Patent Publication Number: US-7708440-B2

Title: Electric ballast and a lighting system

Description:
TECHNICAL FIELD 
     The invention relates to lighting systems such as, for example, headlights, fog lights or the like, and in particular, to an electric ballast for the system. 
     BACKGROUND ART 
     A prior art device described in Japanese Patent Application Publication No. 2001-338506 includes an electric ballast for a vehicle lighting system that comprises a lamp housing with front and rear openings, a front lens closing the front opening, a discharge lamp put in the housing, and a reflector put in the housing to reflect light of the lamp toward the lens. The ballast is formed of a ballast housing closing said rear opening, and an inverter and an igniter which are put in the ballast housing. The ballast is also electrically connected with the lamp via a wire harness (wires and connectors) and a lamp socket. 
     Another prior art device described in Japanese Patent Application Publication No. 2002-367414 includes an electric ballast for a vehicle lighting system that comprises a lamp housing with front and rear openings, a front lens closing the front opening, a cap closing the rear opening, a discharge lamp put in the housing, and a reflector put in the housing to reflect light of the lamp toward the lens. This ballast is formed of an inverter mounted on the inner face of the cap, and an igniter put in a lamp socket within the lamp housing. These inverter and igniter are electrically connected each other through a wire harness including wires. 
     In these prior art devices and other similar prior art devices (e.g., France Patent Publication No. 2776365, U.S. Pat. No. 6,364,515 and Japanese Patent Application Publication Nos. 2001-101908 and 2002-343128), the wires within a lamp housing need be covered with a costly sheath shield such as a mesh shield or the like in the same way as, for example, a device described in Japanese Patent Application Publication No. 2000-195685. Because there is a possibility that noise generated from a discharge lamp caused by polarity inversing of a lamp current enters each portion of a ballast through the wires to cause wrong operation of devices. 
     Other prior art devices described in Japanese Patent Application Publication Nos. 2001-101909 and 2003-317535 are provided with a ballast housing that includes a lamp socket or a discharge lamp in addition to an inverter and an igniter. According to these devices, the need of said sheath shield is eliminated. However, if the ballast housing does not have a shield function, said possibility of the wrong operation remains. In the latter, especially, a seal member (insulating member or elastic moulding) exposed from the inside of the ballast housing touches the lamp housing. The former also has the ballast housing inside the lamp housing, and accordingly its ballast is exposed to high temperature within the lamp housing, so that heat generating parts (high temperature parts) of the ballast become extremely high temperature. 
     It is an object of the present invention to eliminate the need of a shield sheath in a lamp housing, and also to protect heat generating parts of an electric ballast from high temperature in the lamp housing. 
     DISCLOSURE OF THE INVENTION 
     The present invention is an electric ballast attached to the outside of a lighting system. The lighting system comprises a lamp housing with a front opening and a rear opening, a front lens closing the front opening, a discharge lamp put in the lamp housing, and a reflector put in the lamp housing to reflect light of the lamp toward the lens. The electric ballast comprises: a ballast housing which closes the rear opening and is electrically connected with frame ground via at least one of the lamp housing and the reflector; a lamp socket which is put in the front of the ballast housing and directly connects with the lamp; a power converter which is put in the ballast housing and of which output is electrically connected with the socket; and an igniter which is put in the front of the ballast housing and is electrically connected between the power converter and the socket. Heat generating parts of the power converter are put in the rear of the ballast housing, and the rear of the ballast housing functions as a radiator. 
     In this configuration, since the lamp socket and the igniter are put in the front of the ballast housing, attenuation of pulse voltage can be reduced. Since the ballast housing is electrically connected with frame ground in particular, it is possible to achieve better shield effect of the ballast housing with respect to noise from the lamp, and the need of a shield sheath in the lamp housing can be eliminated. As a result, cost down and a compact system are achieved. Moreover, the heat generating parts are put in the rear of the ballast housing and the rear of the ballast housing functions as a radiator, and accordingly the heat generating parts can be protected from high temperature in the lamp housing. Consequently, low heat-resistant heat generating parts can be used and the cost is reduced. 
     In a preferable embodiment, the electric ballast further comprises a loop-shaped elastic coupling with an inner peripheral edge and an outer peripheral edge. The inner peripheral edge and the outer peripheral edge of the elastic coupling are respectively joined to the rear of the reflector and the peripheral edge of the rear opening so that the elastic coupling movably supports the reflector. The ballast housing is fixed on the rear of the reflector and also electrically connected with the reflector. In this configuration, the rear opening side of the lamp housing is made waterproof. By moving the reflector, the optical axis of the lamp can be adjusted. For example, lighting systems suitable for headlights can be provided. 
     In another preferable embodiment, the electric ballast further comprises a loop-shaped elastic coupling with an inner peripheral edge and an outer peripheral edge. The ballast housing is fixed on the rear of the reflector and also electrically connected with the reflector. The inner peripheral edge and the outer peripheral edge of the elastic coupling are respectively joined to the ballast housing and the peripheral edge of the rear opening so that the elastic coupling movably supports the reflector through the ballast housing. In this configuration, the rear opening side of the lamp housing is made waterproof. By moving the reflector, the optical axis of the lamp can be adjusted. For example, lighting systems suitable for headlights can be provided. 
     In other preferable embodiment, the ballast housing is fixed on the lamp housing with the rear opening close, and also electrically connected with the lamp housing. In this configuration, the rear opening side of the lamp housing is made waterproof. For example, lighting systems suitable for fog lights can be provided. 
     In an enhanced embodiment, the electric ballast further comprises a filter which is located between the power converter and the igniter and has two series capacitors connected in parallel with the lamp through the igniter. The ballast housing is electrically connected between the series capacitors. In this configuration, noise from the lamp can be further reduced. 
     In an alternate embodiment, the igniter includes a switch for trigger. The switch is a discharge gap for self-excitation or a semiconductor switch for separately-excitation. For example, in case that the semiconductor switch is used, the upper limit value of pulse voltage can be restricted and accordingly compact systems are realized. 
     In another alternate embodiment, the power converter and the igniter are mounted on the same substrate. According to this configuration, compact systems are realized. 
     In other alternate embodiment, at least one of the power converter and the igniter includes a transformer with windings each of which is formed of pattern wiring of a substrate. According to this configuration, compact systems are realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described in further details. Other features and advantages of the present invention will become better understood with regard to the following detailed description and accompanying drawings where: 
         FIG. 1  is a sectional view of a lighting system, in accordance with a first embodiment of the present invention; 
         FIG. 2  is a sectional view of an electric ballast in  FIG. 1 ; 
         FIG. 3  is a circuit diagram of the electric ballast in  FIG. 1 ; 
         FIG. 4  is a sectional view of an electric ballast, in accordance with a varied embodiment of the present embodiment; 
         FIG. 5  is a sectional view of an electric ballast, in accordance with an alternate embodiment of the present embodiment; 
         FIG. 6  is a sectional view of an electric ballast, in accordance with another alternate embodiment of the present embodiment; 
         FIG. 7A  is a sectional view of an electric ballast seen from the side, in accordance with other alternate embodiment of the present embodiment; 
         FIG. 7B  is a sectional view of the electric ballast of  FIG. 7A  seen from the rear; 
         FIG. 8  is a sectional view of an electric ballast, in accordance with another varied embodiment of the present embodiment; 
         FIG. 9  is a sectional view of an electric ballast, in accordance with an alternate embodiment of the present embodiment; 
         FIG. 10  is a sectional view of a lighting system, in accordance with a second embodiment of the present invention; 
         FIG. 11  is a sectional view of a lighting system, in accordance with a third embodiment of the present invention; 
         FIG. 12  is a sectional view of an electric ballast, in accordance with a varied embodiment of the present embodiment; and 
         FIG. 13  is a sectional view of a lighting system, in accordance with a fourth embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 1  shows a lighting system in accordance with a first embodiment of the present invention. The lighting system of  FIG. 1  is a vehicle lighting system such as headlights, fog lights or the like, and is, for example, a fog light in the first embodiment. This system is formed of a lamp housing  16 , a front lens  17 , a reflector  18 , a discharge lamp  19  and an electric ballast  10 . 
     The lamp housing  16  is, for example, a case in which the reflector  18  and the discharge lamp  19  are put, and has a front opening  16   a  and a rear opening l 6   b . The opening  16   b  is formed at the bottom  161  of the housing  16 . The housing  16  is formed of conductive materials such as, for example, metal or the like. In case of fog lights, the lamp housing is usually connected with frame ground. The housing  16  is also connected with frame ground. 
     The front lens  17  is formed of materials for translucency to close the front opening  16   a . The lens  17  is fixed on the edge of the front opening  16   a  with, for example, adhesive such as hot melt or the like, or a seal such as a rubber packing or the like. That is, the front opening  16   a  side of the housing  16  is made waterproof. 
     The reflector  18  is, for example, a parabolic reflector formed of conductive materials such as metal or the like, and has a hole  181   a  through which the lamp  19  is inserted. The hole  181   a  is formed at the bottom  181  of the reflector  18 . The reflector  18  is also put in the housing  16  so as to reflect light of the lamp  19  toward the lens  17 . 
     As shown in  FIGS. 1 and 2 , the discharge lamp  19  is a single-base type lamp (e.g., HID (high intensity discharge) lamp), and is put in the housing  16 . The lamp  19  is formed of an outer glass envelope  190 , a single base  191  that retains one end of the envelope  190 , an arc tube  192  put in the envelope  190 , an inner electrode  193  located between the base  191  and one end of the tube  192  through the inside of the envelope  190 , an outer electrode  194  located between the base  191  and other end of the tube  192  through the outside of the envelope  190 , and a protection tube  195  covering the outer electrode  194 . 
     The single base  191  is provided therein with a pair of electrodes (not shown) electrically connected with the electrodes  193  and  194 , respectively. The base  191  also has a flange  191   a  that is in contact with the bottom  181  of the reflector  18  in a state that the ballast  10  is attached to the outside of the lighting system. In this state, the rear opening  16   b  side of the housing  16  is made waterproof with a seal packing  160  sandwiched between the edge of the opening  16   b  and the ballast  10 . The packing  160  is, for example, an O-ring such as a rubber molding, an elastic resin or the like. 
     As shown in  FIGS. 2 and 3 , the electric ballast  10  is formed of a ballast housing  11 , a lamp socket  12 , a power converter  13 , an igniter  14  and a filter  15 . 
     The ballast housing  11  is, for example, a case and a cover that are formed of conductive materials such as metal or the like, and has a front opening  11   a , a bottom opening  11   b , and a connecter  110  formed of conductive materials such as metal or the like. The ballast housing  11  is fixed to the outer face of the bottom  161  of the lamp housing  16  by a fixing means (not shown) such as, for example, screws, twist lock connectors or the like, and closes the rear opening  16   b  of the lamp housing  16 . In this state, the ballast housing  11  is electrically connected with the lamp housing  16  by the fixing means and also the contact of the connecter  110  with the outer face of the bottom  161  of the lamp housing  16 . Accordingly, it is possible to reduce noise in the FM band or TV band by polarity inversing of the lamp current from the lamp  19  without said costly sheath shield. 
     The lamp socket  12  has output terminals  121  and  122  of the ballast  10 , and is put in the front  11   c  of the ballast housing  11 . Also, the socket  12  directly connects with the lamp  19  by, for example, bayonet construction to support the lamp  12 . The terminals  121  and  122  are electrically connected with the electrodes of the base  191 , respectively. 
     As shown in  FIGS. 2 and 3 , the power converter  13  includes a power input coupler  130 , an input filter  131 , a DC-DC converter  132 , an inverter  133  and a controller  134 , and is put in the ballast housing  11 . 
     The power input coupler  130  is located at the bottom opening  11   b  of the ballast housing  11 , and is electrically connected with, for example, a 12V DC power source through a wire harness. 
     The input filter  131  is mainly a LC filter, and is located between the coupler  130  and the DC-DC converter  132 . In an example of  FIG. 3 , the filter  131  is formed of electrolytic capacitors  131   a  and  131   b , an inductor, diodes and an RCP (reverse connection protection) circuit. 
     The DC-DC converter  132  includes a forward type DC-DC converter for the inverter  133  and a flyback type DC-DC converter for the igniter  14 , and is formed of a MOSFET  132   a , a transformer  132   b , diodes  132   c - 132   e , capacitors and so on. The converter for the inverter  133  converts DC voltage from the DC power source into a stable light output of lamp  19  (DC voltage). 
     The inverter  133  is formed of, for example, a full bridge module of which output is electrically connected with the socket  12 , and converts the DC voltage from the DC-DC converter  132  into square wave AC voltage. The square wave AC voltage is applied to the lamp  19 . 
     The controller  134  is formed of a power voltage monitor  135 , a detector  136 , an arithmetic unit  137 , an HF (high frequency) driver  138  and an LF (low frequency) driver  139 . The monitor  135  detects DC voltage from the DC power source. The detector  136  includes a VLA detector  136   a  for detecting a value of output voltage of the converter for the inverter  133  and an ILA detector  136   b  for detecting a value of output current of the converter for the inverter  133 . The arithmetic unit  137  provides the HF driver  138  with a control signal that causes a value of output power of the converter for the inverter  133  to be equal to a predetermined value based on both values from the detector  136 . The HF driver  138  provides the MOSFET  132   a  with a PWM signal of which duty and frequency are adjusted in response to the control signal from the arithmetic unit  137 . The LF driver  139  provides the inverter  133  with a signal that alternately turns on and off diagonal pairs of switches (four MOSFETs) in the inverter  133  at a low frequency. 
     As shown in  FIGS. 2 and 3 , said power converter  13  is provided with heat generating parts such as the MOSFET  132   a , the diode  132   c  and so on, and therefore the heat generating parts are put in the rear  11   d  of the ballast housing  11 . And the rear  11   d  functions as a radiator by locating the ballast housing  11  to the rear outside of the lamp housing  16 . Specifically, the MOSFET  132   a , the diode  132   c  and so on are mounted on the rear face of a substrate  13   a , and heat from the heat generating parts is effectively released from the inside of the ballast housing  11  to the outside. Thereby, low-priced parts can be used. In addition, the capacitors  131   a  and  131   b , the transformer  132   b  and so on are mounted on the front face of the substrate  13   a , and the inverter  133  is mounted on a substrate  14   a . These parts are fixed on the substrate  13   a  by, for example, soldering, brazing, conductive adhesive or the like. 
     The igniter  14  is electrically connected between the converter for the igniter  14  in the power converter  13  and the socket  12 , and applies high pulse voltage across the lamp  19  to start the lamp  19 . The igniter  14  is formed of, for example, a pulse transformer  140 , a discharge gap  141  connected in series with a primary winding of the transformer  140 , a capacitor  142  connected in parallel with the primary winding and gap  141 , and so on. The output of the converter for the igniter  14  is electrically connected between the primary winding and the capacitor  142 . A secondary winding of the transformer  140  is inserted in series to one of the output terminals  121  and  122  of the socket  12 , and is located in proximity to the socket  12 . Therefore, since distance between the secondary winding and the socket  12  is short, insulation distance and so on can be easily secured. The insulation distance prevents secondary occurrence of corona discharge in response to the pulse voltage. Attenuation of the pulse voltage is also prevented. 
     The igniter  14  also has a safety function that prevents occurrence of high voltage when the lamp  19  is not installed, and is put in the front  11   c  of the ballast housing  11 . To be concrete, the transformer  140 , the gap  141 , the capacitor  142  and so on are mounted on the substrate  14   a  by, for example, soldering, brazing, conductive adhesive or the like. The substrate  14   a  is, for example, a print board, a resin substrate or the like. 
     The filter  15  includes an inductor (filter choke)  150  and capacitors  151 - 154 , and is located between the converter for igniter  14  in the power converter  13  and the igniter  14 . The inductor  150  and the capacitors  151 - 154  are mounted on the substrate  14   a  with, for example, soldering, brazing, conductive adhesive or the like. The capacitor  153  is connected in series with the capacitor  154 , while the series combination of the capacitors  153  and  154  is connected in parallel with the lamp  19  through the igniter  14 . And the joint of the capacitors  153  and  154  is electrically connected with the ballast housing  11  to be electrically connected with frame ground. Thus, the igniter  14  is protected by the electromagnetic shield and therefore it is possible to reduce noise in the FM band or TV band by polarity inversing of the lamp current from the lamp  19  without the costly sheath shield. 
     Said electric ballast  10  is detachably attached to the outside of the lamp housing  16 . That is, the socket  12  of the ballast  10  is equipped with the base  191  of the lamp  19 , and then the ballast housing  11  is fixed to the rear of the lamp housing  16  by said fixing means while inserting the lamp  19  into the rear opening  16   b  of the lamp housing  16  and the hole  18 la of the reflector  18 . At this point, since the ballast housing  11  is electrically connected with frame ground via the lamp housing  16 , it is possible to achieve better shield effect of the ballast housing  11  with respect to noise from the lamp  19  and the need of a shield sheath in the lamp housing  16  can be eliminated. Consequently, cost down and compact systems are achieved. 
     In an alternate embodiment, the lighting system is a headlight and the ballast housing  11  is electrically connected with the reflector  18 . In case of headlights, the reflector ( 18 ) is usually connected with frame ground. Therefore, the ballast housing  11  is electrically connected with frame ground via the reflector  18 . 
     In another alternate embodiment, the igniter  14  is provided with a semiconductor switch for separately-excitation in stead of the discharge gap  141 . The switch is turned on through a trigger circuit. According to this configuration, the upper limit value of the pulse voltage is restricted, further contributing to the compactness of the system. 
     In a varied embodiment, as shown in  FIG. 4 , parts of the electric ballast  10  are mounted on the same substrate  10   a  instead of the substrates  13   a  and  14   a . The pulse transformer  140  is inserted into a hole of the substrate  10   a  and then fixed on the substrate  10   a . In  FIG. 4 ,  140   a ,  140   b  and  140   c  are the primary winding, the secondary winding and a ferrite core of the transformer  140 , respectively. However, the parts of the electric ballast  10  may be arranged as shown in  FIGS. 5 ,  6 ,  7 A and  7 B. In  FIG. 5 , the transformer  140  is located at a diagonally lower rear side of the socket  12 . In  FIG. 6 , the transformer  140  is located at a diagonally upper rear side of the socket  12  and is inserted into a hole of the substrate  10   a . In  FIGS. 7A and 7B , the output terminals of the socket  12  differ from those of  FIG. 6 . According to these configurations, thin shaped electric ballasts are obtained. 
     In another modified embodiment, as shown in  FIG. 8 , the power converter  13  includes the transformer  132   b  with primary and secondary windings  132   b - 1  and  132   b - 2  each of which is formed of pattern wiring of the substrate (print board)  10   a . As shown in  FIG. 9 , igniter  14  may also include the transformer  140  with the primary and secondary windings  140   a  and  140   b  each of which is formed of pattern wiring of the substrate  10   a . According to these configurations, compact electric ballasts are obtained. 
       FIG. 10  shows a lighting system in accordance with a second embodiment of the present invention. The lighting system of  FIG. 10  is a headlight, and is formed of a lamp housing  26 , a front lens  27 , a reflector  28 , a discharge lamp  29  and an electric ballast  20 . Mainly different points from the first embodiment are explained below. 
     In case of headlights, the reflector is usually connected with frame ground. The reflector  28  is also connected with frame ground. 
     The lamp housing  26  is provided with a pair of vertical movable supports  262  and  263  that adjust a vertical inclination of optical axis of the headlight, and a pair of horizontal movable supports (not shown) that adjust a horizontal inclination of optical axis of the headlight. The lamp housing  26  may be formed of resin or the like. 
     The vertical movable support  262  is formed of, for example, a nut holder  262   a , a bolt  262   b  for aiming and a rib  262   c . The holder  262   a  is fixed to a hole in the rear upper part of the lamp housing  26 . The bolt  262   b  is screwed into the holder  262   a  so as to be inserted into the inside of the lamp housing  26 . The rib  262   c  has a threaded hole into which the tip of the bolt  262   b  is screwed, and is fixed on the rear upper part of the reflector  28 . 
     The vertical movable support  263  is formed of, for example, a boss  263   a , a support axis  263   b  and a bearing  263   c . The boss  263   a  is fixed on the inner face and the rear lower part of the lamp housing  26 . The axis  263   b  has a sphere-shaped tip, and is supported with the boss  263   a  so as to extend the tip forward. The bearing  263   c  is fixed on the rear lower part of the reflector  28 , and holds (grips) the tip of the axis  263   b.    
     For example, the optical axis of the headlight can be inclined downward by turning the bolt  262   b  clockwise, while the optical axis can be inclined upward by turning the bolt  262   b  anti-clockwise. The horizontal movable supports are also formed in the same way as the vertical movable supports. 
     The lamp housing  26  is also provided with pillar-shaped bosses (each of which is denoted by  264 ) at the rear thereof, while a ballast housing  21  of the electric ballast  20  is provided with ribs ( 211 ) respectively corresponding to the bosses ( 264 ) at the sides thereof. Each boss  264  has a threaded hole, and each rib  211  has a through hole. Accordingly, by inserting each screw S as said fixing means into each through hole of the ribs ( 211 ) to fix each screw S into each threaded hole of the bosses ( 264 ), the ballast housing  21  can be fixed at the outside of the concave bottom  261  of the lamp housing  26 . In this case, a rear opening  26   b  of the lamp housing  26  is closed with the ballast housing  21 , and the rear opening  26   b  side is made waterproof with a ring-shaped seal packing  260  sandwiched between the both of them. The packing  260  is attached around a protrusion  212  in the front of the ballast housing  21 . 
     In addition, before the ballast  20  is fixed at the rear of the lamp housing  26 , the wire harness from said DC power source is connected with a power input coupler  230 . The coupler  230  is then put in the lamp housing  26  when the ballast  20  is fixed at the rear of the lamp housing  26 . On account of this, the wire harness and the coupler  230  need not be directly made waterproof. The wire harness may be inserted into the housing from a hole formed at the lower side of the lamp housing  26 , or sandwiched between the lamp housing  26  or the ballast housing  21  and the seal packing  260 . In case of the former, the hole may be closed with a seal such as silicon rubber or the like. 
     Moreover, the ballast housing  21  is electrically connected with the reflector  28  through a connector  210 , and electrically connected with frame ground via the reflector  28 . Accordingly, it is possible to achieve better shield effect of the ballast housing  21  with respect to noise from the lamp  29  and the need of a shield sheath in the lamp housing  26  can be eliminated. As a result, cost down and compact systems are achieved. 
       FIG. 11  shows a lighting system in accordance with a third embodiment of the present invention. The lighting system of  FIG. 11  is, for example, a headlight, and is formed of a lamp housing  36 , a front lens (not shown), a reflector  38 , a discharge lamp  39  and an electric ballast  30 . In  FIG. 11 ,  330  and  360  are a power input coupler and a seal packing, respectively, and vertical and horizontal movable supports are not shown. Mainly different points from the second embodiment are explained below. 
     The lamp housing  36  further comprises a loop-shaped elastic coupling  365  with an inner peripheral edge and an outer peripheral edge. The inner peripheral edge and the outer peripheral edge of the coupling  365  are respectively joined to the rear of the reflector  38  (peripheral edge of the bottom  381 ) and the peripheral edge of the rear opening  36   b  of the lamp housing  36  so that the coupling  365  movably supports the reflector  38 . 
     The ballast housing  31  of the ballast  30  is fixed on the rear (bottom  381 ) of the reflector  38  by a fixing means (not shown) such as, for example, screws, twist lock connectors or the like. The ballast housing  31  is also electrically connected with the reflector  38  through a connector  310 . 
     Thus, since the ballast housing  31  is electrically connected with the reflector  38  through the connector  310 , the ballast housing  31  is electrically connected with frame ground via the reflector  38 . Accordingly, it is possible to achieve better shield effect of the ballast housing  31  with respect to noise from the lamp  39  and the need of a shield sheath in the lamp housing  36  can be eliminated. As a result, cost down and compact systems are achieved. In addition, a high beam and a low beam can be changed each other by moving the reflector  38 . 
     In a varied embodiment, as shown in  FIG. 12 , the loop-shaped elastic coupling  365  is, for example, a rubber molding or the like which permits mechanical expansion and contraction in the radial direction of the rear opening  36   b . In  FIG. 12 , the inner peripheral edge and the outer peripheral edge of the coupling  365  are respectively joined to the opening edge of a cylindrical portion  382  formed at the rear of the reflector  38  and the peripheral edge of the rear opening  36   b  through, for example, glue, crimping, pressure welding or the like. Mainly different points from the third embodiment are explained below. 
     In  FIG. 12 , a hole  381   a  of the reflector  38  is smaller than a flange  391   a  of a single base  391  of the lamp  39 , and the flange  391   a  is in contact with a peripheral edge portion of the hole  381   a  in the reflector  38 . In this state, the flange  391   a  is fixed through an attachment  383  provided at the rear of the reflector  38 . The attachment  383  can be turned around an axis  383   a  fixed at the lower side of the hole  381   a  in the reflector  38 . Therefore, the lamp  39  can be fixed to the reflector  38  by turning the attachment  383  anti-clockwise, while the lamp  39  can be removed from the reflector  38  by turning the attachment  383  clockwise. 
     The ballast housing  31  has a substantially cylindrical side wall and is fixed at the rear of the reflector  38  by electrically and mechanically connecting a lamp socket  32  to the base  391  of the lamp  39  fixed to the reflector  38  with the attachment  383 . In this case, since the packing  360  attached around a cylindrical protrusion  312  of the ballast housing  31  is fastened between the cylindrical portion  382  and the ballast housing  31 , the inside of the lighting system of  FIG. 12  is made waterproof. In  FIG. 12 ,  362  and  363  are a pair of vertical movable supports. The vertical movable support  362  is formed of a nut holder  362   a , a bolt  362   b  for aiming and a rib  362   c , while the vertical movable support  363  is formed of a boss  363   a , a support axis  363   b  and a bearing  363   c.    
     According to the configuration of  FIG. 12 , compact systems are achieved and waterproof property is ensured. Moreover, since the ballast  30  is fixed at the rear of the reflector  38 , the hole  381   a  of the reflector  38  need not be enlarged for adjustment of optical axis of the lamp  39 . As a result, light of the lamp  39  can be preferably reflected toward the lens  37 . The distribution design of light of the lamp  39  also becomes easy. 
       FIG. 13  shows a lighting system in accordance with a fourth embodiment of the present invention. The lighting system of  FIG. 13  is, for example, a headlight, and is formed of a lamp housing  46 , a front lens (not shown), a reflector  48 , a discharge lamp  49  and an electric ballast  40 . Mainly different points from the third embodiment are explained below. 
     The ballast housing  41  of the ballast  40  is directly fixed on the rear of the reflector  48  by a fixing means (not shown) such as, for example, screws, twist lock connectors or the like to be electrically connected with the reflector  48 . 
     The lamp housing  46  further comprises a loop-shaped elastic coupling  465  with an inner peripheral edge and an outer peripheral edge. The inner peripheral edge and the outer peripheral edge of the coupling  465  are respectively joined to the ballast housing  41  and the peripheral edge of the rear opening  46   b  of the lamp housing  46  so that the coupling  465  movably supports the reflector  48  through the ballast housing  41 . 
     Thus, since the ballast housing  41  is electrically connected with the reflector  48 , the ballast housing  41  is electrically connected with frame ground via the reflector  48 . Accordingly, it is possible to achieve better shield effect of the ballast housing  41  with respect to noise from the lamp  49  and the need of a shield sheath in the lamp housing  46  can be eliminated. As a result, cost down and compact systems are achieved. In addition, a high beam and a low beam can be changed each other by moving the reflector  48 . 
     Although the present invention has been described with reference to certain preferred embodiments, numerous modifications and variations can be made by those skilled in the art without departing from the true spirit and scope of this invention.