Correlation between hue angle and lightness of light irradiated wood

The objective of this study was to investigate irradiation characteristics of Beech (Fagus crenata Blume), black locust (Robinia pseudoacacia L.), Japanese cedar (Cryptomeria japonica D. Don) and spruce (Picea abies Karst.) wood samples by sunlight, xenon light and mercury vapour light. The colour change of the samples was evaluated by CIE L*a*b* and L*h*c* colour co-ordinate systems. It was found that the samples showed a rapid colour change at the initial period of treatment but the rate of change decreased with treatment time. It was determined that neither xenon nor mercury lamp light can accurately simulate sunlight. A wide range of colour changes were caused by the applied light sources. In spite of this wide colour range a good linear correlation was found between the lightness and the colour hue. The coefficients of determination (R2) are between 0.7 and 0.96. Accordingly, this linear correlation gives the possibility of following the colour change during photodegradation by measuring only the lightness.