## 4 Conclusions  
This study investigated parameters related to the performance of LED phototherapy devices to ensure their safety. Although LLLT using LED phototherapy devices, which have been recently examined, has no reported principle, it was possible to identify wavelength as the main performance parameter, which is the same for other phototherapy devices. The standard of phototherapy devices equipped with both LED and lasers, such as T company's phototherapy device, needs to be explored in combination with LED and laser standards. The investigation of standards was able to identify the classes of medical laser devices in IEC 60825-1 and their hazard depending on the wavelength in IEC 60825-8, the appendix of IEC 60825-1. However, certain laser standards were found to be applied to 3B or higher classes of a laser. As the samples of T company's device used in this study were used in combination with LED and low-level laser, it was difficult to investigate the standards because of the differentiation between the LED and laser. For LED phototherapy devices, IEC 62471-1, which is the same standard used for lamp-based medical devices, was applied. Referring to IEC 62471-1 and the relevant literature and guidelines, this study derived the performance test method and test parameters for wavelength, the main performance item, and applied them to samples of the T company's device. The derived performance evaluation item was the accuracy test of the wavelength according to IEC 62471-1. The test was to determine whether the LED and laser wavelengths were stable. The test standard was within \(\pm\)5% in the error range corresponding to the test standard of T company. The test method checked whether the measured wavelength shown through the spectrometer was within the error range through the percentage. According to the measurement results, the light sources of the samples complied with the test standard set by the manufacturer. The measured wavelength for samples differed from the set value by 1 to 2 nm in red and blue LEDs, and the accuracy error range of the wavelength was close to 0%. However, laser and IR LEDs, unlike red and blue LEDs, had a difference as large as 2 to 7 nm between the set value and the measured value though they were used regardless of the mode. Moreover, the error range was also shown to be close to 1%, unlike those \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Wavelength**} & \multicolumn{2}{c}{**LASER**} & \multicolumn{2}{c}{**IR LED**} & \multicolumn{2}{c}{**RED LED**} & \multicolumn{2}{c}{**BLUE LED**} \\  & \multicolumn{2}{c}{**Set Value:**} & \multicolumn{2}{c}{**Set Value:**} & \multicolumn{2}{c}{**Set Value:**} & \multicolumn{2}{c}{**Set Value:**} \\  & \multicolumn{2}{c}{**650 nm**} & \multicolumn{2}{c}{**845 nm**} & \multicolumn{2}{c}{**625 nm**} & \multicolumn{2}{c}{**455 nm**} \\ \hline Mode & Sample 1 & Sample 2 & Sample 1 & Sample 2 & Sample 1 & Sample 2 & Sample 1 & Sample 2 \\ \hline H Mode & 654 nm & 652 nm & 838 nm & 840 nm & 627 nm & 627 nm & - & - \\ \hline S Mode & 654 nm & 653 nm & 838 nm & 839 nm & - & - & 455 nm & 454 nm \\ \hline Accuracy of wavelength & H & \(\pm\)0.615\% & \(\pm\)0.31\% & \(\pm\)0.828\% & \(\pm\)0.59\% & \(\pm\)0.32\% & \(\pm\)0.32\% & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Measured values by mode in the samples of T company’s device and the accuracy of wavelength. of the red and blue LEDs. To make it closer to the set value, it is necessary to study the wavelength of phototherapy devices whose accuracy is important for safety. We believe that a study on the wavelength of the phototherapy device similar to the set value would contribute to the safety of LED phototherapy devices and the industrial advancement of phototherapy devices similar to LED phototherapy devices. Conceptualization, J.-Y.L. ; methodology, Y.-S.K. ; verification, S.-G.P. ; formal analysis, J.-Y.L. ; survey, J.-Y.L. ; resources, Y.-S.K. ; data curation, J.-Y.L. ; writing\(-\)original draft, J.-Y.L.