Abstract:
A field emission lamp, capable of preventing the degradation and the non-uniformly distribution of the light intensity of the emitted light, even after long-term usage of the field emission lamp, is disclosed. The anode of the disclosed field emission lamp is not required to be transparent. The disclosed field emission lamp comprises: a transparent shell; an anode unit set inside the transparent shell; a cathode unit set between the anode unit and the transparent shell; and a phosphor layer set above the anode unit. The cathode unit is apart from the phosphor layer with a certain distance. The phosphor layer and the anode unit are both surrounded by the cathode unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a field emission lamp and, more particular, to a field emission lamp enabling long-term usage without brightness degradation and/or unfavorable light uniformity and enabling the anode to be made of a conductive material without high transparency. 
         [0003]    2. Description of Related Art 
         [0004]    Reference with  FIG. 1 , a conventional field emission lamp comprises: a transparent shell  11 , an anode unit  12 , a cathode unit  13 , and a phosphor layer  14 , in which, the transparent shell  11  has an inner surface  111 , and the anode unit  12  is set on a part of the inner surface  111  of the transparent shell  11 . The cathode unit  13  is fixed at the central part of the transparent shell  11  and is surrounded by the anode unit  12 . The phosphor layer  14  is set on the anode unit  12 . 
         [0005]    The cathode unit  13  is apart from the phosphor layer  14  with a certain distance, the anode unit  12  and the cathode unit  13  each electrically connects to contact pins (not shown) and forms a loop with an outer driving circuit (not shown), and therefore the field emission lamp can be driven to provide light by receiving a driving voltage from the outer driving circuit. 
         [0006]    The transparent shell  11  is a transparent tube made of soda-lime glass. Besides, the anode unit  12  is made of ITO (indium-tin oxide) or carbon-nanotube film, and the cathode unit  13  is a metal bar covered with carbon-nanotubes serving as the electron emitter. 
         [0007]    However, a large quantity of electrons may accumulate in the phosphor layer  14  after a long-term operation (with many electrons bombarding the phosphor layer  14 ) of the field emission lamp, and a coulomb aging effect of the phosphor layer  14  may happen and cause brightness degradation and unsatisfactory uniformity of the light transmitted by the field emission lamp. Reference with  FIG. 1 , since the light provided by the phosphor layer  14  passes through the anode unit  12  set in the inner surface  111  of the transparent shell  11 , a certain transparency of the anode unit  12  is needed to ensure the luminous efficacy of the field emission lamp. However, complex steps are required for the forming of the transparent electrode compared with the forming of a metal electrode, and the electrical conductivity of the produced transparent electrode is usually lower than a metal electrode, therefore the lifetime of the applied field emission lamp will be negatively influenced. 
         [0008]    Therefore, it is desirable to provide an improved field emission lamp enabling long-term usage without brightness degradation and/or unfavorable light uniformity and enabling the anode to be made of a conductive material without high transparency. 
       SUMMARY OF THE INVENTION 
       [0009]    An object of the present invention is to provide a field emission lamp enabling long-term usage without brightness degradation and/or unfavorable light uniformity. 
         [0010]    Another object of the present invention is to provide a field emission lamp enabling the anode to be made of a conductive material without high transparency. 
         [0011]    Therefore, the present invention provides a field emission lamp comprising: a transparent shell; an anode unit set inside the transparent shell; a cathode unit set between the anode unit and the transparent shell; and a phosphor layer set above the anode unit, wherein the cathode unit is apart from the phosphor layer with a certain distance, and the cathode unit surrounds the anode unit. 
         [0012]    The present invention also provides a field emission lamp comprising: a first substrate; a second substrate; an anode unit locating between the first substrate and the second substrate, wherein the anode unit is set on part of the surface of the first substrate; a phosphor layer locates between the second substrate and the anode unit, wherein the phosphor layer is set on the anode unit; and a cathode unit locates between the second substrate and the phosphor layer, wherein the cathode unit is apart from the phosphor layer with a certain distance. 
         [0013]    According to the present invention, even with a long-term operation of the field emission lamp, the electrons accumulated in the phosphor layer can be drained efficiently by the anode unit surrounded by the phosphor layer. Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light transmitted by the field emission lamp can be increased. Also, since the anode unit of the field emission lamp of the present example locates in the central part of the field emission lamp (as shown in  FIGS. 2 ,  3 , and  4 ) or locates in a side of the field emission lamp (on the surface of the first substrate as shown in  FIG. 5 ), light emitted from the phosphor layer can be transmitted by the field emission lamp without passing through the anode unit whereby the anode unit can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0014]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic view of a conventional field emission lamp; 
           [0016]      FIG. 2  is a schematic view of a field emission lamp of example 1 of the present invention; 
           [0017]      FIG. 3  is a schematic view of a field emission lamp of example 2 of the present invention; 
           [0018]      FIG. 4  is a schematic view of a field emission lamp of example 3 of the present invention; 
           [0019]      FIG. 5A  is a schematic view of a field emission lamp of example 4 of the present invention; 
           [0020]      FIG. 5B  is a top view of a cathode unit comprising a cathode and an electron-emitting source of the example 4; 
           [0021]      FIG. 6  is a top view of a cathode unit comprising a cathode and an electron-emitting source of the example 5; and 
           [0022]      FIG. 7  is a top view of a cathode unit comprising a cathode and an electron-emitting source of the example 6. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Reference with  FIG. 2 , the field emission lamp of the present example 1 comprises: a transparent shell  21 , an anode unit  22 , a cathode unit  23 , and a phosphor layer  24 . The anode unit  22  is set inside the transparent shell  21 , the cathode unit  23  is set between the anode unit  22  and the transparent shell  21 , the cathode unit  23  is apart from the phosphor layer  24  with a certain distance, and the cathode unit  23  surrounds the anode unit  22  and the phosphor layer  24 . 
         [0024]    In the present example, the cathode unit  23  is set on an inner surface  211  of the transparent shell  21  as shown in  FIG. 2 . The anode unit  22  and the cathode unit  23  each electrically connects to contact pins (not shown) and forms a loop with an outer driving circuit (not shown), and therefore the field emission lamp can be driven to provide light by receiving a driving voltage from the outer driving circuit. 
         [0025]    In the present example, the transparent shell  21  is a transparent tube and is made of soda lime glass. However, the transparent shell  21  may also be made of soda glass, boron glass, lead glass, quartz glass, or alkali-free glass. The cathode unit  23  is an ITO (indium-tin oxide) layer having carbon nanotubes mixed therein, but the cathode unit  23  may also be an IMO (indium molybdenum oxide) layer, an IZO (indium-zinc oxide) layer, or a graphite thin film having carbon nanotubes mixed therein. The anode unit  22  is made of metal such as stainless steel, aluminum alloy, or nickel alloy. 
         [0026]    In the present example, a reflective layer  25  locating between the phosphor layer  24  and the anode unit  22  is further provided to increase the luminous efficacy of the field emission lamp, in which the reflective layer  25  is an aluminum foil. Herein, the reflective layer  25  may also be other metal foil having high reflectivity such as a gold foil, a silver foil, or a tin foil. 
         [0027]    Hence, even after long-term operation (with many electrons emitted from the cathode unit  23  bombarding the phosphor layer  24 ) of the field emission lamp, the electrons accumulated in the phosphor layer  24  can be drained efficiently by the anode unit  22  surrounded by the phosphor layer  24 . Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light provided by the field emission lamp can be increased. 
         [0028]    Reference with  FIG. 2 , since the anode unit  22  of the field emission lamp of the present example locates in the central part of the field emission lamp, light emitted from the phosphor layer  24  can be transmitted from the field emission lamp without passing through the anode unit  22  whereas the anode unit  22  can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0029]    Reference with  FIG. 3 , the field emission lamp of the present example 2 comprises a transparent shell  31 , an anode unit  32 , a cathode unit  33 , and a phosphor layer  34 . The anode unit  32  is set inside the transparent shell  31 , the cathode unit  33  is set between the anode unit  32  and the transparent shell  31 , the cathode unit  33  is apart from the phosphor layer  34  with a certain distance, and the cathode unit  33  surrounds the anode unit  32  and the phosphor layer  34 . 
         [0030]    According to the present example, the cathode unit  33  is set on an inner surface  311  of the transparent shell  31  as shown in  FIG. 3 . The anode unit  32  and the cathode unit  33  each electrically connects to contact pins (not shown) and forms a loop with an outer driving circuit (not shown), and therefore the field emission lamp can be driven to provide light by receiving a driving voltage from the outer driving circuit. 
         [0031]    In the present example, the transparent shell  31  is formed in a hollow bulb shape and is made of soda-lime glass. However, the transparent shell  31  may also be made of soda glass, boron glass, lead glass, quartz glass, or alkali-free glass. The cathode unit  33  is an ITO (indium-tin oxide) layer having carbon nanotubes mixed therein, but the cathode unit  23  may also be an IMO (indium molybdenum oxide) layer, an IZO (indium-zinc oxide) layer, or a graphite thin film having carbon nanotubes mixed therein. 
         [0032]    The anode unit  32  comprises a glass rod  321  and an electrical conductive layer  322  coated on the glass rod  321 . In the present example 2, a reflective layer  35  locating between the phosphor layer  34  and the anode unit  32  is further provided to increase the luminous efficacy of the field emission lamp, in which the reflective layer  35  is an aluminum foil. Herein, the reflective layer  35  may also be another metal foil having high reflectivity such as a gold foil, a silver foil, or a tin foil. 
         [0033]    Hence, even after long-term operation (with many electrons emitted from the cathode unit  33  bombarding the phosphor layer  34 ) of the field emission lamp, the electrons accumulated in the phosphor layer  34  can be drained efficiently by the anode unit  32  surrounded by the phosphor layer  34 . Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light provided by the field emission lamp can be increased. 
         [0034]    Reference with  FIG. 3 , since the anode unit  32  of the field emission lamp of the present example 2 locates in the central part of the field emission lamp, light emitted from the phosphor layer  34  can be transmitted from the field emission lamp without passing through the anode unit  32  whereby the anode unit  32  can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0035]    Reference with  FIG. 4 , the field emission lamp of the present example 3 comprises a transparent shell  41 , an anode unit  42 , a cathode unit  43 , and a phosphor layer  44 . The anode unit  42  is set inside the transparent shell  41 , the cathode unit  43  is set between the anode unit  42  and the transparent shell  41 , the cathode unit  43  is apart from the phosphor layer  44  with a certain distance, and the cathode unit  43  surrounds the anode unit  42  and the phosphor layer  44 . 
         [0036]    In the present example, the transparent shell  31  is formed in a helix form and surrounds the phosphor layer  44  and the anode unit  42  as shown in  FIG. 4 . The anode unit  42  and the cathode unit  43  each electrically connects to contact pins (not shown) and forms a loop with an outer driving circuit (not shown), and therefore the field emission lamp can be driven to provide light by receiving a driving voltage from the outer driving circuit. 
         [0037]    In the present example, the transparent shell  41  is a transparent tube and is made of soda lime glass. However, the transparent shell  41  may also be made of soda glass, boron glass, lead glass, quartz glass, or alkali-free glass. The cathode unit  43  is a metal bar covered with the electron emitter, wherein the electron emitter is preferably carbon-nanotubes and the metal bar is preferably made of stainless steel, aluminum, or nickel. The anode unit  42  is preferably made of metal such as stainless steel, aluminum alloy, or nickel alloy. 
         [0038]    In the present example 3, a reflective layer  45  locating between the phosphor layer  44  and the anode unit  42  is further included to increase the luminous efficacy of the field emission lamp, in which the reflective layer  45  is an aluminum foil. Herein, the reflective layer  45  may also be another metal foil having high reflectivity such as a gold foil, a silver foil, or a tin foil. 
         [0039]    Hence, even after long-term operation (with many electrons emitted from the cathode unit  43  bombarding the phosphor layer  44 ) of the field emission lamp, the electrons accumulated in the phosphor layer  44  can be drained efficiently by the anode unit  42  surrounded by the phosphor layer  44 . Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light transmitted from the field emission lamp can be increased. 
         [0040]    Reference with  FIG. 4 , since the anode unit  42  of the field emission lamp of the present example 3 locates in the central part of the field emission lamp, light emitted from the phosphor layer  44  can be transmitted from the field emission lamp without passing through the anode unit  42  whereby the anode unit  42  can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0041]    Reference with  FIG. 5A , the field emission lamp of the present example 4 comprises a first substrate  51 , a second substrate  52 , an anode unit  53 , a phosphor layer  54 , and a cathode unit  55 . The anode unit  53  locates between the first substrate  51  and the second substrate  52 , and the anode unit  53  is set on part of the surface of the first substrate  52 . The phosphor layer  54  locates between the second substrate  52  and the anode unit  53 , and the phosphor layer  54  is set on the anode unit  53 . The cathode unit  55  comprising a cathode  551  and an electron-emitting source  552  locates between the second substrate  52  and the phosphor layer  54 , and the cathode unit  55  is apart from the phosphor layer  54  with a certain distance. 
         [0042]    In the present example, the first substrate  51  and the second substrate  52  are each a glass sheet made of soda-lime glass, however, the first substrate  51  and the second substrate  52  can also be made of soda glass, boron glass, lead glass, quartz glass, or alkali-free glass, which is not specially limited. The anode unit  53  is made of metal such as silver or aluminum. The cathode  551  is made of ITO (indium-tin oxide), and the electron-emitting source  552  may be a patterned carbon-nanotube film. 
         [0043]    Reference with  FIG. 5B , a top view of a cathode unit comprising a cathode  551  and an electron-emitting source  552  of the present example is shown, in which the electron-emitting source  552  locating on the cathode  551  is formed in a multi-bar shape and is randomly distributed over the whole surface of the cathode  551 . Alternatively, the multi-bar shaped electron-emitting source  552  can be distributed on only parts of the surface of the cathode  551  if required. 
         [0044]    Besides, in other examples, the patterned electron-emitting source may have other patterns such as a pattern with spots or a pattern with rings, as shown in  FIGS. 6 and 7  respectively, in which  FIG. 6  shows an electron-emitting source of the example 5 of the present invention and  FIG. 7  shows an electron-emitting source of the example 6 of the present invention. According to  FIG. 6 , the electron-emitting source  652  has a pattern with spots that are randomly distributed over the whole surface of the cathode  651 . According to  FIG. 7 , the electron-emitting source  752  has a pattern with rings distributing over the whole surface of the cathode  751 . 
         [0045]    Herein, an adequate aperture ratio of the pattern of the electron-emitting source should be considered. For example, when the total surface area of the patterned electron-emitting source increases (i.e. the aperture ratio of the patterned electron-emitting source decreases), the amount of the electrons emitted from the electron-emitting source is increased and therefore the brightness can be increased. However, light emitted from the cathode may be largely shielded by the electron-emitting source while the total surface area of the patterned electron-emitting source increases. Therefore, the adequate aperture ratio of the patterned electron-emitting source should be carefully considered. 
         [0046]    Reference with  FIG. 5A , the anode unit  53  and the cathode unit  55  each electrically connects to contact pins (not shown) and forms a loop with an outer driving circuit (not shown), and therefore the field emission lamp can be driven to provide light by receiving a driving voltage from the outer driving circuit. In order to enhance luminous efficacy, a reflective layer  56  locating between the phosphor layer  54  and the anode unit  53  may be further provided in the present example 4, in which the reflective layer  56  may be an aluminum foil. Alternatively, the reflective layer  56  may also be another metal foil having high reflectivity such as a gold foil, a silver foil, or a tin foil. 
         [0047]    Hence, even after long-term operation (with many electrons emitted from the cathode unit  55  bombarding the phosphor layer  54 ) of the field emission lamp, the electrons accumulated in the phosphor layer  54  can be drained efficiently by the anode unit  53  surrounded by the phosphor layer  54 . Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light transmitted by the field emission lamp can be increased. Besides, reference with  FIG. 5A , since the anode unit  53  of the field emission lamp of the present example 4 locates in a side of the field emission lamp (on the surface of the first substrate  51 ), light emitted from the phosphor layer  54  can be transmitted from the field emission lamp without passing through the anode unit  53  whereby the anode unit  53  can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0048]    According to the present invention, even after long-term operation of the field emission lamp, the electrons accumulated in the phosphor layer can be drained efficiently by the anode unit surrounded by the phosphor layer. Therefore, the coulomb aging effect incurred in the field emission lamp of the prior arts can be resolved, and the brightness and the uniformity of the light transmitted from the field emission lamp can be increased. Also, since the anode unit of the field emission lamp of the present example locates in the central part of the field emission lamp (as shown in  FIGS. 2 ,  3 , and  4 ) or locates in a side of the field emission lamp (on the surface of the first substrate as shown in  FIG. 5 ), light emitted from the phosphor layer can be transmitted from the field emission lamp without passing through the anode unit whereby the anode unit can be made of a conductive material without high transparency, the manufacturing cost can be reduced, and the process steps of the field emission lamp can be simplified. 
         [0049]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.