Longitudinal transmittance of visible and near-infrared light in the wood of 21 conifer species

Light transmittance and reflectance were measured in 21 conifer species using a spectrophotometer equipped with an integrating sphere and light within a wavelength range of 500–1200 nm, to clarify the variety of longitudinal light transmitting properties among wood species. Transmittance values varied not only among different species but also between the sapwood and heartwood within certain species. Transmittance intensity increased from about 600–700 nm and showed peaks or shoulders in the ranges of 870–900 nm and 930–950 nm, and at around 1100 nm in all samples. The spectra tended to show similar patterns for 2 species within the same genus (Chamaecyparis, Abies, Picea, Pinus, Pseudotsuga and Tsuga). Light transmittance differed between the sapwood and the heartwood in several species, and, patterns of the difference differed among the different genera. Peaks at around 1100 nm were observed in both the sapwood and heartwood of all samples. Maximum conductivities of light at these peaks were relatively lower in wood species with helical thickenings (genera Pseudotsuga, Torreya and Taxus). Based on these results, it can be seen that the anatomical characteristics of wood influence the transmittance of light. The density of wood and secondary metabolites occurring in heartwood are also thought to influence the transmittance of light.