# Comparative Study of Blue Light with Ultraviolet (UVC) Radiation on Betacoronavirus 1
## 4 Discussion  
The ongoing pandemic is in dire need of uninterrupted inactivation technology. In this study, we wanted to explore the impact of 405 nm visible light technology for inactivation of betacoronavirus 1 and compared its efficacy with the other germicidal UVC radiation. The 254 and 270/280 nm resulted in the highest log reduction of log\({}_{10}\) 3.17 and log\({}_{10}\) 3.37 at a 10 mJ/cm\({}^{2}\) dose for 3.26 and 288.18 s, respectively. A lower dose of 222 nm (i.e., 3 mJ/cm\({}^{2}\)) resulted in a log\({}_{10}\) 2.50 reduction. The 405 nm visible light resulted in a log\({}_{10}\) 2.84 reduction after 2 h and 40 min with a dose of 17,280 mJ/cm\({}^{2}\). The inactivation dose of 405 nm was achieved from a commercially available light source, and the fluence was well within the safe level. The use of UVC for disinfection purposes has been in practice for centuries but has adverse effects on humans. UVC (200-280 nm) is well known for damaging human tissue, particularly skin. A 254 nm radiation is absorbed by both DNA and RNA, causing severe damage to human cells and tissues. It can cause photokeratitis and erythema ([PERSON], [PERSON], 2019), leading to severe skin burn. This restricts UVC usage to enclosed and unoccupied spaces, making it futile for our desired application. Far-UV 222 nm has a higher irradiation power, which makes the inactivation much faster, and its lower penetration into human skin makes its safe for human exposure [6]. However, a study showed the formation of erythema and cyclobutene pyrimidine dimers (CPDs) after 222 nm irradiation [13]. The use of 222 nm raises concern of ozone generation. Ozone is an unstable gas and can affect the respiratory, cardiovascular, and central nervous systems [25]. The limited studies on the effects of far-UV make its use risky for human exposure. Visible blue light has the potential to be used in occupied spaces. This study showed a significant reduction of betacoronavirus 1 with a very low and safe dose of 405 nm. In past studies, external photosensizers were used in the medium for inactivation by 405 nm. In this study, 405 nm caused inactivation of the Betacoronavirus without any external photosensitizers. The TCID50 method was selected for determining the viral infectivity over a plague assay, as it allows for a faster and more straight forward sample preparation and handling. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Distance between the Virus**} & \multicolumn{3}{c}{**Irradiance of Different Light Sources (W/cm\({}^{2}\))**} \\ \cline{2-5}  & **405 nm** & **222 nm** & **254 nm** & **270/280 nm** \\ \hline
10 & \(1.80\times 10^{-3}\) & \(9.18\times 10^{-4}\) & \(3.50\times 10^{-3}\) & \(3.47\times 10^{-5}\) \\
20 & \(4.46\times 10^{-4}\) & \(3.17\times 10^{-4}\) & \(1.03\times 10^{-3}\) & \(7.33\times 10^{-6}\) \\
30 & \(1.98\times 10^{-4}\) & \(1.32\times 10^{-4}\) & \(5.29\times 10^{-4}\) & \(2.83\times 10^{-6}\) \\
40 & \(1.15\times 10^{-4}\) & \(8.09\times 10^{-5}\) & \(3.19\times 10^{-4}\) & \(1.43\times 10^{-6}\) \\
50 & \(7.36\times 10^{-5}\) & \(5.08\times 10^{-5}\) & \(2.12\times 10^{-4}\) & \(8.51\times 10^{-7}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Irradiances (W/cm\({}^{2}\)) for different UVCs radiations and blue light. Figure 6: The graph shows the relationship between the irradiance and distance for the DIEHL 405 nm LED. Illustration of the inverse square law for calculating the irradiance at varying distances. The PCR technique was not used, as it detects both infectious and noninfectious viruses, which can provide an incorrect estimation. Before using visible light for continuous inactivation, its photobiological hazards to humans should be studied. The IEC 62471 [30] standards have considered the skin, cornea, and retinal hazards. These hazards depend on wavelengths, physiological sensitivity to various wavelengths, angular subtense, and exposure time. The brief mention of eye anatomy is pertinent for understanding the angular subtense.