## 4 Discussion  
The disinfection effect of UV light on bacteria and viruses largely depends on the wavelength. UVC with the shortest wavelength can provide the greatest performance within the UV range and is currently used to disinfect surfaces, equipment, operating rooms, and personal protective equipment (PPE) in healthcare settings [18]. UVC LEDs around 254 to 265 nm has been shown to provide the highest disinfection effect within the UVC range [19]. In this study, we further found that UVC LEDs (275 nm) exhibited  
Figure 4: Disinfection efficacy of UVC light devices was determined by immunofluorescence assay. The irradiated samples were added to Vero E6 cells for 1 day incubation. Cells were fixed and immunostined with anti-SARS-CoV-2 N protein antibody and goat anti-human IgG-Alexa Fluor 488 (green). Cell nucleus was stained with DAPI (blue). Figure 3: Disinfection efficacy of excimer lamp (222 nm) against SARS-CoV-2 was determined by tissue culture infection dose. SARS-CoV-2-containing medium was irradiated with excimer lamp (222 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). a superior disinfection ability against SARS-CoV-2 compared to mercury lamps (254 nm) and excimer lamps (222 nm). The disinfection effect is determined by the cumulative light amount of the ultraviolet light. The cumulative light amount is determined by multiplying the intensity of light and the intensity time. In general, the higher the UVC light intensity, the higher the disinfection effect. Moreover, the longer the irradiation time, the greater the disinfection effect. In addition, the disinfection ability also depends on the wavelength of UVC light. The peak effectiveness at 275 nm is due to the fact that this wavelength is the peak wavelength for RNA/DNA absorption, and hence it can disturb the protein structures effectively. This structural modification will lead to the disintegration of its protein functionality and will hence inactivate the virus. Thus, the UVC light (275 nm) has the strongest disinfection impact even with a lower intensity (79.8 \(\upmu\)W/cm\({}^{2}\)) and is better than the mercury lamps (254 nm) with a higher intensity (850 \(\upmu\)W/cm\({}^{2}\)). [PERSON] et al. demonstrated the inactivation of SARS-CoV-2 using UVC 275 nm LEDs, showing that there is 99.9% inactivation after 1 min of treatment with a dose of 83.1 J/m\({}^{2}\) and a minimum irradiance of 1.385 W/m\({}^{2}\)[20]. In our study, a UVC LED with a lesser irradiation intensity of 79.8 \(\upmu\)W/cm\({}^{2}\) showed better effectiveness by inactivating SARS-CoV-2 with a reduction of more than 99.99% after only 5 s of irradiation. There is an even greater reduction of more than 99.999% after 10 s of irradiation, indicating a better effectiveness than the previously reported values. [PERSON] et al. demonstrated the effect of UVC light with a 254 nm wavelength on SARS-CoV-2 inactivation, showing that a very small dose of less than 4 mJ/cm\({}^{2}\) is enough to achieve full inactivation of the virus [21]. In addition, even at a higher virus input concentration of 1000 MOI, viral replication is totally inactivated with a dose \(\geq\) 16.9 mJ/cm\({}^{2}\). However, their exposure time is quite long in terms of hours. In our study, we found that there is more than a 99.9999% reduction in the virus count even after 20 s of exposure using a mercury lamp at 254 nm, which is more effective than the study mentioned above. There are some challenges for UVC disinfection lighting. UVC lamps used for disinfection may cause health and safety issues depending on the wavelength, dose, and duration of radiation exposure. The risk increases if the device is improperly placed or handled by vmskilled individuals.