## 4 Conclusions  
The scientific contribution of this paper is to present the impact of technological parameters in UV surface refinement using a paint line containing LED and mercury lamps.  
In conclusion, this study indicates the intricate relationship between technological and process parameters in UV surface refinement, offering valuable insights into the optimization of paint line processes using LED and mercury lamps. The findings of this research not only contribute to the current body of knowledge, but also hold significant practical implications for the manufacturing and coating industries, particularly in the context of achieving desired colour coordinates and gloss levels. In essence, this study serves as a stepping stone toward a future where UV surface finishing becomes not only more technologically advanced but also environmentally conscious and economically viable.  
Based on the results of the study, the following conclusions can be drawn:  
* The number of varnish overlays used and the amount of the applied topcoat and basecoat had the greatest impact on colour coordinates L* and b*. Higher coordinates were obtained as the number of overlays and the number of varnishes increased. The interactions between the spread rates of varnish and the mercury lamp power were statistically significant. Increasing the lamp power contributed to the increase in colour coordinates.
* It was estimated that to obtain the highest possible parameter L* = 94., the number of overlays could be increased from 5 to 6, while reducing the amount of the applied basecoat by 10 g/m\({}^{2}\) (from 50 g/m\({}^{2}\) to 40 g/m\({}^{2}\)).
* The statistically significant factors affecting the coatings' gloss were the spread rate of the applied topcoat, the abrasive used, the number of coats used and the mercury lamp power used in the process. An increase in gloss occurred with an increase in the spread rate of the applied topcoat, the number of coats and the abrasive grit size. The mercury lamps were also part of a significant interaction with the amount of the topcoat. The gloss increased as the lamps' power and the spread rate of the topcoat increased.
* LED lamp power did not affect the coatings' optical parameters. A high share of LED lamps in the painting line ensures a higher process stability. Moreover, it can be stated that LED lamps still do not affect the coatings' optical parameters, despite the passage of time and the power reduction, which may be a good prognosis for the extension of LED lamp life. It can also represent a large amount of savings due to the high price of LED modules.  
Conceptualisation, M.H. and T.K.; methodology, M.H., B.L. and T.K.; software, M.H.; validation, M.H., B.L. and T.K.; formal analysis, M.H.; investigation, M.H.; resources, M.H., B.L. and T.K.; data curation, M.H.; writing--original draft preparation, M.H., B.L. and T.K.; writing--review and editing, M.H., B.L., E.A.S. and T.K.; visualization, M.H.; supervision, B.L. and T.K.; project administration, B.L. and T.K.; funding acquisition, E.A.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the funding for PhD students under No. 953.224.012 of the Faculty of Forestry and Wood Technology, Poznan University of Life Sciences.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.