Effects of standard artificial radiation sources (xenon-arc and fluorescent-UV) were compared with natural sunlight to determine activation spectra of four parameters of wood surface photodegradation. Photodegradation effects regarding colour, microtensile strength at zero and finite initial span, as well as chemical changes developed with different intensities in various stages of exposure. Discoloration developed disproportionally faster in early phases of eposure; finite span microtensile strength reached saturation in the middle of the exposure period, whereas zero span strength and chemical changes reached their maxima at the end of exposures. This practically means that, despite very similar character and extent of colour changes, different light sources produced different activation spectra in specific phases of exposure. Activation spectra for retained zero span strength of top strips were very similar in all three exposures. Activation spectra of lower strips were not well differentiated. Relatively narrow wavebands of most active wavelengths between 360 and 435 nm caused greatest proportion of damages. However, visible light of wavelengths up to 510 nm was shown to contribute significantly to surface damages. The observation of interrelationships of different weathering regimes and assessment methods of photochemical processes gave valuable insight into the complexity of the process and brought new findings about the nature of light-induced breakdown of unprotected wood. This knowledge may be employed in further studies of the degradation of this natural polymer, but also in finding new solutions for enhancing light fastness of wood and formulations of protective chemicals and coatings.