Spectral sensitivity of fir wood surfaces under Xenon light exposure

The wavelength sensitivity of unprotected fir wood surfaces was assessed using a series of glass cut-off filters under which three 80 μm thick radial wood strips formed a composite surface layer of wood exposed to xenon light. Colour and microtensile changes in the different layers followed different patterns and intensities. During exposure, the colour and microtensile changes shifted ever deeper into the surface and further into the visible region of the spectrum. A relatively narrow waveband of most active wavelengths was causing the greatest proportion of the recorded photodegradation (360 – 435 nm), whereas visible light of wavelengths up to 515 nm also contributed significantly to surface damaging. This is an important finding, assuming that the current knowledge implicitly assumes that the actinic effect of light progressively increases with a reduction in wavelength. As a consequence, an efficient protection of wood from photodegradation would demand also screening longer wavelengths of UVA light and some violet and blue light wavebands of the visible part of the spectrum.