Abstract:
A laser light source module includes a plurality of unit laser light source modules, each of which emits laser light of one specific color, and when the laser light source module includes unit laser light source modules of at least two colors, and each unit laser light source module has a median of a temperature range in which a practical luminance is obtained, the unit laser light source modules are thermally connected to an evaporator and arrayed in descending sequence of their values of the median from an upstream side in a direction in which a refrigerant flows.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a light source apparatus and a projection-type image display apparatus including the light source apparatus. 
       BACKGROUND ART 
       [0002]    Hitherto, there have been known projection-type image display apparatus including a light source, an optical modulator configured to modulate light emitted from the light source, and a projection unit configured to project, on a projection surface, the light being modulated by the optical modulator. 
         [0003]    In many cases, the related-art projection-type image display apparatus employ a lamp as a light source configured to generate light of three primary colors, and are configured to separate white light, which is emitted from the lamp, with a dichroic mirror into three primary colors: red (R), green (G), and blue (B), modulate the three primary colors based on image information, synthesize the modulated colors with a synthesizing prism, and display the resultant on a screen through a projection lens. 
         [0004]    In recent years, demands for a still higher luminance (higher output), a wider color gamut, and a longer life have been increased. However, it is difficult to achieve a still higher luminance with a lamp light source because the lamp light source causes problems such as increase in heat generation amount, increase in cooling structure in size, noise, and increase in power source in size. It is also difficult to achieve a wider color gamut and a longer life with a lamp light source. 
         [0005]    In view of the above, in recent years, there have been developed, instead of a lamp light source, light sources using a plurality of semiconductor lasers or LEDs having a wide color gamut and long life as light source elements, thereby being capable of obtaining high output, and projection-type image display apparatus using such light sources. 
         [0006]    In order to cause semiconductor lasers, LEDs, and other elements of respective colors (R, G, and B) to stably emit light or oscillate, it is important to keep operating setting temperatures thereof constant. When a light source element is a semiconductor laser, the light emission efficiency of the semiconductor laser increases as the temperature of the semiconductor laser thereof decreases. In general, Peltier elements are used in a technology for cooling semiconductor lasers. However, heat loads of those elements are large, and hence there arise problems such as increase in size of heat pipe and a heat sink, increase in noise due to increased air volume of fans, and increase in power consumption. 
         [0007]    Meanwhile, a cooling method using water cooling can suppress heat loads as compared to a case of using Peltier elements. However, there is a significant difference between the temperatures of water at an inlet of a cooler and at an outlet thereof, and hence temperatures of a plurality of semiconductor lasers cannot be kept constant. As a result, stable output light cannot be supplied. 
         [0008]    As one method for solving the problems described above, there has been proposed a method in which a cooling apparatus including a refrigerant circuit including a compressor, a condenser, a fan, a pressure reducer, and an evaporator (cooler) is used, and latent heat generated by vaporization of refrigerant is utilized (for example, see Patent Literatures 1 and 2). 
         [0009]    In Patent Literature 1, there is proposed a system in which temperature is kept constant by connection of refrigerant pipes to light source elements directly or indirectly through heat pipes. Meanwhile, in Patent Literature 2, there is proposed a system in which temperature is adjusted by controlling heating units provided to light source elements. 
       CITATION LIST 
     Patent Literature 
       [0010]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-042703 (for example, see [0025] to [0028], and FIG. 2) 
         [0011]    Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2009-086269 (for example, see [0026] to [0029], and FIG. 3) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0012]    In Patent Literature 1, no heating unit is provided on a cooling apparatus side, and hence a refrigerant temperature is decreased when the apparatus is activated and a cooling (cooling apparatus) side is activated before a heat source (light source element) side. When the refrigerant temperature reaches a dew point or less, dew condensation occurs in the apparatus to cause short-circuit in the apparatus, leading to apparatus failure. Further, when the apparatus is activated and the heat source side is activated before the cooling side, temperatures of the light source elements are increased due to insufficient supply of refrigerant, leading to apparatus failure. In addition, refrigerant, which is not evaporated in the cooler and is thus in a liquid state, flows into the compressor, leading to compressor failure. Thus, decrease in reliability of the apparatus is a problem. 
         [0013]    In Patent Literature 2, the heating units are directly provided to the light source elements, and hence temperatures of the light source elements are increased when a heating amount of the heating units is larger than a heat generation amount of the light source elements, thereby disadvantageously shortening the lives of the elements. In addition, a heating amount is determined based only on temperatures of the light source elements, and hence a state of refrigerant on a suction side of the compressor cannot be determined. As a result, refrigerant in a liquid state often returns to the compressor, leading to problematic compressor failure. 
         [0014]    The present invention has been made in view of the problems as described above, and has an object to provide a light source apparatus capable of improving reliability and a projection-type image display apparatus including the light source apparatus. 
       Solution to Problem 
       [0015]    According to one embodiment of the present invention, there is provided a light source apparatus including: a laser light source module; a cooling device including a refrigerant circuit in which a compressor, a condenser, an expansion valve, and an evaporator are sequentially circularly connected to each other via a pipe, and which circulates a refrigerant; and a controller configured to control at least the cooling device, in which the laser light source module includes a plurality of unit laser light source modules, each of which emits laser light of one specific color, and when the laser light source module includes unit laser light source modules of at least two colors, and each unit laser light source module has a median of a temperature range in which a practical luminance is obtained, the unit laser light source modules are thermally connected to the evaporator and arrayed in descending sequence of their values of the median from an upstream side in a direction in which the refrigerant flows. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0016]    According to the light source apparatus of the present invention, the unit laser light source modules are thermally connected to the pipe and arrayed in descending sequence of their values of the median of the temperature range in which a practical luminance can be obtained, from the upstream side in the direction in which the refrigerant flows. With this configuration, the reliability of the laser light source modules can be improved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is an overall configuration diagram of a light source apparatus according to Embodiment 1 of the present invention. 
           [0018]      FIG. 2  is an enlarged view of main parts of a cooling apparatus to be mounted in the light source apparatus according to Embodiment 1 of the present invention. 
           [0019]      FIG. 3  is a diagram for illustrating laser light source modules of the light source apparatus according to Embodiment 1 of the present invention, and liquid dispersion therein. 
           [0020]      FIG. 4  is an overall configuration diagram of a projection-type image display apparatus including a light source apparatus according to Embodiment 7 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Embodiments of the present invention are described below with reference to the drawings. Note that, the present invention is not limited to the embodiments described below. Moreover, in the drawings referred to below, the size relationship between components may be different from reality in some cases. 
       Embodiment 1 
       [0022]      FIG. 1  shows a general schematic configuration of a light source apparatus  90  according to Embodiment 1 of the present invention, and  FIG. 2  is an enlarged view of main parts of a cooling apparatus  15  to be mounted in the light source apparatus  90  according to Embodiment 1 of the present invention. 
         [0023]    The light source apparatus  90  according to Embodiment 1 includes laser light source modules  10 , optical units  13 , optical fibers  14 , an optical fiber collecting portion  14   a,  an optical fiber bundle line  14   b,  the cooling apparatus  15 , heat blocks  30 , electric boards  60 , laser light source driving circuit boards  61 , a power source circuit board  62 , and a control circuit board  63 . 
         [0024]    The laser light source modules  10  include a green laser light source module  10   a  configured to emit green (G) laser light, a red laser light source module  10   b  configured to emit red (R) laser light, and a blue laser light source module  10   c  configured to emit blue (B) laser light. 
         [0025]    Further, the laser light source driving circuit boards  61  include a green laser light source driving circuit board  61   a,  a red laser light source driving circuit board  61   b,  and a blue laser light source driving circuit board  61   c  configured to drive the laser light source modules  10  of the respective colors (R, G, and B). The green laser light source module  10   a,  the red laser light source module  10   b,  and the blue laser light source module  10   c  each correspond to a “unit laser light source module” of the present invention. 
         [0026]    Further, the laser light source modules  10  each include an electric terminal portions  12 , and are configured to emit laser light when being supplied with electricity via the electric board  60 . Then, the emitted laser light is guided to the optical fiber  14  via the optical unit  13 . 
         [0027]    The optical fibers  14  are connected to the laser light source modules  10  of the respective colors. Laser light emitted from the laser light source modules  10  is output to the outside of the laser light source through the optical fibers  14 , the optical fiber collecting portion  14   a,  and the optical fiber bundle line  14   b.    
         [0028]    The power source circuit board  62  is a circuit board configured to supply power to the light source apparatus  90 . The control circuit board  63  is a circuit board configured to control the light source apparatus  90 . The control circuit board  63  corresponds to a “controller” of the present invention. 
         [0029]    The cooling apparatus  15  includes a refrigerant circuit in which a compressor  21 , a condenser  22 , an expansion valve  23 , and an evaporator  25  configured to cool the laser light source modules  10  are sequentially circularly connected to each other, via a pipe  20 , and which circulates refrigerant. Further, a fan  24  for ventilation is provided to the condenser  22 . 
         [0030]    Refrigerant flows through the pipe  20 . A plurality of heat blocks  30 , which are radiators, are mounted on the pipe  20  between the expansion valve  23  and the compressor  21 . The evaporator  25  is formed by a segment of the pipe  20  between the expansion valve  23  and the compressor  21 , and the heat blocks  30 . Further, the laser light source modules  10  are joined to the heat blocks  30 . That is, the pipe  20  and the laser light source modules  10  are thermally connected to each other via the heat blocks  30 . The laser light source modules  10  are cooled by refrigerant flowing through the pipe  20 . 
         [0031]    Specifically, high-temperature and high-pressure refrigerant compressed in the compressor  21  exchanges heat with outside air, which is ventilated due to the working of the condenser  22  and the fan  24 , to decrease its temperature, thereby becoming low-temperature and high-pressure refrigerant. At the same time, the condensing heat is rejected to the outside of the light source apparatus  90  by the fan  24 . Next, the refrigerant is decompressed by the expansion valve  23 , and then takes away heat by absorbing evaporation latent heat (that is, cools the laser light source module  10 ), thereby becoming low-temperature and low-pressure refrigerant. This occurs when the refrigerant flows through the pipe  20 , on which the heat blocks  30  are mounted with the laser light source modules  10  joined thereto. Through the series operation of what is called heat pump operation, heat generated by the laser light source modules  10  is continuously discharged to the outside of the light source apparatus  90 , thereby keeping temperatures of the laser light source modules  10  constant. 
         [0032]    Due to this action of the refrigerant circuit, a refrigerant temperature in the pipe  20  of  FIG. 2 , on which the heat blocks  30  are mounted, is decreased to a peripheral temperature of the pipe  20  or less. Further, a temperature of the surface of the pipe  20  on a low-pressure side (the suction side of the compressor  21 ) is decreased to approximate the refrigerant temperature. Further, temperatures at joints between the laser light source modules  10  and the heat blocks  30  are increased due to heat generated from the laser light source modules  10 , but surfaces of the heat blocks  30  other than the joints are less affected by heat. Thus, the temperatures of the surfaces are decreased to approximate the refrigerant temperature. Then, when those temperatures reach a dew point or less, dew condensation occurs on the pipe  20  on the low-pressure side and the surfaces of the heat blocks  30 . 
         [0033]    In order to prevent such dew condensation, in Embodiment 1, the refrigerant circuit, namely, the cooling apparatus  15  includes the heater  26 . Through control of the heater  26 , the refrigerant temperature is adjusted so as not to reach the dew point or less, thereby preventing dew condensation. When the apparatus is activated and the compressor  21  of the cooling apparatus  15  is activated first, temperatures of the pipe  20  and the heat blocks  30  are decreased because the laser light source modules  10  do not generate heat yet, and hence dew condensation occurs on the surfaces of those components. On the other hand, when the laser light source modules  10  are activated first, temperatures of the laser light source modules  10  are immediately increased because the compressor  21  of the cooling apparatus  15  is not activated yet, thereby causing failure of the laser light source modules  10  or shortening the lives of the laser light source modules  10 . 
         [0034]    Accordingly, when the apparatus is activated, the heater  26  is activated first to warm the refrigerant. The compressor  21  is then activated such that the refrigerant temperature is adjusted so as not to reach the dew point or less. After that, the laser light source modules  10  are activated. In this manner, increase in temperature of the laser light source modules  10  is prevented. 
         [0035]    Further, the heater  26  is provided, and hence refrigerant to be sucked into the compressor  21  can be turned into a vapor state at the same time as adjustment of an evaporating temperature of refrigerant. In this case, when the heater  26  is controlled such that refrigerant in the vapor state is sucked into the compressor  21 , it is difficult to perform the simultaneous control as described above if the heater  26  is directly provided to the laser light source modules  10 . Consequently, (when the discharge side of the compressor  21  corresponds to the upstream, and the suction side thereof corresponds to the downstream) refrigerant flowing near the blue laser light source module  10   c  of the laser light source modules  10 , which is located on the most downstream side, may become superheated vapor and may not be cooled, or refrigerant not in the vapor state may be sucked into the compressor  21 . 
         [0036]    Accordingly, the heater  26  is provided in the refrigerant circuit on the low-pressure side (between the evaporator  25  and the suction port of the compressor  21  in Embodiment 1) so that refrigerant in the vapor state can be sucked into the compressor  21  while the evaporator  25  causes refrigerant in a wet state to flow. As a result, not only the reliability of the laser light source modules  10 , but also the reliability of the compressor  21  can be improved. 
         [0037]    Further, no dew condensation collecting container is needed, and a plurality of heaters  26  are not needed in the circuit. Thus, the apparatus can be manufactured at a low cost. The refrigerant temperature may be adjusted merely by controlling the heater  26  depending on a heat generation amount of the laser light source modules  10 , based on the lowest pipe temperatures in the laser light source modules  10  and the suction temperature of the compressor  21 , and hence the refrigerant temperature can be adjusted more easily than in a case of using a plurality of heaters  26 . 
         [0038]    Further, only one heater  26  is provided in Embodiment 1, and hence the cost can be reduced. Further, control of a plurality of heaters  26  is not needed, which means that the control is not complicated and the responsiveness of the apparatus can thus be improved. 
         [0039]    Heaters  26  may be provided on the upstream side of the laser light source modules  10  and the downstream side thereof, respectively. With this configuration, an evaporating temperature of refrigerant can be adjusted by controlling the heater  26  on the upstream side, and a state of refrigerant to be sucked into the compressor  21  can be adjusted by controlling the heater  26  on the downstream side. 
         [0040]    As described above, in the light source apparatus  90  including the cooling apparatus  15  according to Embodiment 1, the occurrence of dew condensation in the apparatus, which causes short-circuit in the apparatus  15 , is prevented due to dew condensation prevention by the heater  26 , and hence the light source apparatus  90  with high reliability is obtained. 
         [0041]    Further, light emitting portion temperatures of laser diodes in the laser light source modules  10  are decreased, and hence the light source apparatus  90  has a characteristic of high opto-electric conversion efficiency. Thus, when the refrigerant temperature is decreased as described above, light output to the outside of the light source apparatus  90  is increased. As a result, the number of laser light source modules  10  necessary for obtaining light output that the light source apparatus  90  is required to output can be reduced, thereby reducing the cost of the light source apparatus  90 . 
         [0042]    Further, refrigerant to be sucked into the compressor  21  can be turned into the vapor state at the same time as the adjustment of the refrigerant temperature by the evaporator  25 . Thus, the reliability of the compressor  21  can be improved. 
         [0043]      FIG. 3  is a diagram for illustrating the laser light source modules  10  of the light source apparatus  90  according to Embodiment 1 of the present invention, and liquid dispersion therein. 
         [0044]    In  FIG. 3 , in the flow direction of refrigerant, the most upstream region is referred to as a region A, the most downstream region is referred to as a region C, and a region between the region A and the region C is referred to as a region B. 
         [0045]    In Embodiment 1, as illustrated in the liquid dispersion in the pipe  20  of  FIG. 3 , a liquid volume of liquid refrigerant is increased in the order of region A&gt;region B&gt;region C for refrigerant in a two-phase gas-liquid state. In the region C, the liquid volume of the refrigerant is small and superheated vapor flows, and hence latent heat of the refrigerant is small. Further, as refrigerant travels downstream, the ratio of vapor refrigerant having a high velocity is increased and pressure loss of the refrigerant is thus increased. The increase in pressure loss decreases an evaporating pressure of the refrigerant and an evaporating temperature thereof, and hence a temperature of a cooling surface is decreased. Accordingly, in the light source apparatus  90  having a refrigerant temperature distribution, the laser light source module  10  having a high median of a control temperature range (a temperature range in which a practical luminance can be obtained) is provided on the upstream side (region A or region B). As a result, the laser light source modules  10  are easily controlled to have a temperature in a desired temperature range, and hence stable wavelengths can be supplied from the laser light source modules  10 . With the above-mentioned configuration, the reliability of the laser light source modules  10  can be improved and stable laser light can thus be emitted. 
         [0046]    In Embodiment 1, as illustrated in  FIG. 3 , the laser light source modules  10  of the respective colors (R, G, and B) are arranged in line, but the arrangement is not limited thereto. Further, the combination of colors and the number of laser light source modules  10  may differ from those of Embodiment 1. The laser light source modules  10  may be arranged in parallel to each other, but for each line, the laser light source module  10  having a high control temperature is preferably arranged on the upstream side. 
       Embodiment 2 
       [0047]    Now, Embodiment 2 of the present invention is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0048]    In Embodiment 1 described above, a case is described in which, among a plurality of laser light source modules  10 , the laser light source module  10  having a high median of the control temperature range is provided on the upstream side of the laser light source module  10  having a low median of the control temperature range. In Embodiment 2, a case is described in which, among a plurality of laser light source modules  10 , the green laser light source module  10   a  is provided on the upstream side of the laser light source modules  10  of other colors. 
         [0049]    The median of the control temperature range of the green laser light source module  10   a  is higher than that of the laser light source module  10  of red or blue. Thus, the green laser light source module  10   a  is provided on the upstream side of the laser light source modules  10  of other colors (in the region A). As a result, the green laser light source module  10   a  is easily controlled to have a temperature in a desired temperature range, and hence a stable wavelength can be supplied from the green laser light source module  10   a.  With this configuration, the reliability of the laser light source modules  10  can be improved and stable laser light can thus be emitted. 
       Embodiment 3 
       [0050]    Now, Embodiment 3 of the present invention is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0051]    In Embodiment 2 described above, a case is described in which, among a plurality of laser light source modules  10 , the green laser light source module  10   a  having the highest median of the control temperature range is provided on the upstream side of the laser light source modules  10  of other colors. In Embodiment 3, among a plurality of laser light source modules  10 , the red laser light source module  10   b  is provided on the downstream side of the laser light source modules  10  of other colors. 
         [0052]    The median of the control temperature range of the red laser light source module  10   b  is lower than that of the laser light source module  10  of green or blue. Thus, the red laser light source module  10   b  is provided on the downstream side of the laser light source modules  10  of other colors (in the region C). As a result, a change in temperature of the red laser light source module  10   b  can be minimized, and the laser light source modules  10  of other colors can have temperatures in the control temperature range. Thus, the light source apparatus  90  can be controlled easily and stable wavelengths can be emitted for all the colors. Further, only one sensor is needed for sensing cooling temperature, and hence the cost can be reduced. 
       Embodiment 4 
       [0053]    Now, Embodiment 4 of the present invention is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0054]    In Embodiment 3 described above, a case is described in which, among a plurality of laser light source modules  10 , the red laser light source module  10   b  having the lowest median of the control temperature range is provided on the downstream side of the laser light source modules  10  of other colors. In Embodiment 4, a case is described in which a temperature of the green laser light source module  10   a  (in the light source apparatus  90 ) is controlled to be included in a range of from the dew point or more to 45 degrees C. or less. 
         [0055]    The green laser light source module  10   a  has temperature dependence on wavelengths due to its element characteristics, and thus does not provide a practical luminance unless otherwise controlled to have a temperature in the range of from the dew point or more to 45 degrees C. or less. When being controlled to have a temperature in this range, the green laser light source module  10   a  can provide a high luminance and a stable wavelength due to its element characteristics. Further, reduction in luminance with respect to reduction in time is small, and hence a long-life light source apparatus  90  can be obtained. Further, the green laser light source module  10   a  is controlled to have a temperature that is the dew point or more, and hence dew condensation of the green laser light source module  10   a  can be prevented. 
       Embodiment 5 
       [0056]    Now, Embodiment 5 of the present invention is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0057]    In Embodiment 4 described above, a case is described in which a temperature of the green laser light source module  10   a  is controlled to be included in the range of from the peripheral temperature or more to 45 degrees C. or less. In Embodiment 5, a case is described in which a temperature of the red laser light source module  10   b  is controlled to be included in a range of from 20 degrees C. or more to 30 degrees C. or less. 
         [0058]    The red laser light source module  10   b  has temperature dependence on wavelengths due to its element characteristics, and thus does not provide a practical luminance unless otherwise controlled to have a temperature in the range of from 20 degrees C. or more to 30 degrees C. or less. When being controlled to have a temperature in this range, the red laser light source module  10   b  can provide a high luminance and a stable wavelength due to its element characteristics. Further, reduction in luminance with respect to reduction in time is small, and hence a long-life light source apparatus  90  can be obtained. 
       Embodiment 6 
       [0059]    Now, Embodiment 6 of the present invention is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0060]    In Embodiment 5 described above, a case is described in which a temperature of the red laser light source module  10   b  is controlled to be included in the range of from 20 degrees C. or more to 30 degrees C. or less. In Embodiment 6, a case is described in which a temperature of the blue laser light source module  10   c  is controlled to be included in a range of from 27 degrees C. or more to 33 degrees C. or less. 
         [0061]    The blue laser light source module  10   c  has temperature dependence on wavelengths due to its element characteristics, and thus does not provide a practical luminance unless otherwise controlled to have a temperature in the range of from 27 degrees C. or more to 33 degrees C. or less. When being controlled to have a temperature in this range, the blue laser light source module  10   c  can provide a high luminance and a stable wavelength due to its element characteristics. Further, reduction in luminance with respect to reduction in time is small, and hence a long-life light source apparatus  90  can be obtained. 
       Embodiment 7 
       [0062]      FIG. 4  is an overall configuration diagram of a projection-type image display apparatus  91  including the light source apparatus  90  according to Embodiment 7 of the present invention. 
         [0063]    Now, Embodiment 7 is described. Description of the same component as that of Embodiment 1 is omitted herein. The parts identical with or corresponding to those of Embodiment 1 are denoted by the same reference symbols. 
         [0064]    In Embodiment 6 described above, a case is described in which a temperature of the red laser light source module  10   b  is controlled to be included in the range of from 20 degrees C. or more to 30 degrees C. or less. In Embodiment 7, the projection-type image display apparatus  91  includes the light source apparatus  90  is described. 
         [0065]    As illustrated in  FIG. 4 , the projection-type image display apparatus  91  according to Embodiment 7 is connected to the optical fiber collecting portion  14   a  of the light source apparatus  90  via the optical fiber bundle line  14   b.  The projection-type image display apparatus  91  includes a unit configured to generate image light through space modulation of laser light and a projection optical system configured to project the image light, and is configured to project images to the outside of the projector with the unit and the projection optical system. 
         [0066]    The projection-type image display apparatus  91  according to Embodiment 6 can achieve high reliability, low cost, and high energy efficiency, 
       REFERENCE SIGNS LIST 
       [0067]      10  laser light source module  10   a  green laser light source module  10   b  red laser light source module  10   c  blue laser light source module  12  electric terminal portion  13  optical unit  14  optical fiber  14   a  optical fiber collecting portion  14   b  optical fiber bundle line  15  cooling apparatus  20  pipe  21  compressor  22  condenser  23  expansion valve  24  fan  25  evaporator  26  heater  26   a  heater 26   b  heater 27  first temperature sensor  28  second temperature sensor  29  heat exchanger  30  heat block  60  electric board  61  laser light source driving circuit board  61   a  green laser light source driving circuit board  61   b  red laser light source driving circuit board 
         [0068]      61   c  blue laser light source driving circuit board  62  power source circuit board  63  control circuit board  90  light source apparatus  91  projection-type image display apparatus