## 4 Conclusions  
The paper investigated comparatively the light-induced colour changes for three hardwood species, namely, European map (_Acer pseudoplatanus_ L.), European ash (_Frazinus exelsior_ L.) and European walnut (_Juglans regia_ L.), as well as the influence of finishing with three types of clear, colourless waterborne lacquers (F1: acrylic-polyurethane, F2: acrylic, F3: polyurethane) on their colour stability. Colour measurements in the CIELab system in conjunction with an artificial accelerated ageing test under the action of UV-VIS radiation, simulating natural light passing through window glass, and two types of test samples were employed to highlight the influence and contributions of the wood substrate and of the coating films to the global colour modifications. Coating films applied on 1 mm clear glass slides were employed as a sort of \"detachable\" finish for this purpose. A different transmittance of the UV and VIS radiation from the artificial source through this glass support and a decrease in light intensity reaching the substrate is a limitation of the experimental method employed, which has to be considered in future research. Direct exposure to UV-VIS light caused visible colour changes for both uncoated and coated wood surfaces, the values of the calculated colour differences (\(\Delta\)E) after 72 h exposure being dependant on both the wood species and the coating material, which were found to be statistically significant influencing factors in interaction. Excepting two situations for walnut, statistically significant higher colour differences were obtained for the uncoated samples: maple (9.36 units), ash (8.39 units), walnut (6.20 units), compared to the coated ones: maple (4.92-5.71 units), ash (2.25-3.94 units), walnut (4.74-7.70 units), depending on the type of coating. From the three coating materials tested, the waterborne polyurethane lacquer represents a good option for all the wood species. The effect of each coating material tested depended on the wood species, as a more powerful influencing factor. The interaction between the wood substrate and the coating material at the interface level needs further investigation. The wood substrate underlying the coating film was found to bring the maximum contribution to the overall colour changes in the clear-coated surfaces, the actual \(\Delta\)E values being influenced by the wood species and the coating film as significant factors. The colour changes \(\Delta\)E in the wood substrates under the simulated \"detachable\" coating films varied in the ranges 4.44-6.02 units for maple, 2.97-4.43 units for ash and 4.51-5.93 units for walnut. The coating films employed in this research demonstrated a fairly good colour stability to UV-VIS light exposure, with colour changes (\(\Delta\)E) up to only 1.30 units, with no statistically significant differences. These results will be employed as a basis for further research looking at efficient methods to stabilise the natural colour of the clear coated wood surfaces against the effect of light in indoor applications, considering the specific contributions of the wood substrate and of the coating films, as well as the particularities of each wood species in relation to their chemical composition. Conceptualisation: M.-J.T. and M.C.T. ; methodology: M.-J.T. and M.C.T. ; supervision: M.C.T., preparation of test samples: M.-J.T. ; colour measurements: M.-J.T. ; data processing: M.-J.T. and M.C.T. ; graphs: M.-J.T. ; writing and editing draft version: M.-J.T. ; revisions: M.C.T. All authors have read and agreed to the published version of the manuscript. This research is part of a budget funded Ph.D. research project undertaken by the principal author within the Doctoral School of the Transilvania University of Brasov-Romania. Not applicable. The data presented in this study are available within the article. The authors would like to express their sincere thanks to the company \"Craiul Muntilor SRL.\", Stuparei village, Valcea county, Romania, for providing the wood material for this research.