## 6 Discussion and Conclusions
In most cases, the shift of the dominant spectrum components towards higher frequencies is observed as the supply voltage increases. Occasionally, though, the direction changes, especially at high supply voltages compared to the nominal value (the case with the CFL lamp). Despite the limited number of tested devices, the presented development leads to further hypotheses that broadband disturbances might be examined throughout the range of permissible voltage supply levels. Current standards ensure the safe use of electrical devices in the power grid environment. Meeting both groups of standards, i.e., emissions and immunity, allows, among other things, to obtain an EU declaration of conformity (DoC). However, there is some divergence between the requirements of the test conditions for immunity and emissions. Emission testing is usually performed under nominal conditions, which in the case of European power networks means 230 V, 50 Hz. At the same time, the statistics of permissible voltage changes in the power grid environment indicate possible voltage changes in the range of \(\pm\)10% of the rated voltage. Therefore, the immunity tests are performed in conditions even going beyond the \(\pm\)10% margin. There is a certain gap between the power supply conditions for immunity and emission tests. One of the motivations is that the design process of electrical equipment nowadays is efficient and able to meet the permissible limits formulated in the existing standards. However, at the same time, it can be stated that the spectrum of modern technologies permanently increases as well as the density of electrical equipment in electrical networks. It formulates an assumption for the realistic scenario of the particular equipment or concentrations of equipment that will not meet the standards when the voltage conditions are not nominal, as already stated in standardized emission tests. The presented results confirmed the influence of power supply conditions on emission levels. Additionally, the presented results support efforts addressed to digital twins of electrical equipment. Described relations between supply voltage level and spectrum of emission can also be useful for designers of filters dedicated to power line communication technologies. Achieved knowledge showing the shift in the dominated bandpass frequencies of non-intentional conducted disturbances emitted by the investigated light sources can be implemented to improve the reliability of intentional transmission. The intention of the presented investigations is mostly to indicate the gap between the laboratory test conditions and real working conditions and their impact on the emission of electrical devices. The aim is to uncover the trend of emission levels in the function of voltage supply conditions. From this point of view, more crucial is the variety of conditions instead of the number of devices investigated. Once trends are observed, it is planned that future research should expand the approach to include statistical evaluation. More statistically meaningful data should be gathered to obtain significant data as a base for deriving broader conclusions. Another hypothesis can be related to a mixed load situation when loads of various sizes and power ratings are connected to the same point of common coupling. The emission at the terminal of a device might be higher than that of the whole electrical installation. Thus, it is especially crucial to consider the emission levels at the terminal of the device. Conceptualization, W.F. and L.M. ; methodology, T.S. ; software, P.K. ; validation, D.K., L.M. and W.F. ; formal analysis, W.F., L.M. and D.K. ; investigation, W.F., L.M. and D.K. ; resources, T.S. ; data curation, P.K. ; writing--original draft preparation, L.M and W.F. ; writing--review and editing, L.M and W.F. ; visualization, W.F. and L.M. ; supervision, P.K. and T.S. ; project administration, D.K. ; funding acquisition, T.S. All authors have read and agreed to the published version of the manuscript.