## 7 Conclusions  
This article has provided an analysis concerning the manner in which automotive VLC systems could be used in light dimming conditions. This can be useful for improving road safety in a variety of scenarios. A broken-down car on the side of the road in the middle of the night could turn on the car's lights-off VLC warning when the battery reaches the minimum allowed voltage instead of shutting down the lights completely.  
Based on the experimental results provided by this article, one can consider that the use of VLC technology in V2V applications is highly promising, even in light-dimming conditions. The intensive evaluation showed that in low to high parasitic lighting conditions, an automotive VLC system can maintain a \(10^{-6}\) BER even when the duty cycle decreases down to 1%. On the other hand, in cases of direct exposure to sunlight, a reduced duty cycle can affect the reliability of the VLC link, affecting the communication distance and increasing the BER.  
Future work on this project will be focused on achieving higher resolution dimming and on evaluating the effects of lights-off communication on the V2V VLC link performances. Toward this aim, the duty cycle should be further decreased in order to be perceived by the human eye as being off. According to [32], LEDs appear to be off for the human eye when a duty cycle of 0.007% is achieved. Nevertheless, general-purpose high-power LEDs, such as the ones used in vehicle lighting systems, have switching times in the 0.1-1 \(\upmu\)s range. Therefore, if the duty cycle is further reduced, the pulse width will be lower than the LED switching time. However, higher resolution dimming could still be achieved by further increasing the bit duration, which is equivalent to a data rate decrease. Nevertheless, further reducing the data rate below 10 kb/s seems inappropriate because such an approach would increase the message latency above the limits accepted by vehicle safety applications, so other modulation techniques must be taken into consideration for better results [15].  
Another step of this project will be to find the optimal ratio for the duty cycle between maximum and minimum intensity of light, in a scenario where the driver is not braking, but the stop lights of the car still transmit the data with an intensity of modulated light dimmed at a level that can be considered as position lights by the current regulations.  
Conceptualization, C.B. and A.-M.C.; methodology, A.-M.C.; software, S.-A.A.; validation, A.-M.C. and M.D.; formal analysis, C.B.; investigation, S.-A.A. and C.B.; resources, M.D.; data curation, C.B. and A.-M.C.; writing--original draft preparation, C.B. and A.-M.C.; writing--review and editing, S.-A.A., C.B., and A.-M.C.; visualization, S.-A.A. and C.B.; supervision, A.-M.C. and M.D.; project administration, M.D.; funding acquisition, A.-M.C. and M.D. All authors have read and agreed to the published version of the manuscript.  
This work was founded by a grant of the Romanian Ministry of Research and Innovation, CCCDI--UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0917, contract 21 PCCDI/2018, within PNCDI III. Part of this work was also supported by Romania National Council for Higher Education Funding, CNFIS, project number CNFIS-FDI-2021-0357.  
Not applicable.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.