Abstract:
The present invention provides a projection apparatus utilizing plural light sources, in which the light source principally irradiating the light valve is switched by moving the relative position between the plural light sources and the mirror for guiding the lights outputted from such light source to the light valve. Also the configuration can be simplified by using commonly the light condensing device for the plural light sources.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a light valve projection apparatus for magnified projection of an image of a liquid crystal panel or a micromirror rocking pixel panel, and more particularly to a projection apparatus equipped, as the light source, with a light source of instantly light emitting type and that of high efficiency and high color presenting ability. The present invention is applicable to a projector of front projection type for direct projection onto a reflective screen, a projection of rear projection type for projection on a transmissive screen, or an apparatus in which either of the foregoing is combined with another equipment, utilizing a transmissive or reflective liquid crystal device or a micro mirror rocking pixel device.  
           [0003]    2. Related Background Art  
           [0004]    There are already commercialized apparatus for magnified projection of the image of a light valve panel such as a liquid crystal device, utilizing a light source such as a metal halide lamp.  
           [0005]    In such apparatus the light emitted from the light source is concentrated on a light valve panel for example through a mirror, and is projected through a projection lens onto a screen.  
           [0006]    The apparatus is known in various types such as a single panel type utilizing a liquid crystal panel, and a three-panel type in which three liquid crystal panels are illuminated by color separation through dichroic mirrors and the transmitted lights are color synthesized, and the liquid crystal panel of transmissive type is adopted for this purpose but that of reflective type is also utilized recently.  
           [0007]    Also instead of the liquid crystal panel, there has been developed a panel in which micromirrors are arrayed on a semiconductor chip as pixels and the micromirror of each pixel is driven in a rocking motion to control the gradation, and such panel is also utilized in a single panel type utilizing color-sequential light sources and a three-panel type in which three panels are illuminated by color separation through dichroic mirrors and the reflected lights are color synthesized.  
           [0008]    The illumination for such projector is required to be of a high illumination intensity in order that the projected image can be viewed on a large screen even in a well lighted room, and, for this reason, the light source is principally composed of a metal halide lamp or a high pressure mercury lamp of high efficiency and high color presenting ability.  
           [0009]    [0009]FIG. 11 shows an example of the configuration of a conventional liquid crystal projector of three panel type.  
           [0010]    In FIG. 11, there are shown a metal halide lamp  1   a  which is a discharge tube, a reflector  1   b  formed in an elliptic or parabolic surface, an electrode  1   c  of the metal halide lamp  1   a , a first fly&#39;s eye lens  7 , dichroic mirrors  8 ,  9 , mirrors  10 ,  11 ,  12 , a cross dichroic prism  13 , a projection lens  14 , a red-color transmissive liquid crystal panel  15 , a green-color transmissive liquid crystal panel  16 , a blue-color transmissive liquid crystal panel  17 , an optical system shielding case  18 , and an external casing  100  containing the entire projection system.  
           [0011]    When a power switch of the apparatus shown in FIG. 11 is turned on, the metal halide lamp  1   a  is energized and starts lighting.  
           [0012]    Then the light emitted from the metal halide lamp  1   a  is converted into a relatively parallel illuminating light by the reflector  1   b  and enters the fly&#39;s eye lens  5 .  
           [0013]    The fly&#39;s eye lens  5  has a composite structure of plural lenses and has an effect, in combination with a fly&#39;s eye lens  7 , of flattening the luminance on an irradiated surface at the rear.  
           [0014]    A mirror  6  bends the optical path of the illuminating light from the fly&#39;s eye lens  5  by 90° for entry into the fly&#39;s eye lens  7 .  
           [0015]    The mirror  6  is provided with a dichroic film for transmitting infrared and ultraviolet light, thereby reducing the infrared and ultraviolet componets in the visible light entering the fly&#39; eye lens  7  and thus reducing heat generation and improving reliability.  
           [0016]    The visible light emerging from the fly&#39;s eye lens  7  enters a dichroic mirror  8  through which blue light is transmitted, then bent in the optical path by a mirror  10  and enters a transmissive liquid crystal panel  17  for blue color.  
           [0017]    On the other hand, in the dichroic mirror  8 , the light of green and red colors, having a wavelength longer than that of blue color, is reflected and enters a dichroic mirror  9 .  
           [0018]    The dichroic mirror  9  has a property of reflecting green light and illuminates a transmissive liquid crystal panel  16  for green color.  
           [0019]    In the dichroic mirror  9 , the light red color, having a wavelength longer than that of the green color, is reflected, then bent in the optical path by mirrors  11 ,  12  and illuminates a transmissive liquid crystal panel  15  for red color.  
           [0020]    The aforementioned liquid crystal panels  15 ,  16 ,  17  respectively for red, green and blue colors receive unrepresented drive signals for the respective colors to display an image in the display area of each panel, thereby optically modulating the illuminating light mentioned above.  
           [0021]    The image displayed on the green liquid crystal panel  16  is being vertically inverted (FIG. 11 being a plan view) electrically or by reversing the front and back surfaces of the panel with respect to the images displayed on the liquid crystal panels  15 ,  17  for other colors, in consideration of the process of image synthesis in a dichroic mirror  13 .  
           [0022]    The image lights from the transmissive liquid crystal panels  15 ,  16 ,  17  for the red, green and blue colors enter a cross dichroic prism  13  respectively from predetermined directions as illustrated, thus being synthesized and emerging as a color image from an illustrated fourth face and enters a projection lens  14  for magnified projection onto a screen.  
           [0023]    Also a configuration employing two light sources is disclosed in the Japanese Utility Model Application Laid-open No. 4-33034 and the Japanese Patent Application Laid-open No. 9-127467.  
         SUMMARY OF THE INVENTION  
         [0024]    An object of the present invention is to provide a preferred configuration employing plural light sources in a projection apparatus.  
           [0025]    If the light source of a projection apparatus of liquid crystal panel type or micromirror rocking pixel panel type is composed of a discharge lamp of high efficiency and high color presenting ability such as a metal halide lamp or a high pressure mercury lamp, there is required a time of at least 2 to 3 minutes until such illuminating lamp reaches a predetermind light amount after the power supply is turned on.  
           [0026]    Also in case of recovery from an instantaneous interruption of the power supply for certain reason, there is required an even longer time (3 to 5 minutes) before the lamp can be turned on again. Thus, there is encountered a serious drawback that the image cannot be projected during such period, particularly in applications requiring urgency, such as important presentations or conferences.  
           [0027]    In such situation, the presence of plural light sources may be advantageous for illuminating the light valve. The present invention is to provide, in case of employing plural light sources, a configuration capable of efficiently illuminating the light valve or a configuration enabling simplification even in case of using plural light sources.  
           [0028]    According to one of the inventions of the present application, there is provided a projection apparatus provided with a light valve which modulates light by two-dimensionally arranged plural pixels and projects thus modulated light, the apparatus comprising:  
           [0029]    a first light source;  
           [0030]    a second light source;  
           [0031]    a mirror for guiding the light from the first light source or the light from the second light source; and  
           [0032]    a movable mechanism for varying the relative position the mirror and the first and second light sources.  
           [0033]    In such configuration, owing to the presence of the movable mechanism for changing the relative position between the mirror and the light sources, there can be switched a state in which the first light source principally irradiates the light valvue and a state in which the second light source principally irradiates the light valve by varying the relative position between the mirror and the light sources.  
           [0034]    In this manner there can be dispensed with a half mirror to be provided on the optical paths of the output lights from the separately provided light sources for using such optical paths partly in common.  
           [0035]    For varying the relative position between the mirror and the light sources, there can be advantageously employed a configuration for moving the position of the mirror or a configuration for moving the position of the light sources.  
           [0036]    According to another of the inventions of the present application, there is provided a projection apparatus provided with a light valve which modulates light by two-dimensionally arranged plural pixels and projects thus modulated light, the apparatus comprising:  
           [0037]    a first light source;  
           [0038]    a second light source; and  
           [0039]    a reflector for condensing the light from the first light source and the light from the second light source;  
           [0040]    wherein the first and second light sources are positioned in the vicinity of the focal point of the reflector.  
           [0041]    This invention allows to extremely simplify the structure of the light source portion, and there can be advantageously employed a configuration in which the first light source and the second light source have different light emitting characteristics (particularly change in the light amount with the lapse of time after the power supply is turned on).  
           [0042]    Also in this invention, there can be employed a configuration in which the first light source includes light regulating means for regulating the light amount irradiating the light valve. For such light regulating means, there can be advantageously employed a control circuit for regulating the amount of the output light of the first light source.  
           [0043]    There is also advantageously employed a configuration in which the light amount of the first light source irradiating the light valve is gradually decreased within a period after the power supply to the second light source is turned on and until the second light source reaches the stably turned-on state.  
           [0044]    There can be reduced the unpleasant feeling on the observed image by such control that the sum of the light amount irradiating the light valve by the first light source and that irradiating the light valve by the second light source approaches a constant value. For such control, there can be employed a control circuit for regulating the amount of the output light of the first light source.  
           [0045]    For realizing such light regulation, there can be adopted a configuration for regulating the light according to correction data, based on the change of the light amount of the second light source as a function of the lapse of time from the start of light emission. The light regulation in such case can be realized with the lapse of time. A timer may be used for realizing the light regulation according to the lapse of time. Also there may be employed a configuration of executing the aforementioned light regulation based on the result of detecting the amount of light irradiating the light valve.  
           [0046]    The aforementioned inventions can be advantageously adopted in case the two light sources have different characteristics, but can more advantageously be employed particularly in case the first light source has a period from the turning-on of the power supply to the stable lighting state shorter than that of the second light source. The period from the turning-on of the power supply to the stable lighting state means a period from the timing of turning-on of the power supply to the timing where the light amount reaches 90% of the light amount at a timing after the lapse of sufficient time from the turning-on of the power supply (namely a stationary light emitting state). It is particularly preferable if the period from the turning-on of the power supply to the stable lighting state in the first light source is shorter by at least 15 seconds than that in the second light source.  
           [0047]    Also in the aforementioned inventions, there can be advantageously adopted a configuration having a timer for controlling the irradiation of the light valve by the light from the first light source, or a configuration having a light amount sensor for controlling the irradiation of the light valve by the light from the first light source. For example, the light amount irradiating the light valve by the light from the first light source can be controlled according to the output value of the sensor for detecting the output light amount of the second light source.  
           [0048]    Also in the aforementioned inventions, there is preferably provided stopping means for stopping the light emission of the second light source for a predetermined period. In this manner, after an interruption of the power supply, the light emission of the second light source can be stopped for the predetermined period. In such case the light valve can be irradiated by the light from the first light source.  
           [0049]    The aforementioned first light source can be composed of a xenon-based lamp, a halogen light bulb, a tungsten light bulb, a fluorescent lamp, a light emitting diode or an electron source-based light source, and the second light source can be advantageously composed of a metal halide lamp or a mercury-sealed discharge lamp.  
           [0050]    Also in the aforementioned inventions, there is preferably adopted a configuration utilizing, as a filter for filtering the light irradiating the light valve, an optical filter to be employed either of a period in which the light valve is principally irradiated by the first light source and a period in which the light valve is principally irradiated by the second light source.  
           [0051]    Also in the aforementioned inventions, there is preferably adopted a configuration having a circuit which executes different operations on the image signal for driving the light valve, respectively in a period in which the light valve is principally irradiated by the first light source and in a period in which the light valve is principally irradiated by the second light source. The aforementioned operation on the image signal can be, for example, an operation of adjusting the contrast, brightness or gamma characteristics of the image. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0052]    [0052]FIG. 1 is a plan view showing the optical layout of a projector in a liquid crystal projection apparatus constituting a first embodiment of the present invention;  
         [0053]    [0053]FIG. 2 is a view showing the structure of a metal halide lamp embodying the present invention;  
         [0054]    [0054]FIG. 3 is a view showing the structure of a halogen lamp unit embodying the present invention;  
         [0055]    [0055]FIG. 4 is a block diagram of a circuit embodying the present invention;  
         [0056]    [0056]FIG. 5 is a flow chart showing the lamp lighting control in a first embodiment of the present invention;  
         [0057]    [0057]FIG. 6 is a flow chart showing the lamp re-lighting control in a first embodiment of the present invention;  
         [0058]    [0058]FIGS. 7A and 7B are respectively a lateral view and an elevation view of a composite lamp unit in the first embodiment of the present invention;  
         [0059]    [0059]FIG. 8 is a plan view showing the optical layout of a projector in a liquid crystal projection apparatus constituting a second embodiment of the present invention;  
         [0060]    [0060]FIGS. 9 and 10 are flow charts showing the function of a projection apparatus in second and third embodiments of the present invention; and  
         [0061]    [0061]FIG. 11 is a view showing the configuration of a conventional projection apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0062]    &lt;First embodiment&gt; 
         [0063]    In the following there will be described a projection apparatus provided with a light source and a projector for illuminating a light valve having a two-dimensional array of plural pixels with the light from the light source thereby projecting the image of the light valve onto a screen, the apparatus comprising a first light source capable of instantaneous lighting, a second light source of high efficiency and high color presenting characteristics, and furthe comprising light source switching means and lighting order control means for the light sources for instantaneously projecting the image by the light source of faster lighting speed at the turning-on of power supply of the apparatus and, when the light source of high efficiency and stable lighting which is limited in the lighting speed is stably lighted, switching the optical path to the latter light source and at the same time turning off the aforementioned light source of faster light speed thereby projecting the image with high efficiency and high color presentation utilizing the latter light source for illumination. FIG. 1, best representing the feature of the present embodiment, is a plan view showing the internal structure of a projector system in the projection apparatus of the present embodiment, wherein shown are a metal halide lamp  1   a  which is a discharge lamp constituting illumination means of a relatively long time (t=B) from the turning-on of the power supply to the stable lighting state, a reflection mirror  1   b  of an elliptical or parabolic shape, an electrode  1   c  of the metal halide lamp  1   a , a halogen lamop constituting illumination means of a relatively short time (t=A) from the turning-on of the power supply to the stable lighting state, a reflection mirror  2   b  of an elliptical or parabolic shape, an electrode  1   c  of the halong lamp  2   a , a movable mirror  3  (a and b), a shutter  4  (c and d), a first fly&#39;s eye lens  5 , a mirror  6 , a second fly&#39;s eye lens  7 , dichroic mirrors  8 ,  9 , mirrors  10 ,  11 ,  12 , a cross dichroic prism  13 , a projection lens  14 , a transmissive liquid crystal panel  15  for red color, a transmissive liquid crystal panel  16  for green color, and a transmissive liquid crystal panel  17  for blue color.  
         [0064]    There are also shown an optical system shielding case  18 , a timing belt  19   a , a connection member  19   b  for connecting the timing belt  19   a  and the movable mirror  3 , a fixing member  19   c  for connecting the timing belt  19   a  and the shutter  4 , timing belt driving pulleys  20   a ,  20   b ,  20   c , a timing belt driving pulley  20   d  linked with a gear, a gear  20   e  engaging with the pulley  20   d  and having a diameter larger than that of the pulley  20   d , a link gear  20   f  meshing with the gear  20   e , a driving motor  21  coaxially connected with the gear  20   f , and an outer casing  100  containing the entire projection system.  
         [0065]    [0065]FIG. 4 is a view showing the electrical configuration of the present embodiment, wherein shown are a red color signal input terminal  101 , a green color signal input terminal  102 , a blue color signal input terminal  103 , a signal processing circuit block  104 , a metal halide lamp lighting circuit  105 , a halogen lamp lighting circuit  106 , a power source circuit  107  for the entire system, a microcomputer  108  constituting control means for controlling the present system, an electric motor drive circuit  109 , a motor  21  for driving the timing belt  19   a , switches  111 ,  112  constituting position sensors for detecting the position of the timing belt  19   a , the shutter  4  or the mirror  3 , and a power supply terminal  110  of the projection apparatus of the present embodiment.  
         [0066]    [0066]FIG. 5 is a flow chart showing the internal control sequence at the start or termination of the function of the projector, and FIG. 6 is a flow chart showing the internal control sequence in an instantaneous interruption process of the projector.  
         [0067]    [0067]FIG. 2 shows the structure of the metal halide lamp unit in the projection system of the present embodiment shown in FIG. 1. The metal halide lamp  1   a  is fixed approximately at the focal point of a reflector  1   b  of an elliptical or parabolic surface, and the electrode  1   c  of the metal halide lamp  1   a  is guided through a small hole provided on the optical axis of the reflector  1   b  opposite to the projecting direction thereof.  
         [0068]    Another electrode, though not shown, consists of a metal wire  1   e  penetrating through the reflector  1   b  in a position on the external periphery thereof and relatively distant from the electrode  1   c  of the metal halide lamp  1   a , and is connected by an insulated wire to the metal halide lamp lighting circuit  105  shown in FIG. 4.  
         [0069]    Also FIG. 3 shows the structure of the halogen lamp unit of the present embodiment. The halogen lamp  2   a  is fixed approximately at the focal point of a reflector  1   b  of an elliptical or parabolic surface, and the electrode  2   c  is extracted to the rear through a relatively small hole provided on the rear part of the optical axis of the reflector  2   b  having an elliptical or parabolic surface, and is connected by an insulated wire to the halogen lamp lighting circuit  106  shown in FIG. 4.  
         [0070]    In the following there will be explained, with reference to a flow chart shown in FIG. 5, the function of the projection apparatus of the present embodiment from a state immediately after an operation switch for shifting to a projection state is turned on (such state being hereinafter called initial state) from a state in which the power supply of the projection apparatus is not turned on or from a stand-by state in which the master power supply is turned on.  
         [0071]    The temperature rise resulting from the heat generation for example by the light sources in the main body is maintained within a safe range by a cooling fan or the like provided in the main body though such colling means will not be explained in detail.  
         [0072]    Referring to the flow chart shown in FIG. 5, immediately after the power supply is turned on or the operation switch for shifting to the projection mode is turned on from a stand-by state in which the master power supply is already turned on in a step S 1 , there is executed initial setting for the microcomputer (step S 2 ) to turn on the halogen lamp  2   a  (step S 3 ). The metal halide lamp  1   a  is also similarly turned on (step S 5 ).  
         [0073]    The halogen lamp  2   a  and the metal halide lamp  1   a  have the following start-up characteristics of the illumination intensity immediately after the start of lighting. The halogen lamp  2   a  has a sufficient intensity from immediately after the start of lighting (in general reaching 90% of the final intensity in about 300 msec), and maintains stable light emission thereafter. Consequently a step S 4  executes activation of the signal processing circuit and output of image, utilizing the halogen lamp  2   a  as the light source.  
         [0074]    On the other hand, in the metal halide lamp  1   a , though the light amount gradually increases, the mercury vapor pressure in the lamp starts to rise at about 20 seconds from the start of lighting, whereupon the lamp voltage starts to increase rapidly and approximately reaches the rated voltage after 2 to 3 minutes. The time required for stabilization of the lamp fluctuates depending on the state of external forced air cooling in the course of start-up of the lamp, presence or absence of the reflector and the glass plate in front of the lamp.  
         [0075]    Until the lamp becomes stabilized, the lighting circuit  105  executes current control by monitoring the lamp voltage. Consequently the start-up state of the light amount is approximately linked with the behavior of the lamp voltage. Stated differently, there is at least required 2 to 3 minutes until the light amount becomes stabilized.  
         [0076]    Also cooling is executed with a cooling fan or the like, though such cooling means is not illustrated, in order to avoid temperature rise of the apparatus resulting from the heat generated by the aforementioned light sources etc.  
         [0077]    In the aforementioned initial state, the mirror  3  is provided in a position  3 ( a ) that reflects the light from the halogen lamp  2   a  onto the fly&#39;s eye lens  5 .  
         [0078]    Also the shutter  4  is provided in a position  4 ( c ) that intercepts the light beam from the metal halide lamp  1   a.    
         [0079]    The mirror  3  is mechanically linked, at an upper portion (outside the optical path) thereof, to the timing belt  19   a  by the coupling member  19   b , and the shutter  4  is mechanically linked, at an upper portion (outside the optical path) thereof, to a position  4 ( c ) of the timing belt  19   a  by the coupling member  19   c.    
         [0080]    The running path of the timing belt  19   a  is determined as shown in FIG. 1 by the four pulleys  20   a ,  20   b ,  20   c ,  20   d.    
         [0081]    The pulley  20   d  is coaxially linked with the gear  20   e  which is larger than the pulley  20   d , and the gear  20   e  engages, at a point on the external periphery thereof, with a gear  20   f  whereby the pulley  20   d  is rotated at a reduced speed by the motor  21  and the timing belt  19   a  is conveyed with a sufficient torque.  
         [0082]    The stopping positions of the mirror  3  and the shutter  4  are determined by unrepresented detection means. Such detection can be achieved by forming projections on a part of the mirror  3  and the shutter  4  or forming a projection or an optical marking on the timing belt  19   a  and detecting such projections or optical marking optically by photointerruptors or mechanically microswitches, or forming electric conductors as projections on a part of the mirror  3  and the shutter  4  or on a part of the timing belt  19   a  and detecting such conductors by electric conduction by contactor members. Also magnetic detection is possible. In the present embodiment, the positions of the mirror  3  and the shutter  4  are controlled, as shown in FIG. 4, by detection with detection switching  111 ,  112  connected to two input ports of the microcomputer  108 , which, through a programmed process, drives the motor  21  by the motor drive circuit  109 , thereby controlling the rotation and the moving direction of the timing belt  19   a.    
         [0083]    Consequently, in the aforementioned initial state, the light from the halogen lamp  2   a  enters, through the mirror  3   a , the first fly&#39;s eye lens  5 . The light transmitted by the fly&#39;s eye lens  5  enters, through the mirror  6 , the second fly&#39;s eye lens  7 , and the light entering the second fly&#39;s eye lens  7  irradiates the dichroic mirror  8 .  
         [0084]    The dichroic mirror  8  is set at such angle that the transmitted light has a blue wavelength, and the light of blue color is deflected in the direction by the mirror  10  and irradiates the liquid crystal panel  17 .  
         [0085]    On the other hand, the green and red lights are reflected by the dichroic mirror  8  and, with the deflection of the optical path by 90°, enters the dichroic mirror  9 .  
         [0086]    The dichroic mirror  9  reflects the green light, which then illuminates the liquid crystal panel  16 .  
         [0087]    Also the dichroic mirror  9  transmits the red light, which, after deflections of the direction of the optical path by the mirrors  11 ,  12 , illuminates the liquid crystal panel  15 .  
         [0088]    The liquid crystal panel  15  displays an image of the red component by a red color signal processing circuit, while the liquid crystal panel  16  displays an image of the green component by a green color signal processing circuit, and the liquid crystal panel  17  displays an image of the blue component by a blue color signal processing circuit. Such electrical configuration is shown in the block diagram in FIG. 4.  
         [0089]    Referring to FIG. 1, the liquid crystal panels  15 ,  16 ,  17  are principally composed of transmissive active matrix liquid crystal panels based on polysilicon TFT&#39;s and having a size of 0.9 to 1.8 inches.  
         [0090]    The blue, green and red images emerging from the liquid crystal panels  15 ,  16 ,  17  enter the cross dichroic prism  13  from respective sides and are synthesized therein, whereby a color image is projected by the projection lens  14  in magnified manner onto the screen. The directions of the images displayed on the liquid crystal panels  15 ,  16 ,  17  are same as those in the conventional configuration explained in the foregoing.  
         [0091]    Then, when the light amount of the metal halide lamp  1   a , after the start of lighting thereof in the step S 5  of FIG. 5, gradually increases and approximately reaches the lighting state of stable light amount after the start-up time of about 2 to 3 minutes, a step S 6  discriminates whether the light amount from the metal halide lamp  1   a  is sufficient. If sufficient, a step S 7  moves the mirror  3  and the shutter  4  to positions of a metal halide lamp mode. More specifically, the motor  21  is activated to convey the timing belt  19   a  in a direction a by the pulleys  20   f ,  20   e ,  20   d  constituting the mechanical transmission system, whereby the mirror  3  reaches a position  3 ( b ).  
         [0092]    On the other hand, the shutter  4  linked also to the timing belt  19   a  is moved in the same rotating direction to a position  4 ( d ). The timing belt  19   a , or the shutter  4 , mirror  3  and rotating mechanism  20  ( 20   a  to  20   f ) are linked with the unrepresented position detecting sensors as explained in the foregoing, and the result of detection is fed back to the microcomputer  108  (FIG. 4) which, through a programmed process, drives the motor  21  by the motor drive circuit  109  to control the rotation and the rotating direction of the timing belt  19   a  thereby controlling the positions of the mirror  3  and the shutter  4  and stopping them at the predetermined positions. Then a step S 8  discriminates whether the movement of the shutter  4  and the mirror  3  has been completed.  
         [0093]    In this manner the light emitted from the metal halide lamp  1   a , which is a discharge lamp, enters the fly&#39;s eye lens  5  through the mirror  3 .  
         [0094]    The optical path after the fly&#39;s eye lens  5  is same as explained in the foregoing, and the light is projected by the projection lens  14  onto the screen.  
         [0095]    At the same time, the light from the halogen lamp  2  is intercepted by the shutter  4  and the halogen lamp is turned off by the light source control circuit  106  after an arbitrary safety time (step  9 ), and the projection thereafter is executed by the metal halide lamp  1   a  as the light source to achieve stable image projection with high efficiency and high color presentation.  
         [0096]    Referring to FIG. 5, a process of tereminating the function of the apparatus is executed by a stop switch control (step S 10 ), stopping of the metal halide lamp  1   a  (step S 11 ), stopping of the signal processing circuit  104  (step S 12 ), returning of the shutter  4  and the mirror  3  to the initial positions (step S 13 ), stopping of fan cooling (step S 14 ), stopping of standby lamp  8  step S 15 ), and warming-up of the microcomputer  108  (step S 16 ).  
         [0097]    In case an instantaneous interruption of the power supply occurs in the stable projection state with high efficiency and high color presentation after the switching of the light source from the halogen lamp  2   a  to the metal halide lamp  1   a , a step S 21  in a flow chart shown in FIG. 6 detects the instantaneous interruption of power supply, then a step S 22  executes a process of turning on the power supply again, and, when the power supply is restored, the unrepresented cooling fan is activated to maintain the interior at a predetermined temperature. Then, after the power turning-on/start control of the step S 1  and the microcomputer initial setting in the step S 2  as shown in FIG. 5, a step S 23  causes the motor  21  to convey the timing belt  19   a  through the gear  20   f , the large gear  20   e  and the pulley  20   d  of the power transmission system thereby returning the shutter  4  and the mirror  3  respectively to the aforementioned positions  4 ( c ) and  3 ( a ).  
         [0098]    Also the halogen lamp  2   a  is immediately turned on (step S 3 ). The light from the halogen lamp  2   a  irradiates the fly&#39;s eye lens  5  to project the image onto the screen (step S 4 ).  
         [0099]    The metal halide lamp  1   a  is subjected to a metal halide lamp re-lighting process. When a step S 24  identifies the re-lighting of the metal halide lamp, a step S 25  suspends the re-lighting of the metal halide lamp  1   a  during a re-lighting prohibition time determined by a timer. The re-lighting prohibition time in the step S 25  is for restoring the reliability of the metal halide lamp, and is in general  2  to several minutes.  
         [0100]    Through the above-described process, the projection apparatus of the present embodiment, when the power supply is restored after instantaneous interruption thereof is immediately capable of image projection without being restricted by the aforementioned re-lighting prohibition time of the metal halide lamp  1   a.    
         [0101]    After the lapse of the re-lighting prohibition time of the metal halide lamp  1   a , the metal halide lamp  1   a  is turned on again (step S 5 ), and there is discriminated whether the light amount of the metal halide lamp  1   a  has reached a predetermined value (step S 6 ). When the predetermined light amount is reached, as in the aforementioned sequence in the initial lighting process, a step S 7  causes the motor  21  to convey the timing belt  19   a  through the gear  20   f , the large gear  20   e  and the pulley  20   d  of the power transmission system thereby moving the shutter  4  to the position  4 ( c ) and the mirror  6  to the position  4 ( d ). Then, when a step S 8  confirms the completion of the movement, a step S 9  utilizes the light from the metal halide lamp  1   a  for illumination through the fly&#39;s eye lens  5 , thereby restoring the image projection with high efficiency and high color presentation.  
         [0102]    In the foregoing embodiment, the lamp having a longer time from the start of lighting to the stable lighting state can be composed of a discharge lamp which is not limited to the metal halide lamp  1   a  explained in the foregoing but can also be a lamp containing mercury-based gas such as a high pressure mercury lamp.  
         [0103]    Also the light source capable of providing a stable light amount immediately after the start of lighting is not limited to the halogen lamp  2   a , but can also be composed of an incandescent lamp such as tungsten bulb, a xenon discharge lamp containing xenon gas, a fluorescent lamp, a light emitting diode, a fluorescent display tube or an electron source-type light source.  
         [0104]    It is also possible to dispense with the shutter  4  and to guide the light, transmitted by the mirror  3  without reflection thereon, directly to the optical system shielding case  18  or the like. In such case, the optical system shielding case  18  is preferably provided with surface treatment such as of black color, in order to reduce light reflection. Also heat dissipation is preferably considered for the optical system shielding case  18  in order to avoid temperature rise thereof resulting from the light irradiation.  
         [0105]    Also instead of switching the two light sources by moving the mirror  3 , similar effects can be obtained by fixing the mirror  3  and the subsequent optical path and moving the halogen lamp  2   a  and the metal halide lamp  1   a.    
         [0106]    As explained in the foregoing, the configuration of employing the halogen lamp  2   a  as the light source within the period required for the stabilization of the light amount of the discharge lamp such as the metal halide lamp  1   a  enables image projection immediately after the turning-on of the power supply to the main apparatus or after the start operation from the stand-by state. Also the image projection can be promptly restored after the instantaneous interruption of the power supply.  
         [0107]    &lt;Second embodiment&gt; 
         [0108]    In the foregoing first embodiment, the light sources are switched by the mirror and the shutter. On the other hand, the projection apparatus constituting a second embodiment of the present invention has a configuration shown in FIGS. 4 and 8, in which the metal halide lamp  1   a  constituted by a discharge lamp and the halogen lamp  2   a  are positioned side by side and are fixed in an approximate focal point of a reflector id having a common elliptical or parabolic surface, and the respective electrodes  1   c ,  2   c  are extracted through the reflector  1   d  and are respectively connected to the lighting circuits  105 ,  106  shown in FIG. 4.  
         [0109]    The metal halide lamp  1   a  and the halogen lamp  2   a  mounted on the common reflector  1   d  and the respective terminals will be hereinafter called a composite lamp unit  201 , of which external view is shown in FIG. 7.  
         [0110]    In the following there will be explained the function of the projection apparatus of the second embodiment, of which principal structure is shown in FIG. 8. In FIG. 8, the light from the composite lamp unit  201  enters the fly&#39;s eye lens  5  through the mirror  3 , and the optical path thereafter is same as in the foregoing first embodiment.  
         [0111]    In the following there will be explained, with reference to a flow chart shown in FIG. 9, the function of the projection apparatus of the present embodiment after the turning-on of the power supply. At first, immediately after the power supply is turned on or the operation switch for shifting to the projection mode is turned on from a stand-by state in which the master power supply is already turned on in a step S 1 , there is executed initial setting for the microcomputer (step S 2 ) to turn on the halogen lamp  2   a  (step S 3 ). The metal halide lamp  1   a  is also similarly turned on.  
         [0112]    The start-up characteristics of the illumination intensity of the two lamps immediately after the start of lighting is, as explained in the foregoing, such that the halogen lamp  2   a  has a sufficient intensity from immediately after the start of lighting (in general reaching 90% of the final intensity in about 300 msec), and maintains stable light emission thereafter. Consequently a step S 4  executes activation of the signal processing circuit thereby achieving image output.  
         [0113]    On the other hand, as explained in the foregoing, the metal halide lamp  1   a  gradually increases the light amount and reaches the final light amount level in about 2 to 3 minutes (step S 5 ). If a step S 6  identifies that the light amount of the metal halide lamp  1   a  is sufficient, a step S 9  turns off the halogen lamp  2   a.    
         [0114]    The reflector  1   d  collectively condenses both lights for entry into the fly&#39;s eye lens  5  whereby the image projection is thereafter achieved in the same manner as in the first embodiment, and, corresponding to the gradual increase in the light amount of the metal halide lamp  1   a , the halogen lamp lighting circuit  106  attenuates the light amount of the halogen lamp  2   a  in time, thereby always maintaining the illuminating light at a constant amount.  
         [0115]    In such case, the microcomputer  108  shown in FIG. 4 controls the halogen lamp lighting circuit  106  thereby gradually attenuating the light amount thereof, based on the data for correcting the light amount increase of the metal halide lamp  1   a.    
         [0116]    More specifically, the electric power loss can be reduced if a chopper control is executed in the halogen lamp lighting circuit  106 .  
         [0117]    The control of the halogen lamp lighting circuit  106  by the microcomputer  108  may also be achieved by parallel control with a digital signal, serial control with a digital signal, or by an analog voltage control by providing the microcomputer  108  with a D/A converter and a port for pulse width modulation (PWM) output. In such case the halogen lamp lighting circuit  106  controls the output voltage by converting the control data from the microcomputer  108  for example into a pulse width thereby controlling the chopper time.  
         [0118]    Referring to FIG. 9, a process of tereminating the function of the apparatus is executed by a stop switch control (step S 10 ), stopping of the metal halide lamp  1   a  (step S 11 ), stopping of the signal processing circuit  104  (step S 12 ), termination of fan cooling (step S 14 ) and stopping of the main lower supply (step S 17 ).  
         [0119]    &lt;Third embodiment&gt; 
         [0120]    In the foregoing second embodiment, the light amount can be further stabilized by providing a light amount sensor in the optical path as shown in FIG. 8, and causing the microcomputer to so control the halogen lamp lighting circuit as to obtain a constant light amount.  
         [0121]    A light amount sensor  200  is provided in a position close to the lower edge of the image area of the liquid crystal panel  16  shown in FIG. 8, and a signal obtained therein is subjected to suitable signal processing such as integration for accommodating external perturbations such as noises and fed back to the microcomputer  108  for digitization by an A/D converter provided therein, whereby the aforementioned halogen lamp lighting circuit  106  is controlled by a sequence for example shown in FIG. 10.  
         [0122]    In FIG. 10, the steps S 1  to S 5  at the turning-on of the power supply are same as those shown in FIG. 9. Thereafter a step S 31  detects the level detection by the light amount sensor, and a step S 32  discriminates whether the light amount is larger than a predetermined value A, and, if larger, a step S 33  decreases the halogen lamp control voltage by a step. Also if a step S 34  discriminates that the halogen lamp drive voltage is smaller than a predetermined voltage B, a step S 9  turns off the halogen lamp whereupon the operation is terminated.  
         [0123]    In such configuration, the light amount sensor can be practically composed of a phototransistor, a photodiode, a solar cell or a CdS sensor.  
         [0124]    Also in such configuration, the light amount of the halogen lamp can be regulated by the voltage, but, since the halogen lamp may be deteriorated at about 50% or lower of the rated voltage, it is necessary to turn off the halogen lamp  2   a  at an even lower driving voltage.  
         [0125]    It is also necessary to pay attention to the light regulating range, even for the light source with faster start-up characteristics.  
         [0126]    Also in the foregoing first embodiment, instead of switching the lamps based on the lighting time from the start of lighting of the metal halide lamp, measured by the microcomputer or the like, it is possible to further improve the precision by switching the lamps upon detection of the predetermined light intensity by a similar light amount sensor. The light amount sensor in such configuration is not illustrated but is preferably provided in a part of the optical path of the metal halide lamp.  
         [0127]    &lt;Fourth embodiment&gt; 
         [0128]    In the foregoing first to third embodiments in which the metal halide lamp  1   a  constituting the first light source and the halogen lamp  2   a  constituting the second light source are switched, the halogen lamp  2   a  generally has a lower color temperature in comparison with the metal halide lamp  1   a.    
         [0129]    Consequently, in a projection apparatus of the present embodiment, a trimming filter is inserted between the halogen lamp  2  and the optical path switching means in order to improve the color temperature, thereby suppressing the fluctuation in the color temperature.  
         [0130]    &lt;Fifth embodiment&gt; 
         [0131]    In addition to the optical improvement in the color temperature explained above, there is provided means for varying the balance of the levels, setups (brightness levels) and gamma corrections of the three color signals of red, blue and green in the signal processing circuits in linkage with the switching control of the light sources, thereby suppressing the fluctuation in the color temperature.  
         [0132]    It is rendered possible to avoid the extreme fluctuation in the color temperature at the switching of the light source, by causing the signal processing circuit  104  shown in FIG. 4 to control the balance of the levels, setups (brightness levels) and gamma corrections of the three color signals of red, blue and green in linkage with the switching control of the light sources.  
         [0133]    The the projection apparatus of the foregoing embodiments, employing the light sources of two kinds, can project an image of practical brightness even immediately after the turning-on of the power supply, and provide a projection image of high efficiency and high color presentation in stepwise manner with the start-up of the light sources. Also the image projection state can be immediately restored in case of an instantaneous interruption of the power supply.  
         [0134]    As explained in the foregoing, the inventions of the present application can provide an advantageous projection apparatus utilizing plural light sources.