FT-IR microspectroscopy was used to monitor the changes in the chemical composition at various depths from the photo-irradiated surface of sugi (Cryptomeria japonica D. Don) sapwood. The radially cut wood face was exposed to artificial solar radiation from a xenon light source at 375 Wm-2 (in a 300 - 700 nm spectral range) for up to 600 h. The IR depth profiling spectra showed that the artificial sunlight caused most significant chemical changes in the outermost wood layer, while some chemical effects penetrated the wood as far as 600 m from the surface to form a thick degraded layer. The results of monitoring some photosensitive absorption bands for various exposure times revealed that there was a continuous growth of the degraded layer whose growth rate became increasingly restricted with exposure time. These results may explain why various depths or thicknesses have been reported for this phenomenon.

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