Primary calibrations of the absolute reflectance of white standard reference materials (barium sulfate and PTFE : polytetrafluoroethylene) are performed in the visible range, from 380 nm to 780 nm, within the total uncertainty of ±0.2 %. For the primary calibration we have constructed an absolute reflectometer by modifying the design of Budde's which was improved from the Sharp-Little system. A Multichannel Array Spectrophotometer(MAS) is used for this system. The measuring time was greatly reduced by using a multichannel array spectrophotometer. It takes only a few seconds to get the spectral reflectances in the full visible range. As white standard reference materials, we selected PTFE (Teflon 7A-J, made by Dupont) and two kinds of barium sulfate (Eastman Kodak and Merck ). The samples were made by pressing the materials in a cylindrical tool made of stainless steel. The d/0 geometry is used for the measurement of reflectance. The measured results agreed with those of other studies within 0.5 %.
The reflectance of PTFE was decreased by increasing the packing density. The reflectance of the barium sulfate showed about 0.5 % difference for the products of two companies. From the results, it is conformed that our system can be used as a primary standard system for the absolute diffuse reflectance and for the colorimetry.
