## 4 Experiment and Simulation
### Performance Test for IoT UV Smart Device and UVB LED Lighting  
IoT UV measurement devices using UVI sensors must be calibrated through comparative experiments with the reference equipment. Their performances can be improved by applying the correction formula that reflects regional characteristics and seasonal characteristics [16]. For the calibration and performance evaluation of the IoT UV measuring device, UVI from the noon (12 p.m.) until the sunset on 21 February 2019 at the latitude of 36.85 and the longitude of 127.15 (Kongiu National University, Korea) was used. A spectrometer (CAS 140 CT-152, Instrument Systems, Munich, Germany) was used as a reference device for the calibration and performance evaluation of the measuring instrument. In addition, a tracking system that follows the sun in the vertical direction by calculating the azimuth and altitude of the sun based on the latitude, longitude, and date of the current location was installed. The correction formula by linear regression analysis was derived based on the UVI value acquired through the IoT UV measurement device and the reference device at the same time for the natural light. The correction formula was applied to the IoT UV measurement device. Figure 7 shows the experimental results of the reference device for the sunlight and the IoT UV measuring device. The measurement results of the IoT UV device are displayed before and after calibration together. The mean absolute percentage error (MAPE) of the data measured by \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Seasonal Conversion Factors**} \\ \hline
**Latitude** & **Item** & **Spring** & **Summer** & **Fall** & **Winter** \\ \hline
30\({}^{\circ}\) N & _ASCF_ & 0.742 & 1.11 & 1.061 & 0.91 \\  & _GCF_ & 0.593 & 0.593 & 0.655 & 0.655 \\ \hline
35\({}^{\circ}\) N & _ASCF_ & 1.049 & 1.104 & 1.029 & 0.842 \\  & _GCF_ & 0.600 & 0.600 & 0.655 & 0.655 \\ \hline
40\({}^{\circ}\) N & _ASCF_ & 1.008 & 1.067 & 0.963 & 0.7 \\  & _GCF_ & 0.608 & 0.608 & 0.681 & 0.681 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Action spectrum conversion factor (_ASCF_) and geometric correction factor (_GCF_) tables. the spectrometer and the IoT UV measurement device before calibration was 45.5%, but after applying the calibration formula, the MAPE could be decreased to about 11.1%. An experiment to check the characteristics of UVB LED general lighting was also conducted. The characteristics of light were measured using the spectrometer (CAS 140 CT-152, Instrument Systems) in the lighting box having a dimension of 120 (w) \(\times\) 120 (d) \(\times\) 200 (h) cm to which outer light does not penetrate. The UVB LED general lighting was fixed at the top of the lighting box, the spectrometer was installed at the bottom, and the distance between the lighting and spectrometer was set to 150 cm considering the installation condition of the general lighting. In addition, the input current of 201 mA was applied in the UVB LED module considering safety in the UV zone of the photobiological safety standard of the lighting (IEC 62417) [30; 31]. Figure 8 shows the measurement results of the UVB LED general lighting. Irradiance for the UVB, UVA, and visible areas of the proposed lighting was measured as 1.65, 9.20, and 2560.09 mW/m\({}^{2}\) in Figure 8a, and the illuminance of the proposed lighting was measured as 509 lux. Therefore, it is assumed that spectral irradiance was implemented for almost all the visible areas. In order to confirm the photobiological safety of the proposed lighting for the UV region, the Near UV (NUV) of 1.4885 mW/m\({}^{2}\) was obtained by integrating the wavelength of 315-400 nm. Figure 8b shows the enlarged UV region. Figure 8c shows the result of applying the Actinic weighting function to the UV region. The Actinic UV irradiance (AUV) was 0.9969 mW/m\({}^{2}\) after applying the weighting function to the wavelength band of 200-400 nm.