Abstract:
A connector includes a plug connector and a receptacle connector which connect a circuit board to a connecting object and allow relative movement therebetween in a common plane or in mutually parallel planes. The receptacle connector includes a receptacle contact including a pair of holding portions and a pair of guide portions which are spaced from each other with the pair of holding portions positioned therebewteen, wherein each guide portion includes a support groove. The plug connector includes a plug contact and a plug insulator which holds the plug contact. The plug contact is linearly elongated and resiliently deformable in a direction of thickness thereof and includes a contact portion that is engaged in the support grooves of the pair of guide portions. The plug insulator includes an opening facing the circuit board, and an accommodation space for accommodating the receptacle contact and the plug contact.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present invention is related to and claims priority of the following co-pending application, namely, Japanese Patent Applications Nos. 2010-165821 filed on Jul. 23, 2010, and 2010-271671 filed on Dec. 6, 2010. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a connector which connects a circuit board and a connecting object while allowing the circuit board and the connecting object to move relative to each other either in a common plane, in which the circuit board and the connecting object both lie, or in mutually parallel planes, in which the circuit board and the connecting object respectively lie, and relates to an LED lighting apparatus using the aforementioned connector. 
         [0004]    2. Description of the Prior Art 
         [0005]    Straight tube LED lighting apparatuses (LED lamps) are usually provided with a translucent tube, a plurality of circuit boards and a plurality of connectors. The translucent tube is formed as a linearly elongated hollow cylinder made of glass or plastic (e.g., polycarbonate). The plurality of circuit boards are planar in shape, arranged inside the translucent tube to lie in a common plane and aligned in the lengthwise direction of the translucent tube, and LEDs are fixed to one-side of the surfaces (undersurfaces) of the plurality of circuit boards. The plurality of connectors connect adjacent connectors of the plurality of connectors. 
         [0006]    When the plurality of circuit boards are installed in the translucent tube, it is sometimes the case that adjacent circuit boards mutually deviate from their design positions in the aforementioned lengthwise direction or the widthwise direction of the translucent tube (directions orthogonal to the lengthwise direction). Therefore, the aforementioned connectors are required to have the capability of absorbing such positional deviations.
   Patent Document 1 (Japanese Unexamined Patent Publication No. 2010-33953) discloses a connector having the capability of absorbing such positional deviations.   
 
         [0008]    This connector is provided with a plurality of receptacle connectors (on-board connectors) which are fixed to one side of the surfaces of a plurality of circuit boards, respectively, and a plurality of plug connectors (coupling connectors), each of which connects two adjacent receptacle connectors of the plurality of receptacle connectors which are fixed to two adjacent circuit boards, respectively. 
         [0009]    Each receptacle connector is provided with a receptacle insulator (housing) having an opening on one side thereof (on the opposite side of the receptacle insulator from the associated circuit board side), and a plurality of receptacle contacts (terminals) which are accommodated in the receptacle insulator in a state of facing the opening and which are each electrically connected to a circuit contained on the associated circuit board. Each receptacle contact has a pair of resilient lugs which are spaced from each other and face each other. 
         [0010]    Each plug connector is provided with a plug insulator (housing), a plurality of plug contacts (coupling terminals) supported by the plug insulator therein, and an insulating plate which covers a surface of the plug insulator. The plug insulator is provided with a pair of support members and an elastically deformable connecting portion which connects the pair of support members. A plurality of support holes are formed through each of the pair of support members in the direction of thickness thereof. Each plug contact is provided with a linear columnar (prismatic-shaped) connecting portion and a pair of legs which respectively project from both ends of the columnar connecting portion in a direction orthogonal to the columnar connecting portion. One and the other of the pair of legs of each plug contact are inserted into a support hole of one support member of the pair of support members and a support hole of the other support member of the pair of support members from one side so that the end of each leg of each plug contact projects toward the circuit board side from the associated support hole. Each leg of each plug contact is rotatable within a slight angular range about its own axis with respect to the associated support hole, and a rotation of the leg causes the columnar connecting portion of the plug contact to rotate with respect to the associated support member. The insulating plate covers each support member from the opposite side of the pair of legs from the ends thereof to prevent each leg of each plug contact from coming off the associated support hole. 
         [0011]    Bringing the pair of support members of each plug connector close to the two receptacle connectors fixed to two adjacent circuit boards, respectively, and inserting the pair of legs of each plug contact into the aforementioned opening of the receptacle insulator cause each leg of each plug contact to enter in between the pair of resilient lugs of the associated receptacle contact to thereby be resiliently held therebetween. As a result, the two adjacent circuit boards are electrically connected to each other via the plug connector and the two receptacle connectors. Therefore, if the connectors disclosed in Patent Document 1 are applied to an LED lighting apparatus such as described above, each circuit board is energized, which causes each LED to emit light. 
         [0012]    In addition, if adjacent circuit boards deviate from each other in the lengthwise direction of the LED lighting apparatus from design positions, at least one leg of each plug contact slides with respect to the associated receptacle contact (the associated pair of resilient lugs thereof) while the aforementioned elastically deformable connecting portion is elastically deformed so as to change the distance between the pair of support members to thereby absorb the positional deviation. 
         [0013]    On the other hand, if adjacent circuit boards deviate from each other in the widthwise direction of the translucent tube, at least one leg of each plug contact rotates with respect to the associated support hole (the aforementioned columnar connecting portion rotates with respect to the pair of support members) while the aforementioned elastically deformable connecting portion is elastically deformed so as to make the pair of support members slide relative to each other in the widthwise direction of the translucent tube to thereby absorb the positional deviation. 
         [0014]    Since the plurality of LEDs and the plurality of connectors are fixed to circuit formation surfaces of the plurality of circuit boards (one side of the surfaces thereof), if the thickness of each connector is increased, the diffusive light that is emitted from the adjacent LEDs is partly intercepted by the connector, which narrows the illumination range (illumination angle) of light emitted from the LEDs. Accordingly, it is desirable that the height (thickness) of each connector be as small as possible. 
         [0015]    However, in Patent Document 1, each plug contact has a structure in which the pair of legs of each plug contact project from the associated columnar connecting portion, and hence, the height of each plug contact increases by the amount of this projection. 
         [0016]    Additionally, the pair of legs of each plug contact are lower in mechanical strength than the associated columnar connecting portion; however, since the pair of legs of each plug contact are made to contact (to be engaged with) the associated receptacle contact (the pair of resilient lugs thereof) in Patent Document 1, there is a possibility of each leg of each plug contact being distorted or damaged when the pair of legs of each plug contact and the associated receptacle contact are brought into contact with (are connected to) each other with a positional deviation therebetween. In addition, since the connector disclosed in Patent Document 1 is structured such that one or more legs of each plug contact rotate if the associated adjacent circuit boards deviate from each other in the lateral or rotational direction, repetitive positional deviations or vibrations applied to the connector causes the legs of each plug contact and the pair of resilient lugs of the associated receptacle contact to vibrate minutely, which may cause damage to the plating that is applied to the legs or the resilient lugs or makes the contact resistance therebetween easy to fluctuate. Therefore, the contact reliability between each plug contact and the associated receptacle contact easily deteriorates. 
         [0017]    In Patent Document 1, since the plug contacts (the columnar connecting portions thereof) are exposed through the clearance between the pair of support members, even though surfaces of the support members of the plug insulator of the plug connector are covered by an insulating plate, there is a possibility of the plug contacts being distorted or sebum (from the hand) of an operator (user) being adhered to the plug contacts when the plug connector is plugged into the receptacle connector. Additionally, the exposure of the plug contacts through the clearance makes it easier for foreign matter such as dust to adhere to the plug contacts, which may become a cause of corrosion of the plug contacts or may cause sparking. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention provides a connector which connects a circuit board and a connecting object while allowing the circuit board and the connecting object to move relative to each other either in a common plane, in which the circuit board and the connecting object both lie, or in mutually parallel planes, in which the circuit board and the connecting object respectively lie, and which makes it possible to achieve a reduction in height of the connector, an improvement in contact reliability, the protection of contacts and an easy and reliable workability in the engaging operation between the plug and receptacle connectors. The present invention also provides an LED lighting apparatus using this connector. 
         [0019]    According to an aspect of the present invention, a connector is provided, including a plug connector and a receptacle connector which are disconnectably connected to each other to connect a circuit board and connecting object to each other in a manner to allow the circuit board and the connecting object to move relative to each other in one of a common plane, in which the circuit board and the connecting object both lie, and in mutually parallel planes, in which the circuit board and the connecting object respectively lie. The receptacle connector includes a receptacle contact which is fixed to one side of the circuit board, the receptacle contact including a pair of holding portions which are resiliently deformable in opposite directions away from each other, and a pair of guide portions which are spaced from each other with the pair of holding portions positioned therebewteen, wherein each guide portion of the pair of guide portions includes a support groove. The plug connector includes a plug contact which is electrically connected to the connecting object, and a plug insulator which holds the plug contact. The plug contact is formed as a plate-shaped member which is linearly elongated in a direction parallel to the plane and resiliently deformable in a direction of thickness of the plate-shaped member, which is held between the pair of holding portions to be movable in the linearly elongated direction, and which includes a contact portion ( 37 ) that is engaged in the support grooves of the pair of guide portions. The plug insulator includes an opening on a portion thereof facing the circuit board, and an accommodation space for accommodating the receptacle contact and the plug contact. 
         [0020]    It is desirable for the connecting object to include another circuit board which lies in a plane in which the circuit board lies, the receptacle contact being fixed to one of both sides of the another circuit board. The plug contact includes at least two the contact portions, one of which is held between the pair of holding portions and another of which is held between a pair of holding portions on the another circuit board; and a supported portion which lies on a straight line passing through the two contact portions. The plug insulator includes a support portion for supporting the supported portion to allow the supported portion to move in both the linearly elongated direction and the direction of thickness of the plate-shaped member. 
         [0021]    It is desirable for the connecting object to include an electric wire which is connected to the plug contact. 
         [0022]    It is desirable for the each guide portion of the pair of guide portions to include an engaging projection formed on an inner surface of the support groove. The plug contact includes at least two lock portions with which the engaging projections of the pair of guide portions are engaged when the plug contact is engaged with the support grooves of the pair of guide portions, each of the lock portions being formed as one of a recess and through-hole. 
         [0023]    It is desirable for the pair of guide portions to include at least two guide leaves which face each other in a lengthwise direction of the plug contact, and for the support groove to be formed on each of the two guide leaves so that all of the support grooves are aligned in the lengthwise direction of the plug contact. 
         [0024]    It is desirable for each of the pair of guide portions to include at least two guide leaves which face each other in a lengthwise direction of said plug contact, and for the engaging projection of each guide portion of the pair of guide portions to include a pair of engaging projections which are respectively formed on both side surfaces on the support groove of at least one of the two guide leaves to be aligned in a direction of thickness of the plug contact. 
         [0025]    It is desirable for the receptacle contact to include a base having a flat plate shape which is fixed to the circuit board, wherein each of the pair of guide portions includes a first guide leaf which extends in a direction orthogonal to the base from an end of the base in the lengthwise direction of the plug contact, and a second guide leaf which extends from an end of the first guide leaf toward at least one of the circuit board and the another circuit board. A free end of the second guide leaf is soldered to one of the circuit board and the another circuit board. 
         [0026]    It is desirable for one of the pair of holding portions to include an engaging protrusion, and for a connecting hole, in which the engaging protrusion is engaged to be movable relative to the connecting hole in the linearly elongated direction, to be formed in the plug contact. 
         [0027]    It is desirable for the other of the pair of holding portions to include a holding protrusion which contacts the plug contact. 
         [0028]    It is desirable for a moving range of each of the contact portions in the direction of thickness of the plate-shaped member in the accommodation space to be wider than a moving range of the supported portion with respect to the support portion in the direction of thickness of the plate-shaped member. 
         [0029]    In an embodiment, an LED lighting apparatus having more than one the connector and more than one the circuit board is provided, wherein at least one LED being is provided on each the circuit board. 
         [0030]    It is desirable for the pair of holding portions to be fixed at different positions in the linearly elongated direction. 
         [0031]    According to the present invention, when a positional deviation occurs between the circuit board and the connecting object adjacent to each other in the elongated direction of the plug contact, this positional deviation is absorbed by a slide movement of the contact portion of the plug contact with respect to the pair of holding portions of the receptacle contact in the elongated direction of the plug contact. Therefore, even if a positional deviation occurs between the circuit board and the connecting object adjacent to each other in the elongated direction of the plug contact, the circuit board and the connecting object can be electrically connected to each other with reliability. 
         [0032]    In addition, the plug contact is a plate-shaped member elongated in one direction which includes no protrusions extending in directions orthogonal to this one direction, thus having a low-profile structure. Accordingly, this low-profile structure makes it possible to achieve a reduction in height of the entire part of the connector. 
         [0033]    Since the plug contact according to the present invention is a substantially straight plate-shaped member having a structure such that the contact portion and the supported portion thereof are aligned, the plug contact has a high mechanical strength against twisting, and the like (compared to a protrusion formed to protrude from a plug contact body). Moreover, stress applied to the plug contact due to a resilient deformation thereof can be effectively dispersed since the plug contact has no bent portion. In addition, since the contact portion, which forms part of the plug contact, is made to be brought in contact with (to be engaged with) the receptacle contact (the pair of holding portions thereof), there is little possibility of the plug contact (the contact portion thereof) being distorted or damaged even if the contact portion of the plug contact and the receptacle contact are brought into contact (engagement)) with each other with a positional deviation therebetween. Accordingly, it is possible to improve the contact reliability between the plug contact and the receptacle contacts. 
         [0034]    Additionally, the entire peripheries of the plug contact and the receptacle contact are protected by the circuit board and the plug insulator because the plug contact and the receptacle contact are accommodated in the accommodation space (of the plug insulator) having an opening on a surface thereof facing the circuit board. Accordingly, the plug contact and the receptacle contact can be prevented from being damaged not only when, but also after, the receptacle contact and the plug contact are connected. Moreover, after the receptacle contact and the plug contact are connected, the electrically conductive portions of each connector are all covered, which makes it possible to increase the insulation performance to an extremely high level. 
         [0035]    Additionally, the plug contact and the receptacle contact can be engaged with each other easily and securely because an engagement of the contact portion of the plug contact in the support grooves of the pair of guide portions causes the contact portion to be guided to a position to be held between the pair of holding portions when the plug contact and the receptacle contact are engaged with each other. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The present invention will be discussed below in detail with reference to the accompanying drawings, in which: 
           [0037]      FIG. 1  is a bottom perspective view of a portion of a first embodiment of a straight tube LED lighting apparatus, according to the present invention, with one of a pair of plug insulators removed for clarity; 
           [0038]      FIG. 2  is a bottom perspective view of a receptacle contact shown in  FIG. 1 ; 
           [0039]      FIG. 3  is a bottom plan view of the receptacle contact; 
           [0040]      FIG. 4  is a side view of the receptacle contact; 
           [0041]      FIG. 5  is a cross sectional view taken along the V-V line shown in  FIG. 4 , viewed in the direction of the appended arrows; 
           [0042]      FIG. 6  is an exploded bottom perspective view of a plug connector shown in  FIG. 1 ; 
           [0043]      FIG. 7  is an exploded top perspective view of the plug connector; 
           [0044]      FIG. 8  is a cross sectional view of a portion of the plug connector, showing a state where a plug contact of the plug connector enters in between a pair of engaging lugs of the plug insulator of the plug connector while resiliently deforming the pair of engaging lugs; 
           [0045]      FIG. 9  is a top perspective view of the plug connector; 
           [0046]      FIG. 10  is a plan view of the plug connector; 
           [0047]      FIG. 11  is a longitudinal central sectional view of the plug connector and the receptacle contact when the plug connector and the receptacle contact are connected; 
           [0048]      FIG. 12  is across sectional view taken along the XII-XII line shown in  FIG. 11 , viewed in the direction of the appended arrows; 
           [0049]      FIG. 13  is a cross sectional view taken along the XIII-XIII line shown in  FIG. 12 , viewed in the direction of the appended arrows; 
           [0050]      FIG. 14  is across sectional view taken along the XIV-XIV line shown in  FIG. 12 , viewed in the direction of the appended arrows; 
           [0051]      FIG. 15  is a cross sectional view taken along the XV-XV line shown in  FIG. 12 , viewed in the direction of the appended arrows; 
           [0052]      FIG. 16  is a bottom view of the portion of the straight tube LED lighting apparatus shown in  FIG. 1  with the pair of plug insulators removed for clarity in a state where adjacent circuit boards deviate from each other in both the forward/rearward direction and the leftward/rightward direction; 
           [0053]      FIG. 17  is a top perspective view of a plug connector and two receptacle connectors of a second embodiment of the straight tube LED lighting apparatus according to the present invention in a state where the plug connector and the two receptacle connectors are in a connected state; 
           [0054]      FIG. 18  is a top exploded perspective view of the plug connector and the two receptacle connectors shown in  FIG. 17  in a disconnected state with the associated circuit boards removed for clarity; 
           [0055]      FIG. 19  is a cross sectional view taken along the XIX-XIX line shown in  FIG. 17 , viewed in the direction of the appended arrows; 
           [0056]      FIG. 20  is a top exploded perspective view of the plug connector of the second embodiment of the straight tube LED lighting apparatus; 
           [0057]      FIG. 21  is a bottom exploded perspective view of the plug connector of the second embodiment of the straight tube LED lighting apparatus; 
           [0058]      FIG. 22  is a plan view of the plug connector of the second embodiment of the straight tube LED lighting apparatus; 
           [0059]      FIG. 23  is a cross sectional view taken along the XXIII-XXIII line shown in  FIG. 22 , viewed in the direction of the appended arrows; 
           [0060]      FIG. 24  is a side view of a receptacle contact of the second embodiment of the straight tube LED lighting apparatus; 
           [0061]      FIG. 25  is a top perspective view of a plug connector and a receptacle connector of a third embodiment of the straight tube LED lighting apparatus according to the present invention in a connected state; 
           [0062]      FIG. 26  is a top exploded perspective view of the plug connector and the receptacle connector shown in  FIG. 25  in a disconnected state with the associated circuit boards removed for clarity; 
           [0063]      FIG. 27  is a cross sectional view taken along the XXVII-XXVII line shown in  FIG. 25 , viewed in the direction of the appended arrows; 
           [0064]      FIG. 28  is a cross sectional view taken along the XXVIII-XXVIII line shown in  FIG. 27 , viewed in the direction of the appended arrows; 
           [0065]      FIG. 29  is a cross sectional view taken along the XXIX-XXIX line shown in  FIG. 27 , viewed in the direction of the appended arrows; and 
           [0066]      FIG. 30  is a plan view of a plug contact integrated with an electric wire and a plug insulator of the third embodiment of the straight tube LED lighting apparatus. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0067]    A first embodiment of a straight tube LED lighting apparatus according to the present invention will be hereinafter discussed with reference to  FIGS. 1 through 16 . In the following descriptions, forward and rearward directions, leftward and rightward directions, and upward and downward directions (vertical direction) of the LED lighting apparatus are determined with reference to the directions of the double-headed arrows shown in the drawings (front, rear, left, right, up and down, respectively). 
         [0068]    The LED lighting apparatus  100  that is shown in  FIG. 1  is provided with a translucent tube  101  (only a part of which is shown by two-dot chain lines in  FIG. 1 ), a plurality of circuit boards CB (only two of which are partly shown in  FIG. 1 ), LED units  102  and a plurality of connectors  10 . The translucent tube  101  extends linearly in the forward/rearward direction. The plurality of circuit boards CB are arranged inside the translucent tube  101  to lie in a common plane and aligned in the forward/rearward direction. The LED units  102  are fixed to circuit formation surfaces formed on the undersurfaces of the plurality of circuit boards CB. Each connector  10  connects facing edges of adjacent circuit boards CB. Each LED unit  102  is provided with a base plate and an LED  103  integrally mounted thereon, and this base plate is connected (soldered) to a circuit (not shown) formed on the bottom (underside) of the associated circuit board CB. 
         [0069]    Each connector  10  is provided with a pair of (front and rear) receptacle contacts  15  fixed to two circuit boards CB that are adjacent to each other, respectively, and a plug connector  30  which connects the pair of receptacle contacts  15 . 
         [0070]    First, the detailed structure of each receptacle contact  15  will be hereinafter discussed with reference to  FIGS. 2 through 5 . 
         [0071]    Each receptacle contact  15  is formed from a thin base material made of a resilient copper alloy (e.g., phosphor bronze, beryllium copper or titanium copper) or a resilient Corson-copper alloy and formed into the shape shown in the drawings by being bent in the direction of thickness of the thin base material after press forming is performed thereon, and is firstly nickel plated, as a base plating, and is subsequently tin or gold plated, as a finish plating. Each receptacle contact  15  can be made by press forming on a plated metal base material. 
         [0072]    Each receptacle contact  15  is rotationally symmetrical in shape (about a vertical axis passing through a center of a base  16  of the receptacle contact  15 ) and is provided with the aforementioned base  16 , a pair of guide lugs (guide portions)  17 , a pair of holding leaves (a first holding leaf  20  and a second holding leaf  23 ) and another pair of holding leaves (another first holding leaf  20  and another second holding leaf  23 ). The base  16  is in the shape of a substantially horizontal flat plate having a substantially rectangular shape in plan view. The pair of guide lugs  17  extend vertically downwards from the front and rear edges of the base  16 , respectively. The front pair of holding leaves  20  and  23  project downwardly from left and right edges of the base  16 , respectively, and the rear pair of holding leaves  20  and  23  project downwardly from right and left edges of the base  16 , respectively. 
         [0073]    Each guide lug  17  is provided on a lower surface thereof with a support groove  18  which is grooved upwardly, and the left and right inner surfaces of a lower part of the support groove  18  are flared downwardly and outwardly to be formed as a pair of guide surfaces  19 , the distance of which therebetween increases in the downward direction. 
         [0074]    The two first holding leaves (holding portions)  20 , which extend downwards from a portion of the right edge of the base  16  in the vicinity of the rear end thereof and a portion of the left edge of the base  16  in the vicinity of the front end thereof, respectively, are each shaped into a substantially letter C in a front view (in cross section), and an engaging protrusion  21  having a hemispherical shape which is integrally formed with the first holding leaf  20  is provided on an inwardly-positioned surface of the outer surface of the first holding leaf  20 . Each first holding leaf  20  is resiliently deformable in the leftward/rightward direction. Additionally, the base  16  is provided, on a portion of the left edge thereof in the vicinity of the fixed end of the left first holding leaf  20 , with a notch which allows the left first holding leaf  20  to easily deform resiliently, and is further provided, on a portion of the right edge thereof in the vicinity of the fixed end of the right first holding leaf  20 , with a notch which allows the right first holding leaf  20  to easily deform resiliently. 
         [0075]    The two second holding leaves (holding portions)  23 , which are respectively formed at the front end of the right edge of the base  16  and the rear end of the left edge of the base  16 , are each shaped into a substantially letter C in front view (in cross section); however, this letter C shape is slightly different from the shape of each first holding leaf  20  as shown in  FIG. 5 . Each second holding leaf  23  is provided, on an inwardly-positioned surface of the outer surface thereof at the same height as the engaging protrusions  21 , with a holding protrusion  24  which is in the shape of a rectangular parallelepiped elongated in the forward/rearward direction and which is integrally formed with the second holding leaf  23 . The end surface of each holding protrusion  24  is formed into a curved surface having a curvature radius of the order of 0.05 to 0.1 mm to be capable of receiving a concentrated load when contacting the associated plug contact  35 . Similar to each first holding leaf  20 , each second first holding leaf is resiliently deformable in the leftward/rightward direction. Additionally, the base  16  is provided, on a portion of the left edge thereof in the vicinity of the fixed end of the left second holding leaf  23 , with a notch which makes the left second holding leaf  23  easy to deform resiliently, and is further provided, on a portion of the right edge thereof in the vicinity of the fixed end of the right second holding leaf  23 , with a notch which makes the right second holding leaf  23  easy to deform resiliently. 
         [0076]    The receptacle contacts  15  are installed to the circuit boards CB in advance outside of the translucent tube  101 . 
         [0077]    To install the receptacle contacts  15  to the aforementioned circuit formation surfaces of the circuit boards CB, the circuit formation surfaces of the circuit boards CB are placed face up, a pneumatic suction device (not shown) positioned above the circuit boards CB attracts the suction surface  25  of the base  16  of each receptacle contact  15  which is formed at a center of the undersurface of the base  16 , subsequently each receptacle contact  15  thus held by the suction device is mounted on the circuit formation surface of the associated circuit board CB by moving the pneumatic suction device, and thereafter the suction device is retracted to be positioned above the receptacle contact  15 . Thereafter, surface mounting technology (SMT) is used to solder each receptacle contact  15  to the aforementioned circuit that is formed on the associated circuit formation surface. 
         [0078]    The detailed structure of the plug connector  30  of each connector  10  will be hereinafter discussed with reference to  FIGS. 6 through 10 . 
         [0079]    The plug connector  30  of each connector  10  is provided with a plug contact  35  and a plug insulator  45 . 
         [0080]    The plug contact  35  is formed by press forming a thin base material made of a resilient copper alloy (e.g., phosphor bronze, beryllium copper or titanium copper) or a resilient Corson-copper alloy, and is firstly nickel plated, as a base plating, and is subsequently tin or gold plated, as a finish plating. The plug contact  35  can be made by press forming a plated metal base material. As shown in the drawings, the plug contact  35  is a plate-shaped member having a symmetrical shape in the forward/rearward direction, extends linearly in the forward/rearward direction and is resiliently deformable in the direction of thickness of the plug contact  35 . 
         [0081]    The plug contact  35  is provided, at upper edges of both ends thereof in the forward/rearward direction, with two engaging recesses  36 , respectively. In addition, the plug contact  35  is provided in front and rear parts thereof with two (front and rear) contact portions  37 , respectively, and is provided in each of the two contact portions  37  with a pair of connecting holes  38  formed as a pair of through-holes elongated and aligned in the forward/rearward direction. 
         [0082]    A central portion of the plug contact  35  in the forward/rearward direction is formed as a central low-profile portion  39  which is smaller in height than the two contact portions  37 , and a central portion of the central low-profile portion  39  constitutes a supported portion  40  of the plug contact  35  which lies on a straight line passing through the two contact portions  37 . 
         [0083]    In addition, the outer edge of the plug contact  35  is chamfered; specifically, the beveled upper edges of the two contact portions  37  serve as beveled guide surfaces for leading the plug contact  35  into the associated receptacle contacts  15 . 
         [0084]    The plug insulator  45  is an integrally-molded element which is molded of an insulating synthetic resin by injection molding. As shown in the drawings, the plug insulator  45  is in the shape of a box, the top of which is fully open. The plug insulator  45  is provided, in the internal space thereof in the front and rear of this internal space, with a pair of (front and rear) accommodation spaces  46 , respectively. 
         [0085]    The plug insulator  45  is provided, in a central portion thereof (the portion between the pair of accommodation spaces  46 ) in the lengthwise direction of the internal space of the plug insulator  45 , with a pair of (left and right) center protuberances (supporting portion/holding portions)  48  which are formed integrally, and each of which is in the shape of a rectangular parallelepiped. Laterally facing surfaces of the left and right center protuberances  48 , except for protrusions  48   a  whose cross section is a trapezoidal shape are formed at the center of the center protuberances  48  (see FIGS.  7 , 8 , 9 , 12  and  13 ), are parallel surfaces (flat surfaces), orthogonal to the leftward/rightward direction, and the distance therebetween (in the leftward/rightward direction) is smaller than the width of each accommodation space  46  (the width thereof in the leftward/rightward direction) and greater than the plate thickness (dimension in the leftward/rightward direction) of the plug contact  35  (the supported portion  40  thereof). Laterally facing surfaces of the protrusions  48   a , except for both the front and rear end portions of the protrusions  48   a  (slant surfaces of the trapezoid) in the front and rear directions, are parallel surfaces (flat surfaces), orthogonal to the leftward/rightward direction. A slit  49  is formed in each center protuberance  48  to be recessed downwardly from the upper surface thereof so that an inner portion of each center protuberance  48  that is positioned on the laterally inner side of the associated slit  49  can be resiliently deformed in the leftward/rightward direction. In addition, the plug insulator  45  is provided with left and right engaging lugs (supporting portion/holding portions)  50  which are integrally formed with the left and right center protuberances  48  to project from the upper edges of the aforementioned facing surfaces thereof toward each other, respectively. The distance between the laterally facing surfaces (edges)) of the left and right engaging lugs  50  (the distance therebetween in the leftward/rightward direction) in a free state thereof is slightly smaller than the plate thickness of the supported portion  40  of the plug contact  35 . Additionally, the upper edges of the laterally facing inner ends of the left and right engaging lugs  50  are chamfered to serve as beveled guide surfaces  51  the distance therebetween decreases in the downward direction (see  FIG. 8 ). 
         [0086]    The plug insulator  45  is provided on inner surfaces of the front and rear walls thereof with two (front and rear) engaging projections (holding portions)  52  which are integrally formed with the plug insulator  45  to project inwardly from the inner surfaces of the front and rear walls of the plug insulator  45 , respectively. Each of the front and rear engaging projections  52  is formed to create space (clearance) between a bottom (undersurface) of the associated accommodation space  46  (an upper surface of the bottom wall of the plug insulator  45 ) and left and right side walls of the plug insulator  45  adjacent to the engaging projection  52 . As shown in the drawings, each engaging projection  52  is bilaterally symmetrical in shape and provided on top with a pair of (left and right) beveled surfaces. In addition, the spacing (distance in the vertical direction) between each engaging projection  52  (the bottom thereof) and the bottom of the associated accommodation space  46  is slightly greater than the height of each end (front and rear ends) of the plug contact  35  at which the engaging recesses  36  are formed, and the distance (in the leftward/rightward direction) between each engaging projection  52  and either of the left and right side walls of the plug insulator  45  adjacent to the engaging projection  52  is greater than the plate thickness of the plug contact  35 . 
         [0087]    Additionally, a pair of (left and right) limit projections  54  is provided in each of the front and rear accommodation spaces  46  of the plug insulator  45 . As shown in the drawings, the distance (in the leftward/rightward direction) between the laterally facing surfaces of each pair of limit projections  54  (which face each other in the leftward/rightward direction) is substantially the same as the distance between the aforementioned laterally facing surfaces of the left and right center protuberances  48  except for the protrusions  48   a . The laterally facing portions of each pair of limit projections  54 , except for the top portions thereof, are each formed into a semi-cylindrical shape, and the top portions of the laterally facing portions of each pair of limit projections  54  are each shaped into a quarter-sphere (half a hemisphere). 
         [0088]    To put the plug contact  35  and the plug insulator  45  together integrally into the plug connector  30 , first the plug contact  35  is positioned immediately above the plug insulator  45  as shown in  FIGS. 6 and 7 . Subsequently, the plug contact  35  is made to be inclined with respect to a center line of the plug insulator  45  in plan view so that one end of the plug contact  35  in the lengthwise direction thereof is positioned immediately above the gap between one of the two engaging projections  52  and the left side wall of one end (front end) of the plug insulator  45  and so that the other end of the plug contact  35  in the lengthwise direction thereof is positioned immediately above the gap between the other engaging projection  52  and the right side wall of the other end (rear end) of the plug insulator  45 . 
         [0089]    Subsequently, with this inclined state maintained, both ends of the plug contact  35  are inserted into the aforementioned two gaps immediately below the engaging projections  52 , respectively. Accordingly, a front part of the plug contact  35  comes in contact with the upper end of the left or right limit projection  54  on the front side while a rear part of the plug contact  35  comes in contact with the upper end of the right or left limit projection  54  on the rear side, respectively, and further insertion of both ends of the plug contact  35  into the aforementioned two gaps causes the aforementioned front and rear parts of the plug contact  35  to enter between the laterally facing surfaces of the front pair of limit projections  54  and between the laterally facing surfaces of the rear pair of limit projections  54  while being resiliently deformed toward the center line of the plug insulator  45  by the upper ends of the aforementioned limit projections  54 , respectively (see the two-dot chain line shown in  FIG. 10 ). Further insertion of both ends of the plug contact  35  into the aforementioned two gaps causes the supported portion  40  of the plug contact  35 , which now extends substantially parallel to a straight line extending in the forward/rearward direction in plan view, to enter between the laterally facing engaging lugs  50  while sliding on (while being guided by) the beveled guide surface  51  of the left or right engaging lug  50 . Thereupon, the supported portion  40  enters between the left and right center protuberances  48  (below the left and right engaging lugs  50 ) while resiliently deforming the left and right engaging lugs  50  in the opposite directions to widen the gap therebetween (see  FIG. 8 ). 
         [0090]    Subsequently, immediately after both the front and rear ends of the plug contact  35  respectively move to positions below the undersurfaces of the front and rear engaging projections  52  and the supported portion  40  of the plug contact  35  moves to a position below the undersurfaces of the left and right engaging lugs  50 , the plug contact  35  resiliently returns to its free state (straight state) by its own resiliency, so that the front end of the plug contact  35  is positioned between the front engaging projection  52  and the bottom of the accommodation space  46  while the rear end of the plug contact  35  is positioned between the rear engaging projection  52  and the bottom of the accommodation space  46  (see  FIGS. 9 and 10 ). 
         [0091]    After the plug connector  30  is assembled in such a manner, a clearance is created between the pair of center protuberances  48  and the plug contact  35 , between each pair of limit projections  54  and the plug contact  35 , between the left side wall of the front end of the plug insulator  45  and the adjacent left side wall of the plug contact  35 , between the right side wall of the front end of the plug insulator  45  and the adjacent right side wall of the plug contact  35 , between the left side wall of the rear end of the plug insulator  45  and the adjacent left side wall of the plug contact  35  and between the right side wall of the rear end of the plug insulator  45  and the adjacent right side wall of the plug contact  35 , so that the plug contact  35  is movable in the leftward/rightward direction relative to the plug insulator  45  by an amount corresponding to those clearances. In addition, the length of the internal space of the plug insulator  45  in the forward/rearward direction is greater than the length of the plug contact  35 , and accordingly, the plug contact  35  is movable in the forward/rearward direction relative to the plug insulator  45  by an amount of clearance in the forward/rearward direction between the accommodation space and the plug contact  35 . Additionally, the gap between the left and right engaging lugs  50  in a free state is smaller than the plate thickness of the plug contact  35  (the supported portion  40  thereof), and the plug contact  35  is required to be resiliently deformed largely if each of the front and rear ends of the plug contact  35  are to move into either of the two gaps on the laterally respective sides of the associated engaging projection  52 . Therefore, there is no possibility of the plug contact  35  from coming off the plug insulator  45  unless the plug contact  35  is intentionally removed from the plug insulator  45 . Namely, the plug contact  35  is held by the plug insulator  45  therein in a state of being allowed to move inside the plug insulator  45  with no load or stress being applied. 
         [0092]    A procedure for connecting the circuit boards CB together using the connectors  10  (the receptacle contacts  15  and the plug connectors  30 ) will be discussed hereinafter. 
         [0093]    The plurality of circuit boards CB are placed onto a fixing plate (not shown), which is formed into a thin plate elongated in the forward/rearward direction and has a plurality of female screw holes formed on the top surface, to be aligned in the forward/rearward direction with the undersurfaces thereof (surfaces opposite to the top surfaces that contain the LED units  102  and the receptacle contacts  15  thereon) facing down. Only two receptacle contacts  15  are fixed to the circuit board CB at the rear end thereof which is positioned at the front end of the array of the plurality of circuit boards CB, and only two receptacle contacts  15  are fixed to the circuit board CB at the front end thereof which is positioned at the rear end of the array of the plurality of circuit boards CB; however, two receptacle contacts  15  are fixed to each of the remaining circuit boards CB at each of the front and rear ends thereof, i.e., four receptacle contacts  15  in total are fixed to each of the remaining circuit boards CB. 
         [0094]    Subsequently, set screws (not shown) are inserted into through-holes (not shown) formed through each circuit board CB to be screwed into associated female screw holes formed in the aforementioned fixing plate to thereby fix each circuit board CB to the fixing plate. 
         [0095]    Subsequently, one plug connector  30  is positioned immediately above each pair of (front and rear) receptacle contacts  15  which face each other in the forward/rearward direction and are respectively fixed to the facing ends of two adjacent circuit boards CD, and thereafter each plug connector  30  is brought down (toward the circuit board CB) to the associated pair of receptacle contacts  15 . Thereupon, as shown in  FIGS. 1 and 11  through  15 , a front part of the plug insulator  45  covers the front receptacle contact  15  so that the front receptacle contact  15  is positioned in the front accommodation space  46  while a rear part of the plug insulator  45  covers the rear receptacle contact  15  so that the rear receptacle contact  15  is positioned in the rear accommodation space  46 . 
         [0096]    Thereupon, the lower edges (upper edges with respect to  FIGS. 1 and 6  through  9 ) of the front and rear contact portions  37  of the plug contact  35  come in contact with the guide surfaces  19  of the front receptacle contact  15  and the guide surfaces  19  of the rear receptacle contact  15 , respectively, so that each contact portion  37  (of the plug contact  35 ) is guided toward the associated support grooves  18  (toward the center of the associated receptacle contact  15  in the widthwise direction thereof) by the associated guide surfaces  19 . Subsequently, the front contact portion  37  of the plug contact  35  enters between the front pair of holding leaves  20  and  23  (between the engaging protrusion  21  and the holding protrusion  24 ) and between the rear pair of holding leaves  20  and  23  (between the engaging protrusion  21  and the holding protrusion  24 ) of the front receptacle contact  15  while the rear contact portion  37  of the plug contact  35  enters between the front pair of holding leaves  20  and  23  (between the engaging protrusion  21  and the holding protrusion  24 ) and between the rear pair of holding leaves  20  and  23  (the engaging protrusion  21  and the holding protrusion  24 ) of the rear receptacle contact  15 . The distance between each engaging protrusion  21  and the adjacent holding protrusion  24  of each receptacle contact  15  in the leftward/rightward direction in a front view when in a free state is smaller than the plate thickness of the plug contact  35 , so that each contact portion  37  of the plug contact  35  slides in between the associated pair of holding leaves  20  and  23  (the engaging protrusion  21  and the holding protrusion  24 ) while pressing (resiliently deforming) these holding leaves  20  and  23  in the opposite direction away from each other. Subsequently, upon each connecting hole  38  of the plug contact  35  reaching the same height as each engaging protrusion  21 , each pair of holding leaves  20  and  23  slightly move toward each other to resiliently return to their original positions to be engaged in the associated connecting hole  38  with a tactile click. In addition, the holding protrusion  24  of each holding leaf  23  comes in contact with a side of the associated contact portion  37 . Therefore, each receptacle contact  15  comes in contact with one contact portion  37  at four points. 
         [0097]    Additionally, as shown in  FIG. 12 , since each limit projection  54  is positioned in the space between the front pair of holding leaves  20  and  23  and the rear pair of holding leaves  20  and  23  of the associated receptacle contact  15  (i.e., in the space immediately above the suction surface  25  of the associated receptacle contact  15 ), each limit projection  54  and the associated receptacle contact  15  do not interfere with each other. 
         [0098]    Moreover, a force which holds the front and rear contact portions  37  of the plug contact  35  by engagement of the front and rear receptacle contacts  15  with the front and rear contact portions  37 , respectively, is large, due to the plug contact  35  (the front and rear contact portions  37  thereof) being laterally held between the left and right engaging protrusions  21  and the right and left holding protrusions  24  of each receptacle contact  15  and due to each engaging protrusion  21  being engaged in the associated connecting hole  38  of the plug contact  35 ; and accordingly, the engaged state between the pair of receptacle contacts  15  and the plug contact  35  is not released unless the plug connector  30  is intentionally moved upwardly (downwardly with respect to  FIG. 1 ). 
         [0099]    In each connector  10 , if the plug connector  30  is connected to the two receptacle contacts  15  so as to extend over the two receptacle contacts  15  in the above described manner, the front and rear contact portions  37  (the front pair of connecting holes  38  and the rear pair of connecting holes  38 ) come in contact with the front and rear receptacle contacts  15 , respectively, via the engaging protrusions  21  and the holding protrusions  24 , any two of the plurality of circuit boards CB adjacent to each other are electrically connected to each other via two receptacle contacts  15  and one plug contact  35 . Therefore, if the aforementioned fixing plate on which the plurality of circuit boards CB and the connectors  10  are integrally mounted is inserted into the translucent tube  101  and a current is passed between the circuit boards CB positioned at both ends of the array of the plurality of circuit boards CB, the LEDs  103  of the LED units  102  that are contained on each circuit board CB emit light, which travels downwardly from the translucent tube  101 . 
         [0100]    If the position of formation of one or more of the aforementioned female screw holes (not shown) in the aforementioned fixing plate and/or the position of formation of one or more of the aforementioned through-holes (not shown) in each circuit board CB deviates from the design position in the leftward/rightward direction and/or the forward/rearward direction, a positional deviation occurs between adjacent circuit boards CB in the leftward/rightward direction and/or the forward/rearward direction as shown in  FIG. 16 . If such a positional deviation occurs, a force in the leftward/rightward direction and/or the forward/rearward direction is applied from each receptacle contact  15  to the associated plug contact  35  (the associated plug connector  30 ). 
         [0101]    However, in each connector  10 , if a force in the leftward/rightward direction is applied to the plug contact  35  from the support grooves  18  of either receptacle contact  15  due to a positional deviation between the associated two adjacent circuit boards CB in the leftward/rightward direction, the supported portion  40  of the plug contact  35  tilts between the left and right center protuberances  48  while being resiliently deformed in the leftward/rightward direction so that the front and rear contact portions  37  move in the leftward/rightward direction, thereby absorbing the aforementioned positional deviation between the associated two adjacent circuit boards CB in the leftward/rightward direction. Each connector  10  is structured so that it is difficult for each contact portion  37  of the plug contact  35  to tilt when the two receptacle contacts  15  and the plug contact  35  are connected together, since each contact portion  37  is guided by the two support grooves  18  of the associated receptacle contact  15  (the widths of the support grooves  18  of each receptacle contact  15  are slightly greater than the contact portions  37  of the plug contact  35 ). Therefore, even if a positional deviation between the associated two adjacent circuit boards CB in the leftward/rightward direction occurs, the effect on the engagement between each contact portion  37  and the associated engaging protrusion  21  and holding protrusion  24  due to the occurrence of the positional deviation is small. Accordingly, in this case also, adjacent circuit boards CB can be electrically connected to each other with reliability via the connectors  10 . 
         [0102]    Additionally, since the distance between each pair of limit projections  54  that face each other is greater than the distance between the laterally facing surfaces of the protrusions  48   a  (see  FIGS. 7 ,  9 ,  12  and  13 ), each contact portion  37  can move by a greater amount than the supported portion  40  in the leftward/rightward direction in the plug insulator  45  of each plug connector  30 , so that each connector  10  can flexibly cope with the positional deviation between adjacent circuit boards CB in the leftward/rightward direction even if the adjacent circuit boards CB deviate largely from each other in the leftward/rightward direction. 
         [0103]    Additionally, since no part of the plug contact  35  is completely fixed (immovable), the plug contact  35  can disperse stress produced with a positional deviation between the associated two adjacent circuit boards CB. 
         [0104]    The amount of positional deviation absorbable by the receptacle contacts  15  and the plug connector  30  of each connector  10  can be adjusted by adjusting the amount of clearance between the internal space of the plug insulator  45  and each receptacle contact  15 . 
         [0105]    In each connector  10 , if a force in the forward/rearward direction is applied to the plug contact  35  from the engaging protrusions  21  or the holding protrusions  24  of the receptacle contacts  15  due to a positional deviation between the associated adjacent circuit boards CB in the forward/rearward direction, this positional deviation is absorbed by a sliding movement of each connecting hole  38  with respect to the associated engaging protrusion  21 . Accordingly, in this case also, adjacent circuit boards CB can be electrically connected to each other with reliability via the connectors  10 . 
         [0106]    The plug contact  35  of each connector  10  is a plate-shaped member extending in one direction and provided with no projections like those of a conventional plug contact, which makes it possible to achieve a reduction in height of the plug contact  35  (as compared with a plug contact having one or more projections). This makes it possible to achieve a reduction in height of the plug connector  30  of each connector  10 , and by extension a reduction in height of each connector  10 . Consequently, the illumination range (illumination angle) of light which is emitted from the LEDs  103  while dispersing can be widened. 
         [0107]    Additionally, the plug contact  35  of each connector  10  is structured such that the two contact portions  37  and the supported portion  40  are aligned, thus having a high mechanical strength against twisting and the like (as compared with a protrusion formed to protrude from a conventional plug contact body). Moreover, stress applied to the plug contact  35  due to a resilient deformation thereof can be effectively dispersed since the plug contact  35  has no bent portion. In addition, in each connector  10 , each contact portion  37  (the connecting holes  38  formed therethrough) that forms part of the plug contact  35  is made to be in contact with (to be engaged with) the associated receptacle contact  15  (the first and second holding leaves  20  and  23  thereof), and accordingly, there is little possibility of the plug contact  35  (the contact portions  37  thereof) being distorted or damaged even if the front and rear contact portions  37  of the plug contact  35  and the front and rear receptacle contacts  15  are brought into contact (engagement) with each other, respectively, with a positional deviation therebetween. Therefore, the contact reliability between each plug contact  35  and the associated receptacle contacts  15  is high. 
         [0108]    In each connector  10 , the receptacle contacts  15  and the plug contact  35  are fully accommodated in the plug insulator  45 , and the entire peripheries of the receptacle contacts  15  and the plug contact  35  are protected by the associated circuit boards CB and the plug insulator  45 . With this structure, the plug contact  35  and the receptacle contacts  15  can be prevented from being damaged when the receptacle contacts  15  and the plug contact  35  are connected and also while in this connected state. Additionally, although the plug insulator  45  is provided in the bottom thereof with three holes (for the removal of a molding die(s) after molding; see  FIG. 6 ) that are formed when the plug insulator  45  is molded, these holes are small and provided in the bottom of the plug insulator  45  when the LED lighting apparatus  100  is assembled, and accordingly, the possibility of sebum or foreign matter entering the inside of the plug insulator  45  through these holes and then adhering to the plug contact  35  or the receptacle contacts  15  is small, which makes it possible to prevent the occurrence of poor contacting, sparking or the like. Additionally, after the receptacle contacts  15  and the plug contact  35  are connected, the electrically conductive portions (e.g., the plug contact  35 , the receptacle contacts  15 , and mounting portions of the circuit boards CB) of each connector  10  are all covered, which makes it possible to increase the insulation performance to an extremely high level. 
         [0109]    A second embodiment of the straight tube LED lighting apparatus according to the present invention will be hereinafter discussed with reference to  FIGS. 17 through 24 . Elements of this embodiment which are similar to or the same as those of the first embodiment of the LED lighting apparatus are designated by the same reference numerals, and a detailed description for such elements is omitted from the following description. 
         [0110]    Each connector  55  that corresponds to each connector  10  of the previous embodiment is provided with a pair of (front and rear) receptacle contacts  60  fixed to two circuit boards CB adjacent to each other, respectively, and a plug connector  68  which connects the pair of receptacle contacts  60 . 
         [0111]    The basic structure of each receptacle contact  60  of the second embodiment is the same as that of each receptacle contact  15  of the first embodiment (similar to each receptacle contact  15 , each receptacle contact  60  is rotationally symmetrical in shape about a vertical axis passing through a center of a base  16  of the receptacle contact  60 ); however, each receptacle contact  60  is different from each receptacle contact  15  in that each receptacle contact  60  is provided at both ends thereof in the forward/rearward direction with a front guide portion  61  and a rear guide portion  61 , respectively. The front and rear guide portions  61  are each provided with a first guide leaf  62  and a second guide leaf  64 . The first guide leaf  62  of the front guide portion  61  and the first guide leaf  62  of the rear guide portion  61  extend vertically downwards from the front and rear ends of the base  16 , respectively, and the second guide leaf  64  of the front guide portion  61  and the second guide leaf  64  of the rear guide portion  61  are formed to extend vertically upwards by bending the lower ends of the first guide leaves  62 . The first guide leaves  62  and the second guide leaves  64  of each receptacle contact  60  are each provided with a support groove  18  so that all the support grooves  18  extend upwardly and are aligned in the forward/leftward direction. Each first guide leaf  62  is provided, on left and right inner side surfaces in the associated support groove  18  in the vicinity of the lower end thereof, with a pair of inward lock projections  63  (see  FIG. 19 ), respectively, which project inwardly toward each other, while each second guide leaf  64  is provided, on left and right inner side surfaces in the associated support groove  18  in the vicinity of the lower end thereof, with a pair of inward lock projections  65 , respectively, which project inwardly toward each other (see  FIG. 18 ). The distance in the left/right direction between the pair of inward lock projections  65  is slightly greater than the distance between the pair of inward lock projections  63 . In addition, each guide portion  61  is provided with a tail lug  66  which projects from the upper end of the second guide leaf  64  to lie in a plane in which the associated base  16  lies. 
         [0112]    Similar to the case of the receptacle contacts  15 , the receptacle contacts  60  are soldered to the circuit formation surfaces of the circuit boards CB using a pneumatic suction device and surface mounting technology (SMT). At this time, as shown in  FIG. 24 , the front and rear tail lugs  66  of each receptacle contact  60  and the upper ends of the facing surfaces of the first guide leaf  62  and the second guide leaf  64  of each guide portion  61  are soldered (fixed) to the circuit formation surface of the associated circuit board CB. 
         [0113]    The plug connector  68  of each connector  55  is provided with a plug contact  70 , a plug insulator  73  and an insulating cover  76 . 
         [0114]    The basic structure of the plug contact  70  is the same as the basic structure of the plug contact  35  of each connector  10 ; namely, the plug contact  70  is provided with two engaging recesses  36 , two contact portions  37 , two pairs of connecting holes  38 , a central low-profile portion  39  and a supported portion  40  (note that the functions of these elements  36  through  40  of the plug contact  70  are the same as those of the plug contact  35  of each connector  10  though slightly different in shape from those of the plug contact  35  of each connector  10 ). However, the plug contact  70  is further provided at four points on each of both sides (left and right sides) thereof with four lock recesses (lock portions)  71  each having a rectangular shape elongated in the forward/rearward direction as viewed from a side of the plug contact  70 , and the lower end of each lock recess  71  reaches the lower edge of the plug contact  70  (namely, the lower end of each lock recess  71  is open downwardly). Although not shown in the drawings, the outer edge of each lock recess  71  is formed into a C-shaped surface (the shape of a letter C in cross section). Additionally, similar to the plug contact  35  of each connector  10 , the outer edge of the plug contact  70  is chamfered. 
         [0115]    The basic structure of the plug insulator  73  is the same as the basic structure of the plug insulator  45  of each connector  10 ; namely, the plug insulator  73  is provided with two accommodation spaces  46 , two center protuberances  48 , two slits  49 , two engaging lugs  50  (beveled guide surfaces  51 ) and two limit projections  54  (note that the functions of these elements  46  through  54  of the plug insulator  73  are the same as those of the plug insulator  45  of each connector  10  though slightly different in shape from those of the plug insulator  45  of each connector  10 ). 
         [0116]    The plug insulator  73  is provided on inner surfaces of the front and rear walls thereof with two (front and rear) engaging projections  74  which are integrally formed with the plug insulator  73  to project inwardly toward each other from the inner surfaces of the front and rear walls of the plug insulator  73 , respectively. Each of the front and rear engaging projections  74  is formed to create a space (clearance) between a bottom (undersurface) of the associated accommodation space  46  (an upper surface of the bottom wall of the plug insulator  73 ) and left and right side walls of the plug insulators  73  adjacent to the engaging projection  74 . The spacing (distance in the vertical direction) between each engaging projection  74  (the bottom thereof) and the bottom of the associated accommodation space  46  is slightly greater than the height of each of both ends (front and rear ends) of the plug contact  70  at which the engaging recesses  36  are formed, and the distance (in the leftward/rightward direction) between each engaging projection  74  and either of the aforementioned left and right side walls of the plug insulator  45  adjacent to the engaging projection  74  is greater than the plate thickness of the plug contact  70 . However, the engaging projections  74  of the plug insulator  73  are different in shape from the engaging projections  52  of the plug insulator  45 . Specifically, each of the front and rear engaging projections  74  of the plug insulator  73  is bilaterally asymmetrical in shape; the rear engaging projection  74  is provided on the top left thereof with a beveled surface and the front engaging projection  74  is provided on the top right thereof with a beveled surface. 
         [0117]    The insulating cover  76  is an integrally-molded element which is molded from an insulating synthetic resin. The insulating cover  76  is provided with a substantially flat base plate portion  77 , and a pair of (left and right) mounting lugs  78  which extends vertically downwards from the bottom of the base plate portion  77 . 
         [0118]    After integrating the plug contact  70  with the plug insulator  73  in a similar manner to the plug connector  30  of each connector  10 , the plug connector  68  that has the above described structure can be assembled by installing the insulating cover  76  to a central part of the plug insulator  73  in the lengthwise direction thereof by making the left and right mounting lugs  78  of the insulating cover  76  engaged in the left and right slits  49  of the plug insulator  73  to be fixed thereto, respectively. Once the plug connector  68  is completely assembled, the left and right edges of the undersurface of the base plate portion  77  respectively come in contact with the upper surfaces of the left and right center protuberances  48 , while the left and right side surfaces of the base plate portion  77  either come in contact with inner surfaces of the left and right side walls of the plug insulator  73  or face the inner surfaces with a minute clearance. Therefore, the central low-profile portion  39  (the supported portion  40 ) of the plug contact  70  is not exposed upwardly. In addition, the insulating cover  76  fixed in place is accommodated in the plug insulator  73 , thus not projecting upwardly from the top of the plug insulator  73 . 
         [0119]    The plug connector  68  of the connector  55  can be connected to two receptacle contacts  60  which are respectively fixed to the facing ends of two circuit boards CB, adjacent to each other, so as to face each other in the forward/rearward direction in a similar connecting procedure to the first embodiment of the straight tube LED lighting apparatus. Upon the plug connector  68  being connected to the two receptacle contacts  60 , the pairs of (left and right) inward lock projections  63  and the pairs of (left and right) inward lock projections  65  of the front receptacle contact  60  and the pairs of (left and right) inward lock projections  63  and the pairs of (left and right) inward lock projections  65  of the rear receptacle contact  60  are each engaged with (come in contact with) the associated lock recess  71  with a tactile click (see  FIG. 19 ). Therefore, an incomplete connection can be prevented from occurring. 
         [0120]    In each connector  55 , if the two receptacle contacts  60  and the plug contact  70  are brought into engagement with each other with some positional deviation therebetween, heavy loads are exerted on the guide portions  61  of each receptacle contact  60 ; however, there is little possibility of the guide portions  61  of each receptacle contact  60  being distorted even if the two receptacle contacts  60  and the plug contact  70  are forced to be engaged with each other because the rigidities of the guide portions  61  are improved by soldering the front and rear tail lugs  66  of each receptacle contact  60  to the circuit formation surface of the associated circuit board CB and also because each guide portion  61  is configured of two guide leaves: the first guide leaf  62  and the second guide leaf  64 . In addition, in each connector  55 , even if an impactive force occurs between the receptacle contacts  60  and the plug contact  70  as a result of bringing the two receptacle contacts  60  and the plug contact  70  into engagement with each other at a relatively high speed, there is little possibility of the guide portions  61  of each receptacle contact  60  being distorted. 
         [0121]    In addition, since each guide portion  61  is constructed from two leaves: the first guide leaf  62  and the second guide leaf  64 , and since each pair of inward lock projections  63  and each pair of inward lock projections  65  are each engaged with the associated lock recess  71 , the engaging and holding force between each receptacle contact  60  and the plug contact  70  of each connector  55  is greater than the engaging and holding force between each receptacle contact  15  and the plug contact  35  of each connector  10 . Therefore, even in the case where the plug contact  70  of each plug connector  68  is connected to two adjacent receptacle contacts  60  so as to hang from these two adjacent receptacle contacts  60 , the plug contact  70  does not come off the associated receptacle connectors  60  by its own weight or vibrations, so that adjacent circuit boards CB can be electrically connected to each other with reliability via the connectors  55 . 
         [0122]    Additionally, since the distance between the pair of inward lock projections  65  of each guide portion  61  of each receptacle contact  60  is slightly greater than the distance between the pair of inward lock projections  63  of each guide portion  61  of each receptacle contact  60 , even if the plug contact  70  rotates (tilts in plan view) in the plug insulator  73  due to, e.g., a substantially large positional deviation between the associated two adjacent circuit boards CB in the leftward/rightward direction, since loads are not only applied to the second guide leaves  64  that are positioned on the outer sides of the first guide leaves  62 , it is difficult for an excessive force to act on between each contact portion  37  (the connecting holes  38  formed therethrough) and the associated support grooves  18  (the associated inward lock projections  63  and  65 ). 
         [0123]    The lower end of each guide portion  61  (at which the first guide leaf  62  and the second guide leaf  64  thereof are joined together) is curved (formed into the shape of a substantially letter U in cross section), and accordingly, each guide portion  61  can be prevented from being distorted or tilted because the plug contact  70  is engaged in the support grooves  18  of each receptacle contact  60  without getting caught or stuck when the plug contact  70  is brought into engagement with the support grooves  18  of each receptacle contact  60  while sliding on the lower ends of each guide portion  61 . 
         [0124]    As shown in  FIG. 24 , when the upper ends of the facing surfaces of the first guide leaf  62  and the second guide leaf  64  of each guide portion  61  are soldered to the circuit formation surfaces of the circuit boards CB, solder fillets (see blackened portions in  FIG. 24 ) are formed thereon, which enhances the mounting strength of each receptacle contact  60  with respect to the associated circuit board CB. 
         [0125]    Each lock recess  71  is greater in dimension (length) in the forward/rearward direction than each pair of inward lock projections  63  and each pair of inward lock projections  65  in the forward/rearward direction, and accordingly, in each connector  55  if a force in the forward/rearward direction is applied to the receptacle contact  60  and/or the plug contact  70  due to a positional deviation between the associated adjacent circuit boards CB in the forward/rearward direction, each pair of inward lock projections  63  and each pair of inward lock projections  65  retain the engagement with the associated lock recess  71  by slidingly moving therein in the forward/rearward direction with respect to the associated lock recess  71 . 
         [0126]    Additionally, since the plug connector  68  of each connector  55  is equipped with the insulating cover  76 , reliable electrical isolation between the central low-profile portion  39  (the supported portion  40 ) of the plug contact  70  and the associated circuit board CB can be achieved. Since the isolating cover  76  is accommodated in the plug insulator  73 , the isolating cover  76  and the associated circuit board CB do not interfere with each other, which makes it possible to achieve a reduction in height of the connector  55 . 
         [0127]    A third embodiment of the straight tube LED lighting apparatus according to the present invention will be hereinafter discussed with reference to  FIGS. 25 through 30 . Elements of this embodiment which are similar to those of the second embodiment of the LED lighting apparatus are designated by the same reference numerals, and a detailed description for such elements is omitted from the following description. 
         [0128]    A connector  80  in this embodiment is for connecting a circuit board CBT which is positioned at either end of the array of circuit boards CB that are aligned in the forward/rearward direction (in  FIG. 25  only the circuit board CBT positioned at the rear end of the array of circuit boards CB is shown) with an electric wire (connecting object)  99  used for supplying power to the circuit board CBT. 
         [0129]    In a similar procedure to the second embodiment of the straight tube LED lighting apparatus, a pair of (left and right) receptacle contacts  60  (only one of which is shown in  FIG. 25 ) are fixed to the undersurface (circuit formation surface) of an end (partly shown by two-dot chain lines in  FIG. 25 ) of the circuit board CBT in the forward/rearward direction which is on the opposite side of the circuit board CBT from the other end thereof that faces the adjacent circuit board CB (not shown in  FIG. 25 ). 
         [0130]    The connector  80  is provided with a receptacle contact  60  and a plug connector  82  which is composed of a plug contact  83  and a plug insulator  88 . 
         [0131]    The plug contact  83  is provided with an engaging recess  36 , a contact portion  37  (having a pair of connecting holes  38 ), a wire connecting strip  84 , a retaining lug  85  and a pair of lock-engaging holes  86  (lock portions) (note that the functions of the engaging recess  36 , the contact portion  37  and the pair of connecting holes  38  are the same as those of the plug contact  70  of each connector  55  though slightly different in shape from those of the plug contact  70  of each connector  55 ). The engaging recess  36  of the plug contact  83  is formed at one end (the left end with respect to  FIG. 27 ) of the plug contact  83 . The wire connecting strip  84  projects rearwardly (the rightward with respect to  FIG. 27 ) from the opposite end of the contact portion  37  from the engaging recess  36 . The retaining lug  85  is formed at a substantially center of the contact portion  37  in the forward/rearward direction. The pair of lock-engaging holes  86  are formed as a pair of (front and rear) through-holes elongated in the forward/rearward direction, and the inner surfaces of both ends of each lock-engaging hole  86  are each formed into a C-shape in cross section. 
         [0132]    The wire connecting strip  84  of the plug contact  83  is connected (by swaging) to a terminal of the electric wire  99  that is sheathed with a flexible outer sheath  98 . 
         [0133]    The plug insulator  88  is an integrally-molded element which is molded of the same insulating synthetic resin as that of the plug insulator  45  or  73 . The plug insulator  88  is provided, at one end thereof in the lengthwise direction thereof, with an end opening  89  having a size allowing the outer sheath  98  (and the electric wire  99 ) which extends toward the other end of the plug insulator  88  to be inserted into and removed from the end opening  89 . The top of the plug insulator  88  is recessed to form an accommodation space  90  in the plug insulator  88 . In addition, the plug insulator  88  is provided therein with a partition wall  91  which partitions the inner end of the end opening  89  from the accommodation space  90 , and the partition wall  91  is provided with a communicating hole  92  having a size (substantially the same width as the contact portion  37 ) that prevents the flexible outer sheath  98  (and the electric wire  99 ) from being inserted and allows the contact portion  37  to be removably inserted. The plug insulator  88  is provided, on an inner surface of the front end wall thereof in the accommodation space  90  which is positioned on the opposite side of the accommodation space  90  from the end opening  89 , with a front end recess  94 . The width (in the leftward/rightward direction) of the front end recess  94  is substantially the same as the wall thickness of the contact portion  37  (the engaging recess  36 ), and the front end recess  94  allows an engaging projection of the plug contact  83  which is formed immediately below the engaging recess  36  to be engaged therein. The plug insulator  88  is further provided, on a undersurface in the accommodation recess  90  and the inner surface of the front end wall (at which the front end recess  94  is provided), with an internal surface groove  95  in which a lower half of the contact portion  37  of the plug contact  83  is engageable. The width (in the leftward/rightward direction) of the internal surface groove  95  is substantially the same as the wall thickness of the contact portion  37 . As shown in  FIG. 28 , the plug insulator  88  is provided, on a side surface thereof in a center part of the internal surface groove  95  in the lengthwise direction thereof (the forward/rearward direction), with an intermediate recess  96  which is recessed (upwards with respect to  FIG. 28 ), and is further provided, on a portion of the plug insulator  88  adjacent to the intermediate recess  96  (on the end opening  89  side), with a retaining projection  97 . 
         [0134]    The plug contact  83 , to which the electric wire  99  (and the outer sheath  98 ) is integrally fixed, is inserted into the accommodation space  90  through the end opening  89  and the communicating hole  92  to be integrated with the plug insulator  88  by fitting the aforementioned engaging projection (formed immediately below the engaging recess  36 ) and a lower half of the contact portion  37  into the front end recess  94  and the internal surface groove  95 , respectively. Thereupon, the plug contact  83  is prevented from moving toward the end opening  89  by the engagement between the retaining lug  85  and the retaining projection  97 , which are positioned inside the intermediate recess  96 ; however, since the plug contact  83  is not totally fixed by the plug insulator  88 , stress applied to the plug contact  83  can be effectively dispersed. 
         [0135]    The plug connector  82  is connected to the receptacle contact  60  contained on the circuit board CBT in a manner similar to that in the previous embodiment; namely, by covering the receptacle contact  60  from below with the plug insulator  88  so that the receptacle contact  60  enters the accommodation recess  90 . Thereupon, each engaging protrusion  21  is engaged in the associated connecting hole  38  of the plug connector  82 , each holding protrusion  24  comes in contact with a side surface of the contact portion  37 , and the pairs of inward lock projections  63  and the pairs of inward lock projections  65  of the receptacle contact  60  are each engaged with (come in contact with) the associated lock-engaging hole  86 . Additionally, a front pair of (left and right) engaging projections  90   a  formed in the accommodation space  90  on laterally facing inner surfaces of the plug insulator  88  are respectively engaged with upper left and right recess portions of each of the first guide leaf  62  and the second guide leaf  64  of the front guide portion  61  (see  FIG. 29 ), and likewise, a rear pair of (left and right) engaging projections  90   a  (see  FIG. 26 ) formed in the accommodation space  90  on laterally facing inner surfaces of the plug insulator  88  are respectively engaged with upper left and right recess portions of each of the first guide leaf  62  and the second guide leaf  64  of the rear guide portion  61 . Therefore, the two circuit boards CBT at the opposite ends of the array of the plurality of circuit boards CB and the front and rear electric wires  99  are electrically connected via the front and rear connectors  80 . Therefore, if a power supply (not shown) passes a current between the front and rear electric wires  99 , the LEDs  103  of the LED units  102  that are contained on each circuit board CB and CBT emit light. 
         [0136]    In addition, since each lock-engaging hole  86  is greater in length in the forward/rearward direction than each engaging projection  63  and  65 , even if a sliding force in the forward/rearward direction acts on the plug contact  83  by, e.g., a twist of the associated electric wire  99  (the associated outer sheath  98 ), each pair of inward lock projections  63  and each pair of inward lock projections  65  retain the engagement with the associated lock-engaging hole  86  by slide movement of the plug contact  83  (the pair of lock-engaging holes  86 ) in the forward/rearward direction with respect to each pair of inward lock projections  63  and each pair of inward lock projections  65 . 
         [0137]    In addition, since each pair of inward lock projections  63  and each pair of inward lock projections  65  of each receptacle contact  60  are each engaged with (in contact with) the associated lock-engaging hole  86 , a force in the downward direction (a force in a direction to make the plug contact  83  disengaged from the associated receptacle contact  60 ) acts on the plug contact  83  (the plug connector  82 ) by a twist of the associated electric wire  99  (the associated outer sheath  98 ), there is no possibility of the plug contact  83  coming off the associated receptacle contact  60 . 
         [0138]    In each connector  80 , upon the plug connector  82  being connected to the receptacle contact  60 , the pairs of (left and right) inward lock projections  63  and the pairs of (left and right) inward lock projections  65  of the receptacle contact  80  are each engaged with the associated lock-engaging hole  86  with a tactile click, so that incomplete connection can be prevented from occurring. 
         [0139]    Additionally, since the plug contact  83  is greater in dimension (height) in the vertical direction than the plug contact  70  and therefore can secure a sufficient strength for the entire plug contact  83 , the plug contact  83  is provided with the lock-engaging holes  86  as through-holes. However, no problem arises even if each lock-engaging hole  86  is formed as a recess (bottomed hole), rather than a through-hole. 
         [0140]    Although the present invention has been described based on each of the above illustrated embodiments, the present invention is not limited solely to these particular embodiments; various modifications to the above illustrated embodiments are possible. 
         [0141]    For instance, in each of the above illustrated first and second embodiments, the supported portion  40  of the plug contact  35  or  70  of each plug connector  30  or  68  can be made immovable with respect to the plug insulator  45  or  73  (the pair of center protuberances  48 ), e.g., by being fixed to the pair of center protuberances  48 . 
         [0142]    It is possible for a spring portion (resiliently deformable portion) that is resiliently deformable in the direction of thickness of the plug contact  35  or  70  to be formed at each end of the plug contact  35  or  70  and for each pair of holding leaves  20  and  23  that holds that spring portion to be each formed as a plate portion having no resiliency. 
         [0143]    Additionally, the plug insulator  45  or  73  can be structured so that the plug contact  35  or  70  is supported only by the front and rear engaging projections  52  or  74  by, e.g., omitting the left and right engaging lugs  50 . 
         [0144]    Although each receptacle contact  15  or  60  is provided with two pairs of holding leaves  20  and  23  (the front pair of holding leaves  20  and  23  and the rear pair of holding leaves  20  and  23 ), it is possible that each receptacle contact  15  or  60  be provided with only one pair of holding leaves  20  and  23  or more than two pairs of holding leaves  20  and  23 . 
         [0145]    Additionally, each guide portion ( 17  or  61 ) of each receptacle contact  15  or  60  can be configured from more than two guide leaves. 
         [0146]    In each of the above illustrated first through third embodiments, the reflectivity of the material of the plug insulator  45 ,  73  or  88  can be optimized, and the surface of the plug insulator  45 ,  73  or  88  can be coated with a non-light absorbing coating. This makes it possible to prevent the connector from absorbing the light of the LEDs  103 . 
         [0147]    Additionally, in the above illustrated first through third embodiments, each connector  10 ,  55  or  80  is applied to the LED lighting apparatus  100 ; however, the same connector can of course be applied to any other electric or electronic apparatus. 
         [0148]    Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.