Abstract:
A backlight unit is presented that contains lamp support structures uniquely fitted to facilitate installation of lamps in a particular orientation. The backlight unit has tube light-emitting lamps, each of which is fitted to an asymmetric lamp holder. Lamp supports fixedly engage the asymmetric lamp holders fitted to the tube type light-emitting lamps. At least one of the lamp holders has an asymmetric hole. An outer case includes the supports to fix and support each lamp. At least one lamp has a treated surface that includes an optical sheet having a light transmittance lower than 100%.

Description:
This application claims the benefit of priority under 35 U.S.C. §119 to Korean application 50546/2004, filed Jun. 30, 2004. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (LCD), and more particularly, to a direct type backlight unit of an LCD. 
     2. Description of the Related Art 
     A cathode ray tube (CRT) is an electrical device for displaying images. CRTs are found in computer monitors, televisions, oscilloscopes, etc. However, CRTs are heavy and bulky and there is a growing demand for slim, light-weight electrical devices. 
     Other types of display devices have been developed to replace the heavy and bulky CRTs, including LCDs utilizing optical property effects, plasma display panels (PDPs) utilizing plasma discharge effects, and electro luminescence displays (ELDs) utilizing electroluminescence effects. 
     Recently, thin, light-weight, low power consuming LCDs have been developed. There is a growing demand for LCDs, which are presently developed enough to function as flat display devices in various devices, including laptop computer monitors, desktop computer monitors, and large electronic display boards. 
     To display an image, LCDs typically transmit light from an external source. Accordingly, most LCDs utilize a backlight unit as an external light source emitting light toward the LCD panel. 
     Generally, a backlight unit includes one or more tubular light-emitting lamps arranged behind an LCD panel. Depending on the arrangement of the lamps, the backlight units are classified as edge type or direct type units. 
     In an edge type unit, a lamp unit is installed at a side of a light guide plate. The lamp unit includes a light-emitting lamp, a lamp holder to hold and protect each end of the lamp, and a lamp reflector with one side inserted in a side edge of the light guide plate. The lamp reflector partially encloses the lamp to reflect light from the lamp toward the light guide plate. Edge type backlight units are typically used in smaller LCDs, including laptop computer LCD monitors and desktop computer LCD monitors. 
     Direct type backlight units have been developed for larger LCDs that are 20-inches or bigger in size. A direct type backlight unit includes a plurality of lamps uniformly arranged below a diffusion plate, emitting light directly to an LCD panel. Because direct type backlight units utilize light more efficiently than edge type backlight units, direct type units are particularly well suited for large sized LCDs requiring more brightness. 
     However, because direct type backlight units usually operate longer and utilize more lamps than edge type backlight units, direct type backlight units in large LCD monitors and LCD TVs are more prone to fail than edge type backlight units. Moreover, edge type backlight units with lamp units at both sides of a light guide plate are less affected when a lamp unit malfunctions. 
     Direct type backlight units are more prone to problems because they include a plurality of lamps under a LCD panel. For example, if one of the lamps is not turned on, there is a noticeable difference in brightness on the part of the LCD screen where the malfunctioning lamp is located. Since LCDs with direct type backlight unit require frequent lamp replacements, it is desirable for them to have a structure well-suited for lamp replacements. Regardless, having to replace lamps in either case decreases luminescence efficiency. 
     Backlight units of the related art will now be described with reference to the accompanying drawings. 
       FIG. 1  is an exploded perspective view of an edge type backlight unit according to the related art;  FIG. 2  is an exploded perspective view of a direct type backlight unit according to the related art. 
     As stated before, edge type backlight units may be used in desktop or laptop computer monitors.  FIG. 1  describes an edge type backlight unit in a desktop monitor. Here the backlight unit includes lamps  10  for a source of light, a light guide plate  11 , a diffusion sheet  12 , a prism sheet  13 , an LCD panel  14  above the prism sheet  13 , a fixture (not shown) under the light guide plate  11 , and a lower reflection plate  16 . The light guide plate  11  guides light from the lamps  10  toward the LCD panel  14 , and the diffusion sheet  12  diffuses light from the light guide plate  11  in an upward direction at a predetermined angle. One or more additional diffusion sheets may be included. The prism sheet  13  refracts and condenses the diffused light, sending the light to the LCD panel  14 . The lower reflection plate  16  reflects light emitted to the fixture toward the LCD panel  14  to minimize light loss. 
     An edge type backlight unit further includes lamp reflectors  18  and lamp holders  17 . Each of the lamp reflectors  18  encloses a portion of the lamp  10  at a position opposite to the light guide plate  11 , such that light emitted in a direction opposite to the light guide plate  11  can be reflected toward the light guide plate  11  to limit loss of light. The lamp holders  17  support the light guide plate  11  and fix their corresponding lamps  10  at a predetermined position. 
     While the backlight unit for the desktop computer in the present example includes lamps  10  at both sides of the light guide plate  11 , backlight units for laptop computers may include a single lamp at one side of the light guide plate. 
     The direct type backlight unit depicted in  FIG. 2  includes a plurality of light-emitting lamps  1 , an outer case  3  to fix and support the light-emitting lamps  1 , and light scattering units  5   a ,  5   b , and  5   c  disposed between the light-emitting lambs and an LCD panel (not shown). 
     The light scattering units  5   a ,  5   b , and  5   c  prevent contours of the light-emitting lamps  1  from appearing on the LCD panel screen. That is, the light scattering units  5   a ,  5   b , and  5   c  receive and scatter non-uniform light from the light emitting lamps  1 , uniformly projecting the light toward the LCD panel so that the LCD panel can display images with a uniform brightness. To increase the light scattering effect, the light scattering units  5   a ,  5   b , and  5   c  include a plurality of diffusion sheets and a plurality of diffusion plates. 
     The direct type backlight unit in  FIG. 2  further includes a reflection plate  7  at the inner bottom of an outer case  3  to reflect light from the light-emitting lamps  1  toward the LCD panel and to decrease light loss. 
     Each of the light-emitting lamps  1  is a cold cathode fluorescent lamp (CCFL). The light-emitting lamp  1  includes a tube and electrodes at both ends. When power is applied to the electrodes, the light-emitting lamp  1  emits light. Each end of the light-emitting lamp  1  is inserted in holes located on opposite sides of the outer case  3 . 
     For each light-emitting lamp  1 , lead wires  9  and  9   a  are connected to electrodes. Each lead wire  9  and  9   a  is joined to another lead wire by a separate connector (not shown), providing a connection to drive a circuit below the outer case  3 . 
     External electrode fluorescent lamps (EEFL) or hot cathode fluorescent lamps (HCFL) may substitute for the light-emitting CCFL lamps  1  in  FIG. 2 . 
       FIGS. 3A to 3C  depict representative lamp support structures used in direct type backlight units according to the related art. 
     In  FIG. 3A , a recessed portion  32  is provided to receive an end of a tube type lamp  30 . In  FIGS. 3B and 3C , the lamp support structures  34  provide an appropriate hole  35  for a particular tube type lamp  30  end. 
     Because the lamps in  FIGS. 3A to 3C  have a tubular shape, the radial, light emitting surface of the lamp may be arbitrarily oriented when the lamp is fixed to the lamp support. 
     This would not be a problem if the light were uniformly emitted from the radial surface of the lamp. However, if light intensity differs depending on the radial direction of the lamp surface, installation of arbitrarily oriented lamps may provide suboptimal performance, including non-uniform brightness and deteriorating image quality. This may be the case when using thin backlight units in which the radial surface of the lamp is treated to produce radially varying light intensities to prevent contours of the lamp from appearing on the LCD panel screen. 
     In the related art, it is not easy to install a surface treated lamp oriented in a proper direction. To do so, would require a loss in productivity. Moreover, even if the lamp were installed in a proper orientation, the vibration and impact associated with long-term use may alter the orientation. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a backlight unit substantially obviating one or more problems due to limitations and disadvantages of the related art. 
     The present invention provides a backlight unit having lamp support structures uniquely fitted for asymmetric lamp holder ends to facilitate installation of the lamp in a particular orientation. In addition, because the lamp surface of the present invention is treated to emit light at different intensities, light can be uniformly projected from the disclosed backlight unit to a panel, such as LCD panel, in which the backlight unit is used. 
     In one aspect, the present invention provides a backlight unit including: a plurality of tube type light-emitting lamps, each lamp fitted to at least one asymmetric lamp holder; a plurality of lamp supports fixedly engaging a plurality asymmetric lamp holders fitted to the tube type light-emitting lamps; and an outer case including the plurality of supports to fix and support each lamp. 
     In another aspect, the present invention provides a backlight unit including: a plurality of tube type light-emitting lamps, each tube type light-emitting lamp fitted to at least one asymmetric lamp holder, where at least one tube type light-emitting lamp has a treated surface emitting light with different intensities; a plurality of lamp supports fixedly engaging a plurality asymmetric lamp holders fitted to the tube type light-emitting lamps; and an outer case including the plurality of supports to fix and support each lamp. 
     In a further aspect, the present invention provides an LCD device, including an LCD panel and a backlight unit, where the backlight unit includes: a plurality of tube type light-emitting lamps, each lamp fitted to at least one asymmetric lamp holder; a plurality of lamp supports fixedly engaging a plurality asymmetric lamp holders fitted to the tube type light-emitting lamps; and an outer case including the plurality of supports to fix and support each lamp. 
     It is to be understood that both the foregoing general description and the following detailed description exemplify the present invention and are intended to illustrate the present invention as set forth in the specification, claims, and appended drawings. exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     Additional advantages and features of the present invention are set forth in the description and claims which follow and will be apparent to those having ordinary skill in the art examining the disclosures therein. The advantages of the present invention may be realized or achieved with the embodiments set forth in the specification, claims, and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate aspects and principles of the related art and of the present invention: 
         FIG. 1  is an exploded perspective view of an edge type backlight unit according to the related art; 
         FIG. 2  is an exploded perspective view of a direct type backlight unit according to the related art; 
         FIGS. 3A to 3C  show lamp support structures of a direct type backlight unit according to the related art; 
         FIGS. 4A and 4B  provide exploded perspective views of a backlight unit according to some aspects of the present invention; 
         FIGS. 5A and 5B  provide a side sectional view and a cross sectional view showing an end of a lamp of a backlight unit according to an aspect of the present invention; 
         FIG. 6  is a sectional view of a lamp support from a backlight unit according to another aspect of the present invention; and 
         FIG. 7  is a perspective view showing the coupling structure between a lamp and a lamp support from a backlight unit according to further aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference to various embodiments of the present invention will now be made, examples of which are described in the specification and claims and illustrated in  FIGS. 4-7 . 
     The present invention relates to a direct type backlight unit and to an LCD device including a backlight unit of the present invention. LCD devices in accordance with the present invention may employ any of the inventive backlight unit embodiments disclosed in the specification and claims. 
     When compared with a backlight unit of the related art, a backlight unit of the present invention characteristically includes a plurality of lamps, lamp holders, and lamp supports, in which the lamp holders and lamp supports share asymmetric structures for fixing lamps to lamp supports in a specific orientation or direction. In a further aspect, the backlight units of the present invention may further include lamps emitting light with different intensities depending on the orientation or direction in which the lamp is placed. 
       FIGS. 4A and 4B  provide exploded perspective views illustrate a backlight unit according to aspects of the present invention.  FIG. 4A  depicts a direct type backlight unit including a plurality of light-emitting lamps  41 , an outer case  43  to fix and support the lamps  41 , and light scattering units  45   a ,  45   b , and  45   c  disposed between the lamps  41  and an LCD panel (not shown). 
     Light scattering units  45   a ,  45   b , and  45   c  are provided to prevent the contours of the lamps  41  from appearing on the LCD panel screen. Accordingly, the light scattering units  45   a ,  45   b , and  45   c  receive non-uniform light from the lamps  41 , scatter the received light, and then uniformly or substantially uniformly project the light toward the LCD panel so that the LCD panel can display images having uniform brightness. To increase the light scattering effect, the light scattering units  45   a ,  45   b , and  45   c  may further include a plurality of diffusion sheets and/or diffusion plates. 
     The direct type backlight unit may further include a reflection plate  47  at an inner bottom of the outer case  43  to reflect light from the lamps  41  toward the LCD panel and reduce the loss of light. 
     The lamps  41  may include cold cathode fluorescent lamps (CCFL), external electrode fluorescent lamps (EEFL), and/or hot cathode fluorescent lamps (HCFL). The lamps  41  include a tube with electrodes at each end. When power is applied to the electrodes, a lamp  41  will emit light. A lamp  41  may further include or be connected to an asymmetric lamp holder (not shown) at each end for coupling with a lamp support  42  in the outer case  43 . 
     For each light-emitting lamp  41 , lead wires  49  and  49   a  are connected to electrodes. The lead wires  49  and  49   a  are extended from each end and joined to another lead wire by a separate connector (not shown), providing a connection to drive a circuit below the outer case  43 . 
     Because the lamps  41  are connected to an asymmetric lamp holder (not shown) at each end, the lamp  41  can be installed in a particular, appropriate orientation by coupling or fitting the lamp holder to a matching lamp support  42  in the outer case  43 . In this way, a fixed orientation of the installed lamp  41  may be maintained even when subjected to vibrations, impact or long term use and may therefore allow light to be uniformly emitted for a substantially long period of time. 
     In a further aspect, hatched lamp portions in  FIG. 4B  are depicted to represent lamps  41  that are surface treated to emit light with different intensities. To achieve different light emitting intensities, a light diffusion pattern may be coated or printed on an upper surface of the lamp  41 . Alternatively, an optical sheet having light transmittance under 100% may be attached to the upper surface of the lamp  41 . By using lamps with different light emitting intensities, light may be more uniformly projected to an LCD panel, resulting in better image quality. 
       FIGS. 5A and 5B  depict a side sectional and cross sectional views of a lamp/lamp holder end that may be used in a backlight unit according to certain aspects of the present invention. In the representative example depicted, a surface of a lamp  50  may be treated to emit light with different intensities. The surface treatment of the lamp  50  in  FIG. 5A  is similar to the treatment indicated by the hatched lamp portions in  FIG. 4B . 
     For example, a light diffusion pattern  52  may printed or coated on a top surface of the lamp  50  to emit light with different intensity. Alternatively, an optical sheet having a light transmittance of less than 100% can be attached to the surface of the lamp  50  instead. In principle, any conventional treatment sufficient to uniformly or substantially uniformly project light from lamps fixedly oriented to e.g., an LCD panel may be used. 
     Lamps  50  may include any tube type light-emitting lamp, including but not limited to CCFL, EEFL, and HCFL lamps. The lamp  50  may further include or be connected to at least one or two asymmetric lamp holders  54  at one or both ends. 
     When assembled, the lamp  50  and/or its lamp holder is coupled to a lamp support (refer to  60  in  FIG. 6 ) disposed on a portion or edge of the outer case.  FIG. 6  is a sectional view of a lamp support  60  for a representative backlight unit according to the present invention;  FIG. 7  is a perspective view illustrating the coupling of a lamp  50 , lamp holder  54  and lamp support  60  with a representative backlight unit according to the present invention. 
     In  FIGS. 6 and 7 , the lamp support  60  is illustrated to define an asymmetric hole  62  for coupling to the lamp holder  54  in or connected to the lamp  50 . The lamp  50 , in conjunction with the lamp holder  54 , lead wires  56 , and lamp support  60  together serve to fix the orientation of the lamp to the holder  56 . Because the hole  62  in the lamp support  60  has an asymmetric shape complementary to the asymmetric shape of the lamp holder  54 , the lamp holder  50  can only be inserted into the complementary hole  62  in the lamp support  60  in a predetermined orientation. 
     By way of example, the asymmetric hole  62  in the lamp holder  60  has a rectangular portion and a semicircular portion; accordingly, as shown in  FIG. 6 , the lamp holder  54  has the complementary shape matching suitable for orientations-specific engagement by asymmetric hole  62 . Accordingly, the lamp  50  can be inserted and maintained in a specific orientation in the lamp holder  60  even when vibration or impact is applied. Thus, the lamp  50  can be easily installed in a desired orientation or direction and can be firmly maintained in a predetermined position for extended periods of time owing to the asymmetric nature of the lamp holder  54  and its complementary lamp support  60  providing an asymmetric hole  62 . 
     To fix a lamp in a particular orientation, the lamp holders and lamp supports may be designed to accommodate a wide variety of complementary three dimensional shapes suitable for maintaining a fixedly orienting the lamps. 
     In view of the advantages and benefits of the present invention, an LCD device employing a backlight unit according to the present invention may display images exhibiting an increased uniformity in brightness, even when the thickness of the LCD if reduced. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, the present invention is intended to cover the modifications and variations of this invention provided they come within the scope of the specification, appended claims and their equivalents.