Backlight unit

A backlight unit, suitable for a large sized LCD device, includes a plurality of fluorescent lamps alternately provided under an LCD panel in at least two parts, formed by dividing a light-emitting surface. Adjacent end parts of the fluorescent lamps are overlapped partially. Each fluorescent lamp is shorter than a length (e.g., horizontal dimension) of the light-emitting surface. A reflective plate is provided below the plurality of fluorescent lamps, and has a rugged part underlying the overlapped portion of the fluorescent lamps. Alternatively or in addition, a light-scattering pattern can be provided in a portion of a light-scattering means, over the overlapped portion of the fluorescent lamps. The rugged part and/or light-scattering pattern prevents obscure rays in the overlapped portion and improves a uniformity of luminance of the backlight unit.

This application claims the benefit of the Korean Application No. 10-2003-0073384 filed on Oct. 21, 2003, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit, and more particularly, to a backlight unit suitable for a large sized LCD device having improved uniformity of luminance.

2. Discussion of the Related Art

A cathode ray tube (CRT), has been widely used for computer monitors and televisions. However, the CRT is heavy and bulky. Thus, display devices, such as a liquid crystal display (LCD), a plasma display panel (PDP) and an electroluminescene display (ELD), have been substituted for the CRT. Among the alternative display devices, the LCD device has been very popular due to the LCD device having a low power consumption, thin profile and lightness in weight. The LCD device has been employed as a monitor for a desktop computer, a large sized television display device, as well as for a laptop computer.

Most LCD devices control the light transmittance from ambient light to display images. In this respect, it is necessary to form an additional light source, such as a backlight unit in an LCD panel. In general, the backlight unit, used as the light source of the LCD device, has a cylindrical fluorescent lamp, which is classified into two types, a direct type and an edge type, according to a disposition of the fluorescent lamp.

In the edge type backlight unit, a lamp unit is provided at one side of a light-guiding plate. The lamp unit is provided with a lamp emitting light. A lamp holder is inserted into both ends of the lamp to protect the lamp. A reflective plate has one side inserted to the light-guiding plate and surrounds the circumference of the lamp, to reflect the light emitted from the lamp to the light-guiding plate. The edge type backlight unit is generally applied to relatively small sized LCD devices, such as the monitors of the laptop computer and the desktop computer. The edge type backlight is advantageous in that it has great uniformity of light, long life span, and a thin profile.

The direct type backlight unit is suitable for a large sized LCD device of 20 inches or more. The direct type backlight unit includes a plurality of lamps arranged in one direction below a light-diffusion plate to directly illuminate an entire surface of the LCD panel with light. The direct type backlight unit has great light efficiency and is commonly used for the large sized LCD devices requiring high luminance, such as televisions.

A related art backlight unit for an LCD device will be described with reference to the accompanying drawings.FIG. 1is a perspective view of a direct type backlight unit, according to the related art.FIG. 2is a plane view of the arrangement of fluorescent lamps in a direct type backlight unit, according to the related art.FIG. 3is a plane view of the arrangement of fluorescent lamps in a direct type backlight unit, according to another embodiment of the related art.

As shown inFIG. 1andFIG. 2, the backlight unit according to the related art includes a plurality of fluorescent lamps1, an outer case3, and light-scattering means5a,5band5c. The outer case3fixes and supports the plurality of fluorescent lamps1, and the light-scattering means5a,5band5care provided between the fluorescent lamps1and an LCD panel (not shown). The light-scattering means5a,5band5cprevent the silhouette of the fluorescent lamps1from being reflected on a display surface of the LCD panel (not shown), and provide a light source with uniform luminance. For improving the light-scattering effect, the light-scattering means includes a diffusion plate5a, a prism sheet5b, and a protection sheet5c. Also, a reflective plate7is provided inside the outer case3for concentrating the light emitted from the fluorescent lamps1to the display part of the LCD panel.

Each fluorescent lamp1is a cold cathode fluorescent lamp (CCFL)1. Electrode parts2aand2bare provided at both ends in a tube of the CCFL, and power supplying wires9aand9bare respectively connected with the electrode parts2aand2b. Both ends of the fluorescent lamp1are inserted into and fixed to both sides of the outer case3. In this state, as a voltage is applied to the electrode parts2aand2b, through the power supplying wires9aand9b, the fluorescent lamp1emits light, and the fluorescent lamp1provides light for the LCD device. Although not shown, the voltage applied to the power supplying wires9aand9bis provided from an inverter, wherein the inverter is provided at the rear of the outer case3.

In the direct type backlight unit, according to the related art as shown inFIG. 2, the fluorescent lamps1are provided at fixed intervals and have a length corresponding to a horizontal line of a light-emitting surface of the backlight unit. Accordingly, the length of the fluorescent lamp1increases with an increase in the horizontal length of the light-emitting surface of the backlight unit. For example, if the LCD device has a size of 30 inches to 40 inches, it is necessary to employ fluorescent lamps having a length of 700□ or more.

As the length of the fluorescent lamp increases, the fabrication process of the fluorescent lamp becomes more difficult. Also, when a relatively long fluorescent lamp is disposed in the backlight unit, the assembling process is complicated. Furthermore, the backlight unit is more susceptible to damage by external forces. In addition, when driving the fluorescent lamp, it is difficult to realize uniform luminance. Also, it is required to maintain a high driving voltage, which may lead to the problem of electro magnetic interference (EMI) by an electric interference of a driving circuit for obtaining stability and driving the LCD panel.

To solve these problems, a different design in a direct type backlight unit, according to the related art, is shown inFIG. 3. As shown inFIG. 3, fluorescent lamps30, each having a length corresponding to a vertical line of the light-emitting surface of the backlight unit, are provided at fixed intervals along a length direction of the light-emitting surface of the backlight unit. Electrode parts32aand32bare formed at both ends of a tube in each fluorescent lamp30, and power supplying wires33aand33bare connected with the electrode parts32aand32b. The backlight unit also includes a reflective plate31.

However, as shown inFIG. 3, if the fluorescent lamps30extend in the vertical direction of the light-emitting surface of the backlight unit, hydrargyrum moves in the tube of the fluorescent lamp30downward. This movement of the hydrargyrum deteriorates the characteristics of the fluorescent lamp30. As a result, it is impossible to obtain uniformity of luminance.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a backlight unit that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide to a backlight unit suitable for a large sized LCD device having a characterizing disposition of fluorescent lamps. Each fluorescent lamp is shorter than a horizontal length of a light-emitting surface of the backlight unit. The lamps are fixed at intervals along a width (vertical) direction of the light-emitting surface. This arrangement improves the endurance of the backlight unit. Also, it is possible to realize a simplified fabrication process of the fluorescent lamp and simplified assembling process of the backlight unit, and to prevent obscure rays in an overlapped portion of the fluorescent lamps.

To achieve these objects and other advantages and in accordance with the present invention, a backlight unit includes a plurality of fluorescent lamps alternately provided under an LCD panel in at least two parts formed by dividing a light-emitting surface. Adjacent end parts of the fluorescent lamps are overlapped partially. Each fluorescent lamp is shorter than a horizontal length of the light-emitting surface. A reflective plate is provided below the plurality of fluorescent lamps. A rugged part on the reflective plate, corresponds to the overlapped portion of the fluorescent lamps.

In another aspect, a backlight unit includes a plurality of fluorescent lamps alternately provided under an LCD panel in at least two parts formed by dividing a light-emitting surface. Adjacent end parts of the fluorescent lamps are overlapped partially. Each fluorescent lamp is shorter than a horizontal length of the light-emitting surface. A reflective plate is provided below the plurality of fluorescent lamps. A reflective sheet is provided on the reflective plate, corresponding to the overlapped portion of the fluorescent lamps. The reflective sheet may be formed of MCPET or ALSET (which is a trademark referring to a reflective layer, such as E60L, which is attached by an adhesive layer to a substrate, such as aluminum or brass).

In yet another aspect, a backlight unit includes a plurality of fluorescent lamps alternately provided under an LCD panel in at least two parts formed by dividing a light-emitting surface. Adjacent end parts of the fluorescent lamps are overlapped partially. Each fluorescent lamp is shorter than a horizontal length of the light-emitting surface. An outer case supports the fluorescent lamps. A reflective plate is provided inside the outer case below the plurality of fluorescent lamps. Light-scattering means are provided on the plurality of fluorescent lamps. A light-scattering pattern is provided on the light-scattering means, corresponding to the overlapped portion of the fluorescent lamps.

DETAILED DESCRIPTION OF THE INVENTION

First and Second Embodiments

FIG. 4AandFIG. 4Bare plane views of the arrangements of backlight units, according to the first and second embodiments of the present invention. InFIG. 4A, a light-emitting surface of a backlight unit is divided into two equal parts.FIG. 4Ashows the arrangement of the fluorescent lamps in the two parts. InFIG. 4B, a light-emitting surface of a backlight unit is divided into three equal parts.FIG. 4Bshows the arrangement of the fluorescent lamps in the three parts.

Generally, as a display surface of an LCD panel becomes large, it is necessary to increase a length of a light-emitting surface of a backlight unit, thereby increasing a length of a fluorescent lamp. If the fluorescent lamp becomes longer, a lamp voltage applied to the fluorescent lamp increases. Thus, as shown inFIG. 4AandFIG. 4B, in the backlight units according to the first and second embodiments of the present invention, the light-emitting surfaces of the backlight units are divided into at least two parts, and the fluorescent lamp is shorter than the length of the light-emitting surface (approx. 1/n, wherein, ‘n’ is a natural number above 2). Then, the fluorescent lamps are alternately provided in the parts divided by a division line (imaginary line).

In the embodiment ofFIG. 4A, the backlight unit includes a plurality of fluorescent lamps50, an outer case (not shown), a reflective plate51, and a light-scattering means (not shown). The fluorescent lamps50are alternately provided in two equal parts formed by dividing the light-emitting surface of the backlight unit, along a width (e.g., vertical dimension) direction. Also, the outer case (not shown) supports the fluorescent lamps50, and the reflective plate51is provided inside the outer case to concentrate light emitted from the fluorescent lamps50on a display part of an LCD panel. Then, the light-scattering means (not shown) is provided between the fluorescent lamps50and the LCD panel (not shown).

As shown inFIG. 4B, the backlight unit includes a plurality of fluorescent lamps100, an outer case (not shown), a reflective plate101, and a light-scattering means (not shown). The fluorescent lamps100are provided by turns in three equal parts formed by dividing the light-emitting surface of the backlight unit twice, along a width direction. Also, the outer case (not shown) supports the fluorescent lamps100, and the reflective plate101is provided inside the outer case to concentrate light emitted from the fluorescent lamps100on a display part of an LCD panel, wherein the reflective plate101is formed of a material having relatively high reflexibility, such as aluminum Al. Then, the light-scattering means (not shown) is provided between the fluorescent lamps100and the LCD panel (not shown). The light-scattering means prevents the silhouette of the fluorescent lamps from being reflected on a display surface of the LCD panel, and provides a light source with uniform luminance. The light-scattering means includes a diffusion plate, a prism sheet, and a protection sheet.

Referring toFIG. 4AandFIG. 4B, the fluorescent lamps50and100are provided to have electrode parts52aand52b,102aand102bdisposed in a zigzag pattern, which at least brings the end portions of the fluorescent lamps50,100adjacent to each other, and more preferably overlaps the end portions of the fluorescent lamps50,100. However, the present invention is not limited to this zigzag pattern. Although not shown, the electrode parts52aand52b,102aand102bmay be disposed along a line in the overlapped portions of the fluorescent lamps. Or, the fluorescent lamps, of which each is shorter than a length of the light-emitting surface, may be alternately disposed in at least two equal parts divided, wherein the fluorescent lamps have different lengths.

Each fluorescent lamp50,100may be formed of a cold cathode fluorescent lamp (CCFL). The electrode parts52aand52b,102aand102bare provided at both ends in a tube of the CCFL, and power supplying wires53aand53b,103aand103bare respectively connected with the electrode parts52aand52b,102aand102b. When voltage is applied to the electrode parts52aand52b,102aand102bthrough the power supplying wires53aand53b,103aand103b, the fluorescent lamp50,100emits light. The voltage, applied to the power supplying wires53aand53b,103aand103b, is provided from an inverter (not shown).

However, if the fluorescent50,100lamps are alternately provided in at least two equal parts formed by dividing the light-emitting surface of the backlight unit, picture quality may be deteriorated due to obscure rays in the overlapped portion of the fluorescent lamps50,100. In order to solve the problem of the obscure rays, the reflective plate51,101has a rugged part corresponding to the overlapped portion of the fluorescent lamps50,100.

FIG. 5AandFIG. 5Bare cross sectional views of a backlight unit taken along lines I–I′ and II–II′ ofFIG. 4A, and taken along lines III–III′, IV–IV′ and V–V′ ofFIG. 4B, according to the first embodiment of the present invention. InFIG. 5AandFIG. 5B, the rugged part of the reflective plate51,101is formed by a method of cutting the reflective plate51,101. However, the reflective plate51,101may have a uniform embossing structure, a non-uniform embossing structure, or an irregular structure of another shape. If the reflective plate51,101has the rugged part, underlying the overlapped portion of the fluorescent lamps50,100, it has a relatively greater efficiency of reflection in the rugged portion than that in other portions of the reflective plate, thereby preventing obscure rays in the overlapped portion of the fluorescent lamps50,100.

FIG. 6AandFIG. 6Bare cross sectional views of a backlight unit taken along lines I–I′ and II–II′ ofFIG. 4A, and taken along lines III–III′, IV–IV′ and V–V′ ofFIG. 4B, according to the second embodiment of the present invention. In the backlight unit according the second embodiment of the present invention, as shown inFIG. 6AandFIG. 6B, the reflective surface51,101has a protruding part54,104, underlying the overlapped portion of the fluorescent lamps50,100. The protruding part54,104may be formed as a uniform embossing structure, a non-uniform embossing structure, or an irregular structure of another shape. The protruding part, underlying the overlapped portion of the fluorescent lamps50,100, has a greater efficiency of reflection as compared to other portions of the reflective plate, thereby preventing obscure rays in the overlapped portion of the fluorescent lamps50,100.

Although not shown, the light-emitting surface of the backlight unit may be divided into at least two parts or sections having different sizes (as opposed to equal sizes as illustrated), and then the fluorescent lamps are alternately provided in the divided parts. In this alternative embodiment, the rugged part or the protruding part would be provided in the reflective plate underlying to the overlapped portion of the fluorescent lamps, thereby obtaining greater efficiency of reflection than that in other portions of the reflective plate, and preventing the obscure rays in the overlapped portion of the fluorescent lamps.

Third Embodiment

FIG. 7AandFIG. 7Bare plane views of the arrangement of a backlight unit according to the third embodiment of the present invention.FIG. 8AandFIG. 8Bare cross sectional views of a backlight unit taken along lines VI–VI′ and VII–VII′ ofFIG. 7A, and taken along lines VIII–VIII′, IX–IX′ and X–X′ ofFIG. 7B, respectively.

In the backlight unit according to the third embodiment of the present invention, as shown inFIG. 7AandFIG. 7B, andFIG. 8AandFIG. 8B, a light-emitting surface is divided into at least two equal parts, and a fluorescent lamp is formed to be shorter than a length (e.g., horizontal dimension) of the light-emitting surface (approx. 1/n, wherein, ‘n’ is a natural number above 2). The fluorescent lamps are alternately provided in the equal parts divided by a division line (imaginary line).

Instead of forming a rugged part or a protruding part in a reflective plate51,101underlying the overlapped portion(s) of the fluorescent lamps50,100, a reflective sheet55,105is adhered on the surface of the reflective plate51,105underlying to the overlapped portion(s) of the fluorescent lamps50,100. Then, the remaining portions of the backlight unit according to the third embodiment of the present invention have the same structure as those according to the first and second embodiments of the present invention. The reflective plate51,101may be formed of a material having great reflexibility, such as aluminum Al. The reflective sheet55,105, adhered on the surface of the reflective plate51,101, may be formed of a reflective material such as MCPET (Micro polyethylene ether phthalein) or ALSET (aluminum/brass+E60L).

Although not shown, the light-emitting surface of the backlight unit may be divided into parts or sections having different sizes (as opposed to equal sizes, as illustrated), and then the fluorescent lamps are alternately provided in the divided parts. In this alternative embodiment, the fluorescent lamp would have different lengths corresponding to the differently sized parts of the backlight unit.

As described above, the reflective sheet55,105is adhered on the surface of the reflective plate51,105corresponding to the overlapped portion of the fluorescent lamps50,100, so that the portion of the reflective plate having the reflective sheet has a greater efficiency of reflection than other portions of the reflective plate, thereby preventing obscure rays in the overlapped portion of the fluorescent lamps.

Fourth Embodiment

FIG. 9AandFIG. 9Bare cross sectional views of a backlight unit according to the fourth embodiment of the present invention.FIG. 9Ais a cross sectional view taken along lines VI–VI′ and VII–VII′ ofFIG. 7A.FIG. 9Bis a cross sectional view taken along lines VIII–VIII′, IX–IX′, and X–X′ ofFIG. 7B.

As shown inFIG. 9AandFIG. 9B, a plurality of fluorescent lamps150,200are disposed in the same manner as those of the first to third embodiments of the present invention, and a light-scattering pattern is formed in light-scattering means160,210. The electrode parts152aand152b,202aand202bare provided at both ends of the lamp, and power supplying wires153aand153b,203aand203bare respectively connected with the electrode parts152aand152b,202aand202b.

InFIG. 9AandFIG. 9B, the backlight unit according to the fourth embodiment of the present invention includes the plurality of fluorescent lamps150,200, an outer case, a reflective plate151,201, the light-scattering means160,210, and the light-scattering pattern157,257. A light-emitting surface of a backlight unit is divided into at least two equal parts, and the fluorescent lamp is shorter than a length (e.g., horizontal dimension) of the light-emitting surface (approx. 1/n, wherein, ‘n’ is a natural number above 2). The fluorescent lamps150,200are alternately provided in the parts divided by a division line (imaginary line). The outer case supports the fluorescent lamps150,200. The reflective plate151,201is provided inside the outer case to concentrate light emitted from the fluorescent lamps on a display part of an LCD panel. The reflective plate151,201is formed of a material having great reflexibility, such as aluminum Al. The light-scattering means160,210is provided between the plurality of fluorescent lamps150,200and the LCD panel (not shown). The light-scattering pattern157,257is provided on the light-scattering means160,210covering an overlapped portion of the fluorescent lamps150,200.

The light-scattering means160,210prevents the silhouette of the fluorescent lamps from being reflected on a display surface of the LCD panel (not shown), and provides a light source with uniform luminance. The light-scattering means160,210is provided with a diffusion plate154,204, a prism sheet155,205, and a protection sheet156,206.

The light-scattering pattern157,257may be coated or printed, or minute materials such as beads or sands of SiO2or GaAs, having a particle size of a few micro-meters to several tens of micro-meters, may be embedded on the diffusion plate154,204, the prism sheet155,205, or the protection sheet156,206corresponding to the overlapped portion of the fluorescent lamps150,200. As a result, the light-scattering pattern157,257is formed to have an embossed surface on the light-scattering means160,210above the overlapped portion of the fluorescent lamps150,200. Preferably, the light-scattering pattern157,257is formed on the diffusion plate154,204or the protection sheet156,206.

As described above, the light-scattering pattern157,257is formed on the surface of the light-scattering means160,210corresponding to the adjacent or overlapped portion of the fluorescent lamps150,200. The light-scattering pattern157,257has a greater efficiency of light-scattering than other portions of the light-scattering means160,210, thereby preventing obscure rays in the overlapped portion of the fluorescent lamps150,200.

Although not shown, the light-emitting surface of the backlight unit may be divided into at least two parts having different size (instead of equal sizes as illustrated), and then the fluorescent lamps are alternately provided in the divided parts. In this alternative embodiment, the light-scattering pattern would be provided in the light-scattering means corresponding to the overlapped portion of the fluorescent lamps.

As described above, the preferred embodiments of the present invention are applied to the large sized LCD device to remove the obscure rays in the overlapped portion of the fluorescent lamps, when a plurality of fluorescent lamps are alternately provided in at least two parts formed by dividing the light-emitting surface of the backlight unit, where the fluorescent lamp is shorter than the entire length of the light-emitting surface of the backlight unit.

The preferred embodiments of the present invention have illustrated a backlight unit using CCFL (cold cathode fluorescent lamp) type lamps. However, the present invention may be applied to backlight units using other lamps, such as EEFL (external electrode fluorescent lamp) type lamps.

The backlight unit, according to the present invention, has several advantages. When fabricating the backlight unit for a large sized LCD device, it is possible to use fluorescent lamps having a relatively short length. Thus, it is possible to use fluorescent lamps without regard to the size of the display device.

Also, as the length of the fluorescent lamp becomes short, it is possible to lower the lamp voltage applied to the fluorescent lamp.

In the present invention, the rugged part is provided in the reflective plate corresponding to the overlapped portion of the fluorescent lamps, or the reflective sheet is adhered on the surface of the reflective plate corresponding to the overlapped portion of the fluorescent lamps, so that the portion of the reflective plate having the rugged part or the reflective sheet has greater efficiency of reflection than other portions of the reflective plate, thereby preventing obscure rays in the overlapped portion of the fluorescent lamps.

In the present invention, the light-scattering pattern is formed on the light-scattering means corresponding to the overlapped portion of the fluorescent lamps. The light-scattering pattern has greater efficiency of light scattering than other portions of the light-scattering means, thereby preventing the obscure rays in the overlapped portion of the fluorescent lamps. Accordingly, it is possible to improve uniformity of luminance.