## 4 Results and Discussion  
All four material samples were exposed to far-UVC light in three iterations. The initial color measurement of the samples was taken before each far-UVC exposure, and subsequent measurements were taken after each iteration of far-UVC exposure. Figure 7 shows the color changes of each sample using red, green, and blue color scales after each iteration of far-UVC exposure. Figure 7: Color changes of material samples using red, green, and blue color scales after each iteration of far-UVC radiant exposure. To accurately evaluate the color changes in the material samples after far-UVC exposure, the \(\Delta E00\) value was calculated for each measurement and presented in Figure 8. The figure also includes heat maps showing the color differences among the different iterations of the measurements. According to the interpretation of \(\Delta E00\) values given in [41], the normally invisible color differences occurred for Sample 3, and a very small difference, visible only to the trained eye, occurred for Sample 4 after all stages of far-UVC exposure. An obvious difference was recorded for Samples 1 and 2. Therefore, it can be concluded that the maximum effect of far-UVC 222 nm radiation is on FRC and PVC materials (Sample 1 and Sample 2). It can be concluded that far-UVC 222 nm radiation has a significant effect on the color of the tested materials, so this should be considered when using far-UVC exposure of 222 nm wavelength for disinfection of surfaces made of these materials. Previous research, such as the study in [42], has shown that both colored fabrics and plastics are discolored by far-UVC light of 254 nm wavelength. However, this study did not  
Figure 8: \(\Delta E00\) changes (**left**) and heatmaps (**right**) of material samples measured in each iteration of radiant exposure. measure the quantitative difference in color (\(\Delta\)E00), so it is not possible to directly compare the effect of exposure to 254 nm and 222 nm far-UVC light on materials. The change in mechanical properties (elasticity modulus, tensile strength, elongation at ULS, and elongation at break) of FRC 0/90\({}^{\circ}\), FRC \(\pm\)45\({}^{\circ}\) and PVC were further evaluated. Each mechanical property of each material was measured five times in each radiant exposure iteration. The change in elasticity modulus after exposing the samples to far-UVC radiant for different times is shown in Figure 9.  
Elasticity modulus test results show that the specific elastic rigidity of the tested PVC samples increased after appropriate far-UVC radiant exposure. FRC shows a decrease in elasticity modulus due to microcrack initiation of the epoxy matrix under far-UVC radiant exposure. In addition, the elasticity modulus decreases more for FRC 0/90\({}^{\circ}\) than for FRC \(\pm\)45\({}^{\circ}\), 16% and 10%, respectively, after 290 J/cm\({}^{2}\) radiant exposure. This phenomenon can be explained by the greater effect of far-UVC radiation on the structure of the FRC 0/90\({}^{\circ}\) matrix. Noticeably, as do all polymers, FRC with epoxy matrix and PVC lose some of the internal intermolecular and molecular bonds, and materials become brittle. Mainly, the decrease in plasticity can be seen in tensile test results by the decrease in elongation at break (Figure 10) and elongation at ultimate strength (ULS) (Figure 11). Figure 10: Elongation at ULS change after specific far-UVC radiant exposure. Figure 9: Elasticity modulus change after specific far-UVC radiant exposure. The largest decrease in elongation at break and ULS is seen in the tensile test results of a \(\pm 45^{\circ}\)-oriented E-glass FRC. The elongation at ULS and elongation at break of the \(\pm 45^{\circ}\) FRC decreased by 26% and 17%, respectively, after 290 J/cm\({}^{2}\) radiant exposure. This result can be explained as an effect of the failure influence of the FRC matrix on the final result. The FRC matrix is uncoated, with no additional UV stabilizers. The results show that it has the highest sensitivity to far-UVC irradiation.