Abstract:
A direct-type backlight unit for a flat panel liquid crystal display includesat least one lamp installed in a housing, a diffusion plate installed above the lamp, a reflection plate having a reflection surface and a back surface installed under the lamp for reflecting light generated by the lamp from the reflection surface to the diffusion plate, and the reflection plate having at least one aperture thereon, and a heat dissipating plate combined with the back surface of the reflection plate.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a backlight unit for flat panel displays, and more particularly, to a direct-type backlight unit having improved heat-dissipating ability for flat panel displays, thereby prolonging the life of the backlight unit. 
   2. Description of the Prior Art 
   Backlight units are known in the art. The backlight unit, which is a key element in the fabrication of liquid crystal displays, is widely used in digital cameras, PDAs, vehicle satellite navigation systems, computer monitors, flat panel TVs and so on. Typically, a backlight unit, which is generally installed underneath a display panel, comprises a light source (or multiple light sources) and a light diffusion means for providing users and consumers with diffused, ample, and comfortable backlighting. Light penetrates the overlying display panel and forms various images controlled by pixel electrodes densely arranged on the display panel. Backlight units are typically divided into two major categories: edge light type and direct-type, where the direct-type backlight unit can provide higher intensity of light and is thus more suited for large size display panels such as TV panels than the edge light type. 
   Referring to  FIG. 1 , a cross-sectional view of a conventional direct-type backlight unit  10  is illustrated. The backlight unit  10  is installed underneath a display panel  12  and comprises a diffusion plate  16 , a reflection plate  18 , and multiple light tubes  14  arranged in parallel in a chamber  30  defined by the diffusion plate  16  and the reflection plate  18 . The reflection plate  18  is used to reflect light generated by the light tubes  14  upward to the overlying diffusion plate  16  thereby increasing light use efficiency of the backlight unit. The diffusion plate  16  is used to diffuse light (or reflected light) by means of shielding, scattering, or refraction. The diffusion plate  16  is typically made of acrylic or polycarbonate (PC) materials having a thickness of about 2 mm to 3 mm and a light transmission ratio of about 50% to 80%. According to a prior art method for generating diffused light, dispersed ink or light shielding tiny dots are printed onto a surface of the diffusion plate  16 . Above the diffusion plate  16 , a diffusing sheet  20  and an optic focusing film  22  are typically provided for enhancing backlighting. The diffusing sheet  20  (also referred to as a protection diffusing sheet) is made of PET or PC and has a higher light transmission ratio than that of the underlying diffusion plate  16 , a lower haze, and a thickness of about 0.11 mm to 0.15 mm. 
   However, the above-mentioned prior art direct-type backlight unit suffers from heat radiation problems. In a practical case, heat accumulated in the chamber  30  reduces lifetime of the light tubes  14  and the high temperature on the diffusion plate  16  causes distortion of the optic focusing film  22 , that, in turn, leads to poor light output performance. An approach to solving this heat buildup problem is using a heat-radiating fan installed at a periphery of the backlight module. Nevertheless, this introduces undesirable dust into the backlight unit casing and also consumes electricity. Consequently, there is a strong need to provide an improved direct-type backlight unit to elongate lifetime of light tubes, and, at the same time, thin down the backlight unit. 
   SUMMARY OF INVENTION 
   Accordingly, one object of the present invention is to provide an improved direct-type backlight unit to solve the above-mentioned problems. 
   According to the present invention, a direct-type backlight unit for a flat panel liquid crystal display comprises at least one lamp installed in a housing, a diffusion plate installed above the lamp, a reflection plate having a reflection surface and a back surface installed under the lamp for reflecting light generated by the lamp from the reflection surface to the diffusion plate, and the reflection plate having at least one aperture thereon, and a heat dissipating plate combined with the back surface of the reflection plate. 
   Other objects, advantages, and novel features of the present invention will be more clearly and readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a cross-sectional view of a conventional direct-type backlight unit. 
       FIG. 2  is a cross-sectional, schematic diagram illustrating a direct-type backlight unit according to the present invention. 
       FIG. 3  is a top view of a reflection plate according to the present invention. 
       FIG. 4  is another example of the reflection plate according to the present invention. 
       FIG. 5  is a cross-sectional schematic diagram of the backlight unit according to another preferred embodiment of the present invention. 
       FIG. 6  is an enlarged view partially showing the cross section of the backlight unit of FIG.  5 . 
       FIG. 7  is an enlarged view partially showing the cross section of another preferred example of the present invention. 
       FIG. 8  is an enlarged view partially showing the cross section of another preferred embodiment of the present invention. 
       FIG. 9  is an enlarged view of the backlight unit according to another preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 2  is a cross-sectional schematic diagram illustrating a direct-type backlight unit  50  according to a first preferred embodiment of the present invention. As shown in  FIG. 2 , the backlight unit  50  is located underneath a display panel  12 . The backlight unit  50  comprises a diffusion film  16 , a reflection plate  58 , and a plurality of lamps  14 . The lamps  14  may be cold cathode fluorescent lamps (CCFL) arranged in a first chamber  60  defined by the diffusion film  16  and the reflection plate  58 . The reflection plate  58  has a horizontal bottom surface and an inclined side surface and may be made of metals such as aluminum, alloys, foamed PET film, or PC resins. The diffusion film  16 , reflection plate  58 , and the lamps  14  are fixed on a housing  54  to ensure that dust is kept outside from entering the backlight unit  50 . Above the diffusion plate  16 , a diffusing sheet  20  and an optic focusing film  22  are optionally installed thereon for enhancing backlighting. It is understood that the number of the diffusing sheet  20  and the number of the optic focusing film  22  and arranging sequence of the two can be adjusted according to desired purposes. A heat-dissipating plate  59  is interposed between the reflection plate  58  and the housing  54  and defines a second chamber  70  with the reflection plate  58 . 
   The heat-dissipating plate  59  is preferably made of materials having high thermal conductivity, for example, metals or alloys such as aluminum, copper, magnesium, titanium, or silver, or polymer composite materials. According to the first preferred embodiment of the present invention, the heat-dissipating plate  59  is attached onto an interior surface of the housing  54 . On the outer surface  80  of the housing  54 , a plurality of fin structures  54   a  are provided for increasing heat radiation area and heat transfer efficiency. The reflection plate  58  has a plurality of convection holes  62  formed thereon, which, as specifically indicated in  FIG. 2 , are preferably arranged directly under the lamps  14 . By doing this, heat generated by the lamps  14  during operation can be transferred to the second chamber  70  from the first chamber  60  through the convection holes  62 . The heat transferred to the second chamber  70  is then transferred to the heat-dissipating plate  59 , such that the lamps  14  in the first chamber  60  can be operated substantially in an equi-temperature environment, thereby prolonging the lifetime of lamps  14 . The dimension and the shape of the convection holes  62  can be changed according to desired purposes and should not limit the present invention thereto. The distance between the reflection plate  58  and the underlying heat-dissipating plate  59  may be in a range from few millimeters to several centimeters. In another embodiment of the present invention, the heat-dissipating plate  59  is attached to the reflection plate  58 . 
     FIG. 3  is a top view of the reflection plate  58  of FIG.  2 . As shown in  FIG. 3 , the reflection plate  58  has columns of convection holes  62  arranged along the length of each of the lamps  14 . The diameter of the convection holes  62  is preferably smaller than the radius of the lamps  14  to minimize light leakage. In a case that the heat-dissipating plate  59  installed under the reflection plate  58  is made of metals, some light passing through the convection holes  62  may be reflected back to the first chamber  60  so as to increase light use efficiency. Further, the convection holes  62  may be tapered holes having a larger diameter facing the first chamber  60  and a smaller diameter facing the second chamber  70 . With the tapered convection holes, the total reflection area across the reflection plate  58  is increased. Referring now to  FIG. 4 , another example of the reflection plate  58  according to the present invention is illustrated in top view way. The convection holes  62  may be through slots, each of which having a width that is smaller than the radius of the lamps  14 . The through slots may have inclined sidewalls for increasing light reflection area. 
     FIG. 5  is a cross-sectional schematic diagram of the backlight unit  50  according to another preferred embodiment of the present invention. As shown in  FIG. 5 , the backlight unit  50  is located underneath a display panel  12 . The backlight unit  50  comprises a diffusion film  16 , a reflection plate  58 , and a plurality of lamps  14 . The lamps  14  are arranged in a first chamber  60  defined by the diffusion film  16  and the reflection plate  58 . The reflection plate  58  has a horizontal bottom surface  58   a  and an inclined side surface  58   b  and may be made of metals such as aluminum, alloys, foamed PET film, or PC resins. The diffusion film  16 , reflection plate  58 , and the lamps  14  are fixed on a housing  54  to ensure that dust is kept from entering the backlight unit  50 . Above the diffusion plate  16 , a diffusing sheet  20  and an optic focusing film  22  are optionally installed thereon for enhancing backlighting. A heat-dissipating plate  59  is interposed between the reflection plate  58  and the housing  54  and defines a second chamber  70  with the reflection plate  58 . 
   Likewise, the heat-dissipating plate  59  is preferably made of materials having high thermal conductivity, for example, metals or alloys such as aluminum, copper, magnesium, titanium, or silver, or polymer composite materials. The heat-dissipating plate  59  is attached onto an interior surface of the housing  54 . On the outer surface  80  of the housing  54 , a plurality of fin structures  54   a  are provided for increasing heat radiation area and heat transfer efficiency. The reflection plate  58  has a plurality of first convection holes  62   a  formed on the horizontal bottom surface  58   a  and a plurality of second convection holes  64  formed on the inclined side surface  58   b . The first convection holes  62   a  are preferably arranged directly under the lamps  14 . Heat generated by the lamps  14  during operation can be transferred to the second chamber  70  from the first chamber  60  through the first convection holes  62   a . The heat transferred to the second chamber  70  is then transferred to the heat-dissipating plate  59 , such that the lamps  14  in the first chamber  60  can be operated substantially in an equi-temperature environment, thereby prolonging the lifetime of lamps  14 . The second convection holes  64  can provide an extra convection path for the air in the chambers  60  and  70 . The dimension and the shape of the first convection holes  62   a  and second convection holes  64  can be changed according to desired purposes and should not limit the present invention thereto. The distance between the reflection plate  58  and the underlying heat-dissipating plate  59  may be in a range from few millimeters to several centimeters. 
     FIG. 6  is an enlarged view partially showing the cross section of the backlight unit  50  of FIG.  5 . As shown in  FIG. 6 , heat generated by the lamps  14  is brought to the second chamber  70  from the first chamber  60  through the second convection holes  64  and the first convection holes  62   a , and then heat is exchanged with the heat-dissipating plate  59  and the housing  54 . Consequently, it is advantageous to use the present invention since the heat-dissipating ability is improved and thus the lifetime of the lamps  14  can be elongated. According to the preferred embodiment of the present invention, the reflection plate  58  and the heat-dissipating plate  59  are fastened on the housing  54  with screws  90  or the like. It is understood that contact area between the reflection plate  58  and the underlying heat-dissipating plate  59  may be increased so that heat transfer may be conducted by means of conduction in addition to convection. 
     FIG. 7  is an enlarged view partially showing the cross section of another preferred embodiment of the present invention. As shown in  FIG. 7 , the bottom of the heat-dissipating plate  59  may be puckered to form wave structures  59   a , so as to increase heat exchange area. 
     FIG. 8  is an enlarged view partially showing the cross section of another preferred example of the present invention. As shown in  FIG. 8 , the bottom of the heat-dissipating plate  59  is attached to the housing  54  and pressed into fin structures  59   b.    
     FIG. 9  is an enlarged view of the backlight unit  50  according to another preferred embodiment of the present invention. As shown in  FIG. 9 , the backlight unit  50  comprises a diffusion film  16 , a reflection plate  58 , and a plurality of lamps  14 . The lamps  14  are arranged in a first chamber  60  defined by the diffusion film  16  and the reflection plate  58 . The reflection plate  58  has a horizontal bottom surface  58   a  and an inclined side surface  58   b  and may be made of metals such as aluminum, alloys, foamed PET film, or PC resins. The diffusion film  16 , reflection plate  58 , and the lamps  14  are fixed on a housing  54  to ensure that dust is kept outside from entering the backlight unit  50 . Above the diffusion plate  16 , a diffusing sheet  20  and an optic focusing film  22  are optionally installed thereon for enhancing backlighting. A heat-dissipating plate  59  is interposed between the reflection plate  58  and the housing  54  and defines a second chamber  70  with the reflection plate  58 . A thin film such as a PE film is attached to the bottom of the reflection plate  58  to seal the second chamber  70 . The sealed second chamber may be filled with heat dissipating materials  70  having high thermal conductivity either in liquid or solid phases. 
   The heat-dissipating plate  59  is preferably made of materials having high thermal conductivity, for example, metals or alloys such as aluminum, copper, magnesium, titanium, or silver, or polymer composite materials. The heat-dissipating plate  59  is attached onto an interior surface of the housing  54 . On the outer surface  80  of the housing  54 , a plurality of fin structures  54   a  are provided for increasing heat radiation area and heat transfer efficiency. The reflection plate  58  has a plurality of first convection holes  62   a  formed on the horizontal bottom surface  58   a  and a plurality of second convection holes  64  formed on the inclined side surface  58   b . The first convection holes  62   a  are preferably arranged directly under the lamps  14 . Heat generated by the lamps  14  during operation can be transferred to the heat-dissipating materials  70  within second chamber  70  from the first chamber  60  through the first convection holes  62   a  and second convection holes  64 . The heat transferred to the second chamber  70  is then transferred to the heat-dissipating plate  59 , such that the lamps  14  in the first chamber  60  can be operated substantially in an equi-temperature environment, thereby prolonging the lifetime of lamps  14 . 
   In contrast to the prior art backlight unit, it is advantageous to use the present invention because the lifetime of CCFL lamps can be elongated due to the significant improvement of heat dissipation. Further, with the use of tapered convection holes and the metallic heat-dissipating plate, light use efficiency and brightness of the backlight unit are not affected. 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.