Patent Publication Number: US-2012044697-A1

Title: Incandescent bulb and light source apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an incandescent bulb, which is used as, for example, a light source for studio lighting, and a light source apparatus equipped with the incandescent bulb. 
     BACKGROUND 
     For example, a large output type incandescent bulb, which is mainly used for studio lighting and the like, is combined with an appropriate lens and a reflection mirror, and may be used as a spotlight light source for a stage or the like. A certain type of such incandescent bulb is configured so that a filament formed in a flat shape is arranged in, for example, a quartz glass bulb, where one end of which is sealed. A plurality of filament segments, each of which is formed by winding tungsten wire material in a shape of a coil, are arranged in parallel to one another along with the tube axis of the bulb (see, for example, Patent literature 1). Since an input of such a planar light emitting incandescent bulb can be made higher than that of the structure, which is arranged so that a single coil filament extends in a form of a line, it serves as a bright light source. 
     PRIOR ART REFERENCE 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Publication No. 2001-319624. 
       
    
     SUMMARY OF THE INVENTION 
     Problems That the Invention to Solve 
     In case where an incandescent bulb having the structure described above is used as alight source for spotlight, it is desired that an incandescent bulb have sufficiently high illuminance and a good light distribution (illuminance characteristics) on an illuminated field (light irradiation face). 
     To meet such a need, for example, a filament is configured as a double coil, which is formed by further winding a single coil filament in the shape of a coil, thereby increasing the input to the filament and improving the incandescent bulb&#39;s intensity. However, the filament having such structure is weak against impacts, such as mechanical vibrations, and tends to deform or disconnect. 
     Hence the present inventors considered installing an incandescent bulb having the structure described above into a lamp fitting in which a general condensing mirror was used, alight source apparatus as shown in  FIG. 4  was made as a trial. 
     A light source apparatus  40  comprises an incandescent bulb  41  having a filament  42 , in which a plurality of filament segments  42 A made from a single coil filament, are arranged in a flat shape and in parallel to one another; a lens  45 , which is arranged at a front side position of the incandescent bulb  41  in a lighting direction (which is a left side direction and is shown in an outline arrow in  FIG. 4 ); and a reflection mirror  48 , which is arranged at a back side position of the incandescent bulb  41  with respect to the lighting direction. The light emitted from the incandescent bulb  41  is directly emitted or is reflected towards the front side by the reflection mirror  48  arranged on the back side of the incandescent bulb  41  to be emitted, through the lens  45 . 
     In the Incandescent bulb  41 , each of the plurality of filament segments  42 A is arranged in a direction extending along with a tube axis C 2  of the bulb (the central axis of the incandescent bulb), i.e. so as to extend in a direction perpendicular to the lighting direction, and while the central axis L 2  of the lens (optical axis) and the central axis L 3  of the reflection mirror (optical axis) are in agreement with each other, they bisect the filament segment  42 A in the incandescent bulb  41  (the central axis C 2  of the incandescent bulb) at right angles. A reference number  44  in  FIG. 4  denotes a mouthpiece insulator that is attached to one end of the bulb  43  by, for example, an adhesive agent and that is made from, for example, ceramics. 
     However, it was found that the light source apparatus  40  having such a structure cannot be configured to meet the required illuminance characteristics. 
     The present invention was made in view of the above circumstances, and an object thereof is to offer an incandescent bulb in which sufficiently high illuminance and a good light distribution on a light irradiation face can be obtained. 
     Moreover, it is another object of the present invention to provide a light source apparatus having the above-mentioned incandescent bulb that emits high usage efficiency light. 
     Means to Solve Problems 
     An incandescent bulb of this invention has a filament constructed from a plurality of filament segments that are made from a single coil formed by winding one wire material that respectively extend along an axial direction of a bulb and are arranged in parallel to form a flat surface, characterized in that a pitch of a plurality of filament segments located at a central part of the bulb is smaller than a pitch of a plurality of filament segments located at a first side portion and a second side portion. 
     Further, a length of a filament formation area in a direction perpendicular to an axial direction of the incandescent bulb of the present invention may preferably be 90% or less of an inner diameter of the incandescent bulb. 
     Furthermore, a ratio (H/W) of a length W of the filament formation area in the axial direction of the incandescent bulb of the present invention to a length H of the filament formation area in a direction perpendicular to the axial direction of the incandescent bulb may preferably be 0.5 or more. 
     Moreover, a light source apparatus of the present invention includes the incandescent bulb and a condensing mirror, characterized in that the incandescent bulb is arranged in a direction extending along with a central axis of the condensing mirror so that two of the filament segments located at the central part of the bulb are located to sandwich the central axis of the condensing mirror. 
     Advantageous Effect of the Invention 
     According to the incandescent bulb of the present invention, since the plurality of filament segments made from a single coil filament is arranged in a flat shape and in parallel to one another, the effective surface area of the filament (an area from which light is emitted) can be enlarged so that high light irradiation ratio can be obtained as a whole from the filament, and in addition, since the pitch of the filament segments located at the central part of the bulb and that of the filament segments located at the both side parts are set to be different from each other so that the illuminance of light from a portion near a central portion of the filament, which is located at the central part of the bulb, may be made relatively higher than that of light from end portions, which are located at both side parts of the bulb, it is possible to obtain the illuminance characteristics having intensity distribution, which are close to those of a point light source, in which the illuminance of a central part of the light irradiation face is high and that therearound is low. 
     Moreover, since the length of the filament formation area in a direction perpendicular to the axial direction of the bulb is set 90% or less of the inner diameter of the bulb, it can be brought into a state where the filament is not too close to the bulb, so that it is possible to prevent the temperature of the bulb from rising locally at time of lighting, whereby a predetermined halogen cycle can be obtained certainly. Furthermore, since the filament can be configured in an approximately square and flat surface shape by making the length of the filament formation area in the axial direction of the bulb, suitable in size, a light distribution having an approximately circular shape can be obtained on the light irradiation face, whereby it is possible to obtain the illuminance characteristics near a point light source. 
     According to the light source apparatus of this invention, since a condensing point of the condensing mirror is formed to be located within an area of the filament of the incandescent bulb, from which the highest illuminance light is emitted and in which the two filament segments located at the central part of the bulb are located, while the illuminance characteristics close to those of a point light source can be obtain on the light irradiation face, the usage efficiency of light emitted from the incandescent bulb can be made high. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram showing a schematic structure of an example of a light source apparatus. 
         FIG. 2  is an explanatory diagram showing a schematic main part of an example of an incandescent bulb. 
         FIG. 3  is a partially enlarged explanatory diagram of part of a filament of the incandescent bulb shown in  FIG. 2 . 
         FIG. 4  is an explanatory diagram showing a schematic structure of an example of a light source apparatus, which is experimentally made by using an incandescent bulb having a filament, wherein the filament is formed by arranging a plurality of filament segments in a flat shape and in parallel to one another. 
     
    
    
     Embodiments FOR CARRYING OUT THE INVENTION 
     Description of an embodiment will be given in detail. 
       FIG. 1  shows an explanatory diagram showing a schematic structure of an example of a light source apparatus,  FIG. 2  is an explanatory diagram showing a schematic main part of an example of an incandescent bulb, and  FIG. 3  is a partially enlarged explanatory diagram of part of a filament of the incandescent bulb shown in  FIG. 2 . 
     This light source apparatus  10  is configured so that an incandescent bulb  20  is held in and fixed to a condensing mirror  11  in a position where the tube axis C 1  of the bulb (the central axis of the incandescent bulb) is in agreement with the central axis L 1  of the condensing mirror (optical axis). The condensing mirror  11  is made up of an ellipsoidal collecting mirror or a paraboloidal condensing mirror that has an approximately quadric surface of revolution as a whole. 
     The condensing mirror  11  is made from heat resisting glass, for example, borosilicate glass and alumina silicate glass or the like. A reflector  12  is provided by forming a dielectric multilayer film on an inner surface thereof. 
     The incandescent bulb  20  is a one end sealing type, in which a cylindrical bulb  21  made of, for example, quartz glass, is provided, at one end of which a sealing portion  22  is formed by sealing and at the other end of which an exhaust pipe remaining portion  21 A is provided. A filament  30  is arranged in the bulb  21 , wherein the filament is formed by winding a wire material, made of, for example, tungsten in a shape of a coil. 
     A mouthpiece insulator  28 , which has a cylindrical shape with a bottom, and which is made from, for example, ceramics or metal, is attached to the sealing portion  22  of the bulb  21  by an adhesive agent. A reference number  29  denotes a metal connection terminal, which is led out outward in an axial direction from the bottom portion of the mouthpiece insulator  28 . 
     The filament  30  is formed so that the central axis of each of a plurality of filament segments, which is made from a single coil, extends approximately parallel to the tube axis C 1  of the bulb, that is, extends along the axis direction of the bulb  21 , and they are arranged in a flat surface shape (two-dimensionally) and in parallel to one another so that they are located on the same flat face. 
     The filament  30  in this embodiment is made up of eight filament segments. Two filament segments  31 , which are located at a central part of the bulb  21  (hereinafter referred to as “middle segments”), are connected to each other at respective ends through a single wire section (a connecting portion)  38 , which curves in an arc shape. The other end of each filament segment  31  is connected through a single wire portion  38  to the other end of a filament segment  32  (hereinafter referred to as an “inner side intermediate segment”), which is located next to the middle segment  31 . One end of each inner side intermediate segment  32  is connected, through a single wire section  38 , to one end of a filament segment  33  (hereinafter referred to as a “outer side intermediate segment”) which is located next to the inner side intermediate segment  32 . The other end of the outer side intermediate segment  33  is connected, through a single wire section  38 , to the other end of a filament segment  34  (hereinafter referred to as an “end portion segment”), which is located next to the outer side intermediate segment  33  and at both side portions of the bulb  21 . A coil shape connecting portion  35  is formed on the one end of each end portion segment  34 . 
     The filament  30  is provided in the bulb  21 , so that each of the connecting portions  35  of the both ends is connected and fixed to an internal lead  23  in a state where the internal rod shape lead  23 , which extends along with the tube axis C 1  of the bulb, is inserted in the inside. The single wire sections  38  of the filament  30  are engaged with respective anchors  25 , which are buried in and fixed to a first glass piece  24 A or a second glass piece  24 B. Wherein, the first and second glass pieces are provided apart from each other in an axial direction in the bulb  21 . 
     While the other end portion and an intermediate portion of the pair of internal leads  23  are respectively buried in and fixed to the first glass piece  24 A and the second glass piece  24 B, one end portion thereof, which is electrically connected to a connection terminal  29  of the mouthpiece insulator  28 , is buried in and fixed to the sealing portion  22 . In addition, a structural material, which is denoted as a reference number  26  in  FIG. 2 , is a supporter, and both end side portions thereof are respectively buried in and fixed to the first glass piece  24 A and the second glass piece  24 B. 
     And, as shown in  FIG. 3 , in the filament  30  of the above-mentioned incandescent bulb  20 , a total of eight filament segments, that is, the two middle segments  31 , the two inner side intermediate segments  32 , the two outer side intermediate segments  33 , and the two end portion segments  34 , are provided to be apart at equal intervals with respect to a direction perpendicular to the tube axis C 1  of the bulb. That is, so that distances d between central axes, each of which adjoins to each other, are equal to one another, wherein the two middle segments  31  are arranged to sandwich the tube axis C 1  of the bulb, and the pitch of the middle segments  31 , that of the inner side intermediate segments  32 , that of the outer side intermediate segments  33 , and that of the end portion segments  34  are different from one another. 
     In this embodiment, a pitch P 1  of the middle segments  31  located at the central part of the bulb  21 , a pitch P 2  of the inner side intermediate segments  32 , a pitch P 3  of the outer side intermediate segments  33 , and a pitch P 4  of the end portion segments  34  located at the both ends of the bulb  21  are set to satisfy relationship of P 1 &lt;P 2 &lt;P 3 &lt;P 4 . The pitch P 1  of the two middle segments  31  located at the central part of the bulb  21  is set the smallest, and the farther the filament segments are from the central part of the bulb  21  in a diameter direction toward the outside, the greater the pitch thereof is set. 
     While the pitch P 1  of the middle segments  31  located at the central part of the bulb  21  among the plurality of the filament segments is small (the coil pitch is set relatively dense), the pitch P 4  of the end portion segment  34  located at the both side portions of the bulb  21  (density of the coil pitch is set relatively low) is large. Since the illuminance of light emitted from the central part of the entire filament  30  can be set relatively higher than that of light emitted from the both side portions thereof, it is possible to obtain the illuminance characteristics close to those of a point light source having an approximately circular shape light distribution on the light irradiation face, in which a illuminance of the central part of the light irradiation face is high and an illuminance therearound is low. 
     It is desirable that a relative value of the pitch of each filament segment be set within a range of, for example, 135-180%, wherein the pitch is taken as 100% when the size of the clearance (gap) between adjoining wires is 0. 
     Moreover, it is desirable that the pitches of the inner side intermediate segment  32 , the outer side intermediate segment  33 , and the end portion segments  34  be respectively set so that pitch ratios of the pitch P 1  of the middle segment  31  to the pitch of the inner side intermediate segment  32 , that of the outer side intermediate segment  33 , and that of the end portion segment  34  (pitch ratio; P 1 /P 2 , P 1 /P 3  and P 1 /P 4 ) are 70% or more. 
     In the above-mentioned incandescent bulb  20 , it is desirable that a filament formation area (an area surrounded by two-dot chain lines in  FIG. 2 ) FA, where the plurality of the filament segments are arranged in a flat shape and in parallel to one another, be configured so that the length (size) W in a direction perpendicular to the axial direction of the bulb  21  is 90% or less of the size of the inner diameter of the bulb  21 , and it is desirable that the ratio (H/W) of the length H (size) of the filament formation area FA in the axial direction of the bulb  21 , to the length W thereof in a direction perpendicular to the axial direction of the bulb  21  be set within a range of 0.5 or more. 
     In the incandescent bulb  20 , when the length W of the filament formation area FA in the direction perpendicular to the axial direction of the bulb  21  and the length H thereof in the axial direction of the bulb  21  are set within the above mentioned ranges and since the formation area FA of the filament  30  has an approximately square and flat shape, a light distribution having an approximately circular shape can be certainly obtained on the light irradiation face, so that it is possible to obtain the illuminance characteristics close to those of a point light source. On the other hand, in case where that of the filament formation area FA in the axial direction of the bulb  21  or a direction perpendicular thereto is too large with respect to the other, a light distribution having an approximately circular shape cannot be certainly obtained on the light irradiation face. Thus, it is difficult to obtain the desirable illuminance characteristics. 
     As mentioned above, the light source apparatus  10  according to the present invention is configured so that the incandescent bulb  20  having the above mentioned structure is held in and fixed to the condensing mirror  11 , in a position where the tube axis C 1  of the bulb is in agreement with the central axis L 1  of the condensing mirror. 
     That is, in the incandescent bulb  20 , the two middle segments  31  of the filament  30  located at the central part of the bulb  21 , in which the pitch thereof is smaller than those of the other the filament segments, are located to sandwich the central axis L 1  of the condensing mirror, so that the condensing point of the condensing mirror  11  (a position on the central axis L 1 ) is formed to be located in an area of the filament  30  within the incandescent bulb  20 , which is irradiated with the highest illuminance light. 
     According to the incandescent bulb  20  of the above-mentioned structure, since the filament  30  is formed so that the plurality of the filament segments, which are respectively made from a single coil, are arranged in a flat shape and in parallel to one another, the effective surface area of the filament  30  (an area from which light is emitted) is enlarged so that the high light irradiation ratio is obtained as a whole in the filament  30 . In addition, while the pitch P 1  of the middle segments  31  of the bulb  21  is set to the smallest value so that the illuminance of light from the middle segments  31 , which are a portion near the central portion located at the central part of the bulb  21 , may be made relatively higher than that of light from the end portion segments  34 , which are end portions located at both side portions of the bulb  21 , the farther the filament segments are from the central part of the bulb  21  in the diameter direction toward the outside thereof. The larger the pitch of the filament segments is the more possible it is to obtain the illuminance characteristics close to those of a point light source, which has a light distribution in which an illuminance of the central part of the light irradiation face is high and an illuminance therearound is low. 
     Moreover, since the length W of the filament formation area FA in a direction perpendicular to the axial direction of the bulb  21  is set at 90% or less of the inner diameter of the bulb  21  in size, it is possible to obtain a state where the filament  30  is not too close to the bulb  21  so that it is possible to prevent the temperature of the bulb  21  from rising locally at the lighting time. As a result, it is possible for a predetermined halogen cycle to certainly work, and when such a state is secured, the length H of the filament formation area FA in the axial direction of the bulb  21  is set an appropriate size, which is within a range in which the ratio (H/W) of the length H of the filament formation area FA in the axial direction of the bulb  21 , to the length W in a direction perpendicular to the axial direction of the bulb  21  is 0.5 or more. Thus, since the formation area FA of the filament  30  can be configured in an approximately square and flat surface shape, a light distribution having an approximately circular shape can be obtained on the light irradiation face, so that it is possible to obtain the illuminance characteristics close to those of a point light source. 
     Furthermore, when the filament formation area FA is arranged so that there is some space between the formation area FA and the bulb  21 , the first glass piece  24 A and the second glass piece  24 B, whose lengths in a direction perpendicular to the axial direction of the bulb  21  are longer than that of the filament formation area FA, can be arranged inside the bulb  21 . 
     Therefore, according to the light source apparatus  10  having the above-mentioned incandescent bulb  20 , when the incandescent bulb  20  is arranged in a direction extending along with the central axis L 1  of the condensing mirror so that the two filament segments  31  located at the central part of the bulb  21  may sandwich the central axis L 1  of the condensing mirror, since the condensing point of the condensing mirror  11  is located at a portion where the two middle filaments  31  of the filament  30  of the incandescent bulb  20  are located and from which the highest illuminance light is emitted, while the illuminance characteristics, which are substantially equal to the illuminance characteristics acquired by the light source apparatus which uses a point light source, can be obtained on the light irradiation face by the structure in which the incandescent bulb  20  according to the present invention is installed inside a common condensing mirror, the usage efficiency of light emitted from the incandescent bulb  20  can be improved. Thus, it can be configured to be suitable for a spot light source. 
     Experimental examples, which were performed to check the effects of the present invention, will be given in below. 
     &lt;Manufacturing Example 1 of Incandescent Bulb&gt; 
     According to the structure shown in  FIGS. 1-3 , an incandescent bulb (hereinafter referred to as an “incandescent bulb 1”) was made. 
     The material of a bulb ( 21 ) was quartz glass and it had the outside diameter of 18 mm, the inner diameter of 15 mm and the overall length of 55 mm. 
     The number of filament segments of a filament ( 30 ) was eight (two middle segments ( 31 ), two inner side intermediate segments ( 32 ), two outer side intermediate segments ( 33 ), and two end portion segments ( 34 )), and the specification of each filament segment and the entire filament ( 30 ) are shown below in Table 1. 
     In Table 1, the “pitch” is shown by a relative value wherein the pitch is taken as 100% when the size of the clearance (gap) between adjoining wires is 0. In addition, the size of clearance between adjoining wires of the middle segments ( 31 ) was 0.09 mm (=the wire diameter 0.19 mm×0.47), the size of clearance between wires of the inner side intermediate segment ( 32 ) was 0.10 mm, the size of clearance between wires of the outer side intermediate segment ( 33 ) was 0.12 mm, and the size of the clearance between wires of the end portion segment ( 34 ) was 0.14 mm. 
     The length (W) of a formation area (FA) of the filament ( 30 ) in a direction perpendicular to the tube axis of the bulb ( 21 ) was 60% of the inner diameter of the bulb ( 21 ) in size, and an aspect ratio (H/W) was 0.9. 
     &lt;Manufacturing Example 1 of Comparative Incandescent Bulb&gt; 
     The incandescent bulb for comparison (hereinafter referred to as an “comparative incandescent bulb  1 ”) was made in which the structure was the same as that of the above-mentioned incandescent bulb 1, except that, as shown below in Table 1, the pitches of eight filament segments, that is, middle segments, inner side intermediate segments, outer side intermediate segments, and end portion segments, and design electric power, were the same as one another. The size of clearance between wires of each filament segment is 0.09 mm. 
     &lt;Manufacturing Example 2 of Incandescent Bulb&gt; 
     An incandescent bulb (hereinafter referred to as an “incandescent bulb 2”) was made in which the structure was the same as that of the above-mentioned incandescent bulb  1 , except that the number of filament segments was six (two middle segments, two intermediate segments, and two end portion segments), and the pitch of each filament segment and design electric power for each filament segment were changed according to Table 1 shown below. In addition, the size of clearance between wires of the middle segments was 0.09 mm, the size of clearance between wires of the intermediate segments was 0.12 mm and the size of clearance between the wires of the end portion segments was 0.15 mm. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Filament 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 Size 
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 (formation 
               
               
                   
                   
                 Wire 
                   
                   
                 Pitch 
                 Design 
                 area) [W 
               
               
                   
                   
                 diameter 
                 Length 
                 Pitch 
                 ratio 
                 power 
                 (mm) × H 
               
               
                   
                 Segments 
                 [mm] 
                 [mm] 
                 [%] 
                 [%] 
                 [W] 
                 (mm)] 
                 Input Power [W] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Incandescent 
                 8 
                 Middle (2) 
                 0.19 
                 8 
                 147 
                 100 
                 69 
                 9 × 8 
                 575 
               
               
                 bulb 1 
                   
                 Inner side 
                 0.19 
                 8 
                 155 
                 95 
                 71 
                 (H/W = 0.9) 
               
               
                   
                   
                 intermediate (2) 
               
               
                   
                   
                 Outer side 
                 0.19 
                 8 
                 163 
                 90 
                 73 
               
               
                   
                   
                 intermediate (2) 
               
               
                   
                   
                 End portion (2) 
                 0.19 
                 8 
                 172 
                 85 
                 75 
               
               
                 Comparative 
                 8 
                 Middle (2) 
                 0.19 
                 8 
                 159 
                 100 
                 72 
                 9 × 8 
                 575 
               
               
                 incandescent 
                   
                 Inner side 
                 0.19 
                 8 
                 159 
                 100 
                 72 
                 (H/W = 0.9) 
               
               
                 bulb 1 
                   
                 intermediate (2) 
               
               
                   
                   
                 Outer side 
                 0.19 
                 8 
                 159 
                 100 
                 72 
               
               
                   
                   
                 intermediate (2) 
               
               
                   
                   
                 End portion (2) 
                 0.19 
                 8 
                 159 
                 100 
                 72 
               
               
                 Incandescent 
                 6 
                 Middle (2) 
                 0.19 
                 13.5 
                 147 
                 100 
                 90 
                 13.5 × 5.5  
                 575 
               
               
                 bulb 2 
                   
                 Intermediate (2) 
                 0.19 
                 13.5 
                 162 
                 91 
                 96 
                 (H/W = 0.4) 
               
               
                   
                   
                 End portion (2) 
                 0.19 
                 13.5 
                 180 
                 82 
                 102 
               
               
                   
               
            
           
         
       
     
     Each of the incandescent bulb 1, the comparative incandescent bulb 1, and the incandescent bulb 2 were respectively installed in the paraboloidal surface condensing mirrors having an opening diameter of 120 mm and a depth of 90 mm producing light source apparatuses referring to the structure of  FIG. 1 , and a lighting test shown below was performed. 
     &lt;Lighting Test&gt; 
     An area of 1 meter long and 1 meter wide is set as a light irradiation face at a position where a separation distance from an opening edge of the paraboloidal surface condensing mirror in a direction of a central axis of the condensing mirror was 5 m, and each incandescent bulb was turned on condition that input power was 575 W, and while the illuminance at center of the irradiation spot formed on the light irradiation face was measured, the usage efficiency of light emitted from the incandescent bulb was measured. A result is shown in table 2 below. The “illuminance at center” is shown in Table 2 by a relative value [%] with respect to the illuminance at center, which was obtained in the light source apparatus concerning the comparative incandescent bulb 1. Moreover, the “usage efficiency of light” is a value represented by a ratio of light flux on the light irradiation face to all light flux of only the incandescent bulb [(light flux on the light irradiation face)/(all light flux)], and is shown by a relative value [%] with respect to the usage efficiency of light obtained in the light source apparatus concerning the comparative incandescent bulb 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Illuminance at 
                   
               
               
                   
                 Filament 
                 center on a light 
                 Usage 
               
               
                   
                 size 
                 irradiation face 
                 efficiency 
               
               
                   
                 [W (mm) × 
                 (relative value) 
                 of light (relative 
               
               
                   
                 H (mm)] 
                 [%] 
                 value) [%] 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Incandescent bulb 1 
                 9 × 8 
                 107 
                 113 
               
               
                   
                 (H/W = 0.9) 
               
               
                 Comparative 
                 9 × 8 
                 100 
                 100 
               
               
                 incandescent bulb 1 
                 (H/W = 0.9) 
               
               
                 Incandescent bulb 2 
                 13.5 × 5.5 
                 95 
                 97 
               
               
                   
                 (H/W = 0.4) 
               
               
                   
               
            
           
         
       
     
     As is evident from the above result, in the incandescent bulb 1 having the filament in which while the pitch of the middle segments located at the central part of the bulb was set to the smallest value, the farther the filament segments are from the central part of the bulb toward the outsides in a diameter direction the greater the pitch thereof is. It was also found that it was possible to obtain light distribution with central illuminance on the light irradiation face, which was higher than that of the comparative incandescent bulb 1 if the input electric power was the same, as the usage efficiency of light became high and improved, for example, by even 13% specifically in the incandescent bulb having the above-mentioned structure. Moreover, in relation to the result in the light source apparatus concerning the incandescent bulb 2, since the filament formation area was formed in an approximately square and flat shape, it was found that in the incandescent bulb  1 , it was possible to certainly obtain the above-mentioned result. 
     DESCRIPTION OF REFERENCE NUMBERS 
     
         
         
           
               10  Light source apparatus 
               11  Condensing mirror 
               12  Reflective face 
               20  Incandescent bulb 
               21  Bulb 
               21 A Exhaust pipe remaining portion 
               22  Sealing portion 
               23  Internal lead 
               24 A First glass piece 
               24 B Second glass piece 
               25  Anchor 
               26  Supporter 
               28  Mouthpiece insulator 
               29  Connection terminal 
               30  Filament 
               31  Middle segment (filament segment) 
               32  Inner side intermediate segment (filament Segment) 
               33  Outer side intermediate segment (filament segment) 
               34  End portion segment (Filament segment) 
               35  Connecting portion 
               38  Single wire section (connecting portion) 
               40  Light source apparatus 
               41  Incandescent bulb 
               42  Filament 
               42 A filament segment 
               43  Bulb 
               44  Mouthpiece insulator 
               45  Lens 
               48  Reflection mirror 
             C 1  Tube axis of a bulb (central axis of an incandescent bulb) 
             C 2  Tube axis of a bulb (central axis of an incandescent bulb) 
             L 1  Central axis of a condensing mirror (optical axis) 
             L 2  Central axis of a lens (optical axis) 
             L 3  Central axis of a reflection mirror (optical axis) 
             P 1  Pitch of middle segments 
             P 2  Pitch of inner side intermediate segments 
             P 3  Pitch of outer side intermediate segments 
             P 4  Pitch of end portion segments 
             d Distance between the central axes of filament segments 
             FA Filament formation area