## 4 Discussion  
The core of this study was to explore the influence of different engine types on the thermal behavior of vehicle headlamps. Specifically, the research questions aimed to determine the following:  
1. Whether the temporal proportion (TP) within different temperature classes (TCs) is affected by the type of engine, comparing battery electric vehicles (BEVs) with internal combustion engine (ICE) vehicles. 2. Whether the temporal proportion (TP) across different temperature classes (TCs) is influenced when BEVs and ICE vehicles are considered separately. 3. Whether ambient vehicle temperatures (ATs) affect the temporal proportion (TP) within different temperature classes (TCs). Figure 9: The calculated temperature center of gravity in the headlamps of the respective ambient temperature classes for ICEs and BEVs along with their linear fit for BEVs (light blue) and ICEs (dark blue). Answering research questions 1 and 2, the analysis of the temperature distribution in the headlights of BEVs and ICE vehicles shows clear differences between the two types of vehicles. The results suggest that BEV vehicles tend to have lower temperatures in their headlights than ICE vehicles. This could be due to the different heat sources and cooling mechanisms of the two vehicle types. While BEVs do not have combustion engines and therefore produce less waste heat, ICE vehicles can reach higher temperatures in the engine compartment and near the lighting units due to the combustion engine and its waste heat. These variations were particularly evident during driving when the temperature data were collected. Regarding research question 3, the statistical analysis using a mixed linear model (MLM) confirmed the significant differences between the temperature classes and showed that the interaction between engine type and ambient temperature class has a significant influence on the temperature distribution. The results of the three-way interaction indicate that the ambient temperature class modulates the effect of engine type on headlamp temperature. This may indicate that the thermal management strategies of the vehicles vary at different ambient temperatures and thus influence the temperature inside the headlamp. However, the lack of convergence of the MLM indicates that the model may not have captured all the relevant variables or interactions. This could be due to the complexity of the data structure or insufficient model specification. Future studies should therefore improve the modelling and possibly consider additional factors that could influence the temperature in the headlamps. The regression analysis shows that as the ambient temperature increases, so does the temperature inside the headlamp. This is consistent with the expectation that higher ambient temperatures lead to higher operating temperatures in the vehicle. The high R\({}^{2}\) values for BEVs and ICEs indicate that the headlamp temperature is linearly related to the ambient temperature. This could be important for the development of cooling systems and thermal management strategies, as it indicates a predictable relationship between the ambient temperature and headlamp temperature. A comparison of the delta of the centroid temperature between the BEVs and the ICEs showed a temperature difference of around 5 \({}^{\circ}\)C.  
Compared to other studies in this research field, the results of the current analysis align with the findings presented by [PERSON], [PERSON], and [PERSON] from Audi AG, reinforcing the claim that battery electric vehicles (BEVs) tend to have a lower thermal load on headlamps when compared to internal combustion engine vehicles (ICEVs). Overall, the results emphasize the importance of thermal management in vehicles, particularly with regard to the reliability and longevity of headlamp systems. The differences in the temperature distribution between BEVs and ICEs could also have an impact on headlamp design requirements.