WO2025021721A1 - Vehicle lighting device comprising a white light source and a light guide provided with a multilayer structure allowing a preset colour to be obtained with a simplified circuit - Google Patents

Abstract

The invention relates to a vehicle lighting device (1) comprising a light guide (6) that is transparent or translucent, and a light source (8A) arranged at one end or on one edge of the light guide (6), the light guide (6) comprising a core (10) and the light source (8A) emitting a beam of white light into the core (10) of the light guide. According to the invention, the light guide (6) comprises a multilayer structure (12) that is attached to the core (10) and comprises a substrate (14), a reflective layer (16), and a layer (18) of electrochromic organic material structured into a plurality of elements (E₁, E₂, …E₉), each element being encapsulated in an electrolyte layer and being connected to a pair of electrodes capable of receiving a voltage, the lighting device (1) further comprising an electrical control circuit (4) configured to control the voltage across the terminals of each pair of electrodes.

Description

Vehicle lighting device comprising a white light source and a light guide with a multilayer structure enabling a predetermined color to be obtained with a simplified circuit

The present invention relates to the field of lighting, in particular lighting for motor vehicles. The invention relates in particular to a vehicle lighting device comprising an at least partially transparent or translucent light guide, as well as a method for controlling such a lighting device. Without this being limiting in the context of the present invention, the lighting device can be mounted in a motor vehicle headlight. The present invention also finds applications in lighting devices intended for photometric lighting and/or signaling functions of a vehicle, for the interior lighting of the latter (mounted for example in the vehicle ceiling light), or in lighting devices producing a signature or visual animations on the vehicle.

State of the art

In the field of automotive lighting, lighting devices mounted in a vehicle headlight are generally known for projecting light beams performing photometric lighting and/or signaling functions. In particular, to perform a direction indicator function of the vehicle, the light beam may be a lighting beam with a scrolling effect, called a "tracer" effect. The latter is obtained by using a lighting device conventionally comprising an at least partially transparent or translucent light guide, two essentially point light sources, of the electroluminescent diode type, arranged at the ends of the light guide, and a device for controlling the two light sources.

Published patent document US 10,436,413 B2 discloses such a lighting device. The control device present within the lighting device is configured to perform the ignition control of each of the light sources. More specifically, during the method of controlling the ignition of the light sources, the two light sources are controlled according to different control laws so as to create a lighting effect of the scrolling or "tracer" type from one side of the light guide to the other side of the light guide. In other words, the light appears to move in the light guide from the first light source to the second light source, until the light guide is fully illuminated.

However, the lighting device described in this patent document requires two light sources, arranged at both ends of the light guide. Furthermore, it does not allow segmentation (also called pixelation) of the light emitted by the light guide. For this purpose, it is known to use a lighting device comprising a light guide, and several essentially point light sources, of the light-emitting diode type, arranged along the entire length of the light guide. Each light source is then configured to emit light in the core of the light guide, and corresponds to a distinct pixel. However, such a solution is unsuitable when it is desired to obtain a flexible light guide and/or one having a particular geometry, due to the arrangement of all the light sources along the light guide. Furthermore, such a solution requires choosing a particular inter-light source distance, which is restrictive, and also results in significant costs due to the multiplicity of light sources.

The present invention improves the situation.

One objective of the invention is to propose a vehicle lighting device comprising an at least partially transparent or translucent light guide, which allows segmentation (or pixelation) of the light guide, while alleviating constraints and reducing costs. Another objective is to propose such a lighting device allowing the use of a flexible light guide and/or having any type of geometry. Yet another objective is to propose such a lighting device allowing a reflected light beam to be obtained at the output of the light guide, the light pixels of which have a specific color allowing standard lighting, all with a simplified control circuit. Yet another objective is to propose such a lighting device producing a specific output color allowing a light signature or visual animation to be obtained day and night (with the same output color).

For this purpose, a first aspect of the invention relates to a vehicle lighting device comprising an at least partially transparent or translucent light guide, and at least one light source arranged at one end of the light guide, the light guide comprising a transparent or translucent core, the light source being configured to emit a white light source beam in the core of the light guide. Here, the term "light guide" means any optical part capable of guiding light along its length by total internal reflection of this light, for example from an entry zone to an exit zone. The core of the light guide extends along a longitudinal axis and is capable of receiving a light beam from the light source and/or from an external source of natural light (such as for example the sun).

In addition, the light guide core is configured to allow light to exit this part via at least one lateral side thereof, i.e. via a face of the optical part whose normal is perpendicular to the longitudinal axis of the part along which the part extends. To do this, for example, the light guide core may comprise return elements for reflecting light rays towards the lateral side. The return elements may be microstructures, prisms, or suspended particles integrated into the light guide core.

The light guide is typically a cylindrical light guide or a surface light guide. Optionally, but preferably, the light guide is an optical fiber, typically a diffusing and/or flexible optical fiber. The light source is preferably an essentially point light source, of the light-emitting diode type. Here, the term "white light" means a light consisting of a set of different colors that constitute the light spectrum visible to the human eye.

According to the invention, the light guide further comprises a multilayer structure attached to the core and comprising a substrate, a reflective layer, and a layer of electrochromic material comprising at least one cell, said at least one cell comprising at least two electrochromic elements, each electrochromic element or said at least two electrochromic elements being encapsulated in an electrolyte layer which is connected to a pair of electrodes capable of receiving an electrical voltage, each electrochromic element being capable of receiving light rays incident by a surface and of returning light rays among the light rays incident from said surface, said returned light rays having a wavelength included in an interval defined at least by a thickness of the layer of electrochromic material, said at least two electrochromic elements having distinct thicknesses when no electrical voltage is applied to them, such that the light rays coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerge from said at least two electrochromic elements. in the core of the light guide respectively with a first and a second predetermined wavelength in the visible spectrum, the light rays then emerging from said at least one cell with a first predetermined color corresponding to a mixture between the colors associated with said first and second predetermined wavelengths; the light device further comprising an electrical control circuit connected to the electrodes of said at least two electrochromic elements and configured to control the electrical voltage at the terminals of the or each pair of electrodes, the electrical voltages imposed by the electrical control circuit on the electrodes of said at least two electrochromic elements being equal, such that when the electrical control circuit imposes a predefined electrical voltage value at the terminals of the respective pair(s) of electrodes of said at least two electrochromic elements, the light rays coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerge from said at least two electrochromic elements in the core of the light guide respectively with a third and a fourth predetermined wavelength in the visible spectrum, and when said at least two electrochromic elements are powered simultaneously, the light rays emerge from said at least one cell with a second predetermined color, distinct from the first color and corresponding to a mixture between the associated colors at said third and fourth predetermined wavelengths.

By virtue of the presence of such a multilayer structure thus configured, the lighting device according to the invention allows segmentation (or pixelation) of the light guide, using one or more light source(s) and/or using natural light from the sun. Furthermore, the lighting device according to the invention allows the use of a flexible light guide and/or one having any type of geometry, unlike the solution of the prior art consisting of having numerous light sources along the light guide. The lighting device according to the invention is also particularly compact, allows a variable inter-element distance, and imposes fewer limitations on the number of frames in the visual animation generated.

In addition, the lighting device according to the invention makes it possible to obtain a reflected light beam at the output of the light guide whose light cells (or pixels) have a specific color allowing standard lighting (typically a regulatory color for an automobile lighting function), all with a simplified electrical control circuit. Indeed, with a single predefined voltage value capable of being applied uniformly to the terminals of the pairs of electrodes of the electrochromic elements of the different cells, the number of electrical connections required to the electrochromic elements is advantageously reduced, and the electrical control circuit is consequently greatly simplified. Furthermore, the color and tone obtained at the output of a given pixel also depend on the (predefined) geometric dimensions of the electrochromic elements making up this pixel. More precisely, for each electrochromic element of a given pixel, by playing on the geometry of this element (in particular on its length), the quantity of light rays passing through this element varies, which gives, for a fixed supply voltage of the element (corresponding to a given color in the visible spectrum), a different tone and proportion of this color in the final mixture of colors obtained at the output of the pixel. Furthermore, the lighting device according to the invention advantageously makes it possible to choose different configurations (shapes and sizes) for the pixels, which makes it possible to optimize the size of the pixels (for the same given mixture of colors) and thus contribute to a reduction in the size of the pixels and therefore to a reduction in the size and final cost of the lighting device.

The light device according to the invention finally makes it possible to generate a specific output color making it possible to obtain a light signature or a visual animation during the day and at night (with the same output color). Indeed, during the day, it is possible to turn off the light source, and it is then the natural light from the sun which causes the reflection of the light rays by the reflective layer with at the reflection output the first predetermined color corresponding to a mixture between the colors associated with the first and second predetermined wavelengths (without any electrical power supply by the control circuit on the electrochromic elements). Conversely, at night, it is possible to turn on the light source, and it is then the light rays from this source which are reflected by the reflective layer with at the reflection output the first predetermined color (without any electrical power supply by the control circuit on the electrochromic elements). In both cases (day and night), it is then possible to reveal a pattern or a light signature of the second predetermined color, via the electrical supply (with the predefined voltage value) of the electrodes of the electrochromic elements of the corresponding pixels.

Indeed, in the present invention, the electrochromic elements of the same pixel are of different thicknesses when no electrical voltage is applied to them. The light rays from the white light source beam and/or from the external source of natural light and reflected by the reflective layer then emerge from the at least two electrochromic elements of the same pixel, in the core of the light guide, respectively with a first and a second predetermined wavelength in the visible spectrum. The thickness of the layer of electrochromic material indeed has an influence on the color perceived by an observer. More precisely, the perceived color is obtained via an interference phenomenon in a Fabry-Pérot cavity formed in each element of each cell of the layer of electrochromic material, the color being obtained by the ratio between the thickness of the cavity, the wavelength and the refractive index.

According to one embodiment of the invention, the light source is a laser source or a light-emitting diode.

According to one embodiment of the invention, the layer of electrochromic material is structured into a plurality of cells of identical composition.

According to a preferred embodiment of the invention, each cell comprises three electrochromic elements, the three electrochromic elements of the same cell having distinct thicknesses when no electrical voltage is applied to them; wherein, for each cell, when no electrical voltage is applied to the three electrochromic elements of the cell, the light rays from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerge from the electrochromic elements in the core of the light guide respectively with a first, a second and a third predetermined wavelength corresponding respectively to the magenta color, the cyan color and the yellow color in the visible spectrum, the light rays then emerging from the cell with a black color corresponding to a mixture between the magenta, cyan and yellow colors; and wherein the electrical control circuit is configured such that, for each cell, when the electrical control circuit applies said electrical voltage value to a first electrochromic element of the cell, to a second electrochromic element of the cell or to a third electrochromic element of the cell, the light rays from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerge from the corresponding element in the core of the light guide with respectively a fourth, a fifth or a sixth predetermined wavelength corresponding respectively to the blue color, the green color or the red color in the visible spectrum, and when the three electrochromic elements of the cell are powered simultaneously, the light rays emerge from the cell with a white color corresponding to a mixture between the blue, green and red colors.

This makes it possible to obtain a reflected light beam at the output of the light guide whose light pixels have a white color, all with a simplified control circuit. The lighting device according to the invention also makes it possible, when all of the electrochromic elements are not electrically powered by the electrical circuit, to generate a so-called "matte panel" effect (in English "black panel"), in other words to hide any transparency effect within the projector comprising the lighting device. It thus becomes possible to easily reveal a white-colored pattern or light signature in an opaque (or black) surface, and to make this luminous lighting activatable (via the electrical power supply of the electrodes of all of the adjacent electrochromic elements of one or more pixels), producing an aesthetic contrast effect. This configuration is also particularly suitable for performing the daytime running light function, or DRL - acronym for "Daytime Running Light" in English - by providing a better quality white color than with a conventional device.

According to one embodiment of the invention, the electrochromic material belongs to the family of organic transparent conductive oxide materials, in particular a transparent conductive polymer of the PEDOT:PSS, PEDOT:Tos, T34bT, or cellulose type. Such a material makes it possible to produce a Fabry-Pérot cavity, which is flexible and transparent. Furthermore, such an electrochromic material is in contact with the electrolyte layer such that under electrical stimulation, for example when applying an electrical voltage to the electrolyte layer, the ions of the electrolyte layer migrate into the layer of electrochromic material. The quantity of “migrating” ions depends on the value of the electrical quantity applied. The more numerous the “migrating” ions, the thicker the layer of electrochromic material becomes.

Oxidation-reduction reactions can occur between the layer of electrochromic material and the “migrating” ions so as to modify the thickness and/or the properties of this layer. Thus, the layer of electrochromic material is electrochemically adjustable.

According to a first embodiment of the invention, the core of the light guide is a core of diffusing and/or flexible optical fiber, the main axis along which the core of the light guide extends being a longitudinal axis. By definition, an optical fiber comprises a core portion and a sheath enveloping the core. Generally, the sheath is transparent while the core portion allows total internal reflection. The refractive index of the core portion is then slightly higher than the refractive index of the sheath enveloping the core. Optical fiber type light guides make it possible to guide light from a light source to various locations without having to suffer significant transmission losses. Such an optical fiber has the advantage, in addition to its flexibility which makes it suitable for certain applications, of having a homogeneous structure (unlike rigid and extruded light guides for example, which have asperities).

According to a second embodiment of the invention, the core of the light guide is a film, the main axis along which the core of the light guide extends forming a preferred axis of propagation of light within said film, the light rays from the white light source beam propagating in said core along said main axis by total internal reflection. This second embodiment of the invention then makes it possible to obtain light signatures or visual animations of the matrix type, and therefore to increase the number of possibilities in terms of animations. In particular, this second embodiment of the invention makes it possible to illuminate a large surface (such as a central panel arranged on the front of the vehicle for example, or to cover the location of a grille), with reduced energy consumption. Additionally, particular light structures and/or patterns may be displayed via this embodiment of the light device, which provides a large, reconfigurable surface area light device for displaying the patterns, while being able to generate a specific output color (e.g., white) during the day or night.

According to a variant of this second embodiment, the light guide further comprises at least one group of light injection elements arranged adjacent to an edge of the film, said at least one light source being coupled to said at least one group of light injection elements such that the light rays from the light source are completely reflected inside the light injection elements and are redirected towards the film.

According to another variant of this second embodiment, the light device comprises several light sources aligned transversely to the main axis at one edge of the film.

Preferably, according to this second embodiment of the invention, the multilayer structure forms a sheet, for example a substantially rectangular sheet, said sheet being in shape correspondence with the film.

More preferably, according to this second embodiment of the invention, the electrochromic material is PEDOT, and said predefined electrical voltage value is equal to 0.9 Volts. Such an electrical voltage value causes an increase in the thickness of each electrochromic element of approximately 70 nm.

According to one embodiment of the invention, the predefined electrical voltage value is between -1 V and +1 V. Such control can be ensured in practice by low electrical voltage levels, less than 1 V in absolute value for the layer of electrochromic material, which induces low energy consumption.

For example, a pair of electrodes comprises a working electrode and an electrode system comprising a counter electrode and a reference electrode.

According to one embodiment of the invention, the substrate of the multilayer structure is provided with a power supply sheet connected on the one hand to the electrical control circuit and on the other hand to the terminals of the or each pair of electrodes.

Advantageously, the power supply sheet consists of a flexible printed circuit board or a film on which electronic components are printed.

Another subject of the invention relates to a vehicle headlight, in particular a motor vehicle headlight, comprising a lighting device according to the invention.

Another subject of the invention relates to a vehicle comprising a lighting device according to the invention.

Here, “vehicle” means any type of vehicle such as a motor vehicle, a moped, a motorcycle, a storage robot in a warehouse, or any other machine capable of carrying at least one passenger or intended for the transport of people or objects.

Another subject of the invention relates to a method for controlling a vehicle lighting device according to the invention, the method being implemented by the electrical control circuit and comprising a step of controlling the simultaneous control of the electrical voltages at the terminals of the respective pair(s) of electrodes of said at least two electrochromic elements of said at least one cell, as a function of a setpoint, said setpoint being such that the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerges from each electrochromic element in the core of the light guide with the third or fourth predetermined wavelength, said setpoint being the predefined electrical voltage value, the light emerging from said at least one cell in the core of the light guide with the second predetermined color in the visible spectrum.

According to a preferred embodiment of the invention, during the control step, the three electrochromic elements of the same cell are powered simultaneously, such that when the electrical control circuit imposes the predefined electrical voltage value at the terminals of the respective pair(s) of electrodes of said three electrochromic elements of the cell, the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer emerges from the corresponding cell in the core of the light guide with a white color in the visible spectrum.

Another subject of the invention relates to a use of a light device according to the invention for performing a photometric lighting and/or signaling function of a vehicle, in particular a direction indicator function of the vehicle.

Other characteristics and advantages of the invention will appear on examining the detailed description below, and the attached drawings in which:

is a schematic representation, in side view, of a lighting device according to a first embodiment of the invention, the lighting device comprising a light source and an electrical control circuit;

is a schematic representation, in longitudinal section, of the lighting device of the according to an exemplary embodiment of the invention, the light device comprising a layer of electrochromic material structured into a plurality of electrochromic elements and being in an operating mode in which the electrochromic elements are not electrically powered by the electrical control circuit;

is a view similar to that of the , in a mode of operation of the lighting device in which all the electrochromic elements of the layer are electrically supplied by the electrical control circuit;

is a schematic representation, in perspective, of a set of three electrochromic elements belonging to the same cell or pixel of the light device according to the invention, the three electrochromic elements being electrically powered by the electrical control circuit according to a particular exemplary embodiment of the invention;

is a schematic representation, in perspective, of a set of three electrochromic elements belonging to the same cell or pixel of the luminous device of the ;

is a schematic representation of the entire , when the three electrochromic elements are electrically supplied by the electrical control circuit;

, , , And are schematic representations, in top view, of possible geometric configurations for the three electrochromic elements according to the example of embodiment of the ;

is a schematic representation, in exploded view and in section, of a lighting device according to a second embodiment of the invention, the lighting device comprising a light source and an electrical control circuit.

In this document, the terms "horizontal", "vertical" or "transverse", "lower", "upper", "top", "bottom", "side" are defined in relation to the orientation of the light device or a part forming part of the light device according to the invention in which it is intended to be mounted in the vehicle. In particular, in this application, the term "vertical" designates an orientation perpendicular to the horizon while the term "horizontal" designates an orientation parallel to the horizon.

On the , an orthogonal reference frame associated with the vehicle lighting device has been shown. This reference frame is composed of three axes X, Y and Z, being called, here, respectively longitudinal axis X, transverse axis Y and vertical axis Z.

Detailed description

There is a schematic representation, in side view, of a vehicle lighting device 1 according to a first embodiment of the invention. The lighting device 1 comprises an at least partially transparent or translucent light guide 6, a light source 8A, and an electrical control circuit 4. The electrical control circuit 4 is for example connected to the electrical network of the vehicle.

As illustrated in Figures 2 and 3, the light guide 6 comprises a transparent or translucent core 10 and a sheath (not shown) enveloping the core 10. The light guide 6 further comprises a multilayer structure 12 attached to the core 10.

The light guide 6 is elongated along a substantially horizontal main direction of extension D1. The light guide 6 is typically a cylindrical light guide or a surface light guide, for example of square or round section. According to one example, the light guide 6 is a diffusing linear optical fiber, folded or not, and made of a flexible material, without this being limiting in the context of the present invention. The optical fiber 6 is advantageously made of a plastic material that is at least partially transparent or translucent, in particular polycarbonate (also called PC) or polymethyl methacrylate (also called PMMA). The optical fiber 6 is for example made of a material close to PMMA for the core of the fiber, and another material close to a fluoropolymer for the sheath. The optical fiber 6 is for example obtained via a prior extrusion process, or via any other known manufacturing process.

As illustrated in Figures 2 and 3, the multilayer structure 12 is composed of the stack of a substrate 14, a reflective layer 16, and a layer of electrochromic material 18.

The substrate 14 is typically a flexible substrate. For example, the flexible substrate 14 is made of silicone, polycarbonate or PMMA. The substrate 14 has for example a thickness of 500 microns. The substrate 14 is for example provided with a power supply sheet connected to the electrical control circuit 4. The power supply sheet is typically made of a flexible printed circuit board or a film on which electronic components are printed.

The reflective layer 16 is typically a metal layer. The metal layer 16 is delimited by a first face and a second face. The first face of the metal layer 16 is in contact with a face of the substrate 14. For example, the metal layer 16 may be made of aluminum, chromium or gold, or also of an alloy of at least two metals among the three metals mentioned above. The metal layer 16 has for example a thickness of between 70 and 100 nm.

The electrochromic material layer 18 is delimited by a third face 18A and a fourth face 18B. By electrochromic is meant a material that changes color when an electrical voltage is applied to it for a short time. The color change is due to the fact that only one specific type of wavelengths, for example wavelengths of a specific value or in a specific visible color spectrum, can emerge from the electrochromic material layer 18 depending on the value of the electrical quantity applied. These specific wavelengths correspond to a color in the visible spectrum and reach the eyes of an observer. The latter therefore has the impression that the material layer 18 has changed color. The material retains the new color after the application as long as electrical voltage is applied to it. The third and fourth faces 18A, 18B of the electrochromic material layer 18 are substantially parallel to each other. The third face 18A of the layer of electrochromic material 18 is in contact with the second face of the metal layer 16. An incident light wave, having a given spectrum of wavelengths, enters through the fourth face 18B and then interferes with the electrochromic material 18. The interference phenomenon leads to the electrochromic material 18 returning light rays through the fourth face 18B, only in a restricted range of wavelengths, or more simply, according to a given color. The color returned by the layer of electrochromic material 18 is conditioned by the thickness of the cavity and/or by the intrinsic properties of the electrochromic material 18, its permittivity in particular, as well as by the reflective layer 16 used.

The electrochromic material is for example a polymer, such as a PEDOT (poly(3,4-ethylenedioxythiophene)) type polymer. The PEDOT material used can be, for example, PEDOT:PSS, also called poly(3,4 ethylenedioxythiophene): poly(sodium styrenesulfonate, or PEDOT:Tos, also called poly(3,4 ethylenedioxythiophene):Tosylate. Other examples of organic transparent conductive oxide materials can be used for the electrochromic material, such as cellulose for example. Such a family of organic transparent conductive oxide materials, also called TCO for "Transparent Conductive Oxide" in English, makes it possible to produce a Fabry-Pérot cavity, which is flexible and transparent. Furthermore, such an electrochromic material is electrochemically adjustable insofar as oxidation-reduction reactions (also commonly called "redox") can occur between this type of material and the electrolyte under electrical stimulation (for example under an electrical voltage). Of course, other materials can be used as long as they have the properties suitable for an automotive application such as ionic conductivity high, a physical appearance in the resting state different from the physical appearance in the excited state, and an ability to form a Fabry Perot cavity regardless of its state. Furthermore, the material can be packaged as a solid cell. No restrictions are attached to the electrochromic material used in the electrochromic material layer 18.

The layer of electrochromic material 18 is here structured into N electrochromic elements. A portion of the multilayer structure with N electrochromic elements E ₁ , E ₂ , E ₃ ,… and E _N , is shown in FIGS. 2 and 3, with N equal to 9. For example, the layer of electrochromic material 18 is structured into a row of N electrochromic elements. In the example illustrated, the row of N electrochromic elements extends along the main direction of extension D1. Each electrochromic element among the N electrochromic elements is encapsulated in an electrolyte solution or gel 15 (visible in FIG. ), to which is connected a pair of electrodes intended to voltage bias the corresponding electrochromic element. The encapsulation and arrangement of the N electrochromic elements and the arrangement of the N pairs of corresponding electrodes on each electrochromic element are carried out similarly to those of a liquid crystal plate. All of the N pairs of electrodes are connected for example to a low-voltage battery (not shown) and connected to the electrical control circuit 4 via the power supply sheet of the substrate 14. More precisely, all of the N electrochromic elements are distributed between a first subgroup of electrochromic elements E ₁ , E ₄ , E ₇ , a second subgroup of electrochromic elements E ₂ , E ₅ , E ₈ and a third subgroup of electrochromic elements E ₃ , E ₆ , E ₉ . The electrochromic elements of the first, second and third subgroup of electrochromic elements are interleaved three by three along the layer of electrochromic material 18. Thus, in the particular embodiment shown in FIGS. 2 and 3, three first electrochromic elements E ₁ , E ₄ , E ₇ belong to the first subgroup of electrochromic elements, three other electrochromic elements E ₂ , E ₅ , E ₈ belong to the second subgroup of electrochromic elements, and three other electrochromic elements E ₃ , E ₆ , E ₉ belong to the third subgroup of electrochromic elements. Each set P ₁ , P ₂ , P ₃ of three adjacent electrochromic elements (E ₁ , E ₂ , E ₃ ), (E ₄ , E ₅ , E ₆ ), (E ₇ , E ₈ , E ₉ ) of the first, second and third subgroup of electrochromic elements forms a cell (or pixel). In fact, the term “pixel” here means an individual cell of the layer of electrochromic material 18, comprising several (here three) electrochromic elements (E ₁ , E ₂ , E ₃ ), (E ₄ , E ₅ , E ₆ ), (E ₇ , E ₈ , E ₉ ). In the exemplary embodiment illustrated in FIGS. 2 and 3, the layer of electrochromic material 18 comprises three pixels P ₁ , P ₂ , P ₃ . In the present invention, the three adjacent electrochromic elements of the same pixel P ₁ , P ₂ , P ₃ have distinct thicknesses when no electrical voltage is applied to them. For example, in the exemplary embodiment of FIGS. 2 and 3, and for a layer of electrochromic material 18 made of PEDOT material, the electrochromic elements E ₁ , E ₄ , E ₇ of the first subgroup of electrochromic elements have a thickness substantially equal to 60 nm, the electrochromic elements E ₂ , E ₅ , E ₈ of the second subgroup of electrochromic elements have a thickness substantially equal to 100 nm, and the electrochromic elements E ₃ , E ₆ , E ₉ of the third subgroup of electrochromic elements have a thickness substantially equal to 150 nm.

The following describes how the color of a pixel among the N/3 pixels of the electrochromic material layer 18 is controlled. Such a pixel acts as a Fabry-Pérot cavity formed by the portion of the third face 18A and the portion of the fourth face 18B corresponding to them. This cavity produces, from the light it receives, interferences of a determined wavelength. These interferences result in multiple reflections of rays of a given wavelength propagating inside the cavity. In fact, it is by an interference phenomenon, and not absorption as when pigments or dyes are used, that the pixel produces, for an observer, a colored rendering. The color is obtained by the ratio between the thickness of the cavity, the wavelength and the refractive index. These three parameters make it possible, by using a reflective layer attached to the cavity, to obtain a reflective colored surface. Such a color is called “structural” because it is obtained by interference of incident light rays with the electrochromic material, and because this approach makes it possible to obtain a color without using pigments or dyes. The layer of electrochromic material 18 is thin at a sub-wavelength scale, for example of the order of a few nanometers thick or between 50 and 800 nm, for example between 75 and 300 nm, and therefore both compact and lightweight. Since the display function is structurally linked to the layer of electrochromic material, the light device 1 is also very robust, in particular to mechanical shocks and temperature variations. A Fabry-Pérot cavity can reflect approximately between 60% and 90% of the incident light intensity, which allows good visibility of the light device 1 in sunny weather. Further details on such an electrochromic material layer 18, as well as how to choose a color from the UV treatment that is applied to the electrochromic material, the intensity of the treatment and its duration in particular, depending on the electrochromic material and depending on the reflective layer 16, are detailed in the article “Tunable Structural Color Images by UV-Patterned Conducting Polymer Nanofilms on Metal Surfaces”, by Shangzi Chen et Al, Advanced Materials, 2021, 33, 2102451, published by Wiley-VCH GmBH.

Each electrochromic element E ₁ , E ₂ , E ₃ ,… and E _N of a given pixel of the electrochromic material layer 18 is thus capable of receiving incident light rays via a surface corresponding to the fourth face 18B of the electrochromic material layer 18, and of returning light rays among the incident light rays from this surface 18B. As indicated above, the returned light rays have a wavelength included in an interval defined at least by properties of the electrochromic material and/or by a thickness of the electrochromic material layer 18. The electrochromic elements (E ₁ , E ₄ , E ₇ ), (E ₂ , E ₅ , E ₈ ), (E ₃ , E ₆ , E ₉ ) of the same subgroup of elements have equal geometric dimensions when not electrically powered.

The light source 8A is arranged at one end of the light guide 6 and is configured to emit a white light source beam into the core 10 of the light guide 6. The light source 8A is advantageously an essentially point light source, in particular of the semiconductor type, for example of the light-emitting diode type or even a laser source.

The electrical control circuit 4 is connected to the electrodes of the first, second and third subgroups of electrochromic elements via the same set of power supply wires belonging to the power supply sheet, these power supply wires being visible in FIGS. 2 and 3 (this makes it possible to greatly simplify the electrical control circuit 4, compared to the previous solutions for which several sets of power supply wires are connected in a differentiated manner to the electrodes of the first, second and third subgroups of electrochromic elements). The electrical control circuit 4 makes it possible to control the electrical voltage at the terminals of the N electrochromic elements of the layer of electrochromic material 18, the electrical voltages imposed by the electrical control circuit 4 on the electrodes of the different electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ) being equal. For example, the electrical voltage at the terminals of each pair of electrodes varies between a minimum electrical voltage of – 1 Volts and a maximum electrical voltage of + 1 Volts. The thickness of the electrochromic material layer 18 has an influence on the color perceived by an observer. For example, a PEDOT layer with a thickness of 150 nm, when it receives a broadband light spectrum light, produces a yellow color by reflection. A PEDOT layer with a thickness of 100 nm, when it receives a broadband light spectrum light, produces a cyan color by reflection. A PEDOT layer with a thickness of 60 nm, when it receives a broadband light spectrum light, produces a magenta color by reflection. In the present invention, the three adjacent electrochromic elements of the same pixel of the electrochromic material layer 18 are of distinct thickness when no electric voltage is applied thereto, and the thickness of the electrochromic material layer 18 itself is a function of the power supply electric voltage supplied by the control electric circuit 4, which therefore influences the color perceived by an observer. For example, for the same electrical supply voltage at the terminals of a pair of electrodes, a layer 18 of PEDOT material with an initial thickness equal to 150 nm produces by reflection a red color (with a wavelength between 620 nm and 630 nm), with an increase in thickness of the layer of approximately 70 nm; a layer 18 of PEDOT material with an initial thickness equal to 100 nm produces by reflection a green color, with an increase in thickness of the layer of approximately 70 nm; and a layer 18 of PEDOT material with an initial thickness equal to 60 nm produces by reflection a blue color (with a wavelength substantially equal to 450 nm), with an increase in thickness of the layer of approximately 70 nm. Thus, and as illustrated in the , when the electrical control circuit 4 imposes the same predefined electrical supply voltage value of between – 1 Volts and + 1 Volts at the terminals of the pairs of electrodes of the different electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ), the light coming from the white light source beam and/or from an external source of natural light (such as for example the sun) and reflected by the reflective layer 16 passes through the electrochromic elements E ₁ , E ₄ , E ₇ of the first subgroup of electrochromic elements and emerges in the core 10 of the light guide 6 with a first predetermined wavelength corresponding to the blue color in the visible spectrum, passes through the electrochromic elements E ₂ , E ₅ , E ₈ of the second subgroup of electrochromic elements and emerges in the core 10 of the light guide 6 with a second predetermined wavelength corresponding to the green color in the visible spectrum, and passes through the elements electrochromic elements E ₃ , E ₆ , E ₉ of the third subgroup of electrochromic elements and emerges in the core 10 of the light guide 6 with a third predetermined wavelength corresponding to the red color in the visible spectrum. As an alternative to the embodiment shown in FIGS. 2 and 3, it is possible in an alternative embodiment to simplify the electrical assembly by applying a voltage across pairs of electrodes of different pixels, these pixels being configured as in the bis. In this case, each pixel or cell of three electrochromic elements E ₁ , E ₂ , E ₃ is provided with two electrodes 19A, 19B, each electrode 19A, 19B being common to the three electrochromic elements E ₁ , E ₂ , E ₃ and being connected to the three electrochromic elements E ₁ , E ₂ , E _3. This alternative embodiment thus makes it possible to reduce the number of electrodes used (and therefore electrical connections between the electrical control circuit 4 and the pixels or cells), and thus to further simplify the electrical assembly.

Thus, when the electrical control circuit 4 imposes the predefined electrical supply voltage value at the terminals of the electrodes of all the electrochromic elements of the same pixel P ₁ , P ₂ , P ₃ given (on the all pixels P ₁ , P ₂ , P ₃ of layer 18 are lit), the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer 16 passes through the electrochromic elements of this pixel P ₁ , P ₂ , P ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a white color corresponding to a mixture between the blue, green and red colors. Indeed, the three adjacent elements (E ₁ , E ₂ , E ₃ ), (E ₄ , E ₅ , E ₆ ), (E ₇ , E ₈ , E ₉ ) of the same given pixel P ₁ , P ₂ , P ₃ are arranged sufficiently close to each other so that the eye of an observer perceives a single white color emitted by this pixel, by mixing the blue, green and red colors emitted by the three adjacent elements. Here, when supplied respectively by the same supply voltage, the elements E ₁ , E ₄ , E ₇ of the first subgroup of elements have a thickness less than the elements E ₂ , E ₅ , E ₈ of the second subgroup of elements, which themselves have a thickness less than the elements E ₃ , E ₆ , E ₉ of the third subgroup of elements. When no electrical supply voltage is applied to the terminals of the electrodes of the electrochromic elements of the same given pixel P ₁ , P ₂ , P ₃ , the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer 16 passes through the electrochromic elements of this pixel P ₁ , P ₂ , P ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a black color corresponding to a mixture between the colors magenta, cyan and yellow.

Furthermore, for each element (E ₁ , E ₂ , E ₃ ), (E ₄ , E ₅ , E ₆ ), (E ₇ , E ₈ , E ₉ ) of a given pixel P ₁ , P ₂ , P ₃ , by playing on the geometry of this element (in particular on its length), the quantity of light rays passing through this element varies, which gives, for a supply voltage of the element fixed at the predefined supply voltage value, a different tone and proportion of the corresponding color (red, green or blue) in the final color mixture obtained at the output of the pixel. More precisely, the quantity of light rays passing through a given electrochromic element E ₁ , E ₂ , E ₃ ,… and E _N , which is a function of the geometry of this element (in particular its length), directly influences the height of the peak of the wavelength corresponding to this element (first, second or third predetermined wavelength) in the final mixture of colors obtained at the output of the pixel.

Thus, the electrical control circuit 4, by receiving an instruction sent for example by a user (the instruction being the predefined electrical supply voltage value), makes it possible to control the electrical voltage at the terminals of each pair of electrodes in order to control the color of the corresponding pixel. More precisely, when the electrical control circuit 4 imposes the predefined electrical voltage value at the terminals of one of the pairs of electrodes of an electrochromic element (depending on whether this electrochromic element belongs to the first, second or third subgroup of electrochromic elements), the light coming from the white light source beam (emitted by the light source 8A) and/or from the external source of natural light and reflected by the reflective layer 16 passes through the corresponding electrochromic element E ₁ , E ₂ , E ₃ ,… E _N , and emerges in the core 10 of the light guide 6 with the first, second or third predetermined wavelength in the visible spectrum. When the three adjacent electrochromic elements of the same pixel are powered simultaneously by the electrical control circuit 4, the particular geometric configuration of the electrochromic elements influences the final mixture of colors obtained at the output of the pixel, the light beam at the output of the pixel having a predetermined color and tone.

The photometric lighting and/or signaling function, or the visual signature or animation, produced by the lighting device 1, is thus made up of the N/3 pixels whose color is controlled by the electrical voltage ordered by the electrical control circuit 4. This photometric lighting and/or signaling function, or this visual signature or animation, is thus customizable.

Figures 4 to 10 show three adjacent electrochromic elements E ₁ , E ₂ , E ₃ which belong to the same pixel P1.

In particular, the represents the three electrochromic elements E ₁ , E ₂ , E ₃ when no supply voltage is applied to the terminals of the electrode(s) of the electrochromic elements. As indicated above, the light from the white light source beam and/or from the external source of natural light and reflected by the reflective layer passes through the electrochromic elements E ₁ , E ₂ , E ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a black color corresponding to a mixture between the colors magenta, cyan and yellow. The represents the three electrochromic elements E ₁ , E ₂ , E ₃ when the same electrical supply voltage is applied to the terminals of the electrode(s) of the electrochromic elements. As indicated previously, the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer passes through the electrochromic elements E ₁ , E ₂ , E ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a white color corresponding to a mixture between the blue, green and red colors.

Figures 6 to 10 illustrate different possible geometric configurations for the three electrochromic elements E₁, E₂, E₃ according to an exemplary embodiment of the invention. The three electrochromic elements E₁, E₂, E₃ can thus be arranged next to each other in a linear alignment ( ), or define concentric ring shapes ( ), or be arranged in the form of a compact stack within a (virtual) rectangular or square shape R1 (figures 8 to 10). It is thus understood that by choosing such examples of geometric configurations for the three electrochromic elements E₁, E₂, E₃, it is possible to advantageously optimize the size of the corresponding pixel by making the latter particularly compact and by supplying it with the same electrical supply voltage across the entire pixel.

There is a schematic representation, in side view, of a portion of a vehicle lighting device 20 according to a second embodiment of the invention. The lighting device 20 comprises a light guide 105, a light source (not shown in the figure for reasons of clarity), and an electrical control circuit (not shown). The electrical control circuit is for example connected to the electrical network of the vehicle.

The light guide 105 is here a surface light guide comprising a flexible sheet 110 provided with a core 111, as well as a multilayer structure (not shown in the ), itself in the form of a sheet and attached to the flexible sheet 110. The core 111, which is in the form of a flexible film, is capable of receiving light rays via a light injection edge 114 and of returning the light rays in a direction X substantially normal to a surface of the sheet which thus extends in a plane YZ on the . The tablecloth 110 is typically rectangular in shape, as illustrated in the .

The light guide 105 further comprises a group 120 of light injection elements 120.1 arranged upstream of the flexible sheet 110.

A "sheet" is an optical element in which one dimension is much smaller than the other two dimensions in space, for example one or more orders of magnitude smaller. As illustrated in the , we consider here a flexible sheet whose thickness along the X axis is at least two orders of magnitude less than its dimensions along the YZ plane in which the flexible sheet 110 extends.

The flexible sheet 110 comprises a set of microstructures 113, here produced in the part of the core 111, capable of returning the light rays guided in the light guide outside the flexible sheet 110, in particular in one or more directions substantially along the X axis. In an exemplary embodiment, the light rays emerge in the +X direction, namely substantially parallel to the vehicle axis Ox, towards the outside of the front face of the vehicle.

The multilayer structure, attached to the flexible sheet 110, is composed of the stack of a substrate, a reflective layer, and a layer of electrochromic material. The layer of electrochromic material comprises electrochromic elements similar to the electrochromic elements E ₁ ,..,E ₉ described in connection with the light device 1 according to the first embodiment of the invention, and which will therefore not be described in more detail here. In particular, the electrochromic elements are distributed in pixels, in other words in groups of electrochromic elements distributed between a first subgroup of electrochromic elements, a second subgroup of electrochromic elements and a third subgroup of electrochromic elements. As in the first embodiment of the invention, the electrochromic elements of the first, second and third subgroups of electrochromic elements have distinct thicknesses when no electrical voltage is applied to them. The electrochromic elements are configured to form Fabry-Pérot cavities in an excited state. The microstructures 113 make it possible to decouple the light rays circulating within the core 111, in other words the microstructures 113 deflect the light rays which propagate in the core 111 of the light guide 105 and return them to the electrochromic elements of the layer of electrochromic material.

The flexible film 111 (or core) is typically rectangular in shape, as illustrated in the . The flexible film 111 may be a substrate film made of polycarbonate, PC, polymethyl methacrylate, PMMA, thermoplastic polyurethane, TUP, or polyethylene terephthalate, PET. The flexible film 111 may have a thickness, i.e. a dimension along the X axis, of between 12 and 1000 micrometers. More specifically, the thickness of the flexible film 111 may be between 50 and 1000 micrometers, for example between 200 and 500 micrometers. Alternatively, it is the flexible sheet 110 which has a thickness of between 200 and 1000 micrometers.

The aforementioned materials, combined with a low thickness as described above, make it possible to obtain a flexible and transparent film 111. Other materials may be provided for the composition of the flexible film 111. However, it is preferable according to the invention to provide deformable and transparent materials.

The flexible sheet 110 extends along a main extension axis D2, which here corresponds to the Y direction on the The main axis D2 along which the film 111 extends forms a privileged axis of propagation of light within the film, the light rays coming from the white light source beam (itself coming from the light source 28 – as will be described later) propagating in the flexible sheet by total internal reflection along said main axis D2.

The sheet 110 may further comprise one or two optional protective layers 112.1 and 112.2, which make it possible to mechanically protect the flexible film 111. In addition, at least one of the protective layers 112.1 and 112.2 may comprise an anti-UV treatment, making it possible to protect the flexible film against UV rays, once the microstructures 113 have been etched. Without such UV protection, the pattern projected by the light guide 105 is likely to degrade over time, in particular when it is exposed to sunlight.

The flexible film 111 and the protective layers 112.1 and 112.2, here forming the flexible sheet 110, are shown in a spaced manner on the , for illustrative purposes only. It will be understood, however, that the protective layers 112.1 and 112.2 may be attached to the flexible film, in particular by lamination. The protective layers 112.1 and 112.2 have a refractive index different from that of the flexible film 111 so as to allow total internal reflection in the flexible film 111.

The 110 sheet being flexible, it is not necessarily included in a plane but can be curved, depending on the position in which it is placed and the mechanical constraints applied to it.

The microstructures 113 may be capable of causing the light rays exiting the flexible film 111 to form a pattern. For this purpose, the microstructures 113 may be etched by ultraviolet printing, so as to reflect the light rays through the surface of the flexible film according to the desired pattern. For example, the microstructures 113 are distributed so as to project homogeneous light over the entire surface of the flexible film 111. This is then referred to as a homogeneous pattern in the following.

Advantageously, the microstructures 113 can be distributed along the Y axis so that a linear density of microstructures 113 is proportional to the distance from the light injection edge 114 through which the light rays injected by a group 120 of light injection elements 120.1 are received. In other words, the further the microstructures 113 are from the light injection edge 114, the more densely they are grouped. Such a distribution advantageously makes it possible to ensure a homogeneous distribution along the Y axis of the light intensity of the pattern emitted by the flexible sheet 110. The group 120 is coupled with at least one light source (not shown in the ) so as to receive the light rays R emitted by said source in each of the light injection elements.

In a variant not shown of this second embodiment of the invention, the group 120 of light injection elements 120.1 is replaced by several light sources aligned transversely to the main axis D2 of extension of the film 111, at an edge of the film 111 (the edge in question being parallel to the direction Z of the previous figure). Each light source is configured to emit a white light source beam directly into the film 111 (in other words, according to this variant of the second embodiment of the invention, there are no more light injection elements).

In a manner similar to the first embodiment of the invention, the electrical control circuit is connected to the electrodes of the first, second and third subgroup of electrochromic elements via the same set of power supply wires. The electrical control circuit makes it possible to control the electrical voltage at the terminals of the electrochromic elements 113 of the layer of electrochromic material, the electrical voltages imposed by the electrical control circuit on the electrodes of the different electrochromic elements 113 being equal (in other words the electrical circuit controls the increase in thickness, and therefore the related change in color, of all the electrochromic elements with the same predefined electrical voltage value). For example, the electrical voltage at the terminals of each pair of electrodes varies between a minimum electrical voltage of -1 Volts and a maximum electrical voltage of +1 Volts (the value of the predefined electrical voltage being for example substantially equal to 0.9 Volts when the electrochromic material of the layer of electrochromic material is PEDOT).

A method of controlling the lighting device 1, 20 previously described, implemented by the electrical control circuit 4, is described below.

When a user or a third-party system of the vehicle wishes to generate a visual animation on the light device 1, 20, the latter sends an instruction to the electrical control circuit 4. This instruction is representative of a set of electrical voltages (of the same value) to be applied to the electrochromic elements of the layer of electrochromic material 18 (via their respective pairs of electrodes). The set of electrical voltages translates a colored pattern to be displayed on the light guide 6 via the electrochromic elements E ₁ , E ₂ , E ₃ ,… E _N , 113. The electrical control circuit 4 can selectively turn off or turn on the electrochromic elements E ₁ , E ₂ , E ₃ ,… E _N , 113, and control the electrical supply voltage of the latter to generate the particular color emitted by them. In the two particular embodiments shown in FIGS. 1 to 11, when the three adjacent electrochromic elements of the same pixel P ₁ , P ₂ , P ₃ are powered simultaneously by the electrical control circuit 4, the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer 16 passes through the electrochromic elements of this pixel P ₁ , P ₂ , P ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a white color in the visible spectrum, the tone of this white color being a function of the particular geometry chosen for the electrochromic elements in question (and dependent on this geometry). When no electrical supply voltage is applied to the electrodes of the three adjacent electrochromic elements of the same pixel P ₁ , P ₂ , P ₃ , the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer 16 passes through the electrochromic elements of this pixel P ₁ , P ₂ , P ₃ and emerges from the pixel, in the core 10 of the light guide 6, with a black color in the visible spectrum, the tone of this black color being a function of the particular geometry chosen for the electrochromic elements in question (and dependent on this geometry). In order to generate a visual animation or to see the light guide 6 illuminated continuously if necessary, the electrical control circuit 4 drives at high frequency the electrical voltage at the terminals of each pair of electrodes, typically at a frequency substantially between 10 Hz and 50 Hz.

The lighting beam generated by the light guide 6 of the lighting device 1 can be used advantageously to perform a regulatory photometric function, in particular a photometric function for lighting and/or signaling a vehicle, and preferably a vehicle direction indicator function. The lighting beam generated by the lighting device 1 can also be used to perform a photometric function of the “daytime running light” type, or even be used within the interior lighting of a vehicle (the light module being for example mounted in the ceiling light of the vehicle), or even to produce a signature or visual animations on the vehicle during the day and at night (with the same output color) .

Claims (16)

Vehicle lighting device (1; 20) comprising an at least partially transparent or translucent light guide (6; 105), and at least one light source (8A; 28) arranged at one end or at one edge of the light guide (6; 105), the light guide (6; 105) comprising a transparent or translucent core (10; 111), the light source (8A; 28) being configured to emit a white light source beam into the core (10; 111) of the light guide (6; 105), the core (10; 111) of the light guide (6; 105) extending along a main axis (D1; D2) and being capable of receiving a light beam from the light source (8A; 28) and/or from an external source of natural light, the light rays from the white light source beam propagating in said core (10; 111) along said main axis (D1; D2) by total internal reflection, said core (10; 111) being configured so as to allow the light rays to exit the core (10; 111) via a lateral exit face whose normal is perpendicular to said main axis (D1; D2),
characterized in that the light guide (6; 105) further comprises a multilayer structure (12; 110) attached to the core (10; 111) and comprising a substrate (14), a reflective layer (16), and a layer of electrochromic material (18) comprising at least one cell (P ₁ , P ₂ , P ₃ ), said at least one cell (P ₁ , P ₂ , P ₃ ) comprising at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113), each electrochromic element (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) or said at least two electrochromic elements being encapsulated in a layer of electrolyte which is connected to a pair of electrodes capable of receiving an electrical voltage, each electrochromic element being capable of receiving light rays incident via a surface (18B) and returning light rays among the light rays incident from said surface (18B), said returned light rays having a wavelength included in an interval defined at least by a thickness of the layer of electrochromic material, said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) having distinct thicknesses when no electrical voltage is applied thereto, such that the light rays from the white light source beam and/or from the external natural light source and reflected by the reflective layer (16) emerge from said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) in the core (10 ; 111) of the light guide (6 ; 105) respectively with a first and a second predetermined wavelength in the visible spectrum, the light rays then emerging from said at least one cell (P ₁ , P ₂ , P ₃ ) with a first predetermined color corresponding to a mixture between the colors associated with said first and second predetermined wavelengths;
and in that the light device (1; 20) further comprises an electrical control circuit (4) connected to the electrodes of said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) and configured to control the electrical voltage at the terminals of the or each pair of electrodes, the electrical voltages imposed by the electrical control circuit (4) on the electrodes of said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) being equal, such that when the electrical control circuit (4) imposes a predefined electrical voltage value at the terminals of the respective pair(s) of electrodes of said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113), the light rays coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer (16) emerge from said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) in the core (10 ; 111) of the light guide (6 ; 105) respectively with a third and a fourth predetermined wavelength in the visible spectrum, and when said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) are powered simultaneously, the light rays emerge from said at least one cell (P ₁ , P ₂ , P ₃ ) with a second predetermined color, distinct from the first color and corresponding to a mixture between the colors associated with said third and fourth predetermined wavelengths. Luminous device (1; 20) according to claim 1, in which the layer of electrochromic material (18) is structured into a plurality of cells (P ₁ , P ₂ , P ₃ ) of identical composition. Luminous device (1; 20) according to claim 2, in which each cell (P ₁ , P ₂ , P ₃ ) comprises three electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113), the three electrochromic elements of the same cell having distinct thicknesses when no electrical voltage is applied to them; wherein, for each cell (P ₁ , P ₂ , P ₃ ), when no electrical voltage is applied to the three electrochromic elements of the cell, the light rays from the white light source beam and/or from the external natural light source and reflected by the reflective layer (16) emerge from the electrochromic elements in the core (10; 111) of the light guide (6; 105) respectively with a first, a second and a third predetermined wavelength corresponding respectively to the magenta color, the cyan color and the yellow color in the visible spectrum, the light rays then emerging from the cell (P ₁ , P ₂ , P ₃ ) with a black color corresponding to a mixture between the magenta, cyan and yellow colors; and wherein the electrical control circuit (4) is configured such that, for each cell (P ₁ , P ₂ , P ₃ ), when the electrical control circuit (4) applies said electrical voltage value to a first electrochromic element (E ₁ , E ₄ , E ₇ ) of the cell, to a second electrochromic element (E ₂ , E ₅ , E ₈ ) of the cell or to a third electrochromic element (E ₃ , E ₆ , E ₉ ) of the cell, the light rays from the white light source beam and/or from the external source of natural light and reflected by the reflective layer (16) emerge from the corresponding element (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) into the core (10 ; 111) of the light guide (6 ; 105) with respectively a fourth, a fifth or a sixth predetermined wavelength corresponding respectively to the blue color, green color or red color in the visible spectrum, and when the three electrochromic elements of the cell (P ₁ , P ₂ , P ₃ ) are powered simultaneously, the light rays emerge from the cell (P ₁ , P ₂ , P ₃ ) with a white color corresponding to a mixture between the blue, green and red colors. Luminous device (1; 20) according to one of the preceding claims, in which the electrochromic material belongs to the family of organic transparent conductive oxide materials, in particular a transparent conductive polymer of the PEDOT:PSS, PEDOT:Tos, T34bT, or cellulose type. Luminous device (1) according to one of the preceding claims, in which the core (10) of the light guide (6) is a core of diffusing and/or flexible optical fiber, the main axis (D1) along which the core (10) of the light guide (6) extends being a longitudinal axis. Luminous device (20) according to one of claims 1 to 4, in which the core (111) of the light guide (105) is a film, the main axis (D2) along which the core (111) of the light guide (105) extends forming a privileged axis of propagation of light within said film (111), the light rays coming from the white light source beam propagating in said core (111) along said main axis (D2) by total internal reflection. The light device (20) of claim 6, wherein the light guide (105) further comprises at least one group (120) of light injection elements (120.1) arranged adjacent to an edge of the film (111), said at least one light source being coupled to said at least one group (120) of light injection elements (120.1) such that light rays from the light source (28) are totally reflected within the light injection elements (120.1) and are redirected towards the film (111). The light device (20) of claim 6, wherein the light device (20) comprises a plurality of light sources aligned transversely to the main axis (D2) at one edge of the film. Luminous device (20) according to one of claims 6 to 8, in which the multilayer structure (110) forms a sheet, for example a substantially rectangular sheet, said sheet (110) being in shape correspondence with the film (111). Luminous device (1; 20) according to one of the preceding claims, in which said predefined electrical voltage value is between -1 V and + 1 V. Luminous device (1; 20) according to one of the preceding claims, in which the substrate (14) of the multilayer structure (12; 110) is provided with a power supply sheet connected on the one hand to the electrical control circuit (4) and on the other hand to the terminals of the or each pair of electrodes. A light device (1; 20) according to claim 11, wherein the power supply sheet consists of a flexible printed circuit board or a film on which electronic components are printed. Vehicle comprising a lighting device (1; 20) according to one of the preceding claims. Method for controlling a vehicle lighting device (1; 20) according to one of claims 1 to 12, the method being implemented by the electrical control circuit (4) and being characterized in that it comprises a step of controlling the simultaneous piloting of the electrical voltages at the terminals of the respective pair(s) of electrodes of said at least two electrochromic elements (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) of said at least one cell (P ₁ , P ₂ , P ₃ ), as a function of a setpoint, said setpoint being such that the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer (16) emerges from each electrochromic element (E ₁ , E ₂ , E ₃ ,…E ₉ ; 113) in the core (10; 111) of the light guide (6; 105) with the third or the fourth predetermined wavelength, said setpoint being the predefined electrical voltage value, the light emerging from said at least one cell (P ₁ , P ₂ , P ₃ ) in the core (10; 111) of the light guide (6; 105) with the second predetermined color in the visible spectrum. Method according to claim 14 when the light device (1; 20) is according to claim 3, in which, during the control step, the three electrochromic elements of the same cell (P ₁ , P ₂ , P ₃ ) are supplied simultaneously, such that when the electrical control circuit (4) imposes the predefined electrical voltage value at the terminals of the respective pair(s) of electrodes of said three electrochromic elements of the cell (P ₁ , P ₂ , P ₃ ), the light coming from the white light source beam and/or from the external source of natural light and reflected by the reflective layer (16) emerges from the corresponding cell (P ₁ , P ₂ , P ₃ ) in the core (10; 111) of the light guide (6; 105) with a white color in the visible spectrum. Use of a light device (1; 20) according to one of claims 1 to 12 for performing a photometric lighting and/or signaling function of a vehicle, in particular a direction indicator function of the vehicle.