Photodegradation of Unmodified and Thermally Modified Wood Due to Indoor Lighting

Considering interior applications, sunlight, both direct through open window and through window glass, and artificial lighting are the main sources of radiation possessing sufficient energy to trigger photodegradation processes in wood. LED lamps, which emit mostly visible light, are becoming the dominant artificial light source in various interiors. In the present study, photodegradation of thermally modified (TM) and unmodified (UM) ash (Fraxinus excelsior), aspen (Populus tremula), and pine (Pinus sylvestris) due to exposure to UV radiation and LED lamps was evaluated and compared by analysing wood discolouration (CIELAB colour space), changes in reflectance and FTIR spectra, and formation of water-soluble components. The results show that, apart from UV radiation, LED lamps may cause considerable photodegradation of both TM and UM wood resulting in visually perceptible colour change, alteration in chemical structure and formation of water-soluble components. Improved photo-stability was observed for TM wood exposed to UV radiation, while even more changes in FTIR spectra were detected for TM than UM wood in the experiment with LED lamps. Comparing TM and UM wood, the changes due to photodegradation were quite similar for TM wood of all species while significant differences were observed in the case of UM wood.