Abstract:
A projector having an image display element for modulating light on the basis of an image signal and a projection lens for projecting light emitted from the image display element on a screen, includes: a lamp which has a light emitting source for emitting light; a reflector which reflects light emitted from the light emitting source; a cover glass which covers an emission surface of light from the reflector; a cooling fan disposed outside the reflector; and an air direction changing unit which changes a direction of cooling air caused by the cooling fan. The air direction changing unit is disposed within a space surrounded by the reflector and the cover glass, and outside an emitted light path of light reflected by the reflector. Cooling air within the space is exhausted outside the projector through the cooling fan.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese applications serial no. JP2004-015114 filed on Jan. 23, 2004 and serial no. JP2004-247710 filed on Aug. 27, 2004, the contents of which are hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     Japanese Patent Laid-open No. 8-262573 discloses the structure in which outside air supplied from an in-flow hole above a lamp house is guided in the direction of a light emitting portion of a light source along an air induction member, directly cools a heat generation portion and flows outside a lamp chamber from a lower out-flow hole.  
         [0003]     Further, Japanese Patent Laid-open No. 2002-189247 discloses the structure in which a blower hole for sending cooling air toward the interior of a reflector is formed, and the air direction changing means for changing the direction of cooling air discharged toward the interior of the reflector is provided.  
         [0004]     Furthermore, Japanese Patent Laid-open No. 10-27518 discloses the technique in which an air-flow is introduced into a reflector from a duct to cool a lamp.  
       SUMMARY OF THE INVENTION  
       [0005]     In recent projectors, a lamp such as an electric bulb of a high power type has been often used. The lamp tends to be high power resulting from higher brightness whereas miniaturization of the entire device is required, and thus the cooling conditions around the light source device are becoming severe.  
         [0006]     In the prior art disclosed in the above-described Japanese Patent Laid-open No. 8-262573, the lowering of the usability of light caused by arranging the air induction member on the light path for light reflected by a reflector has not been recognized sufficiently. In the prior art disclosed in the above-described Japanese Patent Laid-open No. 2002-189247, complicatedness and higher cost of the system caused by arranging an exhaust fan for cooling a discharge lamp were possibly brought forth. In the prior art disclosed in the above-described Japanese Patent Laid-open No. 10-27518, the larger-size of the device caused by providing a duct on the light source device for cooling a light emitting area sufficiently has not been recognized sufficiently.  
         [0007]     It is an object of the present invention to solve the aforementioned problems and provide a projector for achieving the enhancement of reliability of a light source device.  
         [0008]     There is provided a projector having an image display element for demodulating light on the basis of an image signal, and a projection lens for projecting light emitted from the image display element on a screen. The projector includes a lamp which has a light emission source for emitting light, a reflector which reflects light emitted from the light emission source, a cover glass which covers an emission surface of light from the reflector, a cooling fan disposed outside the reflector, and an air direction changing unit which changes a direction of cooling air caused by the cooling fan, disposed outside an emission light path of light reflected by the reflector and within the space surrounded by the reflector and the cover glass, the cooling air within the space being exhausted outside the projector through the cooling fan.  
         [0009]     The present invention is able to achieve the enhancement of reliability of the projector or the light source device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIGS. 1A and 1B  are perspective views showing the front and rear external appearances, respectively, of a projector according to a first embodiment of the present invention.  
         [0011]      FIG. 2  is a perspective view showing the internal structure of the projector according to the first embodiment of the present invention.  
         [0012]      FIGS. 3A and 3B  are longitudinal sectional views showing the structure of a light source device according to the first embodiment of the present invention.  
         [0013]      FIG. 4  is a front view showing the structure of the light source device according to the first embodiment 1 of the present invention.  
         [0014]      FIGS. 5A and 5B  are respectively longitudinal sectional views showing the structure of a light source device according to a second embodiment of the present invention.  
         [0015]      FIGS. 6A and 6B  are longitudinal sectional views showing the structure of a light source device according to a third embodiment of the present invention.  
         [0016]      FIGS. 7A  to  7 C show one example of the structure of the mesh used in the present invention.  
         [0017]      FIGS. 8A and 8B  show one example of the structure of an air direction changing plate used in the present invention.  
         [0018]      FIGS. 9A and 9A  show another example of the structure of an air direction changing plate used in the present invention.  
         [0019]      FIG. 10  shows the internal structure of a projector according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Preferred embodiments of the present invention will be described hereinafter with reference to the drawings. It is to be noted that in the figures, constituent elements having a common function are indicated by the same reference numerals, and a constituent element that is mentioned once previously will not be described repeatedly in order to avoid complexity.  
         [0021]      FIGS. 1A and 1B  are perspective views showing the external appearance of a projector according to a first embodiment of the present invention;  FIG. 1A  shows the front of the projector  1 , and  FIG. 1B  shows the rear of the projector.  
         [0022]     In  FIGS. 1A and 1B , in the projector  1  according to the present invention, an exhaust vent  2  faces in the same direction as a projection lens  10 , that is, faces forward, as shown in  FIG. 1A , and an intake vent  3  is provided on the rear side, as shown in  FIG. 1B . In addition, an operating button  5 , a panel intake vent  4 , and the like are arranged in the surface of the projector  1  to face the outside thereof.  
         [0023]     The projector  1  is actuated by operating the operating button  5  from the outside of the projector. In operation, an image is projected through the projection lens  10  and displayed on a screen or the like not shown.  
         [0024]      FIG. 2  is a perspective view showing the internal structure of the projector  1  according to the first embodiment of the present invention shown in  FIG. 1 .  
         [0025]     In  FIG. 2 , a lamp-cooling duct  200  as lamp-cooling means for cooling a lamp (not shown) as illumination means is provided within the device. The lamp-cooling duct  200  is composed of exhaust ducts  215 ,  216  provided on one side and a lamp duct  213  provided on the other side with respect to a cooling fan  210  located therebetween. In addition, a duct exhaust vent  211  and a duct intake vent  212  are provided on the respective ends of the lamp-cooling duct  200 . It is noted that the duct intake vent  212  and the duct exhaust vent  211  face outside air outside a casing through the intake vent  3  and the exhaust vent  2 , respectively.  
         [0026]     While not shown due to the lamp duct  213 , a light source device (described later) as illumination means is provided under the lamp duct  213 . The outline of actual operation of the projector device is that light generated from the lamp as illumination means is demodulated by light valve means not shown within an optical engine section  6 , after which it is projected on a screen (not shown) outside the device via the projection lens  10  as projection means, and displayed as an image.  
         [0027]      FIGS. 3A, 3B  and  4  show the structure of a light source device used for the projector  1  according to the first embodiment of the present invention shown in  FIG. 1 .  
         [0028]      FIG. 3A  is a longitudinal sectional view showing the structure of the light source, and  FIG. 3B  is an enlarged view of an air direction changing plate  146  and its vicinity surrounded by the dotted line in  FIG. 3A .  FIG. 4  is a front view showing the structure of the light source device.  
         [0029]     In  FIGS. 3A, 3B  and  4 , reference numeral  110  denotes a lamp holder;  120  a lamp;  121  a light emitting tube;  122  a lead;  130  a reflector;  131  a cement portion;  132  the inside portion of the interior of a light source device;  133  the outside portion of the interior of a light source device;  134  an outermost periphery of a reflector;  140  a cap;  141  a cover glass also serving as a lens;  142  a connecting cylinder;  144  an exhaust vent;  145  an intake vent;  146  an air direction changing plate;  150  a mesh;  152  a mesh end;  153  a blade portion;  160  a mesh holder;  210  a cooling fan;  213  a lamp duct; and  730 ,  740 ,  750  arrows each showing a direction and an amount of cooling air, the amount of cooling air being shown by the number of arrows.  
         [0030]     In  FIG. 3 , the light source device is composed of various parts mounted on the lamp holder  110 . That is, the reflector  130 , the connecting cylinder  142 , the mesh  150  having a number of fine meshes arranged, and the cover glass  141  constitute a closed space so as to surround the lamp  120 . This structure can prevent the fragments caused when the lamp bursts up from scattering. Around the lamp are provided the cap  140  having a function to support the entirety, the mesh holder  160  for supporting the connecting cylinder  142 , etc. Further, the lamp  120  has the lead  122  for supplying power to the lamp  120 . As shown in  FIG. 4 , the air direction changing plate  146  is welded or adhered to the mesh  150  under the metal portion of the connecting cylinder  142 .  FIGS. 8A and 8B  show the shape of the air direction changing plate  146 ,  FIG. 8A  showing a section of the air direction changing plate  146 ,  FIG. 8B  showing the front of the air direction changing plate  146 . The air direction changing plate  146  shown in  FIGS. 8A, 8B  is configured, for example, such that a bending angle β  171  is 57 degrees, a plate thickness c  172  is 0.04 mm, a length L  173  is 39 mm, and a width f  174  is 9 mm. The air direction changing plate  146  shown in  FIGS. 8A, 8B  is bent to be a plate curved from a bending position to an extreme end portion thereof. Bending the air direction changing plate  146  as described above allows cooling air to smoothly enter the interior of the light source device. While in the present embodiment, the air direction changing plate  146  is bent to be the plate curved from a bending position to an extreme end portion thereof, the embodiment is not limited to this configuration. That is, the air direction changing plate  146  may be bent to be a straight plate extending from a bending position to an extreme end portion thereof.  
         [0031]     A method for taking air into the light source device shown in  FIG. 3  will be described below. In the present embodiment, air is taken in from the duct intake vent  212 , and the cooling air that cooled the light source device is exhausted to the outside of a casing from the duct exhaust vent  211  by the cooling fan  210 . As described above, the cooling fan  212  is used as an exhaust fan to thereby enhance cooling efficiency. That is, where the cooling fan  212  is used as an intake fan for blowing cooling air against the light emitting tube  121  of the lamp  120  directly, if the air direction changing plate  146  is arranged as shown in  FIG. 5 , the cooling efficiency is not extremely lowered. However, as shown in  FIGS. 3A, 3B  and  6 , when the air direction changing plate  146  is arranged approximately parallel with the optical axis, the air direction changing plate  146  acts as an obstacle to air so that cooling air may not be taken in efficiently. On the other hand, where the cooling fan  212  is used as the exhaust fan as in the present embodiment, cooling air can be taken in smoothly to enhance cooling efficiency.  
         [0032]     Cooling air taken in from the duct intake vent  212  is taken in from the intake vent  145  provided in the connecting cylinder  142 . The taken-in cooling air passes through the mesh  150 , and then is divided by the air direction changing plate  146  so as to enter the inside portion  132  and the outside portion  133  within the interior of the light source device, that is, the cooling air is guided into the light source device. At this time, the cooling air guided into the light source device flows in the direction and amount shown by arrow  730 ; the cooling air is guided into the inside portion  132  in an amount greater than that into the outside portion  133  within the light source device. Then, the cooling air that cooled the light emitting tube  121  mainly is exhausted from the exhaust vent  144  to the outside of the reflector  130 . With the structure of the present embodiment, since the light emitting tube  121  of the lamp  120  can mainly be cooled, the temperature of the light emitting tube  121  of the lamp  120  can be lowered to about 1000° C., whereas to about 1050° C. without the air direction changing plate  146 .  
         [0033]     The shape of the reflector  130  and the location of the air direction changing plate  146  in the light source device shown in  FIG. 3  will be described. The reflector  130  used in the present embodiment is formed in the shape of a parabola surface. The light emitting tube  121  of the lamp  120  is arranged approximately on a focus of the parabola surface so as to reflect the light reflected from the reflector  130  in approximate parallel with the optical axis. In the present embodiment, as shown in  FIG. 4 , the air direction changing plate  146  is arranged approximately parallel with the optical axis at a position in contact with the outermost periphery  134  of the reflector in consideration of less influence on the light reflected from the reflector  130  and miniaturization of the projector. Further, the air direction changing plate  146  is made of a material having a high reflectance and high thermal resistance in order to reflect light incident on the air, direction changing plate  146  out of light emitted from the light emitting tube  121  and emit it through the cover glass  141 . Since this configuration minimizes deterioration of the usability of light emitted from the light source device, higher brightness can be achieved.  
         [0034]     While in the above embodiment, a description has been made of the lamp having a light emitting tube as a light emitting source, the present invention is not limited thereto. The present invention may be applicable to the case of using an LED light source as the light emitting source. That is, since the air direction changing plate  146  is arranged at such a position as to minimize the deterioration of the usability of light from the reflector, the LED light source that is subjected to high temperatures can be cooled.  
         [0035]     Further, the lamp  120  needs different amounts of cooling energy, in a light emitting operation, between the upper and lower portions within the light source device. Here, in the case where the higher service life of the lamp is taken into consideration, it is necessary to make the temperatures in the vertical directions as even as possible, that is, to allow a greater amount of air to pass through a portion where the temperature becomes high. For example, in the case where the amount of cooling energy required on the upper side is greater, when air is caused to flow evenly between upper and lower portions, the temperature of the upper side of the lamp  120  becomes higher by about 30 degrees than the lower side so that a temperature difference between the upper and lower portions of the lamp  120  increases, thus lowering the service life of the lamp  120 . To overcome this disadvantage in the present embodiment, the mesh  150  is configured such that a large number of fine inclined blades are arranged as viewed in an enlarged view, as shown in  FIGS. 7A  (a cross-sectional view),  7 B (a front view), and  7 C (an entire perspective view).  FIG. 7A  is a cross-sectional view taken on line A-A of  FIG. 7B . The general structure of the blade portion  153  of the mesh  150  is that for example, a plate thickness t  157  is 0.1 mm, a width b  158  is 0.2 mm, a width W  155  of a fine hole is 1.25 mm, a height h  156  of the fine hole is 0.7 mm, and an angle of inclination a  159  of the plate is 35 degrees. Under the conditions, the air that passes through the mesh  150  is bent in its advancing direction by the blade portion  153  due to the viscosity of air. A flow of air passes through the mesh  150  as in a streamline  750  after bending with respect to a streamline  740 , thereby making it possible to control the streamlined direction. In this manner, a flow of air bent by the mesh  150  passes mainly the upper side of the lamp  120 , thereby mainly cooling the upper portion of the lamp  120 . The present embodiment employs, as the mesh  150 , a wire net of the kind generally called expand metal. This expand metal is prepared by putting successively alternate dotted line gaps in a metal plate, and thereafter drawing out both ends of the metal plate to form the mesh. With respect to the whole mesh as described, the expand metal construction as the construction inclined in the direction of plate thickness is a construction in which a number of small blades inclined as viewed from the section side are arranged. When air is applied vertically to the mesh in which a number of inclined fine blades are arranged, the air is subjected to friction with the fine small blades and the viscous resistance of air during it passes between the fine blades. Consequently, the air changes its flowing direction along the direction that the fine blades face. With the aforementioned structure, air is caused to flow toward the upper side of the lamp  120  whereby a temperature difference between the upper and lower portions of the lamp  120  can be made within about 10 degrees. This cooling effect achieves the longer service life of the lamp  120 . Further, the mesh  150  shown in  FIG. 4  is prepared by a single wire net so that a flow of cooling air when passing through the intake vent  145  or the exhaust vent  144  may be bent on the upper side. The present invention is not limited thereto, but the mesh  150  may be prepared by the aforementioned method using two wire nets and installed internally of the light source device. In this case, one wire net is configured such that cooling air passing through the side of the intake vent  145  is bent on the upper side whereas the other wire net is configured such that cooling air passing through the side of the exhaust vent  144  is bent on the lower side. Installing the two meshes  150  in a manner as described allows the cooling air to pass through the light source device smoothly.  
         [0036]     In the present embodiment, the cooling fan  210  is an axial flow fan as shown in  FIG. 3 . In this manner, since a relatively expensive Sirocco fan is not used herein, the cost can be reduced. Further, the present embodiment is configured such that as shown in  FIG. 4 , air that cooled the lamp  120  using the cooling fan  210  is exhausted from the exhaust vent  144 . In the normal operating condition, a temperature of a deflector and optical parts such as an image display element is lower by one figure than that of the lamp  120 . Accordingly, it is possible to employ the structure in which the cooling air that cooled a deflector and optical parts such as an image display element may be used to cool the lamp  120  using a duct or the like.  
         [0037]      FIGS. 5A and 5B  are longitudinal sectional views showing the structure of a light source device applied to a projector  1  according to a second embodiment of the present invention.  FIG. 5A  is a longitudinal sectional view showing the structure of a light source device, and  FIG. 5B  is an enlarged view showing an air direction changing plate  146  and its vicinity surrounded by the dotted line in  FIG. 5A . Reference numeral  830  denotes an arrow showing a direction and amount of cooling air, the number of arrows showing the amount of cooling air. Reference numeral  900  denotes an arrow showing light reflecting in the outermost periphery  134  of a reflector out of light emitted from a light emitting tube  121 .  
         [0038]     This embodiment is different from the first embodiment in that the air direction changing plate  146  is arranged to be inclined with respect to the optical axis, and that an elliptical surface reflector is used as a reflector.  
         [0039]     The method for taking outside air into the light source device shown in  FIGS. 5A and 5B  are similar to that of the first embodiment. However, the direction of the air direction changing plate  146  is changed so that the cooling air  830  introduced into the light source device flows in the direction and amount shown at arrow  830 . That is, cooling air is introduced into the inside portion  132  within the interior of the light source device in the amount greater than that into the outside portion  133  within the interior of the light source device, and than that in the first embodiment. With the structure of the present embodiment, a temperature of the light emitting tube  121  of the lamp  120  can be lowered more than that in the first embodiment.  
         [0040]     The following describes the shape of the reflector  130  and the location of the air direction changing plate  146  in the light source device shown in  FIG. 5 . The reflector  130  used in the present embodiment is formed in the shape of an elliptical surface, and the light emitting tube  121  of the lamp  120  is arranged approximately on a first focus of the elliptical surface. Further, the air direction changing plate  146  used in the present embodiment is arranged in consideration of less influence on light reflected from the reflector  130  and miniaturization of the projector. That is, one end close to the inside portion  132  internally of the light source device out of both the ends of the air direction changing plate  146  is arranged at a position in contact with arrow  900 ; the other is arranged at a position in contact with an approximately parallel straight line with respect to the optical axis from the outermost periphery  134  of the reflector similar to the first embodiment. As with the first embodiment, this structure minimizes deterioration of the usability of light emitted from the light source device, thereby enabling achieving higher brightness.  
         [0041]     In the present embodiment, the air direction changing plate  146  is arranged as described above; however, the end close to the interior of the light source device out of both the ends of the air direction changing plate  146  can be also arranged at a position in contact with arrow  900  and approximately parallel to the optical axis. With this arrangement, the air direction changing plate  146  comes close to a cover glass  141 , thus enlarging an area of a space formed by an intake vent  145  and the air direction changing plate  146 . Thus, the usability of cooling air taken in from the intake vent  145  can be enhanced as compared with the first embodiment.  
         [0042]      FIGS. 6A and 6B  are longitudinal sectional views showing the structure of a light source device applied to a projector  1  according to a third embodiment of the present invention.  FIG. 6A  is a longitudinal sectional view showing the structure of the light source device, and  FIG. 6B  is an enlarged view of an air direction changing plate  146  and its vicinity surrounded by the dotted line in  FIG. 6A . Reference numeral  930  denotes an arrow showing the direction and amount of cooling air, the amount of cooling air being shown by the number of arrows.  
         [0043]     In the first and second embodiments, the air direction changing plate  146  is welded or adhered to the mesh  150  under the metal portion of the connecting cylinder  142 . On the other hand, in the present embodiment, the air direction changing plate  146  is welded or adhered directly to the connecting cylinder  142 , so that it can firmly be fixed thereto. However, the method for welding or adhering the air direction changing plate  146  is not limited to the above method but welding or adhesion may be done as in the first and second embodiments.  
         [0044]      FIGS. 9A and 9B  show the shape of the air direction changing plate  146  used in the present embodiment,  FIG. 9A  showing a section of the air direction changing plate  146 , and  FIG. 9B  showing the front of the air direction changing plate  146 . The structure of the air direction changing plate of this embodiment is different from that of the air direction changing plate  146  of  FIG. 8  in the provision of a vent  147  therein. In the present embodiment, this vent  147  is of a circle with a diameter d  147  of 4 mm, for example, as shown in  FIG. 9B . The vent  147  is not limited to a circle but any shape may be employed. The size of the vent  147  is adjusted to optimize the amount of air flowing to the outside portion  133  within the interior of the light source device. Accordingly, cooling air introduced into the light source device flows in the direction and amount indicated at arrow  930 , and the cooling air can be introduced into the inside portion  132  within the interior of the light source device in the amount greater than that into the outside portion  133 .  
         [0045]      FIG. 10  is a general structure view of a projector according to a fourth embodiment of the present invention. The present embodiment employs the light source device used in the first embodiment by way of example. It is needless to say that the light source devices of the second and third embodiments may be used.  
         [0046]     In  FIG. 10 , reference numerals  316 R,  316 G and  316 B denote transmission type liquid crystal panels as image display elements associated with three primary colors R, G, and B, respectively. The liquid crystal panels form images by allowing light from the light source device to be subjected to light intensity modulation according to an image signal by use of an image signal drive circuit not shown. Reference numeral  301  denotes a group of lens arrays composed of two lens arrays;  302  a deflection conversion element for straightening the deflection direction;  303  a mirror;  304  a focusing lens;  305  and  308  dichroic mirrors for color separation;  310  a first relay lens;  312  a second relay lens;  314  a third relay lens;  306 ,  311  and  313  mirrors;  307  and  309  condenser lens;  315 R,  315 G and  315 B incoming side deflectors;  317 R,  317 G and  317 B outgoing side deflectors,  318  a color synthesizing cross prism;  319  a projection lens;  320  a screen;  330  a cooling fan;  340  a power source circuit; and  350  a direction of cooling air.  
         [0047]     Light emitted from the light source device is unified by the lens array group  301 , and projected on the liquid crystal panels  316 R,  316 G and  316 B. At this time, a projection image of one cell lens out of the lens array group  301  is superposed to each of the liquid crystal panel  316 R for red (R), the liquid crystal panel  316 G for green (G), and the liquid crystal panel  316 B for blue (B) by way of the focusing lens  304 , the condenser lenses  307 ,  309 , the first relay lens  310 , the second relay lens  312  and the third relay lens  314 .  
         [0048]     During the above process, light emitted from the light source device is separated into color lights of three primary colors R, G and B, which are incident on the associated liquid crystal panels  316 R,  316 G and  316 B, respectively. It is noted that the dichroic mirror has the red transmission, green and blue reflecting characteristic, and the dichroic mirror  308  has the green reflection, and blue transmission characteristic.  
         [0049]     The liquid crystal panels  316 R,  316 G and  316 B form optical images by allowing an image signal drive circuit not shown together with the incoming and outgoing deflectors  315 R,  315 G and  315 B to control the amount of light transmitting the liquid crystal panels to perform the light intensity modulation for changing grayscale for each pixel.  
         [0050]     Further, the optical images incident brightly on the liquid crystal panels  316 R,  316 G and  316 B are color-synthesized by the cross prism  318  and further projected on the screen  320  by the projection lens  319 , thus, providing a large screen image.  
         [0051]     Next, the method for cooling the interior of the projector will be described with reference to  FIG. 10 . First, the cooling fan  330  is rotated, whereby cooling air  350  is taken in from an intake vent (not shown) provided in the outer periphery of a casing of the projector, for example. In this case, when dust is mixed into an optical unit composed of a reflector, a liquid crystal panel and the like, image quality is deteriorated; therefore, a fine mesh filter is provided at an intake vent for taking in cooling air. The cooling air  350  taken in from the intake vent flows an air passage formed in order of the liquid crystal panel  316 , the incoming side deflector  315 , the outgoing side deflector  317 , the power source circuit  340 , and the interior of the light source device. Then, the cooling air passes through the cooling fan  330 , and is exhausted outside the projector from an exhaust vent (not shown) provided in the outer periphery of the casing of the projector. In this manner, these components are cooled in order of increasing heating temperatures. For example, where a light source device of 130 W is used, the liquid crystal panel  316 , the incoming side deflector  315  and the outgoing side deflector  317  are heated to about 60° C. to about 70° C., the power source circuit  340  to about 100° C., and the light emitting tube  121  to 1050° C. This enables the single cooling fan  330  to cool the interior of the optical unit and the interior of the light source device. In addition, in the above-described structure, an intake fan is further provided in the vicinity of the intake vent, thereby enhancing the cooling efficiency. Such cooling as described above reduces the number of the cooling fans  330  provided in the projector, so that the projector can be miniaturized.  
         [0052]     Alternatively, although not shown, a means, e.g., a wall, that is adapted to separate cooling air is disposed between a power source circuit  340  and an optical unit in order to independently cool the power source circuit  340  and the optical unit. Then, cooling air that cooled the power source circuit  340  and cooling air that cooled the optical unit may be joined so as to cool the interior of the light source device. With such cooling, both the cooling air that cooled the interior of the light source device and the interior of optical unit can be used, thereby enhancing the cooling efficiency.  
         [0053]     Alternatively, although not shown, only the cooling air that cooled the power source circuit  340  may be introduced into the light source device for cooling while the interior of the optical unit is cooled by another cooling structure. In cooling the power source circuit  340  and the interior of the light source device, even if dust should be mixed, this would not directly influence on image quality. Therefore, the filter provided in an intake vent for taking in cooling air may have a coarse mesh. Further, even if no filter is provided therein, no problem occurs. Accordingly, with the above structure, air resistance caused by a filter is so small that the ventilation property of cooling air for cooling the power source circuit  340  and the interior of the light source device is improved, thereby enhancing the cooling efficiency. Further, there is an advantage in that since cooling the interior of the optical unit does not depend on the structure for cooling the power source circuit  340  and the interior of the light source device, designing of the cooling structure suitable for the optical unit is facilitated.  
         [0054]     Furthermore, still alternatively, although not shown, the cooling air that cooled the interior of the optical unit may be introduced into the light source device while the power supply circuit  340  is cooled by another cooling structure. With such cooling, the cooling air that cooled the interior of the optical unit heated to as relatively low as about 60 to about 70° C. is used without using the cooling air that might have cooled the power supply circuit  340  heated to as high as about 100° C., thereby enhancing the cooling efficiency.  
         [0055]     While in the present embodiment, a description has been made of the case where the transmission type liquid panel is applied as an image display element, it is noted needless to say that the present invention can be also applied to image display elements such as a reflection type liquid crystal panel, a DMD (Digital Micromirror Device) panel and the like.