# Development and Effect Analysis of UVB-LED General Lighting to Support Vitamin D Synthesis
## 2 UVB-LED General Lighting  
This study recommended UVB-LED indoor lighting for indoor dwellers for vitamin D synthesis. For this, the test lighting combined the abilities of 500 lux VISIBLE-LED and UVB-LED. To power the VISIBLE-LED and UVB-LED, a power converter and resistor were installed together, as shown in Figure 1.  
Figure 1: UVB-LED general lighting design. The VISIBLE-LED array in Figure 1 used four types of VISIBLE-LED light sources (2700 K, 4000 K, 5000 K, and 6500 K, Samsung LED, Korea). The UVB-LED array had a 100 mW ability using UVB-LED light sources (6060 100 mW, 1 in1 Flat UVB-LED PKG, LG Innotek, Korea). To power each LED array module, 40 W and 10 W constant current AC/DC converters were used, and a drive control system and main controller were installed to control the VISIBLE-LED array. Figure 2 shows the anterior and posterior sides of the UVB-LED general lighting from Figure 1.  
The center of Figure 2a shows the anterior-interior of the VISIBLE-LED modules and the corners show the UVB-LED modules; (b) shows the posterior with the AC/DC converter type 2, main controller, and 4 CH controller; and (c) shows the diffuser attached to the VISIBLE-LED module and the quartz crystal allowing the UVB to penetrate. Particularly, in (c), since an ordinary diffuser or quartz crystal could not be used for the UVB wavelength, a quartz crystal that allowed 99% of the UVB wavelength was used [22]. Additionally, an 82 mA power source was used on the UVB-LED module. To check the properties of the proposed UVB-LED general lighting, a spectral radiometer (CAS 140 CT, Instrument Systems, Germany) was used to execute the experiment in a completely closed system of a lighting cabinet. At this time, the proposed lighting was installed on the vertical top of the spectral radiometer, and the distance from the spectral radiometer was 2.4 m and 2.8 m at the average ceiling height of domestic apartments and general offices, respectively. The height of the lighting was maintained at 150 cm considering normal adults sitting on a chair. Here, the recommended lighting was installed perpendicularly above the spectral radiometer at a distance of 150 cm. Figure 3 shows the results of the photonic effectiveness of the proposed lighting. Figure 2: UVB-LED General Lighting. (**a**) Anterior-interior. (**b**) Posterior-converter and drive control system. (**c**) Anterior-diffuser applied. Figure 3 shows the spectral irradiance analysis results of the proposed lighting. The illuminance was 500 lux, and each irradiance's proportion was 99% at the visible spectrum (380-800 nm), 1% at the UVB spectrum (280-315 nm), and no significant presence for the other wavelengths including UVA was noted. In addition, the illuminance was 500 lux and the intensity of the visible spectrum was 1.80 W/m\({}^{2}\) and UVB was 0.01 W/m\({}^{2}\), and supported the ability to provide the indoor general lighting illuminance as well as the UVB dosage. In addition, to check the optical characteristics of the lighting irradiated to the indoor space when the proposed lighting was applied, the amounts of UVB light from the work plane, which were vertical (0 degrees), 15 degrees, 30 degrees, and 45 degrees from the bottom of the lighting, and the vertical distance from the illumination surface of about 1.5 m, were investigated. The results are shown in Table 1.  
From Table 1, it was confirmed that a similar level (within \(\pm\)20%) of illuminance and UVB light could be provided within 15 degrees when the proposed lighting was applied. Moreover, a photobiological safety evaluation for the UVB-LED showed an AUV (Actinic UV hazard Radiation) and NUV (Near UV hazard Radiation) within the UV light wavelength category [23]. Here, Equations (1) and (2) were used. Equation (1) calculated the AUV, and used weighting function (\(\alpha\)), as suggested in the table of weighting functions according to the wavelength in IEC 62471 [24].