KR20050011901A - back light unit of liquid crystal display device - Google Patents

Abstract

PURPOSE: A backlight unit of a liquid crystal display device is provided to uniformly mix white light, thereby improving the light efficiency. CONSTITUTION: A main light guide plate(51) is formed on the back of a liquid crystal panel in a wedge type structure. A sub light guide plate(52) is formed at a lower end part on one side of the main light guide plate. A light emitting lamp(53) is installed at an incidence surface of the sub light guide plate for emitting light. A first lamp housing(54) surrounds the light emitting lamp for condensing light to the incidence surface of the sub light guide plate. A reflecting plate(55) surrounds the light emitting lamp, the sub light guide plate, and an incidence surface of the main light guide plate. A second lamp housing(56) surrounds an exit surface of the sub light guide plate and the incidence surface of the main light guide plate for condensing light exiting through the sub light guide plate to the incidence surface of the main light guide plate.

Description

Back light unit of liquid crystal display device

The present invention relates to a liquid crystal display (LCD), and more particularly to a backlight unit of a liquid crystal display device suitable for improving the light efficiency.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as TVs, measuring devices, information terminal devices, etc., but the miniaturization of electronic products due to the weight and size of CRT itself It was unable to actively respond to the demand for weight reduction.

Therefore, in the trend of miniaturization and light weight of various electronic products, CRT has a certain limit in weight and size, and is expected to be replaced. Liquid crystal display (LCD) and gas discharge using electro-optic effects Plasma Display Panel (PDP) and Electro Luminescence Display (ELD) using the electroluminescent effect, among others, are being actively studied for the liquid crystal display device.

In order to replace the CRT, a liquid crystal display device having advantages such as small size, light weight, and low power consumption has recently been developed to be able to perform a sufficient role as a flat panel display device. As used in monitors and large information display devices, the demand for liquid crystal display devices continues to increase.

On the other hand, since most of the liquid crystal display devices are light-receiving elements that display an image by controlling the amount of light source coming from the outside, a separate light source, that is, a backlight, is required for irradiating light to the liquid crystal panel. It is divided into edge type and direct type according to the location where the lamp unit is installed.

The light source includes EL (Electro Luminescence), LED (Light Emitting Diode), CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), etc., especially long life, low power consumption and thin can be formed. CCFL is widely used in large color TFT LCDs.

The CCFL method uses a fluorescent discharge tube in which mercury gas containing argon, neon, or the like is sealed at a low pressure in order to use a penning effect. Electrodes are formed at both ends of the tube, and the cathode is formed in a wide plate shape.When voltage is applied, as in the sputtering phenomenon, charged particles in the discharge tube collide with the plate-shaped cathode to generate secondary electrons, which excite surrounding elements to excite the plasma. To form.

These elements emit strong ultraviolet light, which in turn excites the phosphor, causing the phosphor to emit visible light.

In the double-edge method, the lamp unit is installed on the side of the light guide plate for guiding the light, and the lamp unit covers a lamp emitting light, a lamp holder inserted at both ends of the lamp to protect the lamp, and an outer circumferential surface of the lamp, and one side It is provided with a lamp reflector plate fitted to the side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.

The edge method in which the lamp unit is installed on the side of the light guide plate is applied to a relatively small liquid crystal display device such as a monitor of a laptop computer and a desktop computer, and has good uniformity of light and a long service life. It is advantageous to thin the liquid crystal display device.

On the other hand, the direct method began to develop mainly as the size of the liquid crystal display device became larger than 20 inches, and arranged a plurality of lamps in a row on the lower surface of the diffusion plate to direct light directly to the front of the liquid crystal panel. will be.

The direct method is mainly used for a large screen liquid crystal display device requiring high luminance because the light utilization efficiency is higher than that of the edge method.

However, the liquid crystal display device adopting the direct method is used as a large monitor or a television, which takes longer to use than a laptop computer, and because the number of lamps is larger, the failure and life of the lamp in the direct method than the edge method. It is more likely that a lamp that will not turn on appears.

In the direct method, because a plurality of lamps are installed on the bottom of the screen, for example, due to the life and failure of the lamp, if one lamp does not light up, the part where the lamp does not light up becomes significantly darker than the other part. The part will appear immediately on the screen.

For this reason, since the lamp is frequently replaced in the direct method, the lamp unit should be easily disassembled and assembled.

Meanwhile, the configuration of a general backlight assembly is as follows.

1 is a view for explaining the structure of a general backlight assembly.

As shown in FIG. 1, the fluorescent lamp 1, the light guide plate 2, the diffusion material 3, the reflection plate 4, the diffusion plate 5, the prism sheet 6, and the like are constituted.

First, when the voltage is applied to the fluorescent lamp 1, residual electrons present in the fluorescent lamp 1 move to the anode, and the moving residual electrons collide with argon (Ar) to excite argon to proliferate cations, The multiplying cations collide with the cathode to release secondary electrons.

When the emitted secondary electrons flow through the tube to initiate discharge, the flow of electrons by the discharge collides with, and ionizes, the mercury vapor to emit ultraviolet rays and visible light, and the emitted ultraviolet rays excite the phosphor coated on the inner wall of the lamp to display visible light. It emits light and emits light.

Subsequently, the light guide plate 2 is a wave guide for injecting the light emitted from the fluorescent lamp 1 into the surface to emit a surface light source to the top, and has excellent light transmittance. PMMA (Poly Methyl Meth Acrylate) ) Resin is used.

Factors related to light incidence efficiency of the light guide plate 2 include light guide plate thickness versus lamp diameter, the distance between the light guide plate and the lamp, the shape of the lamp reflector, and the like. In general, the fluorescent lamp 1 is thicker than the center of the light guide plate 2. By inclining in the direction, the light incidence efficiency is increased.

The light guide plate 2 of the backlight unit for an LCD includes a printing light guide plate, a V-cut light guide plate, and a scattering light guide plate.

Subsequently, the diffusion material 3 is composed of Si0 ₂ , particles, PMMA, solvent, and the like. At this time, the Si0 ₂ particles described above are used for light diffusion and have a porous particle structure. PMMA is also used to attach Si0 ₂ particles to the lower surface of the light guide plate 2.

The diffusion material 3 is applied to the lower surface of the light guide plate in the form of a dot, and the area of the dot is gradually increased in order to obtain a uniform surface light source on the light guide plate 2. That is, the area ratio occupied by the dot per unit area is smaller in the one closer to the fluorescent lamp 1, and the area ratio occupied by the dot per unit area is larger in the far side from the fluorescent lamp 1.

In this case, the shape of the dot may have various shapes. If the area ratio of the dots per unit area is the same, the same brightness effect may be obtained on the light guide plate regardless of the shape of the dot.

Subsequently, the reflector 4 is installed at the rear end of the light guide plate 2 so that the light emitted from the fluorescent lamp 1 is incident into the light guide plate 2.

The diffusion plate 5 is installed on the light guide plate 2 to which the dot pattern is applied to obtain uniform luminance according to a viewing angle. As the material of the diffusion plate 5, PET or PC (Poly) is used. Carbonate) resin is used, and the upper part of the diffusion plate 5 has a particle coating layer that serves as a diffusion.

Subsequently, the prism sheet 6 is to increase the front luminance of the light that is transmitted through the diffusion plate 5 and reflected. The prism sheet 6 allows only the light of a specific angle to pass therethrough and the light incident at the remaining angle. Total internal reflection occurs and returns back to the bottom of the prism sheet 6. As described above, the returning light is reflected by the reflecting plate 4 attached to the lower part of the light guide plate 2.

The backlight assembly configured as described above is fixed to the mold frame, and the display unit disposed on the upper surface of the backlight assembly is protected by the top chassis, and the top chassis and the mold frame are coupled while receiving the backlight assembly and the display unit therebetween.

Hereinafter, a backlight unit of a conventional liquid crystal display device will be described with reference to the accompanying drawings.

2 is a perspective view illustrating a backlight unit using a conventional fluorescent lamp.

As shown in FIG. 2, the fluorescent lamp 11 is coated on the inner surface to emit light, and the fluorescent lamp 11 is fixed, and the light emitted from the fluorescent lamp 11 is in one direction. A lamp housing 12 for condensing, a light guide plate 13 for supplying the light emitted from the fluorescent lamp 11 to the liquid crystal panel side of the backlight, and light leaking to the opposite side of the liquid crystal panel attached to the lower part of the light guide plate 13 Reflector 14 reflecting light to the light guide plate 13, a diffuser plate 15 positioned above the light guide plate 13 to uniformly diffuse the light emitted from the light guide plate 13, and the diffuser plate 15 A prism sheet 16 positioned above and condensing light diffused from the diffusion plate 15 to a liquid crystal panel, and a protective sheet positioned above the prism sheet 16 to protect the prism sheet 16. 17, storing the components It consists of a main support (18) that secure.

The backlight unit configured as described above is focused on the light incident surface of the light guide plate 13 emitted from the fluorescent lamp 11, passes through the light guide plate 13, passes through the diffuser plate 15, and the prism sheet 16, to the liquid crystal panel. Delivered.

However, as described above, the backlight unit using the conventional fluorescent lamp has low color reproducibility due to the light emission characteristics of the light source itself. In addition, it is difficult to obtain a high brightness backlight unit due to constraints of the size and capacity of the fluorescent lamp.

On the other hand, in recent years, the backlight unit has been used as a function for reading information displayed on the screen of a liquid crystal display in a dark place, but recently, the light guide plate has been formed thinner due to various requirements such as design, low power, and thinning. In addition to the ability to express various colors, technologies for reducing power consumption using LEDs (Light Emitting Diodes) are being made.

3 is a perspective view illustrating a backlight unit using a conventional LED.

As shown in FIG. 3, the LED light sources 22 are disposed on both sides of the light guide plate 21 formed on the rear side of the liquid crystal panel, and the LED light source 22 illuminates the liquid crystal panel so that the screen can be displayed even in a dark place. Can be.

Here, the LED light source 22 is composed of LED lamps 23 arranged one-dimensionally, the LED lamp 23 is a red LED, green LED, blue LED is disposed on the PCB substrate, respectively.

The backlight unit configured as described above turns on the LED lamp 23 of the LED light source 22 when an image is realized on the liquid crystal panel. Voltage is applied to the red, green, and blue LEDs of the three colors of the LED lamp 23, and the red, green, and blue light emitted are color-mixed by scattering in the light guide plate 21 to produce white light. Is illuminated on the back of the liquid crystal panel.

4 is a plan view of a backlight unit using a conventional LED.

As shown in FIG. 4, the LED lamp 23 including the red LED 23a, the green LED 23b, and the blue LED 23c and the light emitted from the LED lamp 23 are evenly distributed on the liquid crystal panel. It consists of the light guide plate 21 for making it.

In this way, the monochromatic light of R, G, and B is emitted from the LED lamp 23 from the LED light source (22 in FIG. 3) to emit white light by using the LED lamp 23 as a light source. In the region "a" of 21, a portion 20 in which the light emitted by each LED lamp 23 does not overlap occurs to produce uniform white light, and in the region "b" of the light guide plate 21, The monochromatic light emitted from R, G, and B can be mixed from the LED lamp 23 to produce uniform white light.

Thus, the backlight unit uses only half of the light guide plate 21 far from the LED light source 22 by forming a light spot on the light guide plate 21 so that only the “b” region of the light guide plate 21 can be effectively used.

By using a light emitting diode (LED) as a light source for illuminating the liquid crystal panel as described above, it is possible to easily reduce the power consumption and miniaturization of electronic devices such as notebook PCs.

On the other hand, LED is a solid element using the photoelectric conversion effect of the semiconductor. In order to emit LED, a DC voltage of about 1.5V needs to be applied, thus eliminating the need for a DA-AC converter, thereby significantly reducing power consumption.

In addition, since LEDs are semiconductor devices, they are more reliable than cathode ray tubes, and are small in size and long in life.

The backlight unit of the conventional liquid crystal display device configured as described above illuminates the liquid crystal panel by mixing white light emitted from red, green, and blue LEDs emitting three primary colors of additive mixed color.

However, in the backlight unit of the conventional liquid crystal display device as described above, there are the following problems.

That is, the red, green, and blue light emitted from each of the red, green, and blue light emitting diodes are mixed, so that white light illuminated by the liquid crystal panel cannot be uniformly mixed, resulting in poor light efficiency and color reproducibility.

An object of the present invention is to provide a backlight unit of a liquid crystal display device which is designed to solve the conventional problems as described above and to improve light efficiency.

1 is a view for explaining the structure of a typical backlight assembly

2 is a cross-sectional view showing a backlight unit using a conventional fluorescent lamp

3 is a cross-sectional view showing a backlight unit using a conventional LED.

4 is a plan view of a backlight unit using a conventional LED

5 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to a first embodiment of the present invention.

6 is a view showing the arrangement of the main light guide plate according to the present invention;

7 is a view showing the shape of the main light guide plate according to the present invention;

8 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to a second exemplary embodiment of the present invention.

Explanation of symbols for the main parts of the drawings

51: main light guide plate 52: sub light guide plate

53: light emitting lamp 54: first lamp housing

55 reflector 56 second lamp housing

57: diffuser 58: prism sheet

59: protective sheet 60: diffusion material

The backlight unit of the liquid crystal display according to the first embodiment of the present invention for achieving the above object is a main light guide plate having a wedge-shaped structure on the back of the liquid crystal panel, and a sub light guide plate configured at a lower end of one side of the main light guide plate And a light emitting lamp configured to emit light at the incident surface side of the sub light guide plate, a first lamp housing configured to wrap around the light emitting lamp to condense and emit light at the incident surface of the sub light guide plate, and A light emitting lamp and a sub light guide plate and a reflecting plate configured to surround an entrance surface of the main light guide plate, and an exit surface of the sub light guide plate and an entrance surface of the main light guide plate are formed to condense the light emitted through the sub light guide plate to condense the main light guide plate. It characterized in that it comprises a second lamp housing that exits the incident surface of the.

In addition, the backlight unit of the liquid crystal display according to the second exemplary embodiment of the present invention may include a main light guide plate having a wedge-shaped structure on the rear surface of the liquid crystal panel, first and second sub light guide plates formed at lower ends of both sides of the main light guide plate; And first and second light emitting lamps configured to be incident on the incidence surface side of the first and second sub light guide plates to surround light, and to surround the first and second light emitting lamps. A first and second lamp housings condensing and exiting light onto an incidence surface of the sub light guide plate, the first and second light emitting lamps and the first and second sub light guide plates, and a first surface configured to surround the incidence surfaces of the main light guide plate. The first and second reflecting plates and the exit surfaces of the first and second sub light guide plates and the incidence surfaces of the main light guide plate are formed to condense the light exiting through the first and second sub light guide plates to condense the incident surfaces of the main light guide plate. Exodus Including the third and fourth lamp housing, which is characterized by comprised.

Hereinafter, the backlight unit of the liquid crystal display according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to a first embodiment of the present invention.

As shown in FIG. 5, a main light guide plate 51 having a wedge-shaped structure on a rear surface of a liquid crystal panel (not shown), and a sub light guide plate configured at a lower end of one side of the main light guide plate 51 ( 52, a light emitting lamp 53 configured to be incident on the incidence surface of the sub light guide plate 52 to emit light, and a wrapper around the light emitting lamp 53 to cover the incidence surface of the sub light guide plate 52. A first lamp housing 54 which condenses and emits light, a reflecting plate 55 configured to surround the incident surface of the light emitting lamp 53, the sub light guide plate 52, and the main light guide plate 51, and the sub A second lamp housing which surrounds the exit surface of the light guide plate 52 and the entrance surface of the main light guide plate 51 to condense the light exiting through the sub light guide plate 52 and exits the entrance surface of the main light guide plate 51. 56 and a main light guide on the main light guide plate 51. A diffuser plate 57 for uniformly diffusing the light emitted from the 51 and a prism sheet positioned on the diffuser plate 57 to condense the light diffused from the diffuser plate 57 and transmit the light to the liquid crystal panel. 58 and a protective sheet 59 positioned above the prism sheet 58 to protect the prism sheet 58.

Here, the light emitting lamp 53 is composed of a red LED, a blue LED, a green LED, and the sub light guide plate 52 mixes red, green, and blue light emitted from the light emitting lamp 53. White light is emitted to the incident surface of the main LGP 51.

In addition, the reflector plate 55 uses an aluminum material, and has a structure in which light emitted from the sub light guide plate 52 is changed into a main light guide plate 51 by changing a path of light through a 180 degree reflector.

In addition, the incident surface of the sub light guide plate 52 is configured to be thinner than the emission surface.

In addition, a diffusion material 60 is coated on the lower surface of the main LGP 51 to diffuse light. In this case, the diffusion material 60 may have a film or pattern shape.

In addition, the first and second lamp housings 54 and 56 are made of aluminum or optical fiber having good reflectance.

The reason for using aluminum or an optical fiber having good reflectance as the first and second lamp housings 54 and 56 in the present invention is to condense the light emitted from the light emitting lamp 53 to sub light guide plate 52 or the main light guide plate. In order to maximize the light efficiency by entering the incident surface of (51).

On the other hand, the optical fiber may be divided into glass optical fiber and plastic optical fiber according to the material.

In addition, the glass optical fiber may be classified into a silica-based optical fiber, a fluorine-based optical fiber, a rare earth-based optical fiber and the like.

Here, the plastic optical fiber generally replaces the existing optical glass material using an optically transparent polymer material because optical glass is fragile, difficult to form, and there is a problem of productivity in processing a shape of a predetermined size or more. Plastic optical fiber (POF) generally uses acrylic polymer as a core material and fluorine polymer as a cladding material.

In addition, the plastic optical fiber is characterized in that the light used as the light source is 650 nm in the visible light region, which is safe for eyes and suitable for near field communication (~ several Km), has good flexibility, and is resistant to vibration and bending, so that it can be used in a narrow space or high speed. Used for trains, automobiles, etc. Also, since it does not generate heat, it is suitable for exhibition lighting or lighting of heat sensitive semiconductor process equipment. It has no influence on electromagnetic waves and is not used for electricity, so it is used for special lighting.

6 is a view showing an arrangement of the main light guide plate according to the present invention.

As shown in FIG. 6, in order to configure the backlight unit in a direct type, a main light guide plate 51 is required, and the main light guide plate 51 is arranged to have a constant interval like a direct lamp (A). From a direction).

7 is a view showing a form of the main light guide plate according to the present invention.

As shown in FIG. 7, the main light guide plate 51 has a wedge type structure, wherein the wedge type structure has a top surface corresponding to the liquid crystal panel and a central portion of the bottom surface protrudes downward. Have

The operation of the backlight unit of the liquid crystal display according to the present invention configured as described above is as follows.

That is, when the display is performed in the liquid crystal display using the backlight unit, when the red LED, the green LED, and the blue LED of the light emitting lamp 53 emit light, the red light, the green light, and the blue light emitted from each LED are the first. The light is collected through the lamp housing 54 and is incident on the sub light guide plate 52.

Subsequently, each light incident on the incidence plane of the sub light guide plate 52 is mixed by scattering in the sub light guide plate 52 to emit white light to the incidence plane of the main light guide plate 51, and the main light guide plate 51. The white light incident on the light exits from the entire surface of the main LGP 51 through scattering to illuminate the entire liquid crystal panel.

The white light incident on the liquid crystal panel is modulated according to the alignment of the liquid crystal material and is transmitted through the color filter of the opposing substrate to output a color image.

Meanwhile, in the present invention, the main light guide plate 51 and the sub light guide plate 52 are divided and disposed by receiving and mixing the respective colors from the light emitting lamp 53 through the sub light guide plate 52 to emit white light. Since the color mixture of the white light finally emitted through the main light guide plate 51 may be maximized, color separation and luminance of the light incident part may be maximized.

8 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to a second exemplary embodiment of the present invention.

Unlike the first embodiment, the second embodiment of the present invention can maximize the light efficiency by configuring sub light guide plates on both lower ends of the main light guide plate.

That is, as shown in FIG. 8, the main light guide plate 71 having a wedge-shaped structure on the rear surface of the liquid crystal panel (not shown), and the first and the second ends formed on the lower ends of both sides of the main light guide plate 71. 2nd sub light guide plates 72 and 73, the 1st, 2nd light emitting lamps 74 and 75 which are comprised in the entrance surface of the said 1st, 2nd sub light guide plates 72 and 73, and emit light, and the said 1st The first and second lamp housings 76, which surround the circumference of the second light emitting lamps 74 and 75, condense and emit light to incident surfaces of the first and second sub light guide plates 72 and 73. 77 and the first and second reflecting plates 78 that surround the first and second light emitting lamps 74 and 75, the first and second sub light guide plates 72 and 73, and the main light guide plate 71. 79 and surrounding the exit surfaces of the first and second sub light guide plates 72 and 73 and the incident surface of the main light guide plate 71 and exiting through the first and second sub light guide plates 72 and 73. To focus the light The third and fourth lamp housings 80 and 81 exiting the incident surface of the main LGP 71 and the upper portion of the main LGP 71 are uniformly diffused to diffuse light emitted from the main LGP 71. A diffusion plate 82, a prism sheet 83 positioned on the diffusion plate 82 to collect and diffuse light diffused from the diffusion plate 82 to a liquid crystal panel, and an upper portion of the prism sheet 83. The protection sheet 84 is positioned to protect the prism sheet 83 is configured.

Here, the diffusion material 85 is coated on the lower surface of the main light guide plate 71 in a film or pattern form.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

As described above, the backlight unit of the liquid crystal display according to the present invention has the following effects.

That is, by using an RGB LED as a direct type, forming a central portion of the main LGP in a wedge shape, and coating a diffusion material on the lower surface of the main LGP, a high brightness backlight unit may be realized.

Claims (12)

A main light guide plate having a wedge-shaped structure on the back of the liquid crystal panel, A sub light guide plate configured at a lower end of one side of the main light guide plate; A light emitting lamp configured to be incident on the incident surface side of the sub light guide plate to emit light; A first lamp housing configured to surround the light emitting lamp to condense and exit light onto an incident surface of the sub light guide plate; A reflection plate configured to surround the light emitting lamp, the sub light guide plate, and an incident surface of the main light guide plate; And a second lamp housing configured to surround the exit surface of the sub light guide plate and the entrance surface of the main light guide plate to condense the light exiting through the sub light guide plate and to exit the entrance surface of the main light guide plate. Backlight unit of the device. The backlight unit of claim 1, wherein the light source unit comprises red, green, and blue light emitting diodes. The light emitting device of claim 1, further comprising: a diffuser plate disposed on the main light guide plate to uniformly diffuse the light emitted from the main light guide plate, and a light diffused from the diffuser plate located on the diffuser plate to transmit the light to the liquid crystal panel. And a protective sheet positioned on the prism sheet to protect the prism sheet. The backlight unit of claim 1, wherein the reflecting plate receives the light emitted from the sub light guide plate through the 180 degree reflector to change the light path to the main light guide plate. The backlight unit of claim 1, wherein an incident surface of the sub light guide plate is thinner than an emitting surface. The backlight unit of claim 1, wherein the first and second lamp housings are made of aluminum or an optical fiber having good reflectance. The backlight unit of claim 6, wherein the optical fiber is a glass optical fiber or a plastic optical fiber. 8. The backlight unit of claim 7, wherein the glass optical fiber is any one of a silica optical fiber, a fluorine optical fiber, and a rare earth optical fiber. The backlight unit of claim 1, wherein a diffusion material is coated on a lower surface of the main light guide plate. A main light guide plate having a wedge-shaped structure on the back of the liquid crystal panel, First and second sub light guide plates configured at lower ends of both sides of the main light guide plate; First and second light emitting lamps configured to be incident on the incidence surface side of the first and second sub light guide plates to emit light; First and second lamp housings configured to surround the first and second light emitting lamps to condense and emit light onto incident surfaces of the first and second sub light guide plates; First and second reflecting plates configured to surround the incident surfaces of the first and second light emitting lamps, the first and second sub light guide plates, and the main light guide plate; A third and a second wrapper configured to surround the exit surface of the first and second sub light guide plates and the incident surface of the main light guide plate to condense the light exiting through the first and second sub light guide plates and to emit the light exiting to the entrance surface of the main light guide plate; The backlight unit of the liquid crystal display device comprising a 4 lamp housing. The backlight unit of claim 10, wherein a diffusion material is coated on a lower surface of the main light guide plate. The backlight unit of claim 10, wherein the first, second, third, and fourth lamp housings are made of aluminum or an optical fiber.