## 3 Results and Discussion
### Light-Induced Colour Changes in the Coated Wood Surfaces
However, when compared to the colour differences for wood exposed under clear glass the differences brought about by the coatings applied on glass were very low, as can be observed in Table 3, where the average data after 72 h light exposure are presented. Figure 6: Light-induced colour changes in the wood substrate (uncoated) exposed under the protective effect of the three types of coatings (F1–F3) applied on clear glass slides (SF1, SF2, SF3), comparative to exposure through clear glass slides (S): (**A**)—maple; (**B**)—ash; (**C**)—walnut. Analysis of paired data by using the one-way Anova test at significance level \(\alpha=0.05\) found no statistically significant differences between the mean \(\Delta\)E values in the areas V1/Z1 and V1/Z2 (\(p\) values higher than 0.05), irrespective of the wood species and the type of coating material (F1, F2, F3). This means that no protective effect of the coating films on the colour changes in the wood substrate under the coating could be observed by the applied method. This statistics result was in good accordance with visual perception when analysing comparatively the light-induced colour changes in the areas V1/Z1 and V1/Z2 on the tested samples. On the other hand, the fact that notable colour changes in the wood substrate occurring under the coated glass (V1/Z1) could be observed and quantified represents an important original contribution of this research. Moreover, the wood species and the type of coating were found as statistically significant influencing factors on the colour change values \(\Delta\)E, determined for the V1Z1 areas after 72 h light/UV exposure, when the respective colour data were analysed by the Anova two-factor test with replication (summary in Table 4). The higher F value indicates wood species as a more important influencing factor than the coating film on the colour changes in the underlying substrate. The interaction of the two factors was not found statistically significant. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Wood Species**} & \multicolumn{6}{c}{**Colour Changes after 72 h Light /UV Exposure**} \\ \cline{2-7}  & \multicolumn{4}{c}{**V1/Z2**} & \multicolumn{4}{c}{**V1/Z1**} \\  & \multicolumn{4}{c}{**Uncoated Wood under Clear Glass (Reference Values)**} & \multicolumn{4}{c}{**Uncoated Wood under Coated Glass**} \\ \cline{2-7}  & & **(F1)** & **(F2)** & **(F3)** & **F1** & **F2** & **F3** \\ \hline \multirow{4}{*}{Maple} & \(\Delta\)E & 4.90 & 5.80 & 5.20 & 4.44 & 6.02 & 5.17 \\  &  
The colour changes in the wood substrate due to light exposure under coated glass slides (V1/Z1) were determined as a simulation of the behaviour (contribution) of wood substrate under the coating films (V2/Z1), situations where there is no effect of the glass. Accordingly, the real colour changes in the substrates underneath the coating films and the associated chemical changes should be higher than those determined by the method applied in this research. This major contribution of the wood substrate to the total colour changes in the clear-coated wood surfaces is an important key point in understanding the occurring phenomena with the view of their correction, as also pointed out by the previous research [35; 47]. For equivalence as exposure situations, the colour and related chemical changes in the substrate in the areas V1/Z1 should be comparable with the colour changes in a wood substrate under the coating film after exposure to light passing through a covering clear glass slide, respectively, areas (V2/Z3) in this research. Light-Induced Colour Changes in the Coating Films--Contribution of Finishing Film to the Overall Colour Changes  
The colour changes (\(\Delta\)E, \(\Delta\)L*, \(\Delta\)a*, \(\Delta\)b*) in the finishing films applied on 1 mm clear glass slides as a result of light exposure for different periods of time are presented in Figure 7. It can be easily observed that for all the three types of coatings, there were registered similar wavy patterns in colour changes.