## 3 Results and Discussion
### Light-Induced Colour Changes in the Coated Wood Surfaces
These were maximal after the first 24 h of exposure and consisted mainly in slight darkening (\(\Delta\)L* negative) and yellowing (\(\Delta\)b* positive). By further light exposure, the initial trend reversed twice. Redness evolved similarly but the changes were very low, close to zero. Consequently, the total colour changes (\(\Delta\)E) after 72 h light exposure for the three types of finishing films were very low: 1.30 units for F1(acrylic-polyurethane), 1.25 units for F2 (acrylic) and 1.07 units for F3 (polyurethane). However, these differences in the means for the three types of coatings were not statistically significant when analysed by one-way Anova in conjunction with [PERSON]'s HSD post hoc test (\(p\) values higher than 0.05 at a significance level \(\alpha\) = 0.05). These low values demonstrate a fairly good colour stability to light exposure for all the tested coating materials. It would result, therefore, in a minimal contribution by the coating films to the overall colour changes in the wood coated surfaces, which strengthens the previous finding about the major contribution of the wood substrate to the total colour changes in the coated wood surfaces. However, the spectral properties of the coating films, meaning their specific capacity of absorbing, transmitting or reflecting/dispersing the UV-VIS radiation remain a key point in understanding and potentially controlling the colour changes in the substrate under the coating films and, finally, of the coated wood surfaces. These issues will be approached in future research. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{6}{c}{**Anova: Two-Factor with Replication (\(\alpha\) = 0.05)**} \\ \hline
**Source of Variation** & **SS** & **df** & **MS** & **F** & \(p\)**-Value** & **F Crit** \\ \hline Wood species (1) & 44.95563 & 2 & 22.47781 & 12.13096 & 2.88142 \(\times\) 10\({}^{-5}\) & 3.123907 \\ Type of coating (2) & 13.78771 & 2 & 6.893853 & 3.720516 & 0.028997068 & 3.123907 \\ Interaction (1)x(2) & 18.01943 & 4 & 4.504858 & 2.431209 & 0.055229542 & 2.498919 \\ Within & 133.4109 & 72 & 1.852929 & & & \\ Total & 210.1737 & 80 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of two-factor Anova test results with replication of the colour change values \(\Delta\)E, after 72 h light exposure, in the areas V1/Z1, considering the wood species (1) and the type of coating (2) as influencing factors. (\(\alpha\)-0.05). Influence of Wood Species and Coating Materials on the Light-Induced Colour Changes in Wood Surfaces  
The experimental results presented and discussed so far highlighted, in most cases, some protective effect of the three types of waterborne coatings (F1-acrylic-polyurethane, F2-acrylic, F3-polyurethane) against the UV-VIS light-induced colour changes in the wood substrates from the three wood species (maple, ash, walnut) under study. This protective effect was dependant on both the coating film and the wood species, which demonstrated different sensitivity to light-induced colour changes, in accordance with the previous research [22; 24; 53]. In order to have a cumulative and comparative image of the effect of clear coating on the colour stability of wood surfaces when exposed to light in indoor conditions, the data on the colour changes (\(\Delta\)E, \(\Delta\)L*, \(\Delta\)a*, \(\Delta\)b*) after 72 h light exposure in the conditions of this research are cumulated in Table 5. The data for uncoated and coated samples (F1, F2, F3) of the three species were also included to allow a final discussion on the influence of both wood species and type of coating. Lower values in colour changes (\(\Delta\)E, \(\Delta\)L*, \(\Delta\)a*, \(\Delta\)b*) mean better colour stability so that the effects of the above-mentioned influencing factors can be easily observed. The statistical significance of the differences between the mean  
Figure 7: Light-induced colour changes in coating films applied on clear glass slides: (**A**). acrylic-polyurethane lacquer F1; (**B**). acrylic lacquer F2; (**C**).