Controlled caustic generator surface lighting device forming a pattern on a target surface

Abstract

The present invention relates to a vehicle turn indicator luminous device (1) comprising: an optical element (10) having a controlled caustic generator surface (12) so as to propagate a pattern over a usable range, a mounting part (2) on which is intended to be mounted a beam generator (3) of rays incident on said generator surface,
the optical element being such that the propagated pattern is projected onto a target surface, visible from the exterior of the lighting device and situated in the usable range.

Claims

1. A vehicle turn indicator luminous device comprising: an optical element having a controlled caustic generator surface, the controlled caustic generator surface being a reflecting or refracting surface formed by irregular patterns of bosses and recesses extending in accordance with a given overall shape and having local variations of the given overall shape, the local variations being distributed over the controlled caustic generator surface so as to confer on the controlled caustic generator surface an object pattern, the local variations being such that a majority of the controlled caustic generator surface is smooth and such that for a beam of rays incident on the controlled caustic generator surface, the beam of rays having a given distribution, the controlled caustic generator surface deviates the beam of rays with different orientations as a function of the local variations, thus forming a deviated beam propagating an identifiable propagated pattern over a usable range extending in an upstream direction and at least as far as an optimum propagation distance, the identifiable propagated pattern corresponding to a distorted shape of the object pattern, and a mounting part on which is to be mounted a beam generator of rays in accordance with the given distribution, so that the beam of rays are incident on the controlled caustic generator surface, wherein the identifiable propagated pattern is projected onto a target surface, which is visible from outside the vehicle turn indicator luminous device and which is situated inside a usable range or at a distance substantially equal to the optimum propagation distance.

2. The vehicle turn indicator luminous device according to claim 1, in which the given distribution is substantially such that for any plane transverse to the a propagation direction, at a given point of that plane, the ray or beam of rays incident at this point come from a single direction.

3. The vehicle turn indicator luminous device according to claim 1, in which the given distribution corresponds to that of a light-emitting diode.

4. The vehicle turn indicator luminous device according to claim 1, wherein the beam generator of rays is in accordance with the given distribution.

5. The vehicle turn indicator luminous device according to claim 1, in which the controlled caustic generator surface comprises at least one smooth portion which represents the majority of the controlled caustic generator surface, a passage from one local variation to the other being smooth inside the at least one smooth portion.

6. The vehicle turn indicator luminous device according to claim 5, wherein the controlled caustic generator surface is smooth, the passage from the one local variation to the other being smooth.

7. The vehicle turn indicator luminous device according to claim 6, in which a passage between certain local variations is formed by an edge.

8. The vehicle turn indicator luminous device according to claim 7, in which the beam generator comprises a light-emitting diode.

9. The vehicle turn indicator luminous device according to claim 8, in which the beam generator further comprises a light source and an optic adapted with the light source to generate a beam of substantially parallel rays.

10. The vehicle turn indicator luminous device according to claim 1 in which the optical element comprises a reflecting surface at least one portion of which is formed by the controlled caustic generator surface.

11. The vehicle turn indicator luminous device according to claim 10 in which the optical element is a mask.

12. The vehicle turn indicator luminous device according to claim 1, further comprising: a housing and an outer lens, the outer lens closing the housing through which exit light rays are emitted by a lighting device, outer lens forming the optical element, the controlled caustic generator surface being formed on a surface of a portion of the closing outer lens, the deviated beam being formed by refraction of rays emitted by the beam generator.

Description

(1) Other features and advantages of the invention will become apparent on reading the following detailed description of nonlimiting examples, for an understanding of which see the appended drawings, in which:

(2) FIG. 1 is a diagrammatic view of a beam generator and an optical element of a luminous device according to a first embodiment of the invention;

(3) FIG. 2 is an enlarged view of a portion of FIG. 1;

(4) FIG. 3 is a diagrammatic view of a beam generator and an optical element of a luminous device according to a second embodiment of the invention;

(5) FIG. 4 represents diagrammatically the propagation of a target pattern by a beam generator and an optical element of a luminous device according to the invention;

(6) FIG. 5 represents diagrammatically a target pattern formed by a beam generator and an optical element of a luminous device according to the invention;

(7) FIG. 6 represents diagrammatically the object pattern of the generator surface enabling generation of the target pattern from FIG. 5;

(8) FIG. 7 represents a first example of a luminous device according to the invention;

(9) FIG. 8 is a diagram of a second embodiment of the invention;

(10) FIGS. 9a to 9f are diagrams of the various generator surface calculation steps.

(11) FIGS. 1 and 2 illustrate an example of a turn indicator luminous device 1 according to the invention. These figures also make it possible to illustrate the general principle of the invention.

(12) According to the invention, the turn indicator luminous device 1 comprises an optical element 10 having a controlled caustic generator surface 12. This generator surface 12 may a reflecting surface or a refracting surface, as shown in FIGS. 1 and 2. This optical element is referred to hereinafter as the caustic generator 10.

(13) The generator surface 12 extends with a given overall shape 13 represented by the vertical dashed line in FIGS. 1 and 2.

(14) More particularly, in the embodiment from FIG. 1, the caustic generator 10 is a transparent plate having an entry face 11 and an exit face. The entry face 11 is arranged facing a light ray beam generator 3 so as to receive the rays r.sub.1, r.sub.2, r.sub.3 emitted by the beam generator 3. The exit face is arranged to receive the rays r.sub.1, r.sub.2, r.sub.3 refracted by the entry face 11.

(15) As in the example shown, the exit face may be formed, notably entirely, by the generator surface 12.

(16) As a general rule, the generator surface 12 features local variations of shape around the given overall shape 13. These local variations are distributed over all of the generator surface 12 and so confer on the whole of the generator surface 12 a relief forming an object pattern.

(17) For example, as shown in FIGS. 1 and 2, these local variations form recesses and bosses on the exit face of said caustic generator 10.

(18) As a general rule, these various local variations are such that the majority of said generator surface 12 is smooth. For the majority of the generator surface 12, this surface is therefore differentiable at any point. In other words, over the smooth areas, it is free of projecting or recessed edges.

(19) As a general rule, these various local variations are such that for the beam of rays r.sub.1, r.sub.2, r.sub.3 incident on the whole of said generator surface 12, these rays r.sub.1, r.sub.2, r.sub.3 having a known given distribution, the generator surface 12 deviates the rays r.sub.1, r.sub.2, r.sub.3 with different orientations as a function of the local variations that they encounter, therefore forming a deviated beam propagating a light pattern over a usable range extending on the upstream side and at least as far as a given finite optimum propagation distance, termed the optimum distance, this propagated pattern corresponding to a distorted projection of the object pattern.

(20) This generator surface 12 with its local variations corresponds to a controlled caustic generator surface.

(21) Indeed, these local variations create local convergences and divergences of the rays. As these variations are local, a majority of rays move away from one another or toward one another without crossing before a certain distance. In the same way as the surface of a swimming pool through which sun rays pass creates a light pattern propagating and projecting onto the bottom of a swimming pool, the generator surface 12 creates a light pattern that propagates, the propagated pattern.

(22) In the case of a swimming pool, this pattern generally propagates over a distance of 3 metres. The propagated pattern is therefore observable when projected onto the bottom of the swimming pool, whether the bottom is at 1.5 m or at 2 m. This bottom therefore forms the screen on which the caustic forming the propagated pattern can be observed.

(23) In the case of a controlled caustic generator surface, like that of the invention, and depending on the local variations, the light pattern propagates at least over a given optimum distance. Beyond this optimum distance D.sub.p, the rays of the deviated beam cross.

(24) In the context of the invention, and as can be seen in the FIG. 4 theoretical diagram, the optimum distance D.sub.p is finite. If a screen is interposed at an intermediate distance D.sub.1 or at another intermediate distance D.sub.2, which are less than the optimum distance D.sub.p, the same pattern will be observed distorted to a greater or lesser degree.

(25) Note that this optimum distance D.sub.p is that at which the pattern will be sharpest. The generator surface can therefore be designed with reference to this definition.

(26) There may equally exist a minimum distance D.sub.0 below which the pattern is not formed. As a general rule this minimum distance D.sub.0 is relatively short. This minimum distance D.sub.0 may be a few centimetres, or even a few millimetres, depending on the application, such as an application to a motor vehicle luminous device. In this latter case it may be less than 1 centimetre (cm).

(27) Equally, the pattern is not lost as soon as the rays cross but afterwards, at a greater maximum distance (not shown). It is however easier to design the generator surface relative to the crossing distance of the rays, which is defined more precisely than the distance at which it is considered that the pattern is lost. In the present application, this ray crossing distance is therefore termed the optimum propagation distance or optimum distance.

(28) In other words, the usable range comprises a downstream portion, from the optimum distance D.sub.p to this maximum distance, and an upstream portion, from the minimum distance D.sub.0 to the optimum distance D.sub.p. The motif that can be observed at the optimum distance D.sub.p, if a screen is placed there, remains identifiable within these upstream and downstream portions.

(29) In the case of the invention, this downstream portion may generally have a value different from that of the upstream portion. In particular, it may be less than more than half thereof.

(30) For example, in a light with a sufficient closing outer lens portion, with an optimum distance D.sub.p of 20 cm, a minimum distance D.sub.0 of 1 cm, the value of the upstream portion would be 19 cm, and the downstream portion could be less than 9.5 cm.

(31) In particular, said caustic generator 10 and its local variations are such that a propagated pattern is projected onto a target surface, which forms the screen, to form there a light pattern, termed the target pattern. This target surface is visible from outside the luminous device 1 and is situated at a distance within the usable range. The target surface may be at or near the optimum distance D.sub.p, which improves sharpness. The target surface is the surface on which the vehicle travels, notably a portion of the road.

(32) As a general rule, to produce the generator surface 12, the latter is notably calculated taking into account the target pattern that it is wished to display, the shape of the target surface and its arrangement relative to the light rays forming the target pattern, together with the given distribution of the rays r.sub.1, r.sub.2, r.sub.3 on emission by the beam generator 3, in particular their incidence on said caustic generator 10.

(33) According to the invention, the given distribution may correspond to substantially parallel rays r.sub.1, r.sub.2, r.sub.3 as shown in FIG. 3, or, notably, as shown in FIGS. 1 and 2, rays distributed substantially globally in an emission cone 14, notably with a divergent light source, such as an LED. This simplifies establishing the angle of incidence of the rays on said caustic generator 10, thus simplifying the calculation of the generator surface 12.

(34) For this, it is possible to consider that the given distribution is such that for any plane perpendicular to the propagation direction, at any point of that plane, the ray or rays incident at that point come from a single direction. Indeed, the distribution of the rays emitted by an LED substantially corresponds to a given distribution of this kind.

(35) To simplify the calculation, it is possible for the surface to comprise numerous discrete elementary surfaces and to compare the latter to the points mentioned in the preceding paragraph.

(36) The turn indicator luminous device 1 may be shipped without the beam generator 3, but have a mounting part 2 on which it is intended to be mounted, so that the rays r.sub.1, r.sub.2, r.sub.3 are incident on said generator surface 12.

(37) In particular, this mounting part 2 and the beam generator 3 may be such that the beam emitted by the beam generator 3 when mounted has a given overall direction relative to said caustic generator 10. There is therefore no need at assembly time to adjust this orientation so that it corresponds to the arrangement enabling generation of the target pattern.

(38) It is to be noted that these caustic generator surfaces do not necessitate great precision as regards the positioning of the beam generator 3. Assembly is therefore simplified.

(39) In the example shown in FIG. 1, the beam generator 3 is mounted on the mounting part 2.

(40) The beam generator 3 may as here be formed by a light-emitting diode (LED). In FIG. 1 there is diagrammatically represented a photo-emitting element 4 of the LED with, stuck on top, a transparent protective dome 5.

(41) The target surface is a surface outside the vehicle, such as the road.

(42) The methods of calculating this generator surface 12 may follow the following procedure, one example of which is shown in FIGS. 9a to 9f: in a step E1, termed the upstream step, shown in FIG. 9a, establish the relations defining the angle of incidence of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 and their distribution at each point of the given overall shape 13, taking into account the given distribution of the rays r.sub.1, r.sub.2, r.sub.3, otherwise making it possible also to define the brightness of each point at the level of the given overall shape 13 on said caustic generator 10, termed the object point p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5, in a step E2, termed the downstream step, which may be executed before, after or at the same time as said upstream step E1, define the luminous distribution over the target surface making it possible to obtain the target pattern, and therefore define the brightness at each point of the target surface 19, termed the target point p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4, then, in a correlation step E3, shown in FIG. 9b, establish a relation between each object point p.sub.1, p.sub.2, p.sub.3, p.sub.4 p.sub.5 and each target point p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4, notably so that each target point p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 that receives light is associated with only one or a set of object points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 making it possible to obtain the brightness at these points required to form the pattern, thereafter, in a step E4/E5 of orientation of the local variations, shown in FIGS. 9c to 9f, as a function of the target points and object points associated by the relation established in the correlation step E3, determine the orientation of the local variations to be applied to the overall shapes so that the rays r.sub.1, r.sub.2, r.sub.3 r.sub.4, r.sub.5 incident at the object points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 are deviated so as to have the orientation enabling them to reach the target points p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 associated therewith via this relation.

(43) The upstream step E1 takes into account the distribution of the rays upon their arrival at the level of the given overall shape 13. The simplest case, not shown, is that of an optical element 10, such as that shown in FIGS. 1 and 9a, formed of a transparent plate the entry face 11 of which and the given overall shape 13 of the generator surface 12 are plane, and with a beam generator 3, such as that from FIG. 3, emitting parallel rays.

(44) In this simple case, the beam generator 3 and said caustic generator 10 are such that the rays are perpendicular to the entry face 11. These rays are therefore not deviated before encountering the exit surface on which the generator surface is formed.

(45) The embodiment from FIGS. 1 and 2 and FIGS. 9a to 9f represents an intermediate case in which the rays are distributed in an initial cone 14 at the outlet of the beam generator 3 and then refracted by the plane entry face, therefore remaining inscribed in a cone, enabling easy determination of the angle of incidence of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 on the overall shape 13, and thus easy determination of the angle of incidence of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 on the generator surface 12.

(46) The embodiment from FIG. 3 represents another intermediate case in which the distribution of the rays r.sub.1, r.sub.2, r.sub.3 is initially simpler, since they are parallel at the exit of the beam generator 3. On the other hand, they are then refracted differently by the entry face 11 because the latter is curved, for example a cylinder with a circular or elliptical section. However, this curvature being defined, it makes it possible to determine the orientation of the rays r.sub.1, r.sub.2, r.sub.3 on their arrival at the level of the given overall shape 13 of the generator surface 12, which for its part is also curved.

(47) In the example shown in FIG. 3, the optical element is a curved transparent plate, the entry face 11 of which and the general shape 13 of the generator surface 12 are cylindrical. So as to have parallel rays, the beam generator 3 may comprise a light source 6, such as a light-emitting diode, and a collimator lens 7 the diopters of which enable parallel orientation of the rays.

(48) More complicated cases can however be envisaged, with rays distributed in an emission cone, a curved, notably cylindrical, entry surface, and a generator surface of given curved overall shape.

(49) It is equally possible to envisage other given distributions of the rays.

(50) Concerning the downstream step E2, the simplest case is then for the target surface 19 to be plane and perpendicular to the overall direction of emission of the rays on arriving at the level of the overall shape 13 of the generator surface 12 to be calculated. The target pattern then corresponds to the propagated pattern.

(51) In more complex cases, account must be taken of the orientation of the plane target surface, at an angle to the overall direction of transmission of the rays on arrival at the level of the generator surface. Such determination remains simple, however. It is more complicated, but achievable, when the target surface is not plane. Account must then be taken of its shape, notably to define it by an equation in order to determine the light distribution, so as to be able to observe the target pattern when projected. In all these more complex cases, the propagated pattern, if defined in a plane perpendicular to the propagation direction thereof, differs from the target pattern.

(52) Thereafter, various methods may be used to carry out the step E3 of correlating the rays incident on the overall shape 13 of the generator surface 12 with the distribution of light over the target surface 19.

(53) As explained above, this correlation step enables determination of which object points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 of the given overall shape 13 are associated with which target points p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 of the target surface 19.

(54) Thanks to the upstream step E1 the orientation of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 on arrival at the level of the given overall shape 13 of the generator surface 12 is known. Moreover, the correlation between target points p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 and object points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 determines the orientation of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 on departing from this given overall shape 13 to join the object points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 to the target points p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 with which they are correlated.

(55) This therefore enables execution of the orientation step E4/E5, by calculating the variation to be assigned to the exit surface relative to this given overall shape 13 at all points of the latter, which enables definition of the generator surface 12.

(56) Once this calculation has been done, it is therefore seen that, as a function of the amplitudes of the local variations, the generator surface 12 is at a greater or lesser distance from the given overall shape 13. To refine the calculation of the generator surface 12, it is therefore possible to repeat the upstream and downstream steps as well as the definition step, considering the arrival of the rays at their departure relative to the shape of the generator surface obtained previously and no longer relative to the given overall shape. The accuracy of this surface and therefore the sharpness of the image will improve with the number of iterations. Moreover, this also enables smoothing of the generator surface.

(57) To carry out the orientation step, it is possible to use Descartes' laws, also known as Snell's laws in some English-speaking countries, or again as Snell-Descartes' laws.

(58) Accordingly, in a substep E4, shown in FIGS. 9c and 9e, for an object point p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5 of the given overall shape 13 or of the generator surface calculated previously, with the direction of arrival and the direction of departure of the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5, it is possible to determine the tangent {right arrow over (t)} and the normal {right arrow over (n)} of the exit surface at that point for which the latter deviates each incident ray r.sub.1, r.sub.2, r.sub.3, r.sub.4, r.sub.5 arriving in the corresponding refraction direction.

(59) In a substep E5, shown in FIGS. 9d and 9f, the generator surface 12 having these normals is determined by determining all of the normals {right arrow over (n)}, also known as normal fields.

(60) FIGS. 9c and 9d illustrate the execution of these two substeps with magnification at the level of the object points p.sub.1, p.sub.2, p.sub.3, not referenced in FIGS. 9c and 9d for greater clarity.

(61) FIGS. 9e and 9f illustrate the execution of these two substeps with magnification at the level of the object points p.sub.4, p.sub.5 not referenced in FIGS. 9e and 9f for greater clarity.

(62) In FIG. 2, there can be seen the local variations of the generator surface 12 relative to the given overall shape 13, which is plane in this example. These local variations correspond to changes of slope, defined by the normal {right arrow over (n)} and/or the tangent {right arrow over (t)} to the generator surface 12 at the level of the local variations. The result of this is that this generator surface 12 departs from the overall shape 13 and forms bosses and recesses.

(63) For greater clarity the normals {right arrow over (n)} and tangents {right arrow over (t)} have been shown here for only three points on the generator surface 12, but the normal and/or the tangent is or are calculated for all the points.

(64) The amplitude of a local variation may in this application be defined as the distance between the local variation and said overall shape 13 along the normal at a given point of the overall shape 13.

(65) If the overall shape is plane, as in FIGS. 1 and 2, any point on the given overall shape can be defined by a dimension in a single direction z perpendicular to this overall shape 13.

(66) There is seen in FIG. 2 a minimum amplitude a.sub.1, by convention negative because it is situated on the upstream side of the generator surface 12, and a maximum amplitude a.sub.2 downstream of the generator surface 12, by positive convention.

(67) Note that in the method shown, it is possible to divide the surface into numerous discrete elementary surfaces and to compare the latter to the points p.sub.1, p.sub.2, p.sub.3, p.sub.4, p.sub.5, p′.sub.1, p′.sub.2, p′.sub.3, p′.sub.4 referred to.

(68) FIG. 5 illustrates the propagated pattern 16, as it will be seen on a flat screen perpendicular to the propagation direction and at a distance equal to or close to the propagation distance. If the target surface is also plane and oriented thus, then this propagated pattern 16 will also be the target pattern 16′ seen in FIG. 5. Otherwise, it will be deformed.

(69) The generator surface 12 that made it possible to produce this propagated pattern 16 is shown in FIG. 6. Because of the relief formed on this surface 12, the object pattern 15 formed by this relief and therefore the local variations can be seen. This object pattern 15, symbolically represented in FIG. 6, corresponds to a distorted shape of the propagated pattern 16.

(70) If the FIG. 5 pattern were also required to be the target pattern 16′ observed by a driver or a third-party observer observing the carriageway, the target pattern being formed by grazing incidence rays relative to the carriageway because coming for example from a headlamp, a rear light or a turn signal lamp, the propagated pattern would then have to be distorted relative to the target pattern, to observe the star on the road as represented in FIG. 5.

(71) According to the invention, and as in FIGS. 1 and 2, the generator surface 12 may be such, and therefore calculated, so that, for the majority of the generator surface 12, namely smooth portions representing the majority of that surface, the passage from one local variation to the other is smooth. This is notably the case of the portion shown in FIG. 2. If for the calculations the local variations are not considered as points but as small zones of the generator surface, notably infinitesimally small zones, the generator surface 12 may moreover be such that, for these smooth portions, the local variations are smooth.

(72) In particular, one of the smooth portions may have a surface representing the majority of the generator surface.

(73) A first example calculation method may be used to calculate this generator surface 12. This is the method disclosed in the document Yue et al. [1]. That document notably indicates the various steps for constructing the generator surface 12 starting from a given example, in particular to establish the relation between the points of the generator surface 12 and those of the target surface.

(74) This first method example enables a totally smooth generator surface 12 to be obtained. The passage from one local variation to the other is smooth.

(75) To establish the relation of the correlation step, notably as in this first method, a condition is set as establishing a bijection between the object points and the target points. Accordingly, the whole of the generator surface 12 is such that: each local variation deviates the incident light rays to form one and only one portion of the target pattern 16′ that is distinct from the portions of the target pattern formed by the other local variations, and for the whole of the target pattern, each portion of the target pattern receives the light rays coming from one and only one local variation.

(76) This method enables good brightness gradients and good resolution. It may for example be used to produce the generator surface 12 from FIG. 1.

(77) According to other methods, for improved contrast and to have darker zones and zones with maximum brightness, it is possible to adapt the local variations so that the generator surface 12 has one or more edges.

(78) Depending on the case, the generator surface 12 comprises: at least one edge delimiting portions of the generator surface with different orientations so as to generate a divergence such that certain zones of the target pattern receive virtually no rays, or even no rays at all, thus forming dark zones, and/or at least one edge delimiting portions of the generator surface with different orientations so as to generate a convergence such that certain zones of the target pattern receive the rays from a plurality of local variations and/or a plurality of portions of this generator surface.

(79) This notably enables production of patterns with lines of light or very clear writing.

(80) A second calculation method may be used for this, for example, to calculate the generator surface 12, as disclosed in the document Schwartzburg et al. [2].

(81) In this second method, no bijection constraint is used in the correlation step. This method is more complex but enables a higher contrast to be obtained, namely a higher ratio between the light zones and the dark zones. This method in fact enables zones to be obtained darker than those of the Yue et al method mentioned above. With this second method it is therefore possible to obtain more marked demarcations between dark zones and light zones. The portions away from the edges are smooth, the passage from one local variation to the other being smooth.

(82) In FIGS. 9a to 9f, for example, the method used does not impose a bijection constraint to establish the target pattern. At certain locations, a plurality of object points p.sub.4, p.sub.5 correspond to a single target point p′.sub.4. The result of this is that the generator surface 12 features a slope variation discontinuity, corresponding to an outward edge 18 on the generator surface 12, and therefore inward in the direction of the incident rays. The local variations on either side of this edge 18 enable concentration of the rays r4, r5 on a line of the target surface, for example to form a sharp intense line.

(83) Away from this edge 18, notably above and below it, the correlation step E3 has led, without constraining it, to a bijective relation between the corresponding object points p.sub.1, p.sub.2, p.sub.3 and the corresponding target points p′.sub.1, p′.sub.2, p′.sub.3.

(84) Whatever the method used, each point on the generator surface 12 is therefore associated with an amplitude that corresponds to a distance from the overall shape 13, this amplitude being defined in a direction parallel to the normal to the overall shape 13 at that point.

(85) As shown in FIGS. 1 and 3, for example, a plane is considered comprising the overall direction of the beam of incident rays. There is considered in this plane the rectangle 17 in which the caustic generator 10 is circumscribed, and this rectangle 17 may have a side length that is four times greater than, and notably six times greater than, that of the amplitude of each local variation relative to the given overall shape 13 at the level of that local variation, and therefore six times greater than the maximum amplitude.

(86) Moreover, the local variations may have a tangent t forming an angle α with the given overall shape between −60 and 60 degrees inclusive, notably between −30 and 30 degrees inclusive.

(87) Combining these slope and amplitude conditions yields optimum results, notably in terms of contrast and sharpness, notably enabling propagation of the propagated pattern over the usable range, in particular at the optimum distance D.sub.p.

(88) It is to be noted that the smaller the light source 4, 6 of the beam generator 3 relative to the generator surface 12, the closer is the projected pattern to the required pattern used for the construction of the generator surface. For example, the side length of the rectangle 17 in which the caustic generator 10 is circumscribed may be at least ten times greater, notably thirty times greater, than that of a side length of that light source 3, 6, notably when that source is a light-emitting diode.

(89) The two embodiments from FIGS. 1 to 3 are aimed at caustic generators 10 functioning by refraction.

(90) Here the generator surface 12 is formed on an optical element 10 specifically dedicated to this. However, it may equally be formed on elements having other functions, such as a closing outer lens of the turn signal lamp or of the automotive lighting and/or signalling device into which the luminous device according to the invention is mounted, an optical lens, a mask.

(91) In the application, “mask” denotes the embellisher intended to mask certain elements such as cables, the bottom of the housing. It is also known as a bezel.

(92) Moreover, FIGS. 1 to 3 illustrate situations in which the generator surface 12 is on the exit face of the caustic generator 10. This is not limiting on the invention, however, and, generally speaking, the optical element can have a generator surface on the entry face and/or the exit face.

(93) FIG. 8 illustrates a third embodiment in which the optical element 10′ or caustic generator 10′ functions by reflection.

(94) Here the caustic generator 10′ is a mirror the reflecting surface of which forms the generator surface 12′, featuring local variations about its plane overall shape 13′.

(95) This mirror 10′ may have one or more edges. Here, there is an inward edge 18′, namely forming the bottom of a recess, delimiting surface portions with an orientation facing one another, the latter portions therefore enabling creation of an intense line of light of particular shape on the target pattern, not shown.

(96) The same construction methods may be applied to this reflecting generator surface 12′, taking into account during the various steps of the method that it is a question of reflection and not of refraction.

(97) In such a case, the upstream step is simplified because the rays r.sub.1, r.sub.2, r.sub.3, r.sub.4 arrive directly on the generator surface 12 in accordance with the given distribution and also depart directly.

(98) FIG. 7 shows a first example of luminous device according to the invention. In the case shown, a vehicle 20 with longitudinal axis X is equipped with two luminous devices according to the invention, which here are respectively integrated in a righthand rear light 21 and a lefthand rear light 22.

(99) For example, each of these two rear lights 21, 22 includes a housing and a corresponding outer lens closing the housing. Each closing outer lens comprise a portion the diopter of which between the outer lens and the exterior forms the generator surface. Each of these generator surfaces receives some of the light rays coming from a light source of the corresponding rear light 21, 22. There could equally be provided a light source specifically dedicated to this generator surface.

(100) The generator surface of the righthand rear light 21 is adapted to generate a target pattern 23 on the road forming a pattern made of a three triangles composition, here warning following vehicles of a change of direction to the right when considering the vehicle traveling direction illustrated by the X arrow.

(101) FIG. 7 being an overhead view, this pattern is stretched out but will be perceived by following vehicles as less stretched. The object pattern, not shown, formed by the relief of the corresponding generator surface has a distorted form of this target pattern made of a three triangles composition.

(102) In this example, it is clear that, in the propagation direction, the distance of the pattern between the generator surface and the target surface, namely the road, is going to vary as a function of the ride attitude of the vehicle 20, for example whether it is laden or not. Here the generator surface is such that when the ride attitude of the vehicle 20 is horizontal, on a horizontal road, the given optimum distance D.sub.p is greater than, for example twice, the distance between the generator surface and the road in the direction of propagation of the propagated pattern. This makes it possible to have a visible sharp target pattern, whatever the orientation of the vehicle 20, in particular its ride attitude. The target pattern therefore remains visible when ascending, descending, braking or accelerating, and whatever the load.

(103) In this example, the generator surface of the righthand rear light 21 receives the light rays from the light source enabling generation of a turn indicator signal.

(104) It is to be noted that the lights could equally be constructed in accordance with the principle shown in FIGS. 1 and 3. In this case, instead of the generator surface being formed on the closing outer lens 9 closing the housing 8, the latter is, as described above, formed on a transparent plate 10 specifically designed to have the generator surface.

(105) In the present invention, the target pattern is a logo, an icon (pictogram), a geometric figure, or an assembly of several logos, icons (pictogram), geometric figures or a combination thereof, such as an icon combined to one or several geometric figures. Advantageously, the geometric figure has a well recognisable shape, such as chevrons, triangles or disks. Advantageously, the icon shows a straight or bent (curved) arrow.

LIST OF REFERENCES

(106) [1] Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita. Poisson-Based Continuous Surface Generation for Goal-Based Caustics, ACM Transactions on Graphics, Vol. 31, No. 3, Article 31 (May 2014). [2] Yuliy Schwartzburg, Romain Testuz, Andrea Tagliasacchi, Mark Pauly. High-contrast Computational Caustic Design, ACM Transactions on Graphics (Proceedings of ACM SIGGRAPH 2014), Vol. 33, Issue 4, Article No. 74 (July 2014)