WO2020053190A1 - Light system for vehicle - Google Patents

Abstract

The invention relates to a light system (1) for a motor vehicle. The system comprises a plurality of electroluminescent sources (10) arranged in a two-dimensional matrix and a device (11) for cooling the plurality of electroluminescent sources from a rear face of the two-dimensional matrix. The system is essentially such that the cooling device (11) is designed to ensure heat transfer by conduction which is higher with a portion (100) of the rear face of the two-dimensional matrix than with the rest of said rear face. It is thereby possible to reduce, particularly by dimensioning the cooling device on a case-by-case basis, the differences in temperature between the electroluminescent sources of the same plurality of electroluminescent sources. The problems of colour shift, control of the light flows and mechanical stresses within the plurality of electroluminescent sources are thereby limited, or even resolved.

Description

 "Vehicle light system"

The present invention relates to the field of lighting systems, in particular lighting, for motor vehicles. The present invention relates more particularly to the cooling of such light systems.

 Lighting systems are known, comprising a plurality of light sources arranged in a two-dimensional array, the light sources of which can be supplied electrically individually. It is thus possible to generate, thanks to the assembly, a luminous flux obeying a specific spatial distribution with a determined regulatory photometric function.

 A problem with this type of lighting system stems from the fact that excessively significant junction temperature differences are observed between the light sources of the same plurality. These differences in junction temperature effectively lead to problems of color shift, control of light fluxes and mechanical tensions (by thermal expansion phenomena) within the plurality of light sources.

 The present invention aims to reduce these problems in order to increase the reliability of lighting systems, in particular lighting, for motor vehicles.

To this end, the present invention relates to a light system, in particular a lighting system, for a motor vehicle, the system comprising at least a plurality of light-emitting sources arranged in a two-dimensional matrix and a device for cooling said at least a plurality of light-emitting sources. from a rear face of the two-dimensional matrix. The light system is essentially such that the cooling device is configured to provide heat transfer by higher conduction with a portion of the rear face of the two-dimensional matrix than with the rest of this rear face.

Thus, the invention provides that the heat transfer provided by the cooling device from the rear face of each two-dimensional matrix is inhomogeneous.

Therefore, it is possible to reduce, in particular by dimensioning the cooling device on a case-by-case basis, the temperature differences between the electroluminescent sources of the same plurality. Problems with color shift, control of the luminous fluxes and of mechanical tensions within the plurality of electroluminescent sources are thus limited, even resolved.

Where appropriate, the light emitting sources of each plurality form a monolithic assembly.

Furthermore, the electroluminescent sources of the at least one plurality can be configured in conjunction with an optical system for shaping the light system. The shaping optic is then arranged opposite the front face of the at least one plurality of light-emitting sources.

According to one feature, said two-dimensional matrix of light-emitting sources is bonded to the cooling device by means of a layer of glue and said portion is located in line with a variation in thickness of the layer of glue applied between said two-dimensional matrix. electroluminescent sources and said cooling device.

According to one feature, said portion is located in line with the light-emitting sources which, among each plurality of light-emitting sources, are intended to receive, in order to carry out at least one determined lighting function of the light system, an electrical power supply greater than one first predetermined threshold value. The first predetermined threshold value is for example equal to 70%, or even equal to 80%, of a maximum electrical supply power admissible by each electroluminescent source. The lighting function determined is preferably that which, among the lighting functions of the system, requires the greatest power supply power compared to the other lighting functions of the system.

According to another particularity, alternative or combinable with the previous ones, each plurality of light-emitting sources being intended, according to its use, to present, in its two-dimensional extent, a first part having a junction temperature greater than a second predetermined threshold value, and a second part having a junction temperature below said second predetermined threshold value, said portion can be located at most to the right of the first part. It is preferably located at the right of 80% of the first part, and even more preferably at the right of 70% of the first part. The second predetermined threshold value is for example between 60% and 90%, preferably between 70% and 80%, of an upper limit junction temperature value at which at least one light-emitting source of the plurality is intended to be carried during its use. The first part can be a central part of the at least a plurality of light-emitting sources and the second part can be a part peripheral to said central part.

According to another particularity, alternative or combinable with the previous ones, each plurality of electroluminescent sources being intended, according to its use, to present, in its two-dimensional extent, a gradient of junction temperature varying spatially between an upper limit temperature and a lower limit temperature , said portion is located at most in line with an area intended to present, during its use, a junction temperature higher by 20 ° C, preferably higher by 30 ° C, than said lower limit temperature.

According to another particularity, alternative or combinable with the previous ones, each plurality of electroluminescent sources being intended, according to its use, to present, in its two-dimensional extent, a gradient of junction temperature varying spatially between an upper limit temperature and a lower limit temperature , said portion is configured so that said upper limit temperature is lower, preferably at least 10 ° C, than a maximum allowable junction temperature of each light-emitting source.

According to another particularity, alternative or combinable with the previous ones, the cooling device comprises at least one main plate made from a thermal conductive material and arranged so as to directly contact said portion of the rear face of the two-dimensional matrix. The material from which the main plate is made preferably has a thermal conductivity greater than 100 W-nT ¹ -K ^_1 . For example, it is a copper-based plate.

In addition to the previous feature, the cooling device may include at least one secondary plate contacting at least one complementary part of the rear face of the two-dimensional matrix relative to the main plate. The secondary plate is based on a material having a lower thermal conductivity, preferably at least two times lower, than a thermal conductivity of the material from which the main plate is made.

As an alternative to the previous feature, the cooling device is configured to ensure no thermal transfer by conduction from the rear face of the two-dimensional matrix outside of said portion.

According to another aspect, the present invention also relates to a motor vehicle comprising a lighting system as introduced above.

Other characteristics and advantages of the present invention will be better understood with the aid of the description which is given below by way of example and of the appended drawings among which:

 - Figures 1 to 3 schematically represent the prior art. Figure 1 is a perspective view of a light system according to the prior art. FIG. 2 represents a top view of the light system illustrated in FIG. 1. FIG. 3 illustrates a map of the isotherms observable over the two-dimensional extent of the plurality of electroluminescent sources in use for a determined lighting function;

 - Figures 4 to 6 schematically represent an embodiment of the invention. Figure 4 is a perspective view of a light system according to the invention. FIG. 5 represents a top view of the light system illustrated in FIG. 1. FIG. 6 illustrates a map of the isotherms observable over the two-dimensional extent of the plurality of electroluminescent sources in use for a determined lighting function; and FIG. 7 illustrates the difference in behavior between a light system according to the prior art and a light system according to the invention in terms of local temperature profiles.

Unless otherwise specified, technical characteristics described in detail for a given embodiment can be combined with technical characteristics described in the context of other embodiments described by way of example and not limitation.

Similarly, unless specifically indicated to the contrary, the terms "downstream" or "before" mean a relative provision of an element of the invention further downstream according to the path of the radiation coming from the light system and leaving the light system. Terms like "upstream" or "backward" have an opposite meaning.

 The term “optics” is understood to mean the front part of a light system, this part comprising all of the refractive media which compose it.

 The term "shaping optics" means an optics configured to deflect at least one of the rays emitted by a light system. By "deflecting" is meant that the direction of entry of the light ray into the shaping optic is different from the direction of exit of the light ray from the shaping optic. The shaping optic comprises at least one optical element such as one or more lenses, one or more reflectors, one or more light guides or a combination of these possibilities.

 "Regulatory photometric function" means a lighting function intended to allow, regulate or secure the movement of motor vehicles. It is for example chosen from a high beam function, a low beam function, a daytime running light function, a position light function, a fog light function, and a signaling light function. We will potentially speak of a specific lighting function to refer to a regulatory photometric function.

 The term “junction temperature” is understood to mean the local temperature of the silicon zone which forms the junction of an electroluminescent source. This temperature can be measured, but it can also be predicted, in particular according to the characteristics of the light-emitting source and the parameters of its use. It is also possible to define a maximum admissible junction temperature as the junction temperature above which the light-emitting source would be deteriorated at least functionally, or even also structurally.

There is shown, in Figures 1 to 3, a light system according to the prior art that we describe below to better illustrate the differences between such a known light system and the light system according to the invention. In order to facilitate comparison between these, the same reference numbers have been assigned to the corresponding components.

 In its broadest acceptance, the invention according to its first aspect relates to a lighting system 1 for a motor vehicle.

As illustrated in FIGS. 1 and 2 as regards the prior art and in FIGS. 4 and 5 as regards the invention, the light system 1 comprises: a plurality of electroluminescent sources 10 arranged in a two-dimensional matrix, and

 a device 1 1 for cooling the plurality of light-emitting sources 10.

 More particularly, the cooling device 1 1 cools the plurality of light-emitting sources 10 from a rear face of the two-dimensional matrix.

 As illustrated in Figures 1 and 4, the cooling device 1 1 can be associated with an additional cooling device 12, taking in the example illustrated the form of a finned heat sink. The invention is in no way limited to the nature of any additional cooling devices 12 which would complement the cooling device 11.

 Advantageously, a control electronics (not shown) is provided which is capable of selectively controlling the electric power delivered to each of the electroluminescent sources of the plurality. This control can be performed as a function of control instructions received from a processing unit (not shown). By way, the light intensity produced by each of the light emitting sources of the plurality is controlled.

If necessary, the plurality of light-emitting sources 10 can comprise, in its two-dimensional extent, at least 20 columns and at least 20 rows of light-emitting sources.

 Each light emitting source can more particularly comprise at least one light emitting diode emitting light. The associated shaping optics can more particularly comprise a matrix of micro-mirrors (also known by the acronym DMD, for the English Digital Micromirror Device) which directs the light rays coming from electroluminescent sources by reflection, for example towards another element of the shaping optics. If necessary, another element of the shaping optics makes it possible to collect the light rays coming from electroluminescent sources in order to concentrate them and direct them towards the surface of the matrix of micro-mirrors. Each micro-mirror can pivot between two fixed positions, so that, each micro-mirror reflecting part of the light rays, actuation and control of the change of position makes it possible to modify the shape of the beam emitted via the focusing optics. fit and ultimately on the road.

According to a second particular embodiment of the light system 1, each electroluminescent source comprises a laser source emitting a beam laser and shaping optics includes a laser scanning system configured to scan, with each emitted laser beam, the surface of a wavelength converter element. The scanning of the beam is accomplished by the scanning system at a speed high enough that the human eye does not perceive its movement in the projected beam. Synchronized control of the ignition of the laser source and of the beam scanning movement makes it possible to generate a pixelated light beam. Here, the scanning system more particularly comprises a plurality of mobile micro-mirrors, making it possible to scan the surface of the wavelength converter element by reflection of the laser beam. The micro-mirrors are for example of the MEMS type (for “Micro-Electro-Mechanical Systems” in English or electromechanical microsystem). However, the invention is in no way limited to this scanning means, and can use other kinds of scanning devices, such as a series of mirrors arranged on a rotating element, the rotation of the element causing a scanning. of the transmission surface by the laser beam.

 According to a third embodiment of the light system 1, the latter comprises an electroluminescent source called in English "solid-state light source". Examples of such light sources include the light emitting diode or LED (acronym for "Light Emitting Diode"), the organic light emitting diode or OLED (acronym for "Organic Light-Emitting Diode"), or the polymer light emitting diode or PLED ( English acronym for “Polymer Light-Emitting Diode”), or micro-LED.

 Preferably, the plurality of electroluminescent sources comprises at least one monolithic set of electroluminescent sources, also called monolithic set. In a monolithic assembly, the electroluminescent sources are believed from a common substrate and are electrically connected so as to be selectively activatable, individually or by subset of electroluminescent sources. The substrate can mainly be made of a semiconductor material. The substrate may include one or more other materials, for example non-semiconductors. Thus, each light emitting source or group of light emitting sources can form a light pixel and can emit light when supplied with electricity.

Furthermore, each electroluminescent source or group of electroluminescent sources can potentially pick up light radiation, if necessary having a substantially determined wavelength and a particular relative direction of propagation, to convert the photons of said light radiation into an electric current. A monolithic assembly can of course take the form of a two-dimensional matrix of light-emitting sources. Such a monolithic assembly allows the arrangement of selectively activatable pixels very close to each other, with respect to conventional light-emitting diodes intended to be soldered on printed circuit boards. In addition, the luminance obtained by the plurality of electroluminescent sources is at least 60 Cd / mm ² , preferably at least 80 Cd / mm ² .

 The monolithic assembly comprises electroluminescent sources of which a main elongation dimension, namely the height, is substantially perpendicular to a common substrate, this height being at most equal to a micrometer.

As mentioned above, the light system 1 can be coupled to electronics for controlling its light emission. The control electronics can thus control (one can also say “control”) the generation and / or the projection of a pixelated light beam by the plurality of light-emitting sources 10. The control electronics can be integrated into the light system 1 The control electronics can be configured to control one or more monolithic assemblies.

 The control electronics can comprise or be arranged jointly with a central processing unit. The latter is generally coupled with a memory on which is stored a computer program which includes instructions allowing the processor to perform steps generating signals allowing the control of the light system 1. The control electronics can thus for example individually control the light emission from each electroluminescent source of a monolithic assembly.

 The control electronics can form an electronic device capable of controlling the light-emitting sources. The control electronics can be an integrated circuit. An integrated circuit, also called an electronic chip, is an electronic component reproducing one or more electronic functions and capable of integrating several types of basic electronic components, for example in a reduced volume (i.e. on a small plate). This makes the circuit easy to implement and integrate for example in a headlight of a motor vehicle.

As an alternative to control electronics, it is envisaged to use an integrated circuit of the ASIC or ASSP type. An ASIC (acronym for "Application-Specific Integrated Circuit") is an integrated circuit developed for at least one application specific (i.e. for a client). An ASIC is therefore a specialized integrated circuit (micro electronics). In general, it combines a large number of unique or tailor-made functionalities. An ASSP (acronym for “Application Specifies Standard Product”) is an integrated electronic circuit grouping together a large number of functionalities to satisfy a generally standardized application. An ASIC is designed for a more specific (specific) need than an ASSP.

 The power supply of the monolithic assemblies is carried out via the control electronics or the integrated circuit of the ASIC or ASSP type, itself supplied with electricity using for example using at least one connector connecting it to a source d 'electricity. The source of electricity can be internal or external to the lighting system 1.

 According to a preferred embodiment of the light system 1, it comprises at least one monolithic assembly taking the form of a two-dimensional matrix, the light emitting sources of which project from a common substrate from which they have grown respectively. Different arrangements of electroluminescent sources can meet this definition of monolithic assembly, since the electroluminescent sources have one of their main dimensions of elongation substantially perpendicular to a common substrate and that the spacing between the sources is small in comparison spacings imposed in known arrangements of flat square chips soldered on a printed circuit board.

As illustrated in Figures 1 and 2, the cooling device 1 1 of the light system 1 according to the prior art is located opposite the two-dimensional extent of the plurality of light emitting sources 10; it extends more particularly under the whole extent of the plurality, or even beyond this extent according to the example illustrated. Such a cooling device 1 1 ensures homogeneous heat transfer by conduction from the rear face of the two-dimensional matrix.

On the contrary, as illustrated in FIGS. 4 and 5, the light system 1 according to the invention is such that the cooling device 1 1 is configured to provide thermal transfer by superior conduction with a portion 100 of the rear face of the two-dimensional matrix. than with the rest of the back side. The cooling device 1 1 according to the invention is therefore fixed to the rear face of the two-dimensional matrix. This fixing is for example carried out in the same way as was the cooling device according to the prior art. It will be noted that, unlike FIGS. 1 and 4, FIGS. 2 and 5 do not represent the additional cooling device 12 which, if necessary, increases the cooling offered by the cooling device 11.

 The portion 100 is represented in FIGS. 4 and 5 by a rectangular outline in bold dashes. However, it can take any form, such as a disc or ring shape, or even a shape with separate parts between them.

 Figures 3 and 6 illustrate maps of the isotherms of the junction temperature (measured or predicted) of the electroluminescent sources included respectively in the light system 1 according to the prior art and in the light system 1 according to the invention. These maps were more particularly obtained by considering that the light systems are used to provide a regulatory photometric function for high beam. This lighting feature and those that require the most power from a compact power supply compared to their other lighting features. Of course, corresponding maps can be obtained for different uses of lighting systems, and in particular for use in low beam or for use in daytime running lights for example. Thus, if the present invention is to be particularly adapted to a regulatory photometric function of high beam, it is also adaptable to other regulatory photometric functions, whether known or to come.

 It can be seen directly that the new dimensioning of the cooling device induces a change in shape of the isotherms. However, the interest of the invention does not lie so much in this change in shape as in the change in value of the isotherms.

 Further analysis of Figures 3 and 6 allows the following observations.

Firstly, the isotherm representing the highest junction temperature is of a higher value in FIG. 6 relative to FIG. 3. Thus, certain electroluminescent sources of the light system according to the invention are brought to a maximum temperature higher than the temperature maximum to which certain electroluminescent sources of the light system according to the prior art are brought.

Secondly, the isotherm representing the lowest junction temperature is of a higher value in FIG. 6 relative to FIG. 3. Thus, certain electroluminescent sources of the light system according to the invention are brought to a minimum temperature higher than the temperature. minimum to which certain electroluminescent sources of the light system according to the prior art are brought. From its first two observations, it appears that the light-emitting sources of the light system 1 according to the invention are generally brought to temperatures higher than those experienced, under the same conditions of use, the light-emitting sources of the light system 1 according to the prior art.

 Another difference also emerges from an analysis of the maps illustrated in FIGS. 3 and 6. This difference is better illustrated in FIG. 7. This difference is due to the fact that the difference between the minimum and maximum junction temperatures to which the electroluminescent sources of the light system according to the invention is reduced by at least 10%, preferably by at least 15%, with respect to the difference between the minimum and maximum junction temperatures to which the electroluminescent sources of the light system are brought according to the prior art.

 This difference is better illustrated in FIG. 7. The curve 23 (from the top) in FIG. 7 illustrates a profile of junction temperature within a light system according to the invention, while the curve 24 (from the bottom) on FIG. 7 illustrates a junction temperature profile within a light system according to the prior art. Illustrated on the one hand is the overall rise in temperature of the light-emitting sources, and on the other hand the reduction in the temperature difference between the minimum and maximum junction temperatures to which the light-emitting sources are brought.

Thus, the invention provides that the heat transfer provided by the cooling device from the rear face of the two-dimensional matrix is not homogeneous. More particularly, the invention provides that the heat transfer provided by the cooling device from the rear face of the two-dimensional matrix is inhomogeneous.

 Thanks to the light system according to the invention, it is possible to further reduce the temperature of certain electroluminescent sources of the plurality, or even of a group, for example compact, of electroluminescent sources of the plurality, with respect to the temperature reduction than know the other electroluminescent sources of plurality.

Thus, it is possible to reduce, in particular by dimensioning the cooling device on a case-by-case basis, the temperature differences between the electroluminescent sources of the same plurality. The problems of color shift, control of light fluxes and mechanical tensions within the plurality of electroluminescent sources are thus limited, even resolved. From a structural point of view, the cooling device 1 1 may comprise at least one plate, called the main plate, 1 1 1 made from a thermal conductive material and arranged so as to directly contact the portion 100 as introduced. above. More particularly, the material from which the main plate 1 1 1 is made may have a thermal conductivity greater than 100 Wm ¹ .K ¹ . By way of nonlimiting examples, the main plate 1 1 1 is based on copper, aluminum or an alloy based on these two elements. Copper having a thermal conductivity greater than 300 Wm ^_1 .K ^{· 1} may be preferred to aluminum whose thermal conductivity is substantially three times lower.

It is not necessary that the cooling device 1 1 be configured to ensure no thermal transfer by conduction from the rear face of the two-dimensional matrix outside of the portion 100 as introduced above. On the contrary, it is envisaged that the cooling device comprises, in addition to the main plate 1 1 1, at least one secondary plate and / or a plurality of studs (not shown) arranged to contact at least one other part, or even a complementary part, of the rear face of the two-dimensional matrix. The secondary plate and / or the studs are then based on a material having a lower thermal conductivity, preferably at least two times lower, than the thermal conductivity of the material on the basis of which the main plate 1 1 1 is made. Preferably, the secondary plate and / or the plurality of studs form (s) a thermal interface with the rear face of the two-dimensional matrix having a thermal conductivity less than or equal to 6 W.rrv ¹ .K ¹ .

According to a variant, at least part of the rear face of the two-dimensional matrix which is situated outside the portion 100 can be simply in contact with air; this denier having a thermal conductivity substantially equal to 0.02 Wm ^_1 .K ^_1 , it appears that the cooling thus obtained by convection is much less than the cooling obtained by conduction thanks to the cooling device 1 1 at the portion 100.

There are different ways of defining the extent of the portion 100 as introduced above relative to the two-dimensional extent of the plurality of light emitting sources 10. Among these different ways, some are detailed below by way of example and in no way limiting. Each of the different definitions of which we detail below is sufficient in itself to define the portion 100. However, it is also possible that these definitions can be combined with one another. These definitions are indeed not mutually exclusive, but may very well complement each other. For example, when the portion 100 is defined by the combination of two of the definitions given below, it is defined by the part congruent to the two definitions. Each definition detailed below may be of its own technical interest. Each combination of definitions envisaged has the technical interest of each of the combined definitions, or even a synergistic interest that goes beyond the simple juxtaposition of the technical interests linked to the combined definitions. A first definition of the extent of the portion 100 relative to the two-dimensional extent of the plurality of light emitting sources 10 is as follows. The portion 100 may be located in line with the light-emitting sources which are intended to receive an electrical power supply greater than a first predetermined threshold value. It can in fact be predetermined that, for a given embodiment of the light system and for a given lighting function, it will be necessary to supply one or more light-emitting source (s) of the plurality with such supply power. . From there, a power supply map of the electroluminescent sources of the plurality can be pre-established. Preferably, the first predetermined threshold value will then be chosen to be equal to 70%, even equal to 80%, relative to the maximum electrical power supply with which at least one source of the plurality will be supplied, or even relatively to the power d maximum permissible power supply from the plurality of light emitting sources. A second definition of the extent of the portion 100 relative to the two-dimensional extent of the plurality of electroluminescent sources is based on the following observation. According to its use, the plurality of light-emitting sources 10 is intended to present, in its two-dimensional extent, a first part having a temperature above a second predetermined threshold value and a second part having a temperature below this second predetermined threshold value. This may more particularly relate to the junction temperatures of the light-emitting sources. It can also be temperatures measured, for example during tests, on the rear face of the two-dimensional matrix. Let us remember that it is moreover possible to link, for example heuristically, the distribution of the power supply of the light-emitting sources and the distribution of the temperature of the light-emitting sources. Mappings corresponding can thus be measured, even predicted. On the basis of this observation, it is possible to define the extent of the portion 100 relative to the two-dimensional extent of the plurality of light emitting sources 10 as being limited to the extent of the first part (the one whose temperature is higher at the second predetermined threshold value).

 The second part can be seen as the complement of the first part on the two-dimensional extent of the plurality of light emitting sources 10.

 The first part can comprise several distinct parts between them. Alternatively, the first part can be made in one piece and concerned a compact group of light-emitting sources. As an alternative or in addition, the first part can be a central part 101 and the second part can be a peripheral part 102 to the central part 101. This latter possibility is illustrated in particular in FIGS. 3 and 6 which, as mentioned above , relate to a use of the plurality of electroluminescent sources 10 in "main beam" mode. A division of the two-dimensional extent of the plurality of electroluminescent sources into a central part 101 and a peripheral part 102 is therefore only suitable for use of the light system 1 according to the invention to achieve a regulatory photometric function of high beam.

 In this context, the portion 100 is located at most to the right of the first part. Preferably, it is located at the right of 80% of the first part. Even more preferably is located at the right of 70% of the first part.

 If any temperature distribution can be split in two with respect to the second predetermined threshold value, it can also be limited by an upper limit temperature value 21 and a lower limit temperature value 22, as illustrated in FIG. 7. The temperature upper limit is then the maximum temperature to which at least one light-emitting source of the plurality is brought during a determined use. The lower limit temperature is then the minimum temperature to which at least one of the plurality of electroluminescent sources is brought during said determined use.

In this context, the second predetermined threshold value is preferably between 60% and 90%, preferably between 70% and 80%, of the upper limit temperature value at which at least one of the plurality of electroluminescent sources is carried during its use. The portion 100 can thus be specifically defined. This definition of the portion 100 is not exclusive of that given previously with respect to the distribution of electrical power supply. On the contrary, it is possible to define a congruent part to these two definitions. In this context, it is also possible to define the portion 100 as being located at most in line with an area intended to present, during the use of the plurality of light emitting sources 10, a temperature greater than 20 ° C., preferably 30 ° C higher than said lower limit temperature 21. Generally, the problems of color shift, control of light fluxes and mechanical tensions within the plurality of electroluminescent sources are attributable to temperature differences within the plurality electroluminescent sources 10 which are greater than 40 ° C, for example substantially equal to 45 ° C. Such a definition of the portion 100 takes advantage of this knowledge of the lighting systems according to the prior art. This definition of the portion 100 is not exclusive of that given previously with respect to the distribution of electrical power supply. On the contrary, it is possible to define a congruent part to these two definitions. Whichever the portion 100 is defined, it is preferable that it be configured so that the upper limit temperature 21 remains, during the use of the plurality of light emitting sources 10, lower, preferably at least 10 ° C, at a maximum junction temperature admissible by at least one light-emitting source. It is thus ensured that the general increase in temperature of the plurality of light emitting sources 10, this increase being induced by the implementation of the invention, as that discussed above, does not lead to a deterioration of some of the light-emitting sources of the plurality 10 and ultimately of the light system 1 according to the invention. According to one embodiment, the two-dimensional matrix of electroluminescent sources is bonded to the cooling device by means of a layer of adhesive (not shown in the figures) and said portion 100 is located at the right of a thickness variation. of the layer of adhesive applied between said two-dimensional matrix of light-emitting sources and said cooling device. Typically, the portion 100 may be in line with a localized refinement of the adhesive layer relative to the rest of the surface of the two-dimensional matrix bonded to the cooling device. This localized variation in thickness may be provided during the application of the adhesive between the two-dimensional matrix and the cooling device, or result from a slight deformation of the two-dimensional matrix (for example by giving it a very substantially arched shape) stuck on the cooling device. The solution proposed by the invention can therefore be seen as an optimization of the position and the size of the contact surface between the plurality of light-emitting sources 10 and the cooling device 11, relative to the two-dimensional extent of the plurality 10. From a general point of view, the contact surface must be limited to the portion 100 of the rear face of the two-dimensional matrix which is intended to know the highest temperatures, during and according to the use which is made. of the light system according to the invention. The invention finds particular application for a plurality of light emitting sources having over its two-dimensional extent significant temperature gradients, which implies that the light emitting sources of the plurality, most often identical to each other, can be brought to different temperatures during and depending on their use. This case is encountered as soon as each light-emitting source can be supplied electrically independently of the other light-emitting sources of the plurality.

 The solution adopted has the particular advantage of not requiring any modification of the architecture of the plurality of light-emitting sources 10 compared to that used in the lighting systems according to the prior art.

 Furthermore, it appears from the foregoing description that the invention is adaptable in size, or even in shape, on a case-by-case basis. This adaptation is deemed to be the responsibility of a person skilled in the art.

The invention is not limited to the embodiments described but extends to any embodiment covered by the appended claims.

Claims

1. Lighting system (1), in particular for lighting, for a motor vehicle, comprising at least a plurality of light-emitting sources (10) arranged in a two-dimensional matrix and a cooling device (1 1) of said at least one plurality of sources electroluminescent (10) from a rear face of the two-dimensional matrix, the light system being characterized in that the cooling device (1 1) is configured to provide thermal transfer by superior conduction with a portion (100) of the rear face of the two-dimensional matrix than with the rest of the back side. 2. Light system (1) according to the preceding claim, wherein said two-dimensional matrix of light emitting sources is bonded to the cooling device (1 1) by means of a layer of adhesive, said portion (100) being located at right a variation in the thickness of the adhesive layer applied between said two-dimensional matrix of light-emitting sources and said cooling device (1 1). 3. Light system (1) according to any one of the preceding claims, in which said portion (100) is located at the level of the light-emitting sources which, among each plurality of light-emitting sources (10), are intended to receive, to achieve minus a determined lighting function of the light system (1), an electrical power supply greater than a first predetermined threshold value. 4. Light system (1) according to the preceding claim, in which the first predetermined threshold value is equal to 70%, even equal to 80%, of a maximum admissible electrical power supply by each light-emitting source. 5. Light system (1) according to any one of the two preceding claims, in which the determined lighting function is that which, among the lighting functions of the light system (1), requires the greatest power supply electric compared to the other lighting functions of the system. 6. Light system (1) according to any one of the preceding claims, in which each plurality of light-emitting sources (10) being intended, according to its use, to present, in its two-dimensional extent, a first part having a junction temperature higher than a second predetermined threshold value, and a second part having a junction temperature lower than said second predetermined threshold value, said portion (100) is located at most to the right of the first part, preferably to the right of 80% of the first part, and even more preferably to the right of 70% of the first part. 7. Lighting system (1) according to the preceding claim, in which the first part is a central part (101) of each plurality of light-emitting sources (10) and the second part is a peripheral part (102) in said central part (101 ). 8. Lighting system (1) according to any one of the two preceding claims, in which the second predetermined threshold value is between 60% and 90%, preferably between 70% and 80%, of a junction temperature value upper limit at which at least one electroluminescent source of the plurality is intended to be worn during its use. 9. Light system (1) according to any one of the preceding claims, in which each plurality of light-emitting sources (10) being intended, according to its use, to present, in its two-dimensional extent, a spatially varying junction temperature gradient between an upper limit temperature (21) and a lower limit temperature (22), said portion (100) is located at most in line with an area intended to present, during its use, a junction temperature greater than 20 ° C, preferably 30 ° C higher than said lower limit temperature (22). 10. Lighting system (1) according to any one of the preceding claims, in which each plurality of light-emitting sources (10) being intended, according to its use, to present, in its two-dimensional extent, a spatially varying junction temperature gradient between an upper limit temperature (21) and a lower limit temperature (22), said portion (100) is configured so that said upper limit temperature (21) is lower, preferably at least 10 ° C, than a temperature maximum allowable junction of each light emitting source. 1 1. Lighting system (1) according to any one of the preceding claims, in which said cooling device (1 1) comprises at least one main plate (1 1 1) made from a thermal conductive material and arranged so as to contact directly said portion (100) of the rear face of the two-dimensional matrix. 12. Light system (1) according to the preceding claim, wherein the material from which the main plate is made has a thermal conductivity greater than 100 W-rrv ¹ -K ¹ , for example a copper-based plate. 13. Lighting system (1) according to any one of the two preceding claims, wherein said cooling device (1 1) further comprises at least one secondary plate contacting at least one complementary part of the rear face of the relatively two-dimensional matrix. to the main plate (1 1 1), the secondary plate being based on a material having a lower thermal conductivity, preferably at least two times lower, than a thermal conductivity of the material from which the main plate is made. 14. Lighting system (1) according to any one of the preceding claims, in which said cooling device (1 1) is configured to ensure no thermal transfer by conduction from the rear face of the two-dimensional matrix outside of said portion. (100). 15. Light system (1) according to any one of the preceding claims, in which the light-emitting sources (10) of each plurality form a monolithic assembly. 16. Motor vehicle comprising a light system (1) according to any one of the preceding claims.