Abstract:
A fluorescent lamp includes an external electrode and an internal electrode provided at opposite ends of a fluorescent tube. A power conductor may connect to the internal electrode extend outside the tube to provide a connection point for the internal electrode. The tube may include an internal support element at a first end of the tube and a substantially self supporting second end of the tube. A method for assembling a backlight includes obtaining a fluorescent lamp with an external electrode at a first end of a tube, an internal electrode at a second end of the tube opposite the first end, and an internal support element at the second end of the tube. The first end of the tube may be substantially self supporting. The method also connects first and second drive connectors to the first and second ends of the tube.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. P2003-90695 filed in Korea on Dec. 12, 2003. The disclosure of Application No. P2003-90695 is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     This invention relates to display backlights and fluorescent lamps used in backlights. 
     2. Related Art 
     Cathode ray tubes (CRTs) are employed as display devices for many products. However, because of their size, weight, and power requirements, CRTs are generally unsuitable for small and light electronic products such as Personal Data Assistants (PDA), portable game machines, and other small products. Alternative displays have therefore been developed, such as liquid crystal display devices (LCDs) and plasma display panels (PDPs). LCDs find widespread use as flat display panels in laptop computers, desktop computers, televisions, and other devices because of their high quality image, lightness, thinness, compact size, and low power consumption. 
     LCDs display information by controlling transmittance of externally generated light through a liquid crystal layer. In some LCDs a backlight is placed behind the LCD panel to illuminate it. The backlight may be a direct illumination backlight or an edge illumination backlight. 
     In an edge illumination backlight, a lamp unit may be provided at a lateral side of a light-guiding plate. The lamp unit may include a fluorescent lamp, a protective lamp holder that receives one or both ends of the fluorescent lamp, and a reflective sheet that directs light emitted from the fluorescent lamp to the light-guiding plate. The edge illumination backlight may have a small enough profile to be used in small devices such as laptop computer displays to provide a uniform and long lighting life cycle. 
     Large LCDs, such as those used in televisions or large computer displays, may use a direct illumination backlight. In the direct illumination backlight, multiple fluorescent lamps may be arranged along a lower surface of a light-diffusion sheet to directly illuminate the LCD. The direct illumination backlight is more efficient than the edge illumination backlight and may provide more luminance. 
     In  FIG. 1 , the backlight  100  may include multiple fluorescent lamps  1 , an outer case  3 , and light-scattering layers  5   a ,  5   b  and  5   c . The fluorescent lamps  1  may be arranged at intervals in the case  3 . The case  3  may fix or support the fluorescent lamps  1  on one or both sides of the case  3 . 
     The light-scattering layers  5   a ,  5   b  and  5   c  may be provided between the fluorescent lamps  1  and an LCD panel (not shown). The light-scattering layers  5   a ,  5   b  and  5   c  may reduce or eliminate the reflection of silhouettes of the fluorescent lamps  1  on the LCD panel, and also may enhance uniform luminance. The layers  5   a ,  5   b , and  5   c  may include multiple light diffusion sheets and a diffusion plate between the fluorescent lamps  1  and the LCD panel. A reflective sheet  7  may be present inside the outer case  3  and may concentrate light emitted from the fluorescent lamps  1  on the LCD panel. 
     In  FIG. 2 , each fluorescent lamp  1  may include internal electrodes  2   a  and  2   b  for receiving power. Each fluorescent lamp  1  may be a Cold Cathode Fluorescent Lamp (CCFL) filled with a discharge gas. Power supply wires  9   a  and  9   b  are connected to the electrodes  2   a  and  2   b  and to a driving circuit through the connector  11 . The power supply wire  9   b  is connected to the electrode  2   b  and the connector  11  and the power supply wire  9   a  is connected to the electrode  2   a  and the connector  11 . One or both of the power supply wires  9   b  and  9   a  may run under or around a side of the outer case  3  to meet with the connector  11  when the fluorescent lamps are positioned in the case  3 . 
     For each of the multiple fluorescent lamps  1 , power supply wires couple the lamp electrodes to a separate connector. The number of wires may be large and their arrangement or routing around the outer case  3  may become complicated, decreasing the operating efficiency, increasing the fabrication cost and complexity, and lowering the yield. In addition, the fluorescent lamp electrodes extend through holes in the outer case  3  to provide access for the power supply wires. In this configuration, the changing of a lamp and routine maintenance on the backlight  100  may be difficult. 
       FIG. 3  shows an External Electrode Fluorescent Lamp (EEFL)  300  developed as an alternative to the fluorescent lamps  1  with internal electrodes. The EEFL  300  may include an external positive (+) electrode  33   a  and an external negative (−) electrode  33   b  at either end of a tube  31 . Compared to Internal Electrode Fluorescent Lamps (IEFL) such as that shown in  FIG. 2 , the EEFL  300  may have a longer lifespan and may run from a single inverter, resulting in size and weight advantages. 
     Luminance may vary over the length of the EEFL  300 . The end of the tube  31  with the positive (+) electrode  33   a  may have a relatively high luminance, while the end of the tube  31  with the negative (−) electrode  33   b  may have a relatively low luminance. The single inverter also may result in a slow start-up speed. Accordingly, the EEFL  300  is not always suitable for a large display such as a television or computer monitor. 
       FIG. 4  shows a perspective view of a direct illumination backlight  400  that includes EIFLs. The External Internal Fluorescent Lamp (EIFL) may be an alternative to the CCFL and EEFL in a direct illumination backlight.  FIG. 5  shows an EIFL that may be used in the backlight  400 . 
     In  FIG. 5 , the EIFL  44  may include a fluorescent substance (not shown) coated on an inner surface of a glass tube  42 . The EIFL  44  may also include discharge gas such as an inert rare gas mixed with hydrargyrum injected into the glass tube  42 . The EIFL  44  may also include an external electrode  56  and an internal electrode  58  that extends into the glass tube  42 . The external electrode  56  may provide the positive (+) electrode on one end of the glass tube, and the internal electrode  58  may provide the negative (−) electrode at the opposite end of the glass tube  42 . A component  45  on the outside of the glass tube  42  may secure or support the internal electrode  58 . 
     In  FIG. 4 , the backlight  400  may include multiple EIFLs  44 , supports  46  and  48 , and power connection plates  50 . The backlight  400  may also include a reflective sheet  52  and a light-diffusion sheet  54 . The EIFLs  44  may be arranged across the backlight  400 . The positive electrodes  58  of the EIFLs  44  may couple to the support  48  and the negative electrodes  56  may couple to the support  46 . 
     Power may be applied to the EIFLs  44  through the supports  46  and  48  and through the power connection plates  50  underneath the supports  46  and  48 . The reflective sheet  52  may be provided below the EIFLs  44  to reflect the light emitted from the EIFLs  44  to the LCD panel. The light-diffusion sheet  54  may be provided above the EIFLs  44  to diffuse the light reflected by the reflective sheet  52 . 
     One or both support members  46  and  48  may comprise conductive silicon rubber that supports the EIFLs  44 . The support  46  may include multiple insertion holes  53   a  that may accept the external electrodes  56 . A conductor  51  may couple one or more external electrodes  56  to apply a positive (+) voltage to the external electrodes  56 . The support  48  may include multiple insertion holes  53   b  that may accept the components  45  that support the internal electrodes  58 . A conductor  55  may couple one or more of the internal electrodes  58  to apply the negative (−) voltage to the ElFLs  44 . 
     The power connection plate  50  may include a copper material such as a copper sheet or a copper tape. The reflective sheet  52  may include concave or convex portions that may alternate along a longitudinal direction and may reflect the light emitted from the fluorescent lamp  44  to the LCD panel. The concave portions of the reflective sheet  52  may accept the EIFLs  44 . The light-diffusion sheet  54  may be spaced from the fluorescent lamps  44  to prevent the EIFL silhouettes from being cast to the LCD panel. 
     In  FIG. 6 , an inverter that drives the backlight  400  may include a high voltage generator  60 . The generator  60  produces the driving voltage for the parallel connected EIFLs  44 . The driving voltage may be applied to the external electrodes  56  through the conductor  51 , causing current flow to the internal electrodes  58  and through the lead wire  55  to generate electric discharge in the EIFLs  44 . The external electrodes  56  may serve as the positive electrodes and the internal electrodes  58  may be grounded. The inverter may drive multiple EIFLs simultaneously. 
     As the size of the display increases, the length of the EIFLs  44  increases. One consequence is that the driving voltage that starts electric discharge in the EIFLs  44  increases. The driving voltage that the inverter is able to produce may limit the size of the display. 
       FIG. 7  shows additional details of an EIFL  70 . The EIFL  70  may include an external electrode  72  outside and at one end of a tube  71 , and an internal electrode  73  provided inside and at the other end of the tube  71 . The EIFL  70  also includes an internal electrode glass bead  74  that may support or secure the power conductor  76 , and includes an external electrode glass bead  78 . The tube  71  may be coated with a fluorescent substance  75 . The power conductor  76  may couple the internal electrode  73 . 
     The EIFL fabrication process separately forms and fixes the glass beads  74  and  78  at opposite ends of the tube  71 . Fabricating the glass beads  74  and  78  may be a complex and costly process. The high driving voltage applied to the external electrode  72  also may result in particularly strong electric fields between the external electrode glass bead  78  and the tube  71 . The resulting stress on the EIFL  70  may reduce its reliability and operating life. 
     The invention is directed to a fluorescent lamp and backlight that overcomes one or more of the potential drawbacks in the related art. 
     SUMMARY 
     A backlight includes a fluorescent lamp with a tube having a first end and a second end opposite the first end. The tube may include an internal support element and internal electrode disposed at the first end of the tube. The second end of the tube may substantially omit any internal support element so that it is substantially self supporting. The backlight may also include a first drive conductor coupled to the first end of the tube and a second drive conductor coupled to the second end of the tube. 
     A fluorescent lamp may include an external electrode at a first end of a tube. The lamp may also include an internal electrode provided at a second end of the tube opposite the first end. A power conductor may couple to the internal electrode and may provide a connection point outside the tube for the internal electrode. An internal support element may be located at the second end of the tube, while the first end of the tube may be substantially self supporting. 
     Other systems, methods, features, and advantages of the invention will be, or will become apparent upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the inventions. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a perspective view of a direct illumination backlight in the related art. 
         FIG. 2  is a fluorescent lamp and connector of  FIG. 1 . 
         FIG. 3  is an External Electrode Fluorescent Lamp (EEFL) in the related art. 
         FIG. 4  is a perspective view of a direct illumination backlight in the related art. 
         FIG. 5  is an External Internal Fluorescent Lamp (EIFL) in the related art. 
         FIG. 6  is a high voltage generator connected to a direct illumination backlight. 
         FIG. 7  is a cross-sectional view of an EIFL. 
         FIG. 8  is a cross-sectional view of an External Internal Fluorescent Lamp embodiment. 
         FIG. 9  is a backlight embodiment coupled to a driver. 
         FIG. 10  is a flow diagram of assembly of an EIFL. 
         FIG. 11  is a flow diagram of assembly of a backlight. 
     
    
    
     DETAILED DESCRIPTION 
     An External Internal Fluorescent Lamp (EIFL) may provide reliability, fabrication, and driving voltage improvements. The EIFL may omit or substantially eliminate one of the internal support elements, such as glass beads, normally present at both ends of a tube. The EIFL may improve reliability and fabrication by eliminating concentrated electric fields at an end of the EIFL. The EIFL also may reduce driving voltage requirements by recapturing a portion of the glass tube normally occupied by an internal glass bead for an external electrode. The EIFL may include the advantages of both a Cold Cathode Fluorescent Lamp (CCFL) and an External Electrode Fluorescent Lamp (EEFL). 
       FIG. 8  is a cross-sectional view of an EIFL  80 . The EIFL  80  is shown as a straight tube, but may take other shapes. The EIFL  80  may include an external electrode  86  that covers all or a portion of one end of a tube  81 . The EIFL also may include an internal electrode  87  inside and at the other end of the tube  81 . A power conductor  84  may couple the internal electrode  87  and may emerge from the tube  81 . The power conductor  84  may be used to apply power to the internal electrode  87 . 
     The EIFL  80  may also include a fluorescent substance  88  on the inner surface of the tube  81 . The fluorescent substance  88  may be omitted from the all or part of the ends of tube  81  near the electrodes  86  and  87 . The EIFL  80  may include a support element, shown in  FIG. 8  in the form of a glass bead  82 , at the internal electrode end of the tube  81 . The internal electrode  87  and/or the power conductor  84  may pass in whole or in part through the glass bead  82  for support, strength, and stiffening. The EIFL  80  may omit or substantially eliminate a support element such as a glass bead at the external electrode end of the tube  81  so that it is substantially self supporting. The support elements may be formed from glass, resin, rubber, epoxy or other materials. The support element may take shapes other than a bead or circular structure, and may be uneven, rough, or otherwise irregular in shape. 
     In initial stages of manufacture of the EIFL  80 , such as before injecting lamp gas into the tube  81 , there may be little or no pressure difference between the inside and the outside of the EIFL  80 . An end of the tube  81  may be sealed without forming a support element and without experiencing the effects of a pressure differential between the inside and outside of the EIFL  80 . The first end that is sealed may be the external electrode end of the tube  81 . The external electrode  86  may be formed in a taping, dipping, plating, or other process that forms a conductor on the external surface of the tube  81 . 
     A pressure differential may arise at subsequent stages of manufacture of the EIFL  80 . When the lamp gas has been injected into the tube  81  and one end of the tube has been sealed, the inside of the tube  81  may experience a pressure lower than the outside of the tube  81 . A support element such as the glass bead  82  may be added, deposited, or formed at the opposite end of the tube  81 . The internal electrode  87  and the power conductor  84  may be provided adjacent to the glass bead  82 . The glass bead  82  helps prevent the pressure differential from collapsing the glass tube  81 . 
     Forming a glass bead at one end of the lamp may simplify fabrication of the EIFL  80  and may decrease the fabrication cost by eliminating one or more process steps that form a second support element in the tube  81 . In one implementation the glass bead is omitted or substantially eliminated from the external electrode end of the tube  81 . A reduction in electric field concentration at the external electrode end of the tube  81  may result during EIFL operation and the reliability of the tube  81  may increase. 
     Without the glass bead at one end of the tube  81 , an electrode may cover that end that was occupied by the glass bead. For example, the external electrode  86  may function over the area normally occupied by the glass bead at the external electrode end of the tube  81 . Eliminating the glass bead may increase the effective length of the tube  81  by the diameter of the eliminated glass bead without physically lengthening the tube  81  and without a corresponding increase in drive voltage to activate the tube  81 . 
     In  FIG. 9 , a direct illumination backlight  900  may include one or more EIFLs  80 . The EIFLs  80  may be connected in parallel at a regular or irregular spacing. A first drive conductor  83  may be provided to connect one or more external electrodes  86  of the EIFLs  80  to one another. A second drive conductor  85  may be provided to connect one or more of the power conductors  84  to one another. 
     The backlight  900  may also include a reflective layer (not shown) below the EIFLs  80  to reflect light emitted by the EIFLs  80  toward an LCD panel. The backlight  900  also may include one or more light diffusing layers (not shown) above the EIFLs  80  to diffuse light directly received from the EIFLs  80  or light reflected from the reflective layer. The light diffusing layers may enhance uniform illumination of the LCD panel. 
     An AC current or voltage source, such as an inverter  90 , may connect to one or more of the ElFLs  80 . The inverter  90  may drive or more of the EIFLs  80  simultaneously through the first and second drive conductors  83  and  85 . In one implementation, the internal electrodes  87  may remain un-grounded or otherwise float with respect to ground, and an AC voltage may be applied to both sides of the EIFLs  80  through the internal electrodes  87  and external electrodes  86 . The driving voltage waveforms  92  and  94  show that the AC voltage on the external electrodes  86  may be out of phase with the AC voltage on the internal electrodes  87 . Driving the external electrodes  86  and internal electrodes  87  substantially out of phase, such as approximately 180 degrees out of phase, may reduce the magnitude of the driving voltage by one-half and may enhance stable EIFL  80  operation. 
     In  FIG. 10 , an assembly process for the EIFL  80  includes providing a tube  81  (Act  1002 ). The internal surface of the tube  81  is coated with one or more radiation absorption and re-radiation substances for any desired wavelengths, such as a fluorescent substance (Act  1004 ). Alternatively, the tube  81  may be coated with a substance that does not emit radiation. One end of the tube  81  is then sealed without forming a glass bead at that end (Act  1006 ). The glass bead may be omitted or substantially eliminated from either end of the tube  81  corresponding to the external electrode  86 . In  FIG. 10 , the glass bead is omitted from the external electrode end of the EIFL  80 . 
     In the open end of the tube  81 , the internal electrode assembly  82 ,  84 , and  87  may be inserted (Act  1008 ). The internal electrode assembly  82 ,  84 , and  87  includes a glass bead  82 , an internal electrode  87 , and a power conductor  84 . The glass bead  82  may be placed, deposited, or otherwise formed in the open end of the tube  81 . The power conductor  84  is coupled to the internal electrode  87  and extends outside of the tube  81 . The glass bead  82  may be formed adjacent to or around the internal electrode  87  and/or power conductor  84 . 
     The tube  81  may be filled with a discharge gas (Act  1010 ). The discharge gas may be selected to excite the fluorescent substance that coats the internal surface of the tube  81 . 
     The internal electrode end of the tube  81  is then sealed (Act  1012 ). The external electrode  86  is then formed on the end of the tube  81  opposite the internal electrode  87  (Act  1014 ). A dipping, taping, or other conductor deposition process may form the external electrode  86 . 
     The assembly process for a backlight shown in  FIG. 11  may include providing one or more EIFLs  80  (Act  1102 ). The EIFLs may be arranged in a case or frame (Act  1104 ). A first drive conductor may connect one or more of the EIFL external electrodes together (Act  1106 ). One or more of the EIFL internal electrodes may connect together through a second drive conductor (Act  1108 ). 
     The conductors for the internal and external electrodes may be connected to a driving circuit for the ElFLs (Act  1110 ). The driving circuit may be a DC to AC inverter or other type of current or voltage driver. The backlight may also be provided with a reflective layer below the EIFLs (Act  1114 ). One or more diffusion layers may be provided above the EIFLs (Act  1116 ). The reflective layer and the diffusion layers may enhance luminance and uniform illumination of the LCD panel. 
     The EIFL omits or substantially eliminates a support element at one end of the tube  81 . In one embodiment the support element is eliminated from the external electrode end of the EIFL. The EIFL may be effectively lengthened by the diameter of the omitted glass bead without increasing the drive voltage or current for firing the EIFL. Omitting the support element may also ease electric field concentration on one end of the tube  81 , prolonging EIFL life and reliability. 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.