Equipment is described for monitoring both reflectance and transmittance properties of the visible spectrum of wood at the cellular level. The apparatus consists of three separate units: 1) a light source and wavelength monitoring system. 2) a light microscope with fluorite optics in a special nosepiece assembly so constructed that both reflectance and transmittance measurements can be made, including a method of programing area and shape of microscopic field to be measured, and, 3) a data sensing and readout system suitable for either digital display or computer tape preparation. Exploratory measurements comparing transmittance data for eastern redcedar sapwood and heartwood zones are presented. -- AATA