Patent Publication Number: US-11378244-B2

Title: Headlight apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a technique for a headlight apparatus to be mounted on a vehicle. 
     BACKGROUND ART 
     A headlight apparatus for a vehicle includes a mechanism for emitting a low beam (that is, a headlight for passing each other) and a high beam (that is, a headlight for driving). The low beam is defined to be able to illuminate a road surface of 40 meters ahead. The high beam is defined to be able to illuminate a road surface of 100 meters ahead. In a case where there is an oncoming vehicle or the like, it is defined to use the low beam instead of the high beam in order to prevent a risk due to glare. A cutoff line for the low beam indicates a boundary line for cutting off and shielding an upper light of an illumination light. 
     A conventional headlight apparatus has a configuration in which a shade that is a light shielding component is provided, or a configuration in which a light source is disposed so that an optical axis of the light source is inclined as means for forming a cutoff line for a low beam, for example. 
     Further, in recent years, semiconductor light source devices such as a light emitting diode (LED) have been developed as solid light sources. Ones each using an LED as a light source have been developed for a headlight apparatus for a vehicle. 
     As an example of the conventional technique related to the headlight apparatus described above, there is Japanese Patent Application Publication No. 2015-133170 (Patent document 1). Patent document 1 describes that a headlight unit for a vehicle that can be reduced in weight and size and can suppress an influence of sunlight while ensuring an amount of light emitted from the headlight unit for the vehicle to the outside by a light emitting diode (LED) is provided. 
     Further, Non-Patent document 1 describes that height of 25 meter is realized as a head lamp for a vehicle by using an LED. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     
         
         Patent document 1: Japanese Patent Application Publication No. 2015-133170 
       
    
     Non-Patent Documents 
     
         
         Non-Patent document 1: Thin Lens Solutions for Lighting, A. Perrotin, Valeo Lighting System, Angers, France, 12th International Symposium on Automotive Lightning —ISAL 2017—Proceedings of the Conference: Volume 17, p 155-158. 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In a case where a shade that is a light shielding component is provided as means for forming a cutoff line for a low beam or in a case where a light source is disposed so that an optical axis of the light source is inclined, for example, the conventional headlight apparatus needs to have a thickness thicker than a certain level in a height direction of the headlight apparatus. For that reason, the conventional headlight apparatus has room for improvement in view of thinner. Further, for example, in a case where the conventional headlight apparatus is configured so that a light from the light source is shielded by the shade, light utilization is wasted due to the shielded light, and the conventional headlight apparatus also has room for improvement in view of the light utilization efficiency. 
     It is an object of the present invention to provide a technique capable of realizing a thinner thickness and improvement of light utilization in a case where a mechanism for emitting a low beam and a high beam is provided with respect to a technique for a headlight apparatus. 
     Means for Solving the Problem 
     A representative embodiment of the present invention is characterized by a headlight apparatus that has a configuration described below. 
     A headlight apparatus according to one embodiment is a headlight apparatus to be mounted on a vehicle. The headlight apparatus includes a low beam headlight configured to emit a low beam. The low beam headlight includes: a solid light source for the low beam; a light source condensing optical system for the low beam configured to condense a light emitted from the solid light source for the low beam, the light source condensing optical system for the low beam being disposed on an optical axis of the solid light source for the low beam; a light distribution controlling light guide for the low beam disposed on the optical axis, a light from the light source condensing optical system for the low beam entering the light distribution controlling light guide for the low beam, the light distribution controlling light guide for the low beam being configured to control light distribution thereof and emit a light; and a projector lens for the low beam disposed on the optical axis, the light from the light distribution controlling light guide for the low beam entering the projector lens for the low beam, the projector lens for the low beam being configured to project a light. The light distribution controlling light guide for the low beam includes: an incident surface that the light from the light source condensing optical system for the low beam enters; a plurality of total reflection surfaces; and an emission surface from which the light to the projector lens for the low beam is emitted. In this case, a first light of incident light from the incident surface is emitted from the emission surface without reaching the plurality of total reflection surfaces, and a second light of the incident light is emitted from the emission surface via multiple times of total reflection by the plurality of total reflection surfaces. 
     A headlight apparatus according to one embodiment is a headlight apparatus to be mounted on a vehicle. The headlight apparatus includes a high beam headlight configured to emit a high beam. The high beam headlight includes: a solid light source for the high beam; a light source condensing optical system for the high beam configured to condense a light emitted from the solid light source for the high beam, the light source condensing optical system for the high beam being disposed on an optical axis of the solid light source for the high beam; a light distribution controlling light guide for the high beam disposed on the optical axis, a light from the light source condensing optical system for the high beam entering the light distribution controlling light guide for the high beam, the light distribution controlling light guide for the high beam being configured to control light distribution thereof and emit a light; and a projector lens for the high beam disposed on the optical axis, the light from the light distribution controlling light guide for the high beam entering the projector lens for the high beam, the projector lens for the high beam being configured to project a light. The light distribution controlling light guide for the high beam include: an incident surface that the light from the light source condensing optical system for the high beam enters; and an emission surface from which the light to the projector lens for the high beam is emitted. In this case, at least one of the incident surface or the emission surface of the light distribution controlling light guide for the high beam has a vertically asymmetrical shape in the vertical direction on a sectional surface formed by a direction of the optical axis and the vertical direction. 
     Effects of the Invention 
     According to the representative embodiment of the present invention, it is possible to realize thin and improvement of light utilization efficiency with respect to a technique for a headlight apparatus in a case where a mechanism for emitting a low beam and a high beam is provided. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a view illustrating a configuration of a vehicle on which a headlight apparatus according to an embodiment of the present invention is mounted; 
         FIG. 2  is a perspective view illustrating a configuration of the whole of the headlight apparatus according to the embodiment; 
         FIG. 3  is a perspective view illustrating a configuration of the inside of the headlight apparatus according to the embodiment; 
         FIG. 4  is a view illustrating a horizontal section of a low beam headlight and a light path of a low beam in the headlight apparatus according to the embodiment; 
         FIG. 5  is a view illustrating a vertical section of the low beam headlight and the light path of the low beam in the headlight apparatus according to the embodiment; 
         FIG. 6  is a view illustrating a horizontal section of a high beam headlight and a light path of a high beam in the headlight apparatus according to the embodiment; 
         FIG. 7  is a view illustrating a vertical section of the high beam headlight and the light path of the high beam in the headlight apparatus according to the embodiment; 
         FIG. 8  is a perspective view illustrating a configuration of a light source condensing optical system for the low beam in the headlight apparatus according to the embodiment; 
         FIG. 9  is a perspective view illustrating a configuration of a light source condensing optical system for the high beam in the headlight apparatus according to the embodiment; 
         FIG. 10  is a view illustrating a horizontal section of the light source condensing optical system for the low beam and the light path in the headlight apparatus according to the embodiment; 
         FIG. 11  is a perspective view illustrating a configuration of an incident side of a light distribution controlling light guide for the low beam in the headlight apparatus according to the embodiment; 
         FIG. 12  is a perspective view illustrating a configuration of an emission side of the light distribution controlling light guide for the low beam in the headlight apparatus according to the embodiment; 
         FIG. 13  is a top view of the light distribution controlling light guide for the low beam in the headlight apparatus according to the embodiment; 
         FIG. 14  is a view illustrating a horizontal section of the light distribution controlling light guide for the low beam and a light path in the headlight apparatus according to the embodiment; 
         FIG. 15  is a view illustrating a vertical section of the light distribution controlling light guide for the low beam and the light path in the headlight apparatus according to the embodiment; 
         FIG. 16  is a perspective view illustrating a configuration of an incident side of alight distribution controlling light guide for the high beam in the headlight apparatus according to the embodiment; 
         FIG. 17  is a perspective view illustrating a configuration of an emission side of the light distribution controlling light guide for the high beam in the headlight apparatus according to the embodiment; 
         FIG. 18  is a view illustrating a vertical section of the light distribution controlling light guide for the high beam in the headlight apparatus according to the embodiment; 
         FIG. 19  is a view illustrating light flux area shapes of an incident surface and an emission surface of the light distribution controlling light guide for the high beam in the headlight apparatus according to the embodiment; and 
         FIG. 20  is a view illustrating light distribution characteristics of the low beam and the high beam in the headlight apparatus according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that in all of the drawings for explaining the embodiment, the same reference numeral is generally assigned to the same unit, and its repeated explanation will be omitted. 
     Embodiment 
     A headlight apparatus according to an embodiment of the present invention will be described with reference to  FIG. 1  to  FIG. 20 . The headlight apparatus according to the embodiment indicates a configuration in a case where LEDs are particularly used as a solid light source. By using the LEDs, it is possible to make the apparatus thinner and smaller. In that case, in order to realize the thinness of the whole apparatus, it is necessary to configure the apparatus so as to make components other the light LEDs thinner. For that reason, the headlight apparatus according to the embodiment does not adopt a configuration in which a shade that is a light shielding member is provided for a low beam emitting mechanism. The headlight apparatus according to the embodiment realizes thin and high light utilization efficiency by devising structures of a light source condensing optical system and a light distribution controlling light guide in addition to the LEDs. Specifically, the headlight apparatus according to the embodiment forms a low beam and a cutoff line thereof by using multiple times of total reflection inside the light guide. 
     [Vehicle and Headlight Apparatus] 
       FIG. 1  is a perspective view of an outline configuration of a vehicle  2  on which a headlight apparatus  1  according to the embodiment is mounted. (A) of  FIG. 1  illustrates the headlight apparatus  1  ( 1   a ,  1   b ) respectively mounted at right and left positions of a front portion of the vehicle  2 . The headlight apparatus  1  includes a headlight apparatus  1   a  provided at the right side of the front portion, and a headlight apparatus  1   b  provided at the left side of the front portion. 
     Note that an X direction, a Y direction, and a Z direction are indicated as directions for explanation. The X direction is a first horizontal direction, and corresponds to a lateral direction, a crosswise direction, or a width direction of the vehicle  2  or the headlight apparatus  1 . The Y direction is a vertical direction, and corresponds to a height direction of the vehicle  2  or the headlight apparatus  1 . The Z direction is a second horizontal direction, and corresponds to a front-back direction of the vehicle  2  or an optical axis direction of the headlight apparatus  1 . 
     (B) of  FIG. 1  illustrates an enlarged portion including the headlight apparatus  1   a  provided at the right side illustrated in (A). This headlight apparatus  1  ( 1   a ) is roughly classified into a low beam headlight  10  and a high beam headlight  20 , by which the headlight apparatus  1  ( 1   a ) is configured. The low beam headlight  10  is a low beam emitting mechanism; is disposed at a position near the outside in the X direction of the front portion of the vehicle  2 ; and is configured by plural rows, for example, three rows of low beam units. The high beam headlight  20  is a high beam emitting mechanism; is disposed at a position near the inside in the X direction of the front portion of the vehicle  2 ; and is configured by plural rows, for example, two rows of high beam units. 
     Note that the headlight apparatus  1   b  provided at the left side has a similar configuration to that of the headlight apparatus  1   a  provided at the right side in a substantially symmetrical form. The headlight apparatuses  1  ( 1   a ,  1   b ) provided at the right and left sides have different light distributions from each other, which are substantially symmetrical in shape, and respectively have suitable light distributions. Specifically, although it will be described later, light distribution characteristics are designed so that the headlight apparatus  1  illuminates a roadside strip side more widely than an oncoming vehicle side on an optical axis of the headlight apparatus  1 . 
     [Headlight Apparatus] 
       FIG. 2  and  FIG. 3  illustrate a perspective view of a configuration of the headlight apparatus  1  according to the embodiment (for example, the headlight apparatus  1   a  provided at the right side).  FIG. 2  illustrates appearance of the whole headlight apparatus  1 .  FIG. 3  illustrates a configuration of the inside of the headlight apparatus  1 . 
     In  FIG. 2 , the low beam headlight  10  and the high beam headlight  20 , which are main ports of a main body of the headlight apparatus  1 , are housed in a headlight case  30 . A heat sinks  31  is fixed to a back side of the headlight case  30 , that is, a rear side thereof in the Z direction that corresponds to light source sides of the low beam headlight  10  and the high beam headlight  20 . 
     Aside surface of a front side of the headlight case  30  in the Z direction is opened, and respective projector lenses of the low beam headlight  10  and the high beam headlight  20  are disposed so as to be exposed. As a projector lens for low beam  11 , three projector lenses  11   a ,  11   b , and  11   c  are disposed in the X direction on the low beam headlight  10  side. As a projector lens for the high beam  21 , two projector lenses  21   a  and  21   b  are disposed in the X direction on the high beam headlight  20  side. 
     In  FIG. 3 , the low beam headlight  10  is configured by three rows of low beam units  10   a ,  10   b , and  10   c  in the X direction as three low beam units each of which has a similar structure to each other. The high beam headlight  20  is configured by two rows of high beam units  20   a  and  20   b  in the X direction as two high beam units each of which has a similar structure to each other. 
     An LED substrate  32  is fixed in the headlight case  30  so as to extend long in the X direction on an X-Y plane that is a side surface of the back side in the Z direction. The heat sink  31  is fixed to a surface of the LED substrate  32  that faces the rear side in the Z direction. The heat sink  31  has a plurality of fins, and dissipates heat of a plurality of LEDs. Although they are not visible in  FIG. 3 , as illustrated in  FIG. 4  and the like, a plurality of LEDs (LED elements) is implemented as solid light sources on the X-Y plane that is a main surface of the LED substrate  32  and faces a front side in the Z direction. The plurality of LEDs is total five LEDs that correspond to five rows of beam emitting mechanisms (including the low beam units and the high beam units), and includes three LEDs for the low beam and two LEDs for the high beam. A circuit for controlling each of the plurality of LEDs to be turned on or off and the like are implemented on the LED substrate  32 . Note that in the embodiment, plurality of LEDs is implemented on one LED substrate  32 , but it may be configured so that plural pieces of LED substrates on each of which one or more LEDs are implemented are used. By using the LEDs, it is possible to realize the thin headlight apparatus  1  having low power consumption, a long life, a low cost, and excellent environmental protection. 
     LED collimators constituting a light source condensing optical system is disposed at positions of optical axes of the respective LEDs on the LED substrate  32  at the front side along the Z direction that is the optical axis direction. In the low beam headlight  10  side, three LED collimators  13   a ,  13   b , and  13   c  are disposed in the X direction as an LED collimator  13  that is a light source condensing optical system for the low beam. In the high beam headlight  20  side, two LED collimators  23   a  and  23   b  are disposed in the X direction as LED collimators  23  that is a light source condensing optical system for the high beam. 
     A light source unit of the low beam headlight  10  in the headlight apparatus  1  according to the embodiment is configured by an LED for the low beam (an LED  12  illustrated in  FIG. 4  and the like), which is a fixed light source for the low beam, and the LED collimator  13  that is a light source condensing optical system for the low beam. The LED collimator  13 , which is the light source condensing optical system for the low beam, condenses a light emitted from the LED, and executes a predetermined light distribution control to emit the light. Similarly, a light source unit for the high beam headlight  20  is configured by an LED for the high beam (an LED  22  illustrated in  FIG. 6  and the like), which is a fixed light source for the high beam, and the LED collimators  23  each of which is a light source condensing optical system for the high beam. 
     A light distribution controlling light guide is disposed at a predetermined position separated by a space of a predetermined distance at the front side in the Z direction with respect to each of the LED collimators. The low beam headlight  10  includes a light guide  14  that is a light distribution controlling light guide for the low beam. The light guide  14  includes three light guides  14   a ,  14   b , and  14   c  that are disposed by three rows in the X direction. The high beam headlight  20  includes a light guide  24  that is a light distribution controlling light guide for the high beam. The light guide  24  is one light guide disposed by one row in the X direction. Each of the light guide  14  and the light guide  24  is fixed to the headlight case  30 . The light guide  14  at the low beam is configured by three light distribution control lenses for the low beam, which are independently provided for the three rows of low beam units  10   a ,  10   b , and  10   c . The light guide  24  at the high beam is configured as one light distribution control lens for the high beam shared by two rows of high beam units  20   a  and  20   b.    
     A projector lens is disposed at a predetermined position separated by a space of a predetermined distance at the front side in the Z direction with respect to each of the light guides. The projector lens for low beam  11  is disposed for the light guide  14  at the low beam side. The projector lens for the high beam  21  is disposed for the light guide  24  at the high beam side. Each of the projector lenses is fixed to the headlight case  30 . The projector lenses  11  and  21  constitute a projection optical system that enlarges and projects illumination light to a space in front of the headlight apparatus  1 , that is, the vehicle  2  together with a predetermined light distribution control. 
     In the embodiment, each of the projector lenses  11  and  21  of the low beam unit and the high beam unit is configured by one aspherical lens. This aspherical lens is configured by a biconvex lens that respectively has convex shapes on an incident side and an emission side toward the outside thereof, each of an incident surface and an emission surface is an aspherical surface. 
     Further, in particular, the projector lens for low beam  11  is configured as one component so that the three projector lenses  11   a ,  11   b , and  11   c  of three rows of low beam units  10   a ,  10   b , and  10   c  are connected in series in the X direction. The projector lens for the high beam  21  is configured as one component so that the two projector lenses  21   a  and  21   b  of the two rows of high beam units  20   a  and  20   b  are connected in series in the X direction. Each of the projector lenses is not limited to such a configuration, and can be any configuration. 
     The high beam headlight  20  realizes illumination of a road surface of 100 meters ahead, and the low beam headlight  10  realizes illumination of a road surface of 40 meters ahead. The low beam has light distribution in a direction slightly diagonally downward with respect to the optical axis in a horizontal direction (the Z direction). 
     In the embodiment, the low beam headlight  10  has a configuration in which a correspondence relation between the light source units (each including the LED and the LED collimator  13 ) and the light guides  14  is 3:3 in consideration of the amount of light, positioning accuracy, and the like. The low beam headlight  10  is not limited to this configuration, and can be any configuration. For example, the low beam headlight  10  may be configured so that the plurality (for example, three) of light guides  14  ( 14   a ,  14   b , and  14   c ) is connected to each other in the X direction to form one part. For example, the low beam headlight  10  may be configured so that the plurality (for example, three) of LED collimators  13  ( 13   a ,  13   b , and  13   c ) is connected to each other in the X direction to form one part. 
     In the embodiment, the high beam headlight  20  has a configuration in which a correspondence relation between the light source units (each including the LED and the LED collimator  23 ) and the light guide  24  is 2:1 in consideration of reduction of the number of parts. The high beam headlight  20  is not limited to this configuration, and can be any configuration. For example, the high beam headlight  20  may be configured so that the correspondence relation between the light source units and the light guides  24  is 2:2 as a plurality (for example, two) of independent light guides. 
     A configuration to control the headlight apparatus  1  is as follows. A predetermined controller (for example, an engine control unit) mounted on the vehicle  2  controls the headlight apparatus  1 . When the high beam is turned on, the controller gives a control signal to the LED substrate  32  so as to turn on all five LEDs in the high beam headlight  20  and the low beam headlight  10  described above. The LED substrate  32  turns on the five LEDs in accordance with the control signal. Further, when the low beam is turned on, the controller gives a control signal to the LED substrate  32  so as to turn on the three LEDs at the low beam headlight  10  side and turn off the two LEDs at the high beam headlight  20  side. The LED substrate  32  turns on the three LEDs and turns off the two LEDs in accordance with the control signal. Note that as another control example, it is possible to turn on only the two LEDs at the high beam headlight  20  side, or to turn on or off the selected individual LEDs. 
     Note that in the headlight apparatus according to the embodiment, the plurality (for example, five) of LEDs, the plurality of low beam units, and the plurality of high beam unit are used in order to secure the amount of illumination. The number of LEDs, the number of low beam units and the number of high beam units are not limited those according to the embodiment, and each can be any number. 
     [Low Beam Headlight (1)] 
       FIG. 4  illustrates a configuration of a horizontal section (an X-Z plane) at a position of an optical axis (indicated by an alternate long and short dash line) of the LED, which corresponds to a case where the low beam headlight  10  and a light path are viewed from the above vertically (the Y direction).  FIG. 4  illustrates a portion of one row of low beam unit in the X direction, but each row has the similar configuration. The LED  12  that is the LED for the low beam is implemented on the main surface of the LED substrate  32 . The optical axis of the LED is a line perpendicular to a light emitting face (the X-Y plane) of the LED. 
       FIG. 4  illustrates an emission surface F 1  of the LED collimator  13 , an incident surface F 2  and an emission surface F 3  of the light guide  14 , and an incident surface F 4  and an emission surface F 5  of the projector lens  11 . Further,  FIG. 4  illustrates a light  401 , a light  402 , and a light  403 . The light  401  is a light emitted from the LED collimator  13 , and is an incident light to the light guide  14 . The light  402  is a light emitted from the light guide  14 , and is an incident light to the projector lens  11 . The light  403  is a light emitted from the projector lens  11 . The light  402  that is the light emitted from the light guide  14  contains light fluxes (light fluxes for the low beam)  15   a  and  15   b , which are indicated as a plurality of beams. The light  403  that is the light emitted from the projector lens  11  is a low beam configured by a light flux  15   c  for the low beam. 
     The light flux  15   a  indicates a light flux corresponding to a first light, which is a part of the light that does not pass through the total reflection inside the light guide  14  and is emitted as it is without being cut of the incident light to the incident surface F 2  of the light guide  14  based on the light  401  and the light emitted from the emission surface F 3 . The light flux  15   b  indicates a light flux corresponding to a second light, which is the other part of the light that is reused while being cut via multiple times of total reflection inside the light guide  14  and is emitted of the incident light to the incident surface F 2  of the light guide  14  based on the light  401  and the light emitted from the emission surface F 3 . In particular, the light flux  15   b  includes a light flux that is caused to move to the outside in the X direction due to the total reflection. 
     [Low Beam Headlight (2)] 
       FIG. 5  illustrates a configuration of a vertical section (a Y-Z plane) at the position of the optical axis, which corresponds to a case where the low beam headlight  10  and the light path illustrated in  FIG. 4  are viewed from the side thereof (the X direction). In  FIG. 5 , a thickness T 1  in the Y direction indicates a thickness of the headlight apparatus  1  (the low beam headlight  10 , in particular). This thickness T 1  indicates a rough thickness corresponding to a range in which the LED substrate  32 , the LED  12 , the LED collimator  13 , the light guide  14 , and the projector lens  11 , which are main components except for the headlight case  30  and parts such as screws, are accommodated. In the headlight apparatus  1  according to the embodiment, this thickness T 1  can be reduced up to about 20 mm. 
     In  FIG. 4  and  FIG. 5 , all light fluxes from the emission surface F 1  of the LED collimator  13  enter the incident surface F 2  of the light guide  14 . All light fluxes from the emission surface F 3  of the light guide  14  enter the incident surface F 4  of the projector lens  11 . So long as this condition is satisfied, a direction of the light emitted from the light guide  14  is not limited particularly. In  FIG. 4 , the light flux  15   c  for the low beam from the emission surface F 5  of the projector lens  11  becomes a light flux that converges to a focal point due to a refraction action and then spreads in the X direction. In  FIG. 5 , the light fluxes from the emission surface F 1  of the LED collimator  13  enters the incident surface F 2  of the light guide  14  as a light flux narrowed down to the extent toward the optical axis in the Y direction, and travels toward the emission surface F 3  or a total reflection surface. The light fluxes from the emission surface F 3  of the light guide  14  enters the incident surface F 4  of the projector lens  11  as an image inverted up and down in the Y direction. The light fluxes from the emission surface F 5  of the projector lens  11  become the light flux  15   c  for the low beam that is directed slightly diagonally downward from the optical axis in the Y direction due to the refraction action. 
     [High Beam Headlight (1)] 
       FIG. 6  illustrates a configuration of a horizontal section (the X-Z plane) at a position of the optical axis (indicated by an alternate long and short dash line), which corresponds to a case where the high beam headlight  20  and a light path are viewed from the above vertically (the Y direction).  FIG. 6  illustrates a portion of one row of high beam unit in the X direction, but each of rows has the similar configuration. 
     An LED  22  that is an LED for the high beam is implemented on the main surface of the LED substrate  32 . Note that the same LED element may be used for the LED  12  that is the LED for the low beam and the LED  22  that is the LED for the high beam, or a different LED element may be used for each of the LED  12  and the LED  22 . 
       FIG. 6  illustrates an emission surface G 1  of the LED collimator  23 , an incident surface G 2  and an emission surface G 3  of the light guide  24 , and an incident surface G 4  and an emission surface G 5  of the projector lens  21 . Further,  FIG. 6  illustrates a light  601 , a light  602 , and a light  603 . The light  601  is a light emitted from the emission surface G 1  of the LED collimator  23 , and is an incident light to the incident surface G 2  of the light guide  24 . The light  602  is a light emitted from the emission surface G 3  of the light guide  24 , and is an incident light to the incident surface G 4  of the projector lens  21 . The light  603  is a light emitted from the emission surface G 5  of the projector lens  21 . The light  603  is a high beam configured by a light flux  25  for the high beam. 
     [High Beam Headlight (2)] 
       FIG. 7  illustrates a configuration of a vertical section (the Y-Z plane) at the position of the optical axis, which corresponds to a case where the high beam headlight  20  and the light path illustrated in  FIG. 6  are viewed from the side thereof (the X direction). The LED substrate  32 , the LED  22 , the LED collimator  23 , the light guide  24 , and the projector lens  21 , which are main components of the high beam headlight  20 , are accommodated within a range of the thickness T 1  in the Y direction. The thickness T 1  at the high beam headlight  20  side illustrated in  FIG. 7  is the same as the thickness T 1  at the low beam headlight  10  side illustrated in  FIG. 5 . 
     In  FIG. 6  and  FIG. 7 , all light fluxes from the emission surface G 1  of the LED collimator  23  enter the incident surface G 2  of the light guide  24 . Almost of light fluxes from the emission surface G 3  of the light guide  24  enters the incident surface G 4  of the projector lens  21 . Light fluxes from the emission surface G 1  of the LED collimator  23  enter the incident surface G 2  of the light guide  24  as a light flux narrowed down to the extent toward the optical axis in the X direction and the Y direction. In  FIG. 7 , the light fluxes from the emission surface G 3  of the light guide  24  enter the incident surface G 4  of the projector lens  21  as an image inverted up and down in the Y direction. The light fluxes from the emission surface G 5  of the projector lens  21  become the light flux  25  for the high beam that is a substantially parallel light along the direction of the optical axis (the Z direction). 
     [Light Source Condensing Optical System for Low Beam (1)] 
       FIG. 8  illustrates a perspective view of a configuration of the LED collimator  13  that is a light source condensing optical system for the low beam in the low beam headlight  10 . As an outline of functions thereof, the LED collimator  13  has a function to condense the light from the LED  12  and convert the light into a light substantially parallel to the road surface of the vehicle  2  (the corresponding Z direction). Specifically, as illustrated in  FIG. 4  and  FIG. 5 , the light emitted from the LED collimator  13  is a light that is condensed so as to be narrowed down to the incident surface F 2  of the light guide  14  to the extent. 
     The LED collimator  13  includes an incident side element  131 , an emission side element  132 , and installation units  133 . Each of the installation units  133  is a unit for positioning and mounting the LED collimator  13  with respect to the LED  12  ( FIG. 4 ) of the LED substrate  32  so as to be fixed to the main surface of the LED substrate  32 . The installation units  133  respectively have screw holes, for example, and are provided at both sides of the incident side element  131  and the emission side element  132  in the X direction. 
     The incident side element  131  has a substantially conical shape (see  FIG. 10 , which will be described in detail later). As illustrated in  FIG. 4  and the like, the incident side element  131  is disposed so as to face a light emitting face of the LED  12  on the optical axis of the LED  12 . 
     The emission side element  132  has a refractive element  132 A and a refractive element  132 B. The refractive element  132 A is arranged in an area including a bottom surface of a cone of the incident side element  131 . The refractive element  132 B is arranged at a central portion corresponding to the optical axis. The refractive element  132 B is integrally formed at the central portion of the refractive element  132 A. The emission side element  132  can be configured as a lens structure by integrally molding. 
     As illustrated in  FIG. 4  and  FIG. 5 , the refractive element  132 B provided at the central portion is configured as a convex lens having a convex shape at the front side in the Z direction in order to strengthen light distribution of the central portion in the vicinity of the optical axis. 
     As illustrated in  FIG. 4  and  FIG. 5 , the refractive element  132 A provided at an outer circumferential side has a cylinder shape, and is configured as a concave lens (in other words, a cylindrical lens) having a concave shape in the front side in the Z direction. This cylinder shape is a columnar surface shape corresponding to a one-dimensional curved surface, which has a curved line (with a different curvature) in the X direction, and has a straight line in the Y direction. 
     As illustrated in  FIG. 4  and  FIG. 5 , the light fluxes of the light (the light  401 ) emitted from the emission side element  132  of the LED collimator  13  have predetermined light distribution in which narrowing in the Y direction is stronger than narrowing in the X direction. As a result, the light fluxes of the incident light to the light guide  14  by the light emitted from the LED collimator  13  become a horizontally (the X direction) long elliptical shape (an area  1101  illustrated in  FIG. 11 , which will be described later) at a position of the incident surface F 2 . In this design of the light distribution, the light fluxes of the incident light to the light guide  14  is narrowed down to a narrower area compared with the light fluxed of the light emitted from the LED collimator  13 . 
     [Light Source Condensing Optical System for High Beam (1)] 
       FIG. 9  illustrates a perspective view of a configuration of the LED collimator  23  that is a light source condensing optical system for the high beam in the high beam headlight  20 . As an outline of functions thereof, the LED collimator  23  has a function to condense the light from the LED  22  and convert the light into a condensed light so as to be narrowed down to the extent toward the optical axis in the Y direction with respect to the light guide  24  as illustrated in  FIG. 6  and  FIG. 7 . 
     The LED collimator  23  includes an incident side element  231 , an emission side element  232 , and installation units  233 . As well as the installation units  133 , each of the installation units  233  is a unit for positioning and mounting the LED collimator  23  with respect to the LED  22  ( FIG. 6 ) of the LED substrate  32  so as to be fixed to the main surface of the LED substrate  32 . 
     Similarly, the incident side element  231  has a substantially conical shape. As illustrated in  FIG. 6  and the like, the incident side element  231  is disposed so as to face a light emitting face of the LED  22  on the optical axis of the LED  22 . 
     The emission side element  232  has a refractive element  232 A and a refractive element  232 B. The refractive element  232 A is arranged in an area including a bottom surface of a cone of the incident side element  231 . The refractive element  232 B is arranged at a central portion corresponding to the optical axis. The refractive element  232 B is integrally formed at the central portion of the refractive element  232 A. The emission side element  232  can be configured as a lens structure by integrally molding. 
     As illustrated in  FIG. 6  and  FIG. 7 , the refractive element  232 B provided at the central portion is configured as a convex lens having a convex shape at the front side in the Z direction in order to strengthen light distribution of the central portion in the vicinity of the optical axis. 
     As illustrated in  FIG. 6  and  FIG. 7 , the refractive element  232 A provided at an outer circumferential side has a substantially planar shape, and is configured as a flat lens. 
     As illustrated in  FIG. 6  and  FIG. 7 , the light fluxes of the light (the light  601 ) emitted from the emission side element  232  of the LED collimator  23  have predetermined light distribution in which narrowing in the Y direction is stronger than narrowing in the X direction. As a result, the light fluxes of the incident light to the light guide  24  by the light emitted from the LED collimator  23  become a horizontally (the X direction) long elliptical shape (an area  1601  illustrated in  FIG. 16 , which will be described later) at a position of the incident surface G 2 . In this design of the light distribution, the light fluxes of the incident light to the light guide  24  is narrowed down to a narrower area compared with the light fluxed of the light emitted from the LED collimator  23 . 
     [Light Source Condensing Optical System for Low Beam (2)] 
       FIG. 10  illustrates a horizontal section (the X-Z plane) and a light path of the LED collimator  13  illustrated in  FIG. 8 . 
     Specifically, the incident side element  131  includes a concave portion  135  and a refractive element  134  provided on an incident side, and a side surface reflector  136 . The concave portion  135  and the refractive element  134  are disposed so as to face the light emitting face of the LED  12  on the optical axis of the LED  12 . An opening surface of the concave portion  135  is disposed at a position of the light emitting face of the LED  12 . The refractive element  134  is formed in a bottom surface of the concave portion  135 . The refractive element  134  is configured as a convex lens that has a convex shape at the incident side. 
     The side surface reflector  136  has a paraboloidal surface obtained by rotating a sectional surface of a substantially parabola around the optical axis. The light is totally reflected on the paraboloidal surface inside the side surface reflector  136 . The light emitted from the light emitting face of the LED  12  has light distribution in which the light is emitted in each direction around the optical axis by using the optical axis as the center. The paraboloidal surface of the side surface reflector  136  is designed within a range of an angle that allows total reflection of the light thereof in each direction. 
     A part of the light emitted from the LED  12  enters the refractive element  134  in the concave portion  135  to undergo a refraction action, thereby becoming a substantially parallel light to go toward the refractive element  132 B provided at the central portion of the emission side element  132 , in particular. The light transmits the refractive element  132 B to undergo a refraction action, and is emitted toward the optical axis as a light flux that is narrowed down to the extent. 
     The other part of the light emitted from the LED  12  transmits a side surface of the concave portion  135  to travel to the side surface reflector  136 , and is totally reflected by the paraboloidal surface to go toward the emission side element  132 . At that time, the total reflection by the paraboloidal surface causes the light to be narrowed down toward the optical axis in the X direction and the Y direction. The light transmits the refractive element  132 A provided at the outer circumference, in particular, to undergo the refraction action, and is emitted as a substantially parallel light flux in the X direction as illustrated in  FIG. 4 , and a light flux narrowed down toward the optical axis in the Y direction as illustrated in  FIG. 5 . 
     The LED collimator  23  provided at the high beam side has a configuration of the incident side that is similar to the configuration of the LED collimator  13  provided at the low beam. 
     The LED collimators  13  and  23  can be manufactured by a general molding processing method using a resin material having visible light transmittance and heat resistance, such as polycarbonate (PC) or silicone, for example. 
     As described above, in the embodiment, the LED collimators  13  and  23  allow the light emitted from the LEDs  12  and  22  to be to be extracted efficiently and used. Note that the headlight apparatus  1  according to the embodiment is configured so as to use the plurality of the LED collimators  13  and  23  independent for each row, but the configuration thereof is not limited to such a configuration, and can be any configuration. A configuration in which a plurality of LED collimators  13  is integrated into one structure, and a configuration in which a plurality of LED collimators  23  is integrated into one structure are also possible. A configuration of the light distribution of the light emitted from the LED collimators  13  and  23  is not limited to the configuration described above, and can be any configuration. 
     [Light Distribution Control Light Guide for Low Beam (1)] 
     A configuration of the light guide  14 , which is the light distribution controlling light guide for the low beam in the low beam headlight  10 , will be described with reference to  FIG. 11  to  FIG. 15 .  FIG. 11  illustrates a perspective view of the configuration of the light guide  14  that is the light distribution controlling light guide for the low beam.  FIG. 11  illustrates a perspective view when the incident surface F 2  is viewed from the rear side in the Z direction (the LED collimator  13  side).  FIG. 12  illustrates a perspective view regarding the light guide  14  illustrated in  FIG. 11  when the emission surface F 3  is viewed from the front side in the Z direction (the projector lens  11  side).  FIG. 13  illustrates a top view (the X-Z plane) when the light guide  14  is viewed from the above in the Y direction in a planar view.  FIG. 14  illustrates an example of a horizontal section and beams at an optical axis position of the light guide  14 .  FIG. 15  illustrates a configuration of the total reflection by the vertical section (the Y-Z plane) of the light guide  14 . 
     In  FIG. 11 , the light guide  14  includes an incident unit  141 , an emission unit  142 , total reflection units  143 , installation units  149 , and the like. Further, in the present embodiment, the light guide  14  is roughly classified into a first light guide unit  14 F and a second light guide unit  14 E. With respect to a reference line C 1 , the light guide  14  has the first light guide unit  14 F at the rear side in the Z direction, and has the second light guide unit  14 E at the front side in the Z direction. The first light guide unit  14 F and the second light guide unit  14 E correspond to configuration examples of members in a case where the light guide  14  is manufactured by injection molding. Depending upon a shape of each of the members and the design of an index of refraction thereof, a plurality of total reflection surfaces is formed inside the light guide  14  as illustrated in  FIG. 15 . Each of the total reflection surfaces is formed at a boundary of the member of the light guide  14  (resin, which will be described later) and the outside air due to a difference the indices of refraction between the member and the air. 
     In  FIG. 11 , the light guide  14  has the incident unit  141  at the rear side in the Z direction in the vicinity of the optical axis in the X direction, and respectively has the total reflection units  143  at both right and left sides in the X direction with respect to the incident unit  141 . Each of the right and left total reflection units  143  further has the total reflection units  143  at upper and lower positions in the Y direction, respectively. The installation units  149  are respectively provided at both outer sides with respect to the right and left total reflection units  143 . As illustrated in  FIG. 3 , each of the installation units  149  is a part for positioning and fixing the light guide  14  with the other light guides  14  or the light guide  24 , and the headlight case  30 , which are disposed next to each other in the X direction, and has a screw hole, for example. 
     The incident unit  141  has the incident surface F 2  in the vicinity of the optical axis indicated by an alternate long and short dash line. The incident surface F 2  has a substantially planar shape ( FIG. 14 ) in the X direction, and a curved surface shape ( FIG. 15 ) in the Y direction. 
     On the incident surface F 2 , an area  1101  is an area that has a horizontally long elliptical shape into which the incident light (the light  401 ) enters. Like the area  1101 , a light flux of the incident light (the light  401 ) to the incident surface F 2  of the light guide  14  has light distribution of an elliptical shape that is relatively horizontally long (the X direction). This light distribution is designed in such a manner in order to have a horizontally wide characteristic ((A) of  FIG. 20 , which will be described later) as light distribution characteristics of the low beam. 
     [Light Distribution Control Light Guide for Low Beam (2)] 
     In  FIG. 12 , the light guide  14  has the emission unit  142  in a horizontally long area including a center, right and left in the X direction at an upper portion in the Y direction (a portion of an upper side with respect to a reference line C 2  and the second light guide unit  14 E). The emission unit  142  has the emission surface F 3  in the area. As illustrated in  FIG. 13 , the emission surface F 3  has a flat surface parallel to the X direction in a central area in the X direction (referred to as a “first emission surface”), which is provided at the opposite side of the incident unit  141 , and respectively has oblique flat surfaces that face the optical axis in areas at right and left sides (referred to as a “second emission surface” and a “third emission surface”). 
     The second light guide unit  14 E is provided at a lower side in the Y direction with respect to the emission surface F 3  and the reference line C 2  in a shape that protrudes toward the front side in the Z direction. The second light guide unit  14 E has the total reflection unit  143 , and in particular, a first total reflection surface (the cutoff surface  143 C), a second total reflection surface, and a third total reflection surface are formed (total reflection surfaces f 1  to f 3  illustrated in  FIG. 15 ). The first light guide unit  14 F includes the incident surface F 2  and the emission surface F 3 , and in particular, a fourth total reflection surface and a fifth total reflection surface are formed in the total reflection unit  143  (total reflection surfaces f 4  and f 5  illustrated in  FIG. 15 ). Note that more specifically, the second light guide unit  14 E is configured by two parts on the right and left in the X direction as parts by the injection molding. 
     The emission surface F 3  has an area (a first emission area)  1201  regarding the emitted light in the central area (the first emission surface). This area  1201  has a semi-elliptical shape obtained by cutting an area at a lower side from the reference line C 2  from a horizontally (the X direction) long ellipse, in other words, a semi-elliptical shape that has an arc at an upper side and a string at the lower side. This area  1201  is an area where the first light of an incident light to the incident surface F 2  that does not pass through the total reflection is mainly emitted. 
     Further, in the emission surface F 3 , with respect to the central area (the first emission surface), an area regarding the emitted light (a second emission area)  1202  is provided in an area at the right side in the X direction (the second emission surface), and an area regarding the emitted light (a third emission area)  1203  is provided in an area at the left side thereof (the third emission surface). Similarly, each of these areas  1202  and  1203  has a semi-elliptical shape obtained by cutting an area at a lower side. These areas  1202  and  1203  are areas where the second light of the incident light to the incident surface F 2  is mainly emitted via the total reflection. The second light is emitted from these areas  1202  and  1203  so as to be reused via multiple times of total reflection by the plurality of total reflection surfaces inside the light guide  14 . The second light is converted into a light that travels outward in the X direction with the multiple times of total reflection even though the light is a light that enters the central area ( FIG. 14 ). 
     Further,  FIG. 12  illustrates the light flux  15   a  for the low beam corresponding to the light emitted from the area  1201  and the light flux  15   b  for the low beam corresponding to the light emitted from the areas  1202  and  1203 . A light flux  15   d  for the low beam corresponds to the overall emission light (the light  402 ) from the emission surface F 3  of the light guide  14 , which is a combination of the light flux  15   a  for the low beam and the light flux  15   b  for the low beam, and has light distribution that is wide in the X direction. 
     The cutoff surface  143 C is formed as a sloop at the lower side in the Y direction so as to be adjacent to the emission surface F 3  (including the areas  1201 ,  1202 , and  1203 ) of the emission unit  142 . The cutoff surface  143 C is a component for forming a cutoff line of the low beam. The first light that travels toward the emission surface F 3  of the incident light is emitted from the emission surface F 3  (the areas  1201 ,  1202 , and  1203 ) as it is without undergoing total reflection, and becomes the light flux  15   a  for the low beam. The second light that does not travel to the emission surface F 3  but travels toward the cutoff surface  143 C (the first total reflection surface) of the incident light is totally reflected by the cutoff surface  143 C for the first time, and travels toward the second total reflection surface. The second light then repeats total reflection by each of the plurality of total reflection surfaces (the second total reflection surface to the fifth total reflection surface) inside the light guide  14  to reach the emission surface F 3  that is provided at an upper side in the Y direction, and is emitted from the emission surface F 3  (the areas  1201 ,  1202 , and  1203 ). 
     [Light Distribution Control Light Guide for Low Beam (3)] 
       FIG. 13  illustrates that the total reflection surface of each of the total reflection units  143  is formed as a sloop that faces the optical axis in a top view (the X-Z plane) corresponding to  FIG. 12  and the like. As illustrated in  FIG. 14 , in the light guide  14 , the plurality of total reflection surfaces of the plurality of total reflection units  143  is designed so that an emission position on the emission surface F 3  is shifted outward in the X direction with respect to an incident position on the incident surface F 2  due to the total reflection of the second light. Specifically, as illustrated in  FIG. 13 , the plurality of total reflection surfaces including the cutoff surface  143 C (the first total reflection surface) is disposed with a relationship to be curved by an angle θ 1  of about 10° to 15° with respect to the central flat surface (the first emission surface) of the emission surface F 3  by using the optical axis as an axis of symmetry. As a result, a right and left opening/closing angle θa in the total reflection unit  143  (the cutoff surface  143 C and the like) of the second light guide unit  14 E at a lower side of the emission surface F 3  when viewed from the X-Z plane is about 150° to 160°. As a result, the wide light flux  15   d  for the low beam in the X direction is realized while reusing the incident light by the total reflection. 
     [Light Distribution Control Light Guide for Low Beam (4)] 
     In  FIG. 14 , the second light of the incident light to the incident surface F 2  of the incident unit  141 , for example, a beam L 41  moves outward in the X direction (for example, a right side) due to multiple times of total reflection (indicated by broken lines and points) by the plurality of total reflection surface inside the light guide  14 , and becomes a beam L 42 . The beam L 42  is emitted forward in the Z direction from the emission surface F 3  of the emission unit  142  (in particular, the area  1202  at the right side in  FIG. 12 ) as a part of the light flux  15   b  for the low beam. 
     [Light Distribution Control Light Guide for Low Beam (5)] 
       FIG. 15  illustrates a vertical section at the first total reflection surface (the cutoff surface  143 C) that corresponds to the optical axis position in the light guide  14 . As illustrated in  FIG. 15 , the light guide  14  has a polyhedron shape including a plurality of total reflection surfaces inside thereof. In the embodiment, the light guide  14  includes the five total reflection surfaces f 1  to f 5  as the plurality of total reflection surfaces. 
     The incident surface F 2  of the incident unit  141  has a cylinder shape with convexity outwardly, which has a curved surface with a radius of curvature r 1 . The radius of curvature r 1  is about 7.5 mm. Note that as illustrated in  FIG. 15 , the first light of the incident light to the incident surface F 2 , for example, a beam L 10  is emitted from the emission surface F 3  as it is without passing through the total reflection surfaces f 1  to f 5 . 
     The total reflection surface f 5  that is the fifth total reflection surface is provided on the total reflection unit  143  at the upper side in the Y direction so as to be adjacent to the incident surface F 2 . The emission surface F 3  of the emission unit  142  is provided at the front side in the Z direction with respect to the total reflection surface f 5 . The emission surface F 3  of the emission unit  142  has a flat surface (the first emission surface) on the X-Y plane, and has the cutoff surface  143 C as the total reflection surface f 1  that is the first total reflection surface on the total reflection unit  143  that is provided at the lower side in the Y direction with respect to the emission surface F 3  thereof. The total reflection surface f 2  that is the second total reflection surface is provided on the total reflection unit  143  at the lower side in the Y direction so as to be adjacent to the total reflection surface f 1 . The total reflection surface f 3  that is the third total reflection surface is provided on the total reflection unit  143  at the rear side in the Z direction and the upper side in the Y direction so as to be adjacent to the total reflection surface f 2 . The incident surface F 2  is provided at the upper side in the Y direction so as to be adjacent to the total reflection surface f 3 . 
     The beam L 1  indicates an example of the second light of the incident light to the incident surface F 2 . The beam L 1  first enters a point p 1  of the cutoff surface  143 C (the total reflection surface f 1 ). An angle γ indicates an incident angle at that time. A line V indicates a normal line against the point p 1  of the cutoff surface  143 C. The beam L 1  is totally reflected at the point p 1  of the cutoff surface  143 C to become a beam L 2 . Subsequently, the beam L 2  enters a point p 2  of the total reflection surface f 2  (the second total reflection surface), and is totally reflected to become a beam L 3 . Subsequently, the beam L 3  enters a point p 3  of the total reflection surface f 3  (the third total reflection surface), and is totally reflected to become a beam L 4 . Subsequently, the beam L 4  enters a point p 4  of the total reflection surface f 4  (the fourth total reflection surface), and is totally reflected to become a beam L 5 . Subsequently, the beam L 5  enters a point p 5  of the total reflection surface f 5  (the fifth total reflection surface), and is totally reflected to become a beam L 6 . The beam L 6  is emitted from the emission surface F 3 . Note that the points p 2  to p 5  and the corresponding total reflection surfaces exist on another sectional surface whose positions in the X direction are different from each other. 
     The total reflection surfaces f 1  to f 5  respectively have outwardly convex cylinder shapes having curved surfaces with radii of curvature R 1  to R 5 . Each of the radii of curvature R 1  to R 5  is preferably 15 to 30 mm. Note that as a modification example, the total reflection surface may be configured by a flat surface. A relative angle of any two of the plurality of total reflection surfaces (the total reflection surfaces f 1  to f 5 ) of the light guide  14  is adjusted and designed so that a light cut by the total reflection surface of the incident light is efficiently emitted from the emission surface F 3  by multiple times of total reflection through the total reflection surfaces. Further, as a modification example, a reflective coating may be formed on a part of the total reflection surfaces. In particular, the total reflection surface f 5  needs to reflect the beam so as to be substantially parallel to the emission surface F 3  by one reflection. Thus, an incident angle of the light flux becomes close to a critical angle. Therefore, it may be more significant to form a reflective coating on the total reflection surface f 5  in consideration of an error such as a mounting angle. 
     In particular,  FIG. 15  illustrates an angle β regarding the cutoff surface  143 C that is the first total reflection surface. The angle β is an angle with respect to the optical axis (the Z direction). A critical angle θc of the total reflection is illustrated on the cutoff surface  143 C. A line C is a line that forms the critical angle θc from the line V. The critical angle θc is an angle that is obtained in accordance with an index of refraction of a member of the light guide  14 . The angle β of the cutoff surface  143 C is set so that the incident angle γ of the beam (for example, the beam L 1 ) of the light flux  15   b  for the low beam becomes larger than the critical angle θc by a predetermined angle α (γ=θc+α). This angle α is 3° or larger. 
     Depending upon the configuration of the light guide  14  that satisfies the angle condition described above, the light leaking out from the cutoff surface  143 C becomes zero, that is, the reflection by the cutoff surface  143 C becomes total reflection. This makes it possible to form a good cutoff line for the low beam. 
     [Light Distribution Control Light Guide for Low Beam (6)] 
     In order to form the light guide  14  at low cost, injection molding using a transparent resin is preferable as a manufacturing method and a constituent material. The light guide  14  can be formed by the injection molding using the transparent resin. As the transparent resin, for example, acrylic resin (in particular, PMMA: polymethyl methacrylate), polycarbonate (PC), cycloolefin resin, and the like are suitable. In the embodiment, the light guide  14  is formed by using the PMMA as the transparent resin, for example. In that case, in a case where a critical angle obtained from an index of refraction of 1.49 of the PMMA in a visible light is the critical angle θc and the index of refraction of the PMMA is n, there is a relationship of Sin θc=1/n. Therefore, the critical angle θc becomes about 42°. The angle β of the cutoff surface  143 C is set on the basis of this critical angle θc. 
     As described above, the incident light to the light guide  14  is narrowed down to the extent through the LED collimator  13 . The beam corresponding to the second light of the incident light obliquely enters the cutoff surface  143 C as in the example of the beam L 1 . The shape including the plurality of total reflection surfaces is designed so as to satisfy a condition that this beam becomes larger than the critical angle θc of the cutoff surface  143 C by the predetermined angle α (for example, 3°). 
     Further, while satisfying this condition, it is necessary to convert the direction (the corresponding angle) of the beam of the incident light into a front direction from the emission surface F 3  (the front side in the Z direction) by means of multiple times of total reflection by the plurality of total reflection surfaces of the light guide  14 . For that purpose, it is necessary to use at least five times of total reflection as the configuration of the plurality of total reflection surfaces of the light guide  14 . Note that in case of four times of total reflection, suitable light distribution cannot be realized due to the condition of the critical angle. Further, it can also be configured so as to increase the number of times of total reflection to six times or seven times. However, in that case, a size thereof including the thickness of the light guide  14  becomes larger. 
     Further, it is desirable that a shape of the light flux comprehensively emitted from the emission surface F 3  is formed into a uniform semi-elliptical shape having an arc at an upper side thereof as illustrated in  FIG. 12 . This is due to compatibility with the cutoff line for the low beam, that is, because final light distribution characteristics of the low beam are caused to have a shape with a string at an upper side thereof and an arc at a lower side thereof as illustrated in (A) of  FIG. 20 , which will be described later. The second light that enters the cutoff surface  143 C (the first total reflection surface) of the incident light becomes a semi-elliptical shape having an arc at a lower side thereof. An optical image of the second light is inverted up and down in the Y direction due to total reflection. In order for a semi-elliptical shape to have an arc at an upper side thereof when the light flux of the second light is emitted from the emission surface F 3 , the number of times of total reflection is set to an odd number as a condition. Note that in a case where the number of times of total reflection is set to an even number, the optical image of the second light becomes a semi-elliptical shape having an arc at a lower side thereof on the emission surface F 3 , thereby being different from a semi-elliptical shape having an arc at an upper side thereof of the first light. 
     In consideration of each of the conditions described above, it is optimal that the number of times of total reflection by the light distribution controlling light guide for the low beam is five times. Correspondingly, in the headlight apparatus  1  according to the embodiment, the light guide  14  has the five total reflection surfaces f 1  to f 5  for five times of total reflection. As a result, the light guide  14  realizes suitable light distribution of the light emitted for the low beam while having a thickness as small as possible. 
     [Light Distribution Control Light Guide for High Beam (1)] 
     The light guide  24  that is the light distribution controlling light guide for the high beam in the high beam headlight  20  will be described with reference to  FIG. 16  to  FIG. 19 .  FIG. 16  illustrates a perspective view of a configuration of the light guide  24 .  FIG. 16  illustrates a perspective view of the light guide  24  when the incident surface G 2  of the incident unit of the light guide  24  is viewed from the rear side in the Z direction (the LED collimator  23  side).  FIG. 17  illustrates a perspective view of the light guide  24  when the emission surface G 3  of the emission unit of the light guide  24  is viewed from the front side in the Z direction (the projector lens  21  side).  FIG. 18  illustrates a vertical section (the Y-Z plane) of the light guide  24  at the optical axis position.  FIG. 19  illustrates a planar configuration of the X-Y plane when the incident surface G 2  and the emission surface G 3  of the light guide  24  are viewed in the Z direction. Note that  FIG. 16  and  FIG. 17  illustrate a light flux from one LED collimator  23  for one light guide  24 , but as illustrated in  FIG. 3  and  FIG. 19 , in an implementation example, one light guide  24  has two light fluxes from two LED collimators  23 . 
     In  FIG. 16 , the light guide  24  includes an incident unit  241 , an emission unit  242 , installation units  249 , and the like. Each of the installation unit  249  is a unit for positioning and mounting the light guide  24  to the headlight case  30 . 
     The incident unit  241  has the incident surface G 2  that extends long in the X direction. The incident surface G 2  has a cylinder shape with convexity to the incident side, and has a curved surface whose curvature is different depending upon a position in the Y direction. This incident surface G 2  has a vertically asymmetrical shape in the Y direction. The incident surface G 2  has an asymmetrical shape between an upper portion and a lower portion with respect to a reference line C 3  indicated by a broken line, which extends in the X direction corresponding to the optical axis position. Specifically, with respect to the reference line C 3 , the upper portion has a curved surface whose curvature is larger than that of the lower portion. 
     An area  1601  of the light flux of the incident light (the light  601 ) from the LED collimator  23  is illustrated at the optical axis position on the incident surface G 2 . As illustrated in  FIG. 6  and  FIG. 7 , the area  1601  has a slightly horizontally (the X direction) long elliptical shape in accordance with light distribution of a light condensed from the LED collimator  23 . 
     In  FIG. 17 , the emission unit  242  of the light guide  24  has the emission surface G 3  that extends long in the X direction. The emission surface G 3  has a planar shape in the X-Y plane. An area  1602  of the light flux of the emitted light is illustrated at the optical axis position on the emission surface G 3 . In contrast to the elliptical shape of the area  1601 , the elliptical shape of the area  1602  becomes a shape in which a portion of an upper side is narrowed compared with a portion of a lower side with respect to a reference line C 4  that extends in the X direction corresponding to the optical axis position. 
     [Light Distribution Control Light Guide for High Beam (2)] 
       FIG. 18  illustrates the cylinder shape of the incident surface G 2  in the incident unit  241  of the light guide  24 . In this cylinder shape, a radius of curvature R 21  is 2 to 5 mm, for example, in an area of an upper side in the Y direction with respect to the optical axis (indicated by an alternate long and short dash line), and a radius of curvature R 22  is 5 to 20 mm, for example, in an area of a lower side thereof. The radius of curvature R 21  in the area of the upper side is smaller than the radius of curvature R 22  in the area of the lower side (R 21 &lt;R 22 ). In the incident light (the light  601 ) from the LED collimator  23 , for example, a beam that enters the area of the upper side of the incident surface G 2  is greatly refracted compared with a beam that enters the area of the lower side. For example, a beam L 61  of the upper side becomes a beam L 62 , which is emitted. A beam L 63  of the lower side becomes a beam L 64 , which is emitted. Correspondingly, on the emission surface G 3  of the emission unit  242 , an area of a light flux for the high beam that corresponds to the emitted light (the light  602 ) becomes a vertically asymmetrical shape in the Y direction. 
     In  FIG. 19 , (A) illustrates the areas  1601  of the light fluxes of the incident light on the incident surface G 2 , and (B) illustrates the areas  1602  of the light fluxes of the emitted light on the emission surface G 3 . Note that  FIG. 19  illustrates a state where light fluxes of two kinds of incident lights from two LED collimators  23  are generated in one light guide  24 . 
     In (A), the incident surface G 2  has an area  1901  of an upper side and an area  1902  of a lower side with respect to a reference line C 3  that extends in the X direction corresponding to the optical axis position. Curvature of the area  1901  of the upper side is larger than that of the area  1902  of the lower side. Each of the areas  1601  of the incident light has a portion of an upper side (indicated by a dot pattern) for entering the area  1901  of the upper side and a portion of a lower side (indicated by a diagonal line pattern) for entering the area  1902  of the lower side with respect to the reference line C 3 . The portion of the upper side has a semi-elliptical shape with an arc at the upper side, and the portion of the lower side has a semi-elliptical shape with an arc at the lower side. 
     Similarly, (B) illustrates the areas  1602  of the light fluxes of the emitted light on the emission surface G 3  with respect to the reference line C 4 . Each of these areas  1602  has a portion of an upper side (indicated by a dot pattern) for entering an area  1903  of the upper side and a portion of a lower side (indicated by a diagonal line pattern) for entering an area  1904  of the lower side. As well as (A), the portion of the upper side and the portion of the lower side respectively have semi-elliptical shapes. The portion of the upper side in the area  1602  of the emitted light is refracted through the light guide  24 , thereby becoming a shape in which a length thereof in the Y direction is narrowed compared with that of the portion of the upper side illustrated in (A). 
     Note that as described above, the shape of the light guide  24  at the high beam side is not limited to the configuration with the vertically asymmetrical shape on the incident surface G 2  of the incident unit  241 , and can be any configuration. Similarly, it may be configured so as to have a vertically asymmetrical shape at a predetermined position on the optical axis within a range from the incident surface G 2  to the emission surface G 3 . 
     [Light Distribution Characteristics] 
     (A) of  FIG. 20  illustrates light distribution characteristics of the low beam by the low beam headlight  10 . This low beam corresponds to the light  403  emitted from the projector lens  11  and the light flux  15   c  for the low beam illustrated in  FIG. 4  and the like. In a graph illustrated in  FIG. 20 , a horizontal axis indicates an angle [deg. (°)] in the horizontal direction (the X direction), and a vertical axis indicates an angle [deg. (°)] in the vertical direction (the Y direction).  FIG. 20  illustrates light distribution when the rear side thereof (that is, a vehicle side) is viewed from the front side in the Z direction (that is, a point at infinity side) in case of the headlight apparatus  1   a  provided at the right side of the vehicle  2  illustrated in  FIG. 1 . 
     In (A), a straight line of the horizontal axis corresponds to a cutoff line CL of the low beam. As illustrated in (A) of  FIG. 20 , this light distribution of the low beam has light distribution at a substantially lower side of the vertical direction (the Y direction) with respect to the cutoff line CL. In the present embodiment, there is a distribution in a range of about 0° to −12° in the Y direction. Moreover, this light distribution has wide light distribution in the horizontal direction (the X direction) in an area of the lower side. In the present embodiment, there is a distribution in a range of about −50° to +50° in the X direction. Namely, the low beam has a wider illumination in the X direction than the high beam. As a result, the headlight apparatus  1  can illuminate, as the low beam, a wide area including the right and left in front of the vehicle  2 . 
     Note that an area at the left side in the X direction has light distribution slightly wider toward the upper side with respect to the cutoff line C compared with an area at the right side thereof. This light distribution is designed as a horizontally asymmetrical shape as suitable light distribution corresponding to the headlight apparatus  1   a  provided at the right side so that a roadside strip (the left side in  FIG. 20 ) can be illuminated more than an oncoming vehicle (the right side in  FIG. 20 ). 
     Similarly, (B) of  FIG. 20  illustrates light distribution characteristics of the high beam of the high beam headlight  20 . As illustrated in (B) of  FIG. 20 , this light distribution of the high beam has light distribution in which an area at an upper side in the Y direction is wider than an area at a lower side with respect to a straight line of a horizontal axis (corresponding to the cutoff line CL) as a reference. In the present embodiment, the Y direction has a distribution in a range of about −5° to +10°, and the X direction has a distribution in a range of about −20° to +20°. This high beam has light distribution that is more concentrated in the center than the low beam. Each of the areas  1602  of the light fluxes of the light emitted from the light guide  24  illustrated in (B) of  FIG. 19  has a wide shape at the lower side. However, as illustrated in (B) of  FIG. 20 , the light distribution has a wide shape at the upper side through a flip vertical action on a light path. Thus, the high beam has suitable light distribution with strong light distribution in the center. 
     Further, in the headlight apparatus  1  according to the embodiment, when the high beam is illuminated, both the low beam of (A) and the high beam of (B) are controlled so as to be turned on (ON) as described above. For that reason, the light distribution of the high beam of (B) is designed to have a shape in which the area at the lower side is wider than the area at the upper side with respect to the reference straight line of the horizontal axis (corresponding to the cutoff line CL). Since the area at the lower side in the high beam can be supplemented by the light of the low beam, it is designed as light distribution with a relatively wide upper side in this manner. Thus, in the headlight apparatus  1  according to the embodiment, the suitable light distribution is realized by synthesis and combination of the low beam and the high beam. 
     [Effects and the Like] 
     According to the headlight apparatus of the embodiment, it is possible to realize thin and improvement of light utilization efficiency in a case where a mechanism for emitting a low beam and a high beam is provided. In addition, it is possible to realize suitable light distribution characteristics required for the low beam and the high beam. In the headlight apparatus  1  according to the embodiment, LED elements (the LEDs  12  and  22 ) that easily realizes thinner than a conventional light source device are used as solid light sources. Further, the headlight apparatus  1  uses light source condensing optical systems (the LED collimators  13  and  23 ) that match the LED elements. The headlight apparatus  1  includes light guides (the light guides  14  and  24 ) devised to be capable of realizing thin in accordance with the configuration of the LEDs and the LED collimators. 
     In the low beam headlight  10  side, this light guide  14  is configured so as to have the plurality of total reflection surfaces at portions except for the incident surface F 2  and the emission surface F 3  in order to form a cutoff line for the low beam. In other words, this light guide  14  itself includes a cutoff line forming function. In the headlight apparatus  1 , by using this light guide  14 , it is not necessary to provide a shade or the like, which is a light shielding member, that is, any space or cost for providing the shade or the like is not required. 
     In the headlight apparatus  1  according to the embodiment, the LEDs, the LED collimators, the light guides, and the projector lenses are disposed along the optical axis direction, whereby the thickness of the whole apparatus can be realized to be thinner like the thickness T 1  illustrated in  FIG. 5 . Since the thin headlight can be realized, for example, this can contribute improvement of the degree of freedom in an exterior design (or design) of a vehicle. Further, in addition, the headlight apparatus  1  reuses the light from the LED  12  at the low beam headlight  10  side without leaking the light due to the structure of total reflection by the light guide  14 , thereby realizing efficient light distribution. Much component (for example, 60% or higher) of 100% of the light energy from the LED  12  can be used as the low beam, and this makes it possible to heighten light utilization efficiency compared with the conventional ones. 
     Further, in the headlight apparatus  1  according to the embodiment, as illustrated in  FIG. 15 , by adopting the structure of the light guide  14  that satisfies the condition regarding the critical angle of total reflection, the cutoff line of the low beam can be set to a suitable linear shape as illustrated in (A) of  FIG. 20 . In the light distribution of the low beam, it is possible to avoid the light from wastefully leaking from the cutoff line to the upper side thereof, and this makes it possible to realize suitable light distribution. 
     Further, in the headlight apparatus  1  according to the embodiment, suitable light distribution of the high beam can be realized at the high beam headlight  20  side. As illustrate in  FIG. 16  and the like, the light guide  24  particularly has a vertically asymmetrical cylinder shape at the incident surface G 2  side. This makes it possible to make the headlight apparatus  1  thinner and realize suitable light distribution of the high beam. Further, the headlight apparatus  1  according to the embodiment not only can be made thinner, but also can realize a suitable beam in the configuration of combination of the high beam headlight  20  and the low beam headlight  10 . 
     The following are also possible as headlight apparatuses according to other embodiments. In the headlight apparatus  1  according to the embodiment described above, the low beam headlight  10  that is the low beam emitting mechanism and the high beam headlight  20  that is the high beam emitting mechanism are independently configured, and they are disposed in parallel in the X direction. The headlight apparatus according to the other embodiment can be configured so as to include only the low beam headlight  10 , or to include only the high beam headlight  20 . Further, in a case where a thickness of the headlight apparatus in the Y direction is made larger and a width thereof in the X direction is made smaller, the headlight apparatus can be configured so that the low beam headlight  10  and the high beam headlight  20  are disposed in an overlapping manner in the Y direction. 
     As the headlight apparatus according to still another embodiment, the headlight apparatus may be configured so as to add optical elements, such as a polarization converting element, a light distribution control element, another lens, or a mirror, onto the light path in addition to the components such as the light guide described above. 
     As described above, the present invention has been described specifically on the basis of the embodiment. However, the present invention is not limited to the embodiment described above, and the present invention may be modified into various forms without departing from the substance thereof. The configuration of the embodiment can be added with the other configuration, deleted or replaced thereby. 
     REFERENCE SIGNS LIST 
       1 ,  1   a  . . . headlight apparatus,  10  . . . low beam headlight,  20  . . . high beam headlight,  10   a ,  10   b ,  10   c  . . . low beam unit,  20   a ,  20   b  . . . high beam unit,  11 ,  21  . . . projector lens,  12 ,  22  . . . LED,  13 ,  23  . . . LED collimator,  14 ,  24  . . . light guide,  32  . . . LED substrate, F 1 , F 3 , F 5  . . . emission surface, and F 2 , F 4  . . . incident surface.