Abstract:
According to one or more arrangements, a lighting device such as a lamp may include a cover a device body. The device body may have a projection having a support surface at one end and an attachment portion to which the cover is configured to attach. In one or more examples, while the cover is configured to attach to the attachment portion, the cover may be configured to cover the supporting surface of the projection. The cover portion may include a translucent cover portion in some configurations. Additionally or alternatively, the supporting surface of the projection portion may be disposed closer to a center of the cover portion than the attachment portion. In one example, the projection portion may be disposed closer to the cover portion center by a distance equal to a height of the projection portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/794,429 filed Jun. 4, 2010, which is a continuation of U.S. application Ser. No. 11/399,492 filed Apr. 7, 2006 which issued as U.S. Pat. No. 7,758,223 on Jul. 20, 2010. U.S. Pat. No. 7,758,223 claims priority to Japanese Patent Application No. 2005-112339 filed Apr. 8, 2005, Japanese Patent Application No. 2005-221571 filed Jul. 29, 2005, Japanese Patent Application No. 2005-221688 filed Jul. 29, 2005; and Japanese Patent Application No. 2005-371406 filed Dec. 26, 2005. The entire contents of all of the applications mentioned above are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects described herein relate to a lamp using a semiconductor element like a light-emitting diode as a light source, and more particularly a structure for efficiently radiating the heat generated by a light source during lighting of a lamp. 
     2. Description of the Related Art 
     A light-emitting diode is well known as a light source for a lamp compatible with an incandescent lamp. The output of the light-emitting diode is lowered and the life is reduced, as the temperature is increased. Therefore, it is necessary to control the increase of the temperature of the light-emitting diode in the lamp using the light-emitting diode as the light source. 
     For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-243809 discloses an LED lamp, which prevents overheat of a light-emitting diode by increasing the heat radiation of the light-emitting diode. The conventional LED lamp is provided with a spherical body, a metal substrate, and light-emitting diodes. The spherical body is composed of a metallic radiator having a base at one end and an opening at the other end, and a translucent cover. The metallic radiator has a shape spreading from one end to the other end like a bugle. 
     The metal substrate is fixed to the opening of the metallic radiator through a high heat conductivity member having electrical insulation. The light-emitting diode is supported by the metal substrate and covered by the translucent cover. 
     The heat generated by the light-emitting diode during lighting of the LED lamp is transmitted from the metal substrate to the metallic radiator through the high heat conductivity member. The heat transmitted to the metallic radiator is radiated to the atmosphere from the peripheral surface of the metallic radiator. This prevents overheat of the light-emitting diode, and increases the luminous efficiency of the LED lamp. 
     According to the LED lamp disclosed by the published Japanese patent applications, the metallic radiator to radiate the heat of the light-emitting diode and the metal substrate to mount the light-emitting diode are different components. In this structure, though the metal substrate and the metallic radiator are connected through the high heat conductivity member, it is unavoidable to generate a thermal resistance in a joint of the metal substrate and the metallic radiator. Thus, the conduction of heat between the metal substrate and the metallic radiator disturbed, and the heat of the light-emitting diode cannot be efficiently transmitted from the metal substrate to the metallic radiator. There is a point to be improved to control the temperature increase of the light-emitting diode. 
     Moreover, in the above-described LED lamp, a lighting circuit to light the light-emitting diode is an indispensable component. When the lighting circuit is incorporated in the LED lamp, it is requested that the size of the LED lamp is not increased by the lighting circuit. It is also known that when the temperature of the lighting circuit is increased, the reliability of the circuit operation is decreased and the life is reduced. Therefore, it is essential to prevent overheat of the lighting circuit when the lighting circuit is incorporated in the LED lamp. 
     The above-mentioned published Japanese patent applications do not describe about the lighting circuit. The LED lamps disclosed in these applications do not satisfy the demand for preventing the large size of the LED lamp and overheat of the lighting circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a perspective view of a lamp according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view of the lamp according to the first embodiment of the present invention; 
         FIG. 3  is a sectional view of the first embodiment of the present invention, with a base, an outer shell and a translucent cover separated; 
         FIG. 4  is a sectional view taken along line F 4 -F 4  of  FIG. 2 ; 
         FIG. 5  is a sectional view taken along line F 5 -F 5  of  FIG. 2 ; 
         FIG. 6  is a perspective view of a lamp according to a second embodiment of the present invention; 
         FIG. 7  is a sectional view of the lamp according to the second embodiment of the present invention; 
         FIG. 8  is a sectional view of a lamp according to a third embodiment of the present invention; 
         FIG. 9  is a sectional view of a lamp according to a fourth embodiment of the present invention; 
         FIG. 10  is a sectional view of the lamp according to the fourth embodiment of the present invention, with a base, an outer shell and a translucent cover separated; 
         FIG. 11  is a sectional view taken along line F 11 -F 11  of  FIG. 9 ; 
         FIG. 12  is a sectional view of a lamp according to a fifth embodiment of the present invention; 
         FIG. 13  is a sectional view of a lamp according to a sixth embodiment of the present invention; 
         FIG. 14  is a sectional view taken along line F 14 -F 14  of  FIG. 13 ; 
         FIG. 15  is a sectional view showing a positional relationship between a lead wire and an insulating cylinder in a sixth embodiment of the present invention; 
         FIG. 16  is a front view showing a positional relationship between a wiring board to support a light-emitting diode and a light source support in a sixth embodiment of the present invention; 
         FIG. 17  is a plan view of an insulating material used in the sixth embodiment of the present invention; 
         FIG. 18  is a sectional view taken along line F 18 -F 18  of  FIG. 17 ; 
         FIG. 19  is a sectional view taken along line F 19 -F 19  of  FIG. 17 ; 
         FIG. 20  is a perspective view of the insulating cylinder used in the sixth embodiment of the present invention; 
         FIG. 21  is a sectional view of a lamp according to a seventh embodiment of the present invention; 
         FIG. 22  is a sectional view showing a positional relationship among a light source support of an outer shell, a light source, a light source cover and a holder in the seventh embodiment of the present invention; 
         FIG. 23  is a sectional view showing a positional relationship among the light source cover, the holder and a heat shielding cover in the seventh embodiment of the present invention; 
         FIG. 24  is an exploded perspective view showing a positional relationship among the outer shell, a heat conduction sheet and the light source in the seventh embodiment of the present invention; 
         FIG. 25  is a perspective view of a separated light source cover of the seventh embodiment of the present invention; 
         FIG. 26  is a sectional view of a lamp according to an eighth embodiment of the present invention; 
         FIG. 27  is a plan view of the lamp according to the eighth embodiment of the present invention; 
         FIG. 28  is a sectional view of a lamp according to a ninth embodiment of the present invention; and 
         FIG. 29  is a plan view of the lamp according to the ninth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of the present invention will be explained hereinafter with reference to  FIG. 1  to  FIG. 5 . 
       FIG. 1  and  FIG. 2  show a bulb-type lamp  1  compatible with an incandescent lamp. The lamp  1  includes an outer shell  2 , a light source  3 , a translucent cover  4 , a lighting circuit  5 , an insulating member  6 , and a base  7 . 
     The outer shell  2  is made of metallic material such as aluminum with excellent heat conductivity. As shown in  FIG. 2  and  FIG. 3 , the outer shell  2  has a peripheral wall  8  and an end wall  9 . The peripheral wall  8  and the end wall  9  are formed integrally. The peripheral wall  8  is cylindrical. The outer circumference of the peripheral wall  8  is a heat radiating surface  10  exposed outside the lamp  1 . The heat radiating surface  10  is tapered with the outside diameter decreased gradually from one end to the other end along the axial direction of the peripheral wall  8 . 
     The end wall  9  closes one end of the peripheral wall  8 . The end wall  9  forms a circular plate light source support  11 . The light source support  11  has a flat supporting surface  11   a  exposed outside the outer shell  2 . 
     In the first embodiment, the heat radiating surface  10  of the outer shell  2  may be knurled and stain finished. This can increase the area of the heat radiating surface  10 . The heat radiating surface  10  may be coated with a protection film to prevent rusting. If a black protection film is coated, the efficiency of heat radiation from the heat radiating surface  10  to the atmosphere is increased. 
     As shown in  FIG. 2  and  FIG. 3 , the outer shell  2  has a receptacle  12 . The receptacle  12  is defined by a space surrounded by the peripheral wall  8  and the end wall  9 , and positioned inside the heat radiating surface  10 . The receptacle  12  has an open end  12   a  opposite to the end wall  9 . The open end  12   a  is positioned at the other end of the peripheral wall  8 . 
     The peripheral wall  8  has an inner peripheral surface exposed to the receptacle  12 . An engaging groove  8   a  is formed on the inner peripheral surface. The engaging groove  8   a  is positioned at the open end  12   a  of the receptacle  12 , and continued in the circumferential direction of the peripheral wall  8 . A recession  14  is formed in the outer circumference of the end wall  9 . The recession  14  is circular surrounding the light source support  11 , and opened outward of the outer shell  2 . 
     As shown in  FIG. 2  to  FIG. 4 , the light source support  11  has one screw hole  15  and a pair of through holes  16   a  and  16   b . The screw hole  15  is positioned at the center of the light source support  11 . The through holes  16   a  and  16   b  are positioned parallel to each other on both sides of the screw hole  15 . One end of the screw hole  15  and the ends of the through holes  16   a  and  16   b  are opened to the supporting surface  11   a  of the light source support  11 . The other end of the screw hole  15  and the other ends of the through holes  16   a  and  16   b  are opened to the receptacle  12 . 
     As shown in  FIG. 4  and  FIG. 5 , the light source  3  includes four light-emitting diodes  18  shaped like a chip, for example. The light-emitting diodes  18  are an example of a point source of light, and mounted in two lines on a circular wiring board  19 . The wiring board  19  has an insulating substrate  20 . The insulating substrate  20  has a first surface  20   a  and a second surface  20   b . The second surface  20   b  is positioned on the opposite side of the first surface  20   a.    
     A pattern layer  21  and a resist layer  22  are stacked on the first surface  20   a  of the insulating substrate  20 . The pattern layer  21  is made of metal foil such as copper. The resist layer  22  covers the pattern layer  21 . A thermal diffusion layer  23  and a resist layer  24  are stacked on the second surface  20   b  of the insulating substrate  20 . The thermal diffusion layer  23  is made of metal foil with excellent heat conductivity such as an alloy. The thermal diffusion layer  23  is thicker than the pattern layer  21  to ensure heat capacity. As shown in  FIG. 5 , the thermal diffusion layer  23  is divided into four areas  23   a ,  23   b ,  23   c  and  23   d . The areas  23   a ,  23   b ,  23   c  and  23   d  are separated, and correspond to the mounting positions of the light-emitting diodes  18 . The resist layer  24  covers the thermal diffusion layer  23 . The light-emitting diodes  18  are mounted on the first surface  20   a  of the insulating substrate  20 , and electrically connected to the pattern layer  21 . 
     As the wiring board  19 , a pattern layer, a thermal diffusion layer and a resist layer may be stacked on a metal substrate with excellent heat conductivity. However, considering the cost, it is desirable to use a resin substrate made of epoxy resin mixed with glass powder as the insulating substrate  20 , and to stack a pattern layer, a thermal diffusion layer and a resist layer on the resin substrate. 
     The wiring board  19  is stacked on the light source support  11  with the thermal diffusion layer  23  faced to the supporting surface  11   a  of the light source support  11 . The wiring board  19  is fixed to the light source support  11  through a screw  26 . The screw  26  is inserted into the screw hole  15  penetrating the center of the wiring board  19 . With this insertion of the screw, the wiring board  19  is fixed tightly to the supporting surface  11   a  of the light source support  11 , and the wiring board  19  is thermally connected to the light source support  11 . 
     Therefore, the heat generated by the light-emitting diode  18  is transmitted from the insulating substrate  20  to the thermal diffusion layer  23 , and diffused widely to every corner of the thermal diffusion layer  23 . The heat diffused to the heat diffusion layer  23  is transmitted to the light source support  11  through the resist layer  24 . 
     According to the first embodiment, a heat conduction path from the wiring board  19  to the supporting surface  11   a  is formed in the light source support  11  of the outer shell  2 . To control the thermal resistance of the heat conduction path, it is desirable to fill a heat-conducting substance consisting mainly of silicon, such as grease between the wiring board  19  and the supporting surface  11   a.    
     The translucent cover  4  is a globe made of synthetic resin, for example, and is formed spherical having an opening  4   a  at one end. The translucent cover  4  is held by the outer shell  2  by fitting an edge  4   b  defining the opening  4   a  into the recession  14  of the outer shell  2 . The translucent cover  4  hides the light source support  11 , light-emitting diodes  18  and wiring board  19 . Therefore, the light-emitting diodes  18  are faced to the inside surface of the translucent cover  4 . 
     The lighting circuit  5  is used to light up the light-emitting diodes  18 , and unified as one module. As shown in  FIG. 2 , the lighting circuit  5  has a wiring board  28  and circuit components  29 . The wiring board  28  has a first surface  28   a  and a second surface  28   b  positioned on the opposite side of the first surface  28   a . The circuit components  29  are mounted on the first surface  28   a  of the wiring board  28 . The circuit components  29  have lead terminals. The lead terminals are soldered to conductor patterns (not shown) printed on the wiring bard  28 , penetrating through the wiring board  28 . 
     The lighting circuit is housed in the receptacle  12  of the outer shell  2 . The lighting circuit  5  has lead wires  30   a  and  30   b  electrically connected to the light-emitting diodes  18 , and a lead wire (not shown) electrically connected to the base  7 . The lead wires  30   a  and  30   b  are led to the wiring board  19 , penetrating through the through holes  16   a  and  16   b  formed on the end wall  9 . The lead wires  30   a  and  30   b  are connected to the pattern layer  21  of the wiring board  19  by means of soldering. Therefore, as shown in  FIG. 2 , when the translucent cover  4  is directed to the lamp  1  located on the outer shell  2 , the lighting circuit  5  is suspended from the light support  11  by the lead wires  30   a  and  30   b.    
     The insulating member  6  is an example of insulating layer for electrically insulating between the outer shell  2  and the lighting circuit  5 . The insulating member  6  is a molding using synthetic resin material, such as polybutylene terephthalate. As shown in  FIG. 2 , the insulating member  6  is cup-shaped having a cylindrical peripheral wall  32   a  and a closed wall  32   b  closing one end of the peripheral wall  32   a . The closed wall  32   b  has a pair of through holes  33   a  and  33   b  to pass the lead wires  30   a  and  30   b . The axial length A of the insulating member  6  is shorter than the axial length B from the light source support  11  to the engaging groove  8   a  of the outer shell  2 . 
     The insulating member  6  is fit in the receptacle  12  through the open end  12   a . Therefore, the peripheral wall  32   a  of the insulating member  6  covers the internal circumference of the peripheral wall  8  of the outer shell  2 , and the closed wall  32   b  of the insulating member  6  covers the inside surface of the end wall  9  of the outer shell  2 . The insulating member  6  partitions the outer shell  2  and the lighting circuit  5 . 
     The base  7  is used to supply a current to the lighting circuit  5 . The base  7  has a metal base shell  35 , and a connecting member  36  fixed to the base shell  35 . The base shell  35  is removably screwed into a lamp socket of a not-shown light fixture. The connecting member  36  is a molding using synthetic resin material, such as polybutylene terephthalate, and has electrical insulation. The connecting member  36  has a peripheral surface  36   a , which is formed to have a cylindrical hollow and curved circularly. 
     As shown in  FIG. 2 , the connecting member  36  has a distal end  37  to fit in the inside of the open end  12   a  of the receptacle  12 . The distal end  37  has an engaging projection  38  on the peripheral surface. The engaging projection  38  engages with the engaging groove  8   a  when the distal end  37  is fit inside the open end  12   a . By this engagement, the outer shell  2  and the base  7  are coaxially connected. The connecting member  36  is interposed between the base shell  35  and the outer shell  2 , insulating them electrically and thermally. 
     In the state that the connecting member  36  is connected to the outer shell  2 , the peripheral surface  36   a  of the connecting member  36  is continued to the heat radiating surface  10  of the outer shell  2 . A step  39  is formed in the base of the distal end  37 . The step  39  has a flat surface, which is continued in the circumferential direction of the connecting member  36 , and extending in the radial direction of the connecting member  36 . The step  39  butts against the open end  12   a , when the distal end  37  of the connecting member  36  is inserted into the open end  12   a  of the receptacle  12 . This controls the insertion depth of the distal end  37  of the connecting member  36  into the receptacle  12 . 
     As the insertion depth of the distal end  37  is controlled, a space S is generated between the distal end  37  of the connecting member  36  and the peripheral wall  32   a  of the insulating member  6 . The existence of the space S prevents interference of the distal end  37  with the insulating member  6  before the engaging projection  38  engages with the engaging groove  8   a . In other words, Failure in engagement between the engaging projection  38  and the engaging groove  8   a  caused by a dimensional tolerance of the connecting member  36  and outer shell  2  is prevented. Therefore, the base  7  can be surely connected to the open end  12   a  of the receptacle  12 . 
     In the lamp  1  of the first embodiment, when the lamp  1  is lit, the light-emitting diodes  18  are heated. The light-emitting diodes  18  are cooled in the following process, in addition to the cooling by conviction of the air generated within the translucent cover  4 . 
     The heat of the light-emitting diodes  18  are transmitted to the light source support  11  of the outer shell  2  through the wiring board  19 . The heat transmitted to the light source support  11  is transmitted from the end wall  9  to the heat radiating surface  10  through the peripheral wall  8 , and radiated to the outside of the lamp  1  through the heat radiating surface  10 . 
     The light source support  11  receiving the heat of the light-emitting diodes  18  is formed integrally with the peripheral wall  8  having the heat radiating surface  10 . There is no joint to disturb the conduction of heat on the heat conduction path from the light source support  11  to the heat radiating surface  10 , and the thermal resistance of the heat conduction path is decreased. Therefore, the heat of the light-emitting diodes  18  transmitted to the light source support  11  can be efficiently escaped to the heat radiating surface  10 . 
     In addition, in the first embodiment, the circular recession  14  surrounding the light source support  11  is formed in the end wall  9  of the outer shell  2 , and the recession  14  is opened outward of the outer shell  2 . The existence of the recession  14  increases the surface area of the outer shell  2 , and increases the amount of heat radiation from the outer shell  2  though the shape of the outer shell  2  is restricted by the appearance of the lamp  1 . 
     As a result, the cooling performance of the light-emitting diodes  18  is increased, and overheat of the light-emitting diodes  18  is prevented. Therefore, the decrease of the light-emitting efficiency of the light-emitting diodes  18  can be controlled, and the life of the light-emitting diodes  18  can be made long. 
     Moreover, the light-emitting diodes  18  are mounted on the wiring board  19  having the thermal diffusion layer  23 , and the heat generated by the light-emitting diodes  18  are diffused to every corner of the wiring board  19  through the thermal diffusion layer  23  of the wiring board  19 . Therefore, the heat of the light-emitting diodes  18  can be transmitted from a wide area of the wiring board  19  to the light source support  11 . This improves the heat conduction from the light-emitting diodes  18  to the light source support  11 , and increases the cooling performance of the light-emitting diodes  18 . 
     Further, the lamp  1  of the first embodiment has the receptacle  12  to contain the lighting circuit  5  inside the outer shell  2 . This eliminates the necessity of arranging the lighting circuit  5  and outer shell  2  in the axial direction of the lamp  1 . Therefore, the length of the lamp  1  in the axial direction can be reduced, and the compact lamp  1  can be provided. 
     The lighting circuit  5  contained in the receptacle  12  is electrically insulated from the outer shell  2  through the insulating member  6 . Therefore, the lighting circuit  5  can be incorporated in the outer shell  2 , while the outer shell  2  is made of metal to increase the heat radiation performance. 
     The cup-shaped insulating member  6  for electrically insulating the outer shell  2  and the lighting circuit  5  is a synthetic resin molding with the heat conductivity lower than the outer shell  2 . Therefore the insulating member  6  can thermally shield the lighting circuit  5  from the outer shell  2 , and prevents conduction of the heat of the light-emitting diodes  18  to the lighting circuit  5  through the outer shell  2 . As a result, the lighting circuit  5  is protected from the heat of the light-emitting diodes  18 . This prevents a malfunction of the lighting circuit  5 , and makes the life of the lighting circuit  5  long. 
     The receptacle  12  containing the lighting circuit  5  is surrounded by the peripheral wall  8  and the end wall  9  of the outer shell  2 , and the open end  12   a  of the receptacle  12  is closed by the base  7 . In other words, the lighting circuit  5  is contained in a space portioned by the outer shell  2  and base  7 . The air outside the lamp  1  does not flow in this space. This prevents adhesion of dust in the air to the lighting circuit  5  causing a tracking phenomenon. 
       FIG. 6  and  FIG. 7  show a second embodiment of the invention. 
     The second embodiment is different from the first embodiment in the outer shell  2  and translucent cover  4 . The other components of the lamp  1  and technical effects are the same as those of the first embodiment. Therefore, the same components as those of the first embodiment are given same reference numerals, and explanation of these components will be omitted. 
     As shown in  FIG. 6  and  FIG. 7 , in the lamp  1  according to the second embodiment, the outside diameter of the peripheral wall  8  of the outer shell  2  is constant except the end portion adjacent to the open end  12   a  of the receptacle  12  of the outer shell  2 . Therefore, the outer shell  2  is shaped like a straight cylinder. 
     A globe as the translucent cover  4  has a reflection portion  41   a  and a projection portion  41   b . The reflection portion  41   a  has an opening  42   a  opened to the light source support  11 , and an edge  42   b  defining the opening  42   a . The edge  42   b  is fit in the recession  14  of the outer shell  2 . The reflection portion  41   a  is tapered to increase the diameter gradually from the edge  42   b . A light reflection film  43  is stacked on the inside surface of the reflection portion  41   a.    
     The projection portion  41   b  is formed integrally with the reflection portion  41   a  so as to continue to the reflection portion  41   a . The projection portion  41   b  is faced to the light reflection film  43  and light-emitting diodes  18 . 
     With the translucent cover  4  formed as described above, a part of the light from the light-emitting diodes  18  can be reflected to the projection portion  41   b  by using the light reflection film  43 . Therefore, most of the light from the light-emitting diodes  18  can be condensed by the projection portion  41   b , and projected to the outside of the lamp  1 . 
     As shown in  FIG. 7 , the outer shell  2  has a stopper  45  at the corner defined by the peripheral wall  8  and the end wall  9 . The stopper  45  is formed circular, projecting from the inside surface of the peripheral wall  8  and continuing to the inner circumference of the peripheral wall  8 . The stopper  45  is not limited to the circular form. For example, stoppers projecting from the inner circumference of the peripheral wall  8  may be arranged with intervals in the circumferential direction of the peripheral wall  8 . 
     The inside diameter of the stopper  45  is smaller than the outside diameter of the closed wall  32   b  of the insulating member  6 . Therefore, the stopper  45  is interposed between the end wall  9  and the closed wall  32   b  of the insulating member  6 , even in the state that the insulating member  6  is fit in the receptacle  12  of the outer shell  2 . As a result, the light source support  11  on the end wall  9  is separated from the insulating member  6 , and a gap  46  is provided therebetween. 
     According to the lamp  1  of the second embodiment, the existence of the gap  46  keeps the light source support  11  to receive the heat of the light-emitting diodes  18  non-contacting with the insulating member  6 . The gap  46  functions as a heat shielding space to prevent conduction of heat from the light source support  11  to the insulating member  6 , and the heat of the light-emitting diodes  18  are difficult to transmit directly from the light source support  11  to the insulating member  6 . 
     Therefore, though the lighting circuit  5  is contained in the outer shell  2  which receives and radiates the heat of the light-emitting diodes  18 , the influence of heat to the lighting circuit  5  can be minimized. This prevents a malfunction of the lighting circuit  5 , and makes the life of the lighting circuit  5  long. 
       FIG. 8  shows a third embodiment of the invention. 
     The third embodiment is different from the first embodiment in the method of fixing the translucent cover  4  to the outer shell  2 . The other components of the lamp  1  and technical effects are the same as those of the first embodiment. Therefore, the same components as those of the first embodiment are given same reference numerals, and explanation of these components will be omitted. 
     As shown in  FIG. 8 , the edge  4   b  of the translucent cover  4  is fixed to the recession  14  of the outer shell  2  through a silicon-based adhesive  51 . The adhesive  51  is filled in the recession  14 . The recession  14  is formed surrounding the light source support  11 , and caved in toward the base  7  from the supporting surface  11   a  to fix the wiring board  19 . Therefore, the adhesive  51  is provided at the position displaced to the base  7  from the light-emitting diodes  18  on the wiring board  19 . 
     According to the lamp  1  of the third embodiment, the adhesive  51  to fix the translucent cover  4  to the outer shell  2  is filled in the recession  14  caved in from the supporting surface  11   a  of the light source support  11 . Therefore, the light from the light-emitting diodes  18  is difficult to apply directly to the adhesive  51 . This prevents deterioration of the adhesive  51 , even if the light from the light-emitting diodes  18  includes an ultraviolet ray. Therefore, the translucent cover  4  is securely fixed to the outer shell  2  for a long period. 
       FIG. 9  to  FIG. 11  shows a fourth embodiment of the invention. 
     The fourth embodiment is different from the third embodiment in the shape of the light support  11  of the outer shell  2 . The other components of the lamp  1  and technical effects are the same as those of the third embodiment. Therefore, the same components as those of the third embodiment are given same reference numerals, and explanation of these components will be omitted. 
     As shown in  FIG. 9  to  FIG. 11 , the end wall  9  of the outer shell  2  has a projection  61  projecting from the light source support  11  to the translucent cover  4 . The projection  61  is formed circular one size smaller than the light source support  11 . The projection  61  is formed integrally with the end wall  9 , and surrounded coaxially by the recession  14  to fix the translucent cover  4 . Therefore, one step  62  is formed between the projection  61  and light source support  11 . The step  62  is circular continuing to the circumferential direction of the projection  61 . 
     A flat supporting surface  63  is formed at the end of the projection  61 . The supporting surface  63  is placed inside the translucent cover  4  more closely to the center than the end wall  9  of the outer shell  2 . Therefore, the supporting surface  63  is farther from the recession  14  by the distance equivalent to the height of the projection  61 . 
     In the fourth embodiment, the wiring board  19  with the light-emitting diodes  18  mounted is fixed to the center of the supporting surface  63  through the screw  26 . The wiring board  19  is thermally connected to the supporting surface  63 . The screw hole  15  and through holes  16   a / 16   b  are opened to the supporting surface  63 , penetrating through the projection  61 . 
     According to the lamp  1  of the fourth embodiment, the projection  61  projecting to the translucent cover  4  is formed in the light support  11  of the outer shell  2 , and the wiring board  19  having the light-emitting diodes  18  is fixed to the end surface  63  of the projection  61 . Therefore, the light-emitting diodes  18  are displaced to be inside the translucent cover  4  more closely to the center than the end wall  9  of the outer shell  2 . This efficiently guides the light from the light-emitting diodes  18  to the inside of the translucent cover  4 , and permits radiation of the light from here to the outside of the translucent cover  4 . 
     Further, the existence of the projection  61  increases the surface area and heat capacity of the light source support  11 . This increases the amount of heat radiation from the outer shell  2 , though the shape of the outer shell  2  is restricted by the appearance of the lamp  1 . As a result, the cooling performance of the light-emitting diodes  18  is increased, overheat of the light-emitting diodes  18  is prevented, and the life of the light-emitting diodes  18  can be made long. 
     The light-emitting diodes  18  are farther from the adhesive  51  filled in the recession  14  by the distance equivalent to the height of the projection  61 . In other words, the light from the light-emitting diodes  18  to the recession  14  is blocked by the outer circumference of the projection  61 , and the light from the light-emitting diodes  18  is difficult to apply directly to the adhesive  51 . 
     This prevents deterioration of the adhesive  51 , even if the light from the light-emitting diodes  18  includes an ultraviolet ray. Therefore, the translucent cover  4  is securely fixed to the outer shell  2  for a long period. 
       FIG. 12  shows a fifth embodiment of the invention. 
     The fifth embodiment is different from the second embodiment in the shape of the light source support  11  of the outer shell  2 . The other components of the lamp  1  and technical effects are the same as those of the second embodiment. Therefore, the same components as those of the second embodiment are given same reference numerals, and explanation of these components will be omitted. 
     As shown in  FIG. 12 , the end wall  9  of the outer shell  2  has a projection  71  projecting from the light source support  11  to the translucent cover  4 . The projection  71  is formed circular one size smaller than the light source support  11 . The projection  71  is formed integrally with the end wall  9 , and surrounded coaxially by the recession  14  to fix the translucent cover  4 . Therefore, one step  72  is formed between the projection  71  and light source support  11 . The step  72  is circular continuing to the circumferential direction of the projection  71 . 
     A flat supporting surface  73  is formed at the end of the projection  71 . The supporting surface  73  is placed inside the reflection portion  41   a  of the translucent cover  4  more closely to the center than the end wall  9  of the outer shell  2 . Therefore, the supporting surface  73  is farther from the recession  14  by the distance equivalent to the height of the projection  71 . 
     In the fifth embodiment, the wiring board  19  with the light-emitting diodes  18  mounted is fixed to the center of the supporting surface  73  through the screw  26 . The wiring board  19  is thermally connected to the supporting surface  73 . The screw hole  15  and through holes  16   a / 16   b  are opened to the supporting surface  73 , penetrating through the projection  71 . 
     According to the lamp  1  of the fifth embodiment, the light-emitting diodes  18  are displaced to be inside the reflection portion  41   a  of the translucent cover  4  more closely to the center than the end wall  9  of the outer shell  2 . This efficiently guides the light from the light-emitting diodes  18  to the inside of the translucent cover  4 . Therefore, the light from the light-emitting diodes  18  can be reflected to the projection portion  41   b  through the light reflection film  43 , and radiated from the projection portion  41   b  to the outside of the translucent cover  4 . 
     Further, the existence of the projection  71  increases the surface area and heat capacity of the light source support  11 . This increases the amount of heat radiation from the outer shell  2 , though the shape of the outer shell  2  is restricted by the appearance of the lamp  1 . As a result, the cooling performance of the light-emitting diodes  18  is increased, overheat of the light-emitting diodes  18  is prevented, and the life of the light-emitting diodes  18  can be made long.  FIG. 13  to  FIG. 20  shows a sixth embodiment of the invention. 
     The sixth embodiment is different from the first embodiment in the method of supporting the lighting circuit  5  to the receptacle  12  of the outer shell  2 . The other components of the lamp  1  and technical effects are the same as those of the first embodiment. Therefore, the same components as those of the first embodiment are given same reference numerals, and explanation of these components will be omitted. 
     As shown in  FIG. 13  and  FIG. 14 , the wiring board  28  constituting the lighting circuit  5  is formed rectangular in the axial direction of the peripheral wall  8  of the outer shell  2 . The wiring board  28  has first to fourth edges  81   a ,  81   b ,  81   c  and  81   d . The first and second edges  81   a  and  81   b  are extended along the axial direction of the peripheral wall  8 . The third and fourth edges  81   c  and  81   d  are extended along the radial direction of the peripheral wall  8 . The third edge  81   c  butts against the closed wall  32   b  of the insulating member  6 . The fourth edge  81   d  faces to the base  7 . 
     A first engaging part  82   a  is formed at the corner of the wiring board  28  defined by the first edge  81   a  and fourth edge  81   d . Similarly, a second engaging part  82   b  is formed at the corner of the wiring board  28  defined by the second edge  81   b  and fourth edge  81   d . The first and second engaging parts  82   a  and  82   b  are formed by notching two corners of the wiring board  28  rectangularly. The first and second engaging parts  82   a  and  82   b  are not limited to the notching. For example, projections projecting to the peripheral wall  8  may be provided at two corners of the wiring board  28 , and these projections may be used as the first and second engaging parts  82   a  and  82 . Or, two corners themselves of the wiring board  28  may be used as the first and second engaging parts  82   a  and  82   b.    
     The wiring board  28  projects from the open end  12   a  of the receptacle  12  to the inside of the connecting member  36  of the base  7 . In other words, the wiring board  28  extends over the outer shell  2  and the base  7 , and the fourth edge  81   d  is placed inside the connecting member  36 . 
     As shown in  FIG. 13 , the circuit components  29  composing the lighting circuit  5  include a condenser  83 . The condenser  83  is weak to heat, and has a characteristic that the life is reduced when heated. The condenser  83  is mounted at the end portion of the first surface  28   a  of the wiring board  28  adjacent to the fourth edge  81   d  by means of soldering. 
     Further, the lead terminal of each of the circuit components  29  projects from the second surface  28   b  of the wiring board  28 , penetrating the wiring board  28 . Chip components  84  are mounted on the second surface  28   b.    
     As shown in  FIG. 14 , a pair of stoppers  85   a  and  85   b  is formed on the internal circumference of the connecting member  36 . The stoppers  85   a  and  85   b  project from the internal circumference of the connecting member  36  so as to correspond to the first and second engaging parts  82   a  and  82   b  of the wiring board  28 . The stoppers  85   a  and  85   b  contact the first and second engaging parts  82   a  and  82   b  of the wiring board  28 . Therefore, the wiring board  28  is held between the stoppers  85   a  and  85   b  of the base  7  and the end wall  9  of the outer shell  2 . 
     As shown in  FIG. 17  to  FIG. 19 , a pair of guides  87   a  and  87   b  is formed integrally on the internal circumference of the peripheral wall  32   a  of the insulating member  6 . The guides  87   a  and  87   b  are faced to each other in the radial direction of the peripheral wall  32   a , and projected from the internal circumference of the peripheral wall  32   a . Further, the guides  87   a  and  87   b  are extended along the axial direction of the peripheral wall  32   a.    
     An engaging groove  88  is formed in the guides  87   a  and  87   b . The first and second edges  81   a  and  81   b  are fit slidable in the engaging grooves  88 . The engaging grooves  88  are extended linearly along the axial direction of the peripheral wall  32   a . One ends of the engaging grooves  88  are closed by the closed wall  32   b  of the insulating member  6 . The other ends of the engaging grooves  88  are opened to the other end of the peripheral wall  32   a.    
     When installing the lighting circuit  5  in the receptacle  12 , insert the wiring board  28  into the inside of the peripheral wall  32   a  of the insulating member  6  by setting the third edge  81   c  of the wiring board  28  to the front. Insertion of the wiring board  28  is performed, while inserting the first and second edges  81   a  and  81   b  of the wiring board  28  into the engaging grooves  88 . When inserting the wiring board  28  into the inside of the peripheral wall  32   a , the third edge  81   c  of the wiring board  28  butts against the closed wall  32   b  of the insulating member  6 . This determines the insertion depth of the wiring board  28  into the insulating member  6  without taking special care. This improves the workability when installing the lighting circuit  5  in the receptacle  12 . 
     After inserting the wiring board  28  into the inside of the peripheral wall  32   a  of the insulating member  6 , connect the connecting member  36  of the base  7  to the open end  12  of the outer shell  2 . By this connection, the stoppers  85   a  and  85   b  of the connecting member  36  contact the first and second engaging parts  82   a  and  82   b  of the wiring board  28 . Therefore, the wiring board  28  is held between the end wall  11  of the outer shell  2  and the stoppers  85   a  and  85   b , holding the lighting circuit  5  not to move in the axial direction of the peripheral wall  8 . As the first and second edges  81   a  and  81   b  of the wiring board  28  are fit in the engaging grooves  88  of the insulating member  6 , the lighting circuit  5  is held not to move in the circumferential direction of the peripheral wall  8 . Further, by intensifying the fitting of the first edge  81   a  of the wiring board  28  in the engaging groove  88 , the lighting circuit  5  can be held not to move in the peripheral direction of the peripheral wall  8  only by fitting the first edge  81   a  in the engaging groove  88 . 
     Therefore, the lighting circuit  5  is held unmovable in the receptacle  12  of the outer shell  2 . 
     As shown in  FIG. 13 , the wiring board  28  of the lighting circuit  5  partitions the inside of the peripheral wall  32   a  of the insulating member  6  into two areas  89   a  and  89   b  along the radial direction. The areas  89   a  and  89   b  are opened to a space  90  inside the base  7 , and connected with each other through the space  90 . 
     The first and second surfaces  28   a  and  28   b  of the wiring board  28  are not directed to the light source support  11  which receives the heat of the light-emitting diodes  18 , and faced to the peripheral wall  32   a  of the insulating member  6 . Therefore, the soldered parts of the lead terminals of the circuit components  29  to the wiring board  28  are separated away from the closed wall  32   b  of the insulating member  6  contacting the light source support  11 , preventing the influence of heat to the soldered parts. 
     Further, the condenser  83  adjacent to the fourth edge  81   d  of the wiring board  28  is placed in the space  90  inside the base  7 , and separated away from the light source support  11  which receives the heat of the light-emitting diodes  18 . Therefore, the condenser  83  is difficult to be influenced by the heat of the light-emitting diodes  18 , and increased in the durability. 
     In addition, as a part of the lighting circuit  5  is placed in the space  90  inside the base  7 , the lengths of the insulating member  6  and the outer shell  2  in the axial direction can be reduced. This is advantageous to make the lamp  1  compact. However, when the length of the outer shell  2  in the axial direction is reduced, the area of the heat radiating surface  10  is decreased. To solve this problem, increase the outside diameter of the outer shell  2  to compensate for the decrease of the area of the heat radiating surface  10 . 
     As shown in  FIG. 13  and  FIG. 16 , the circuit components  29  mounted on the first surface  28   a  of the wiring board  28  are higher than the chip components  84  mounted on the second surface  28   b . Therefore, the wiring board  28  of this embodiment is offset to the center line X 1  of the lamp  1 , so that the area  89   a  between the first surface  28   a  and the peripheral wall  32   a  of the insulating member  6  becomes larger than the area  89   b  between the second surface  28   b  and the peripheral wall  32   a  of the insulating member  6 . 
     As a result, the high circuit components  29  can be separated as far as possible from the peripheral wall  8  of the outer shell  2 , and the circuit components  29  are difficult to be influenced by the heat of the light-emitting diodes  18  transmitted to the peripheral wall  8 . At the same time, a certain capacity can be ensured in the area  89   b  between the second surface  28   b  and the peripheral wall  8  of the outer shell  2 . Therefore, even if the lead terminals of the circuit components  29  are projected to the area  89   b  from the second surface  28   b  of the wiring bard  28 , the lead terminals are difficult to be influenced by the heat of the light-emitting diodes  18  transmitted to the peripheral wall  8 . This prevents overheat of the part where the lead terminals are soldered to the wiring board  28 . 
     According to the lamp  1  of the sixth embodiment, the wiring board  28  of the lighting circuit  5  is contained in the receptacle  12  of the outer shell  2  in the state that the first and second surfaces  28   a  and  28   b  are faced to the internal circumference of the peripheral wall  32   a  of the insulating member  6 . Therefore, the first or second surface  28   a  or  28   b  of the wiring board  28  is not faced to the closed wall  32   b  of the insulating member  6 . 
     Therefore, a substantially enclosed space is not formed between the wiring board  28  and closed wall  32   b , and the heat generated by the lighting circuit  5  or the heat of the light-emitting diodes  18  transmitted to the light source support  11  is difficult to stay at the end portion of the receptacle  12  adjacent to the light source support  11 . This prevents overheat of the light source support  11 , and is advantageous to increase the cooling performance of the light-emitting diodes  18 . 
     Further, the wiring board  28  extends over the outer shell  2  and the base  7 , and the size of the wiring board  28  is not restricted by the inside diameter of the insulating member  6 . This increases the flexibility of determining the size of the wiring board  28  and laying out the circuit parts  29  on the wiring board  28 , and makes it easy to design the lighting circuit  5 . 
     The sixth embodiment shows a structure to prevent a short circuit between the outer shell  2  and lead wires  30   a  and  30   b.    
     As shown in  FIG. 14  and  FIG. 15 , a pair of through holes  16   a  and  16   b  formed in the light source support  11  has a small diameter part  91 , a large diameter part  92  and a step  93 . The step  93  is positioned in the boundary between the small diameter part  91  and large diameter part  92 . 
     An insulating cylinder  94  is fit in the through holes  16   a  and  16   b . The insulating cylinder  94  is made of synthetic resin material having electric insulation such as polybutylene terephthalate. The insulating cylinder  94  extends over the small diameter part  91  and large diameter part  92 , covering the inside surfaces of the through holes  16   a  and  16   b.    
     The insulating cylinder  94  has an insertion hole  95  to pass the lead wires  30   a  and  30   b . The insertion hole  95  extends over the through holes  33   a  and  33   b  of the insulating member  6 . As shown in  FIG. 15 , an open edge adjacent to the through holes  33   a  and  33   b  of the insertion hole  95  is expanded in the diameter by chamfering. This prevents the lead wires  30   a  and  30   b  from being caught by the open edge of the insertion hole  95  when the lead wires  30   a  and  30   b  are guided from the through holes  33   a  and  33   b  to the insertion hole  95 . 
     The insulating cylinder  94  is fit in the through holes  16   a  and  16   b  from the supporting surface  11   a  of the light source support  11 . By fixing the wiring board  28  onto the supporting surface  11   a , the insulating cylinder  94  is held between the wiring board  28  and the step  93  of the through holes  16   a  and  16   b , and the insulating cylinder  94  is held by the light source support  11 . Therefore, it is unnecessary to bond the insulating cylinder  94  to the light source support  11 . This makes it easy to assemble the lamp  1 . 
     The lead wires  30   a  and  30   b  have a core  96  using a copper wire, for example, and an insulating layer  97  to cover the core  96 . The insulating layer  97  is removed at the ends of the lead wires  30   a  and  30   b . Therefore, the core  96  is exposed to the outside of the insulating layer  97  at the ends of the lead wires  30   a  and  30   b . The exposed core  96  is electrically connected to the wiring board  28  by means of soldering. 
     If the insulating layer  97  is unevenly removed, the length of the core  96  exposed to the insulating layer  97  fluctuates. For example, as shown in  FIG. 15 , when the lead wire  30   a  is guided from the through hole  33   a  to the through hole  16   a , the exposed core  96  may be positioned inside the through hole  16   a . The insulating cylinder  94  fit in the through hole  16   a  is interposed between the exposed core  96  and the through hole  16   a , electrically insulating the core  96  and light source support  11 . 
     Therefore, a short circuit between the exposed core  96  and light source support  11  can be prevented by the insulating cylinder  94 . 
     The exposed core  96  is inserted from the insertion hole  95  into a pair of through holes  98  formed on the wiring board  19 , and guided onto the wiring board  19  through the through holes  98 . The end of the exposed core  96  is soldered to a land (not shown) formed on the wiring board  19 . 
     The wiring board  28  of the lighting circuit  5  is offset to the center line X 1  of the lamp  1  as already described. Therefore, as shown in  FIG. 16 , each through hole  98  can be placed between the adjacent areas  23   a  and  23   b , and  23   c  and  23   d  of the thermal diffusion layer  23 . This does not decrease the area of the thermal diffusion layer  23 , though the through hole  98  penetrates the wiring board  19 . Therefore, the heat of the light-emitting diodes  18  can be efficiently transmitted to the light source support  11  through the thermal diffusion layer  23 , and prevents overheat of the light-emitting diodes  18 . 
       FIG. 21  to  FIG. 25  shows a seventh embodiment of the invention. 
     A lamp  100  according to the seventh embodiment has an outer shell  101 , a light source  102 , a light source cover  103 , a cover holder  104 , a lighting circuit  105 , an insulating member  106 , a base  107 , and a heat shielding cover  108 . 
     The outer shell  101  is made of metal material with excellent heat conductivity, such as aluminum. As shown in  FIG. 24 , the outer shell  101  has a peripheral wall  110  and an end wall  111 . The peripheral wall  110  and the end wall  111  are formed integrally. The peripheral wall  110  is shaped like a straight cylinder. The outer circumference of the peripheral wall  110  is a heat radiating surface  112 . 
     The end wall  111  closes one end of the peripheral wall  110 . The end wall  111  forms a circular plate light source support  113 . The light source support  113  has a flat supporting surface  114  on the opposite side of the peripheral wall  110 . 
     A receptacle  116  is formed inside the outer shell  101 . The receptacle  116  is defined by a space surrounded by the peripheral wall  110  and end wall  111 , and positioned inside the heat radiating surface  112 . A stopper  117  is formed at a corner defined by the peripheral wall  110  and the end wall  111 . The stopper  117  is formed circular, projecting to the inside surface of the peripheral wall  110  and continuing in the circumferential direction of the peripheral wall  110 . The receptacle  116  has an open end  116   a  facing to the end wall  111 . The open end  116   a  is positioned at the other end of the peripheral wall  110 . An engaging groove  118  is formed in the internal circumference of the peripheral wall  110 . The engaging groove  118  is positioned at the open end  116   a  of the receptacle  116 , and formed circular continuing in the circumferential direction of the peripheral wall  110 . 
     A recession  119  is formed in the outer circumference of the end wall  111 . The recession  119  is circular surrounding the light source support  113 . A male screw  121  is formed in the internal circumference of the recession  119 . Instead of the male screw  121 , a female screw may be formed on the outer circumference of the recession  119 . 
     As shown in  FIG. 24 , a pair of through holes  122   a  and  122   b  and a pair of projections  123   a  and  123   b  are formed on the supporting surface  114  of the light source support  113 . The through holes  122   a  and  122   b  are arranged with an interval in the radial direction of the light source support  113 . The projections  123   a  and  123   b  are cylindrical, and project vertically from the supporting surface  114 . The projections  123   a  and  123   b  are arranged with an interval in the radial direction of the light source support  113 . The arrangement direction of the through holes  122   a  and  122   b  is orthogonal to the arrangement direction of the projections  123   a  and  123   b.    
     As shown in  FIG. 21  and  FIG. 24 , the light source  102  has a base  125 , a wiring board  126 , and a chip-shaped light-emitting element  127 . The base  125  is made of metal material with excellent heat conductivity, such as an aluminum alloy. The wiring board  126  is stacked on the base  125 . The light-emitting element  127  is a light-emitting diode, for example, and mounted at the center of the wiring board  126 . 
     The light-emitting element  127  is covered by a transparent semispherical protection glass  128 . The wiring board  126  has lands  129 . The lands  129  are arranged with an interval in the circumferential direction of the wiring board  126 , just like surround the protection glass  128 . The wiring board  126  is covered by a not-shown insulating layer except the protection glass  128  and lands  129 . 
     As shown in  FIG. 24 , a pair of lead wire insertion parts  131   a  and  131   b , a pair of first engaging parts  132   a  and  132   b , and a pair of second engaging parts  133   a  and  133   b  are formed in the outer circumference of the base  125  and the wiring board  126 . The lead wire insertion parts  131   a  and  131   b , first engaging parts  132   a  and  132   b , and second engaging parts  133   a  and  133   b  are U-shaped notches. The lead wire insertion parts  131   a  and  131   b , the first engaging parts  132   a  and  132   b , and the second engaging parts  133   a  and  133   b  are not limited to the notches. They may be circular holes, for example. 
     The lead wire insertion parts  131   a  and  131   b , the first engaging parts  132   a  and  132   b , and the second engaging parts  133   a  and  133   b  are alternately arranged with an interval in the circumferential direction of the base  125  and wiring board  126 . In other words, the lead wire insertion parts  131   a  and  131   b , the first engaging parts  132   a  and  132   b , and the second engaging parts  133   a  and  133   b  are positioned among the adjacent lands  129 . 
     As shown in  FIG. 21  and  FIG. 22 , the base  125  of the light source  102  is stacked on the supporting surface  114  of the light source support  113 . A heat conduction sheet  135  having elasticity is interposed between the supporting surface  114  of the light source support  113  and the base  125 . The heat conduction sheet  135  is made of resin composed mainly of silicon, for example, and formed circular one size larger than the light source  102 . The heat conduction sheet  135  thermally connects the base  125  of the light source  102  and the light source support  113 . 
     The heat conduction sheet  135  has escapes  136   a ,  136   b ,  136   c ,  136   d ,  136   e  and  136   f  on the periphery with an interval. The escapes  136   a ,  136   b ,  136   c ,  136   d ,  136   e  and  136   f  are U-shaped notches, for example. The escape  136   a  and  136   b  correspond to the lead wire insertion parts  131   a  and  131   b . The escapes  136   c  and  136   d  correspond to the first engaging parts  132   a  and  132   b . The escapes  136   e  and  136   f  correspond to the second engaging parts  133   a  and  133   b.    
     In the state that the heat conduction sheet  135  is held between the light source support  113  and base  125 , the projections  123   a  and  123   b  projecting from the supporting surface  114  are tightly fit in the first engaging parts  132   a  and  132   b  through the escapes  136   c  and  136   d  of the heat conduction sheet  135 . This fitting prevents movement of the light source  102  in the circumferential and radial directions of the light source support  113 . As a result, the light-emitting element  127  is positioned on the center line of the outer shell  101 , and the lead wire insertion parts  131   a  and  131   b  are aligned with the escapes  136   a  and  136   b.    
     As shown in  FIG. 21  and  FIG. 22 , the light source cover  103  has a lens  138  and a lens holder  139 . The lens  138  is used to control luminous intensity distribution of the lamp  101 , and is formed as one boy made of transparent material, such as glass and synthetic resin. 
     The lens  138  has a light reflecting plane  140 , a light radiating plane  141 , a recession  142 , and a flange  143 . The light reflecting plane  140  is spherical, for example. The light radiating plane  141  is flat and faced to the light reflecting plane  140 . The recession  142  is caved in from the center of the light reflecting plane  140  to the light radiating plane  141  to permit fitting-in of the protection glass  128 . The recession  142  has a light entrance plane  144  surrounding the protection glass  128 . The flange  143  projects from the outer circumference of the lens  138  to the outside of the radial direction of the lens  138 . The flange  143  adjoins the light radiating plane  141 , and continues in the circumferential direction of the lens  138 . 
     The lens holder  139  is a part separated from the lens  138 , and cylindrical surrounding the lens  138 . As shown in  FIG. 25 , the lens holder  139  has a pair of holder elements  146   a  and  146   b . The holder elements  146   a  and  146   b  are made of non-translucent synthetic resin material having electrical insulation, and formed semi-cylindrical. 
     The holder elements  146   a  and  146   b  have a pair of projections  147   a  and  147   b  and a pair of recessions  148   a  and  148   b . The projections  147   a  and  147   b  of one holder element  146   a  fit in the recessions  148   a  and  148   b  of the other holder element  146   b . The projections  147   a  and  147   b  of the other holder element  146   b  fit in the recessions  148   a  and  148   b  of one holder element  146   a . By this fitting, the holder elements  146   a  and  146   b  are butted against each other, and assembled as the cylindrical lens holder  139 . 
     An engaging groove  149  is formed in the internal circumference of the lens holder  139 . The engaging groove  149  is positioned at one end along the axial direction of the lens holder  139 , and continued in the circumferential direction of the lens holder  139 . Projections  151   a  and  151   b  paired with a receiving part  150  are formed at the other end along the axial direction of the lens holder  139 . 
     The receiving part  150  faces to the outer circumference of the wiring board  126  of the light source  102 , and has notches  152 . The notches  152  are arranged with an interval in the circumferential direction of the lens holder  139 , so as to correspond to the lands  129  of the light source  102 . The projections  151   a  and  151   b  correspond to the second engaging parts  133   a  and  133   b  of the light source  102 , and project from the other end of the lens holder  139  to the light source  102 . 
     As shown in  FIG. 25 , the holder elements  146   a  and  146   b  are butted against each other with the lens  138  interposed therebetween. By this arrangement, the flange  143  of the lens  138  is fit in the engaging groove  149 , and held between the holder elements  146   a  and  146   b . As a result, the lens  138  is held inside the lens holder  139 , and the light radiating plane  141  of the lens  138  closes one end of the lens holder  139 . 
     As shown in  FIG. 21  and  FIG. 22 , the light source  102  is held between the light source cover  103  and the light source support  113  of the outer shell  101 . Specifically, the receiving part  150  of the lens holder  139  contacts the wiring board  126  of the light source  102 , just like avoiding the lands  129 . Further, the projections  151   a  and  151   b  projecting from the lens holder  139  fit tightly in the second engaging parts  133   a  and  133   b  of the light source  102 . This fitting prevents movement of the light source cover  103  in the circumferential and radial directions of the light source  102 . Therefore, the protection glass  128  covering the light-emitting element  127  fits in the recession  142  of the lens  138 , and the lead wire insertion parts  131   a  and  131   b  or the first engaging parts  132   a  and  132   b  engage with the notches  152  of the receiving part  150 . 
     Therefore, the position of the light source cover  103  is determined to the light source  102 , so that the optical axis X 2  of the lens  138  shown in  FIG. 21  is aligned with the light-emitting element  127 . 
     As shown in  FIG. 21 , the cover holder  104  is formed as a cylinder or a square cylinder made of metal material with excellent heat conductivity, such as an aluminum alloy. The cover holder  104  has the same outside diameter of the outer shell  101 , and the inside diameter and length capable of covering the light source  102  and light source cover  103  continuously. 
     A pressing part  155  is formed at one end of the cover holder  104 . The pressing part  155  is a flange projecting from the internal circumference to the inside of the radial direction of the cover holder  104 . A circular connecting part  156  is formed coaxially at the other end of the cover holder  104 . The connecting part  156  projects from the other end of the cover holder  104  to the recession  119  of the outer shell  101 . The connecting part  156  has a diameter smaller than the cover holder  104 . A step  157  is formed in the boundary between the connecting part  156  and the other end of the cover holder  104 . The step  157  has a flat surface continued to the circumferential direction of the cover holder  104 . 
     A female screw  158  is formed in the internal circumference of the connecting part  156 . The female screw  158  can be fit over the male screw  121  of the recession  119 . If a female screw is formed in the outer circumference of the recession  119  instead of the male screw  121 , a male screw may be formed in the outer circumference of the connecting part  156 . 
     The cover holder  104  is connected coaxially with the outer shell  101  by fitting the female screw  158  over the male screw  121  of the recession  119 . As the cover holder  104  is connected, the pressing part  155  of the cover holder  104  butts against one end of the lens holder  139 . The lens holder  139  is pressed to the light source support  113  of the outer shell  102 . Therefore, the light source cover  103  is held between the pressing part  155  of the cover holder  104  and the light source  102 . 
     As shown in  FIG. 21  and  FIG. 22 , when the cover holder  104  is connected to the outer shell  102 , the outer circumference of the end wall  111  of the outer shell  102  butts against the step  157  of the cover holder  104 . This increases the contacting area of the outer shell  102  and the cover holder  104 , and increases a heat conduction path from the outer shell  102  to the cover holder  104 . 
     The lighting circuit  105  is used to light the light-emitting element  127 , and contained in the receptacle  116  of the outer shell  102 . As the lighting circuit  105  is installed inside the outer shell  101 , it is unnecessary to arrange the outer shell  101  and lighting circuit  105  in the axial direction of the lamp  100 . Therefore, the length of the lamp  100  in the axial direction can be reduced, and the compact lamp  100  can be provided. 
     As shown in  FIG. 21 , the lighting circuit  105  has a wiring board  160  and circuit components  161 . The lighting circuit  105  is electrically connected to the light source  102  through two lead wires  162  and  162   b  shown in  FIG. 24 . The lead wires  162   a  and  162   b  are guided onto the wiring board  126  of the light source  102  through the lead wire insertion parts  131   a  and  131   b  of the light source  102  from the through holes  122   a  and  122   b  of the light source support  113 . The ends of the lead wires  162   a  and  162   b  are soldered to the two lands  129 . The insulating member  106  is an example of an insulating layer for electrically insulating the outer shell  101  and the lighting circuit  105 . The insulating member  106  is a molding using synthetic resin material such as polybutylene terephthalate. As shown in  FIG. 21 , the insulating member  106  is cup-shaped having a cylindrical peripheral wall  163   a  and a closed wall  163   b  closing one end of the peripheral wall  163   a.    
     The insulating member  106  is fit in the receptacle  116  through the open end  116   a . Therefore, the peripheral wall  163   a  of the insulating member  116  butts contacts the internal circumference of the peripheral wall  110  of the outer shell  101 , and the closed wall  163   b  of the insulating member  116  butts against the stopper  117 . The stopper  117  is interposed between the light source support  113  and the closed wall  163   b  of the insulating member  116 . Therefore, the light source support  113  and closed wall  163   b  are separated, and a gap  165  is provided between them. 
     The existence of the gap  165  keeps the light source support  113  thermally connected to the light source  102  non-contacting with the insulating member  106 . The gap  165  functions as a heat shielding space to prevent conduction of heat from the light source support  113  to the insulating member  106 , and the heat of the light source  102  is difficult to transmit directly from the light source support  113  to the insulating member  106 . 
     Therefore, though the lighting circuit  105  is contained in the outer shell  101  which receives the heat of the light source  102 , the lighting circuit  105  can be protected against the heat of the light source  102 . This prevents a malfunction of the lighting circuit  105 , and makes the life of the lighting circuit  105  long. 
     The closed wall  163   b  of the insulating member  106  has a not-shown pair of through holes. The through holes are formed to pass the lead wires  162   a  and  162   b , and opened to the receptacle  116  and the gap  165 , penetrating the closed wall  163   b.    
     The base  107  is used to supply an electric current to the lighting circuit  105 . The base  107  has a metal base shell  167  and a connecting member  168  fixed to the base shell  167 . The base shell  167  is removably connected to a lamp socket of a light fixture. The lamp  100  of the seventh embodiment is configured to be fit to a lamp socket with the base  107  faced up as shown in  FIG. 21 . 
     The connecting member  168  is a molding using synthetic resin material such as polybutylene terephthalate. The connecting member  168  has electrical insulation, and heat conductivity lower than the outer shell  101 . 
     The connecting member  168  has a distal end  169  fit inside the open end  116   a  of the receptacle  116 . An engaging projection  170  is formed in the outer circumference of the distal end  169 . The engaging projection  170  engages with the engaging groove  118  when the distal end  169  is fit inside the open end  116   a . By this engagement, the outer shell  101  and the base  107  are coaxially connected. The connecting member  168  is interposed between the base shell  167  and the outer shell  101 , and insulates them electrically and thermally. 
     As shown in  FIG. 21 , the connecting member  168  has an outer circumference  171  larger than the diameter of the distal end  169 . The outer circumference  171  projects coaxially to the outside of the radial direction of the outer shell  101 . A circular supporting wall  172  is formed in the outer circumference  171  of the connecting member  168 . The supporting wall  172  coaxially surrounds the distal end  169  of the connecting member  168 . A male screw  173  is formed on the outer peripheral surface of the supporting wall  172 . 
     The heat shielding cover  108  is a molding using synthetic resin material, and formed like a hollow cylinder. The heat shielding cover  108  has heat conductivity lower than the outer shell  101 . As shown in  FIG. 21 , the heat shielding cover  108  has the inside diameter and length capable of coaxially surrounding the outer shell  101  and cover holder  104 . 
     A female screw  174  is formed in the internal circumference of one end of the heat shielding cover  108 . An engaging part  175  is formed at the other end of the heat shielding cover  108 . The engaging part  175  is a flange projecting from the internal circumference of the other end of the heat shielding cover  108  to the inside of the radial direction. The inside diameter of the engaging part  175  is smaller than the outside diameter of the cover holder  104 . 
     The female screw  174  of the heat shielding cover  108  is fit over the male screw  173  of the connecting member  168 . By this fitting, the engaging part  175  of the heat shielding cover  108  is caught by one end of the cover holder  104 . Therefore, the cover  108  is connected to the connecting member  168  of the base  107 , surrounding the outer shell  101  and cover holder  104  coaxially. 
     A heat radiating path  176  is formed between the heat shielding cover  108  and the outer shell  101 , and between the heat shielding cover  108  and the cover holder  140 . The heat radiating path  176  surrounds the outer shell  101  and cover holder  104 , and continues in the radial direction of the lamp  100 . 
     One end of the heat radiating path  176  is closed by the outer circumference  171  of the connecting member  168 . Exhaust ports  177  are formed in the outer circumference  171  of the connecting member  168 . The exhaust ports  177  are arranged with an interval in the circumferential direction of the connecting member  168 , and connected to one end of the heat radiating path  176 . The other end of the heat radiating path  176  is closed by the engaging part  175  of the heat shielding cover  108 . Suction ports  178  are formed in the engaging part  175  of the heat shielding cover  108 . The suction ports  178  are arranged with an interval in the circumferential direction of the heat shielding cover  108 , and connected to the other end of the heat radiating path  176 . 
     In the seventh embodiment, the suction ports  178  are formed in the engaging part  175  of the heat shielding cover  108 . Instead of the suction ports  178 , projections contacting one end of the cover holder  104  may be formed at the other end of the heat shielding cover  108 , and gaps between adjacent projections may be used as suction ports. Similarly, through holes opened to the heat radiating path  176  may be formed at the other end of the heat shielding cover  108 , and used as suction ports. 
     Further, instead of forming the exhaust ports  177  in the base  107 , through holes opened to the heat radiating path  176  may be formed at one end of the heat shielding cover  108 , and used as exhaust ports. 
     Next, explanation will be given on a procedure of assembling the lamp  100 . 
     First, fit the insulating member  106  in the receptacle  116  of the outer shell  101 , and install the lighting circuit  105  in the receptacle  116  covered by the insulating member  106 . Next, guide the two lead wires  162   a  and  162   b  extending from the light circuit  105 , to the through holes  122   a  and  122   b  of the light source support  113  through the through holes of the closed wall  163   b.    
     Then, place the heat conduction sheet  135  on the supporting surface  114  of the light source support  113 , and stack the base  125  of the light source  102  on the heat conduction sheet  135 . In this time, fit the projections  123   a  and  123   b  of the light source support  113  in the first engaging parts  132   a  and  132   b  of the light source  102  through the escapes  136   c  and  136   d  of the heat conduction sheet  135 . This fitting determines the relative positions of the light source  102  and the light source support  113 . Guide the lead wires  162   a  and  162   b  from the through holes  122   a  and  122   b  to the adjacent two lands  129  through the lead wire insertion parts  131   a  and  131   b  of the light source  102 , and solder the lead wires  162   a  and  162   b  to the lands  129 . 
     Next, place the light source cover  103  on the wiring board  126  of the light source  102 . In this time, fit the projections  151   a  and  151   b  projected from the lens holder  139 , in the second engaging parts  133   a  and  133   b  of the light source  102 . This fitting determines the relative positions of the light source  102  and the light source support  103 . Therefore, the optical axis X 2  of the lens  138  coincides with the center of the light-emitting element  127 , and the receiving part  150  of the lens holder  139  butts against the outer circumference of the wiring board  126 . 
     Next, insert the female screw  158  of the cover holder  104  onto the male screw  121  of the outer shell  102 , and connect the cover holder  104  coaxially with the outer shell  101 . As the cover holder  104  is connected, the pressing part  155  of the cover holder  104  butts against one end of the lens holder  139 , and presses the lens holder  139  toward the light source support  113 . As a result, the light source  102  is pressed to the supporting surface  114  of the light source support  113  through the lens holder  139 , and the heat conduction sheet  135  is tightly held between the supporting surface  114  and the base  125  of the light source  102 . 
     The heat conduction sheet  135  is elastically deformed and tightly stuck to the supporting surface  114  and the base  125 . This eliminates a gap between the supporting surface  114  and the base  125  disturbing the conduction of heat, and provides good conduction of heat between the supporting surface  114  and the base  125 . In other words, comparing the case that the heat conduction sheet  135  is not used, the heat conduction performance from the light source  102  to the light source support  113  is improved. 
     At the same time, the engagement of the male and female screws  121  and  158  is made tight by a repulsive force of the heat conduction sheet  135  to elastically return to the original form. Therefore, the cover holder  104  is difficult to become loose. 
     For example, when the accuracy of the supporting surface  114  and base  125  is high, the heat conduction sheet  135  can be omitted. Instead of the heat conduction sheet  135 , conductive grease composed mainly of silicon may be used. 
     When the light source  102  is pressed to the light source support  113 , a revolving force generated by insertion of the cover holder  104  acts on the light source cover  103  and light source  102 . As already explained, the relative position of the light source  102  to the light source support  113  is determined by the fitting of the projections  123   a  and  123   b  with the first engaging parts  132   a  and  132   b . Similarly, the relative position of the light source cover  103  to the light source  102  is determined by the fitting of the projections  151   a  and  151   b  with the second engaging parts  133   a  and  133   b.    
     Therefore, the light source cover  103  and the light source  102  do not rotate following the cover holder  104 . An unreasonable force causing a break and a crack is not applied to the soldered part between the lands  129  of the light source  102  and the lead wires  162   a  and  162   b . The lamp  100  can be assembled without giving a stress to the soldered part between the lead wires  162   a  and  162   b  and the lands  129 . 
     Next, fit the base  107  to the outer shell  101 . This work is performed by fitting the distal end  169  of the base  107  in the open end  116  of the outer shell  101 , and engaging the engaging projection  170  with the engaging groove  118 . 
     When fitting the base  107  to the outer shell  101 , the lighting circuit  105  may receive a force of pressing to the light source support  113 , from the connecting part  168  of the base  107 . This force is transmitted to the light source  102  through the lead wires  162   a  and  162   h.    
     The light source  102  is held between the light source cover  103  and the light source support  113 . Even if a force is applied to the light source  102  through the lead wires  162   a  and  162   b , the light source  102  will not be separated from the supporting surface  114  of the light source support  113 . Therefore, the tight contact between the light source  102  and the light source support  113  is maintained, and the optical axis X 2  of the lens  138  will not be deviated from the center of the light-emitting element  127 . 
     Finally, fit the heat shielding cover  108  to the outside of the outer shell  101  and the cover holder  104 , and insert the female screw  174  of the heat shielding cover  108  onto the male screw  173  of the connecting member  168 . By the insertion, the engaging part  175  of the heat shielding cover  108  is caught by one end of the cover holder  104 . As a result, the heat shielding cover  108  is connected to the base  107 , surrounding coaxially the outer shell  101  and the cover holder  104 , and the assembling of the lamp  100  is completed. 
     In the state that the assembling of the lamp  100  is completed, the heat radiating path  176  positioned inside the heat shielding cover  108  is opened to the atmosphere through the suction ports  178  and exhaust ports  177 . 
     In the lamp  100  of the seventh embodiment, when the lamp  100  is lit, the light-emitting element  127  is heated. The heat of the light-emitting element  127  is transmitted from the base  125  of the light source  102  to the light source support  113  through the heat conduction sheet  135 . The heat transmitted to the light source support  113  is transmitted to the heat radiating surface  112  from the end wall  110  through the peripheral wall  110 , and radiated from the heat radiating surface  112  to the heat radiating path  176 . 
     The light source support  113  receiving the heat of the light-emitting element  127  is formed integrally with the peripheral wall  110  having the heat radiating surface  112 , and there is no joint disturbing the conduction of heat in a heat conduction path from the light source support  113  to the radiating surface  112 . Therefore, the thermal resistance of the heat conduction path can be controlled to small, and the heat of the light-emitting element  127  transmitted to the light source support  113  can be efficiently escaped to the heat radiating surface  112 . At the same time, as the whole surface of the heat radiating surface  112  is exposed to the heat radiating path  176 , the heat radiation from the heat radiating surface  112  is not disturbed. This improves the cooling performance of the light-emitting element  27 . 
     Further, as the metal cover holder  104  is screwed into the outer shell  101 , the engagement of the female screw  174  and the male screw  173  thermally connects the outer shell  101  and the cover holder  104 . Therefore, the heat of the outer shell  101  is transmitted also to the cover holder  104 , and radiated from the outer peripheral surface of the cover holder  104  to the heat radiating path  176 . Therefore, the heat radiating area of the lamp  100  can be increased by using the cover holder  104 , and the cooling performance of the light-emitting element  127  is improved furthermore. 
     When the heat of the light-emitting element  127  is radiated to the heat radiating path  176 , an ascending current is generated in the heat radiating path  176 . Therefore, the air outside the lamp  100  is taken in the heat radiating path  176  through the suction ports  178  positioned at the lower end of the lamp  100 . The air taken in the heat radiating path  176  flows from the lower to upper side in the heat radiating path  176 , and is radiated to the atmosphere through the exhaust ports  177 . 
     The outer circumference of the cover holder  104  and the heat radiating surface  112  of the outer shell  101  are exposed to the heat radiating path  176 . The heat of the light-emitting element  127  transmitted to the cover holder  104  and the outer shell  101  is taken away by the heat exchange with the air flowing in the heat radiating path  176 . Therefore, the cover holder  104  and the outer shell  101  can be cooled by the air, and overheat of the light-emitting element  127  can be prevented. This prevents decrease of the light-emitting efficiency of the light emitting element  127 , and makes the life of the light-emitting element  127  long. 
     The heat shielding cover  108  to cover the cover holder  104  and the outer shell  101  is made of synthetic resin material with a low heat conductivity. Therefore, the heat of the cover holder  104  and the outer shell  101  is difficult to transmit to the heat shielding cover  108 , and the temperature of the heat shielding cover  108  is decreased to lower than the outer shell  101 . 
     According to the seventh embodiment, the connecting member  168  to fit with the heat shielding cover  108  is made of synthetic resin, and the connecting member  168  thermally insulates the outer shell  101  and the heat shielding cover  108 . Further, the engaging part  175  of the heat shielding cover  108  to contact the cover holder  104  has the suction ports  178 . Even if the heat of the cover holder  104  is transmitted to the engaging part  175  of the heat insulating cover  108 , the engaging part  175  is cooled by the air flowing into the heat radiating path  176  through the suction ports  178 . Therefore, the heat shielding cover  108  is difficult to be influenced by the heat of the cover holder  104 , and the temperature increase of the heat shielding cover  108  can be prevented. 
     According to the lamp  100  of the seventh embodiment, even if the operator holds the heat insulating cover  108  by hand when replacing the lamp  100  during lighting or immediately after turning off the lamp, the operator does not feel hot. Therefore, the operator does not drop the lamp  100  when touching the lamp and surprised by the heat, and can safely replace the lamp  100 . 
     In the seventh embodiment, fine holes may be formed in the heat insulating cover  108 . Instead of holes, slits may be formed along the axial or circumferential direction of the heat shielding cover  108 . 
       FIG. 26  and  FIG. 27  show an eighth embodiment of the invention. 
     The eighth embodiment is different from the seventh embodiment in the configuration for radiating the heat of the outer shell  101  and the cover holder  104 . The other components of the lamp  100  and technical effects are the same as those of the seventh embodiment. Therefore, the same components as those of the seventh embodiment are given same reference numerals, and explanation of these components will be omitted. 
     The lamp  100  according to the eighth embodiment has the following configuration instead of the heat shielding cover  108  in the seventh embodiment. As shown in  FIG. 26  and  FIG. 27 , the outer shell  101  has first heat radiating fins  200 . The first heat radiating fins  200  project radially from the heat radiating surface  112  of the outer shell  101 . The first heat radiating fins  200  are extended in the axial direction of the outer shell  101 , and arranged with an interval in the circumferential direction of the outer shell  101 . 
     The cover holder  104  has second heat radiating fins  201 . The second heat radiating fins  201  project radially from the outer circumference of the cover holder  104 . The second heat radiating fins  201  are extend in the axial direction of the cover holder  104 , and arranged with an interval in the circumferential direction of the cover holder  104 . 
     The first and second heat radiating fins  200  and  201  continue each other along the axial direction of the lamp  100 . Therefore, the first and second heat radiating fans  200  and  201  are thermally connected, and directly exposed to the outside of the lamp  100 . 
     The distal edges of the first heat radiating fins  200  are covered by first edge covers  202 . Similarly, the distal edges of the second heat radiating fins  201  are covered by second edge covers  203 . The first and second edge covers  202  and  203  are mode of synthetic resin. The first and second edge covers  202  and  203  have heat conductivity lower than the outer shell  101  and the cover holder  104 . 
     According to the lamp  100  of the eighth embodiment, the existence of the first heat radiating fins  200  increase the heat radiating area of the heat radiating surface  112  of the outer shell  101 . Likewise, the existence of the second heat radiating fins  201  increases the heat radiating area of the peripheral surface of the cover holder  104 . Therefore, the heat of the light-emitting element  127  transmitted to the outer shell  101  and the cover holder  104  can be efficiently radiated to the outside of the lamp  100 . This can prevent the decrease of the light-emitting efficiency of the light-emitting element  127 , and make the life of the light-emitting element  127  long. 
     Further, the first and second edge covers  202  and  203  covering the distal edges of the first and second heat radiating fins  200  and  201  have heat conductivity lower than the outer shell  101  and the cover holder  104 . Therefore, the heat of the outer shell  101  and the cover holder  104  is difficult to transmit to the first and second edge covers  202  and  203 , and the temperatures of the first and second edge covers  202  and  203  can be decreased to lower than the outer shell  101  and the cover holder  104 . 
     As a result, even if the operator holds the first and second heat radiating fins  200  and  201  by hand when replacing the lamp  100  during lighting or immediately after turning off the lamp, the operator does not feel hot. Therefore, the operator does not drop the lamp  100  when touching the lamp and surprised by the heat, and can safely replace the lamp  100 . 
       FIG. 28  and  FIG. 29  show a ninth embodiment of the invention. 
     The ninth embodiment is developed from the eight embodiment. The configuration of the lamp  100  is the same as the eight embodiment. Therefore, the same components as those of the eighth embodiment are given same reference numerals, and explanation of these components will be omitted. 
     The lamp  100  of the ninth embodiment has an outside cylinder  220  surrounding the first and second heat radiating fins  200  and  201 . The outside cylinder  220  is formed like a hollow cylinder with the diameter larger than the outer shell  101  and the cover holder  104 . The outside cylinder  220  has the length extending over the peripheral wall  110  of the outer shell  101  and the cover holder  104 . The inner peripheral surface of the outside cylinder  220  contacts the first and second edge covers  202  and  203 . Therefore, the outside cylinder  220  extends over the adjacent first and second heat radiating fins  200  and  201 . 
     In other words, the outside cylinder  220  faces to the heat radiating surface  112  through the first heat radiating fins  200 , and faces to the peripheral surface of the cover holder  104  through the second heat radiating fins  201 . Therefore, a heat radiating path  221  is formed between the heat radiating surface  112  of the outer shell  101  and the outside cylinder  220 , and between the peripheral surface of the cover holder  104  and the outside cylinder  220 . The heat radiating path  221  continues in the axial direction of the lamp  100 . The first and second heat radiating fins  200  and  201  are exposed to the heat radiating path  221 . The heat radiating path  221  has one end  221   a  and the other end  221   b . The one end  221   a  of the heat radiating path  221  is opened to the atmosphere from the lower end of the second heat radiating fins  201 , when the lamp  100  is lit with the base  107  faced up. Likewise, the other end  221   b  of the heat radiating path  221  is opened to the atmosphere from the upper end of the first heat radiating fins  200 , when the lamp  100  is lit with the base  107  faced up. 
     The outside cylinder  220  is made of material with heat conductivity lower than the outer shell  101  and the cover holder  104 . For example, when the outside cylinder  220  is made of heat shrinking synthetic resin, it is desirable to heat the outside cylinder  220  to shrink by the heat, after fitting the outside cylinder  222  to the outside of the outer shell  101  and the cover holder  104 . The inner circumference of the outside cylinder  220  is pressed to the first and second edge covers  202  and  203 , and the outside cylinder  220  is connected integrally with the outer shell  101  and the cover holder  104 . This facilitates fitting of the outside cylinder  220 . 
     In the lamp  100  of the ninth embodiment, when the heat of the light-emitting element  127  is radiated to the heat radiating path  221 , an ascending current is generated in the heat radiating path  221 . Therefore, the air outside the lamp  100  is taken in the heat radiating path  221  through one end  221   a  of the heat radiating path  221 . The air taken in the heat radiating path  221  flows from the lower to upper side in the heat radiating path  221 , and is radiated to the atmosphere through the other end  221   b  of the heat radiating path  221 . 
     The heat of the light-emitting element  127  transmitted to the cover holder  104  and the outer shell  101  is taken away by the heat exchange with the air flowing in the heat radiating path  221 . Therefore, the outer shell  101  having the first heat radiating fins  200  and the cover holder  104  having the second heat radiating fins  201  can be cooled by the air, and overheat of the light-emitting element  127  can be prevented. This prevents decrease of the light-emitting efficiency of the light emitting element  127 , and makes the life of the light-emitting element  127  long. 
     The outside cylinder  220  is made of synthetic resin material with the heat conductivity lower than the outer shell  101  and the cover holder  104 . Therefore, the heat of the cover holder  104  and the outer shell  101  is difficult to transmit to the outside cylinder  220 , and the temperature of the outside cylinder  220  is decreased to lower than the outer shell  101  and the cover holder  104 . 
     As a result, even if the operator holds the outside cylinder  220  by hand when replacing the lamp  100  during lighting or immediately after turning off the lamp, the operator does not feel hot. Therefore, the operator does not drop the lamp  100  when touching the lamp and surprised by the heat, and can safely replace the lamp  100 . 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.