## 3 Results  
For the UVC LED (275 nm) disinfection test, the untreated SARS-CoV-2 titer (10\({}^{7}\) TCID\({}_{50}\)/mL) was reduced to 10\({}^{2.77}\) TCID\({}_{50}\)/mL after 5 s of irradiation. The viral titer was further reduced to below the detection limit (10\({}^{1}\) TCID\({}_{50}\)/mL) after longer UVC LED exposure for 10, 20, and 40 s (Figure 1). The Log reduction values (LRVs) were 4.23, >6, >6, and >6 for 5, 10, 20, and 40 s of irradiation, respectively (Table 2).  
For the mercury lamp (254 nm) disinfection test, the untreated SARS-CoV-2 titer (10\({}^{6.67}\) TCID50/mL) was reduced to 10\({}^{5.5}\) and 10\({}^{3.33}\) TCID\({}_{50}\)/mL after exposure to a mercury lamp for 5 and 10 s, respectively. After longer treatment for 20 and 40 s, the SARS-CoV-2 titer was further reduced to less than 10\({}^{1}\) TCID\({}_{50}\)/mL (Figure 2). The LRVs were 1.17, 3.34, >6, and >6 for 5, 10, 20, and 40 s of irradiation, respectively (Table 2).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Radiation (\(\upmu\)/cm\({}^{2}\))**} \\ \hline
**Exposure Time** & **5 s** & **10 s** & **20 s** & **40 s** \\ \hline UVC LED (275 nm) & 399 & 798 & 1596 & 3192 \\ \hline Mercury lamp (254 nm) & 4250 & 8500 & 17,000 & 34,000 \\ \hline Excimer lamp (222 nm) & 35 & 70 & 140 & 280 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Radiation (\(\upmu\)/cm\({}^{2}\)) of UV light devices.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Log-Reduction Value (LRV)**} \\ \hline
**Exposure Time** & **5 s** & **10 s** & **20 s** & **40 s** \\ \hline UVC LED (275 nm) & 4.23 & \textgreater{}6 & \textgreater{}6 & \textgreater{}6 \\ \hline Mercury lamp (254 nm) & 1.17 & 3.34 & \textgreater{}6 & \textgreater{}6 \\ \hline Excimer lamp (222 nm) & 0.33 & 0.6 & 1.83 & 1.33 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Log-reduction value of UV light devices.  
For the excimer lamp (222 nm) disinfection test, the untreated SARS-CoV-2 titer (\(10^{6.83}\) TCID\({}_{50}\)/mL) was reduced to \(10^{6.5}\), \(10^{6.23}\), \(10^{5}\), and \(10^{5.5}\) TCID\({}_{50}\)/mL after exposure to an excimer lamp for 5, 10, 20, and 40 s, respectively (Figure 3). The LRVs were 0.33, 0.6, 1.83 and 1.33 for 5, 10, 20 and 40 s of irradiation, respectively (Table 2).  
Figure 1: Disinfection efficacy of UVC LED (275 nm) against SARS-CoV-2 was determined by tissue culture infection dose. SARS-CoV-2-containing medium was irradiated with UVC LED (275 nm) at room temperature for the indicated time periods. The virus-containing medium was 10-fold serially diluted and added to Vero E6 cells for 4-day incubation. Cells were then fixed, stained, and scored for infection. TCID\({}_{50}\) was calculated by Reed and Muench Method (1938).  
Figure 2: Disinfection efficacy of mercury lamp (254 nm) against SARS-CoV-2 was determined by tissue culture infection dose. SARS-CoV-2-containing medium was irradiated with mercury lamp (254 nm) at room temperature for the indicated time periods. The virus-containing medium was 10-fold serially diluted and added to Vero E6 cells for 4-day incubation. Cells were then fixed, stained, and scored for infection. TCID50 was calculated by Reed and Muench Method (1938).  
To confirm the effects of irradiation with UV light devices, we also used an immunohistochemical assay to detect the SARS-CoV-2 N protein expression. As shown in Figure 4, SARS-CoV-2 N protein expression was greatly reduced by exposure to UVC LEDs (275 nm) and the mercury lamp (254 nm), but not much by the excimer lamp (222 nm).