Calibration of a light module with electroluminescent elements

Description

[0001] This application concerns the calibration of a light module comprising a light source, for a motor vehicle capable of emitting a beam of light rays along a longitudinal axis.

[0002] A light module is defined as any device capable of emitting light, particularly for lighting and / or signaling and / or interior lighting in a motor vehicle.

[0003] Such a lighting module incorporates a light source for this purpose. Light sources used for lighting and signaling in motor vehicles are increasingly made up of light-emitting diodes (LEDs), primarily due to their advantages in terms of size and battery life compared to conventional light sources. Furthermore, the use of LEDs in lighting and / or signaling modules has allowed market players (car manufacturers and designers of lighting and / or signaling devices) to add a creative touch to the design of these devices, particularly through the use of an ever-increasing number of these LEDs to create optical effects.

[0004] For example, we know of light modules including an imager capable of spatially modulating the light intensity of a light beam from a light source.

[0005] An example of such a light module is illustrated with reference to the figure 1 .

[0006] The light module 1 includes a light source 100, such as a light-emitting diode source or a laser diode source capable of emitting a light beam 108. The light source 100 can be controlled by a control module 102, also called " driver "

[0007] The light beam 108 is collimated by a collimation unit 101, which may include one or more lenses.

[0008] The beam 108 is thus collimated towards an imager 103 which spatially modulates the light intensity of the beam and directs the modulated beam towards a projection unit 104. The projection unit 104 may include lenses and a reflector and is capable of projecting the light beam outwards from the motor vehicle, in order to perform a lighting function.

[0009] In such a light module comprising several units performing respective functions, manufacturing or assembly defects are likely to affect the homogeneity of the beam. For example, when the light module is designed to obtain a reference image on a screen 105, some pixels of the image obtained by projection of the light beam 108 may, in practice, differ from corresponding pixels of the reference image.

[0010] The reference image can, for example, be a homogeneous white rectangle in which all pixels have the same light intensity. However, the image obtained by a light module 1 with a defect may appear on the screen 205 as illustrated with reference to the figure 2 .

[0011] On the figure 2 , the image 201 obtained by projection onto the screen includes dark areas 202, and the image 201 thus differs from the homogeneous reference image.

[0012] Such defects can be caused by: the optics of collimation and projection units 101 and 104. In this case, and as illustrated on the figure 2 , a vignetting effect may appear on the projected image 201; a defect in the light source 100 causing an inhomogeneous light beam 108 from the outset; a defect in the imager 103, in particular a defect in the global or local transmission or reflection coefficient of the imager 103; a manufacturing tolerance of the elements of the light module, this tolerance being able to impact the size or shape of said elements; a defect in the positioning of the elements of the light module relative to each other during their assembly.

[0013] There is therefore a need to correct or compensate for manufacturing or assembly defects in a light module. Such a need is by no means specific to the light module 1 illustrated in the... figure 2 and applies to any light module. Document EP 2 416 139 A1 discloses an example of a method and system for calibrating a light module.

[0014] A first aspect of the invention relates to a method for calibrating a light module according to claim 1.

[0015] The use of a light source with electroluminescent elements grouped into individually addressable subsets, each corresponding to a pixel in the projected image, allows for the correction of defects in the light module—defects that are unavoidable during manufacturing or assembly. Furthermore, such correction or calibration is performed without requiring any modifications to the optical elements of the light module: the correction relies on storing modified power supply values ​​for at least some of the electroluminescent element subsets. Electroluminescent elements are inherently capable of accepting a power supply different from a nominal value, and thus, calibration does not degrade the light source.

[0016] In one embodiment, the method may further include a step of heating the light module to a given temperature value, and, during the storage step, the modified supply value may be stored in association with an identifier of the subassembly comprising the first electroluminescent element and with the given temperature value.

[0017] Indeed, the operating ranges of electroluminescent elements are highly dependent on the ambient temperature. Therefore, it is particularly advantageous to store the modified supply value in conjunction with the temperature value at which it is calculated.

[0018] In addition, the steps of the process can be iterated, and, at each iteration, the light module can be brought to a temperature value different from the temperature value of the previous iteration.

[0019] Thus, the accuracy of the calibration is improved and the images projected by the light module are close to the reference image regardless of the temperature surrounding the light module.

[0020] Finally, the process can be applied to several pixel power supply values. The correction can then be performed for a temperature at a given power supply value, or by interpolation between the stored values ​​of these different parameters.

[0021] A second aspect of the invention relates to a computer program comprising instructions for implementing the steps of the process according to the first aspect of the invention, when these instructions are executed by a processor.

[0022] A third aspect of the invention relates to a calibration system for a light module according to claim 5.

[0023] An example not forming part of the invention relates to a light module comprising: at least one light source comprising a set of electroluminescent elements arranged on the same substrate, said set of electroluminescent elements comprising subsets of at least one electroluminescent element, each subset being capable of being individually powered; a memory storing power supply values ​​in association with identifiers of subsets of electroluminescent elements; a control unit capable of powering the subsets of the electroluminescent source according to the associated power supply values; in which, upon receipt of a modified supply value in association with a given identifier of a subset of electroluminescent elements, the memory is capable of storing the modified supply value in association with the given identifier of the subset, and in which the control unit supplies the identified subset according to the modified supply value.

[0024] In one embodiment, the light module may further include a temperature sensor capable of measuring a current temperature value, in particular a current temperature value near the light source, specifically on the light source itself. Upon receiving a modified supply value associated with a given identifier of a subset of electroluminescent elements and a given temperature value, the memory is capable of storing the modified supply value associated with the given identifier of the subset and the given temperature value. If a subset identifier is associated with several modified supply values ​​and their respective temperature values, the control module is capable of selecting the modified supply value associated with the temperature value closest to the current temperature value.Alternatively, the control module is capable of calculating an interpolation of the supply value based on the supply values ​​corresponding to a lower temperature, in particular the temperature immediately below, and to a higher temperature, in particular the temperature immediately above the current temperature value.

[0025] Thus, the defects of the light module are precisely compensated regardless of the surrounding temperature.

[0026] In addition, the light module may also include a focusing unit capable of focusing a light beam from the light source, an imager capable of spatially modulating the light intensity of the focused beam, and a projection unit capable of projecting the modulated light beam outwards from the light module.

[0027] In addition, the imager can be a micro-mirror array.

[0028] According to one embodiment of the invention, the electroluminescent elements can be electroluminescent rods of submillimeter dimension or electroluminescent dots.

[0029] The use of electroluminescent rods or dots of submillimeter size improves the accuracy of the correction, due to their small size.

[0030] Other features and advantages of the invention will become apparent upon examination of the detailed description below, and the accompanying drawings in which: there figure 1 illustrates a light module according to prior art; the figure 2 illustrates an image projected onto a screen by a light module according to the prior art, including defects; the figure 3 illustrates a calibration system for a light module according to one embodiment of the invention; the figure 4 illustrates a light source of a light module according to one embodiment; the figure 5 is a cross-sectional view of a light source of a light module according to a given embodiment; the figure 6 is a diagram illustrating the steps of a process according to an embodiment of the invention.

[0031] There figure 3 illustrates a calibration system for a light module 2 according to an embodiment of the invention.

[0032] As an illustration, a light module 2 has been represented whose structure is close to that of the light module 1 of the figure 1 : the light module 2 includes a light source 100, a collimation unit 101, a control unit 102, an imager 103 and a projection unit 104. The common elements between the light module 2 and the light module 1 are therefore identified by common references.

[0033] The invention proposes a method for calibrating the light module 2, in which the light source 100 is a light source comprising a plurality of electroluminescent elements arranged on the same substrate. The electroluminescent elements are distributed into subsets of at least one electroluminescent element, each subset being individually addressable. In certain embodiments, a subset comprises several individually controllable electroluminescent elements. It will thus be understood that the invention applies to any light module comprising a source consisting of a plurality of electroluminescent elements, regardless of the optical system used to project a light beam outside the light module 2.

[0034] As will be better understood from the following, the use of such a light source makes precise calibration possible and allows manufacturing and assembly defects to be compensated for at lower costs.

[0035] The 103 imager can be a DMD-type micromirror array, for " Digital Micromirror Device "In English, a transparent or reflective LCD module or an L-COS module, for " Liquid Crystal On Silicon "

[0036] The light source 100, and in particular each of the sub-assemblies of electroluminescent elements, is controlled by the control unit 102, which is further connected to a memory 106 according to the invention. The light module 2 may further include an interface 107 capable of exchanging data with a calibration module 109.

[0037] Such an interface 107 is optional according to the invention since the calibration process can provide that the calibration module 109 directly accesses the memory 106 of the light module 2.

[0038] The light module 2 can also include a temperature sensor 208 capable of measuring current and ambient temperature values.

[0039] The calibration module 9 may include an interface 111 and a processor 110, suitable for connection to a camera 112 placed in front of the screen 105. In one embodiment, the camera 112 is integrated into the calibration module 109.

[0040] There figure 4 illustrates a set of 15 electroluminescent elements according to an example.

[0041] On the figure 4 For example, the electroluminescent elements are submillimeter-sized electroluminescent rods 80, which will hereafter be called electroluminescent rods. These electroluminescent rods 80 originate from a single substrate 10. Each electroluminescent rod 80, here formed using gallium nitride (GaN), extends perpendicularly, or substantially perpendicularly, from the substrate 10, here made of silicon. Other materials, such as silicon carbide, could be used for the substrate without departing from the scope of the invention. For example, the electroluminescent rods 80 could be made from a compound based on aluminum nitride and gallium nitride (AlN / GaN), or from a compound based on aluminum, indium, and gallium (AlN / GaN / InGaN).

[0042] On the figure 2 , the substrate 10 has a lower face 12, on which a first electrode 14 is attached, and an upper face 16, in projection of which extend the electroluminescent rods 80 and on which a second electrode 18 is attached.

[0043] Note that only one subset of 80 electroluminescent rods is represented on the figure 4 However, as explained above, the set of electroluminescent elements may comprise several subsets of at least one electroluminescent element. In this case, one or more electrodes 14 and 18 may be dedicated to the same subset, so that each subset can be powered individually, i.e., independently of the other subsets.

[0044] Different layers of materials are superimposed on the upper face 16, notably after the growth of the electroluminescent rods from the substrate here.

[0045] Among these different layers, there can be at least one layer of electrically conductive material, in order to allow the electrical supply of the electroluminescent rods 80. This layer is etched in such a way as to connect the rods of each individually addressable subset of the first set 2 of the light source 6 to each other.

[0046] The 80 submillimeter-sized electroluminescent rods extend from the substrate 10 and include, as can be seen on the figure 2 , each a core 19 made of gallium nitride, around which are arranged quantum wells 20 formed by a radial superposition of layers of different materials, here gallium nitride and gallium-indium nitride, and a shell 21 surrounding the quantum wells also made of gallium nitride.

[0047] Each rod extends along a longitudinal axis 22 defining its height, the base 23 of each rod being arranged in a plane 24 of the upper face 16 of the substrate 10.

[0048] The electroluminescent rods 80 advantageously have the same shape. Each of these electroluminescent rods 80 is delimited by an end face 26 and a circumferential wall 28 extending along the longitudinal axis. When the electroluminescent rods 80 are doped and polarized, the resulting light emitted from the light source 100 is primarily emitted from the circumferential wall 28, it being understood that some light rays may also emerge, at least in small quantities, from the end face 26. As a result, each electroluminescent rod 80 acts as a single light-emitting diode, and the density of the electroluminescent rods 80 enhances the luminance of the light source 100.

[0049] The circumferential wall 28 of an electroluminescent rod 80, corresponding to the gallium nitride shell, is covered by a layer of transparent conductive oxide TCO 29 which forms the anode of each rod complementary to the cathode formed by the substrate.

[0050] This circumferential wall 28 extends along the longitudinal axis 22 from the substrate 10 to the terminal face 26, the distance from the terminal face 26 to the upper face 16 of the substrate, from which the electroluminescent rods 80 originate, defining the height of each electroluminescent rod 80. As an example, it can be predicted that the height of an electroluminescent rod 80 is between 1 and 10 micrometers, while it can be predicted that the largest transverse dimension of the terminal face, perpendicular to the longitudinal axis 22 of the electroluminescent rod concerned, is less than 2 micrometers.

[0051] It is also possible to define the surface area of ​​an electroluminescent rod 80, in a plane of section perpendicular to this longitudinal axis 22, within a determined range of values, and in particular between 1.96 and 4 square micrometers.

[0052] These dimensions, given as a non-limiting example, allow us to distinguish a light source 100 comprising electroluminescent rods from a light source with plane light-emitting diodes.

[0053] The invention also covers the case in which the electroluminescent rods 80 of the light source 100 are planar light-emitting diodes. It thus applies to any light source 100 comprising a plurality of electroluminescent elements.

[0054] Other specific dimensions of the light source 100 according to the invention may also be provided, and in particular a dimension of the illuminating surface, for example, of no more than 10 x 10 mm². The density of the electroluminescent rods 80 and the area of ​​the illuminating surface can also be calculated so that the luminance obtained by the plurality of electroluminescent rods is, for example, at least 60 cd / mm². The optimal dimension of the illuminating surface of the light source 100 will depend on the intended function.

[0055] The height of the 80 electroluminescent rods can also be changed within the light source 100, so that some electroluminescent rods may have a different height from other electroluminescent rods.

[0056] The shape of the electroluminescent rods 80 can also vary, particularly in the cross-section of the rods and the shape of the terminal face 26. This has been illustrated on the figure 4 , electroluminescent rods having a generally cylindrical shape, and in particular a polygonal cross-section, here more specifically hexagonal. It is understood that it is important that the light can be emitted through the circumferential wall, whether this wall has a polygonal or circular shape, for example.

[0057] Furthermore, the terminal face 26 can have a substantially flat shape and be perpendicular to the circumferential wall, so that it extends substantially parallel to the upper face 16 of the substrate 10, as illustrated in the figure 4 , or it may have a convex or pointed shape at its center, so as to multiply the directions of emission of light exiting this terminal face, as illustrated on the figure 5 .

[0058] On the figure 4 The 80 electroluminescent rods are arranged in a two-dimensional matrix constituting a subset. Such a subset can, for example, correspond to a pixel of the projected image, and the light source 100 can thus comprise several subsets corresponding to respective pixels. A subset comprises at least one electroluminescent rod 80.

[0059] This arrangement could be such that the electroluminescent rods are arranged in a staggered pattern. The invention covers other rod arrangements, including rod densities that can vary from one subset to another.

[0060] The light source 100 may further include, as illustrated on the figure 5 , a layer 30 of a polymer material in which 80 electroluminescent rods are at least partially embedded. The layer 30 can thus extend over the entire extent of the substrate or only around a single pixel.

[0061] The polymer material, which can notably be silicone-based, makes it possible to protect the 80 electroluminescent rods without hindering the diffusion of light rays.

[0062] It is generally possible to integrate into this layer 30 of polymer material wavelength conversion means, and for example phosphors, capable of absorbing at least a part of the rays emitted by one of the electroluminescent rods 80 and of converting at least a part of said absorbed excitation light into an emission light having a wavelength different from that of the excitation light.

[0063] The light source 100 may further include a coating 32 of light-reflecting material, which is arranged between the electroluminescent rods 80 to deflect the rays initially directed towards the substrate 10, towards the terminal face 26 of the electroluminescent rods 80. In other words, the upper face 16 of the substrate 10 may include a reflective means that redirects the light rays, initially directed towards the upper face 16, towards the output face of the light source 100. This recovers rays that would otherwise be lost. This coating 32 is arranged between the electroluminescent rods 80 on the transparent conductive oxide layer 29.

[0064] There figure 6 is a diagram illustrating the steps of a calibration process for the light source 2, according to an embodiment of the invention.

[0065] In an optional step 600, the light module 2 is brought to a specific temperature. "Temperature adjustment" refers to placing the light module 2 in an environment with a temperature that closely matches the specified temperature. The accuracy of the temperature adjustment can be improved without adding extra sensors by accessing the temperature reading from the light module 2's temperature sensor 208. Alternatively, the temperature adjustment can be performed by turning on the light source for a period of time that allows it to reach a stable temperature.

[0066] At step 601, all the electroluminescent elements of the light source 100 are powered by the control circuit 102. In the example described below, and to clarify the disclosure of the invention, all sub-assemblies are powered with the same current value. It will be understood, however, that depending on the lighting function to be performed, the sub-assemblies of electroluminescent elements may be powered by different currents. The command to power the light source may originate from a control unit not shown in the diagram. figure 3 The control unit can be integrated into the light module 2 or, alternatively, can be integrated into the calibration module 109 which then sends a switch-on command to the light module to trigger the supply of the light source 100 by the control unit 102.

[0067] When the light source 2 is powered, a projected image is obtained on the screen 105, such as the projected image illustrated on the figure 2 For example, each pixel of the projected image corresponds to at least one subset of electroluminescent elements.

[0068] The image projected onto the screen 105 is acquired at a stage 602 by the camera 112, then transmitted to the processor 110 for processing.

[0069] The image projected and acquired by the camera can be compared, pixel by pixel, to a reference image, at step 603. As explained above, in the example considered, the reference image is a white image in which all pixels have equal light intensity.

[0070] Thus, for the first pixel of the projected image, step 603 consists of comparing the difference between the light intensity of the first pixel and the light intensity of a corresponding pixel in a reference image, against a predetermined threshold. A corresponding pixel is defined as a pixel having approximately the same spatial coordinates in the reference image as the first pixel in the projected and acquired image. To this end, the projected and acquired image can be resized to be of a size and format comparable to the reference image.

[0071] The predetermined threshold can correspond to a given number of candelas, for example. The higher the predetermined threshold, the less significant the correction provided by the calibration process. Conversely, a low predetermined threshold allows for a projected image very close to the reference image.

[0072] At step 604, following the comparison step 603, it is checked whether the comparison is positive, that is, whether the difference obtained is greater than the predetermined threshold.

[0073] If so, the process continues to step 605. Otherwise, the process proceeds directly to step 606.

[0074] At step 605, depending on the difference between the light intensity of the first pixel and the light intensity of the corresponding pixel, the processor 110 can determine a modified supply value of at least one first electroluminescent element of the subset corresponding to the first pixel.

[0075] If the calibration module 109 has access to the current values ​​supplied by the driver unit 102 of the light module 2, the modified supply value can be a current value expressed in amperes. However, it is possible that the calibration module 109 does not have access to the supply values ​​supplied by the driver unit 102, in which case the modified supply value can be a multiplicative factor, which can then be applied to the driver unit 102 to power the first electroluminescent element of the subassembly corresponding to the first pixel.

[0076] For example, if the first pixel is brighter than the corresponding pixel in the reference image, the multiplicative factor is less than 1 in order to decrease the current delivered to the first electroluminescent element of the subset, provided that the first electroluminescent element can be controlled independently of other electroluminescent elements in the same subset. Otherwise, the current delivered to the subset containing the first element is reduced.

[0077] If the first pixel is less bright than the corresponding pixel in the reference image, the multiplicative factor is greater than 1 to increase the current delivered to the first electroluminescent element of the subset, provided that the first electroluminescent element can be controlled independently of other electroluminescent elements in the same subset. Otherwise, the current delivered to the subset containing the first element is increased.

[0078] At step 606, it is checked whether the comparison step 603 has been performed for all pixels of the projected and acquired image. If so, the process continues to step 607. Otherwise, steps 603 to 606 are repeated for the next pixel of the projected and acquired image.

[0079] To allow for adjustment of the power supply to certain electroluminescent elements of the light source 100, the modified power supply value(s) are stored at step 607 in the memory 106 of the light module 2, along with an identifier of the subassembly containing the electroluminescent element for which the modified power supply value was determined. Note that the memory 106 may be an internal memory of the control unit 102.

[0080] The subset identifier, according to a first implementation, identifies only the subset. This implementation allows for handling the case where the electroluminescent elements of the same subset cannot be individually controlled and all receive the same power supply, which is specific to the subset.

[0081] Alternatively, the subassembly identifier is supplemented with an identifier for the electroluminescent element to which the modified power supply value applies. This implementation allows for handling the case where the electroluminescent elements of the same subassembly can be controlled individually. In this case, step 607 consists of storing the modified power supply value in association with the subassembly identifier and the identifier of the electroluminescent element for which the modified power supply value was determined.

[0082] In the case where the temperature setting step 600 has been implemented, step 607 can consist of storing the modified supply value in association with the subassembly identifier, possibly with the identifier of the electroluminescent element, and furthermore with the temperature value of the temperature setting step 600. The temperature value can either come from the temperature sensor 208 or be transmitted by the calibration unit 109.

[0083] In one embodiment, the process is iterated for different temperature adjustments at different temperature values, advantageously obtaining several calibrations of the light module at different temperatures. In this case, it is checked in step 608 whether further temperature adjustments remain to be performed. If so, the process is iterated and returns to step 600 for a temperature adjustment at a different temperature value than that of the previous iteration. Otherwise, the calibration process is completed in step 609.

[0084] To perform calibration for different power supply levels, steps 601 to 607 are repeated for a given temperature, varying the power supply level in step 601.

[0085] Storing modified supply values ​​in the light module 2 allows the supply of the electroluminescent elements to be adapted to manufacturing and assembly defects of the light module 2, when the control unit 102 supplies the electroluminescent elements according to the initial or modified supply values ​​which are stored in the memory 106.

[0086] In the case where a subset of electroluminescent elements is stored in association with several modified supply values ​​and their respective temperature values, the control unit 102 can take into account a current temperature measured by the temperature sensor 208 to select one of several modified supply values. The control unit 102 can, for example, select the modified supply value associated with the temperature value closest to the current temperature.

[0087] Thus, the present invention makes it possible to compensate for manufacturing and assembly defects, and more generally any defect in the light module, without requiring modification of the optical material of the light module 2. Such calibration is made possible in particular by the use of a source comprising electroluminescent elements such as submillimeter-sized electroluminescent rods. Furthermore, such electroluminescent elements generally accept a power supply different from the nominal supply value, which allows the invention to be implemented.

[0088] Another way to compensate for the shortcomings of the light modulator would be, in the case of a light module 2 as illustrated in detail on the figure 2, to modify the reflection coefficients of the DMD 103 micro-mirror matrix, in order to increase the reflection coefficients, or ON / OFF ratio, in the shadow areas of the projected image and to decrease the reflection coefficients in the overly bright areas of the projected image.

[0089] However, such an alternative solution has the drawback of requiring a margin to increase the ON / OFF ratio. Consequently, the DMD 103 micromirror array is not used optimally, and the resulting beam has a reduced overall intensity. The solution presented with reference to the figures described above has the advantage of not having this drawback.

[0090] Of course, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms, and other variations that a person skilled in the art might consider within the scope of the present invention.

Claims

1. Method for calibrating a light module (2), said light module comprising a light source (100) comprising a set of electroluminescent elements (8) arranged on a single substrate (10), said method comprising the following steps: - powering (601) all of the electroluminescent elements so as to obtain an image projected by the light module (2) onto a screen (105, 205) located outside the light module (2), the projected image comprising a set of pixels, each pixel corresponding to at least one subset of at least one electroluminescent element of the light source, each subset being capable of being individually powered by current; - for each pixel of the projected image, comparison (603) of a difference between a light intensity of said pixel and a predefined light intensity of a corresponding pixel of a reference image, said corresponding pixel having substantially the same spatial coordinates in the reference image as the pixel in the projected and acquired image, with a predetermined threshold; - in the event that, for at least one given pixel of the projected image, the difference is greater than the predetermined threshold, determining (605) a modified power value of at least one first electroluminescent element of the subassembly corresponding to the given pixel; - storing (607), in a memory (106) of the light module, the modified power value in association with an identifier of the subassembly comprising the first electroluminescent element.

2. Method according to claim 1, further comprising a step of heating (600) the light module (2) to a given temperature value, wherein, during the storage step (607), the modified power value is stored in association with the identifier of the subassembly comprising the first electroluminescent element and with the given temperature value.

3. Method according to claim 2, wherein the steps of the method are repeated, and wherein, at each repetition, the light module is heated to a temperature value different from the temperature value of the previous repetition.

4. Computer program comprising instructions for implementing the steps of the method according to one of claims 1 to 3, when these instructions are executed by a processor.

5. System for calibrating a light module, said light module comprising a light source comprising a set of electroluminescent elements arranged on the same substrate, said system comprising: - a control unit for controlling the power supply to all of the electroluminescent elements in order to obtain an image projected by the light module onto a screen of said system, said screen being located outside the light module (2), the projected image comprising a set of pixels, each pixel corresponding to at least one subset of at least one electroluminescent element of the light source, each subset being capable of being individually supplied with current; - a camera (112) adapted to acquire images of the image projected onto the screen; - a processor (110) for, for each pixel of the projected image, comparing a difference between a light intensity of said pixel and a predefined light intensity of a corresponding pixel of a reference image, said corresponding pixel having substantially the same spatial coordinates in the reference image as the pixel in the projected and acquired image, with a predetermined threshold; - said processor being further adapted, in the event that, for at least one given pixel of the projected image, the difference is greater than the predetermined threshold, determine a modified power value of at least one first electroluminescent element of the subassembly corresponding to the given pixel, in order to store the modified power value in association with an identifier of the subassembly comprising the first electroluminescent element in a memory (106) of said light module.