Patent Publication Number: US-9423111-B2

Title: Illumination device

Description:
FIELD OF THE INVENTION 
     The present invention relates to an illumination device in which an organic EL (Eletro Luminescence) element is used as a light source. 
     BACKGROUND OF THE INVENTION 
     An organic EL element is capable of emitting high-brightness light at a low voltage and capable of producing different emission colors depending on the kind of organic compounds contained therein. In addition, the organic EL element can be easily formed into a flat light emitting panel. In recent years, therefore, attention has been given to the use of the organic EL element as a light source for an illumination device. 
     As an illumination device of this kind, there is available an illumination device that includes a light source unit using an organic EL element as a light source, a base unit for holding the light source unit and an electrode fixed to the base unit and used in supplying an electric current to the light source unit (see, e.g., Japanese Patent Application Publication No. 2012-104504). 
     In the illumination device referred to above, the electrode is fixed to the base unit. Therefore, limitations are imposed on the arrangement of the light source unit. This reduces the degree of freedom in arranging the light source unit. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides an illumination device including a light source unit provided with an organic EL element as a light source, which is capable of increasing the degree of freedom in arranging the light source unit. 
     In accordance with an embodiment of the present invention, there is provided an illumination device, including: a plurality of flat light source units; and an elongated base unit to which the light source units are removably attached, wherein the base unit includes one or more connectors connected to the light source units and used in supplying an electric current to the light source units and a plurality of connector attachment portions arranged at a specified interval along a longitudinal direction of the base unit, the connectors being removably attached to the connector attachment portions. 
     Each of the light source units may be configured such that, when mounted to the base unit, the length of each of the light source units in the longitudinal direction of the base unit becomes an integral multiple of the distance between the connector attachment portions. 
     Each of the connectors may be arranged in a border position of the light source units adjoining each other when the light source units are mounted to the base unit in a mutually-adjoining relationship along the longitudinal direction of the base unit, each of the connectors configured to electrically interconnect the light source units adjoining each other. 
     The base unit may include a pair of parallel sides extending in the longitudinal direction of the base unit, a transverse length of the base unit being equal to the length of each of the light source units in a transverse direction of the base unit. 
     The base unit may include an engaged portion arranged along one longitudinal side thereof and a held portion arranged along the other longitudinal side thereof, the engaged portion and the held portion being used in mounting the light source units to the base unit; and each of the light source units may include an engaging portion provided in a central region of one edge portion of a mounting surface of each of the light source units facing the base unit when the light source units are mounted to the base unit and configured to engage with the engaged portion of the base unit and a holding portion provided in a central region of the other edge portion of the mounting surface and configured to engage with the held portion of the base unit. 
     The engaged portion and the held portion may differ in shape from each other, the engaged portion engaging with only the engaging portion, the held portion engaging with only the holding portion. 
     Each of the light source units may be configured to be able to swing toward the base unit in a state that the engaging portion is brought into engagement with the engaged portion of the base unit, the holding unit resiliently biased away from the engaging portion. 
     The held portion may include a claw extending toward the engaged portion; the holding portion includes a claw engageable with the claw of the held portion; the claws of the held portion and the holding portion are configured to, when each of the light source units is swung toward the base unit with the engaging portion brought into engagement with the engaged portion of the base unit, make contact with each other and generate a force by which the holding portion is slid toward the engaging portion. 
     Each of the light source units may include current supplying terminals upstanding from the mounting surface, the current supplying terminals inserted into each of the connectors. 
     The current supplying terminals may be provided near the engaging portion on the mounting surface, the connector attachment portions provided near the engaged portion in the base unit. 
     Each of the connectors may include terminal receivers extending along the transverse direction of the base unit when the connectors are attached to the base unit, the terminal receivers configured to grip the current supplying terminals. 
     The current supplying terminals may be provided in the opposite end portions of the mounting surface along a direction orthogonal to a direction interconnecting the engaging portion and the holding portion, the current supplying terminals being electrically connected to each other. 
     Each of the current supplying terminals may include a positive terminal and a negative terminal arranged side by side along a direction parallel to the direction interconnecting the engaging portion and the holding portion. 
     The base unit may include an end cap into which the current supplying terminals are inserted, the end cap having a surface made of an insulating material. 
     The base unit may include an input connector arranged in one longitudinal end portion thereof, the current supplying terminals inserted into the input connector, the input connector configured to electrically connect the current supplying terminals to a commercial power source, a driver or another illumination device. 
     The current supplying terminals may be inserted into the end cap are electrically connected via conductors to current supplying terminals provided outside the base unit. 
     The conductors may be extracted outward through a conductor extraction portion provided in the engaged portion or the held portion. 
     The held portion may include cutouts arranged in positions corresponding to the holding portions of the light source units mounted to the base unit. 
     With such configuration, the connectors for use in supplying an electric current to the light source units are removably attached arbitrary connector attachment portions. Therefore, the degree of freedom in arranging the light source units with respect to the base unit can be increased by changing the arrangement of the connectors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view showing an illumination device according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of the illumination device shown in  FIG. 1 ; 
         FIG. 3  is a circuit diagram of the illumination device shown in  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of a light source unit making up the illumination device; 
         FIG. 5  is a perspective view of the light source unit; 
         FIG. 6A  is a plan view of the light source unit as seen at the side of a mounting surface, and  FIG. 6B  is a section view taken along line VIB-VIB in  FIG. 6A ; 
         FIGS. 7A and 7B  are perspective views showing different light source units; 
         FIG. 8  is an exploded perspective view of an input connector making up the illumination device; 
         FIG. 9  is a perspective view of the input connector; 
         FIG. 10  is a view showing how to attach the input connector to a base unit; 
         FIG. 11  is a view illustrating how to attach the connector of the illumination device to the base unit; 
         FIG. 12  is a plan view showing how to connect the connector to a current supplying terminal provided in the light source unit; 
         FIG. 13  is a perspective view showing how to connect the connector to the current supplying terminal; 
         FIG. 14  is a horizontal section view of the base unit with certain portions thereof illustrated on an enlarged scale; 
         FIGS. 15A through 15C  are views illustrating operations which are performed to mount the light source unit to the base unit; 
         FIG. 16  is a view showing an operation which is performed to remove the light source unit from the base unit; 
         FIGS. 17A through 17C  are views showing arrangement patterns of the light source units with respect to the base unit; 
         FIGS. 18A and 18B  are side views of an illumination device according to a first modified example of the foregoing embodiment; 
         FIG. 19  is a plan view of an illumination device according to a second modified example of the foregoing embodiment; and 
         FIG. 20  is a plan view of an illumination device according to a third modified example of the foregoing embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An illumination device according to an embodiment of the present invention will now be described with reference to  FIGS. 1 through 17 . As shown in  FIGS. 1 and 2 , the illumination device  1  includes a plurality of light source units  2  and an elongated base unit  3  to which the light source units  2  are removably mounted. The base unit  3  includes a plurality of connectors  4  connected to the light source units  2  and used in supplying an electric current to the light source units  2  and a plurality of connector attachment portions  31  to which the connectors  4  are removably attached. The connector attachment portions  31  are provided at a specified interval along the longitudinal direction of the base unit  3 . In the illustrated example, the connector attachment portions  31  are provided at an interval of 75 mm starting from one longitudinal end of the base unit  3 . 
     A plurality of light source units  2  is mounted to one base unit  3 . In the illustrated example, three light source units  2   a ,  2   b  and  2   c  differing in size from one another are mounted to the base unit  3 . Each of the light source units  2   a ,  2   b  and  2   c  is formed into a rectangular flat plate shape and is mounted to the base unit  3  on its mounting surface  2 A. Each of the light source units  2   a ,  2   b  and  2   c  is configured such that, when mounted to the base unit  3 , the length of the side (hereinafter referred to as “longitudinal side”) of each of the light source units  2   a ,  2   b , and  2   c  extending along the longitudinal direction of the base unit  3  is equal to an integral multiple of 75 mm (the distance between the connector attachment portions  31 ). In the illustrated example, the lengths of the longitudinal sides of the light source units  2   a ,  2   b , and  2   c  are 75 mm, 150 mm and 300 mm (see  FIG. 2 ), respectively. Each of the light source units  2   a ,  2   b , and  2   c  is configured that such that, when mounted to the base unit  3 , the length of the side (hereinafter referred to as “transverse side”) of each of the light source units  2   a ,  2   b , and  2   c  extending along the transverse direction of the base unit  3  is 75 mm. The light source units  2   a ,  2   b  and  2   c  are arranged in an order of  2   a ,  2   b  and  2   c  along the longitudinal direction of the base unit  3  in a mutually adjoining relationship. 
     Each of the light source units  2   a ,  2   b  and  2   c  includes an engaging portion  21  and a holding portion  5  arranged on the mounting surface  2 A thereof and used in mounting each of the light source units  2   a ,  2   b  and  2   c  to the base unit  3 . The engaging portion  21  is provided at a position corresponding to the center of one longitudinal side of each of the light source units  2   a ,  2   b  and  2   c . The holding portion  5  is provided at a position corresponding to the center of the other longitudinal side of each of the light source units  2   a ,  2   b  and  2   c.    
     Each of the light source units  2   a ,  2   b  and  2   c  includes a pair of current supplying terminals  22  and  23  upstanding from the mounting surface  2 A thereof. The current supplying terminals  22  and  23  are arranged nearer to the engaging portion  21  than to the holding portion  5  on the mounting surface  2 A and are provided in the opposite end regions of the mounting surface  2 A in the direction orthogonal to the direction interconnecting the engaging portion  21  and the holding portion  5 . The current supplying terminal  22  includes a positive terminal  22   a  and a negative terminal  22   b  which are arranged side by side along the direction parallel to the direction interconnecting the engaging portion  21  and the holding portion  5 . Similarly, the current supplying terminal  23  includes a positive terminal  23   a  and a negative terminal  23   b  which are arranged side by side along the direction parallel to the direction interconnecting the engaging portion  21  and the holding portion  5 . The positive terminals  22   a  and  23   a  are electrically connected to each other via a printed wiring substrate to be described later. Likewise, the negative terminals  22   b  and  23   b  are electrically connected to each other via the printed wiring substrate. 
     The base unit  3  is formed into an elongated rectangular flat plate shape and is attached to, e.g., a ceiling or a wall on its attachment surface  3 A. In the illustrated example, the longitudinal dimension of the base unit  3  is set equal to 525 mm (=75 mm+150 mm+300 mm), i.e., the sum of the lengths of the longitudinal sides of the light source units  2   a ,  2   b , and  2   c  (see  FIG. 2 ). In other words, the light source units  2   a ,  2   b , and  2   c  are arranged over the total longitudinal length of the base unit with no clearance left therebetween. Further, the transverse dimension of the base unit  3  is set equal to 75 mm, i.e., the length of the transverse side of each of the light source units  2   a ,  2   b , and  2   c.    
     The base unit  3  has a pair of longitudinal sides extending parallel to each other. The base unit  3  includes an engaged portion  32  and a held portion  33  arranged along one longitudinal side and the other longitudinal side, respectively. The engaged portion  32  engages with the engaging portion  21  of each of the light source units  2 . The held portion  33  engages with the holding portion  5  of each of the light source units  2 . The connector attachment portions  31  mentioned earlier are provided near the engaged portion  32  on the base unit  3 . 
     The base unit  3  has an input connector attachment hole  34  arranged near the engaged portion  32  in one longitudinal end portion of the base unit  3  and used to attach an input connector  6  into which the current supplying terminal  23  of the light source unit  2   c  is inserted. The input connector  6  is used to electrically connect a commercial power source, a driver or another illumination device  1  to the current supplying terminal  23  of the light source unit  2   c.    
     The base unit  3  includes an end cap attachment portion arranged near the engaged portion  32  in the other longitudinal end portion of the base unit  3  and used to attach an end cap  35  into which the current supplying terminal  22  of the light source unit  2   a  is inserted. The end cap  35  is configured so that it can also be mounted to the input connector attachment hole  34 . The end cap  35  electrically interconnects the positive terminal  22   a  and the negative terminal  22   b  of the current supplying terminal  22  of the light source unit  2   a  or leads out conductors respectively connected to the positive terminal  22   a  and the negative terminal  22   b  so that the conductors can be connected to another illumination device (see  FIGS. 19 and 20  to be described later). Each of the conductors is formed of, e.g., a lead wire or an electrically conductive metal plate coated with an insulating material except the portions connected to the positive terminal  22   a  and the negative terminal  22   b . In the present embodiment, the end cap  35  electrically interconnects the positive terminal  22   a  and the negative terminal  22   b  of the current supplying terminal  22  of the light source unit  2   a.    
     In order to facilitate the removal of each of the light source units  2   a ,  2   b , and  2   c  mounted to the base unit  3 , the held portion  33  of the base unit  3  includes a plurality of cutouts  37  provided in positions corresponding to the respective holding portions  5  of the light source units  2   a ,  2   b , and  2   c . The holding portion  5  of the light source unit  2   a  is arranged in a position corresponding to the middle position between the connector attachment portions  31 . The holding portions  5  of the light source units  2   b  and  2   c  are arranged in positions corresponding to the connector attachment portions  31 . In a corresponding relationship with the light source units  2   a ,  2   b  and  2   c , the cutouts  37  are provided at an interval of 37.5 mm starting from one longitudinal end of the base unit  3 . 
     The base unit  3  includes conductor extraction portions  38  formed in the engaged portion  32  and the held portion  33  near the input connector attachment hole  34 . The conductors such as lead wires led out from the input connector  6  attached to the input connector attachment hole  34  pass through the conductor extraction portions  38 . The base unit  3  further includes conductor extraction portions  39  formed in the engaged portion  32  and the held portion  33  near the end cap attachment portion  36 . The conductors led out from the end cap  35  attached to the end cap attachment portion  36  pass through the conductor extraction portions  39 . 
     The connectors  4  are attached to the connector attachment portions  31  so that the connectors  4  can be arranged at the border positions of the light source units  2  adjoining each other. In the illustrated example, the connector  4   a  is arranged at the border position of the light source units  2   a  and  2   b . The connector  4   b  is arranged at the border position of the light source units  2   b  and  2   c . The current supplying terminal  23  of the light source unit  2   a  and the current supplying terminal  22  of the light source unit  2   b  are inserted into the connector  4   a . The current supplying terminal  23  of the light source unit  2   a  and the current supplying terminal  22  of the light source unit  2   b  are electrically connected to each other by a terminal receiver (see the description made later) arranged in the connector  4   a . The current supplying terminal  23  of the light source unit  2   b  and the current supplying terminal  22  of the light source unit  2   c  are inserted into the connector  4   b . The current supplying terminal  23  of the light source unit  2   b  and the current supplying terminal  22  of the light source unit  2   c  are electrically connected to each other by a terminal receiver (see the description made later) arranged in the connector  4   b.    
     As shown in  FIG. 3 , the illumination device  1  is connected to a lighting circuit. The lighting circuit includes an AC/DC converter for converting an alternating current supplied from a commercial power source AC to a direct current, a DC/DC converter for converting a DC voltage to a desired DC voltage, and a driver for controlling the supply of the voltage-converted direct current to the illumination device  1 . The AC/DC converter, the DC/DC converter and the driver are embedded in a ceiling or a wall to which the illumination device  1  is attached. The direct current supplied from the driver flows, in series, in an order of the input connector  6 , the light source unit  2   c , the connector  4   b , the light source unit  2   b , the connector  4   a , the light source unit  2   a , and the end cap  35 . 
     As shown in  FIGS. 4 through 6B , the light source unit  2   a  includes a light emitting panel  24  having a rectangular flat plate shape, a printed wiring board  25  for supplying an electric current to the light emitting panel  24  and a package  7  for accommodating the light emitting panel  24  and the printed wiring board  25 . 
     The light emitting panel  24  uses an organic EL element as a light source. The light emitting panel  24  includes a light-transmitting substrate, a light emitting portion, and a sealing member for sealing the light emitting portion, which are arranged in order from the side of a light emitting surface  2 B. The light emitting portion includes, e.g., a positive electrode formed of a transparent conductive film, a light emitting layer containing a light-emitting organic material, and a light-reflecting negative electrode, which are arranged in order from the side of the light-transmitting substrate. The sealing member serves to isolate the light emitting portion from ambient air, particularly moisture and oxygen, thereby preventing the light emitting portion from getting deteriorated. 
     The printed wiring board  25  includes terminal insertion portions  25   a  into which the positive terminals  22   a  and  23   a  of the light source unit  2   a  are inserted and terminal insertion portions  25   b  into which the negative terminals  22   b  and  23   b  of the light source unit  2   a  are inserted. The positive terminals  22   a  and  23   a  and the negative terminals  22   b  and  23   b  of the light source unit  2   a  are respectively inserted into the terminal insertion portions  25   a  and  25   b  and, therefore, are electrically connected to the printed wiring board  25 . The terminal insertion portions  25   a  are electrically connected to each other by a wiring pattern (indicated by a dot line in  FIG. 4 ) formed on the printed wiring board  25 . The terminal insertion portions  25   b  are electrically connected to each other by a wiring pattern (indicated by a dot line in  FIG. 4 ) formed on the printed wiring board  25 . 
     The package  7  is formed into a rectangular box shape. The package  7  includes a case  8  covering the opposite surface of the light emitting panel  24  from the light emitting surface  2 B and a light-transmitting cover  9  engaging with the case  8  and covering the light emitting surface  2 B of the light emitting panel  24 . The engaging portion  21  and the holding portion  5  are provided on the surface (the mounting surface  2 A) of the case  8 . The engaging portion  21  includes a claw  21   a  extending in the opposite direction from the holding portion  5  and engaging with the held portion  32  of the base unit  3 . 
     The holding portion  5  includes a base  52  fixed to the mounting surface  2 A by screws  51 , springs  53  extending from the base  52  in the opposite direction from the engaging portion  21  (hereinafter referred to as “the engaging direction of the holding portion  5 ”) with one ends of the springs  53  fixed to the base  52 , and a claw  54  fixed to the other ends of the springs  53 . The claw  54  extends in the engaging direction of the holding portion  5  and engages with the held portion  33  of the base unit  3 . The holding portion  5  includes projections  55  extending from the claw  54  in a direction parallel to the longitudinal side of the base unit and restraint portions  56  upstanding from the mounting surface  2 A to restrain the projections  55  from moving in the engaging direction of the holding portion  5 . The restraint portions  56  include accommodation portions  56   a  for accommodating the projections  55  and walls  56   b  arranged at the side of the engaging direction of the holding portion  5  with respect to the accommodation portions  56   a  so as to make contact with the projections  55  (see  FIGS. 6A and 6B ). Thus, the claw  54  (indicated by dots in  FIG. 6A ) is resiliently biased in the engaging direction of the holding portion  5 , whereby the claw  54  can slide in the engaging direction of the holding portion  5 . 
     The case  8  is formed into a rectangular box shape so as to have an opening on the surface facing the light emitting panel  24 . The case  8  includes recess portions  81  defined on the inner circumferential surface thereof and used in bringing the case  8  into engagement with the cover  9 , and holes  82  formed on the mounting surface  2 A thereof so that the current supplying terminals  22   a ,  22   b ,  23   a , and  23   b  can protrude outward through the holes  82 . The case  8  further includes a groove  83  formed on the side surface thereof near the holding portion  5  so that a jig (see the description made later) for use in removing the light source units  2  from the base unit  3  can pass through the groove  83 . 
     The cover  9  includes a rectangular light-transmitting member  91  covering the light emitting surface  2 B of the light emitting panel  24 , a rectangular frame  92  covering the peripheral edge of the light-transmitting member  91  and a plurality of protrusion portions  93  protruding outward from the respective sides of the frame  92  and engaging with the recess portions  81  of the case  8  (see  FIG. 4 ). 
     As shown in  FIGS. 7A and 7B , the light source units  2   b  and  2   c  have the same configuration as the light source unit  2   a , except that the lengths of the sides thereof extending in the longitudinal direction of the base unit  3  are two or four times as large as the length of the light source unit  2   a . As the light source units  2  become longer, the distance from the longitudinal opposite ends thereof to the engaging portion  21  and the holding portion  5  grows larger. For this reason, there is likelihood that, when the light source units  2  are mounted to the base unit  3 , the light source units  2  may be shaken with respect to the base unit  3  and further that the light source units  2  may be unstably held by the base unit  3 . In light of this, it is preferred that the lengths of the longitudinal sides of the light source units  2  be set substantially equal to or smaller than the length of the light source unit  2   c  (300 mm which is four times greater than the length of the light source unit  2   a ). Alternatively, two or more sets of engaging portions  21  and holding portions  5  may be provided in each of the light source units  2 . The lengths of the longitudinal sides of the light source units  2  are not limited to the lengths of the light source units  2   a ,  2   b , and  2   c  but may be, e.g., three times as large as the length of the light source unit  2   a.    
     As shown in  FIGS. 8 and 9 , the input connector  6  includes a positive terminal insertion hole  61  into which the positive terminal  23   a  of the light source unit  2   c  is inserted and a negative terminal insertion hole  62  into which the negative terminal  23   b  of the light source unit  2   c  is inserted. The input connector  6  further includes a terminal receiver  63  for gripping the positive terminal  23   a  inserted into the positive terminal insertion hole  61 , a terminal receiver  64  for gripping the negative terminal  23   b  inserted into the negative terminal insertion hole  62 , and tubular accommodation portions  65  and  66  for accommodating the terminal receivers  63  and  64 . The input connector  6  further includes a hook portion  67  used in attaching the input connector  6  to the base unit  3  and a screw hole  68  used in screw-fixing the input connector  6  to the base unit  3 . 
     The terminal receiver  63  is formed by bending a leaf spring. The terminal receiver  63  includes a base portion  63   a  extending along the longitudinal direction of the base unit  3  when the input connector  6  is attached to the base unit  3  and a pair of extension portions  63   b  extending from the opposite ends of the base portion  63   a  along the substantially transverse direction of the base unit  3  so that the tip ends of the extension portions  63   b  can make contact with each other. Upon the positive terminal  23   a  of the light source unit  2   c  being resiliently gripped by the extension portions  63   b , the terminal receiver  63  is electrically connected to the positive terminal  23   a . The terminal receiver  64  has the same structure as the terminal receiver  63 . The terminal receiver  64  is electrically connected to the negative terminal  23   b  of the light source unit  2   c.    
     As shown in  FIG. 10 , the input connector  6  is fixed to the base unit  3  so that the accommodation portions  65  and  66  can be exposed at the side of the attachment surface  3 A of the base unit  3 . This fixing is performed by bringing the hook portion  67  of the input connector  6  into engagement with a catch portion  34   a  provided in the input connector attachment hole  34  of the base unit  3  and then tightening a screw through the screw hole  68  of the input connector  6  and a screw hole  34   b  formed in the base unit  3 . Conductors (not shown) such as lead wires electrically connected to the positive terminal and the negative terminal of the aforementioned driver (not shown) are inserted into the accommodation portions  65  and  66  of the input connector  6  exposed at the side of the attachment surface  3 A of the base unit  3 . The conductors are respectively connected to the terminal receivers  63  and  64 . As a consequence, the input connector  6  and the driver are electrically connected to each other. 
     As shown in  FIG. 11 , the connector  4   a  is formed into a flat rectangular box shape. The connector  4   a  includes a positive terminal insertion hole  41  into which the positive terminal  23   a  of the light source unit  2   a  is inserted and a negative terminal insertion hole  42  into which the negative terminal  23   b  of the light source unit  2   a  is inserted. The positive terminal insertion hole  41  and the negative terminal insertion hole  42  are formed on one surface of the connector  4   a . The connector  4   a  further includes a positive terminal insertion hole  43  into which the positive terminal  22   a  of the light source unit  2   b  is inserted and a negative terminal insertion hole  44  into which the negative terminal  22   b  of the light source unit  2   b  is inserted. The positive terminal insertion hole  43  and the negative terminal insertion hole  44  are formed on the one surface of the connector  4   a . The connector  4   a  further includes a plurality of lugs  45  formed on the side surface thereof and used in bringing the connector  4   a  into engagement with the connector attachment portions  31 . 
     Each of the connector attachment portions  31  includes a bent portion  31   a  formed by bending a portion of the surface of the base unit  3  on which the light source units  2  are mounted, and a plurality of depressed portions  31   b  formed in the bent portion  31   a  so as to come into engagement with the lugs  45  of the connector  4   a . The connector  4   a  is removably attached to the connector attachment portions  31  by bringing the lugs  45  into engagement with the depressed portions  31   b  of the connector attachment portions  31 . 
     As shown in  FIGS. 12 and 13 , the connector  4   a  includes a terminal receiver  46  for gripping the positive terminal  23   a  of the light source unit  2   a  inserted into the positive terminal insertion hole  41  and a terminal receiver  47  for gripping the negative terminal  23   b  of the light source unit  2   a  inserted into the negative terminal insertion hole  42 . The connector  4   a  further includes a terminal receiver  48  for gripping the positive terminal  22   a  of the light source unit  2   b  inserted into the positive terminal insertion hole  43  and a terminal receiver  49  for gripping the negative terminal  22   b  of the light source unit  2   b  inserted into the negative terminal insertion hole  44 . In  FIGS. 12 and 13 , a portion of the connector  4   a  and the case  8  are not shown. 
     The terminal receivers  46  to  49  are configured just like the terminal receivers  63  and  64  of the aforementioned input connector  6 . Each of the terminal receivers  46  to  49  includes a pair of extension portions extending along the substantially transverse direction of the base unit  3 . The corresponding current supplying terminal is resiliently gripped by the extension portions. Each of the terminal receivers  46  and  48  and each of the terminal receivers  47  and  49  are one-piece formed by bending a single leaf spring. Thus, the positive terminal  23   a  of the light source unit  2   a  and the positive terminal  22   a  of the light source unit  2   b  are electrically connected to each other through the terminal receivers  46  and  48 . The negative terminal  23   b  of the light source unit  2   a  and the negative terminal  22   b  of the light source unit  2   b  are electrically connected to each other through the terminal receivers  47  and  49 . 
     The connector  4   b  has the same structure as the aforementioned connector  4   a . The connector  4   b  electrically interconnects the positive terminal  23   a  of the light source unit  2   b  and the positive terminal  22   a  of the light source unit  2   c  and also electrically interconnects the negative terminal  23   b  of the light source unit  2   b  and the negative terminal  22   b  of the light source unit  2   c.    
     The outer surfaces of the connectors  4   a  and  4   b , the input connector  6  and the end cap  35  are formed of an insulating material. Accordingly, it is possible to prevent a user from undergoing electric shock when mounting the light source units  2  to the base unit  3  or when replacing the light source units  2 . It is also possible to prevent occurrence of tracking. 
     As shown in  FIG. 14 , the engaged portion  32  of the base unit  3  includes a claw  32   a  extending toward the held portion  33  so as to engage with the claw  21   a  of the engaging portion  21  (see the left enlarged view). In the meantime, the held portion  33  of the base unit  3  includes a claw  33   a  extending toward the engaged portion  32  so as to engage with the claw  54  of the holding portion  5  (see the right enlarged view). The engaged portion  32  and the held portion  33  differ in shape from each other. The engaged portion  32  engages with only the engaging portion  21 . The held portion  33  engages with only the holding portion  5  (the claw  54 ). 
     The claw  33   a  of the held portion  33  includes an engaging surface  33   b  making contact with the claw  54  when the claw  33   a  of the held portion  33  engages with the claw  54  of the holding portion  5 , an apex portion  33   c  and a non-engaging surface  33   d  existing at the opposite side of the apex portion  33   c  from the engaging surface  33   b . The claw  33   a  is formed such that the apex portion  33   c  thereof is positioned nearer to the attachment surface  3 A of the base unit  3  than the base end  33   e  of the non-engaging surface  33   d.    
     The claw  54  of the holding portion  5  includes an engaging surface  54   a  making contact with the claw  33   a  when the claw  54  of the holding portion  5  engages with the claw  33   a  of the held portion  33 , an apex portion  54   b , and a non-engaging surface  54   c  existing at the opposite side of the apex portion  54   b  from the engaging surface  54   a . The claw  54  is formed such that the apex portion  54   b  thereof is positioned nearer to the mounting surface  2 A of each of the light source units  2  than the base end  54   d  of the non-engaging surface  54   c.    
     Next, the operation for mounting the light source unit  2  to the base unit  3  will be described with reference to  FIGS. 15A through 15C . Initially, as shown in  FIG. 15A , the light source unit  2  is obliquely put into the base unit  3  so that the engaged portion  32  of the base unit  3  and the engaging portion  21  of the light source unit  2  can come close to each other. Then, as shown in  FIG. 15B , the light source unit  2  is swung toward the base unit  3  in a state that the engaged portion  32  and the engaging portion  21  are kept in engagement with each other. Thus, the claw  54  (the holding portion  5 ) of the light source unit  2  and the claw  33   a  (the held portion  33 ) of the base unit  3  are brought into contact with each other through the non-engaging surfaces  54   c  and  33   d  thereof. 
     In this regard, the non-engaging surface  54   c  of the claw  54  is slidable on the non-engaging surface  33   d  of the claw  33   a . Therefore, the claw  54  slides on the non-engaging surface  33   d . As a result, there is generated a force by which the claw  54  is caused to slide toward the engaging portion  21 . Consequently, as shown in  FIG. 15C , the apex portion  54   b  of the claw  54  goes over the apex portion  33   c  of the claw  33   a , whereby the claw  54  (the holding portion  5 ) and the claw  33   a  (the held portion  33 ) come into engagement with each other. In this manner, using the slope of the non-engaging surfaces  54   c  and  33   d  of the claws  54  and  33   a , the force generated by the swing operation is converted to a force by which the holding portion  5  is slid toward the engaging portion  21 . This makes it possible to easily mount the light source unit  2  to the base unit  3 . 
     Next, the operation for removing the light source unit  2  from the base unit  3  will be described with reference to  FIG. 16 . Since the held portion  33  of the base unit  3  is provided with the cutout  37 , the holding portion  5  of the light source unit  2  can be pushed from the outside of the illumination device  1 . When removing the light source unit  2  from the base unit  3 , the holding portion  5  is pushed with a finger, thereby sliding the holding portion  5  inwardly of the light source unit  2  and releasing the engagement of the holding portion  5  and the held portion  33 . Thereafter, the operation for mounting the light source unit  2  to the base unit  3  is performed in the reverse order. 
     If a plurality of illumination devices  1  is arranged in a mutually-adjoining relationship through the respective held portions  33  (see, e.g.,  FIG. 19 ) or if an obstacle exists at one side of the illumination device  1 , there may be a case when it is impossible to insert a finger even though a user wishes to push the holding portion  5 . In this case, an elongated jig  96  with a curved tip end is inserted through the groove  83  of the case  8 . The holding portion  5  is pushed by the tip end of the jig  96 , thereby releasing the engagement of the holding portion  5  and the held portion  33 . Alternatively, the engagement of the holding portion  5  and the held portion  33  may be released by hooking the light source unit  2  with the tip end of the jig  96  and pulling the jig  96  so that the light source unit  2  can be spaced apart from the base unit  3 . 
     With the illumination device  1  of the present embodiment described above, the connectors  4  can be removably attached to any of the connector attachment portions  31 . Therefore, the degree of freedom in arranging the light source units  2  can be increased by changing the arrangement of the connectors  4  as shown in  FIGS. 17A through 17C . 
     The arrangement of the light source units  2   a ,  2   b , and  2   c  is not limited to the order of  2   a ,  2   b , and  2   c . For example, as shown in  FIG. 17A , the light source units  2   a ,  2   b , and  2   c  may be arranged in the order of  2   b ,  2   c , and  2   a  by changing the positions of the connectors  4 . As shown in  FIG. 17B , the light source units  2  may be composed of a single kind of light source unit. For example, the connectors  4  may be attached to all the connector attachment portions  31 . Seven light source units  2   a  may be arranged in a mutually-adjoining relationship. The light source units  2  need not be necessarily arranged in a mutually-adjoining relationship. For example, as shown in  FIG. 17C , the light source units  2   a  and dummy panels  26  (indicated by dots in  FIG. 7C ) as light source units having no light emitting panel may be alternately arranged in a mutually-adjoining relationship. 
     Since the length of the longitudinal side of each of the light source units  2   a  is equal to an integral multiple of the distance between the connector attachment portions  31 , the connector attachment portions  31  are always arranged in positions corresponding to the ends of the light source units  2 . The light source units  2  adjoining each other are electrically connected by the connectors  4 . Each of the light source units  2  is configured to supply an electric current to the adjoining light source unit  2  through the inside thereof. For this reason, the illumination device  1  has a simple structure with no exposed lead wires. This enables a general user to easily perform the task of replacing or rearranging the light source units  2 . 
     The longitudinal sides of the base unit  3  are parallel to each other. The transverse length of the base unit  3  is equal to the length of the side of each of the light source units  2   a ,  2   b , and  2   c  extending in the transverse direction of the base unit  3 . For this reason, each of the light source units  2   a ,  2   b , and  2   c  can be arranged in an arbitrary region along the longitudinal direction of the base unit  3 . 
     Since the holding portion  5  of the light source unit  2  is slidable, it becomes easy to perform the operation for attaching the light source unit  2  to the base unit  3  and the operation for removing the light source unit  2  from the base unit  3 . Thus, the light source unit  2  can be replaced with ease. By making the holding portion  5  slidable, it becomes possible to attach and remove the light source unit  2  in such a manner that the light source unit  2  does not protrude beyond the base unit  3 . This makes it possible to arrange the light source units  2   a ,  2   b , and  2   c  in a close proximity with one another and to reduce the gaps between the light source units  2   a ,  2   b , and  2   c . As a consequence, when energizing all the light source units  2   a ,  2   b , and  2   c , it is possible to obtain a natural light emitting surface  2 B while keeping the borders between the light source units  2   a ,  2   b , and  2   c  invisible. 
     The engaged portion  32  of the base unit  3  engages with only the engaging portion  21  of the light source unit  2 . The held portion  33  of the base unit  3  engages with only the holding portion  5  of the light source unit  2 . Thus, the light source unit  2  is prevented from being attached to the base unit  3  in a wrong direction. 
     The current supplying terminals  22  and  23  of the light source unit  2  are provided nearer to the engaging portion  21  on the mounting surface  2 A than to the holding portion  5 . The connectors  4  (the connector attachment portions  31 ) are provided near the engaged portion  32  of the base unit  3 . For this reason, if the engaging portion  21  of the light source unit  2  and the engaged portion  32  of the base unit  3  are caused to come close to each other when mounting the light source unit  2  to the base unit  3 , the current supplying terminals  22  and  23  are partially inserted into the insertion holes  41  to  44  of the connectors  4  (indicated by dots in  FIG. 15A ). If the light source unit  2  is swung toward the base unit  3  in this state, the engaging portion  21  and the engaged portion  32  come into engagement with each other. At the same time, the current supplying terminals  22  and  23  are completely inserted into the insertion holes  41  to  44  of the connectors  4 . In this manner, the engagement of the engaging portion  21  and the engaged portion  32  and the insertion of the current supplying terminals  22  and  23  into the connectors  4  can be simultaneously performed by the swing operation. This helps enhance the operability. 
     Since the current supplying terminals  22  and  23  are partially inserted into the insertion holes  41  to  44  of the connectors  4  prior to the swing operation, it is possible to make sure that the light source unit  2  is attached to the base unit  3  in a right position. Inasmuch as the current supplying terminals  22  and  23  are inserted into the insertion holes  41  to  44  of the connectors  4  by the swing operation, it is possible to prevent the light source unit  2  from getting out of alignment with respect to the base unit  3  during the swing operation. 
     The extension portions of the terminal receivers  46  to  49  of the connectors  4  and the extension portions of the terminal receivers  63  and  64  of the input connector  6  extend along the substantially transverse direction of the base unit  3  (see  FIG. 12 ). For that reason, when the light source unit  2  is swung with respect to the base unit  3 , the terminal receivers  46  to  49  do not impede the swing operations of the current supplying terminals  22  and  23 . It is therefore possible to smoothly perform the swing operation. Since the current supplying terminals  22  and  23  are arranged in the end portions of the light source unit  2 , a space for accommodating other members can be provided in the central region of the light source unit  2 . This makes it possible to reduce the thickness of the light source unit  2 . 
     Next, an illumination device according to a first modified example of the present embodiment will be described with reference to  FIGS. 18A and 18B . In the illumination device  11  of the first modified example, two base units  3  are connected to each other at a joint portion J. One of the light source units  2  is arranged to extend over the joint portion J. In the illustrated example, two base units  3  each having a longitudinal dimension of 900 mm are connected to each other, thereby forming an illumination device  11  having a total length of 1800 mm. The arrangement in which one of the light source units  2  extends over the joint portion J can be realized in case of using the light source units  2   b  or the light source unit  2   c  having a length more than twice as large as the distance between the connector attachment portions  31  (75 mm). In case of using the light source unit  2   b , however, the holding portion  5  thereof is positioned in the joint portion J. Therefore, the engagement of the light source unit  2   b  and the base unit  3  becomes unstable. Accordingly, as shown in  FIG. 18A , it is desirable to arrange the light source unit  2   c  in such a way that the holding portion  5  thereof is not positioned in the joint portion J. 
     In a case where the light source units  2  are composed of three kinds of light source units  2   a ,  2   b  and  2   c  as set forth above, only the light source unit  2   c  can be appropriately used as the light source unit  2  extending over the joint portion J. This limits the arrangement patterns of the light source units  2 . In light of this, as shown in  FIG. 18B , there may be further provided a light source unit  2   d  whose side extending along the longitudinal direction of the base unit  3  has a length of 225 mm. The light source unit  2   d  can extend over the joint portion J without the holding portion  5  thereof being positioned in the joint portion J. If the light source unit  2   d  as well as the light source unit  2   c  is used as the light source unit  2  extending over the joint portion J, the degree of freedom in arranging the light source units  2  becomes higher than when only the light source unit  2   c  is used as the light source unit  2  extending over the joint portion J. 
     With the illumination device  11  of the first modified example, it is possible to interconnect two base units  3 . The number of the base units  3  connected to one another is not limited to two but may be three or more. 
     Next, an illumination device according to a second modified example of the present embodiment will be described with reference to  FIG. 19 . In the illumination device  12  of the second modified example, eight illumination devices  11  described above are arranged along the transverse direction of the base unit  3  in a mutually-adjoining relationship. In  FIG. 19 , the light source units  2 , the connectors  4  and the connector attachment portions  31  are not shown. 
     In the illumination device  12 , the illumination device  11  arranged at one end (the upper end in the illustrated example) of the illumination device  12  includes an input connector  6  arranged in one longitudinal end portion thereof and an end cap  35  arranged in the other longitudinal end portion thereof. The input connector  6  is connected to the driver set forth above. In the meantime, each of the remaining illumination devices  11  includes end caps  35  arranged in the longitudinal opposite end portions thereof. In order to distinguish the two end caps  35  of each of the remaining illumination devices  11  from each other, the end cap  35  positioned at the upstream side of an electric circuit will be referred to as “upstream end cap  35   a ” and the end cap  35  positioned at the downstream side of the electric circuit will be referred to as “downstream end cap  35   b”.    
     The current supplying terminals (not shown) inserted into the downstream end cap  35   b  of each of the illumination devices  11  are electrically connected via conductors  30  such as lead wires to the current supplying terminals arranged outside the base unit  3 . In the illustrated example, the current supplying terminals inserted into the downstream end cap  35   b  are electrically connected via the conductors  30  to current supplying terminals (not shown) inserted into the upstream end cap  35   a  of the adjoining illumination device  11  existing at the downstream side in the electric circuit. Thus, the respective illumination devices  11  are electrically serially connected to one another. The conductors  30  are arranged to extend through conductor extraction portions  38  and  39 . 
     The light emitting layer of the organic EL element is formed by, e.g., applying a light-emitting organic material injected from a slit nozzle. In this case, the width of the light emitting layer cannot be set larger than the width of the slit nozzle. This makes it difficult to obtain an illumination device having a large light-emitting surface. With the illumination device  12 , a plurality of illumination devices  11  can be electrically connected to one another in a mutually-adjoining state. It is therefore possible to obtain an illumination device having a large light-emitting surface as a whole. The conductors  30  are arranged to extend through the conductor extraction portions  38  and  39  and, therefore, are not exposed to the outside of the illumination device  12 . As a consequence, it is possible to improve the external appearance of the illumination device  12 . 
     Next, an illumination device according to a third modified example of the present embodiment will be described with reference to  FIG. 20 . In the illumination device  13  of the third modified example, two illumination devices  1  described above are serially connected to each other by conductors  30  such as lead wires. One illumination device  1   a  includes an input connector  6  arranged in one longitudinal end portion thereof and an end cap  35  (a downstream end cap  35   b ) arranged in the other longitudinal end portion thereof. The other illumination device  1   b  includes an upstream end cap  35   a  arranged in one longitudinal end portion thereof and a downstream end cap  35   b  arranged in the other longitudinal end portion thereof. The conductors  30  electrically interconnect the current supplying terminals (not shown) inserted into the end cap  35   b  of the illumination device  1   a  and the current supplying terminals (not shown) inserted into the end cap  35   a  of the illumination device  1   b.    
     With the illumination device  13 , a plurality of illumination devices  1  can be electrically connected to one another in a simple configuration. The number of the illumination devices  1  connected to one another is not limited to two but may be three or more. 
     The illumination device according to the present invention is not limited to the aforementioned embodiment and the modified examples thereof but may be modified in many different forms. For example, the length of the side of the light source unit extending along the longitudinal direction of the base unit need not necessarily be an integral multiple of the distance between the connector attachment portions but may be an arbitrary length. A pair of longitudinal sides of the base unit need not necessarily be parallel to each other. The method of mounting the light source units to the base unit is not limited to engagement of the engaged portion and the engaging portion and engagement of the held portion and the holding portion. For example, the light source units may be screw-fixed to the base unit. The light source of each of the light source units is not limited to the organic EL element but may be, e.g., an LED or a fluorescent lamp. 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.