Patent Publication Number: US-2013229794-A1

Title: Illuminating light source and illuminating device

Description:
TECHNICAL FIELD 
     The present invention relates to a light source including a light-emitting element. 
     BACKGROUND ART 
     Compared to a conventional light source, light-emitting diodes (LEDs), which are semiconductor light-emitting elements, are small and efficient and have a long life. In addition, there are recent market needs for saving energy and resource. Therefore, these needs boost the demand for light sources using LEDs (hereinafter, such a light source is also simply referred to “LED light source”). Conventional light sources and LEDs are different in lighting principle, and are completely different in shape. However, there has been a demand for LED light sources having a similar appearance to the conventional light sources. In response to this demand, various LED light sources that substitute for light bulbs and fluorescent lamps have been commercialized. 
     LEDs are able to keep the luminous flux close to the initial level for a long time period, compared to the conventional light source such as a filament bulb and a fluorescent lamp. The use of a LED light source reduces the frequency of replacement, and it is therefore expected that the light source using the LED reduces maintenance costs. 
     Generally, in an LED light source, an LED disposed on a mount is covered with a light-transmissive outer shell made of glass or resin. Thus, the LED is protected by the outer shell and emits light through the outer shell to the outside. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] 
       
    
     Japanese Patent Application Publication No. 2009-43447
     [Patent Literature 2]   

     Japanese Patent Application Publication No. 2004-187109 
     SUMMARY OF INVENTION 
     Technical Problem 
     Although the LED keeps the luminous flux close to the initial level, if dust attaches to the surface of the outer shell of the light source due to long use, such dust causes a reduction in luminous flux transmitted to the outside. Since the conventional light source with a short life is regularly replaced to a new one having no dust, such a problem has not been seriously considered. 
     However, even if an LED light source with a longer life than the conventional light source is used, the maintenance costs and frequency do not decrease as expected since it could be necessary to remove dust so as to prevent reduction of the luminous flux. 
     In addition, a conventional light source is driven by alternating current, and an electric field generated around the light source reverses its direction in the same cycle as the cycle of drive. In contrast, an LED is driven by direct current, and an electric field generated around the light source using the LED maintains a fixed direction. Such a condition also keeps the surface of the LED light source charged, and therefore dust attracted to the LED light source due to an electric charge is presumed to easily attach to the surface. In particular, it is believed that dust attracted due to an electric charge will be notable when an outer shell is formed of an electrically-insulative material such as glass, resin, etc. 
     The present invention has been achieved in view of the above problem, and an aim thereof is to provide a light source capable of preventing an electric charge from being stored on the outer surface of the outer shell and reducing the attachment of dust due to an electric charge. 
     Solution to Problem 
     In order to the above problem, an aspect of a light source pertaining to the present invention provides a light source to be attached to a lighting fixture, comprising a light-emitting element; an outer shell that houses therein the light-emitting element; and a base provided at the outer shell, wherein the outer shell is electrically-insulative and light-transmissive, the outer shell has an electrically-conductive member provided on at least one of an outer surface and an inner surface thereof, and the electrically-conductive member is electrically connected to a grounding terminal of the lighting fixture. 
     Here, the expression “electrically connected” includes a case in which the electrically-conductive member and the grounding terminal are directly connected to each other and a case in which the electrically-conductive member and the grounding terminal are indirectly connected to each other. In addition, “base” is a component electrically connected to the lighting fixture, and may have a terminal for receiving power or a terminal for grounding (earthing), for example. 
     With such a structure, the light source is able to discharge an electric charge stored on the outer surface of the outer shell to the outside of the light source by using the electrically-conductive member. Thus, the light source is able to reduce the attachment of dust to the outer surface of the outer shell. 
     Further, according to an aspect of the light source pertaining to the present invention, electric resistance between the grounding terminal and a point on the electrically-conductive member that is electrically farthest from the grounding terminal is within a range from 1Ω to 1 MΩ. 
     With the above structure, a lower resistance value is able to prevent charge from being stored, and to reduce the attachment of dust due to an electrostatic charge. 
     Further, according to an aspect of the light source pertaining to the present invention, the electrically-conductive member is made of a light-transmissive metal oxide coating. 
     With the above structure, it is possible to suppress reduction in luminous flux caused by the electrically-conductive member. 
     Further, according to an aspect of the light source pertaining to the present invention, the electrically-conductive member is made of light-transmissive metal oxide particles. 
     With the above structure, it is possible to suppress the effect of reduction in luminous flux caused by the electrically-conductive member, and to cause the electrically-conductive member to perform the function of diffusing light. 
     Further, according to an aspect of the light source pertaining to the present invention, the electrically-conductive member is made of metal particles. 
     With the above structure, it is possible to easily provide the low resistance electrically-conductive member at the outer surface of the outer shell. 
     Further, according to an aspect of the light source pertaining to the present invention, the electrically-conductive member is made of metal. 
     With the above structure, it is possible to provide the low resistance electrically-conductive member at the outer surface of the outer shell. 
     Further, the electrically-conductive member has a function of diffusing light. 
     With the above structure, it is possible to diffuse light emitted by the light-emitting element. 
     Further, according to an aspect of the light source pertaining to the present invention, the electrically-conductive member is made of a transparent conductive film. 
     With the above structure, it is possible to increase productivity, and when the outer shell breaks, to prevent the broken pieces of the outer shell from scattering around. 
     Further, the electrically-conductive member includes a light-transmissive metal oxide coating and a strip-like conductive coating, the light-transmissive metal oxide coating being provided at a certain area of the outer surface of the outer shell to which the base is not attached, and the strip-like conductive coating being arranged in a longitudinal direction of the outer shell on an upper surface of the light-transmissive metal oxide coating. 
     With the above structure, it is possible to effectively discharge an electric charge stored on the entire outer surface of the outer shell to the outside. 
     Further, the base includes a grounding terminal connected to the grounding terminal of the lighting fixture, and the electrically-conductive member is connected to the grounding terminal of the base. 
     With the above structure, it is possible to reliably electrically connect the electrically-conductive member and the grounding terminal of the lighting fixture to each other. 
     Further, one aspect of the light source pertaining to the present invention provides a lighting apparatus comprising a light source and a lighting fixture to which the light source is detachably attached, wherein the light source is the light source of any one of Claims  1  through  10 , the lighting fixture includes a grounding terminal, and the grounding terminal and an electrically-conductive member of the light source are electrically connected to each other. 
     Here, the expression “electrically connected” includes a case in which the electrically-conductive member and the grounding terminal are directly connected to each other and a case in which the electrically-conductive member and the grounding terminal are indirectly connected to each other. 
     With the above structure, it is possible to prevent the attachment of dust. 
     Advantageous Effects of Invention 
     The present invention provides a light source having an electrically-conductive member provided on at least one of the outer surface and the inner surface of the electrically-insulative and light-transmissive outer shell, and when a grounding terminal of a lighting fixture to which the light source is attached and the electrically-conductive member are electrically connected to each other, the light source is able to discharge an electric charge stored on the outer surface of the outer shell to the outside via the electrically-conductive member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a light source pertaining to Embodiment 1 of the present invention, as viewed from the side facing a base for grounding. 
         FIG. 2  is a perspective view of the light source, as viewed from the side facing a base for receiving power. 
         FIG. 3  is a view of the light source for explaining the internal structure of the base for grounding. 
         FIG. 4  is a partial cross-section diagram of the light source for explaining the structure of an outer shell. 
         FIG. 5  is a view of the light source for explaining the base for grounding. 
         FIG. 6  is a view for explaining the light source attached to a lighting fixture. 
         FIG. 7  is a view for explaining a light source pertaining to Embodiment 2 of the present invention attached to a lighting fixture. 
         FIG. 8  is a front view of a light source pertaining to Embodiment 3 of the present invention. 
         FIG. 9  is a partial cross-sectional view of the light source for explaining the structure of an outer shell. 
         FIG. 10  is a view for explaining a circuit of the light source. 
         FIG. 11  is a view for explaining the light source attached to a lighting fixture. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     The following describes a light source pertaining to Embodiment 1 of the present invention with reference to  FIGS. 1-6 . 
       FIGS. 1 and 2  are perspective views of the light source pertaining to the present embodiment. Such a light source  1  is attached to a lighting fixture, and can be substituted for a conventional straight tube fluorescent lamp, for example. 
       FIG. 3  shows the internal structure of a base for grounding the light source  1 , which is described later. LED modules  2  shown in  FIG. 3  include a plurality of LED elements (unillustrated), which are semiconductor light-emitting elements, arranged in line on the main surface of an elongated rectangular plate-like mounting substrate  2   c.  The opposite surface of the mounting substrate  2   c  is provided with and in contact with a mount  3  made of material with high thermal conductivity, such as aluminum. The mount  3  serves as a heatsink. The LED modules  2 , along with the mount  3 , are built in the outer shell  4 . 
     Note that since the LED modules  2  and the mount  3  are in contact with each other, heat generated by the LED modules  2  can be effectively conducted to the outer shell  4  via the mount  3 . The heat conducted to the outer shell  4  is discharged from the outer surface thereof. 
     The outer shell  4  is a long and thin cylinder, and made of electrically-insulative and light-transmissive material such as resin, glass or ceramic. On one end of the outer shell  4  is provided with a base  5 , and on the other end is provided with a base  6 . The base  5  includes two pin terminals  5   a  and  5   b  used for receiving power (hereinafter, the base  5  is referred to as “power receiving base”). The base  6  includes one pin terminal  6   a  that is used for grounding (earthing) and connected to the mount  3  (hereinafter, the base  6  is referred to as “grounding base”). 
     Each of the terminals  5   a,    5   b  and  6   a  of the bases  5  and  6  should be positioned in a particular direction. When the light source  1  is attached to a lighting fixture  11 , a second electrically-conductive member  7   b  provided on the outer surface of the outer shell  4  faces toward the lighting fixture  11  (see  FIG. 6 ). 
     The outer shell  4  has an electrically-conductive member  7   a  on the outer surface or the inner surface thereof or both. In the present embodiment, the first electrically-conductive member  7   a  is provided on the outer surface. The first electrically-conductive member  7   a  is a light-transmissive conductive coating made of a conductive metal oxide such as indium tin oxide, zinc oxide, or tin oxide (in this case, the first electrically-conductive member  7   a  is metal oxide film). The first electrically-conductive member  7   a  is applied to spread from the one end to the opposite end over the outer surface of the outer shell  4 . Even though the outer surface of the outer shell  4  is covered with the first electrically-conductive member  7   a,  the effect of reduction in luminous flux caused by the electrically-conductive member  7   a  is suppressed since the first electrically-conductive member  7   a  made of the metal oxide film is light-transmissive. 
     On the first electrically-conductive member  7   a  (i.e., on the conductive coating), the second electrically-conductive member  7   b  made of metal is provided. The second electrically-conductive member  7   b  extends from the terminal  6   a  of the grounding base  6  on the outer shell  4  in a lengthwise direction thereof, and reaches just before the power receiving base  5 . The second electrically-conductive member  7   b  is fixed to the first electrically-conductive member  7   a.  The first electrically-conductive member  7   a  and the second electrically-conductive member  7   b  are electrically connected to each other, and form an electrically-conductive member  7  (see  FIG. 4 ). The second electrically-conductive member  7   b  is fixed to the first electrically-conductive member  7   a  by pressure bonding, with screws or conductive solder, for example. 
     The first electrically-conductive member  7   a,  which is the conductive coating, has a thickness from 0.1 μm to 0.5 μm, and resistivity from 1×10 −4  Ωcm to 1×10 −3  Ωcm. The first electrically-conductive member  7   a  is formed by a general thin-film forming method such as the sputter method, the deposition method, the sol-gel method and the CVD method. Other methods may be used. 
     The second electrically-conductive member  7   b  is a thin-film conductor (conductive film) made of aluminum in the shape of a strip (tape) that is 2 mm in width and 0.5 mm in thickness, for example. In the present embodiment, the second electrically-conductive member  7   b  is provided at the whole area of the outer shell  4  in the lengthwise direction except for an area of the outer shell  4  close to the power receiving base  5 . 
     As shown in  FIG. 3 , an end portion of the second electrically-conductive member  7   b  bends in the grounding base  6  to be close to the central axis of the outer shell  4 , and the end portion is connected to the terminal  6   a  (hereinafter, grounding terminal) inside the grounding base  6 . 
     The bend portion of the second electrically-conductive member  7   b  that is connected to the grounding terminal  6   a  may be divided into two parts such that the two parts sandwich the pin terminal  6   a,  or may be in the shape of a ring through which the terminal  6   a  passes, for example. In the present embodiment, the second electrically-conductive member is directly electrically connected to the terminal  6   a.  Alternatively, the electrically-conductive member  7  and the terminal  6   a  may be electrically connected to each other via another electrically-conductive member. 
     The first electrically-conductive member  7   a  is not limited to the conductive coating. For example, a transparent conductive film may be used as the first electrically-conductive member  7   a  to wrap up the outer shell  4 . The transparent conductive film is formed by dry coating a conductive material made of indium tin oxide, zinc oxide, tin oxide, etc., on a resin film made of PET, PES, PC, PAR, etc., by various methods, such as the sputter method, the ion plating method, etc. 
     The transparent conductive film is generally in the form of a roll and easily wound around the cylindrical outer shell  4 . It is therefore possible to increase productivity, and furthermore, when the outer shell breaks, the transparent conductive film prevents the broken pieces of the outer shell from scattering around. In this case, the transparent conductive film is more effective when wrapped around the outer shell  4  so as to expose the conductive coating to the outside. 
     The first electrically-conductive member  7   a  constituting the electrically-conductive member  7  may be made of a light-transmissive resin member including at least one of metal particles and conductive particles. The metal particles may be made of copper, gold, silver, aluminum, iron, and alloy composed of these metals. The conductive particles may be made of metal oxide particles made of indium tin oxide, zinc oxide, tin oxide, etc. The light-transmissive resin member is made of silicone resin, etc., and is formed by coating the outer surface of the outer shell  4  with the silicone resin, etc. 
     In this case, if light-transmissive metal oxide particles are included as an electrically-conductive member, the effect of reduction in luminous flux caused by the electrically-conductive member is suppressed, and the electrically-conductive member has the function of diffusing light. Additionally, if the electrically-conductive member is made of resin including metal particles, the low resistance electrically-conductive member is easily arranged on the outer surface of the outer shell. 
     The diameter of each of conductive particles may be from several nm to 100 μm. Further, the electrically-conductive member has the function of diffusing light, and diffuses light emitted by the LED modules  2 . The diameter of each particle is preferred to be from 1 μm to 100 μm to achieve the function of diffusing light. 
     The second electrically-conductive member  7   b  may have adhesiveness. In this case, the second electrically-conductive member  7   b  is made of conductive resin including conductive particles such as metal or metal oxide, for example. Alternatively, a metal conducting wire is brought into contact with the outer surface of the outer shell  4  as the second electrically-conductive member  7   b,  and the wire is coated with a transparent adhesive and adhered to the outer shell  4 , for example. The conductive particles may be made of copper, gold, silver, aluminum, iron, and alloy composed of these metals, for example. Alternatively, the conductive particles may be made of conductive metal oxide such as indium tin oxide, zinc oxide and tin oxide, or mixed material of these oxide. The diameter of each of conductive particles may be from several nm to 100 μm. 
     The second electrically-conductive member  7   b  is not limited to a thin-film conductor made of aluminum described above. For example, the second electrically-conductive member  7   b  may be formed by a thin-film forming method such as the deposition method of depositing metal such as aluminum, or by plating method. 
     In order to discharge an electric charge stored on the outer surface of the outer shell  4  to the outside, the lower resistance between the grounding terminal  6   a  and a point on the outer surface of the outer shell  4  that is electrically farthest from the grounding terminal  6   a  is more desirable. In other words, the lower resistance value between the grounding terminal  6   a  and a point on the outer surface of the outer shell  4  that has the highest resistance value is more desirable. It is preferable that the resistance value be 1 MΩ or less, and it is more preferable that the resistance value be 1 kΩ or less. 
     Although reducing the resistance value to zero is not practical, it is more preferable to reduce the resistance value down to a range of 1Ω to 300Ω. In the present embodiment, the resistance value can be reduced to 100Ω or less by covering the entire outer surface of the outer shell  4  with the electrically-conductive member (to be exact, with the first electrically-conductive member  7   a ). 
     As in the present embodiment, by covering a substantially entire part of the outer surface of the outer shell  4  with the first electrically-conductive member  7   a  and further providing the strip-like second electrically-conductive member  7   b  made of metal to substantially the whole part of the outer shell  4  in the lengthwise direction, it is possible to reduce the resistance value to 30Ω or less, or further to 1Ω or less. 
     The outer shell  4  may have an electrically-conductive member at least on the outer surface thereof without having the first electrically-conductive member  7   a.  That is, only the second electrically-conductive member  7   b  may constitute the electrically-conductive member  7 . Alternatively, only the first electrically-conductive member  7   a  may constitute the electrically-conductive member  7  without the second electrically-conductive member  7   b.    
     The positional relationship between the first electrically-conductive member  7   a  and the second electrically-conductive member  7   b  may be inverted. That is, the second electrically-conductive member  7   b  may be formed (positioned) on part of the outer surface of the outer shell  4 , and the first electrically-conductive member  7   a  may be formed (applied) on the second electrically-conductive member  7   b  so as to cover the entire outer surface of the outer shell  4 . 
     The second electrically-conductive member  7  may be formed of a plurality of strip-like members, may spirally wind around the outer shell  4 , may branch into two or more, and may be in the form of a net. As the area of the outer shell  4  coated with the electrically-conductive member  7  increases, the above-mentioned resistance value decreases. 
     Since reflection and absorption of light by the electrically-conductive member  7  reduces the luminous flux, it is more desirable that the electrically-conductive member  7  have a higher light transmittance. By providing an innovation in material, thickness and layer structure of the electrically-conductive members, the electrically-conductive member may have the function of antireflection. 
     Each of the grounding base  6  and the power receiving base  5  that is provided at either end of the outer shell  4  is formed of two parts made of resin. For example, as shown in  FIGS. 3 and 5 , the two parts consist of a first part  6   c  and a second part  6   d.  The electrically-conductive member  7 , the terminal  6   a,  the outer shell  4   a,  etc., are arranged in the first part  6   c,  subsequently the first part  6   c  is covered by the second part  6   d  shown in  FIG. 5 , and the first part  6   c  is then fixed to the second part  6   d  by screws  8  so as to be integrated together into one unit. Similarly, the base  5  is formed. 
     In the present embodiment, one end of the electrically-conductive member  7  (to be exact, the second electrically-conductive member  7   b ) is in the base  6 , and accordingly, the connection area of the electrically-conductive member  7  with the grounding terminal  6   a  are not seen from an external viewpoint. Therefore, a light source with the high appearance quality can be provided. 
     Each of the bases  5  and  6  may be a metallic base shaped as a bottomed cylinder, which is fit onto one end of a conventional fluorescent lamp. Such metallic bases are required to be electrically-insulative from the terminals  5   a  and  5   b  that are used for receiving power. Alternatively, other types of bases may be used (for example, G13), and new types of bases may be used. 
     The outer shell  4  pertaining to the present embodiment is a straight tube. As shown in  FIG. 1 , the outer shell  4  serves as a housing (envelope) that houses the LED modules  2  and the mount  3 , which is a heatsink. The outer shell  4  is an elongated cylinder having openings at both ends, and has annular cross section. The outer shell  4  is formed of a light-transmissive member that is electrically-insulative such as a glass tube, a plastic tube, or a ceramic tube. 
     In the present embodiment, the outer shell  4  has the same size as that of a straight tube with open ends, which is used to form a fluorescent lamp defined by the Japan Industrial Standards (JIS) for example. 
     The outer surface or the inner surface of the outer shell  4  diffuses light emitted by the LED modules  2  by being partially or entirely treated with opal glass. 
     As shown in  FIG. 3 , each of the LED modules  2  is chip on board (COB) type, and a line light source. Each LED module  2  includes the mounting substrate  2   c,  a plurality of LEDs arranged on the mounting substrate  2   c,  and a sealing member  2   a.  The sealing member  2   a  seals the linearly-arranged LEDs and is made of phosphor-containing resin including silicone resin in which phosphor particles disperse, for example. 
     In the present embodiment, the plurality of LED modules  2  are arranged in line on the mount  3 . Alternatively, only one LED module may be used. 
     LEDs of each LED module  2  are linearly arranged on the mounting substrate  2   c,  and on each of the LED modules, eight LED sequences each including three LEDs electrically connected in series are electrically connected in parallel. In the outer shell  4 , eight LED modules  2  are arranged in line on the mount  3 . The adjacent LED modules  2  are electrically connected to each other. That is, eight LED modules, on each of which the eight LED sequences each including three LEDs connected in series connected in parallel, are connected in series. 
     When the LEDs are connected as above, one end of each LED sequence and the opposite end of each LED sequence are respectively a high-potential end and a low-potential end, and accordingly, one end of the outer shell  4  is a high-potential end and the opposite end is a low-potential end. Since direct current power flows from one end of the light source  1  to the opposite end of the light source  1  in a fixed direction, the electric field maintains the fixed direction, and this produces an electric charge on the outer surface of the outer shell  4 . 
     As a result, if the outer shell  4  is not covered by (provided with) the electrically-conductive member  7 , the outer surface of the outer shell  4  is electrically charged and dust is easily to attach to the outer shell  4 . However, since the outer shell  4  is coated with the electrically-conductive member  7 , an electric charge is not stored, and it is therefore possible to prevent dust from attaching to the outer shell  4 . 
     That is, when the electric field around the light source  1  maintains the fixed direction, or when an electric charge is easily stored, the present invention is more effective. This applies to the case where a direction of the maintained electric field varies according to the point on the outer shell  4 , i.e., when potential within the outer shell  4  is differently distributed. 
     By preventing dust from attaching to the outer shell  4 , it is possible to suppress reduction in luminous flux due to dust, and to provide a high-quality lamp that keep the luminous flux close to the initial level for a long time period. In addition, due to the prevention of the attachment of dust, the maintenance activities and costs for dust removal can be lower, or even unnecessary, 
     In particular, since the electrically-conductive member  7  includes the first electrically-conductive member  7   a  formed throughout the outer surface of the outer shell  4  and the strip-like second electrically-conductive member  7   b  formed on the first electrically-conductive member  7   a,  the charge stored throughout the outer surface of the outer shell  4  is effectively discharged from the second electrically-conductive member  7   b  to the outside, via the first electrically-conductive member  7   a,  which is formed throughout the outer surface of the outer shell  4 . 
     Here, the first electrically-conductive member  7   a  is continuous in the circumferential direction. Alternatively, the first electrically-conductive member may be continuous on the outer surface of the outer shell  4  in the circumferential direction with the exception of one area that extends in the form of a strip in the longitudinal direction, and the second electrically-conductive member may cover the strip-like area in which the first electrically-conductive member is not formed and part of the first electrically-conductive member adjacent to the strip-like area, for example. In this case as well, it is possible to effectively discharge the charge stored throughout the outer surface of the outer shell  4  from the second electrically-conductive member via the first electrically-conductive member, which is formed throughout the outer surface of the outer shell  4 , to the outside of the light source  1 . 
     The mounting substrate  2   c  may be formed of a ceramic substrate made of alumina or light-transmissive aluminum nitride, an aluminum substrate made of aluminum alloy, a transparent glass substrate, and a flexible printed circuit (FPC) made of resin, for example. 
     The mounting substrate  2   c  is provided with power receiving/supplying units (external connection terminals) (unillustrated) that directly supply power to the LEDs. The external connection terminals are provided at both ends of the mounting substrate  2   c  to supply power, via a land (unillustrated), to both ends of the plurality of LEDs that are linearly arranged. 
     The power receiving base  5  contains a lighting circuit (unillustrated) including a circuit that converts alternating voltage to direct voltage. The pair of terminals  5   a  and  5   b  provided at the power receiving base  5  receive alternating power supplied from a commercial alternating power source, and supply alternating power to the lighting circuit. Subsequently, the power is supplied to the mounting substrate  2   c  via the lighting circuit. 
     One of the external connection terminals on the mounting substrate  2   c  at the high-potential end is connected to the lighting circuit via an insulation-covered lead wire (unillustrated). Another one of the external connection terminals on the mounting substrate  2   c  at the low-potential end is provided far from the power receiving base  5 , and accordingly this terminal is connected to one end of a different lead wire (unillustrated). In the neighborhood of the grounding base  6 , the different lead wire is folded back toward the power receiving base  5 , and the different lead wire runs along the back surface of the mount  3 , such that another end of the different lead wire is connected to the lighting circuit positioned in the power receiving base  5 . 
     The mount  3 , which is a heatsink on which the mounting substrate  2   c  is mounted, is electrically connected to the terminal  6   a  of the grounding base  6  via an insulation-covered lead wire  9 , and discharges an electric charge stored on the mount  3  by lighting. The lead wire  9  and the mount  3  are pressed and fixed to each other with a screw  10 , but may be fixed to each other by using other methods. 
     The outer shell  4  and the mount  3  are bonded together with adhesive (unillustrated). From a perspective of heat dissipation, it is preferable that the adhesive have thermal conductivity that is 1 W/m·K or greater, and from a perspective of weight reduction, it is preferable that the adhesive have a specific gravity that is 2 g/cm 3  or less. The adhesive is made of silicone resin or cement, for example. 
       FIG. 6  shows the light source  1  attached to a lighting fixture  11 . The power receiving base  5  is inserted into a socket  12  for supplying power, and the grounding base  6  is inserted into a socket  13  for grounding (hereinafter, this socket is referred to as “grounding socket”). 
     The socket  12  for supplying power has the function of supplying power to the two pin terminals  5   a  and  5   b  for receiving power. The socket  13  for grounding has the function of grounding the grounding terminal  6   a  to a fixture and the like. 
     From the socket  12  for supplying power, alternating or direct power (here, alternating) is supplied to the power receiving base  5 . When the grounding base  6  is electrically connected to a grounding terminal (unillustrated) contained in the grounding socket  13  that corresponds with the grounding terminal  6   a  of the grounding base  6 , a resistance value between the base  6  and the connected grounding terminal is set low enough for grounding. 
     A resistance value at a point on the outer surface of the outer shell  4  that is electrically farthest from the unillustrated grounding terminal contained in the grounding socket  13  is substantially the same as that from the grounding terminal  6   a.  Since the grounding terminal  6   a  of the light source  1  is electrically connected to the unillustrated grounding terminal contained in the grounding socket  13 , the grounding terminal contained in the grounding socket  13  is electrically connected to the electrically-conductive member  7 , and the charge stored on the outer surface is discharged (moves to the grounding socket  13 ). As a result, dust is prevented from attaching to the light source  1 . 
     Due to the prevention of the attachment of dust, the maintenance activities and costs for dust removal can be lower, or even unnecessary. The lighting apparatus including the light source  1  and the lighting fixture  11  offers the above effects. 
     When the grounding terminal (unillustrated) contained in the grounding socket  13  is electrically connected to the grounding terminal (unillustrated) of the lighting fixture  11 , the grounding terminal contained in the grounding socket has the same potential as the lighting fixture  11 . This improves the effect of preventing the attachment of dust. 
     When the light source  1  is attached to the lighting fixture  11 , the second electrically-conductive member  7   b  provided on the outer surface of the outer shell  4  faces toward the lighting fixture  11 . That is, when the lighting fixture  11  attached to the ceiling is viewed from below, the second electrically-conductive member  7   b  is behind the outer shell  4  and is not seen. 
     In the present embodiment, the mount  3  is housed in the tubular outer shell  4 , but is not limited to this. For example, the mount itself may be configured as part of a body, and a surface of the mount on which the LED modules are not mounted may be the outer surface. That is, the outer shell may be configured with a metal body and a light-transmissive outer shell. The metal body is a mount-cum-body made of metal such as aluminum with a semicircular cross-section. The light-transmissive outer shell is a cap with a substantially semicircular cross-section, and is attached to the metal body to cover the LED modules. In other words, the metal body and the light-transmissive outer shell may constitute the entire body of the lamp (i.e., outer shell). In this case, the metal body and the terminal of the grounding base are connected to each other with a lead wire, for example. 
     Although description has been made on the straight tube LED lamp receiving power from the one end thereof, the LED lamp may receive power from both ends thereof. In this case, each of both bases has one terminal for receiving power, and at least one of the bases may have a terminal for grounding. 
     In the present embodiment, the base  5  includes the pair of terminals for receiving power, and the other base includes the terminal for grounding. Alternatively, a member attached to one end of the outer shell may have a pair of terminals for receiving power and a terminal for grounding, and this member may be used as a base. In this case, a lid may be fit to the other end of the outer shell so as to close the other end. 
     Further, the terminals for receiving power and the terminal for grounding may be provided at any point on the outer shell other than the ends thereof. To be specific, any one of these terminals may be provided at the central part of the outer shell. To be more specific, a fixture grounding terminal ( 15 ) of a lighting fixture  14  in Embodiment 2 described later may be attached to the electrically-conductive member of the light source, for example. 
     Further, the bases  5  and  6  in the present embodiment include the terminals at the surfaces of the both ends of the bases each of which is shaped as a bottomed cylinder and formed of the two integrated part made of resin. Alternatively, the terminals may be provided on circumferential surfaces of the bases. 
     Embodiment 2 
     The following describes a light source pertaining to Embodiment 2 of the present invention with reference to  FIG. 7 . The present embodiment is different from Embodiment 1 according to which the base  6  has the grounding terminal  6   a.  In the present embodiment, the lighting fixture  14  is provided with a grounding terminal. Here, the light source is the same light source  1  described in Embodiment 1. 
     Hereinafter, the grounding terminal provided at the lighting fixture  14  is referred to as “fixture grounding terminal” such that this terminal can be distinguished from the grounding terminal provided at the base in Embodiment 1. The fixture grounding terminal  15  has resilience and electrical conductivity, and is made of plate-like phosphor bronze, etc., with a bent portion. 
     In the present embodiment, the fixture grounding terminal  15  is in contact with the electrically-conductive member  7  provided on the outer surface of the outer shell  4  of the light source  1  when the light source  1  is attached to the lighting fixture  14 . 
     Using the length of the light source  1  as a reference, the fixture grounding terminal  15  is attached to a point that is one fourth from each end of the light source  1 . 
     The resilience of the fixture grounding terminal  15  enables close contact between the fixture grounding terminal  15  and the outer surface of the outer shell  4 , and the fixture grounding terminal  15  is electrically connected to the electrically-conductive member  7 , which can discharge a stored charge. 
     According to the lighting fixture  14  pertaining to the present embodiment, the fixture grounding terminal  15  is in contact with intermediate points on the long and thin outer shell  4  in the longitudinal direction thereof. Accordingly, the distance from the fixture grounding terminal  15  to a point on the electrically-conductive member  7  that is electrically farthest from the fixture grounding terminal  15  on the outer surface of the outer shell  4  can be short. 
     That is, the electric resistance between the fixture grounding terminal  15  and a point on the electrically-conductive member  7  that is farthest from the fixture grounding terminal  15  can be small. 
     To be specific, when the grounding terminal  6   a  of the base  6  is used as a grounding terminal as in Embodiment 1, a point that is farthest from the grounding terminal is an end of the electrically-conductive member  7  close to the base  5 . Therefore, the distance between the grounding terminal and the point that is farthest from the grounding terminal is substantially the full length of the electrically-conductive member  7 . 
     In contrast, when the fixture grounding terminal  15  is in contact with the electrically-conductive member  7  at the intermediate points thereof, as in Embodiment 2, the distance between the grounding terminal and a point that is farthest from the grounding terminal is shorter than the full length of the electrically-conductive member  7 . The distance is shorter than the distance of Embodiment 1, and the electric resistance therebetween in Embodiment 2 is smaller than that in Embodiment 1. 
     For example, when the fixture grounding terminal  15  is arranged to be in contact with the midpoint of the light source  1  in the longitudinal (tube axis) direction of the light source  1 , points that are farthest from the grounding terminal are both ends close to the base  5  and the base  6  on the electrically-conductive member  7 . Therefore, the distance between the grounding terminal and the point that is farthest from the grounding terminal is substantially the half of the electrically-conductive member  7 . That is, compared to Embodiment 1, the electric resistance value therebetween can be halved. 
     Further, in the present embodiment, the fixture grounding terminal  15  is attached to a point that is one fourth from each end of the light source  1 , using the length of the light source  1  as a reference. Therefore, the distance between the grounding terminal and the point that is farthest from the grounding terminal is substantially one fourth of the electrically-conductive member  7 . Accordingly, compared to Embodiment 1, the electric resistance value therebetween can be reduced to one fourth. 
     As a result, it is possible to more effectively discharge an electric charge stored on the surface of the outer shell  4 , and a greater effect of preventing the attachment of dust can be obtained. If a plurality of fixture grounding terminals  15  are attached, the effect can be enhanced. 
     The present structure is also effective to a lighting fixture formed by altering a fixture for a conventional fluorescent lamp, since the socket  16  does not need to include a grounding terminal. As a matter of course, the present structure may be used together with Embodiment 1 shown in  FIG. 6 . 
     Embodiment 3 
     The following describes the overall structure of a light source  32  pertaining to Embodiment 3 of the present invention that uses an LED, with reference to  FIGS. 8-11 . A light source pertaining to Embodiment 3 of the present invention shown in  FIG. 8  includes an LED module  17 , two lead wires  18  and  19  for supplying power to the LED, a stem  20 , a light-transmissive outer shell  21 , a circuit  22  having electronic components, and a base  23 . The circuit  22  and the lead wires  18  and  19  for receiving power inside the base  23  are indicated by a dotted line. 
     The LED module  17  is made up of a rectangular plate-like substrate  17   a  on which are mounted a plurality of LEDs in line. Substantially at the center of the hollow outer shell  21  therein, the LED module  17  is housed. 
     Both ends of the LED module  17  are supported by the two lead wires  18  and  19  for supplying power, for example. The lead wires  18  and  19  for supplying power are supported by the stem  20 . An opening of the outer shell  21  is covered by the stem  20 . The base  23  is attached to the outer shell  21  so as to hide the covered part. 
     The base  23  contains the lighting circuit  22  that converts alternating voltage to direct voltage, and supplies power to the LED. One end of each of the two lead wires  18  and  19  extending from the stem  20  to the outside of the outer shell  21  is connected to the lighting circuit  22 . A pair of lead wires extend from the lighting circuit  22 , and one end of each of the lead wires is connected to the base  23 . To be specific, one end of one of the pair of lead wires is electrically connected to a screw  23   a  of the side surface of the base, and one end of the other one of the pair of lead wires is electrically connected to an eyelet  23   b  of the bottom of the base. 
     The outer shell  21  is made of glass, which is electrically-insulated material.  FIG. 9  shows a partial cross section of the outer shell  21 . The outer surface of the outer shell  21  is entirely covered with an electrically-conductive member  24 , which is a light-transmissive and electrically-conductive film, with the exception of an area that falls within 10 mm from the base  23 . 
     The area that falls within 10 mm from the base  23  is not covered with the electrically-conductive member in order to electrically insulate the base  23  and the electrically-conductive member  24 . The electrically-conductive member  24  is configured and formed in the same manner as the first electrically-conductive member  7   a  in Embodiment 1, and therefore a description thereof is omitted. 
     The LED module  17  pertaining to the present embodiment is made up of a mounting substrate made of ceramic on which are mounted  12  LEDs (unillustrated) emitting blue light in line, and a light-transmissive resin sealing member  17   b  including phosphor particles (unillustrated) such as YAG seals the LEDs. The LEDs are electrically connected in series to one another by a conductive pattern (unillustrated) which are provided on the mounting substrate, and Ag wires (unillustrated). 
     The LED module  17  includes power receiving terminals  17   c  and  17   d  provided at both ends thereof. The power receiving terminals  17   c  and  17   d  are electrically and mechanically connected to ends (the other ends) of the lead wires  18  and  19  for receiving power, respectively, through the use of solder. 
     Each of the lead wires  18  and  19  that supply power to the LED module  17  may be a single wire, or may be a composite wire formed by joining an inner lead wire, a Dumet wire, and an outer lead wire in this order. In each case, it is preferable that the lead wires  18  and  19  be strong enough to support the LED module  17 . 
     The inner lead wire extends from the stem  20  to the inside of the outer shell  21  and is connected to the power receiving terminals  17   c  and  17   d  of the LED module. The outer lead wire extends to the outside of the outer shell  21  (inside of the base  23 ) and is connected to the lighting circuit  22  for driving. It is preferable that each of the interior lead wire and the outer lead wire be made of a metal wire including copper, which is highly thermally conductive. 
     The stem  20  is made of soft glass, for example. When the lead wires  18  and  19  for receiving power are made of the above composite wires, an intermediate part made of a Dumet wire is sealed by the stem  20 . Since the stem  20  is sealed at the opening of the spherical outer shell  21 , the inside of the outer shell  21  and the outside of the outer shell  21  are electrically connected via the lead wires  18  and  19  while the airtightness in the outer shell  21  is kept. 
     The outer shell  21  is in the A-type shape (JIS C7710) like a general incandescent bulb. To be specific, the outer shell  21  has a sphere and a tube part, and the diameter of the tube part decreases as the distance from the center of the sphere increases. The outer shell  21  is made of transparent silica glass, for example, and the LED module  17  arranged at the center of the outer shell  21  can be seen from the outside of the outer shell  21 . The shape of the outer shell  21  is not limited to the A-type shape, and may be selected from the G-type shape, the E-type shape or the like in accordance with the intended use of the light source  32 . 
     In the present embodiment, the outer shell  21  and the stem  20  are made of glass, for example. In accordance with the intended use of the light source  32 , the outer shell  21  and the stem  20  may be made of resin such as acryl, and the outer shell  21  may be made of glass and the stem may be made of resin. 
       FIG. 10  shows the structure of a lighting circuit. The lighting circuit  22  containing electronic components includes a rectifying circuit, a smoothing circuit, a current adjustment circuit and the like. To be specific, the rectifying circuit is realized by a diode bridge  26 , the smoothing circuit is realized by a capacitor  27 , and the current adjustment circuit is realized by a resistance  28 . These circuits are housed in the base  23 . 
     Input terminals of the diode bridge  26  act as input terminals  29  of the lighting circuit  22 , and one end of the capacitor  27  and one end of the resistance  28  act as output terminals  30  of the lighting circuit  22 . The input terminals  29  are electrically connected to the base  23 . One of the input terminals  29  is connected to the screw  23   a  of the side surface of the base, and the other of the input terminals  29  is connected to the eyelet  23   b  of the bottom of the base. 
     The output terminals  30  of the lighting circuit  22  are connected to the outer lead wires of the lead wires  18  and  19  for receiving power. That is, the output terminals  30  are electrically connected to the LED module  17  (LED chip sequence  31 ). 
     In the present embodiment, the base  23  is an E26 base. The base  23  is attached to a lighting fixture ( 33 ) having a socket for an E26 base connected to a commercial alternating power source  25 . 
     In the present embodiment, the E26 base is used, for example, but the base is not limited to this. A base different in size and shape may be selected in accordance with the intended use. Further, the power source is not limited to the commercial alternating power source, and may be a direct current power source, i.e., battery (in this case, the structure of the above lighting circuit  22  is changed). Furthermore, the lighting circuit is not limited to the above rectifying circuit, for example, and a light adjusting circuit and a boost circuit may be selected and combined as appropriate. 
       FIG. 11  shows the light source  32  pertaining to Embodiment 3 attached to a lighting fixture  33 . The lighting fixture  33  is a light fixture generally called a downlight. When the lighting fixture  33  is attached to the ceiling, light emitted from the light source  32  is reflected by a reflector  33   a  and the floor is irradiated with the reflected light as a spotlight. 
     The reflector  33   a  is provided with fixture grounding terminals  34 . When the light source  32  is attached to the lighting fixture  33 , the fixture grounding terminals  34  and the electrically-conductive member  24  provided on the outer surface of the outer shell  21  are electrically connected to each other. 
     The fixture grounding terminals  34  have resilience and electrical conductivity, and are made of plate-like phosphor bronze, etc., with a bent portion. This causes the fixture grounding terminals  34  to closely attach to (are in contact with) the electrically-conductive member  24  provided on the outer surface of the outer shell  21 , and to be electrically connected to the electrically-conductive member  24 . As a result, an electric charge stored on the outer surface is discharged, and dust is prevented from attaching to the outer surface. The lighting apparatus including the light source  32  and the lighting fixture  33  offers the above effects. 
     According to the light source and the lighting fixture pertaining to the present invention in each embodiment, the light source  1  is provided with the terminal  6   a  having the function of grounding and the lighting fixture  33  is provided with the terminals  34  having the function of grounding so as to discharge an electric charge stored on the light sources  1  and  32  via the lighting fixture to the outside of the light sources  1  and  32 . Therefore, it is possible to prevent dust, etc., from attaching to the light sources  1  and  32 . 
     Although description has been made on an LED lamp substituted for a straight tube fluorescent lamp or a typical bulb in each embodiment, the present invention can be adopted in an LED lamp substituted for a conventional circular fluorescent tube or a single-based fluorescent lamp. 
     Further, even when a direct current power source is connected, the light source is prevented from being charged, and it is therefore possible to prevent dust, etc., from attaching to the light source. Further, even when the light-emitting elements are driven by a direct current, the light source is prevented from being charged, and it is therefore possible to prevent dust, etc., from attaching to the light source. 
     Furthermore, the electric resistance between a point on the electrically-conductive member  24  that is electrically closest to the grounding terminals  34  and a point on the electrically-conductive member  24  that is electrically farthest from the grounding terminals  34  is within a range from 1Ω to 1 MΩ. It is therefore possible to discharge an electric charge stored on the outer surface of the outer shell to the outside. 
     In each embodiment, the electrically-conductive members  7   a  and  24  are respectively arranged on a certain area of the outer surface of the outer shells  4  and  21 . Alternatively, the electrically-conductive members  7   a  and  24  may be arranged only on a certain area irradiated with light (which is part of the outer surface of the outer shell), or the outer surface of the outer shell may be provided with first annular electrically-conductive members at a certain distance therebetween in the longitudinal direction of the outer shell, and a second electrically-conductive member may be further provided in the longitudinal direction so as to connect the first electrically-conductive members to one another, for example. 
     Further, although the first electrically-conductive member  7   a  and the electrically-conductive member  24  are arranged throughout the outer surface of the outer shells  4  and  21  in the embodiments, an electrically-conductive member may not be provided at a certain area. For example, the electrically-conductive member may have a plurality of through holes that are evenly (regularly) arranged. 
     Further, although the electrically-conductive members  7  and  24  in the embodiments are provided on the outer surface of the outer shells  4  and  21 , the electrically-conductive members  7  and  24  may be provided on the inner surface of the outer shells  4  and  21 . 
     That is, when the electrically-conductive member is provided on the inner surface of the outer shell, an electric charge stored on the inner surface is discharged to the outside of the light source via the grounding terminal, and the lighting fixture and the electrically-conductive member have the same electric potential. As a result, the outer surface of the electrically-insulative outer shell sandwiched by the lighting fixture and the electrically-conductive member has the same electric potential, and it is therefore possible to prevent dust from attaching to the outer shell. 
     The effect of providing the electrically-conductive member on the inner surface of the outer shell is that since the electrically-conductive member cannot be touched from the outside, disconnection of the electrically-conductive member can be prevented. 
     Further, if electrically-conductive members are provided on both the outer surface and the inner surface of the outer shell, even when the electric resistance value of the electrically-conductive member on the outer surface becomes high due to disconnection, etc., the electrically-conductive member on the inner surface can prevent reduction of the effect of preventing the attachment of dust. 
     In the above embodiment, each of the LED modules  2  and  17  is chip on board (COB) type, and the LED modules  2  and  17  respectively include the mounting substrates  2   c  and  17   a  on which LED chips (bare chips) are directly implemented. The LED modules  2  and  17  are not limited to this. For example, the LED module may be a package type, i.e., a surface mount device (SMD). In this case, the LED chips are implemented within a cavity molded by resin, etc., and the cavity is sealed by phosphor-containing resin. 
     Further, although an LED has been shown as a semiconductor light-emitting element in the above embodiments, a semiconductor laser and an organic electro luminescence (EL) may be used. 
     In addition to the above, a variety of modifications conceived by the person skilled in the art without departing from the scope of the present invention are included in the scope of the present invention. Further, without departing from the spirit of the present invention, any combination of the components in the embodiments may be used. 
     INDUSTRIAL APPLICABILITY 
     The light source pertaining to the present invention is able to keep the luminous flux close to the initial level for a long time period by preventing the outer surface of the outer shell from being charged, and reducing the attachment of dust due to an electric charge, and is able to reduce or eliminate the maintenance activities and costs for dust removal. 
     REFERENCE SIGNS LIST 
       1 ,  32  light source 
       2 ,  17  LED module 
       3  mount 
       4 ,  21  outer shell 
       5 ,  6 ,  23  base 
       5   a,    5   b,    6   a  terminal 
       7 ,  7   a,    7   b,    24  electrically-conductive member 
       8 ,  10  screw 
       9 ,  18 ,  19  lead wire 
       11 ,  14 ,  33  lighting fixture 
       12 ,  13 ,  16  socket 
       15 ,  34  fixture grounding terminal 
       20  stem 
       22  circuit 
       26  diode bridge 
       27  capacitor 
       28  resistance 
       29  input terminal 
       30  output terminal 
       31  LED chip sequence