in which the liquid crystal panel LP is located ( 200 is installed on the upper surface of the light guide plate 100. Light entering the light splitting part 200 is vertically branched toward the liquid crystal panel LP by total internal reflection.

5 is a plan view showing a tiled arrangement of the LED according to an embodiment of the present invention, Figure 6 is a plan view showing a honeycomb arrangement of the LED according to an embodiment of the present invention.

The white light LED 310 and the insertion groove 110 of the lower surface of the light guide plate 100 corresponding thereto are regularly arranged in a tiled manner as shown in FIG. 5.

Alternatively, as shown in FIG. 6, the white light LED 310 and the insertion groove 110 in the lower surface of the light guide plate 100 are disposed in a honeycomb shape. The white light LED 310 may be the LED assembly 300A described above. At this time, each of the white light LED 310 and the insertion groove 110 is further provided with a light compartment 500 in the lower portion of the light guide plate to partition each other. The light compartment 500 is not a hardware structure, and represents an effective area of light when light from one LED assembly 300A diffuses in all directions by total internal reflection inside the light guide plate. The effective area of the light may overlap with the effective area of the light emitted from the LED assemblies adjacent to each other.

7A to 7C are perspective and enlarged perspective views illustrating the light splitter illustrated in FIG. 3. Such an optical splitter may be applied to the second to fourth embodiments to be described later. Referring to FIG. 7A, the light splitting parts 200 are disposed on the upper surface of the light guide plate 100 to vertically branch light propagated by total internal reflection in the light guide plate toward the liquid crystal panel. The light splitter 200 may be integrally formed with the light guide plate 100.

In addition, an inverted truncated light branch 200a as shown in FIG. 7B or an inverted prism shaped light branch 200b as shown in FIG. 9C may be used.

In more detail, the upper diameter D ₁ , the lower diameter D ₂ , and the height H of the inverted truncated light diverging portion 200a shown in FIG. 7B may be divided into light beams so that the diverged light may be branched perpendicular to the light guide plate 100. The angle α formed between the side of the base 200a and the top surface of the light guide plate 100 is combined between about 45 degrees and 75 degrees. In addition, the inverted prism type light splitting portion 200b shown in FIG. 7B has a width D ₃ , a length L, a height E, and a width D ₄ of the lower surface of the light splitting portions 200a and 200b. The angle β formed between the side surface and the upper surface of the light guide plate 100 is made to be in the range of about 45 degrees to 75 degrees.

FIG. 8 is a partially enlarged plan view of the light partition shown in FIG. 6. 8 illustrates a method of arranging the light splitter 200 on an upper surface of the light guide plate 100 based on the LED assembly. After the light emitted from the LED assemblies 300A and 300B proceeds through the photoconductor 400a, the light is guided into the light guide plate 100 through the insertion groove 110 formed in the lower part of the light guide plate 100, and spreads to the side surface. At this time, the LED light is strong in the area A close to the LED assemblies 300A and 300B and the insertion groove 110, and is diffused and weakened in the far area B. Since the intensity of light branched from all the light splitting parts 200 and rising vertically should be equal, the size of the bottom surface D ₂ of the inverted conical light splitting part 200a into which the light enters the light splitting part 200 or the inverse prism light splitting is performed. The lower surface of the base 200b should be larger as the size of D ₂ is farther from the positions of the photoconductor 400a and the insertion groove 110. Alternatively, when the size of the light splitter 400 is the same, the number of the light splitters 400 per unit area should increase as the distance from the region A close to the insertion groove 110 increases. Since the light intensity decreases in inverse proportion to the square of the distance from the LED assemblies 300A and 300B, the number of the light splitting parts 400 should increase in proportion to the square of the distance from the LED assemblies 300A and 300B. .

FIG. 9 is a graph showing simulation results of a first embodiment of the present invention utilizing light tools, which are programs for designing lighting by three-dimensional solid modeling. FIG. 9 shows a luminance angular distribution measured on a direct backlight unit according to the present invention, and it can be seen that light is emitted vertically with a viewing angle of about 90 degrees required for an LCD.

10 is a cross-sectional view of the direct type backlight unit according to the second embodiment.

Referring to FIG. 10, in the first embodiment, the white light LED 310 using the phosphor and one blue LED or the ultraviolet LED is simple in structure and convenient to apply, but has a disadvantage in poor image quality. RGB LEDs 320 with red, green and blue LEDs are used. In this case, in order to achieve high image quality, the R, G, and B light emitted from the RGB LED 320 are simultaneously incident into the photoconductor 400a, and the white light is mixed evenly while guided by total internal reflection inside the photoconductor 400a. Make The white light may be diffused from the light diffusion surface 410a provided on the light guide 400a to be incident into the light guide plate 100 so that the RGB LED 320 may be used as a light source. The RGB LED 320, the LED cup 350, the photoconductor 400a, and the light diffusion surface 410a are all defined as an RGB LED assembly 300B. The method of arranging the RGB LED 320 or the RGB LED assembly 300B on the light guide plate 100 may use the method of FIG. 5 or 6 as in the case of using the white light LED assembly 300A.

11A and 11B are cross-sectional views and partially enlarged perspective views of a direct backlight unit according to a third embodiment of the present invention. In the first and second embodiments, the light emitted from the white LED 310 or the RGB LED 320 is guided into the light guide plate 100 using the light guide 400a. In the case of using the photoconductor 400a as in the previous embodiment, the photoconductor 400a should be made integral with the LEDs 310 and 320, and the light diffusion surface 410a on the upper portion of the photoconductor 400a may be a light guide plate. It should be inserted into the insertion groove 110 of the bottom of the (100). Thus, there is a risk that the light guide 400a is in contact with the insertion groove 110 and is damaged by a slight horizontal movement in the process of inserting the light diffusion surface 410a into the insertion groove 110.

In the third embodiment, to solve this problem, as shown in FIG. 11A, a plurality of inverted cone-shaped photoconductors 410b inserted and inserted into the insertion grooves 110 are used without using the photoconductors 400a. To guide light directly from the white light LED 310 into the light guide plate 100. The condenser lens 360 may be installed on the front surface of the LED 310 to make light emitted from the LED 310 into parallel light and be incident on the diffraction grating 120. Referring to FIG. 11B, a reflective material is coated on the surface of the inverse cone-shaped photoconductor 410b to reflect the light emitted from the white light LED 310 and to enter the light guide plate 100. Light incident on the light guide plate 100 is branched toward the liquid crystal panel LP through the light branch 200.

12A to 12C are cross-sectional views illustrating a direct type backlight unit according to a fourth embodiment of the present invention. According to FIGS. 12A to 12C, the diffraction grating 120 is replaced with the photoconductor 400a of FIG. 3 and the inverted conical photoconductor 410b of FIG. 11A to guide the light of the LED into the light guide plate 100. I use it. By doing so, it is not necessary to form the insertion groove 110 in the light guide plate 100, so that the process may be simpler. In this case, the diffraction grating 120 may have a sine cross section as shown in FIG. 12A, and a cross grating may be used as shown in FIG. 12B. In addition, by installing the condenser lens 360 on the front surface of the LED 310, the light emitted from the LED 310 is made into parallel light and incident on the diffraction grating 120, thereby further increasing the efficiency of the light. LED assembly 300C is included. When the light emitted from the LED 310 is guided into the light guide plate 100 through the diffraction grating 120, the plane of the diffraction grating 120 must have a plurality of concentric circles as illustrated in FIG. Is achieved. The spacing p of the adjacent diffraction gratings 120 is preferably smaller than about 3 μm so that the diffracted light can be bent at an angle so that the light guide plate 100 can travel by total internal reflection.

Thus, according to the direct type backlight unit of the present invention, it is possible to effectively dissipate the heat generated by the LED while realizing a much thinner thickness than the conventional LED backlight. In addition, since it is a direct backlight, it is possible to apply division driving technology, achieve high contrast ratio, and reduce power consumption. In addition, since the illumination light having an appropriate viewing angle and vertical luminance illuminates the liquid crystal panel by the plurality of light splitting parts 200, it is possible to remove an optical sheet such as a diffusion plate or a prism sheet, which is advantageous in cost reduction. In addition, when inducing the light of the RGB LED 320 together into the photoconductor 400a, it is possible to achieve a sufficient color mixing to eliminate the color blur effect, and at the same time to achieve a high image quality by the RGB LED 320 light It works.

13 to 14 are cross-sectional views and plan views illustrating a direct type backlight unit according to a fifth embodiment of the present invention. In the first to fourth embodiments, the direct type backlight unit of the present invention is applied to the LCD. In the fifth embodiment, the direct type backlight unit is applied to a billboard or an indoor lighting device.

Conventional advertising lighting device has a disadvantage in that the fluorescent light or incandescent light in the interior, the electrical efficiency is low, the volume is large, and the shape of the light source in the inside partially appears.

Referring to FIG. 13, the direct type backlight unit includes all of the light guide plate 100, the light splitter 110, and the LED assemblies 300A, 300B, and 300C, which are described above, and an advertisement board in which advertisement contents are engraved thereon. ) Is different. By using the plurality of micro lenses 220 shown in FIG. 14 instead of the inverted truncated cone or inverted prism-shaped light splitter 200 applied in FIG. 13, a wider diffusion angle required for the lighting apparatus may be secured. The diameter of the microlens 220 is applicable in the range of about 5㎛ to about 300㎛, in order to obtain a sufficient diffusion angle and uniformity may be used in combination of several kinds of microlenses having different diameters. As the distance from the LED assemblies 300A, 300B, and 300C increases, the density of the microlenses increases so as to be proportional to the square of the distance, thereby increasing the uniformity of the light diffused out from the billboard.

A similar effect can be obtained in place of the micro lens 220 of FIG. 14, and an optical branch 200 formed to form a cross section of a sinusoidal lattice or a binary lattice described in the gray lattice 120 can also be used. Scattering pastes with dispersed bead are also possible.

The inner side 130 of the edge of the billboard AP may be reflected to prevent light loss. In addition, the flat form of the billboard may be produced in various forms including letters as illustrated in FIG. 15.

In this way, when the direct type backlight unit using the LED is applied to an advertisement board (AP) or an indoor lighting device, high efficiency, small volume, and uniform illumination are possible.

1 is a cross-sectional view of a liquid crystal display device employing a conventional direct type backlight unit.

2 is a cross-sectional view of a conventional direct type liquid crystal display device using LED as a light source.

3 is a cross-sectional view illustrating a direct type backlight unit according to a first embodiment of the present invention.

4 is an enlarged partial view of P shown in FIG. 3.

FIG. 5 is a plan view illustrating a tiled arrangement of the LED illustrated in FIG. 3.

FIG. 6 is a plan view illustrating a honeycomb arrangement of the LED illustrated in FIG. 3.

7A to 7C are perspective and enlarged perspective views illustrating the light splitter illustrated in FIG. 3.

FIG. 8 is a partially enlarged plan view of the light partition illustrated in FIG. 6.

9 is a graph of simulation results for the first embodiment of the present invention.

10 is a cross-sectional view of the direct type backlight unit according to the second embodiment.

11A and 11B are cross-sectional views and partially enlarged perspective views of a direct backlight unit according to a third embodiment of the present invention.

12A to 12C are cross-sectional views illustrating a direct type backlight unit according to a fourth embodiment of the present invention.

13 to 15 are cross-sectional views and plan views illustrating a direct type backlight unit according to a fifth embodiment of the present invention.

<Brief description of the main parts of the drawing>

100 ... Light guide plate 200 ... Light branch

300A, 300B, 300C ... LED Assembly 310,320 ... LED

400a, 400b ... Photoconductor 500 ...

Claims (11)

A light guide plate having a plurality of insertion grooves or a plurality of diffraction gratings formed on a lower surface thereof; A plurality of light splitting parts disposed on an upper surface of the light guide plate to split light traveling through the light guide plate upward by total internal reflection; A plurality of LEDs respectively disposed below the insertion groove or the diffraction grating; And And a plurality of photoconductors or a plurality of condensing lenses, disposed between the insertion groove or the diffraction grating and the LED, to guide the light from the LED into the light guide plate. The method according to claim 1, The photoinductor, Induces the light of the LED incident to the bottom to the top by total internal reflection, And a light diffusion surface disposed at an upper portion inserted into the insertion groove so that light directed upwardly is incident on the light guide plate. The method according to claim 1, The photoinductor, The inverted cone shape is inserted into the upper portion of the insertion groove, the direct type backlight unit, characterized in that the reflecting material is coated on the surface to reflect the light from the LED to enter the light guide plate. The method according to any one of claims 1 to 3, The light splitting unit is a direct type backlight unit, characterized in that formed integrally with the light guide plate. The method according to claim 1, The optical branching unit, A direct type backlight unit, characterized in that the shape of a reverse circular truncated cone or reverse prism. The method according to claim 5, And a side angle of the light splitting part and an upper surface of the light guide plate is in a range of 45 degrees to 75 degrees. The method according to claim 1, The optical branching portion, A direct type backlight unit, characterized in that the cross-sectional shape forms a sinusoidal grating or binary grating. The method according to claim 1, The optical branching unit, A direct type backlight unit, characterized in that a plurality of micro lenses (Micro lenses). The method according to claim 1, The diffraction grating, The direct type backlight unit, characterized in that arranged in a plurality of concentric circles on the plane. The method according to claim 1, The diffraction grating, A direct type backlight unit, characterized in that the shape of the cross section is a sine grating or a binary grating. The method according to claim 1, The LED, A direct type backlight unit, characterized in that the RGB LED or a white light LED with red, green, blue LED.

Images