KR100780193B1 - Backlight unit - Google Patents

Abstract

Provided is a backlight unit for a liquid crystal display device using LED. The backlight unit according to the present invention includes a lower reflector; A plurality of LEDs arranged on the lower reflector; And a side reflector surrounding the lower reflector and inclined upward, and a phosphor is applied to an inner surface of the side reflector to correct color unevenness.

LCD (Liquid Crystal Display), Backlight Unit, LED, Color Uniformity

Description

Backlight Unit {BACKLIGHT UNIT}

1A and 1B are a perspective view and a schematic plan view of a conventional backlight unit, respectively.

1C is a photograph showing color uniformity of a conventional backlight unit.

2A and 2B are a sectional view and a plan view, respectively, of a backlight unit according to an embodiment of the present invention.

3A and 3B are plan and cross-sectional views, respectively, of a backlight unit according to another embodiment of the present invention.

4 and 5 are plan views of a backlight unit according to various embodiments of the present disclosure.

<Description of the symbols for the main parts of the drawings>

101: lower reflector 102: side reflector

104: LED 105: phosphor

106: bulkhead

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit of an LCD (liquid crystal display) using an LED (Light Emitting Diode). More particularly, the use of a phosphor in a reflector suppresses color unevenness. The present invention relates to a backlight unit capable of improving color uniformity.

In general, LCDs used in notebooks, LCD-TVs, mobile communication terminals, etc. are a light-receiving element, and require a backlight unit in addition to the liquid crystal panel. In the backlight unit, an edge-lighting method in which light from a light source installed on a side of a light guide plate installed in parallel with the liquid crystal panel is incident on the liquid crystal panel by the light guide plate, and in parallel with the liquid crystal panel instead of using the light guide plate. There is a direct-lighting method in which a plurality of light sources are disposed on the rear surface of the diffuser plate so that light is directly incident on the liquid crystal panel.

Conventionally, a CCFL (Cold Cathode Fluorescent Lamp) or EEFL (External Electrode Fluorescent Lamp) is used as a light source of a backlight unit of an LCD. However, these conventional light sources have a problem in that their lifetime is shortened as the gas pressure of the plasma changes, and an inverter for obtaining a high operating voltage of several hundred volts required for plasma discharge is required. In addition, when applied to a portable product, most of the power is consumed by the backlight. At this time, there is a problem that a conventional light source such as CCFL or EEFL has an excessive power consumption due to poor power consumption efficiency.

In order to solve the above problem, there is a backlight unit using an LED (Light Emitting Diode). LEDs generate unique light depending on the type of impurities and the type of semiconductor material. For example, when the semiconductor material is gallium phosphide, it emits red light (wavelength 700 nm) when the impurities are zinc and oxygen atoms, and emits green light (wavelength 550 nm) when the impurities are nitrogen atoms. The LED has advantages in that the LED is smaller in size, longer in life, and has high energy efficiency and low operating voltage since electrical energy is directly converted into light energy. Therefore, a method of generating white light using an LED having such an advantage as a light source of an LCD backlight unit has been proposed. That is, white light was generated by mixing light by combining the LEDs generating blue light (B), green light (G), and red light (R). In the case of a direct type backlight unit using an LED as a light source, a light is emitted to the liquid crystal panel by changing a path of light upward or downward through light emitted from the lower surface or the side surface using a reflector. However, if the LEDs emitting red light (R) are close to the reflector, the red spots are red, and if the LEDs emitting green light (G) and blue light (B) are close to the reflector, the green spots and blue spots ( Blue spot) occurs, and color uniformity is lowered.

1A and 2B are a perspective view and a plan view schematically showing an LCD backlight unit using a conventional LED. As shown in FIG. 1A, the backlight unit 10 includes an LED 12 disposed on the lower reflector 11 at regular intervals and an inner sidewall of the backlight unit 10 faces upward when the lower reflector 11 is surrounded. It has a photographic side reflector 13. The light directed downward among the light emitted from the LED 12 is reflected by the lower reflector 11 and emitted upward. In addition, the light emitted to the side of the LED 11 is emitted to the upper side reflected by the side reflector 13 in which the inner side wall is inclined upward. 2B is a plan view schematically illustrating the arrangement of LEDs in the LCD backlight unit. Referring to FIG. 2B, an LED emitting green light G (hereinafter referred to as a green LED G) and an LED emitting blue light B (hereinafter referred to as a blue LED B) near the side reflector 13 are described. ) Is arranged. In this case, when the green LED G is near the side reflector 13, the green light G is predominantly generated by the green light G reflected and emitted by the side reflector 13 to generate green spots. Similarly, when there is a blue LED (B) near the side reflector 13, blue spots occur. Therefore, color unevenness occurs and overall color uniformity of the backlight unit is lowered.

 1C is a photograph of color uniformity of the lower right corner of the LCD. As you go to the lower part of the picture and to the right side, the color is different from the center of the picture, and color unevenness appears.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a backlight unit which corrects color unevenness by using a phosphor for a reflector to improve color uniformity.

In order to achieve the above technical problem, the backlight unit according to the present invention includes a lower reflector; A plurality of LEDs arranged on the lower reflector; A side reflector may be formed to surround the lower reflector and be inclined upward. A phosphor may be applied to an inner surface of the side reflector to correct color unevenness.

The plurality of LEDs may include a red LED, a green LED, and a blue LED. The LEDs closest to the side reflector may be green or blue LEDs, and the red LEDs may be disposed inside the LEDs closest to the side reflector.

Preferably, a red phosphor may be coated on an inner surface of the side reflector, and a red phosphor and a green phosphor may be coated on an inner surface of the side reflector. More preferably, a red phosphor may be applied to an inner surface of the side reflector adjacent to the green LED, and a green phosphor may be applied to an inner surface of the side reflector adjacent to the blue LED.

The red phosphor may be made of a material selected from the group consisting of (ZnCd) S: AgCl, (ZnCd) S: AgAuCl, (ZnCd) S: AgAuAl, ZnGa ₂ S ₄ : Mn, SrY ₂ , and the green phosphor is SrGa _It may be made of a material selected from the group consisting of ₂ S ₄ : Eu, ZnS: CuAl, ZnS: CuAuAl, SrGa ₂ S ₄ : Eu, ZnGa ₂ S ₄ : Eu, SrS: Ce.

In one embodiment of the present invention, the partition is surrounded by the side reflector and formed between the plurality of LEDs on the lower reflector further partitions the plurality of LEDs by area, wherein the sidewall of the partition can be coated with a phosphor have. The partition wall may be disposed in the horizontal or vertical direction on the lower reflector in parallel with the side reflector. In addition, the partition wall may be arranged in a matrix form on the lower reflector, the partition wall may be disposed in a honeycomb form having a plurality of hexagonal shapes on the lower reflector.

The plurality of LEDs may include a red LED, a green LED, and a blue LED, and the LEDs closest to the side reflector and the partition wall may be green or blue LEDs, and the red LEDs may be disposed inside the LEDs closest to the side reflector and the partition wall. Is preferred.

A red phosphor may be applied to the inner surface of the side reflector and the side wall of the partition, and a red phosphor and a green phosphor may be applied to the inner surface of the side reflector and the side of the partition. Preferably, a red phosphor may be applied to the inner surface and the sidewall of the side reflector adjacent to the green LED, and a green phosphor may be applied to the inner surface and the sidewall of the side reflector adjacent to the blue LED.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention may be exaggerated for clarity in order to more fully describe the present invention to those skilled in the art, and the same elements are denoted by the same reference numerals in the drawings.

2A and 2B are schematic cross-sectional and plan views, respectively, of the backlight unit according to the present invention. Referring to FIG. 2A, the backlight unit 100 according to the present invention surrounds a plurality of LEDs 104 and the lower reflector 101 arranged on the lower reflector 101 and the lower reflector 101, and thus, the backlight unit 100 of the backlight unit 100. A phosphor 105 including a side reflector 102 that is inclined upward is used for correcting color unevenness on the surface of the side reflector.

The lower reflector 101 serves to change the path of light emitted from the plurality of LEDs 104 arranged on the lower reflector 101 to the lower surface of the light reflecting to the upper surface through reflection. In addition, the side reflector 102 also emits light emitted to the side of the light emitted from the LED 104 to the upper surface.

The backlight unit irradiates white light to the back of the LCD panel, so that the color embodied in the LCD panel can be displayed more clearly. In order to implement white light, the plurality of LEDs 104 may be implemented by combining red, green, and blue LEDs. The three primary colors of light, red, green, and blue, combine to turn white light. 2B is a plan view schematically illustrating the arrangement of LEDs in the backlight unit according to the present invention. Referring to FIG. 2B, the LEDs disposed closest to the side reflector 102 are blue LEDs (B) or green LEDs (G), and the red LEDs (R) are the LEDs closest to the side reflectors 102 (blue LEDs ( B) or green LED (G)) is placed inside. The red LED (R) does not affect the green or blue phosphor because red has a long wavelength and does not excite the green or blue phosphor. Therefore, it is desirable to place the red LED R as far from the reflector as possible.

In the case of the green LED G adjacent to the reflector 102, green spots may occur due to the green light emitted directly from the green LED G to the upper part of the backlight unit and the green light reflected from the reflector 102 and emitted to the upper part of the backlight unit. In addition, in the case of the blue LED B adjacent to the inner side of the reflector 102, blue spots may occur due to the blue light reflected by the inner side of the reflector 102 and emitted to the upper side of the backlight. In this case, a red phosphor or a red and green phosphor may be applied to at least a portion of the inner surface of the side reflector 102. The red phosphor and the green phosphor are coated together to prevent red staining because red is highly visible. Preferably, a red phosphor 105a is applied to the inner side of the portion of the reflector 102 adjacent to the green LED G so that the green LED G can occur around the inner side of the portion of the adjacent reflector 102. Smudges can be corrected. In addition, by applying the green phosphor 105b to the inner side of the portion of the reflector 102 adjacent to the blue LED B, the blue spots generated around the reflector 102 adjacent to the blue LED B may be corrected. Accordingly, color uniformity of the backlight unit 100 is improved. In addition, the green phosphor or the red phosphor may be applied not only to the inner surface of the side reflector 102 but also to a portion of the bottom surface of the lower reflector 101 in contact with the inner surface of the side reflector 102 and the lower reflector 101. This can further improve color correction.

The red phosphor 105a refers to all phosphors that absorb green and emit red. Preferred examples of phosphors corresponding to this group are (ZnCd) S: AgCl, (ZnCd) S: AgAuCl, (ZnCd) S: AgAuAl, ZnGa ₂ S ₄ : Mn, SrY ₂ and the like. The green phosphor 105b refers to all phosphors that absorb blue and emit green, and preferred examples of the phosphors corresponding to this group include SrGa ₂ S ₄ : Eu, ZnS: CuAl, ZnS: CuAuAl, SrGa ₂ S ₄ : Eu , ZnGa ₂ S ₄ : Eu, SrS: Ce and the like.

The LED 104 is divided into a large chip having a width and length of 1 mm or more and a small chip having a size of about 0.3 mm according to its size. In the case of using a large chip, it is difficult to mix the light generated from each LED than in the case of using a small chip, which may cause more color unevenness. In this case, when the phosphor is applied to the inner surface of the side reflector 102 as described above, color unevenness can be effectively suppressed.

3A and 3B are plan and cross-sectional views, respectively, of a backlight unit 200 according to another embodiment of the present invention. The embodiment of FIG. 3 is a variation of the embodiment of FIG. 2, in that there is a partition 106 formed on the lower reflector 101 in the horizontal or vertical direction parallel to the side reflector 102. The partition 106 changes the path of light emitted to the side from the LED adjacent to the partition 106 through reflection to emit light to the top of the backlight unit 200. A plurality of LEDs 104 are arranged in the divided area divided by these partition walls 106. The plurality of LEDs 104 are a blue LED (B), a green LED (G), and a red (R) LED. Among the plurality of LEDs 104, the blue LED (B) and the green LED (G) are disposed close to the side reflector 102 or the partition wall 106, and the red LED (R) is the side reflector 102 or the partition wall 106. It is preferable to arrange inward than the LED (blue LED (B) or green LED (G)) nearest to the (). The phosphor 105 is also applied to at least a portion of the side surface of the partition 106 such that the phosphor 105 is applied to at least a portion of the inner surface of the side reflector 102. In this way, the green uniformity or the blue irregularity that may occur in the divided region divided by the partition wall 106 may be corrected to improve color uniformity of the entire backlight.

On the other hand, in order to more vividly display the image displayed on the liquid crystal display device, the liquid crystal panel of the liquid crystal display device is divided into a plurality of areas, and the luminance of the backlight in each divided area unit according to the gray level value of each divided area. The values can be adjusted individually. In this manner, dividing the liquid crystal panel of the liquid crystal display into divided regions and individually adjusting the backlight luminance values of the portions corresponding to the divided regions is referred to as local dimming. The divided regions divided by the partition wall 106 may individually adjust the luminance value of the backlight for each divided region. In this case, local dimming can be implemented with improved color uniformity.

4 is a plan view of a backlight unit 300 according to another embodiment of the present invention. The embodiment of FIG. 4 is a variation of the embodiment of FIG. 2, which differs in that it has a matrix-shaped partition wall 106 on the lower reflector 101 and a phosphor 105 is used for the partition wall 106. . The partition wall 106 is formed to be inclined toward the upper portion of the backlight unit 300, thereby changing the path of the light emitted from the LED through reflection to emit light to the upper portion of the backlight unit 300. The phosphor 105 is applied to the inner surface portion of the side reflector 102 and the side portion of the partition 106. Arrange a plurality of LEDs (not shown) on the divided region divided by the partition wall 106, and place a blue LED or a green LED in a portion closest to the side reflector 102 or the partition wall 106, and a red LED. It is preferable to arrange the inside of the side reflector 102 or the partition wall 106 closer to the blue LED or the green LED. Red phosphors or red and green phosphors may be applied to the inner surface of the side reflector and at least a portion of the side wall of the barrier rib. For example, a green phosphor is applied to the inner side of the side reflector 102 adjacent to the blue LED (B) and the side of the partition 106, and the inner surface and the partition of the side reflector 102 adjacent to the green LED (G). A red phosphor can be applied to the side surface of 106.

5 is a plan view of a backlight unit 400 according to another embodiment of the present invention. The embodiment of FIG. 5 is a modification of the embodiment of FIG. 2, and has a hexagonal partition wall 106 on the lower reflector 101, and differs in that the phosphor 105 is used for the partition wall 106. . By applying the phosphor 105 to a portion of the lower surface reflector 101 adjacent to the side reflector 102 and the lower surface reflector 101, color correction may be further improved to improve overall color uniformity. In addition, the phosphor 105 may be applied to a portion of the lower surface reflector 101 in contact with the partition 106 and the lower surface reflector 101.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. In addition, it will be apparent to those skilled in the art that the present invention may be substituted, modified, and changed in various forms without departing from the technical spirit of the present invention described in the claims.

As described above, according to the present invention, the red LED of the LED of the backlight unit is disposed as far as possible from the side reflector and the partition wall, and the red or green phosphor is applied to the side reflector and the partition wall, so that the blue light may be generated around the side reflector or the partition wall. Or by correcting the green spots to suppress color spots and increase the color uniformity of the backlight unit. In addition, by forming a partition on the lower surface of the reflector, the luminance value of the backlight may be individually adjusted for each divided area divided by the partition to implement local dimming while improving color uniformity.

Claims (15)

Lower reflector; A plurality of LEDs arranged on the lower reflector; And A side reflector surrounding the lower reflector and inclined upwardly; And a phosphor is applied to the inner surface of the side reflector to correct color unevenness. The method of claim 1, The plurality of LEDs are made of a red LED, a green LED, a blue LED, The LED closest to the side reflector is a green or blue LED, And the red LED is disposed inward from the LED nearest to the side reflector. The method of claim 2, And a red phosphor is coated on the inner surface of the side reflector. The method of claim 3, And a red phosphor and a green phosphor are coated on the inner surface of the side reflector. The method of claim 4, wherein A red phosphor is applied to the inner surface of the side reflector adjacent to the green LED, And a green phosphor is coated on an inner surface of the side reflector adjacent to the blue LED. The method according to claim 3 or 4, The red phosphor is made of a material selected from the group consisting of (ZnCd) S: AgCl, (ZnCd) S: AgAuCl, (ZnCd) S: AgAuAl, ZnGa ₂ S ₄ : Mn, SrY ₂ . The method of claim 4, wherein The green phosphor is made of a material selected from the group consisting of SrGa ₂ S ₄ : Eu, ZnS: CuAl, ZnS: CuAuAl, SrGa ₂ S ₄ : Eu, ZnGa ₂ S ₄ : Eu, SrS: Ce unit. The method of claim 1, A partition wall surrounded by the side reflector and formed between the plurality of LEDs on the lower reflector to divide the plurality of LEDs into regions; The back light unit, characterized in that the phosphor is coated on the side wall. The method of claim 8, The plurality of LEDs are made of a red LED, a green LED, a blue LED, The LED closest to the side reflector and the partition wall is a green or blue LED, And the red LED is disposed inward from the LED nearest to the side reflector and the partition wall. The method of claim 9, And a red phosphor is coated on an inner surface of the side reflector and a side surface of the partition wall. The method of claim 9, And a red phosphor and a green phosphor are coated on the inner surface of the side reflector and the side surface of the partition wall. The method of claim 11, Red phosphor is applied to the inner surface and the side wall of the side wall reflector adjacent to the green LED, And a green phosphor is coated on the inner surface and the sidewall of the side wall of the side reflector adjacent to the blue LED. The method of claim 8, And the partition wall is disposed on the lower reflector in a horizontal or vertical direction parallel to the side reflector. The method of claim 8, The partition wall is a backlight unit, characterized in that arranged in a matrix form on the lower reflector. The method of claim 8, The partition wall is a backlight unit, characterized in that arranged in the honeycomb shape having a plurality of hexagonal shapes on the lower reflector.

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