Patent Publication Number: US-2012033421-A1

Title: Light source device and projection type display apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a light source device and a projection type display apparatus that use a plurality of light source lamps. 
     BACKGROUND ART 
     In order to realize large-sized images with high luminance displayed by a projection type display apparatus, a projection type display apparatus having a multi-lamp type light source device including a plurality of light source lamps is proposed. For example, Patent Document 1 (Japanese Patent Application Kokai Publication No. 2001-359025, paragraphs 0013 to 0018 and FIG. 1) proposes a light source device for a projection type display apparatus, in which light fluxes from two light source lamps disposed facing each other are synthesized through the use of a prism disposed near light converging points of the light source lamps. Furthermore, Patent Document 2 (Japanese Patent Application Kokai Publication No. 2005-115094, paragraphs 0099 to 0108, FIG. 9, FIG. 10.A and FIG. 10.B) proposes a structure, in which light fluxes from two light source lamps are guided to an entrance end face of a rod integrator through the use of two synthesizing mirrors disposed so as to be tilted toward different directions from each other. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Patent Application Kokai Publication No. 2001-359025 
     Patent Document 2: Japanese Patent Application Kokai Publication No. 2005-115094 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the apparatus described in Patent Document 1, since the two light source lamps are disposed facing each other with the prism therebetween, an increase occurs in a proportion of light reaching light emitting portions of the light source lamps facing each other relative to loss light of the light source lamps. Thus, there are problems that light utilization efficiency is lowered and that the lives of the light source lamps are shortened by a rise in temperature of the light source lamps resulting from incidence of the loss light. 
     Furthermore, in the apparatus described in Patent Document 2, since each synthesizing mirrors are disposed at a position deviated in a direction perpendicular to an optical axis of the rod integrator, an increase occurs in an incident angle of each light flux emitted from each light source lamp, reflected at each synthesizing mirror and entering the rod integrator (as a result of this, an increase occurs in a converging angle in the case where two light fluxes reflected by two synthesizing mirrors and entering the rod integrator is regarded as a single light flux). In order to reduce (compensate for) an adverse effect of resulting from a fact that the light flux entering the rod integrator has a large converging angle (i.e., insufficient uniformity of the light intensity), the rod integrator has a tapered part. However, in such structure, the number of reflections of light beams within the rod integrator has variations and there is a problem that the uniformity of the light intensity at an exit end face of the rod integrator (as a result of this, luminous intensity uniformity) is degraded. 
     Therefore, the present invention is made to solve the problems of the above-described conventional art, and an object of the present invention is to provide a projection type display apparatus with high light utilization efficiency and high luminous intensity uniformity on a screen that can realize longer lives of light source devices. 
     Means of Solving the Problem 
     According to the present invention, a light source device includes a light intensity equalizing unit including an entrance end and an exit end, the light intensity equalizing unit converting a light flux incident on the entrance end into a light flux with an equalized intensity distribution, which is emitted from the exit end; a first light source unit emitting a first light flux; at least one bending unit guiding the first light flux emitted from the first light source unit to the entrance end of the light intensity equalizing unit; and a second light source unit emitting a second light flux traveling toward the entrance end of the light intensity equalizing unit, wherein the first light source unit, the second light source unit and the bending unit are arranged so that there is no part where an optical axis of the first light flux from the first light source unit through the bending unit to the entrance end of the light intensity equalizing unit and an optical axis of the second light flux from the second light source unit to the entrance end of the light intensity equalizing means agree with each other, and the optical axis of the first light flux immediately before incidence on the entrance end and the optical axis of the second light flux from the second light source unit to the entrance end are substantially parallel to each other. 
     EFFECTS OF THE INVENTION 
     According to the present invention, high light utilization efficiency and high luminous intensity uniformity on a screen can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically illustrating a structure of a projection type display apparatus according to a first embodiment of the present invention; 
         FIG. 2A  is a diagram schematically showing a distribution of a light flux at an entrance end of a light intensity equalizing element in a comparative example,  FIG. 2B  is a diagram schematically showing a distribution of a light flux at an entrance end of a light intensity equalizing element in the first embodiment, and  FIG. 2C  is a diagram schematically showing another example of a distribution of the light flux at the entrance end of the light intensity equalizing element in the first embodiment; 
         FIG. 3  is a diagram schematically illustrating an arrangement of a bending mirror in the comparative example; 
         FIG. 4  is a diagram illustrating a structure of a principal part of the projection type display apparatus according to the first embodiment; 
         FIG. 5  is an explanatory diagram illustrating a structure for calculating a relationship among an off-center amount of a central ray of a first light flux from a first light source lamp, an off-center amount of a central ray of a second light flux from a second light source lamp and light utilization efficiency; 
         FIG. 6  is a diagram showing a result of calculation of a relationship among the off-center amount of the central ray of the first light flux from the first light source lamp, the off-center amount of the central ray of the second light flux from the second light source lamp and the light utilization efficiency; 
         FIG. 7  is a diagram showing a result of calculation of a relationship between the off-center amount d 3  shown in  FIG. 4  and the light utilization efficiency; 
         FIG. 8  is a diagram illustrating an example of a shape of a bending mirror; 
         FIG. 9  is a diagram illustrating another example of a shape of a bending mirror; 
         FIG. 10  is a diagram schematically illustrating a structure of a projection type display apparatus according to a second embodiment of the present invention; 
         FIG. 11  is a diagram schematically illustrating a structure of a projection type display apparatus according to a third embodiment of the present invention; 
         FIG. 12  is a diagram schematically illustrating a structure of a projection type display apparatus according to a fourth embodiment of the present invention; 
         FIG. 13A  is a diagram schematically showing a distribution of the first light flux from the first light source lamp at the entrance end of the light intensity equalizing element in the first embodiment and an off-center amount of a central ray of the first light flux, and  FIG. 13B  is a diagram schematically showing a distribution of the second light flux from the second light source lamp at the entrance end of the light intensity equalizing element and an off-center amount of a central ray of the second light flux; 
         FIG. 14  is a diagram illustrating a typical ray of the first light flux having the distribution shown in  FIG. 13A  at the entrance end of the light intensity equalizing element; 
         FIG. 15  is a diagram illustrating a typical ray of the second light flux having the distribution shown in  FIG. 13B  at the entrance end of the light intensity equalizing element; 
         FIG. 16  is a diagram illustrating an example of distributions of the first light flux from the first light source lamp and the second light flux from the second light source lamp at the entrance end of the light intensity equalizing element according to the first embodiment; 
         FIG. 17  is a diagram illustrating another example of a distribution of the first light flux emitted from the first light source lamp and a distribution of a second light flux emitted from the second light source lamp at the entrance end of the light intensity equalizing element according to the first embodiment; 
         FIG. 18  is a diagram conceptually illustrating behavior of loss light at the entrance end of the light intensity equalizing element according to the first embodiment; and 
         FIG. 19  is a diagram illustrating an example of a shape of a bending mirror. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
       FIG. 1  is a diagram schematically illustrating a structure of a projection type display apparatus according to a first embodiment of the present invention. As shown in  FIG. 1 , the projection type display apparatus according to the first embodiment includes a light source device  10  for emitting a light flux with equalized intensity; an image display element (light valve)  61  for modulating a light flux L 3  emitted from the light source device  10  on the basis of an input image signal, thereby converting it into image light L 4 ; and a projection optical system  62  for enlarging and projecting the image light L 4  on a screen  63 . Although the image display element  61  of reflection type is shown in  FIG. 1 , the image display element  61  may be an image display element of transmission type. The image display element  61  is, for example, a liquid crystal light valve, a digital micromirror device (DMD) or the like. In the case of a projection type display apparatus of rear projection type, the screen  63  is a part of the projection type display apparatus. Furthermore, arrangements of the light source device  10 , the image display element  61 , the projection optical system  62  and the screen  63  are not limited to the examples shown in the drawing. 
     The light source device  10  includes a first light source lamp  11  as a first light source means which is a first light source unit for emitting a first light flux L 1 ; a second light source lamp  12  as a second light source means which is a second light source unit disposed in parallel with the first light source lamp  11 , for emitting a second light flux L 2 ; a light intensity equalizing element  15  as a light intensity equalizing means which is a light intensity equalizing unit for converting an incident light flux at an entrance end  15   a  into a light flux with an equalized intensity distribution and emitting it from an exit end  15   b;  and a relay optical system  13  for guiding the first light flux L 1  emitted from the first light source lamp  11  to the entrance end  15   a.    
     In the first embodiment, the first light flux L 1  emitted from the first light source lamp  11  and the second light flux L 2  emitted from the second light source lamp  12  are converging light fluxes respectively. To put it more precisely, a central component of the first light flux emitted from a light emitting center of the first light source lamp  11  out of the first light flux L 1  and a central component of the second light flux emitted from a light emitting center of the second light source lamp  12  out of the second light flux L 2  are converging light fluxes respectively. Since an illuminator of the first light source lamp  11  or the second light source lamp  12  has a finite size, strictly speaking, a light flux is also emitted from positions other than the light emitting center and the light flux emitted from the positions other than the light emitting center does not converge at a light converging point, at which the central component of the first light flux and the central component of the second light flux converge. Furthermore, the light flux emitted from the positions other than the light emitting center also converges at a circumferential area of the light converging point of the central component of the first light flux or the central component of the second light flux, while the light flux converging at the circumferential area has a certain extent. Each structure of the first light source lamp  11 , the second light source lamp  12  and the relay optical system  13 , and arrangements of the first light source lamp  11 , the second light source lamp  12  and the relay optical system  13  with reference to the light intensity equalizing element  15  are determined so that there is no part where an optical axis  11   c   1 ,  11   c   2 ,  11   c   3  (i.e., a central ray of the first light flux L 1 ) of the first light flux L 1  from the first light source lamp  11  through the relay optical system  13  to the entrance end  15   a  of the light intensity equalizing element  15  and an optical axis  12   c  (i.e., a central ray of the second light flux L 2 ) of the second light flux L 2  from the second light source lamp  12  to the entrance end  15   a  of the light intensity equalizing element  15  agree with each other, and the optical axis  11   c   3  of the first light flux L 1  immediately before incidence on the entrance end  15   a  and the optical axis  12   c  of the second light flux L 2  are substantially parallel to each other. 
     The wording “arrangements . . . are substantially parallel to” means that the first light source lamp  11 , the second light source lamp  12  and the relay optical system  13  are arranged so that the optical axis  11   c   3  of the first light source lamp  11  (i.e., the central ray of the first light flux emitted from the first light source lamp  11  at the entrance end  15   a  of the light intensity equalizing element  15 ) and the optical axis  12   c  of the second light source lamp  12  (i.e., the central ray of the second light flux emitted from the second light source lamp  12  at the entrance end  15   a  of the light intensity equalizing element  15 ) are parallel or are almost assumed to be parallel.  FIG. 1  shows a case where the first light source lamp  11 , the second light source lamp  12 , the relay optical system  13  and the light intensity equalizing element  15  are arranged so that the first optical axis  11   c   3  of the first light source lamp  11  and an optical axis  15   c  of the light intensity equalizing element  15  are parallel, and also the second optical axis  12   c  of the second light source lamp  12  and the optical axis  15   c  of the light intensity equalizing element  15  are parallel. Furthermore, the relay optical system  13  includes a first bending mirror  13   a  and a second bending mirror  13   d  which are bending units for bending an optical path of the first light flux L 1 , and two lens elements  13   b  and  13   c.    
     Instead of provision of the relay optical system, it is possible to use a structure in which the first light source lamp  11  and the second light source lamp  12  are arranged so that the optical axis  11   c   1  of the first light source lamp  11  and the optical axis  12   c  of the second light source lamp  12  intersect at right angle and a single bending mirror is provided for guiding the first light flux L 1  to the entrance end  15   a  of the light intensity equalizing element  15 . In this case, a bending mirror or a bending mirror nearest to the entrance end  15   a  of the light intensity equalizing element  15  such as the above-described second bending mirror  13   d  is referred to as a final bending unit. 
     The first light source lamp  11  includes, for example, an illuminator  11   a  for emitting white light and an ellipsoidal mirror  11   b  disposed around the illuminator  11   a.  The ellipsoidal mirror  11   b  reflects a light flux emitted from a first focus corresponding to a first center of ellipse and collects it on a second focus corresponding to a second center of the ellipse. The illuminator  11   a  is disposed near the first focus of the ellipsoidal mirror  11   b  and a light flux emitted from the illuminator  11   a  converges near the second focus of the ellipsoidal mirror  11   b.  Further, the second light source lamp  12  includes, for example, an illuminator  12   a  for emitting white light and an ellipsoidal mirror  12   b  disposed around the illuminator  12   a.  The ellipsoidal mirror  12   b  reflects a light flux emitted from a first focus corresponding to a first center of ellipse and collects it on a second focus corresponding to a second center of the ellipse. The illuminator  12   a  is disposed near the first focus of the ellipsoidal mirror  12   b  and a light flux emitted from the illuminator  12   a  converges near the second focus of the ellipsoidal mirror  12   b.    
     Furthermore, parabolic mirrors can be used as a substitute for the ellipsoidal mirrors  11   b  and  12   b.  In this case, it is effective to substantially parallelize light fluxes emitted from the illuminators  11   a  and  12   a  by the parabolic mirrors and then to collect it by a condenser lens (not shown in the drawing). Moreover, concave mirrors other than the parabolic mirrors can also be used as a substitute for the ellipsoidal mirrors  11   b  and  12   b.  Furthermore, the number of the light source lamps may be three or more. 
     Regarding the first light flux L 1  in  FIG. 1 , a state where the light flux emitted from the illuminator  11   a  converges near a first light converging point F 1  of the ellipsoidal mirror  11   b  is conceptually illustrated. Similarly, regarding the second light flux L 2 , a state where the light flux emitted from the illuminator  12   a  converges near a light converging point F 3  of the ellipsoidal mirror  12   b  is conceptually illustrated. In the actual light source lamps, since the illuminators are not ideal point light sources and have a finite size, the light fluxes L 1  and L 2  generally includes not only a light flux component converging at the light converging point but also a lot of light flux components not converging at the light converging point (light flux components distributed outside the light flux component converging at the light converging point), as shown in  FIG. 1  as a straight line (a broken line). The light fluxes that do not converge at the light converging point are illustrated in  FIG. 14  and  FIG. 15  to be described below. 
     Further, in the projection type display apparatus according to the first embodiment, the first light source lamp  11  and the first bending mirror  13   a  are arranged so that the first light converging point F 1  of the first light flux L 1  is positioned closer to the light intensity equalizing element  15  in comparison with the first bending mirror  13   a.  Moreover, the lens element  13   b,  the lens element  13   c,  the second bending mirror  13   d  and the light intensity equalizing element  15  are arranged so that the first light flux L 1  which converges at a first light converging point F 1  is then collected at a second light converging point F 2  by the lens  13   b,  the lens  13   c  and the second bending mirror  13   d,  and the second light converging point F 2  (final converging point) is disposed near the entrance end  15   a  of the light intensity equalizing element  15 . The second light flux L 2  which is collected by the ellipsoidal mirror  12   b  directly converges at a light converging point F 3  near the entrance end  15   a  of the light intensity equalizing element  15 , through no optical element. Furthermore, in the projection type display apparatus according to the first embodiment, a first incidence position where the central ray of the first light flux L 1  (i.e., the optical axis  11   c   3 ) (being parallel to the optical axis  11   c   3  and parallel to the optical axis  15   c  of the light intensity equalizing element  15  in the first embodiment) enters the entrance end  15   a,  and a second incidence position where the central ray of the second light flux L 2  (i.e., the optical axis  12   c ) (being parallel to the optical axis  15   c  of the light intensity equalizing element  15  in the first embodiment) enters the entrance end  15   a  are different positions from each other. Moreover, both of the positions are deviated from the optical axis  15   c  of the light intensity equalizing element  15  (positions shifted at distances of off-center amounts d 1  and d 2  to be described below). The first light converging point F 1  is disposed closer to the light intensity equalizing element  15  in comparison with the first bending mirror  13   a  in  FIG. 1 , but the position is not limited to this example. 
     It is desirable that the second bending mirror  13   d  as the final bending unit be disposed so as not to block the central ray (which coincides with the optical axis  12   c ) of the second light flux L 2  traveling from the second light source lamp  12  toward the entrance end  15   a.  It is more desirable that arrangement be adopted so as to block no central component of the light flux. The central component of the light flux means a light flux component emitted from a light emitting center of a light source lamp and converging at the light converging point. 
     A position of an end portion  13   e  of the second bending mirror  13   d  on a side of the optical axis  12   c  of the second light source lamp  12  (a side surface connecting a light reflecting surface and a back surface thereof) in a direction perpendicular to the optical axis  15   c  is normally on or near the optical axis  15   c.  However, for example, if the light emitting intensity of the first light source lamp  11  is larger than the light emitting intensity of the second light source lamp  12 , in order to increase the light utilization efficiency of the whole apparatus, it is desirable that the end portion  13   e  be positioned closer to the optical axis  12   c  (the central ray of the second light flux L 2 ) of the second light source lamp  12  in comparison with the optical axis  15   c.  Conversely, for example, if the light emitting intensity of the second light source lamp  12  is larger than the light emitting intensity of the first light source lamp  11 , in order to increase the light utilization efficiency of the whole apparatus, it is desirable that the end portion  13   e  be positioned closer to the central ray (optical axis  11   c   3 ) of the first light flux L 1  in comparison with the optical axis  15   c.    
     A degree of blocking the second light flux L 2  by the second bending mirror  13   d  depends on not only its position but also its size. In order to reduce the degree of blocking the second light flux L 2 , it is desirable that the second bending mirror  13   d  be smaller in size. Conversely, in order to increase the first light flux L 1  traveling toward the entrance end  15   a,  it is desirable the second bending mirror  13   d  be larger in size. It is desirable that the second bending mirror  13   d  have a reflecting surface which is large in size enough to reflect the whole of the central component of the first light flux. Therefore, in the first embodiment, as shown in  FIG. 1 , the second bending mirror  13   d  that can reflect the whole of the central component of the first light flux is disposed at a position where the first light flux L 1  and the second light flux L 2  converge enough and no central component of the second light flux is blocked. Furthermore, it is possible to adopt a structure where the second bending mirror  13   d  cannot reflect a part of the central component of the first light flux or blocks part of the central component of the second light flux. 
     The light intensity equalizing element  15  has a function of equalizing light intensity (i.e., reducing illumination irregularities) of the first light flux L 1  and the second light flux L 2 , in cross sections of the light fluxes (i.e., in planes which are orthogonal to the optical axis  15   c  of the light intensity equalizing element  15 ). For example, the light intensity equalizing element  15  is a polygonal pillar-shaped rod (i.e., a pillar-shaped element whose cross section is polygonal in shape) which is made of transparent material such as glass, resin or the like and is structured so that inside of side walls is entirely a reflection surface, or the light intensity equalizing element  15  is a pipe (pipe-shaped element) which is assembled into a tube shape with a light reflection surface inside and whose cross section is polygonal in shape. If the light intensity equalizing element  15  is a polygonal-pillar rod, light is reflected several times according to total internal reflection function at an interface between the transparent material and air, and then the light is exited from the exit end. If the light intensity equalizing element  15  is a polygonal pipe, light is reflected several times according to reflection function by a surface mirror facing inward, and then the light is exited from the exit end (exit opening). If the light intensity equalizing element  15  has an appropriate length in a light-flux travelling direction, light which has been internally reflected several times is irradiated in a superposition manner near the exit end  15   b  of the light intensity equalizing element  15 , and substantially-equalized intensity distribution can be obtained near the exit end  15   b  of the light intensity equalizing element  15 . 
       FIGS. 2A and 2B  are explanatory diagrams schematically illustrating distributions of light fluxes at the entrance end  15   a  of the light intensity equalizing element  15 . In  FIGS. 2A and 2B , a dense-colored (nearly black) portion is an area where a light flux is strong (bright), and the light flux is weaker (darker) where color is thinner (closer to white).  FIG. 2A  shows an example of distribution of a light flux at the entrance end of the light intensity equalizing element, in the case of a comparative example in which a single light source lamp is used.  FIG. 2A  shows the distribution that light intensity peaks near a center of the entrance end  15   a  and gradually darkens toward periphery. On the other hand,  FIG. 2B  shows an example of distribution of light fluxes at the entrance end  15   a  of the light intensity equalizing element  15 , in the case of the present invention in which two light source lamps are used.  FIG. 2B  shows the example that, at the entrance end  15   a  of the light intensity equalizing element  15 , a light irradiation area by the first light source lamp  11  and a light irradiation area by the second light source lamp  12  partially overlap one another. 
     A description will be made as to a reason why the light flux at the entrance end  15   a  has the distribution shown in  FIG. 2A  when a single light source lamp is used. If the illuminator of the light source lamp is an ideal point light source, a light flux emitted from the illuminator converges at the light converging point of the ellipsoidal mirror ideally. However, since the illuminator has a finite size (in general, a diameter in a direction of the optical axis is about 0.8 mm to 1.5 mm) and there are influences resulting from arrangement accuracy of the illuminator, shape accuracy of the ellipsoidal mirror and so on, actually the converging light flux has a distribution as shown in  FIG. 2A . Furthermore, since the converging light flux has the distribution as shown in  FIG. 2A , all of the light flux does not enter the entrance end  15   a  of the light intensity equalizing element  15  and a part of the light flux propagates outside the entrance end  15   a,  thereby not being used for image projection. 
       FIG. 3  is a diagram schematically showing an arrangement of a bending mirror in a comparative example.  FIG. 3  shows a structure that a single light source lamp (not shown in the drawing) is provided, a central ray of a light flux (an optical axis  111   c ) from the light source lamp to the bending mirror  113  is orthogonal to an optical axis  115   c  of a light intensity equalizing element  115  and a central ray of a light flux L 1  reflected by the bending mirror  113  agrees with the optical axis  115   c  of the light intensity equalizing element. In the comparative example shown in  FIG. 3 , since the bending mirror  113  which has a sufficiently large reflection surface can be obtained, the light flux L 1  from the light source lamp can be bent with loss reduced. 
       FIG. 4  is a diagram showing a structure of a principal part of the projection type display apparatus according to the first embodiment.  FIG. 4  shows the second bending mirror  13   d  and the light intensity equalizing element  15 . In the first embodiment, elements are arranged so that the light converging point F 2  of the first light flux L 1  from the relay optical system  13  (shown in  FIG. 1 ) and the second focus of the ellipsoidal mirror  12   b  of the second light source lamp  12  (shown in  FIG. 1 ) (the light converging point F 3 ) are near the entrance end  15   a  of the light intensity equalizing element  15 . Furthermore, it is structured that there is no part where the first optical axis  11   c   3  which is one of the optical axes of the first light flux L 1  from the first light source lamp  11  and is closer to the light intensity equalizing element  15  in comparison with the bending mirror  13   d  and the second optical axis  12   c  of the second light flux from the second light source lamp  12  agree with each other, and the first optical axis  11   c   3  and the second optical axis  12   c  are substantially parallel to each other. 
     In a case where the first light flux L 1  from the first light source lamp  11  enters the entrance end  15   a  of the light intensity equalizing element  15  by the relay optical system  13 , and at the same time, the second light flux L 2  from the second light source lamp  12  enters the entrance end  15   a  of the light intensity equalizing element  15 , the second bending mirror  13   d  cannot have an enough size so as not to block the second light flux L 2  from the second light source lamp  12  as much as possible. For this reason, in the structure shown in  FIG. 4 , the first light flux L 1  and the second light flux L 2  are inevitably lost in some degree. 
     Suppose a central ray L 10  (an optical axis  13   c   1 ) of the first light flux L 1  which is bent by the second bending mirror  13   d  and a central ray L 20  (the optical axis  12   c ) of the first light flux L 2  are caused to agree with the optical axis  15   c  of the light intensity equalizing element  15 , optical loss further increases. For this reason, in the projection type display apparatus according to the first embodiment, the off-center amount d 1  of the central ray L 10  of the first light flux L 1  which is bent by the first bending mirror  13  with reference to the optical axis  15   c  of the light intensity equalizing element  15  and the off-center amount d 2  of the central ray L 20  of the second light flux L 2  with reference to the optical axis  15   c  of the light intensity equalizing element  15  are set to values more than 0. 
       FIG. 5  is an explanatory diagram showing a structure for calculating a relationship between the off-center amounts d 1  and d 2  and light utilization efficiency. As shown in  FIG. 5 , if it is structured so that the central ray L 10  of the first light flux from the first light source lamp  11  enters in a position of the off-center amount d 1 , for example, the first light flux L 1  from the first light source lamp  11  converges at a position at a distance of the off-center amount d 1 , at the entrance end  15   a  of the light intensity equalizing element  15 , and thus the light utilization efficiency is lowered at the entrance end  15   a  of the light intensity equalizing element  15 . Similarly, as shown in  FIG. 5 , if it is structured so that the central ray L 20  of the second light flux from the second light source lamp  12  enters a position of the off-center amount d 2 , for example, the second light flux L 2  from the second light source lamp  12  converges at a position at a distance of the off-center amount d 2 , at the entrance end  15   a  of the light intensity equalizing element  15 , and thus the light utilization efficiency is lowered at the entrance end  15   a  of the light intensity equalizing element  15 . 
       FIG. 13A  is a diagram schematically showing a distribution of the first light flux L 1  from the first light source lamp  11  at the entrance end  15   a  of the light intensity equalizing element  15  in the first embodiment and the off-center amount d 1  of the central ray (optical axis  11   c   3 ) of the first light flux L 1 , and  FIG. 13B  is a diagram schematically showing a distribution of the second light flux L 2  from the second light source lamp  12  at the entrance end  15   a  of the light intensity equalizing element  15  and the off-center amount d 2  of the central ray (optical axis  12   c ) of the second light flux L 2 . Furthermore,  FIG. 14  is a diagram illustrating a typical ray (examples of light ray not converging on the light converging point F 2 ) L 1   a,  L 1   b  of the first light flux L 1  having the distribution shown in  FIG. 13A  at the entrance end  15   a  of the light intensity equalizing element  15 .  FIG. 15  is a diagram illustrating a typical ray (examples of light ray not converging on the light converging point F 3 ) L 2   a,  L 2   b,  L 2   c,  L 2   d  of the second light flux L 2  having the distribution shown in  FIG. 13B  at the entrance end  15   a  of the light intensity equalizing element  15 . 
     The off-center amount d 1  is a distance from the optical axis  15   c  of the light intensity equalizing element  15  to the optical axis  11   c   3  of the first light flux L 1 , and the off-center amount d 2  is a distance from the optical axis  15   c  of the light intensity equalizing element  15  to the optical axis  12   c  of the second light flux L 2 . As has already been described, since the illuminators  11   a  and  12   a  are lamps having a certain size and there are errors in position of the illuminators  11   a  and  12   a,  errors in shape and position of the ellipsoidal mirrors  11   b  and  12   b,  and other errors, the first light flux L 1  includes the light flux components (e.g., the light rays L 1   a  and L 1   b ) not converging at the light converging point F 2  as shown in  FIG. 14  and the second light flux L 2  includes the light flux components (e.g., the light rays L 2   a,  L 2   b,  L 2   c  and L 2   d ) not converging at the light converging point F 3  as shown in  FIG. 15 . As a result, as has been indicated in  FIGS. 2A and 2B  and  FIGS. 13A and 13B , the converging light flux from the light source lamp travels as a light flux having a distribution (extent) to the entrance end  15   a.    
       FIG. 16  is a diagram illustrating an example of a distribution of the first light flux L 1  from the first light source lamp  11  and a distribution the second light flux L 2  from the second light source lamp  12  at the entrance end  15   a  of the light intensity equalizing element  15  according to the first embodiment. In the example shown in  FIG. 16 , the entrance end  15   a  is a rectangle having a long side and a short side, a position (first incidence position) of the central ray  11   c   3  of the first light flux L 1  at the entrance end  15   a  and a position (second incidence position) of the central ray  12   c  of the second light flux L 2  at the entrance end  15   a  are deviated in opposite directions with reference to the optical axis  15   c  of the light intensity equalizing element  15  (positions with the off-center amounts d 1  and d 2 ). Furthermore, in the example shown in  FIG. 16 , the first incidence position (position of the optical axis  11   c   3  in  FIG. 16 ) and the second incidence position (position of the optical axis  12   c  in  FIG. 16 ) are positions on the first reference line H 0  extending in a direction of the long side and passing through the optical axis  15   c  of the light intensity equalizing element  15 . 
       FIG. 17  is a diagram illustrating another example of a distribution of the first light flux L 1  emitted from the first light source lamp  11  and a distribution of the second light flux L 2  emitted from the second light source lamp  12  at the entrance end  15   a  of the light intensity equalizing element  15  according to the first embodiment. In the example shown in  FIG. 17 , the entrance end  15   a  is a rectangle having a long side and a short side. A position of the central ray  11   c   3  of the first light flux L 1  (first incidence position) and a position of the central ray  12   c  of the second light flux L 2  (second incidence position) on the entrance end  15   a  are positions (positions with the off-center amounts d 1 , d 2 ) deviated to opposite sides in a direction of the long side relative to the optical axis  15   c  of the light intensity equalizing element  15  and are positions (positions with off-center amounts v 1 , v 2 ) deviated to opposite sides in a direction of the short side relative to the optical axis  15   c  of the light intensity equalizing element  15 . It is desirable that whether the positions of two light fluxes entering the entrance end  15   a  should be arranged in a direction of the long side as shown in  FIG. 16  or in a slanting direction (or a diagonal direction) as shown in  FIG. 7  be determined in consideration of the improvement of the light utilization efficiency and the improvement of the light luminous uniformity on a screen. 
       FIG. 18  is a diagram conceptually illustrating behavior of loss light at the entrance end  15   a  of the light intensity equalizing element  15  according to the first embodiment. If the first light flux L 1  and the second light flux L 2  are deviated by the off-center amounts d 1 , d 2 , the converging light fluxes converge on positions deviated by the off-center amounts d 1 , d 2  and the light flux that does not enter the entrance end  15   a  of the light intensity equalizing element  15  (i.e., loss light that cannot be used) increases. In  FIGS. 13A and 13B , the loss light that is headed for the entrance end  15   a  of the light intensity equalizing element  15  but does not enter the entrance end  15   a  is indicated as part of the first light flux L 1  and the second light flux L 2  and as an outer part of the entrance end  15   a.    
       FIG. 6  is a diagram showing a result of a simulation calculation of a relationship between the off-center amounts d 1 , d 2  and light utilization efficiency B. The simulation in  FIG. 6  is a calculation example on condition that a cross section of the light intensity equalizing element  15  is a rectangle of 7 mm×4.5 mm. In  FIG. 6 , the light utilization efficiency B is indicated as a ratio to the light utilization efficiency when the off-center amounts d 1 , d 2  are 0, that is, when the central ray of the incident light flux to the light intensity equalizing element  15  agrees with the optical axis  15   c  of the light intensity equalizing element  15  as shown in  FIG. 4 . Strictly speaking, in the simulation in  FIG. 6 , the light utilization efficiency B of the second light flux is calculated under the condition that there is no loss light blocked by the second bending mirror  13   d.  Regarding the first light flux, the light utilization efficiency B shown in  FIG. 6  is obtained under the condition that the second bending mirror  13   d  has sufficient size and there is no loss light that is not reflected by the second bending mirror  13   d  and therefore cannot enter the entrance face  15   a.    
     From  FIG. 6 , when the off-center amount d 1  is 0, the light utilization efficiency B is 1. When the off-center amount d 1  is 0.5 mm, the light utilization efficiency B is 0.99. When the off-center amount d 1  is incremented in the order of 1 mm, 1.5 mm, and 2 mm one after another, the light utilization efficiency B decreases in the order of 0.97, 0.92, and 0.84. In the first embodiment, for example, the light utilization efficiency B is high and not less than 0.9, and both of the off-center amounts d 1  and d 2  are set to 1.5 mm in order to make it difficult to block the second light flux L 2  from the second light source lamp  12  by the first bending mirror  14  (i.e., so as to reduce the interference). However, the off-center amounts d 1  and d 2  can be determined on the basis of various kind of factors such as a shape, a size, arrangement of each element, a traveling direction of the light flux, an optical feature of each element, required performance and the like. 
     In  FIG. 6 , when a cross-sectional profile of the light intensity equalizing element  15  is 7 mm×4.5 mm and the off-center amount d 1  is set to 1.5 mm, as shown in  FIG. 13A , a distribution on the entrance end  15   a  of the light intensity equalizing element  15  and the converging are deviated by 1.5 mm. Likewise, when the off-center amount d 2  is set to 1.5 mm, a distribution on the entrance end  15   a  of the light intensity equalizing element  15  is also deviated by 1.5 mm as shown in  FIG. 13B . As described above, when the off-center amounts d 1  and d 2  are set to 1.5 mm, distributions of the converging light flux from the light source lamp  11  and the light source lamp  12  on the entrance end  15   a  of the light intensity equalizing element  15  includes partially overlapped converging light fluxes of each lamp as shown in  FIG. 2B , and thus the light utilization efficiency can be improved. 
       FIG. 7  is a diagram showing a result of a simulation calculation of a relationship between an off-center amount d 3  and light utilization efficiency C. As shown in  FIG. 4 , in the first embodiment, the end portion  13   e  of the first bending mirror  13   d  which is an end on a side of the optical axis  15   c  of the light intensity equalizing element  15  is disposed on the optical axis  15   c  of the light intensity equalizing element  15  or is disposed closer to the first light source lamp  11  (an upper part of  FIG. 4 ) in comparison with the optical axis  15   c  of the light intensity equalizing element  15 , in order to avoid an interference with the second light flux L 2  from the second light source lamp  12  as much as possible.  FIG. 7  shows the result of the simulation calculation of the light utilization efficiency C when the off-center amount d 1  in  FIG. 4  is fixed to 1.5 mm and the off-center amount d 3  varies. The light utilization efficiency C in  FIG. 7  is indicated by a ratio relative to the light utilization efficiency when the off-center amount d 3  is 1 mm.  FIG. 7  shows a change in the light utilization efficiency C when the off-center amount d 3  changes from 1 mm to 5 mm.  FIG. 7  indicates that if the off-center amount d 3  is small, a light flux from the relay optical system  13  is blocked by a side surface of the light intensity equalizing element  15  (an upper part of the light intensity equalizing element  15  in  FIG. 4 ) and thus the light utilization efficiency C is low. If the off-center amount d 3  increases from 1 mm, the light utilization efficiency C gradually increases; and if the off-center amount d 3  is 3 mm and 3.5 mm, the light utilization efficiency C is the highest. 
     In the first embodiment, although two light source lamps are used and the second bending mirror  13   d  is disposed in the synthesizing unit, part of the light fluxes from the two light source lamps  11  and  12  becomes loss light which cannot enter the entrance end  15   a  of the light intensity equalizing element  15 . As shown in  FIG. 18 , main kinds of the loss light are a light flux L 11  which is a light flux emitted from the light source lamp  11  and passing through without reflecting by the bending mirror  13   d,  a light flux L 12  which is reflected by the bending mirror  13   d  and then does not enter the entrance end  15   a  of the light intensity equalizing element  15 , and a light flux L 13  which is not reflected by the bending mirror  13   d  and then travels toward outside the entrance end  15   a  of the light intensity equalizing element  15 . Furthermore, regarding the light flux of the light source lamp  12 , the loss light includes a light flux L 21  which is absorbed or reflected by a back surface of the bending mirror  13   d  and a light flux such as L 22  which cannot enter the entrance end  15   a  of the light intensity equalizing element  15 . The bending mirror  13   d  is placed at a position and is formed to have a size so that the first light flux L 1  is reflected and directed toward the entrance end  15   a  as much as possible and the blocked second light flux L 21  can be reduced as little as possible. 
     In  FIG. 7 , the change of the light utilization efficiency C has been described. Since a component of the loss light L 11  in the light flux emitted from the light source lamp  11  increases if the off-center amount d 3  is small, the light utilization efficiency of the light source lamp  11  decreases. On the other hand, regarding the light flux from the light source lamp  12 , since the degree of converging of the light flux increases as the light flux approaches the entrance end  15   a  of the light intensity equalizing element  15 . In contrast to this, if the off-center amount d 3  gradually increases, the light utilization efficiency of the light source lamp  11  increases and the light utilization efficiency of the light source lamp  12  decreases, the entire light utilization efficiency C of the light source lamp  12  and the light source lamp  22  increases until the off-center amount d 3  becomes a certain predetermined value increases as a whole. However, if the off-center amount d 3  exceeds the predetermined value and becomes too large (in  FIG. 7 , the off-center amount d 3  exceeds 3.5 mm), the second bending mirror  13  is disposed on the light fluxes with large diameter of the light source lamp  11  and the light source lamp  12  (i.e., where convergence is insufficient) and the loss light component increases and the light utilization efficiency C decreases. 
       FIG. 8  is a diagram illustrating an example of a shape of the second bending mirror (final bending unit)  13 . The bending mirror  13   d  shown in  FIG. 8  is disposed so that the end portion  13   e  on a side of the light intensity equalizing element  15  is aligned with the optical axis  15   c  of the light intensity equalizing element  15 . In other words, the end portion  13   e  is placed so as to be parallel to the central ray (i.e., optical axis  12   c ) of the second light flux L 2 . In order to guide the first light flux L 1  from the first light source lamp  11  to the entrance end  15   a  of the light intensity equalizing element  15  as much as possible, it is desirable that the reflecting surface  13   f  of the second bending mirror  13   d  be formed as large as possible. On the other hand, in order to avoid interference between the second bending mirror  13   d  and the second light flux L 2  from the second light source lamp  12  as much as possible, it is desirable that the second bending mirror  13   d  be formed as small as possible. Therefore, as shown in  FIG. 8 , the end portion  13   e  of the second bending mirror  13   d  on a side of the optical axis  15   c  of the light intensity equalizing element  15  is formed so that the reflecting surface  13   f  is larger than the back surface  13   g  of the second bending mirror  13   d.  In  FIG. 8 , an angle between the reflecting surface  13   f  and the end portion  13   e  of the second bending mirror  13   d  is made to be an acute angle (less than 90 degrees) and the end portion  13   e  and the optical axis  15   c  are arranged to be substantially parallel to each other. It is possible to adopt a structure in which an angle between the end portion  13   e  and the optical axis  15   c  is a predetermined angle, and a distance between a part of the end portion  13   e  on a side near the entrance face  15   a  and the optical axis  15   c  is shorter than a distance between a part of the end portion  13   e  on a side far from the entrance face  15   a  and the optical axis  15   c.  Accordingly, the light utilization efficiency of the first light flux L 1  from the first light source lamp  11  increases as well as the interference between the second light flux L 2  of the second light source lamp  12  and the second bending mirror  13   d  decreases, thereby increasing the light utilization efficiency of the second light source lamp  12 . 
       FIG. 9  is a diagram illustrating another example of a shape of the second bending mirror (final bending unit). The bending mirror  13   d   2  shown in  FIG. 9  is disposed so that the end portion  13   e   2  on a side of the light intensity equalizing element  15  is aligned with the optical axis  15   c  of the light intensity equalizing element  15 . In order to guide the first light flux L 1  from the first light source lamp  11  to the entrance end  15   a  of the light intensity equalizing element  15  as much as possible, it is desirable that the reflecting surface  13   f   2  of the second bending mirror  13   d   2  be formed as large as possible. On the other hand, in order to avoid the interference between the second bending mirror  13   d   2  and the second light flux L 2  and the second light source lamp  12  as much as possible, it is desirable that the second bending mirror  13   d   2  be formed as small as possible. Therefore, as shown in  FIG. 9 , a side of the second bending mirror  13   d   2  facing the optical axis  15   c  of the light intensity equalizing element  15 , namely, the end portion  13   e   2  facing the second light flux is formed to have a convex curved surface  13   g   2  of the second bending mirror  13   d   2  so that the reflecting surface  13   f   2  is larger than the back surface  13   g   2 . In  FIG. 9 , an angle between the reflecting surface  13   f   2  of the second bending mirror  13   d   2  and the end portion  13   e   2  is an acute angle (less than 90 degrees). The reason why the end portion  13   e   2  is formed to have a convex surface, if an angle between the reflecting surface  13   f   2  and the end portion  13   e   2  is too small, structures become weak and hard to manufacture and makes it difficult to be manufactured. For this reason, a corner  13   h  of the end portion  13   e  in the second bending mirror  13   d  of  FIG. 8 , as shown in  FIG. 9  as a corner  13   h   2  of the end portion  13   e   2 , is shaved, and thus the second light flux L 2  from the second light source lamp through the light intensity equalizing element  15  to the entrance end  15   a  is hard to be blocked. That is, an edge of the reflecting surface  13   f   2  on a side of the optical axis  15   c  of the light intensity equalizing element  15  is the nearest to the central ray of the second light flux (i.e., optical axis  12   c  of the second light flux L 2 ). In other words, it is formed so that a first distance is not more than a second distance, where a distance from a side of the reflecting surface  13   f   2  which is nearest to the central ray of the second light flux the first distance is denoted by the first distance, and a distance from a part nearest to the central ray of the second light flux L 2 , out of a side surface of the reflecting surface  13   d   2  which faces the second light flux L 2 , to the central ray of the second light flux L 2  is denoted by the second distance. Even if the second bending mirror having the structure of  FIG. 9  is adopted, the light utilization efficiency of the first light flux L 1  from the first light source lamp  11  increases, the interference between the second light flux L 2  from the second light source lamp  12  and the second bending mirror  13   d   2  decreases, and the light utilization efficiency of the second light source lamp  12  can be increased. 
     In  FIG. 8  and  FIG. 9 , although the structures in which the reflecting surfaces  13   f,    13   f   2  of the second bending mirrors  13   d,    13   d   2  are larger than the back surfaces  13   g,    13   g   2  are described, such idea is applied to a shape on a side of the optical axis  15   c  of the light intensity equalizing element  15 . For example, as shown in  FIG. 19 , in a second bending mirror  13   d   3 , if a back surface  13   g   3  is formed to have the same shape as a light reflecting surface  13   f   3  of the light intensity equalizing element  15  on a side of the optical axis  15   c,  the reflecting surface  13   f   3  and the back surface  13   g   3  become the same size. Even if it is structured as shown in  FIG. 19 , the light utilization efficiency can be increased by making an angle between the light reflecting surface  13   f   3  and an end portion (side surface)  13   f   2  acute in a similar manner to the cases in  FIG. 8  and  FIG. 9 . In other words, if the structures are formed so that a first distance (e.g., u 1 ) from an end portion of the reflecting surface  12   f   3  which is the nearest to the central ray  12   c  of the second light flux L 2  to the central ray  12   c  of the second light flux L 2  is not more than a second distance (e.g., u 2 ) from a part of the side surface  13   f   2  which is the nearest to the central ray  12   c  of the second light flux L 2  to the central ray  12   c  of the second light flux L 2  (i.e., u 1 ≦u 2 ), the light utilization efficiency can be improved. However, as shown in  FIG. 9 , even if u 1 &gt;u 2 , the light utilization efficiency can be improved by making a value (u 1 −u 2 ) as small as possible. 
     As described above, in the projection type display apparatus according to the first embodiment, it is structured that the first light source lamp  11  and the second light source lamp  12  are disposed substantially in parallel, it is arranged so that the first optical axes  11   c   1 ,  11   c   2  and  11   c   3  of the first light source lamp  11  and the second optical axis  12   c  of the second light source lamp  12  agree at nowhere with each other, and thereby a structure that high light utilization efficiency is obtained and the light source lamp  11  and the light source lamp  12  are free from influence of loss light from each other can be achieved. 
     Further, in the projection type display apparatus according to the first embodiment, since the light converging points of the first light source lamp  11  and the second light source lamp  12  are disposed near the entrance end  15   a  of the light intensity equalizing element  15 , an optical system with high light utilization efficiency can be provided. 
     Furthermore, the projection type display apparatus according to the first embodiment has a structure that the relay optical system  13  is disposed between the first light source lamp  11  and the second light converging point F 2 , the first light flux L 1  converges near the entrance end  15   a  of the light intensity equalizing element  15 , and the second light flux L 2  from the second light source lamp  12  is directly collected near the entrance end  15   a  of the light intensity equalizing element  15 , and thereby an optical system with high light utilization efficiency can be provided. 
     Moreover, in the projection type display apparatus according to the first embodiment, since the second bending mirror  13   d  is structured so that the reflection surface  13  differs from the back surface  13   g  in shape and is larger than the back surface  13   g,  an optical system with high light utilization efficiency can be provided. 
     The projection type display apparatus according to the first embodiment can have a mirror adjusting means (a mechanism  27  shown in  FIG. 11  described later) as a bending adjusting unit capable of adjusting any of a position, an angle and both of them of any of the bending mirror  13   a,  the bending mirror  13   d  and both of them. In this case, even if a difference in size or positional deviations occur in the light source lamp  11  and the light source lamp  12 , the amount of incident light on the light intensity equalizing element  15  can be adjusted by adjustment of the mirror adjusting means, and thereby an optical system with high light utilization efficiency can be provided. Moreover, in the case where such mirror adjusting means is provided, when either one of the light source lamp  11  or the light source lamp  12  is lighted, a position of the bending mirror  13   d  is shifted to a side of the other light source lamp which is not lighted (if only the light source lamp  11  is lighted, the bending mirror  13   d  is shifted to a side of the optical axis  12   c  of the light source lamp  12 , and if only the light source lamp  12  is shifted, the bending mirror  13   d  is shifted to a side of the optical axis  11   c  of the light source lamp  11 .). 
     In the projection type display apparatus according to the first embodiment, it is also available that the light source lamp  11  or the light source lamp  12  or both of the lamps includes/include a light source lamp adjusting means (not shown in the drawings) being capable of adjusting a position or an angle or both of the position and the angle of the light source lamp. In this case, even if the light source lamp  11  and the light source lamp  12  shift in position or differ in size, amount of incident light on the light intensity equalizing element  15  can be adjusted by the light source lamp adjusting means, and thereby an optical system with high light utilization efficiency can be provided. 
     Further, in the projection type display apparatus according to the first embodiment, if the light intensity equalizing element  15  is structured by a pipe-shaped element whose inner surface is a light reflection surface, a holding structure of the light intensity equalizing element  15  can be easily designed and heat radiation performance can be improved. 
     Furthermore, in the projection type display apparatus according to the first embodiment, if the light intensity equalizing element  15  is a pillar-shaped optical element being structured with transparent material and having a polygonal cross section, the light intensity equalizing element  15  can be easily designed. 
     In the projection type display apparatus according to the first embodiment, the elements are arranged so that the light converging points are disposed closer to the light intensity equalizing element  15  in comparison with the second bending mirror  13   d,  and thereby the bending mirror can be prevented from heating. Therefore, in the projection type display apparatus according to the first embodiment, simplification of the structure and cost reduction of the apparatus can be realized without adding a cooling device or the like. 
     Second Embodiment 
       FIG. 10  is a diagram schematically illustrating a structure of a light source device  20  in a projection type display apparatus according to a second embodiment of the present invention. The light source device  20  shown in  FIG. 10  can be used as a light source device for the projection type display apparatus shown in  FIG. 1  (the first embodiment). A first light source lamp  21 , a second light source lamp  22  and a relay optical system  23  in  FIG. 10  are similar in structure to the first light source lamp  11 , the second light source lamp  12  and the relay optical system  13  in  FIG. 1  (the first embodiment), respectively. Illuminators  21   a  and  22   a,  ellipsoidal mirrors  21   b  and  22   b,  and optical axes  21   c   1 ,  21   c   2 ,  21   c   3  and  22   c  in  FIG. 10  are similar in structure to the illuminators  11   a  and  12   a,  the ellipsoidal mirrors  11   b  and  12   b,  and the optical axes  11   c   1 ,  11   c   2 ,  11   c   3  and  12   c  in  FIG. 1 , respectively. The projection type display apparatus according to the second embodiment differs from the above-described projection type display apparatus according to the first embodiment in a structure of a light intensity equalizing element  25 . As shown in  FIG. 10 , in the second embodiment, the light intensity equalizing element  25  is structured so that lens arrays  25   a  and  25   b  having a plurality of lens elements arranged in a two-dimensional array are disposed in line in a direction of an optical axis  25   c.  A first light flux L 1  from the first light source lamp  11  and a second light flux L 2  from the second light source lamp  12  are guided by lens elements  26   a  and  26   b  to the light intensity equalizing element  25 . The light intensity equalizing element  25  having such structure makes it possible to equalize intensity distribution in a cross section of an illumination light flux and to prevent illumination irregularities. The projection type display apparatus according to the second embodiment can be reduced in size in a direction of the optical axis  25   c,  in comparison with the case where the light intensity equalizing element is structured by a rod which is an optical element. 
     Except for the respects described above, the second embodiment is the same as the above-described first embodiment. 
     Third Embodiment 
       FIG. 11  is a diagram schematically illustrating a structure of a light source device  30  in a projection type display apparatus according to a third embodiment of the present invention. The light source device  30  shown in  FIG. 11  can be used as a light source device of the projection type display apparatus shown in  FIG. 1  (the first embodiment). A first light source lamp  31 , a second light source lamp  32 , a relay optical system  33  and a light intensity equalizing element  35  in  FIG. 11  are similar in structure to the first light source lamp  11 , the second light source lamp  12 , the relay optical system  13  and the light intensity equalizing element  15  in  FIG. 1 , respectively. Illuminators  31   a  and  32   a,  ellipsoidal mirrors  31   b  and  32   b,  optical axes  31   c   1 ,  31   c   2 ,  31   c   3  and  32   c,  an entrance end  35   a,  an exit end  35   b  and an optical axis  35   c  in  FIG. 11  are similar in structure to the illuminators  11   a  and  12   a,  the ellipsoidal mirrors  11   b  and  12   b,  the optical axes  11   c   1 ,  11   c   2 ,  11   c   3  and  12   c,  the entrance end  15   a,  the exit end  15   b  and the optical axis  15   c  in  FIG. 1 , respectively. The projection type display apparatus according to the third embodiment differs from the above-described projection type display apparatus according to the first embodiment in a respect that the first light source lamp  31 , the second light source lamp  32 , the relay optical system  33  and the light intensity equalizing element  35  are arranged so that the optical axes  31   c   1 ,  31   c   2  and  31   c   3  of a first light flux L 1  and the optical axis  35   c  of the light intensity equalizing element  35  are not parallel and the optical axis  32   c  of a second light flux L 2  and the optical axis  35   c  of the light intensity equalizing element  35  are not parallel. Thus, the first light source lamp  31  and the second light source lamp  32  are arranged so that the optical axis  31   c   1  of the first light flux L 1  at a time immediately after emission from the first light source lamp  31  and the optical axis  32   c  of the second light flux L 2  at a time immediately after emission from the second light source lamp  32  have a larger interval therebetween as the light fluxes travel further. According to the structure in the third embodiment, a size of the light source device  30  can be shortened in a longitudinal direction in  FIG. 11 . 
     Furthermore, as shown in  FIG. 11 , the projection type display apparatus can have a mirror adjusting means (mechanism  27 ) capable of adjusting any of a position, an angle and both of them of any of a bending mirror  33   a,  a bending mirror  33   d  and both of them. Moreover, the projection type display apparatus can have a light source lamp adjusting means (mechanism  28 ) capable of adjusting any of a position, an angle and both of them of any of the light source lamp  11 , the light source lamp  12  and both of them. The mechanisms  27  and  28  include mechanical structures for moving or rotating a structural component supporting the bending mirror or the light source lamp. The mechanisms  27  and  28  may include a driving source such as a motor for driving the mechanical structure forming them. Furthermore, the mechanism  27  and  28  can be applied to other embodiments. 
     Although, in  FIG. 11 , the first light source lamp  31  is disposed at an upper side of  FIG. 11  and the second light source lamp  32  is disposed at a lower side of  FIG. 11 , they can be inversely disposed. It is also practicable that either the optical axis of the first light source lamp  31  or the optical axis of the second light source lamp  32  ( 31   c   1  or  32   c ) is disposed in parallel with the optical axis  35   c  of the light intensity equalizing element  35 . 
     Although it is possible that each of the optical axis of the first light flux at a time immediately after emission from the first light source lamp  31  and the optical axis of the second light flux at a time immediately after emission from the second light source lamp  32  has an inclination angle within a range of about ±15 degrees from a horizontal direction in  FIG. 11 , it is desirable for the inclination angle to be within a range of ±5 degrees, in order to achieve sufficient performance of the first light source lamp  31  and the second light source lamp  32 . Furthermore, in consideration of such as facility to make a structure of the relay optical system  33 , it is more desirable that the inclination angles of the optical axis of the first light source lamp  31  and the optical axis of the second light source lamp  32  be within a range of ±3 degrees from the horizontal direction in  FIG. 11  (or that an angle between the optical axis of the first light source lamp  31  and the optical axis of the second light source lamp  32  be 6 degrees or less). 
     Except for the respects described above, the third embodiment is the same as the above-described first or second embodiment. Furthermore, the first light source lamp  31  or the second light source lamp  32  in the third embodiment can be applied to the light source device in the second embodiment. 
     Fourth Embodiment 
       FIG. 12  is a diagram schematically illustrating a structure of a light source device  40  in a projection type display apparatus according to a fourth embodiment of the present invention. The light source device  40  shown in  FIG. 12  can be used as the light source device for the projection type display apparatus shown in  FIG. 1  (the first embodiment). A first light source lamp  41 , a second light source lamp  42 , a relay optical system  43  and a light intensity equalizing element  45  in  FIG. 12  are similar in structure to the first light source lamp  11 , the second light source lamp  12 , the relay optical system  13  and the light intensity equalizing element  15  in  FIG. 1 , respectively. Illuminators  41   a  and  42   a,  ellipsoidal mirrors  41   b  and  42   b,  optical axes  41   c   1 ,  41   c   2 ,  41   c   3  and  42   c,  an entrance end  45   a,  an exit end  45   b  and an optical axis  45   c  in  FIG. 12  are similar in structure to the illuminators  11   a  and  12   a,  the ellipsoidal mirrors  11   b  and  12   b,  the optical axes  11   c   1 ,  11   c   2 ,  11   c   3  and  12   c,  the entrance end  15   a,  the exit end  15   b  and the optical axis  15   c  in  FIG. 1 , respectively. 
     The projection type display apparatus according to the fourth embodiment differs from the above-described projection type display apparatus according to the first embodiment in a respect that a light blocking plate  46  is provided adjacent to the entrance end  45   a  of the light intensity equalizing element  45  and is a blocking unit for blocking (reflecting or absorbing) loss light L 5  which does not reach a second bending mirror  43   d  in a light flux from the first light source lamp  41 . Furthermore, the light blocking plate  46  also has a function of blocking (reflecting or absorbing) a light flux which is emitted from the first light source lamp  41  and travels toward a side of the light intensity equalizing element  45  (an upper surface of the light intensity equalizing element  45  in  FIG. 12 ). Any material is available for the light blocking plate  46 , if it does not transmit light. 
     It is desirable that the light blocking plate  46  be disposed at a position so as not to block the light flux L 1  traveling from the first light source lamp  41  toward the second bending mirror  43   d.  It is also desirable that the light blocking plate  46  have such a position, a size (a length and a width) and a shape as to block the loss light L 5  which does not reach the second bending mirror  43   d  in the light flux from the first light source lamp  41  as much as possible. 
     As shown in  FIG. 12 , in the fourth embodiment, the loss light L 5  which does not reach a first bending mirror  73  in the light flux traveling from the first light source lamp  41  and loss light in a light flux traveling from the second light source lamp  72  can be blocked by the light blocking plate  46 . For this reason, the loss light traveling from the first light source lamp  41  toward a side surface of the light intensity equalizing element  45  decreases, and thus there is an effect that thermal influence on the light intensity equalizing element  45  can be reduced. 
     Except for the respects described above, the fourth embodiment is the same as the above-described first embodiment. Furthermore, the light blocking plate  46  can be applied to the above-described second or third embodiment. 
     EXPLANATION OF REFERENCE CHARACTERS 
       10 ,  20 ,  30 ,  40  light source device;  11 ,  21 ,  31 ,  41  first light source lamp;  11   a,    21   a,    31   a,    41   a  illuminator;  11   b,    21   b,    31   b,    41   b  ellipsoidal mirror;  11   c   1 ,  11   c   2 ,  11   c   3 ,  21   c   1 ,  21   c   2 ,  21   c   3 ,  31   c   1 ,  31   c   2 ,  31   c   3 ,  41   c   1 ,  41   c   2 ,  41   c   3  optical axis of first light source lamp;  12 ,  22 ,  32 ,  42  second light source lamp;  12   a,    22   a,    32   a,    42   a  illuminator;  12   b,    22   b,    32   b,    42   b  ellipsoidal mirror;  12   c,    22   c,    32   c,    42   c  optical axis of second light source lamp;  13 ,  23 ,  33 ,  43  relay optical system;  15 ,  25 ,  35 , light intensity equalizing element;  15   a,    25   a,    35   a,    45   a  entrance end of light intensity equalizing element;  15   b,    25   b,    35   b,    45   b  exit end of light intensity equalizing element;  15   c,    25   c,    35   c,    45   c  optical axis of light intensity equalizing element;  27  mirror adjusting means; light source lamp adjusting means;  61  image display element;  62  projection optical system;  63  screen;  46  light blocking plate; L 1  first light flux; L 2  second light flux; L 3  exit light from light intensity equalizing element; L 4  image light; L 5  first loss light; L 10  central ray of first light flux; L 20  central ray of second light flux; F 1  first light converging point; F 2  second light converging point; F 3  third light converging point.