## 1 Introduction  
Mobility is fundamental for most human activities; thus, the safety of the transportation system is a stringent research topic for the automotive industry, for vehicle manufacturers, and for the academic community. Preoccupation with this aspect has been an important subject for more than a century of automotive history, not only through controlling driver behavior, but also through improvements made in the design of vehicles and road infrastructures. Nowadays, intelligent systems implemented in cars and transport infrastructures are widespread, providing innovative services in terms of safety [1]. Increasing concern in this area has led to the implementation of new concepts, which incorporate state-of-the-art wireless communications technologies that enable smart vehicles to share information with other vehicles and with the transportation network, in order to limit the risk of accidents [2; 3; 4] and to improve the efficiency of road transportation. Being superior to incandescent bulbs and fluorescent tubes in terms of efficiency, life term expectancy, and high tolerance to humidity, LEDs are on the way to becoming the new normal in lighting [6; 7]. Thus, their market share is gradually increasing, as LEDs are replacing other lighting solutions not only in home settings but also in vehicle lighting systems and in transportation lighting infrastructures (see Figure 1). Furthermore, due to their fast-switching ability, LEDs also enable the usage of the visible light spectrum for data transmission, in addition to their main lighting or signaling function. In short, Visible Light Communications (VLC) technology involves a VLC emitter that has a lighting function and a VLC receiver. In order to enable the information transfer, the data to send are modulated onto the VLC emitter's optical carrier at frequencies that are unperceivable by the human eye. The VLC receiver converts the modulated light into an electrical signal, from which data can be extracted by various processing techniques. Thus, the VLC technology can turn virtually any LED light source into a data transmission device, standing out as one of the possible solutions in communication-based vehicle safety applications [1; 4; 5]. In this area, the performances of automotive VLC systems have continuously improved [4; 5; 6; 7; 8; 9; 10; 11], although there are still challenges that require further attention [5]. Therefore, if a vehicle has to deal with an unexpected event, various data, including inter-vehicle distance [12; 13; 14], can be passed to the rear vehicles, in order to avoid an accident or a traffic jam. In road transport applications, there are currently many LED light sources as part of the road infrastructure and of the vehicle lighting systems, so VLC technology is easier to implement [5], while providing many advantages, such as low latencies [10; 11], and being complementarity to 802.11p RF-based technology [15], where the VLC technology can counteract most common vulnerabilities associated with RF interferences in heavy traffic scenarios. Dissimilar to any other wireless communication technology, in VLC, the data carrier is visible to the human eye. Under these circumstances, the IEEE 802.15.7 standard for short-range optical communications [16; 17] introduces strict requirements, according to which the use of a light source in data transmission applications must not affect in any way the main function of the device. As the lighting function is considered of a higher priority compared to the data transmission function, several obstacles emerge, whereas technical solutions have already been found [11; 17; 18]. One of the conditions the standard imposes is related to light dimming. Thus, the VLC emitter must be able to support light dimming while providing optical wireless data transfer. If it is to apply this regulation to vehicular applications, one can understand that light dimming is less stringent, whereas the use cases that could integrate light dimming are less numerous.