UV-C reflectance ratios and irradiance of each material

Using a UV–visible–Near InfraRed (UV–Vis–NIR) spectrophotometer (UV-3600, Shimazu Co., Ltd. Kyoto, Japan), a source light was dispersed into monochrome light in the UV-C wavelengths through diffraction grating. The resulting UV to visible light (240–780 nm) irradiated the sample materials. The light reflected back from the surface of the sample materials was measured using the integrating sphere attachment of the spectrophotometer and the reflectance ratios were calculated. The UV-C reflectance ratios of Stucco with different mixing ratios and particle sizes of each material was measured.

By changing formulation and particle size of CaCO₃ and BaSO₄, we created a sample of Stucco using powder materials and thickener. Water was added to these material at room temperature to make a paste, which was applied to the plasterboard by an artisan. Based on these reflectance data, the Stucco was modified to improve the UV-C reflectance. The Modified Japanese Stucco prepared by this paper’s authors was based on JIS A 6919 Japanese Industrial Standards (JIS) for Stucco¹⁸ (“^{Supplementary data}”).

The irradiated materials on which UV-C reflectance ratios were measured are follows: aluminum foil (MY FOIL, UACJ Foil Co., Ltd. Tokyo, Japan), aluminum plate ({"type":"entrez-nucleotide","attrs":{"text":"N96620","term_id":"2748158","term_text":"N96620"}}N96620, Nippon Light Metal Co., Ltd. Tokyo, Japan), commercial Japanese Stucco (Shikkui Kurumu Uchi^®, Nippon Plaster Co., Ltd. Tochigi, Japan), white wallpaper (FE6716, Sangetsu Co., Ltd. Aichi, Japan), white paint (Suisei-Wide V, Nippe Home Products Co., Ltd. Tokyo, Japan), and the Modified Japanese Stucco blended by the authors. The other metals examined were stainless steel plate (SUS304 2B, Nippon Steel Stainless Steel Co., Ltd. Tokyo, Japan), and copper plate (C1100P, Mitsubishi Materials Corporation Co., Ltd. Tokyo, Japan). In addition, common Japanese cedar lumber, mortar and concrete were measured.

Using a UV irradiance meter (UV-M02, Orc Manufacturing Co., Ltd. Tokyo, Japan), UV-C irradiance at the agar media after passing through various test boxes was also measured. The test boxes in which UV-C irradiance was measured are follows: aluminum foil (back side, matt), authors’ Modified Stucco, commercial Stucco, and white wall paper.