Patent Publication Number: US-11028990-B2

Title: Single-piece optical motor-vehicle part comprising a structural modification

Description:
The present invention relates to an optical part intended to be mounted in a motor-vehicle lighting device. Particularly, the invention relates to an optical part that is placed in front of one or more light sources in order to propagate the light rays emitted by said one or more sources. More particularly, the invention relates to an optical part comprising a plurality of entrance dioptric interfaces and/or a plurality of exit dioptric interfaces. 
     As known, optical modules able to generate a pixel beam the projection of which forms an image composed of pixels already exist. Said pixels are organized into at least one horizontal and/or vertical row and each of the pixels may be selectively activated. 
     Such an optical module is used in addition to a second optical module able to generate a main lighting and signalling beam in order to form a lighting and signalling beam incorporating an adaptive function. 
     By way of example, in the case of a low beam, the pixel beam is turned on with a bottom segment of the low beam in order to produce an additional lighting function, namely a dynamic bending light (DEL). This function allows the inside of the corner that the vehicle is being driven round or entering to be illuminated. 
     In another example, the pixel beam is turned on with a segment of high beam in order to produce an adaptive driving beam (ADB) the aim of which is to provide the driver of the vehicle with better visibility while preventing the driver of an oncoming vehicle from being subjected to glare. 
     Simply put, the optical module able to generate a pixel beam comprises a plurality of elementary light sources that are selectively activatable and arranged in a matrix array of elementary light sources, and an optical part that is placed in front of said matrix array and that projects a light beam forwards. 
     The optical part comprises light guides that are on the whole arranged in parallel directions, and one entrance dioptric interface and/or one exit per guide. The number of guides corresponds to the number of elementary light sources. Alternatively, the number of guides is higher than the number of elementary light sources. 
     Generally, the elementary light sources may be light-emitting diodes (LEDs). 
     For each light guide, the entrance dioptric interface is placed at one end of said guide so as to form the entrance for light through which light rays pass to enter into the guide. Each entrance dioptric interface is placed facing one elementary light source. 
     The exit is placed at another end of the guide and thus forms an exit for the light rays. 
     The exits of the guides are imaged by one or more projecting optics so as to form a pixel beam. 
     In this case, the pixels correspond to the exits of the light guides. 
     However, it has been observed that the current configuration of the optical part comprising the light guides occasions the presence of parasitic light rays. 
     In the context of the present invention, by parasitic light rays what is meant is rays that are output by a first light source placed facing a first entrance dioptric interface, but that end up in the neighbouring guides located on either side of said first entrance dioptric interface. These rays then propagate through a guide that is not intended therefor. 
     Light rays that propagate into a first light guide and that exit through the exit dioptric interfaces of other light guides located on either side of said first guide are also considered to be parasitic light rays. 
     Parasitic rays may be recognized in the image projected by the optical module. Specifically, because of the parasitic rays, the outside edges of the pixels do not have the expected shapes and the beam comprises luminous regions of extra brightness, this degrading the quality of the pixel beam. 
     The technical problem that the invention aims to solve is therefore that of providing a more precise pixel beam that achieves lighting of good quality. 
     To this end, a first subject of the invention is a single-piece optical vehicle part comprising:
         a plurality of entrance dioptric interfaces and/or a plurality of exit dioptric interfaces;   at least one junction between two adjacent entrance dioptric interfaces and/or at least one junction between two adjacent exit dioptric interfaces.       

     According to the invention, the junction between two adjacent entrance dioptric interfaces and/or the junction between two adjacent exit dioptric interfaces has at least one structural modification allowing light to be absorbed and/or scattered. 
     In this way, the structural modification plays the role of a barrier that scatters and/or absorbs the parasitic light rays. In particular, by virtue of the structural modification, the light rays of a first elementary light source, located facing a first entrance dioptric interface, are absorbed or scattered at the junction between this first entrance dioptric interface and an adjacent entrance dioptric interface. Therefore, far fewer light rays output from the first light source can propagate through the guide there beside. 
     In a case where the light guides are followed by exit dioptric interfaces, the exit dioptric interface located downstream of a first light guide is called the first exit dioptric interface and the exit dioptric interface that is located downstream of a second light guide placed beside the first guide is called the second exit dioptric interface. 
     Just as for the entrance dioptric interfaces, by virtue of the structural modification present at the junction between the first exit dioptric interface and the second exit dioptric interface, light rays propagating through the first light guide are absorbed or scattered at said junction. 
     Both in the case of entrance dioptric interfaces and in the case of exit dioptric interfaces, the structural modification at the junction between the adjacent dioptric interfaces allows either the light intensity of the image of the parasitic rays formed by the optical part to be decreased, or the formation of the image of the parasitic rays by the exit dioptric interface that precedes the neighbouring light guide to be prevented. 
     Therefore, by virtue of the structural modification, the risk of delivering excess light intensity to the pixel is decreased. Therefore, the lighting device bearing the optical part will not be penalized during approval. 
     Thus, by virtue of the optical part according to the invention, the optical module bearing said part generates a clear and precise light beam while respecting the conditions of regulations. 
     The optical part according to the invention may optionally have one or more of the following features:
         only the junctions between the adjacent entrance dioptric interfaces have the structural modification; in certain models of the optical part, the parasitic light rays are more present at the junctions between the adjacent entrance dioptric interfaces; thus, the precision of the pixels is improved by introducing the structural modification at said junctions so as to prevent or scatter parasitic light rays;   only the junctions between the adjacent exit dioptric interfaces have the structural modification; thus, in certain models of the optical part, the parasitic rays are more present at the exit dioptric interfaces; the structural modification is therefore produced in the place where there is the highest probability of deviation of the light rays toward the adjacent exit dioptric interfaces;   the one or more junctions between two dioptric interfaces form a line of separation of the two corresponding dioptric interfaces, the structural modification being arranged along this line of separation; it is here a question of one embodiment of the entrance dioptric interfaces and/or of the exit dioptric interfaces, to which embodiment the invention is applied;   according to the preceding paragraph, the structural modification, arranged along the line of separation, extends depthwise into the material of the optical part; thus, the effectiveness of the structural modification is further improved at depth in the optical part;   the entrance dioptric interfaces and/or the exit dioptric interfaces are spaced apart from one another so that a gap separates the adjacent entrance dioptric interfaces and/or the adjacent exit dioptric interfaces, the gap comprising walls that together form the junction between the dioptric interfaces that it separates; it is here a question of another embodiment of the entrance dioptric interfaces and/or exit dioptric interfaces, to which embodiment the invention may be applied;   according to the preceding paragraph, at least one structural modification is produced in the gap between the adjacent entrance dioptric interfaces and/or between the adjacent exit dioptric interfaces; in addition, the structural modification is located at the bottom of the gap; the applicant has observed, in the configuration in which the adjacent dioptric interfaces are separated by a gap, parasitic light rays pass through the bottom of the gap in order to enter into the adjacent guide; thus, to prevent or decrease parasitic rays, the structural modification is produced at the bottom of the gap;   at least one structural modification is produced in the gap between the adjacent entrance dioptric interfaces, and in addition, the structural modification is located as close as possible to the adjacent entrance dioptric interfaces; the applicant has also observed that light rays have a tendency to propagate into the adjacent guide by passing through a portion of the gap which is located closest to the entrance dioptric interfaces;   at least one structural modification is produced in the gap between the adjacent exit dioptric interfaces, and in addition the structural modification is located as close as possible to the adjacent exit dioptric interfaces;   the junction between two adjacent entrance dioptric interfaces and/or the junction between two adjacent exit dioptric interfaces has a total area, called the total junction area; in addition, said structural modification partially occupies the total junction area of the junction in question; by way of example, in the case where the junction is composed of the walls of the gap, the total area of the junction is the area of these walls; thus, one portion of the area of these walls is modified structurally so as to scatter and/or absorb the parasitic rays on contact;   the structural modification is produced by laser; by way of example, the laser may be a YAG laser or fibre laser; in this case, the optical part must be made of a material compatible with the laser, i.e. from a material that converts under the excitation of the laser so as to scatter and/or absorb the light rays;   the structural modification is produced by graining; by way of example, the optical part is produced from a polymer and the graining may be carried out during the step of moulding the optical part;   the structural modification is produced by depositing a reflective, absorbent and/or scattering coating.       

     Unless otherwise indicated, the terms “front”, “rear”, “lower”, “upper”, “top”, “bottom”, “side”, “right”, “left”, refer to the direction of emission of light out of the corresponding optical part. Unless otherwise indicated, the terms “upstream” and “downstream” refer to the direction of propagation of the light in the object to which they relate. 
     Moreover, the terms “horizontal”, “vertical” or “transverse” are defined with respect to the orientation with which the optical part is intended to be fitted in the vehicle. In particular, in this patent application, the term “vertical” designates an orientation perpendicular to the plane of the horizon whereas the term “horizontal” designates an orientation parallel to the plane of the horizon. 
    
    
     
       Other features and advantages of the invention will become apparent on reading the detailed description of the nonlimiting examples that follow, for the comprehension of which the reader is referred to the appended drawings, in which: 
         FIG. 1  illustrates a perspective view of a single-piece optical part according to a first embodiment, said view showing a front face of the optical part; 
         FIG. 2  illustrates another perspective view of the optical part of  FIG. 1 , showing a rear face of the optical part; 
         FIG. 3  illustrates a front view of details of the portion P (framed by the dashed box) of the front face of the optical part of  FIG. 1 , said view showing structural modifications of the optical part; 
         FIG. 4  illustrates a schematic cross section in a plane H 1  illustrated in  FIG. 3 , which shows the path of the light rays output from various light sources; 
         FIG. 5  illustrates the image of two pixels generated by a projection system that projects the image of the guide exits of the optical part of  FIG. 1 , said part comprising no structural modifications; said image is in the form of isolux curves at a distance of 25 metres in front of an optical module bearing the optical part of  FIG. 1 ; 
         FIG. 6  illustrates a schematic cross section in a plane H 2  illustrated in  FIG. 4 ; said cross section shows a horizontal segment of the optical part of  FIG. 1  comprising structural modifications; 
         FIG. 7  illustrates the image of two pixels generated by a projecting system that projects the image of the guide exits of the optical part of  FIG. 3 , said part comprising structural modifications; said image is in the form of isolux curves at a distance of 25 metres in front of an optical module bearing the optical part of  FIG. 3 ; 
         FIG. 8  illustrates a schematic view of a horizontal segment of a single-piece optical part having gaps between the adjacent entrance dioptric interfaces; said optical part does not comprise structural modifications; 
         FIG. 9  illustrates the image of a luminous strip generated by the optical part of  FIG. 8 , and the zones illuminated by the parasitic light rays, and a curve of the corresponding variation in light intensity; 
         FIG. 10  illustrates a schematic view of a horizontal segment of a single-piece optical part having gaps between the entrance dioptric interfaces; said gaps comprising structural modifications according to a second embodiment of the invention; 
         FIG. 11  illustrates the image of a luminous strip generated by the optical part of  FIG. 10 , the zones illuminated by the parasitic light rays, and a curve of the corresponding variation in light intensity. 
     
    
    
     With reference to  FIG. 1  and to  FIG. 2 , the optical part  100  according to a first embodiment comprises three rows of optical elements, namely a first row  11 , a second row  12  and a third row  13  of optical elements. Each row comprises juxtaposed light guides and lenses. 
     In the rest of the description, the optical elements of the first row  11  are also called the first optical elements  11 . The optical elements of the second row  12  are also called the second optical elements  12 . The same goes for the optical elements of the third row  13 , which are also called the third optical elements  13 . 
     The optical part  100  composed of these three rows  11 ,  12  and  13  of optical elements is produced in a single part, hence the name “single-piece optical part”. 
     The first row  11  of optical elements comprises first light guides  110  and a first lens  115 . 
     Each first light guide  110  comprises an entrance face and an exit. The entrance face forms a first entrance dioptric interface  111 . 
     The first lens  115  extends laterally so as to cover the exits of the first light guides  110 . In addition, the first lens  115  is arranged so that the exits of the first light guides  110  are coplanar with the focal plane of said first lens  115 . 
     The first lens  115  has a curved surface  116 . In the illustrated example, the curved surface  116  is convex toward the front and arranged so that it forms a first exit dioptric interface  112  of the first optical element  11 . Optionally, the curved surface  116  may be the shape of a segment of a sphere, i.e. curved toward the front horizontally and vertically, so as to spread the beam generated by the first optical element  11 . 
     The first entrance dioptric interfaces  111  are placed in contact beside one another so as to form a transverse row  113  of first entrance dioptric interfaces  111 . 
     In the illustrated example, the first light guides  110  and the first lens  115  form a single part. It will be noted here that the light guides do not separate from one another between the first entrance dioptric interfaces  111  and the exit dioptric interface of the lens  115 . 
     In the second row, each second optical element  12  comprises a second guide  120  followed by a second lens  125 . The second guide  120  extends longitudinally from the rear to the front along the optical axis L of the optical part  100 . Each second guide  120  comprises an entrance face and an exit. The entrance face forms a second entrance dioptric interface  121 . 
     Unlike the first optical element  11 , the second optical element comprises one lens per guide. Each second lens  125  also comprises a curved surface  126 . 
     Each second lens  125  is placed downstream of the corresponding second guide  120  so that the exit of said guide is in the focal plane of said lens. The curved surface  126  of the second lens  125  is oriented toward the front so as to form a second exit dioptric interface  122 . 
     The second exit dioptric interfaces  122  are placed in contact side-by-side. 
     The third row  13  of optical elements has the same configuration as the first row  11  of optical elements. 
     Each third optical element  13  comprises a third light guide  130  and a third lens  135 . 
     Each third light guide  13  comprises an entrance face forming a third entrance dioptric interface  131  and an exit placed in a focal plane of the corresponding third lens  135 . 
     As for each third lens  135 , it comprises a curved surface  136  oriented toward the front so as to form a third exit dioptric interface  132 . 
     The third entrance dioptric interfaces  131  are placed in contact beside one another so as to form a transverse row  133  of third entrance dioptric interfaces. In the same way, the third exit dioptric interfaces  132  are placed in contact beside one another so as to form a transverse row  134  of third exit dioptric interfaces. 
     Whatever the row, the entrance dioptric interfaces are visible on the back face  15  of the optical part  100  whereas the exit dioptric interfaces are visible on the front face  14  of the optical part  100 . 
     The particularity of the first optical elements  11  is that the first light guides  110  extend vertically so as to have the row  113  of the first entrance dioptric interfaces  111  and the first exit dioptric interface  112  at two different levels. Here, the row  113  of the first entrance dioptric interfaces  111  is placed above the first exit dioptric interface  112 . 
     The third optical elements  13  also comprise the third light guides  130 , which extend vertically. The row  133  of the third entrance dioptric interfaces  131  and the row  134  of the third exit dioptric interfaces  132  are at two different levels. Here, the row  133  of the third entrance dioptric interfaces  131  is placed below the row  134  of the third exit dioptric interfaces  132 . 
     For each of the second optical elements  120 , the entrance dioptric interface  121  is at the same level as the exit dioptric interface  122 . 
     The single-piece optical part  100  is placed in front of the light-emitting means that are, here, composed of a plurality of elementary light sources  3 . By way of example, the elementary light source  3  is a light-emitting diode (also called an LED). 
     In the illustrated example, the elementary light sources  3  are arranged in a plurality of transverse rows. The number of rows of elementary light sources corresponds to the number of rows of light guides, which are three in number here. 
     The optical part  100  is positioned with respect to the emitting means so that each row  113 ,  123 ,  133  of entrance dioptric interfaces  111 ,  121 ,  131  is placed facing a row of elementary light sources  3 . 
     More precisely, as illustrated in  FIG. 4 , each first entrance dioptric interface  111  is directly opposite one elementary light source  3  of a first row  31  of elementary light sources. Likewise, each second entrance dioptric interface  121  is directly opposite one elementary light source  3  of a second row  32  of elementary light sources. Lastly, each third entrance dioptric interface  131  is directly opposite one elementary light source  3  of a third row  33  of elementary light sources. 
     For ease of reading, the elementary light sources forming part of the first row of sources will also be called the first elementary light sources  310 . The same goes for the light sources of the second row and of the third row, below respectively referenced  320  and  330 . 
       FIG. 4  shows in detail the path of the light rays output from the elementary light sources  310 ,  320  and  330  in the optical part  100 . 
     As regards the first elementary light sources  310 , each first source  310  emits first rays R 1  that enter into the optical part by the first entrance dioptric interface  111 . 
     The first rays R 1  are then reflected by a first reflecting surface  311  that is positioned facing the first entrance dioptric interface  111 . Here, the first reflecting surface  311  is configured so as to collimate the first rays R 1  and to direct them toward a second reflecting surface  312 . After the second reflecting surface  312  has been reached, the reflected first rays R 1  are directed longitudinally toward the first exit dioptric interface  112 . The latter projects the first rays R 1  forward in order to form a first beam  315 . 
     The first beam  315  is projected by a projecting system (not illustrated in the figures). The image of the first unitary beam  315  has a shape corresponding to that of the first light sources  310 . By way of example, the image of the first beam  315  forms a bottom low-beam portion. 
     The second light source  320  emits the second light rays R 2  e.g. which pass through the second entrance dioptric interface  121  in order to enter into the optical part  100 . The second entrance dioptric interface  121  is schematically represented by a plane for the sake of simplicity, but it is advantageously slightly convex so as to produce a relief in the direction of the second source  320 . 
     Once inside the optical part  100 , the second light rays R 2  then propagate by total internal reflection until they reach the second exit dioptric interface  122 . The latter thus projects forward the second light rays R 2  so as to form a second unitary beam  325 . 
     The second unitary beam  325  is projected by a projecting system (not illustrated in the figures). The image of the second unitary beam  325  comprises a pixel the shape of which corresponds to that of the second exit dioptric interface  122 . 
     The third light source  330  emits third rays R 3  that enter into the optical part via the third entrance dioptric interface  131 . The third rays R 3  are then reflected by a third reflecting surface  313  placed substantially at the same level as the third entrance dioptric interface  133 . 
     The reflected third rays R 3  are then directed upward and, here, toward a fourth reflecting surface  314  that steers them toward the third exit dioptric interface  132 . The latter projects the third rays R 3  forward so as to form a third unitary beam  335 . 
     Here, the second and third rows of optical elements  12  and  13  are arranged so as to generate a pixel beam. A pixel beam contains a number of unitary beams each of which is produced by one elementary light source in conjunction with one optical element. The image of the unitary beam comprises one pixel. 
       FIG. 5  illustrates, by way of example and schematically, a first image I 1  of two unitary pixel beams  325  each generated using a second light source  320  and using a second optical element  12 . The first image I 1  is obtained by projecting the second beam onto a screen at 25 m. 
     The first image I 1  is projected onto the screen in an orthogonal coordinate system R composed of a vertical ordinate axis V and of a horizontal abscissa axis H. The vertical axis V corresponds to a vertical axis above the road and the horizontal axis H symbolizes the horizon. 
     Here, the first image I 1  comprises two pixels  4  of rectangular shape. 
     The applicant has observed that the general shape of the pixels  4  contains imperfections, in particular on the two lateral edges  41  of each pixel  4 . Specifically, for each pixel  4 , the two lateral edges  41  are not straight lines as expected. Each lateral edge  41  comprises a curved portion  43  followed by an inclined line  42  that joins a lower edge  44  of the pixel  4 . This means that the pixel  4  has an irregular trapezium shape comprising a lateral protrusion. 
     This irregular shape has a disadvantageous effect on the pixel beam. Specifically, the pixels  4  are positioned one beside one another. Thus, in the case of a pixel such as illustrated in  FIG. 5 , the laterally protruding curved portion  43  overlaps with a laterally protruding curved portion  43  of a neighbouring pixel. 
     This therefore creates a zone of overlap S in which the light intensity is higher than it is inside each pixel  4 . Therefore, a light beam with a nonuniform distribution of light is obtained, this decreasing the quality of the light beam. 
     The applicant has identified that the poor formation of the pixels is due to parasitic light rays. Specifically, in a given row of optical elements, a minority of the light rays that propagate through a light guide may enter into the neighbouring guide at the junction between two exit dioptric interfaces of these guides. The rays, which are thus said to be “lost” or “parasitic”, exit via the exit dioptric interface of the neighbouring light guide. These parasitic rays form irregularities in the pixel imaged by the neighbouring light guide. The effect is applicable for each light guide and its neighbours to the left and to the right. The same goes for each row of optical elements. 
     To solve this problem, the applicant proposes, according to one example of the invention, a structural modification at the junction of the exit dioptric interfaces, when there is a risk of leakage of the light rays from one guide to another to reach the exit dioptric interface of the other guide. 
     According to the invention and in this example, the junction  6  between two adjacent exit dioptric interfaces  122  or  132  may form a line of separation  6  of said dioptric interfaces. The lines of separation  6  are visible on the front face  14  of the optical part  100  in  FIG. 1 . 
     In this example, the structural modification consists in heating the material of the line of separation  6  so as to change the nature of the material thereof. 
     In the illustrated example, the optical part  100  being formed from polycarbonate (PC), the junction  6  between two adjacent exit dioptric interfaces  122  or  132  is thus formed from this material. 
     Polycarbonate is known for its transparency. The junction  6  between two adjacent exit dioptric interfaces is therefore initially transparent. 
     Using a high-temperature heat source, the junction  6  is heated until there is a change in the composition of the material, here until the transparency of the junction  6  converts into an opaque and dark appearance, close to the colour black. 
     In this way, the junction  6  has a new aspect forming an opaque barrier that stops all the light rays making contact therewith. 
     This processing is also called blackening of the junction. During this processing, initially, gas escapes and the surface of the junction burns. Subsequently, the junction changes from the transparent colour to the black colour. 
     In the illustrated example, the processing is applied to all the junctions of the exit dioptric interfaces of the second and third rows of optical elements. Here, given that the second and third exit dioptric interfaces  122 ,  132  of the optical part have the same widthwise dimension, the junctions  6  between the adjacent exit dioptric interfaces are aligned. 
     Thus, it is enough to pass the heat source in a straight line in order to convert the nature of the material of all the junctions of the exit dioptric interfaces of the second and third rows of optical elements. 
     By way of example, the heat source used is a laser source, in particular an yttrium aluminium garnet (YAG) laser source of a wavelength of 1064 nm. A fibre laser source with a wavelength between 1050 nm and 1070 nm may also be used. 
     The structural modification of the junctions  6  between the second and third exit dioptric interfaces  122  or  132  has been represented by darklines  7  in  FIG. 3 . 
     In particular, the structural modification  7  of the junctions  6  between the second exit dioptric interfaces  122  may be seen in  FIG. 6 . Here, the structural modification  7  is produced at the junction  6  between two adjacent exit dioptric interfaces  122 . 
     The duration of processing of the junction  6  is such that the structural modification  7 , here the conversion to black colour of the material, extends depthwise into the material of the optical part  100  so as to form an opaque wall  73  inside the material. Here, the opaque wall  73  extends in the longitudinal direction L from the junction  6 . The extent of the wall  73  in the longitudinal direction L depends on the duration of processing of the junction  6 . 
     Thus, this opaque wall  73  absorbs any parasitic light ray Rp that has the tendency to propagate into the one or more guides that are not intended therefor. The structural modification significantly improves the quality of the projected image of the beam. 
       FIG. 7  illustrates a second image  12  showing pixels  5  generated using second exit dioptric interfaces  122  the junction  6  of which between two adjacent dioptric interfaces  122  comprises a structural modification  7  such as illustrated in  FIG. 6 . These pixels  5  now have a regular rectangular shape with straight lateral edges  51 , this avoiding the overlap of pixels  5  juxtaposed side-by-side. 
     Thus, the pixel beam resulting from these unitary pixel beams has a uniform light-intensity distribution, the sign representative of a quality beam that procures a better visual comfort for users. 
     The structural modification such as described above could be applied to the first entrance dioptric interfaces  111  of the first row  113 . Specifically, the first entrance dioptric interfaces  111  are placed in contact with one another. A line of separation is located between two adjacent first entrance dioptric interfaces  111 . In other words, this line of separation forms a junction that separates two adjacent first entrance dioptric interfaces  111 . 
       FIG. 8  partially illustrates an optical part  201  having gaps between adjacent entrance dioptric interfaces. Here, the optical part  200  comprises a row  23  of juxtaposed optical elements  2 . 
     Each optical element  2  comprises a light guide  20 . Each light guide comprises an entrance face forming an entrance dioptric interface  80 . Each entrance dioptric interface  80  is placed directly opposite a corresponding elementary light source  24  so that most of the light rays emitted by said light source pass through the entrance dioptric interface  80  in order to then propagate through the light guide  20 . 
     The light propagates from the rear to the front along an optical axis L of the optical part  201 , as illustrated by the arrow L in  FIG. 8 . 
     According to the invention and as in this example, the entrance dioptric interfaces  80  are spaced apart from each other so that a gap  90  separates the adjacent entrance dioptric interfaces  80 . The gap  90  comprises walls that together form the junction  90  between the entrance dioptric interfaces  80  that it separates. 
     Here, the gap  90  comprises three walls, including a right lateral wall  90   a , a left lateral wall  90   b  and a bottom wall  90   c.    
     The bottom wall  90   c  is perpendicular to the direction of propagation of the light. 
     The lateral walls  90   a  and  90   c  here have mirror symmetry with respect to a main axis I of the gap. Here, the main axis I of the gap passes through the middle of the bottom wall  90   c  and is parallel to the direction of propagation of the light. In addition, the lateral walls are slightly inclined, oppositely, with respect to this main axis I. 
     In  FIG. 8 , only one light source  24  is shown. This light source  24  is placed facing a first entrance dioptric interface  81  followed by a first guide  21 . The first entrance dioptric interface is spaced apart from its neighbouring entrance dioptric interface  82 , which is also called the second entrance dioptric interface  82 , by a first gap  91 . 
     This first gap  91  comprises the right lateral wall  911  that connects the bottom wall  913  to the first entrance dioptric interface  81  and the left lateral wall  912  that connects the bottom wall  913  to the second entrance dioptric interface  82 . 
     This structure is repeated for the other gaps of the same row. 
     The optical part  201 , such as design, may occasion the presence of parasitic light rays. 
     Specifically, in the example of the light source  24  placed in front of the first entrance dioptric interface  81 , i.e. the source illustrated in  FIG. 8 , a minority of the light rays of this source  24  may propagate through neighbouring guides close to the first light guide  21  by passing through the gaps. 
       FIG. 8  schematically illustrates one possible path of the parasitic light rays. 
     The parasitic ray, starting from the light source  24 , initially travels so as to make contact with the left lateral wall  912  of the first gap  91 , in a location located close to the second entrance dioptric interface  82 . The parasitic ray then enters via refraction into the second light guide  22  that is the neighbour to the left of the first light guide  21 . 
     The parasitic ray then propagates inside the second light guide in a lateral propagation direction T in order to then be directed toward the right lateral wall  921  of a second gap  92 . 
     Here, the second gap  92  is that placed between the second entrance dioptric interface  82  and the entrance dioptric interface of a third guide  23  that is the neighbour to the left of the second guide  22 . This entrance dioptric interface is also called the third entrance dioptric interface  83 . 
     By exiting from the second light guide  22 , then after having passed through the second gap  92 , the parasitic ray enters into the third light guide  23  by passing through a left lateral wall  932  of the second gap  92 , this lateral wall also forming the right lateral wall of the third guide  23 . 
     In the third light guide  23 , the parasitic ray continues to propagate laterally. It exits from the third light guide  23  by passing through the right lateral wall  931  of a third gap  93 , that interposed between the third entrance dioptric interface  83  and a fourth entrance dioptric interface  84  of a fourth light guide  24 . 
     Here, the parasitic ray makes contact with the wall of the bottom  933  of the third gap  93  and enters into the interior of the optical part  201  by refraction. Everything then occurs as though the wall of the bottom  933  were illuminated. Thus, the image of the illuminated wall of the bottom  933  is projected to infinity by the projecting system of the optical part. 
     The above description shows that certain light rays output from an elementary light source may not enter into the light guide that is associated therewith but propagate through neighbouring light guides by refraction by passing through the gaps separating the entrance dioptric interfaces of these guides. These light rays are therefore called parasitic light rays. 
     The propagation of the parasitic light rays may cause imperfections in the light beam generated by the optical part. These imperfections are in particular shown in  FIG. 9 , and may as here correspond to regions of extra brightness in zones that are already illuminated or may slightly illuminate zones that should be turned off. 
     Specifically,  FIG. 9  illustrates an image of a beam generated by the elementary light source and by the optical part shown in  FIG. 8 . This image is also called the third image  13 . 
     The third image  13  is obtained on a vertical screen located at a distance from a luminous module containing the optical part  201 , for example at 25 metres, and directly opposite said module. 
     The image  13  is projected onto the screen in an orthogonal coordinate system R composed of a vertical ordinate axis V and a horizontal abscissa axis H. The vertical axis V corresponds to a vertical axis above the road and the horizontal axis H symbolizes the horizon. 
       FIG. 9  also shows, below the image of the beam, the curve C of the variation in the light intensity along the horizontal axis H of the coordinate system R. 
     It may be seen that the image  13  of the beam comprises a pixel  25  of rectangular shape and imperfections, here three thin lines of light  26 . 
     The lines of light  26  are formed by the parasitic light rays projected by the luminous module. 
     Specifically, the parasitic light rays propagate through the neighbouring guides and are imaged by a projecting optic in order to form one or more lines of light in the location where there is a pixel that belongs to the neighbouring guide. 
     The pixel  27  that belongs to the neighbouring guide, here the second, third and fourth light guides  22 ,  23  and  24 , is illustrated by the dashed rectangles in  FIG. 9 . 
     Therefore, the one or more lines of light  26  add light intensity to that of the pixel  27  of the neighbouring guide. 
     In the case where the pixel  27  of the neighbouring guide is placed in a location where the light intensity must remain below a limiting value, the presence of the one or more lines of light  26  is undesirable, because it runs the risk of increasing the light intensity above the regulatory value and/or of generating a visual discomfort. 
     The probability of this situation occurring increases as the light intensity of the one or more lines of light  26  increases. Now, in the illustrated example, the curve C of the variation in the light intensity of the image indicates that the lines of light have a quite high light intensity. The lines of light  26  therefore deliver a surplus of light intensity to the pixels belonging to the neighbouring guides. Thus, the value of the light intensity, measured in the location where there is a superposition of the line of light  26  and the pixel  27 , generates a visual discomfort, or even a risk that the set regulatory value will be exceeded. 
     Moreover, the presence of these lines of light prevents the pixels formed by the neighbouring light guides from being completely turned off. Specifically, when the light sources placed directly opposite the neighbouring guides, here the second, third and fourth light guides  22 ,  23 ,  24 , are turned off, the corresponding pixels are also turned off. However, if the light source  24  located facing the first light guide  21  remains turned on, the parasitic rays remain. Thus, the lines of light  26  remain turned on in the location of the pixels of the neighbouring guides that are however turned off. It is therefore possible to have residual light that may subject an oncoming driver to glare. 
     To solve these problems in this example, the applicant proposes a structural modification at the junction of the entrance dioptric interfaces, according to one embodiment of the invention. 
     Here, it is a question of modifying the structure of the gap  90 ,  91 ,  92 ,  93  between the adjacent entrance dioptric interfaces  81 ,  82 ,  83  and  84 . More precisely, a graining  70  is produced locally on at least one wall of the gap, as illustrated in  FIG. 10 . 
     In other words, if the walls forming the gap have a total area ST, the graining partially occupies this total area ST. 
     As illustrated in  FIG. 10 , the graining  70  may be formed on the left lateral wall  912  of the first gap  91  and as close as possible to the second entrance dioptric interface  82 . Here, it is a question of a first graining zone  71  that is illustrated by a bar encircled by dashed lines. 
     The longitudinal extent of the graining zone  71  depends on the configuration of the light guides and on the configuration of the entrance dioptric interfaces. 
     It will be noted that a graining zone similar to the first graining zone  71  could be produced in the gaps separating the entrance dioptric interfaces  121  of the second row  123  of the illustrated optical part  100  in the first embodiment. 
     In the embodiment of  FIG. 10 , there may also be a second graining zone  72  located in the wall of the bottom  933  of the third gap  93 . 
     The graining is produced in cleverly chosen locations, for example, in the wall of the bottom or in the lateral wall and as close as possible to the entrance dioptric interface, because these locations are on the path very often traced by the parasitic light rays. 
     Depending on the configuration of the optical part, the graining may be produced locally in other locations through which the parasitic light rays pass. 
     Of course, the graining may be produced identically in the gaps in order to effectively scatter the parasitic light rays of all the elementary light sources. 
     By way of example, each gap may comprise graining on the wall of the bottom, and on a portion of the lateral walls that is located close to the entrance dioptric interfaces. 
       FIG. 11  shows the advantageous technical effect achieved by the structural modification on the obtained pixel beam. 
       FIG. 11  illustrates an image  14  of the beam generated by the elementary light source and by the optical part  200  shown in  FIG. 10 . This image is also called the fourth image  14 . 
     The image  14  is obtained under the same conditions as those of  FIG. 9 . It is shown in a coordinate system that is identical to the coordinate system of  FIG. 9 . 
     In  FIG. 11 , the image  14  comprises the pixel  25  corresponding to the elementary light source  24  and the strips of light  46  corresponding to the parasitic light rays. 
     In contrast, unlike  FIG. 9 , the strips of light  46  due to the parasitic light rays have a more extensive shape with a lower light intensity than that of the lines of light in  FIG. 9 . 
     Specifically, by virtue of the presence of the graining zones  71  and  72  in the gaps, the parasitic light rays are scattered on contact with said zones. This allows these strips of light  46  to be spread and the light intensity of the strips to be considerably decreased. 
     Therefore, the strips of light  46  output from the optical part  201  comprising the structural modifications  70 ,  71 ,  72  add a low or even negligible intensity to that of a pixel  27  corresponding to a neighbouring guide. Thus, the value of the light intensity, measured in the location where there is a superposition of the strip of light  46  and the pixel  27 , improves visual comfort and/or decreases the risk of exceeding the value set by regulation. 
     Of course, it is possible to modify the junction between the adjacent entrance dioptric interfaces and/or between the adjacent exit dioptric interfaces differently. 
     For example, in the configuration mentioned by way of example with reference to  FIG. 8 , instead of having graining zones, a reflective, absorbent and/or scattering coating could be applied to the junction between the adjacent entrance dioptric interfaces. 
     The coating may partially occupy the total area of the walls forming the junction. It may be positioned in locations that are on the path of propagation of the parasitic light rays, in particular on the wall of the bottom, on the lateral walls and close to the entrance dioptric interfaces. For example, the coating may be positioned in the same locations as the graining zones  71 ,  72  of the example described above. 
     In the case of a reflective coating, the latter may be applied to all the lateral walls, or even also to the bottom of the gaps.