FR 3110955 A1 20211203 FR 2005612 A 20200527 The invention provides an automotive lighting device (10) comprising a circuit element (1), a solid-state light source (2) and a radiation layer (3). The circuit element comprises a first face (11), a second face (12) opposite to the first face and a side edge (13). The solid-state light source (2) is arranged in the first face of the circuit element (1). The radiation layer (3) is arranged on the second face (12) of the circuit element, wherein the radiation layer (3) has an emissivity higher than 0.5 and more particularly, higher than 0.8. Figure pour l’abrégé : figure 1a Automotive lighting device This invention is related to the field of automotive lighting devices, and more particularly, to the temperature management of these devices. Automotive lighting market can be considered one of the most competitive ones and new lighting functionalities are constantly required. However, heat dissipation is a phenomenon common to all the lighting devices having solid-state light sources. Heat dissipation is traditionally carried out by some conductive elements which dissipate the heat produced by the light source. This heat is conveyed by means of thermal conduction until it arrives to the main heatsink. The main heatsink comprises elements to increase the heat dissipation by thermal convection, for an efficient heat transmission between the lighting device and the surrounding air. However, these heatsinks are heavy and voluminous, so they affect negatively to the position of other elements within the lighting device. This problem has been assumed until now, but a solution therefor is sought. The invention provides an alternative solution for this problem by an automotive lighting device comprising a circuit element with a first face, a second face opposite to the first face and a side edge; at least a solid-state light source arranged in the first face of the circuit element; and a radiation layer arranged on the second face of the circuit element, wherein the radiation layer has an emissivity higher than 0.5 and more particularly, higher than 0.8. The term "solid state" refers to light emitted by solid-state electroluminescence, which uses semiconductors to convert electricity into light. Compared to incandescent lighting, solid state lighting creates visible light with reduced heat generation and less energy dissipation. The typically small mass of a solid-state electronic lighting device provides for greater resistance to shock and vibration compared to brittle glass tubes/bulbs and long, thin filament wires. They also eliminate filament evaporation, potentially increasing the lifespan of the illumination device. Some examples of these types of lighting comprise semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma or gas The circuit element may be a printed circuit board or a similar element which performs the function of providing physical support and electrical connections to the light sources. This lighting device does not need a heavy heat sink, since the radiation layer is in charge of dissipating the heat by radiation, instead of by convection, as traditional heat sinks do. This means saving weight and volume in the lighting device. In some particular embodiments, the first face of the circuit element comprises a copper layer and the at least one solid-state light source is arranged in the copper layer by means of a solder mask. This way of attaching the solid-state light sources to the copper layer of the first face of the base may be also used with the present invention. In some particular embodiments, the second face of the circuit element comprises a metallic base which is attached to the copper layer by means of a dielectric element. The metallic base provides a mechanic support for the elements which are attached thereto, since the mechanical stability is important to keep the projected light source in the correct direction. In some particular embodiments, the radiation layer is directly deposited on the metallic base. This direct deposition is useful to avoid any intermediate layers, which may affect to the heat dissipation and add weight and volume to the lighting device. In some particular embodiments, the radiation layer comprises resin and/or a polyamide, and/or a ceramic compound and/or talc and/or a paint coating. These are advantageous examples of materials to be used in the lighting device of the invention, due to their emissivity and easiness of use in automotive applications. In some particular embodiments, the metallic base comprises aluminium and/or an aluminium alloy. In some particular embodiments, the radiation layer is obtained by processing the second face of the circuit element. This alternative is interesting since it does not involve the use of a different material, but just working on the existing elements. In some particular embodiments, the process comprises an oxidation, corrosion or anodising of the second face of the circuit element. All of these processes are aimed to increase the emissivity of the metallic base and then increase the heat dissipation. In some particular embodiments, the automotive lighting device further comprises a sealing element which is arranged in contact with the circuit element to provide a seal of the lighting device. This sealing element provides the support to act as a watertight cap in the lighting device. This allows a totally new concept in the building of a lighting device, since no additional cap is needed. In some particular embodiments, the radiation layer has a thickness comprised between 0.5 and 2 mm. This thickness is enough to convey the heat produced by the light sources. In some particular embodiments, the solid-state light source is configured to be part of a daytime running light functionality, a position light or a turn indicator functionality. This lighting device is suitable to be used both with daytime running light functionality and turn indicator arrangements, since it does not affect the zones where the light sources are installed. In some particular embodiments, the automotive lighting device further comprises an optical element suitable for receiving light emitted by the light source and for shaping the light into a light pattern projected outside the lighting device. An optical element is an element that has some optical properties to receive a light beam and emit it in a certain direction and/or shape, as a person skilled in automotive lighting would construe without any additional burden. Reflectors, collimators, light guides, projection lenses, etc., or the combination thereof are some examples of these optical elements. Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealised or overly formal sense unless expressly so defined herein. In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures: and [Fig 1b] show a front view and a rear view of some elements of a particular embodiment of an automotive lighting device according to the invention. shows a transverse cut of the circuit board of a particular embodiment of an automotive lighting device according to the invention. and [Fig 3b] show a front view and a rear view of a particular embodiment of an automotive lighting device according to the invention. shows an automotive vehicle comprising an automotive lighting device as described in the previous figures. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate: 1 Printed circuit board 2 LED 3 Radiation layer 4 Sealing joint 5 Reflector 6 Copper layer 7 Solder mask 8 Aluminium base 10 Automotive lighting device 11 First face of the printed circuit board 12 Second face of the printed circuit board 13 Side edge of the printed circuit board 100 Automotive vehicle The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein. Accordingly, while embodiment can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate. and [Fig 1b] show a front view and a rear view of some elements of a particular embodiment of an automotive lighting device according to the invention. Firstly, there is a printed circuit board 1 comprising a first face 11, a second face 12 opposite to the first face 11 and a side edge 13. The first face 11 comprises a copper layer and a plurality of LEDs 2 arranged on the copper layer by means of a solder mask. The second face 12 comprises an aluminium base and a radiation layer 3 which has been directly deposited on it, so only the side 13 of the aluminium base is seen. This radiation layer comprises an emissive paint coating with an emissivity around 0.8 and a thickness of about 1 mm. Other materials are also suitable for this purpose, while their emissivity is higher than 0.5. In fact, in other embodiments, there is not a deposited layer as such, but is the back surface of the aluminium base which is modified to improve the emissivity on this face of the printed circuit board 1. The LEDs 2 generate an amount of heat while their normal operation. However, their temperature must stay under control, since an excessive temperature would affect to their operation and may even cause the failure of the LED. There are derating protocols to decrease the current of the LED in the event this temperature overcomes a predetermined threshold. This heat is transmitted by conduction to the aluminium base and then to the radiation layer 3. The radiation layer 3 dissipates the heat by radiation, without the need of an airflow or an air volume to receive this heat. This contributes to a lighter and smaller lighting device. shows a transverse cut of the printed circuit board 1 of a particular embodiment of an automotive lighting device according to the invention. This lateral view shows the different elements which were presented in the previous figures. The printed circuit board 1 comprises a first face 11 and a second face 12 opposite to the first face 11. The first face 11 comprises a copper layer 6 and a plurality of LEDs 2 (only one of them is shown in this figure) arranged on the copper layer 6 by means of a solder mask 7. In turn, the second face 12 comprises an aluminium base 8 and a radiation layer 3 which has been directly deposited on it. In this figure, it is more clearly shown how the heat generated by the LEDs 2 is transmitted by conduction to the aluminium base 8 and then to the radiation layer 3. The radiation layer 3 dissipates the heat by radiation, without the need of an airflow or an air volume to receive this heat. Further, this printed circuit board 1 may act as a cap for a lighting device 10, as seen in and [Fig 3b]. A sealing joint 4 is placed in contact with the printed circuit board 1 to create a watertight assembly with the rest of the housing of the lighting device 10. The LEDs 2 of the lighting device 10 are intended to provide a daytime running light functionality. For this aim, a light guide 5 is also provided in the lighting device 10, to receive the light produced by the LEDs 2 and project it as a daytime running light pattern outside the lighting device 10. shows an automotive vehicle 100 comprising an automotive lighting device 10 as described in the previous figures. The assembly of this lighting device 10 may be lighter and smaller than the traditional ones, thus decreasing the volume and weight of the lighting device and offering more design possibilities to the car manufacturer. Automotive lighting device (10) comprising a circuit element (1) with a first face (11), a second face (12) opposite to the first face and a side edge (13); at least a solid-state light source (2) arranged in the first face of the circuit element (1); and a radiation layer (3) arranged on the second face (12) of the circuit element, wherein the radiation layer (3) has an emissivity higher than 0.5 and more particularly, higher than 0.8. Automotive lighting device (10) according to claim 1, wherein the first face of the circuit element (1) comprises a copper layer (6) and the at least one solid-state light source (2) is arranged in the copper layer by means of a solder mask (7). Automotive lighting device (10) according to claim 2, wherein the second face (12) of the circuit element (1) comprises a metallic base (8) which is attached to the copper layer (6) by means of a dielectric element. Automotive lighting device (10) according to claim 3, wherein the radiation layer (3) is directly deposited on the metallic base (8). Automotive lighting device (10) according to claim 4, wherein the radiation layer comprises resin and/or a polyamide, and/or a ceramic compound and/or talc and/or a paint coating. Automotive lighting device (10) according to any of claims 3 to 5, wherein the metallic base (8) comprises aluminium and/or an aluminium alloy. Automotive lighting device according to any of the preceding claims, wherein the radiation layer (3) is obtained by processing the second face (12) of the circuit element. Automotive lighting device according to claim 6, wherein the process comprises an oxidation, corrosion or anodising of the second face (12) of the circuit element. Automotive lighting device according to any of the preceding claims, further comprising a sealing element (4) which is arranged in contact with the circuit element (1) to provide a seal of the lighting device (10). Automotive lighting device according to any of the preceding claims, wherein the radiation layer (3) has a thickness comprised between 0.5 and 2 mm. Automotive lighting device (10) according to any of the preceding claims, wherein the solid-state light source (2) is configured to be part of a daytime running light functionality, a position light or a turning indicator functionality. Automotive lighting device (10) according to any of the preceding claims, further comprising an optical element (5) suitable for receiving light emitted by the light source (2) and for shaping the light into a light pattern projected outside the lighting device (10).