Application of Near Infrared Spectroscopy (NIR) to light-irradiated wood

Materials and methods Specimens prepared under air-dried condition were the sapwood of Japanese cypress (Chamaecyparis obutusa), and the heartwood of Japanese cedar (Cryptomeria japonica), Japanese beech (Fagus crenata), and hackberry (Celtis occidentalis). The dimension of each sample was 50 mm in width, 50 mm in length, and 10 mm in thickness. This widelong surfaces (i.e. flat grain) were irradiated with simulated sunlight from a carbon arc for up to 80 hours. After the samples recovered their air-dried condition, the following measurements were performed. The color of specimens was measured by a colorimeter (SE-2000: Nippon Denshoku Industries Co., Ltd.). The CIELAB color parameters (L*, a*, and b*) were obtained from the colorimeter and the difference in the L* (i.e.; DL*) and chroma coordinates (i.e.; Da* and Db*) were calculated. The measured colors before light-irradiation for each sample were used as control. Table 1 shows the color of specimens before irradiation. Near infrared (NIR) diffusely reflected spectra ranging from 800 to 2500 nm with an increment of 10 nm were measured using a spectrophotometer (InfraAlyzer 500: Bran + Luebbe Co.).