## 1 Introduction  
In the context in which the demand for wireless communication technologies is exponentially increasing in almost every domain [1; 2; 3], the 300 GHz radio-frequency (RF) and Microwave bandwidth becomes insufficient [4]. Thus, the usage of optical wireless communications (OWC) technologies [5] has become a promising alternative, as it provides almost unlimited bandwidth (i.e., more than 2000 times greater than RF and Microwave). Among OWC technologies, visible light communications (VLC) are of special interest from various points of view, providing the simultaneous usage of the visible light (380-780 nm) for illumination and communication purposes [6; 7]. This dual use provides a significant energy efficiency, which is also improved by the use of solid state lighting sources providing cost-effective lighting and fast switching performances [8]. Moreover, the implementation cost of this communication technology is also reduced, because, unlike the RF and Microwave spectrum, the visible light spectrum is unregulated and, thus, communication licensing costs are eliminated. In addition to these technical advantages, a significant quality of VLC is that, unlike other communication technologies [9; 10], this one is completely safe for human health. Based on the upper-mentioned advantages, VLC technology is suitable for numerous applications. Thus, indoor VLC usage focuses on high data rate applications [11; 12; 13] and indoor localization [14; 15]. On the other hand, outdoor VLC are strongly orientated toward automotive applications, including here communication-based vehicle safety applications [16; 17; 18] and inter-vehicle distance determination [19; 20]. In these last cases, the use of the VLC technology in automotive applications is strongly favored by the wide distribution of LED lighting sources as part of vehicle lighting systems and transportation infrastructure, as illustrated in Figure 1. In this context, the development of automotive VLC systems emerged as a hot research topic addressing infrastructure to vehicle (I2 V) [16; 21; 22] and vehicle to vehicle (V2V) [18; 23; 24] applications. Regarding vehicular applications, the existing RF-based communication solutions [25; 26] perform well, but they are less reliable in a high vehicle density context [27; 28]. In this situation, VLC-based systems could be used as a standalone solution or as a complementary technology for improved reliability and RF spectrum offloading [17; 27]. The use of VLC in vehicular applications is favored by the specificity of the communications. Unlike RF-based communications, VLC are less affected by problems, like channel congestion, mutual interferences, or multipath. Consequently, the VLC technology could support the requirements that are imposed for vehicular communications in terms of high packet delivery ratio and reduced latencies [29; 30]. VLC are a direct line of sight technology, which means that the problems generated by channel congestion and mutual interferences are mitigated by the spatial isolation between the neighboring VLC channels. The VLC technology is currently considered to have high potential for vehicular applications; however, some are rather reserved regarding its immediate applicability due to existing challenges. An important step in confirming the potential of VLC technology in automotive applications is found in [18]. In this paper, the authors present the conclusions regarding the experimental testing of a V2V VLC link. This system has been tested in the real-world driving scenario and the results showed that VLC can provide almost continuous connectivity, even in mobile conditions and at highway speeds. These tests also indicated that the distance is the main factor affecting the link performances, again pointing out that middle to long range automotive VLC applications remain a challenge in the real-life use case. Figure 1: LED light sources integration in the transportation domain as part of vehicle lighting sources and of the transportation infrastructure.