Patent Publication Number: US-2015070927-A1

Title: Moisture removal device, lighting device for mounting on vehicle, and light source lighting device

Description:
TECHNICAL FIELD 
     The present invention relates to a moisture removal device using a plate-like or film-like electrolyte member, a light assembly for on-vehicle use (lighting device for mounting on vehicle) that removes moisture inside the assembly using the moisture removal device, and a light-source lighting device incorporating the moisture removal device. 
     BACKGROUND ART 
     With respect to light assemblies for on-vehicle use, such as headlamps and the like, in some cases, moisture that is being potentially included in a resin constituting respective members of the assembly, or moisture that has been intruded from the outside because of expansion and contraction of air in the light assembly due to repetitive light-on and light-off operations by a light source in the light assembly, is condensed on a low temperature portion inside the light assembly. 
     In particular, a lens that constitutes an externally-exposed front face of the light assembly and projects light from the light source ahead of the vehicle, is a portion that often becomes a temperature lower than the other portions, so that a dew condensation is likely to occur at the inner side of the lens. To make matters worse, the lens is transparent and thus water droplets due to condensed water produced at the inner side is likely to be visually recognized as a haze, thereby degrading merchantability of the light assembly. 
     It should be noted that, nowadays, in the light assemblies each having a complex shape that constitutes a part of the vehicle body line, a higher-to-lower difference in temperature distribution of the air in the light assembly is large, so that a low temperature portion is likely to be developed and thus a dew condensation is likely to be evident at the low temperature portion. 
     Meanwhile, as compared to the conventional light sources such as light bulbs in which a tungsten filament is red heated, new light sources such as discharge lamps and LEDs (Light Emitting Diodes) need lower power for lighting, and thus the temperature rise inside each of their light assemblies is moderate as a whole. Accordingly, expansion and contraction of air in the light assembly are reduced, so that the moisture intruded in the light assembly becomes hardly dischargeable to the outside. As a result, the moisture is likely to be accumulated in the light assembly, thereby making a dew condensation likely to be evident. 
     Note that in the conventional light assemblies, generally, a hydrophilic antifogging coating is applied to the inner side of the lens so as to prevent the water due to dew condensation from becoming water droplets of small particles, namely, from forming a haze. 
     As a measure for preventing the haze formation, in a lamp for vehicle (light assembly) according to Patent Document 1, for example, such a configuration is applied in which a baffle plate for accelerating formation of a favorable convection flow in its housing (casing) is provided so as to discharge the moisture out of the housing through an inspiratory port, so that the moisture going around to its front lens is decreased and thus the dew condensation hardly occurs. This makes it possible to reduce the antifogging coating applied to the front lens. 
     However, although the moisture in the housing can be brought to such a respiratory port by means of convection flow, since the moisture is not sufficiently discharged through the respiratory port in some cases, there is a possibility that the moisture remains in the inner side of the housing. 
     Instead, it is conceivable to actively remove the moisture in the light assembly using a moisture removal device. Examples of conventional moisture removal devices are given in Patent Documents 2 to 4. 
     A moisture removal device for vehicle according to Patent Document 2 is configured to dehumidify an atmosphere around an evaporator for vehicle&#39;s air conditioner using a proton-conductive type electrolyte film. The moisture removal device is arranged as its anode side being open to a casing of the evaporator and its cathode side being open to an engine room so that the temperature of the cathode side is increased by use of exhaust heat from the engine room, to thereby enhance its dehumidifying effect. It should be noted that this moisture removal device is provided for finally discharging moisture in a vehicle cabin to the engine room, and not for discharging moisture in a headlamp to the outside. 
     Meanwhile, a moisture prevention structure according to Patent Document 3 is configured by placing in a casing, an electronic component and an electrolyte generating means that converts the intruded moisture to an electrolyte and by filling around them with a resin by injection so that the moisture contained in the resin is decomposed and discharged by flowing a current through the electrolyte generating means. This enhances a moisture-prevention property of the electronic component placed in the engine room of the vehicle. It should be noted that this moisture prevention structure is provided for discharging the moisture intruded in the resin-sealed casing, and not for discharging moisture in a headlamp to the outside. 
     Meanwhile, an article storage/safekeeping apparatus according to Patent Document 4 is configured by providing a proton conductive member on a wall portion of a housing for storage or safekeeping of an article so that the moisture in the housing is discharged out of the housing. Although this apparatus is provided for discharging the moisture in the housing to the outside of the housing, this housing subject to moisture prevention is not a headlamp. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Application Laid-open No. 2004-199198 
         Patent Document 2: Japanese Patent Application Laid-open No. 2007-62562 
         Patent Document 3: Japanese Patent Application Laid-open No. H11-59289 
         Patent Document 4: Japanese Patent Application Laid-open No. H05-103941 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Patent Document 1 is given for accelerating discharge of the moisture in the housing of a headlamp by use of convection flow, and thus not to actively discharge the moisture from the headlamp. Thus, there is a problem that the moisture discharge effect becomes insufficient. 
     Meanwhile, Patent Documents 2 to 4 are each directed to a configuration of actively discharging moisture by use of an electrolyte member; however, its subject is not a headlamp, and thus no assumption is made about actively discharging the moisture accumulated in a housing of a complex-shape headlamp. 
     In addition, since a headlamp is mounted on a portion in vicinity of which the engine of the vehicle exists, there is likelihood that a combustible gas such as gasoline, etc., exists around this portion. While at the same time, the electrolyte member is generally configured by laminating on each surface of an electrolyte film, a platinum catalyst layer and a carbon electrode layer, so that a reaction of decomposing into or coupling of, an oxygen ion and a hydrogen ion occurs at the catalyst layer as a surface layer of the electrolyte member. In some cases, this oxygen reacts with the combustible gas to generate heat; however, no description is made about such heat generation in Patent Documents 2 to 4. Further, there is a conceivable risk that the electrolyte film deteriorates or even results in its firing due to the heat generation; however, no description is made about how to deal therewith in Patent Documents 2 to 4. 
     Accordingly, there is a problem that the moisture removal devices in Patent Documents 2 to 4 are difficult to be used without modification for a headlamp. 
     The present invention has been made to solve the problems as described above, and an object of the invention is to provide a moisture removal device that suppresses the electrolyte member from being heated up, while exerting a sufficient dehumidifying effect, and a light assembly for on-vehicle use and a light-source lighting device which employ the moisture removal device. 
     Means for Solving the Problems 
     A moisture removal device of this invention comprises: 
     a plate-like or film-like electrolyte member; a pair of electrode members that sandwich therebetween and make electrically contact with, the electrolyte member from both sides thereof, so as to apply a predetermined voltage to the electrolyte member; and a housing that accommodates the electrolyte member and the pair of electrode members, and has an opening portion which is made open to an inside of a light assembly when the housing is fixed to the light assembly; wherein the pair of electrode members are formed of a material consisting mainly of a metal, and either one of the electrode members is arranged at a position where it closes the opening portion of the housing. 
     A lighting assembly for on-vehicle use of the invention comprises the aforementioned moisture removal device, to thereby remove moisture in a housing (casing) that accommodates a light source. 
     A light-source lighting device of the invention comprises: a plate-like or film-like electrolyte member; a pair of electrode members that sandwich therebetween and make electrically contact with, the electrolyte member from both sides thereof, so as to apply a predetermined voltage to the electrolyte member; and a housing (of the lighting device) that accommodates the electrolyte member and the pair of electrode members, and has an opening portion which is made open to an inside of a light assembly when the housing is fixed to the light assembly; wherein the pair of electrode members are formed of a material consisting mainly of a metal, and either one of the electrode members is arranged at a position where it closes the opening portion of the housing (of the lighting device). 
     Effect of the Invention 
     According to the invention, because the pair of electrodes are formed of a material consisting mainly of a metal, the electrolyte member can be suppressed from being heated up. Thus, the moisture removal device is usable even in an atmosphere in which a combustible gas exists. 
     According to the invention, because of employing the moisture removal device that is usable in an atmosphere in which a combustible gas exists, it is possible to remove the moisture to thereby suppress the dew condensation in a light assembly for on-vehicle use that is arranged near an engine. 
     According to the invention, because of employing the dehumidifying-function-containing light-source lighting device that is usable in an atmosphere in which a combustible gas exists, it is possible to remove the moisture to thereby suppress the dew condensation in a light assembly for on-vehicle use that is arranged near an engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a configuration of a headlamp according to Embodiment 1 of the present invention, in a case where a moisture removal device is mounted on its rear surface. 
         FIG. 2  is a cross-sectional view showing a configuration of a headlamp according to Embodiment 1 of the invention, in a case where a moisture removal device is mounted on its lower surface. 
         FIG. 3  is diagrams each showing an external appearance of the moisture removal device according to Embodiment 1, in which shown at  FIG. 3(   a ) is a front view, at  FIG. 3(   b ) is a bottom view, and at  FIG. 3(   c ) is a side view. 
         FIG. 4  is an example of cross-sectional view of the moisture removal device taken along A-A line in  FIG. 3 . 
         FIG. 5  is another example of cross-sectional view of the moisture removal device taken along A-A line in  FIG. 3 . 
         FIG. 6  is a cross-sectional view showing a configuration of a headlamp according to Embodiment 1 of the invention, in a case where a moisture removal device is mounted on its maintenance cover. 
         FIG. 7  is a diagram illustrating a fixing method of a headlamp and a moisture removal device according to Embodiment 2 of the invention. 
         FIG. 8  is a diagram illustrating a fixing method of a headlamp and a moisture removal device according to Embodiment 3 of the invention. 
         FIG. 9  is a partial cross-sectional view showing a configuration example in which projection portions are formed on an inner circumferential surface of a cylindrical convex portion of a moisture removal device. 
         FIG. 10  is a diagram illustrating a fixing method of a headlamp and a moisture removal device according to Embodiment 4 of the invention. 
         FIG. 11  is a partial cross-sectional view showing a state where the headlamp and the moisture removal device are fixed together by the fixing method shown in  FIG. 10 . 
         FIG. 12  is a partial cross-sectional view showing a configuration example corresponding to that shown in  FIG. 11  provided that concave portions are substituted with cutout holes. 
         FIG. 13  is a partial cross-sectional view showing a configuration example in which claw portions are formed on an inner circumferential surface of a cylindrical convex portion of a moisture removal device. 
         FIG. 14  is a diagram illustrating a fixing method of a headlamp and a moisture removal device according to Embodiment 5 of the invention. 
         FIG. 15  is a partial cross-sectional view showing a state where the headlamp and the moisture removal device are fixed together by the fixing method shown in  FIG. 14 . 
         FIG. 16  is a partial cross-sectional view showing a configuration example that uses an elastic member having an O-ring like shape. 
         FIG. 17  is a partial cross-sectional view showing another configuration example that uses an elastic member having an O-ring like shape. 
         FIG. 18  is a cross-sectional view showing a configuration of a moisture removal device according to Embodiment 6 of the invention. 
         FIG. 19  is a circuit diagram showing a basic power source circuit that constitutes a power source unit shown in  FIG. 18 . 
         FIG. 20  is a circuit diagram showing another example of power source circuit that constitutes the power source unit shown in  FIG. 18 . 
         FIG. 21  is a circuit diagram showing a power source circuit that constitutes a power source unit of a moisture removal device according to Embodiment 7 of the invention. 
         FIG. 22  is a cross-sectional view showing a configuration of a headlamp according to Embodiment 8 of the invention, in a case where power is supplied from an LED lighting device to a moisture removal device. 
         FIG. 23  is a cross-sectional view showing a configuration of a headlamp according to Embodiment 8, in a case where an LED lighting device and a moisture removal device are integrated with each other. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Hereinafter, for illustrating the invention in more detail, embodiments for carrying out the invention will be described according to the accompanying drawings. 
     Embodiment 1 
     As shown in  FIG. 1  and  FIG. 2 , a headlamp  1  that is one of light assemblies for on-vehicle use (on-vehicle lighting fixtures), is configured with a housing that is formed of a front lens  2  and a casing  3 , and that accommodates a projection lens  4  placed on an optical axis extending in a vehicle front-rear direction, an LED (light source)  5  disposed backward from the projection lens  4 , a mirror reflector  6  that reflects light from the LED  5  toward the projection lens  4 , and a heat sink  7  on which the LED  5  is placed. In the configuration example in  FIG. 1 , a mounting hole  8  is formed on a rear surface of the casing  3  and a moisture removal device  10  is mounted to the mounting hole  8 . In the configuration example in  FIG. 2 , the mounting hole  8  is formed on a lower surface of the casing  3  and the moisture removal device  10  is mounted thereto. 
     External appearances of the moisture removal device  10  are shown in  FIG. 3 , and a cross-sectional view taken along A-A line therein is shown in  FIG. 4 . In the moisture removal device  10 , a cylindrical convex portion  12  is protrusively formed in a housing  11 . On an end face of the cylindrical convex portion  12 , an opening portion  13  is formed. In the cylindrical convex portion  12 , a plate-like or film-like electrolyte member  14  is accommodated; to a surface of the electrolyte member  14  at the side toward the opening portion  13 , a positive-side electrode member  19  is electrically connected; and to a surface at the other side, a negative-side electrode member  20  is electrically connected. The electrode members  19 ,  20  are configured with electrode portions  15 ,  16  that sandwich therebetween and make electrically contact with, the electrolyte member  14 , and lead portions  17 ,  18  that are connected to an external power source (unshown), respectively. Note that the electrode portion  15  of the positive-side electrode member  19  is arranged at a position where it closes the opening portion  13 . Further, on the housing  11 , a connector portion  21  and a vent port  22  are formed. 
     The positive-side electrode member  19  and the negative-side electrode member  20  are each formed of a material consisting mainly of a metal. The electrode portions  15 ,  16  are each formed into almost the same shape as that of the electrolyte member  14  and a mesh-like form, and are in contact with almost all front surface and almost all back surface of the electrolyte member  14 , respectively. End portions of the lead portions  17 ,  18  are routed to the connector portion  21 . In Embodiment 1, a voltage (for example, 12V) of an on-vehicle battery is converted into a predetermined voltage (for example, 3V) by a power source device, which is then supplied to the connector portion  21  through power source lines. At the connector portion  21 , the power source lines are connected to the end portions of the lead portions  17 ,  18 , so that the predetermined voltage is applied to the electrolyte member  14 . 
     In Embodiment 1, a fluororesin proton-conductive electrolyte is used as the electrolyte member  14 , and the electrolyte member  14  is configured to adsorb in-air moisture (humidity). Since the proton-conductive electrolyte is the same as the material for fuel cells, it is large in market volume (production volume) and is thus inexpensive. In other words, the moisture removal device  10  can be achieved with low cost. 
     Note that catalyst layers consisting mainly of platinum or the like, are formed on the surface layers of the electrolyte member  14 , and the electrolyte member  14 , in a state covered with the electrode portions  15 ,  16 , closes the opening portion  13 . When a positive voltage is applied to the electrode portion  15  and a negative voltage is applied to the electrode portion  16 , the moisture adsorbed in the electrolyte member  14  is decomposed into an oxygen ion and a hydrogen ion. Then, gaseous oxygen is discharged from the side of the positive-side electrode portion  15  while gaseous hydrogen is discharged from the side of the negative-side electrode portion  16 . Note that, the hydrogen generated at that time reacts with surrounding oxygen to create water (water vapor) in some cases. Thus, seemingly, moisture is absorbed through the positive-voltage applied surface of the electrolyte member  14  and is then discharged through the negative-voltage applied surface thereof. 
     When the cylindrical convex portion  12  of the moisture removal device  10  is mounted to the mounting hole  8  of the headlamp  1 , the electrolyte member  14  absorbs from the side of the electrode portion  15 , moisture in the headlamp  1  through the opening portion  13 , followed by decomposing it into oxygen and hydrogen, to thereby discharge hydrogen or water from the side of the electrode portion  16  into the housing  11 . The hydrogen or water discharged into the housing  11  is discharged to the outside through the vent port  22 . Thus, it is possible to decrease the amount of water, namely, humidity, in the headlamp  1 . When the amount of water in the headlamp  1  is decreased, as a matter of course, moisture that condenses on the front lens  2  is reduced, so that occurrence of dew condensation in the headlamp  1  is suppressed. 
     Thus, even if the headlamp  1  has a complex shape, it is possible to actively discharge moisture therein, to thereby suppress occurrence of dew condensation on the front lens  2 . As a result, it is possible to reduce the antifogging coating applied to the front lens  2 . Further, it is unnecessary to provide, as in a conventional manner, a complex structure for inducing dew condensation to occur at portions other than on the front lens  2 . 
     By the way, since the catalyst layers are formed on the surface layers of the electrolyte member  14 , a reaction of decomposing into or coupling of an oxygen ion and a hydrogen ion occurs though being minute. This functions, if there is a combustible gas such as gasoline, etc., in the air, to promote a reaction of the combustible gas with oxygen in the air. 
     On this occasion, the reaction of the combustible gas with oxygen in the air is accompanied by heat generation, which is minute, so that if the temperature of the electrolyte member  14  is not lowered by dissipating the reaction heat, the electrolyte member  14  itself is deteriorated due to temperature rise. 
     Further, in a situation where unfavorable conditions coexist, there is concern that the reaction heat is not dissipated but stayed around the electrolyte member  14  resulting in its firing when the temperature rises excessively. 
     Thus, in the moisture removal device  10  of Embodiment 1, in order to promote dissipation of the reaction heat, the front and back surfaces of the electrolyte member  14  are wholly covered with the mesh-like electrode portions  15 ,  16  that ensure air-permeability while using a highly heat-conductive metal. Thus, even when there is the combustible gas near the electrolyte member  14  and the combustible gas reacts with oxygen in the air at the surface of the electrolyte member  14 , the reaction heat is transferred and diffused by the metallic electrode portions  15 ,  16  to be dissipated, and thus never locally stays. As a result, the temperature of the electrolyte member  14  does not rise excessively, so that the electrolyte member  14  never deteriorates due to heat generation. Further, since such temperature rise does not occur, the electrolyte member  14  never catches fire. 
     Furthermore, by closing the opening portion  13  with the robust electrode portion  15  made of a metal to thereby eliminate exposure of the electrolyte member  14 , it is possible to prevent a foreign substance, etc., from making contact with the electrolyte member  14 . Thus, it can be avoided that the electrolyte member  14  is broken due to an accidental action. 
     Next, a modified example of the moisture removal device  10  will be described with reference to  FIG. 5 . 
     In the moisture removal device  10  shown in  FIG. 5 , metal plates each having almost the same shape as that of the electrolyte member  14  and a plurality of small holes formed therein, are used as electrode portions  15   a ,  16   a . Namely, even though the metal plates with high heat-conductivity are used, air-permeability is ensured by the small holes formed in the electrode portions. Note that buffer members  23 ,  24  in a form like a steel wool that is a fibrous metal packed as a felt, for example, are placed between the electrolyte member  14  and the electrode portions  15   a ,  16   a , in order to make uniform pushing forces applied to the front and back surfaces of the electrolyte member  14  without interrupting moisture from entering or leaving the electrolyte member  14  and flow of the current from the electrode portions  15   a ,  16   a.    
     Further, a bottomed cylindrical support member  26  is attached inside the housing  11 , and an elastic member  25  such as a spring is arranged in the support member  26 . The elastic member  25  pushes the electrode portion  16   a  toward the electrolyte member  14 , so that the electrode portion  16   a , the buffer member  24 , the electrolyte member  14 , the buffer member  23  and the electrode portion  15   a  are placed in a contact state to each other, and thus a preferable electrical connection and heat-dissipation effect can be achieved. Note that since the electrode portion  15   a  is latched onto the fringe portion of the opening portion  13 , it does not drop out of the opening portion  13  into the headlamp  1 . Further, since a vent hole  27  is formed on the support member  26 , the moisture (humidity) passing through the electrolyte member  14  is discharged to the outside by passing through the vent hole  27  and the vent port  22 . 
     Consequently, it is possible to achieve a preferable heat-dissipation effect for the electrolyte member  14  while ensuring its dehumidifying effect, without interrupting preferable electrical connection and passage of moisture inside/outside the electrolyte member  14 . Further, since the opening portion  13  is closed with the robust electrode portion  15   a  made of a metal, it can be avoided that the electrolyte member  14  is broken due to an accidental action. 
     Note that in the moisture removal device  10  shown in  FIG. 5 , the buffer members  23 ,  24  may be omitted so long as the shapes of the electrode portions  15   a ,  16   a  are shapes not interrupting passage of moisture toward the electrolyte member  14 , flow of the current, and dissipation of the heat. 
     As described above, by forming the electrode portions  15 ,  16  or the electrode portions  15   a ,  16   a  using a material consisting mainly of a highly heat-conductive metal to thereby develop a configuration having a sufficient heat-dissipation ability, it is possible to make the amount of heat dissipation larger than the amount of heat generation by the reaction of oxygen in the air with the combustible gas. Thus, even when the moisture removal device  10  is used in an environment where the combustible gas exists, the electrolyte member  14  is avoided from being heated up locally, and thus can be prevented from catching fire. Further, the electrolyte member  14  is suppressed from deterioration due to heat generation, so that the dehumidifying capability can be maintained for a long period of time. 
     Next, a procedure of mounting the moisture removal device  10  to the headlamp  1  will be described. 
     First, a waterproof member  9  having an O-ring like shape is attached to the outer surface of the cylindrical convex portion  12 , and the opening portion  13 -side of the cylindrical convex portion  12  is inserted into the mounting hole  8  of the casing  3 . Then, the casing  3  and the housing  11  are fixed together by a given fixing means so that the opening portion  13  is placed in a state protruding to the inside of the headlamp  1 . Details of the fixing method will be described in Embodiment 2 and later. 
     Because the opening portion  13  is arranged at a position protruding inwardly from the casing  3  of the headlamp  1 , the electrolyte member  14  arranged on the inner side of the opening portion  13  becomes easily exposed to the moisture in the headlamp  1 , namely, becomes easily in contact with inner air. Meanwhile, since the waterproof member  9  closes a gap between the outer surface of the cylindrical convex portion  12  and the mounting hole  8 , it is possible to prevent water from intruding into the headlamp  1 . 
     As shown in  FIG. 1 , in the case where the moisture removal device  10  is mounted on the rear surface of the headlamp  1 , the moisture (humidity) in the air in the headlamp  1  can be discharged to the outside. Since the rear portion of the headlamp  1  is placed in the engine room, in some cases when the vehicle is traveling, on-road water is splashed from the lower side up to the rear portion of the headlamp  1 ; however, the rear face of the headlamp  1  is hardly spattered with the water, and thus, it is just enough to provide a simple drip-proof structure on the moisture removal device  10 . 
     On the other hand, in the case where the moisture removal device  10  is mounted on the lower surface of the headlamp  1  as shown in  FIG. 2 , not only the moisture (humidity) in the air in the headlamp  1  but also water in the form of liquid accumulated at the bottom can be discharged to the outside. However, the lower face of the headlamp  1  is likely to be spattered with the water, and thus it is desired to provide on the moisture removal device  10 , a waterproof structure that takes into account the water spatter from the lower side. 
     Note that the portion of the moisture removal device  10  to be mounted is not limited to the portions shown in  FIG. 1  and  FIG. 2 . Another example will be described below, with reference to  FIG. 6 . 
     Headlamps  1  that employ as a light source a light bulb in which a tungsten filament is red heated, are each provided with a maintenance opening portion  30  that allows replacement of the light bulb when it failed, on the rear surface of the headlamp  1 , and a maintenance cover  31  that closes the opening portion. 
     Meanwhile, the LED  5  has a long life and thus is rarely subject to replacement; however, even in headlamps  1  with a structure that employs the LED  5  as a light source, in many cases, there are included the maintenance opening portion  30  and the maintenance cover  31  that closes the opening portion. This is intended to use the maintenance opening portion  30  in a work for introducing wiring members into the headlamp  1 , in assembling works of attaching components in the headlamp  1  or making connection of an internal wiring, for example. 
     Thus, as shown in  FIG. 6 , a corresponding portion to the mounting hole  8  in  FIG. 1  and  FIG. 2  is formed on the maintenance cover  31 , and the moisture removal device  10  is mounted to that portion. In the assembling works, the maintenance cover  31  mounted with the moisture removal device  10  is fixed to the maintenance opening portion  30 . This makes it unnecessary to form the mounting hole  8  for mounting the moisture removal device  10  on the casing  3  of the headlamp  1 . Further, since the moisture removal device  10  is unified to the maintenance cover  31  that is originally included in the headlamp  1 , one type of the moisture removal device  1  may be commonly used for headlamps  1  that are different in shape or the like. 
     Note that it is allowable to employ such a configuration in which the housing  11  of the moisture removal device  10  is integrally formed with the maintenance cover  31 . 
     Next, operational timings of the moisture removal device  10  will be described. 
     For example, power is constantly supplied from the external power source to the moisture removal device  10 , to thereby always activate the dehumidifying function. In this case, since long time dehumidification can be established, it is allowable to make the electrolyte member  14  compact. Thus, the moisture removal device  10  can be achieved with low cost. 
     Meanwhile, for example, power may be supplied to the moisture removal device  10  in conjunction with the operation of the engine. Namely, during an IG (ignition) switch being turned ON, the power is supplied, and during turned OFF, the power supply is suspended. During the engine operating, its surrounding temperature rises, so that the catalytic activity of the electrolyte member  14  is enhanced to thereby improve the dehumidification efficiency. Further, because of being in conjunction with the IG switch, the operation and its suspension of the moisture removal device  10  can be controlled arbitrarily, and thus it becomes easy to deal with an accidental behavior when occurs. 
     Meanwhile, for example, power may be supplied to the moisture removal device  10  in conjunction with the operation of the headlamp  1  mounted with the moisture removal device  10  or another light assembly for on-vehicle use (for example, a position lamp). Namely, during lighting, the power is supplied, and during lighting-off, the power supply is suspended. During the headlamp  1  being lighted, the temperature in the headlamp  1  rises, so that a convection flow is produced to thereby agitate the inside air. Thus, by causing the moisture removal device  10  to operate in this duration, it is possible to perform a highly-efficient dehumidifying operation. Accordingly, it is unnecessary to use such an electrolyte member  14  that is excessively large in size. Furthermore, the power source of the moisture removal device  10  can be used in common with the power source of the lighting device for the headlamp  1  or the other light assembly for on-vehicle use, so that the system configuration of the headlamp  1  including the moisture removal device  10  becomes simplified. 
     As described above, according to Embodiment 1, the moisture removal device  10  is configured to include: the plate-like or film-like electrolyte member  14 ; the pair of electrode members  19 , 20  that sandwich therebetween, and make electrically contact with, the electrolyte member  14  from both sides thereof, so as to apply a predetermined voltage to the electrolyte member; and the housing  11  that accommodates the electrolyte member  14  and the pair of electrode members  19 ,  20 , and has the opening portion  13  which is made open to the inside of the headlamp  1  when the housing is fixed to the headlamp  1 ; wherein the pair of electrode members  19 ,  20  are formed of a material consisting mainly of a metal, and the positive-side electrode member  19  is arranged at a position where it closes the opening portion  13 . Thus, because heat is transferred to be dissipated by the electrode members  19 ,  20  made of a metal, the electrolyte member  14  can be suppressed from being heated up, so that it becomes possible to use the moisture removal device  10  even in the engine room where a combustible gas exists. Accordingly, occurrence of dew condensation on the front lens  2  can be suppressed by mounting the moisture removal device  10  to the headlamp  1 . 
     Further, according to Embodiment 1, since a proton-conductive electrolyte that is large in market volume and thus is inexpensive is used as the electrolyte member  14 , the moisture removal device  10  can be achieved with low cost. 
     Further, according to Embodiment 1, since it is configured so that the voltage is constantly applied to the electrolyte member  14 , it is allowable to make the electrolyte member  14  compact, on the assumption that the dehumidification is performed for a long time. Thus, the moisture removal device  10  can be achieved with low cost. 
     Instead, it may be configured so that the voltage is applied to the electrolyte member  14  in conjunction with the operation of the engine. In the case of this configuration, since the dehumidification operation can be performed in an environment with a higher surrounding temperature, it is possible to enhance the dehumidification efficiency. 
     Instead, it may be configured so that the voltage is applied to the electrolyte member  14  in conjunction with the operation of the headlamp  1  or another light assembly mounted on the vehicle on which the headlamp  1  is mounted. In the case of this configuration, since the temperature in the headlamp  1  rises, so that a convection flow is produced to thereby agitate the inside air, it is possible to perform a highly-efficient dehumidifying operation. Further, since the power source can be used commonly for the lighting device of the light source, it is possible to achieve the moisture removal device  10  with a simplified system configuration. 
     Further, according to Embodiment 1, the moisture removal device  10  is configured to be fixed on the surface opposite to an emitting face of the light from the LED  5 , or on the lower-side surface, of the housing formed of the front lens  2  and the casing  3 . Thus, it is possible to mount the moisture removal device  10  on a portion according to each purpose. 
     Further, according to Embodiment 1, the headlamp  1  is provided with the maintenance cover  31  and the moisture removal device  10  is configured to be fixed to the maintenance cover  31 . Thus, such a configuration member of the headlamp  1  can be used in a common manner. In addition, it is possible to achieve the moisture removal device  10  that can be attached/detached with reduced effort. 
     Embodiment 2 
       FIG. 7  is a diagram illustrating a fixing method of a headlamp  1  and a moisture removal device  10  according to Embodiment 2, and shows an example of their configurations to be fixed by screw. Note that, in  FIG. 7 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 6 , so that their description is omitted here. 
     In the case illustrated in the figure, a configuration example is shown in which screw holes (fixing portions)  40  are formed at four locations around the mounting hole  8  formed on the casing  3  of the headlamp  1 . In the moisture removal device  10  to be mounted to the headlamp  1  with the above configuration, screw passing holes (fixing members)  41  are formed at four locations on the housing  11 . By means of four screws (fixing members)  42 , the housing  11  of the moisture removal device  10  is fixed to the casing  3  of the headlamp  1 . Further, in order to prevent water from intruding into the headlamp  1  through a gap between the mounting hole  8  and the cylindrical convex portion  12 , the waterproof member  9  having an O-ring like shape is arranged between the moisture removal device  10  and the headlamp  1 . 
     Note that, in  FIG. 7 , the electrolyte member  14 , although hidden inside the cylindrical convex portion  12  and thus not seen, is desired to be arranged at a position protruding inwardly from the casing  3  of the headlamp  1 , so as to be easily exposed to the moisture in the headlamp  1 . 
     Further, the locations and the number of the screw holes  40  and the screw passing holes  41  are not limited to those in  FIG. 7 , and may be arbitrarily determined. 
     The fixing members employed by the moisture removal device  10  may be any members corresponding to the fixing portion of the headlamp  1  and thus may have a configuration other than that using the screws  42  as shown in  FIG. 7 . For example, in the case where the housing  11  of the moisture removal device  10  is to be fixed to the casing  3  of the headlamp  1  in a state being pushed thereto by use of a fixing member such as a spring, etc., there is formed on the housing  11 , a groove, a projection or the like for determining position of the spring so as to prevent its displacement. Note that, also in this case, in order to prevent water from intruding into the headlamp  1 , the waterproof member  9  is arranged between the moisture removal device  10  and the headlamp  1 . 
     As described above, according to Embodiment 2, the moisture removal device  10  is configured to include the fixing members, such as the screws  42 , etc., corresponding to the fixing portions of the headlamp  1 , so that the fixing members fix the housing  11  to the casing  3  of the headlamp  1 . Thus, it is possible to provide the moisture removal device  10  that is mountable to the headlamp  1 . 
     Embodiment 3 
       FIG. 8  is a diagram illustrating a fixing method of a headlamp  1  and a moisture removal device  10  according to Embodiment 3, and shows an example of their configurations to be fixed by a bayonet mechanism. Note that, in  FIG. 8 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 6 , so that their description is omitted here. 
     Cutout portions  43  are formed at two locations of the mounting hole  8  formed on the casing  3  of the headlamp  1 , and projection portions  44  to be fitted in the cutout portions  43  are protrusively formed at two locations on the cylindrical convex portion  12  of the moisture removal device  10 . Then, the cylindrical convex portion  12  is inserted into the mounting hole  8  while the cutout portions  43  and the projection portions  44  are kept fitted together. After completion of insertion, the moisture removal device  10  is rotated about the center axis of the cylindrical convex portion  12  to thereby latch the projection portions  44  onto the inner-side fringe portion of the mounting hole  8 , so that the moisture removal device  10  is fixed to the casing  3  of the headlamp  10 . Further, in order to prevent water from intruding into the headlamp  1  through the gap between the mounting hole  8  with the cutout portions  43  and the cylindrical convex portion  12  with the projection portions  44 , the waterproof member  9  having an O-ring like shape is arranged between the moisture removal device  10  and the headlamp  1 . 
     Note that, in  FIG. 8 , the electrolyte member  14 , although hidden inside the cylindrical convex portion  12  and thus not seen, is desired to be arranged at a position protruding inwardly from the casing  3  of the headlamp  1 , so as to be easily exposed to the moisture in the headlamp  1 . 
     Further, the locations and the number of the cutout portions  43  and the projection portions  44  are not limited to those in  FIG. 8 , and may be arbitrarily determined. 
     Further, in  FIG. 8 , there is given a configuration in which the projection portions  44  are formed on the outer circumferential surface of the cylindrical convex portion  12 ; however, it may be another configuration in which the projection portions  44  are formed on the inner circumferential surface of the cylindrical convex portion  12 .  FIG. 9  is a partial cross-sectional view showing a configuration example in which the projection portions  44  are formed on the inner circumferential surface of the cylindrical convex portion  12 . In the casing  3  of the headlamp  1 , a cylindrical wall  45  is formed that protrudes from the fringe portion of the mounting hole  8  to the outside of headlamp  1 , and at the end portion of the cylindrical wall  45 , a flange  46  and a plurality of cutout portions  43  are formed. On the inner circumferential surface of the cylindrical convex portion  12  of the moisture removal device  10 , a plurality of projection portions  44  to be fitted in the cutout portions  43  are protrusively formed. Then, the cylindrical wall  45  is inserted into the cylindrical convex portion  12  while the cutout portions  43  and the projection portions  44  are kept fitted together. After completion of insertion, the moisture removal device  10  is rotated about the center axis of the cylindrical convex portion  12  to thereby latch the projection portions  44  onto the fringe  46 , so that the moisture removal device  10  is fixed to the casing  3  of the headlamp  1 . 
     Note that the electrolyte member  14  and the unshown electrode members  19 ,  20 , etc., are arranged at a location that is a distance back from the flange  46  toward the housing  11 . Even in this arrangement, the air in the headlamp  1  makes contact with the electrolyte member  14  through the cylindrical wall  45 . Thus, it is possible to remove the moisture. 
     As described above, according to Embodiment 3, the moisture removal device  10  is configured to include the cylindrical convex portion  12  protrusively formed in the housing  11  and having the opening portion  13  on its end face, and the projection portions  44  formed on a circumferential surface of the cylindrical convex portion  12 , so that the housing  11  is fixed to the headlamp  1  in such a manner that the cylindrical convex portion  12  is inserted into the mounting hole  8  formed on the headlamp  1  and the projection portions  44  are latched onto the periphery of the mounting hole  8 . Thus, it is possible to provide the moisture removal device  10  that is easily mountable to the headlamp  1 . 
     Embodiment 4 
       FIG. 10  is a diagram illustrating a fixing method of a headlamp  1  and a moisture removal device  10  according to Embodiment 4 of the invention, and shows an example of their configurations to be fixed by a claw portion.  FIG. 11  is a partial cross-sectional view showing a state where the moisture removal device  10  is fixed to the headlamp  1 . Note that, in  FIG. 10  and  FIG. 11 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 6 , so that their description is omitted here. 
     At two locations on the outer side of the cylindrical convex portion  12  of the moisture removal device  10 , claw portions  47  having elasticity and concave portions  48  that can accommodate the claw portions  47  are provided. Then, the cylindrical convex portion  12  is inserted into the mounting hole  8  while the claw portions  47  are being elastically deformed toward their respective concave portions  48 . After completion of insertion, the claw portions  47  return to their outer positions and are latched onto the inner-side fringe portion of the mounting hole  8 , to thereby fix the moisture removal device  10  to the casing  3  of the headlamp  1 . Further, in order to prevent water from intruding into the headlamp  1  through a gap between the mounting hole  8  and the cylindrical convex portion  12 , the waterproof member  9  having an O-ring like shape is arranged between the moisture removal device  10  and the headlamp  1 . 
     Note that, in  FIG. 11 , there is given a configuration in which the concave portions  48  that are formed on the outer circumferential surface of the cylindrical convex portion  12 , have a depth that does not allow the concave portions to penetrate through the wall of the cylindrical convex portion  12 ; however, it may be another configuration in which cutout holes  49  that penetrate through the wall of the cylindrical convex portion  12  are formed.  FIG. 12  is a partial cross-sectional view showing a configuration example in which the cutout holes  49  are formed on the cylindrical convex portion  12 . With this configuration, the air in the headlamp  1  flows in not only through the opening portion  13  but also through the cutout holes  49 . Thus, in order to isolate the air in the headlamp  1  and the outside air, the electrolyte member  14  and the unshown electrode members  19 ,  20 , etc., are placed a distance back from the cutout holes  49  toward the housing  11 . 
     Further, in  FIG. 10  to  FIG. 12 , there is given a configuration in which the claw portions  47  are formed on the outer circumferential surface of the cylindrical convex portion  12 ; however, it may be another configuration in which the claw portions  47  are formed on the inner circumferential surface of the cylindrical convex portion  12 .  FIG. 13  is a partial cross-sectional view showing a configuration example in which the claw portions  47  are formed on the inner circumferential surface of the cylindrical convex portion  12 . On the casing  3  of the headlamp  1 , a cylindrical wall  45  is formed that protrudes from the fringe portion of the mounting hole  8  to the outside of headlamp  1 , and at the end portion of the cylindrical wall  45 , a flange  46  is formed. On the inner circumferential surface of the cylindrical convex portion  12  of the moisture removal device  10 , a plurality of the claw portions  47  are formed. Then, the cylindrical convex portion  12  is brought to insertion with the cylindrical wall  45  while the claw portions  47  are being elastically deformed. After completion of insertion, the claw portions  47  return to their inner positions and are latched onto the outer periphery of the cylindrical wall  45  or onto the flange  46 , to thereby fix the moisture removal device  10  to the casing  3  of the headlamp  1 . 
     Note that the electrolyte member  14  and the unshown electrode members  19 ,  20 , etc., are arranged at a location that is a distance back from the flange  46  toward the housing  11 . Even in this arrangement, the air in the headlamp  1  makes contact with the electrolyte member  14  through the cylindrical wall  45 . Thus, it is possible to remove the moisture. 
     As described above, according to Embodiment 4, the moisture removal device  10  is configured to include the cylindrical convex portion  12  protrusively formed in the housing  11  and having the opening portion  13  on its end face, and the claw portions  47  having elasticity and formed on a circumferential surface of the cylindrical convex portion  12 , so that the housing  11  is fixed to the headlamp  1  in such a manner that the cylindrical convex portion  12  is inserted into the mounting hole  8  formed on the headlamp  1  and the claw portions  47  are latched onto the periphery of the mounting hole  8 . Thus, it is possible to provide the moisture removal device  10  that is easily mountable to the headlamp  1 . 
     Embodiment 5 
       FIG. 14  is a diagram illustrating a fixing method of a headlamp  1  and a moisture removal device  10  according to Embodiment 5 of the invention, and shows an example of their configurations to be fixed by an elastic member.  FIG. 5  is a partial cross-sectional view showing a state where the moisture removal device  10  is fixed to the headlamp  1 . Note that, in  FIG. 14  and  FIG. 15 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 6 , so that their description is omitted here. 
     At the end portion of the cylindrical convex portion  12  of the moisture removal device  10 , a large-diameter portion  50  having a diameter larger than the outer diameter of the base end portion is formed. To the mounting hole  8  formed on the casing  3  of the headlamp  1 , a circular elastic member  51  is attached beforehand. Then, the cylindrical convex portion  12  is press-fitted into the fitting hole  52  of the elastic member  51  while the large-diameter portion  50  is pushing out the fitting hole, to thereby fix the moisture removal device  10  to the casing  3  of the headlamp  1  using a repulsive force (elastic force) of the elastic member  51 . By forming the large-diameter portion  50  on the cylindrical convex portion  12 , it becomes possible to firmly mount the cylindrical convex portion  12  to the elastic member  51 , so that with a simple configuration, the moisture removal device  10  is prevented from dropping out. In addition, the elastic member  51  functions concurrently as the waterproof member  9  in the above configuration. 
     Note that, in  FIG. 14  and  FIG. 15 , there is shown a case of using the elastic member  51  having a grommet (bush) like shape; however, the shape of the elastic member  51  is not limited thereto.  FIG. 16  and  FIG. 17  are partial cross-sectional views each showing a configuration example that uses an elastic member  51  having an O-ring like shape. 
     In the configuration example of  FIG. 16 , a cylindrical wall  53  is formed that protrudes inwardly from the fringe portion of the mounting hole  8  formed on the casing  3  of the headlamp  1 . Then, between the inner surface of the cylindrical wall  53  and the outer surface of the cylindrical convex portion  12 , the elastic member  51  having an O-ring shape is placed so as to abut these surfaces, to thereby fix the moisture removal device  10  to the casing  3  of the headlamp  1  using a repulsive force of the elastic member  51 . 
     In the configuration example of  FIG. 17 , a cylindrical wall  54  is formed that protrudes outwardly from the fringe portion of the mounting hole  8  formed on the casing  3  of the headlamp  1 . On the housing  11  of the moisture removal device  10 , a cylindrical wall  55  is formed so that it surrounds the outer surface of the cylindrical convex portion  12 . Then, between the outer surface of the cylindrical wall  54  and the inner surface of the cylindrical wall  55 , the elastic member  51  having an O-ring shape is placed so as to abut these surfaces, to thereby fix the moisture removal device  10  to the casing  3  of the headlamp  1  using a repulsive force of the elastic member  51 . 
     As described above, according to Embodiment 5, the moisture removal device  10  is configured to include the cylindrical convex portion  12  protrusively formed in the housing  11  and having the opening portion  13  on its end face, and the cyclic elastic member  51 , so that the housing  11  is fixed to the headlamp  1  using the elastic force of the elastic member  51  in such a manner that the cylindrical convex portion  12  is inserted into the mounting hole  8  formed on the headlamp  1  and the elastic member  51  is arranged between the mounting hole  8  and the cylindrical convex portion  12 . Thus, it is possible to provide the moisture removal device  10  that is easily mountable to the headlamp  1 . 
     Embodiment 6 
       FIG. 18  is a cross-sectional view showing a configuration of a moisture removal device  10  according to Embodiment 6. Note that, in  FIG. 18 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 6 , so that their description is omitted here. 
     The moisture removal device  10  according to Embodiment 1 is configured to receive a power supply, for example, of 3V, through the connector portion  21 , and thus a power source device that converts 12V of the on-vehicle battery to 3V is separately required. In contrast, according to Embodiment 6, a power source unit  60  for converting 12V to 3V is built in the moisture removal device  10  so that the device can be connected to the on-vehicle battery by way of the power source unit  60 . Electronic components that constitute the power source unit  60  are mounted on a circuit board  61  to which the end portions of the lead portions  17 ,  18  are connected. Further, a vent hole  62  is formed on the circuit board  61 . 
     In  FIG. 19 , a basic power source circuit that constitutes the power source unit  60  is shown. In this example, a constant voltage circuit is constituted by a resistor R 1  and a zener diode D 1 . This makes unnecessary the power source device that is separately provided in Embodiment 1. 
     Note that, at the time of high humidity, the resistance component of the electrolyte member  14  is decreased to thereby increase the flow of the current, so that, in some cases, it becomes unable to flow a sufficient output current by the above circuit configuration using the resistor R 1  and the zener diode D 1 . Thus, the power source unit  60  may be configured with a power IC for constant voltage circuit, in order to flow a large output current to thereby cause the moisture removal device  10  to sufficiently exhibit its function at the time of high humidity. In an example of circuit configuration shown in  FIG. 20 , a constant-voltage power source is constituted by a power (source) IC (Integrated Circuit)  64 , capacitors C 1 , C 2  for stabilizing the operation of the power IC  64 , a protection diode D 2  and an overvoltage protection element  65  such as a varistor or the like. 
     As described also in Embodiment 1, the dehumidifying function may be always activated by constantly supplying power from the on-vehicle battery  63  to the power source unit  60 . Instead, the power may be supplied in conjunction with the operation of the engine. Further, the power may be supplied in conjunction with the lighting operation of the light assembly for on-vehicle use, such as the headlamp  1  or the like. 
     Note that, in the case where the power source unit  60  is built in the moisture removal device  10 , it is desirable that the moisture removal device  10  be formed into a waterproof structure in order to prevent water from intruding into the power source unit  60  to cause an abnormal operation. Thus, in the configuration example of  FIG. 18 , a partition wall  70  is provided in the housing  11  at a border between the power source unit  60  and the outer air, and a vent hole  71  of the partition wall  70  is closed by an air-permeable waterproof member  72 . The air-permeable waterproof member  72  does not allow water to permeate therethrough but allow water vapor to permeate therethrough. Thus, the operation of the moisture removal device  10  for discharging the moisture in the headlamp  1  by converting it into hydrogen or water vapor is not inhibited. The moisture (humidity) that is discharged into the moisture removal device  10  after passing through the electrolyte member  14 , is discharge from the vent port  22  to the outside through the vent hole  62  formed in the circuit board  61  of the power source unit  60  and the vent hole  71  formed in the partition wall  70 . Meanwhile, if water intrudes from the vent port  22  into the housing  11 , since the water is prevented by the partition wall  70  from intruding into the side of the power source unit  60 , it is possible to avoid an abnormal operation of the power source unit  60  due to water immersion, to thereby enhance the reliability. 
     The electrode members  19 ,  20  that sandwich the electrolyte member  14  of the moisture removal device  10 , are arranged alongside of a wall surface of the housing  11  that serves to fix the electrode members  19 ,  20 , and thus, there is no airtightness between the electrode members  19 ,  20  and the housing  11  unless a special configuration is given therefor. In other words, an air passageway for making communication between the inside and the outside of the headlamp  1 , is formed through gaps between the electrode members  19 ,  20  and the housing  11 , and through the vent hole  62 , the vent hole  71  and the vent port  22 . Thus, it is possible to relieve the pressure produced due to expansion and contraction of air in the headlamp  1 . 
     Note that even in the conventional headlamp  1 , a ventilation component is mounted which is provided with: an air passageway for expansion and contraction of the inner air; and an air-permeable waterproof member that prevents water from intruding through the air passageway. However, since the moisture removal device  10  shown in  FIG. 18  has also a function of the conventional ventilation component, the conventional ventilation component is unnecessary and thus may be omitted. 
     As described above, according to Embodiment 6, the moisture removal device  10  is configured to include the power source unit  60  that converts the voltage of the on-vehicle battery  63  to a predetermined voltage to be applied to the electrolyte member  14 , and then supplies it to the pair of the electrode members  19 ,  20 . Thus, it is possible to achieve the moisture removal device  10  that can receive a power supply directly from the on-vehicle battery  63 . 
     Further, according to Embodiment 6, the moisture removal device  10  is configured to include the vent port  22  for making communication between the inside and the outside of the housing  11 , and the air-permeable waterproof member  72  arranged in the housing  11  and nearer to the vent port  22  than to the electrolyte member  14 . Thus, it becomes possible to avoid the abnormal operation due to water immersion, to thereby achieve the moisture removal device with high reliability. Further, the conventional-type ventilation component for the headlamp  1  may be omitted, so that it is possible to improve ease of assembly of the headlamp  1  to thereby reduce its cost. 
     Embodiment 7 
       FIG. 21  is a circuit diagram showing a configuration example developed from the above power source unit  60 , of a moisture removal device  10  according to Embodiment 7. Note that, in  FIG. 21 , the same reference numerals are given for the same or equivalent parts as in  FIG. 18  to  FIG. 20 , so that their description is omitted here. 
     As described previously, the electrolyte member  14  has a property of changing its resistance value depending on an amount of water due to absorption of moisture. Thus, according to Embodiment 7, under utilization of this property, it is configured to use the electrolyte member  14  as a humidity sensor, so that power is supplied from the power source unit  60  to the electrolyte member  14  arbitrarily in conjunction with the humidity in the headlamp  1 . 
     As shown in  FIG. 21 , the power source unit  60  includes a DC/DC converter  69  configured with a switching element Tr 1  such as a transistor, a diode D 3 , a coil L 1  and a capacitor C 3 , to generate a voltage to be applied to the electrolyte member  14  (for example, 3V) by use of the DC/DC converter  69 . Further, a resistor R 2  is serially connected between the DC/DC converter  69  and the electrolyte member  14 , and a switching element Tr 2 , such as a transistor, is connected in parallel with the resistor R 2 . 
     A control unit  66  is configured with a microcomputer that includes a CPU (Central Processing Unit), output terminals OUT 1 ,  2 , analog input terminals A/D 1 ,  2 , and so on. The control unit  66  outputs from the output terminal OUT 1 , an activation signal for the switching element Tr 1  through a driver  67 , to thereby control the operation of the DC/DC converter. A control power source  68  generates power for activating the control unit  66 . 
     The control unit  66 , when causing the electrolyte member  14  to perform dehumidifying operation, turns on the switching element Tr 2  to thereby apply a voltage of 3V output by the DC/DC converter to the electrolyte member  14 . 
     In contrast, when using the electrolyte member  14  as a humidity sensor, the switching element Tr 2  is turned off by the control unit  66  so as to place the resistor R 2  in serial connection, to thereby apply a voltage to the electrolyte member  14 . On this occasion, the control unit  66  detects a value of divided voltage between the resistor R 2  and the electrolyte member  14  as a terminal voltage value of the input terminal A/D 2 . 
     If the resistor R 2  is set to a given resistance value, a resistance value between the terminals of the electrolyte member  14  can be calculated from a ratio between the voltage across the terminals of the resistor R 2  and the voltage across the terminals of the electrolyte member  14  (a ratio between the terminal voltages at the input terminals A/D 1 ,  2 ). The resistance value between the terminals of the electrolyte member  14  corresponds to an amount of water due to absorption of moisture, namely, a humidity in the internal space of the headlamp  1 , so that the humidity can be estimated based on the resistance value between the terminals. 
     The control unit  66  periodically estimates the humidity in the headlamp  1 , and when the humidity is higher than a predetermined threshold value, turns on the switching element Tr 2  to apply the output voltage of the DC/DC converter  69  to the electrolyte member  14 , so that the dehumidifying operation is performed. In contrast, when the humidity is the threshold value or lower, the control unit suspends the DC/DC converter  69 , so that no dehumidifying operation is performed. This makes it possible to cause the moisture removal device  10  to perform the operation when necessary and to suspend the operation when unnecessary, so that the life of the electrolyte member  14  can be prolonged while reducing the applied power to the moisture removal device  10 . 
     Further, since the DC/DC converter  69  is acceptable to output a large current, its capability is further enhanced than that of the power source unit  60  illustrated in  FIG. 20  of Embodiment 6. Thus, not only in the case of dealing with the moisture in the air, but also in the situation where a water droplet or water (liquid) adheres to the electrolyte member  14  so that its resistance is decreased and thus the flow of the current is increased, it is possible to remove moisture, in other words, to discharge water. Note that the power source unit  60  may be configured so that the humidity in the headlamp  1  is detected using a different humidity sensor from the electrolyte member  14 . 
     As describe above, according to Embodiment 7, the moisture removal device  10  is configured to use the electrolyte member  14  as a moisture sensor, to thereby operate in conjunction with the humidity in the headlamp  1  detected using the electrolyte member  14 . Thus, it becomes possible to perform dehumidification operation only at the time the humidity in the headlamp  1  is high, so that the life of the electrolyte member  14  can be prolonged while reducing the applied power. 
     Note that the power source unit  60  to be used in each of Embodiments 1 to 5 and 7 may be configured as an independent power source device so that this power source device converts 12V of the on-vehicle battery  63  to 3V and supplies it to the moisture removal device  10 . Further, the power source device may be mounted to the headlamp  1  together with a light-source lighting device and the like. With this configuration, a wiring from the vehicle-body side to the light-source lighting device or the like, can be commonly used, and thus, no special wiring is necessary to be laid from the vehicle-body side to the moisture removal device  10 . Thus, it is possible to achieve the headlamp  1  that is easy to be handled. 
     Embodiment 8 
       FIG. 22  is a cross-sectional view showing a configuration of a headlamp  1  according to Embodiment 8. Note that, in  FIG. 22 , the same reference numerals are given for the same or equivalent parts as in  FIG. 1  to  FIG. 17 , so that their description is omitted here. 
     To a connector portion  81  of an LED lighting device (light-source lighting device)  80  equipped with a power source for moisture removal device, a power line extending from the on-vehicle battery is connected. The LED lighting device  80  equipped with a power source for moisture removal device converts, using its built-in DC/DC converter (unshown), the power of the on-vehicle battery applied through the connector portion  81 , to the power for lighting the LED  5 , and then supplies it to the LED  5  through a power line for lighting  82 . 
     In Embodiment 8, such a configuration is employed in which the power for causing the moisture removal device  10  to perform dehumidifying operation is supplied by the LED lighting device  80  equipped with a power source for moisture removal device. For example, the power for dehumidification by the moisture removal device  10  is taken out from a secondary winding of a transformer in the DC/DC converter that is built in the LED lighting device  80  equipped with a power source for moisture removal device, and is supplied to the moisture removal device  10  through a power line for dehumidification  83 . Instead, another configuration may be employed in which the LED lighting device  80  equipped with a power source for moisture removal device, has a built-in power source unit  60  as shown in  FIG. 19  to  FIG. 21 , so that the power of the on-vehicle battery applied through the connector portion  81  is converted to the power for dehumidification and supplied to the moisture removal device  10  through the power line for dehumidification  83 . 
     Note that, in  FIG. 22 , although a configuration example is shown in which the moisture removal device  10  is mounted on the maintenance cover  31 , it may be mounted on the casing  3  as shown in  FIG. 1  or  FIG. 2 . 
     Furthermore, the LED lighting device  80  equipped with a power source for moisture removal device, and the moisture removal device  10  may be integrated with each other. In  FIG. 23 , the headlamp  1  is shown that mounts thereon a dehumidifying-function-containing LED lighting device  90  in which a dehumidifying function is incorporated. In this example, an integrated housing  91  is used that integrates a housing of the LED lighting device  80  equipped with a power source for moisture removal device, and the housing  11  of the moisture removal device  10 . On the integrated housing  91 , an opening portion  13  is formed similarly to the housing  11  of the moisture removal device  10 . Further, in the integrated housing  91 , the respective components such as the electrolyte member  14 , the electrode members  19 ,  20 , etc., that constitute the moisture removal device  10 , are accommodated. In addition, in the integrated housing  91 , the respective components such as the DC/DC converter, etc., that constitute the LED lighting device  80  equipped with a power source for moisture removal device, are accommodated. The dehumidifying-function-containing LED lighting device  90  with this configuration converts the power of the on-vehicle battery to the power for lighting the LED  5  thereby supplying it to the LED  5  through the power line for lighting  82 , as well as converts to the power for dehumidification by the moisture removal device  10  thereby supplying it to the electrolyte member  14  in the integrated housing  91 . 
     As described above, according to Embodiment 8, the headlamp  1  is configured to include the LED lighting device  80  equipped with a power source for moisture removal device that converts the voltage of the on-vehicle battery  63  to a predetermined voltage for lighting and supplies it to the LED  5 , wherein the LED lighting device  80  equipped with a power source for moisture removal device converts the voltage of the on-vehicle battery  63  to a predetermined voltage to be applied to the electrolyte member  14  and supplies it to the moisture removal device  10 . Thus, it is unnecessary to individually provide the respective power sources for the LED  5  and the moisture removal device  10 , and thus the headlamp  1  can be achieved with a simple configuration. 
     Further, according to Embodiment 8, the headlamp  1  is configured to include the dehumidifying-function-containing LED lighting device  90  that has a function of converting the voltage of the on-vehicle battery  63  to a predetermined voltage for lighting and supplying it to the LED  5 , and a dehumidifying function; wherein, the housing  11  of the moisture removal device  10  is formed as the integrated housing  91  that is integrally configured with the housing of the dehumidifying-function-containing LED lighting device  90 ; the integrated housing  91  accommodates the components of the LED lighting device  80  equipped with a power source for moisture removal device, the electrolyte member  14  and the pair of electrodes  19 , 20 ; the opening portion  13  is formed that is made open to the inside of the headlamp  1  when the integrated housing  91  is fixed to the casing  3  of the headlamp  1 ; and the dehumidifying-function-containing LED lighting device  90  converts the voltage of the on-vehicle battery  63  to the predetermined voltage to be applied to the electrolyte member  14  and supplies it to the pair of the electrode members  19 ,  20  in the integrated housing  91 . Thus, it is unnecessary to independently provide the moisture removal device  10 , and thus the headlamp  1  can be achieved with a simple configuration. 
     Note that in Embodiments 1 to 8, there are shown the cases of using the LED  5  as a light source; however, a discharge lamp, a tungsten filament light bulb or the like may be used other than the LED. 
     Further, other than the headlamp  1 , the light assembly for on-vehicle use may be a tail lamp, a fog lamp, a turn-signal lamp, a position lamp, or the like. For the light assembly that has a large light emitting area, namely, whose dew condensation is likely to be visually recognized, the moisture removal device  10  is effective. 
     Other than the above, unlimited combination of the respective embodiments, modification of any configuration element in the embodiments and omission of any configuration element in the embodiments may be made in the present invention without departing from the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     As described above, the moisture removal device according to the invention is configured to transfer and dissipate the heat generated by the electrolyte member by use of the electrode members made of a metal, so that it is suited to be used for alight assembly for on-vehicle use arranged in an engine room where a combustible gas exists. 
     DESCRIPTION OF REFERENCE NUMERALS and SIGNS 
     
         
         
           
               1 : headlamp,  2 : front lens,  3 : casing,  4  projection lens,  5 , LED,  6 : mirror reflector,  7 : heat sink,  8 : mounting hole,  9 : waterproof member,  10 : moisture removal device,  11 : housing,  12 : cylindrical convex portion,  13 : opening portion,  14 : electrolyte member,  15 ,  15   a ,  16 ,  16   a : electrode portions,  17 ,  18 : lead portions,  19 : positive-side electrode member,  20 : negative-side electrode member,  21 : connector portion,  22 : vent port,  23 ,  24 : buffer members,  25 : elastic member,  26 : support member,  27 : vent hole,  30 : maintenance opening portion,  31 : maintenance cover,  40 : screw hole,  41 : screw passing hole,  42 : screw,  43 : cutout portion,  44 : projection portion,  45 : cylindrical wall,  46 : flange,  47 : claw portion,  48 : concave portion,  49 : cutout hole,  50 : large-diameter portion,  51 : elastic portion,  52 : fitting hole,  53 : cylindrical wall,  54 : cylindrical wall,  55 : cylindrical wall,  60 : power source unit,  61 : circuit board,  62 : vent hole,  63 : on-vehicle battery,  64 : power IC,  65 : overvoltage protection element,  66 : CPU,  67 : driver,  68 : control power source,  69 : DC/DC converter,  70 : partition wall,  71 : vent hole,  72 : air-permeable waterproof member,  80 : LED lighting device equipped with a power source for moisture removal device,  81 : connector portion,  82 : power line for lighting,  83 : power line for dehumidification,  90 : dehumidifying-function-containing LED lighting device,  91 : integrated housing.