# Designing Safe General LED Lighting that Provides the UVB Benefits of Sunlight
## 4 Results and Discussion  
The environment for measuring the optical characteristics of lighting was set as shown in Figure 5. First, a lighting box with a volume of 120 \(\times\) 120 \(\times\) 200 cm was used to cut off extraneous light, and a light was set in the upper part of it. In the lower part, a spectral radiometer was installed, and the distance between the light and the spectral radiometer was kept at 150 cm. The brightness of the light was adjusted to 500 lux. The spectral radiometer used was a CAS 140 CT device capable of measuring wavelengths in the range of 200-800 nm. Figure 5 shows an environment for measuring the optical characteristics of the proposed lighting. In this experiment, to confirm the optical characteristics of the proposed lighting, one kind of commercial LED lights was measured and compared together, and the results are shown in Figure 6.  
Figure 6a shows the result of the measurement of LED lighting (merlot lighting, 655 \(\times\) 318 \(\times\) 83 mm) on the market that can be mounted on ceilings, showing the spectral irradiance of general lighting. Figure 6b is the proposed general UVB LED indoor lighting. It shows the measurement result when 200 mA is applied after applying four UVB LED light sources with the 20-mW output standard. Unlike the general lighting in Figure 6a, the proposed lighting in Figure 6b had a spectral distribution in the  
Figure 5: Environment for measuring optical characteristics. Figure 6: Spectral distribution of commercial and proposed general lighting. (**a**) General (normal) lighting; (**b**) proposed lighting (UV and visible). UV (280-400 nm) band. As a result of the experiment, the total irradiance of the proposed lighting of the UV and visible light had an irradiance of 1.75 W/m\({}^{2}\). The EUV on which the erythema-weighted function of Equation (6) was applied in the spectral distribution in Figure 7b was calculated to check if erythema occurred on the skin. The calculated EUV was 0.00325794 W/m\({}^{2}\), which is equivalent to 1/200 of that of natural light as shown in Figure 2. When exposed to the proposed lighting system for 16 h, the EUV dose was about 187.66 J/m\({}^{2}\), which would not cause erythema for general skin types (Skip Types 1-6) [14]. In addition, a chemical hazard weighting function was applied for the UV zone to check the hazard on the human body by UVB-LED, with the results illustrated in Figure 7.  
Figure 7a shows the actinic hazard weighting function as well as the weighted value approaching the maximum of 1 at 300 nm or less. Figure 7b shows the spectral distributions before and after the application of the actinic hazard weighting function to the UV area of the proposed lighting. When the actinic hazard weighting function was applied, the hazard distribution was adjusted to the range of 280-320 nm from the existing UV wavelength range. The results of applying this to the AUV and NUV formulas (Equations (6) and (7)) are shown in Table 5. The measured values of AUV and NUV of the proposed lighting were 0.001 W/m\({}^{2}\) and 0.002 W/m\({}^{2}\), respectively, which are lower than the reference values of 0.001 W/m\({}^{2}\) and 10 W/m\({}^{2}\). Their hazard ratings are all considered Exempt, which is the safest rating. We also applied the vitamin D synthesis amount (Equation (8)) derived from the previous study to confirm whether the synthesis of vitamin D is supported by the EUVB dose of the proposed lighting [33]. \[Vitamin\ D=\frac{\text{EUV}\big{[}\text{W}/\text{m}^{2}\big{]}\ \times\ \text{Etimes}\ \text{[s]}\ \times\ \text{Earea}\ [\%]\ \times\ 40\text{IU}}{\text{MED}\ \big{[}\text{J}/\text{m}^{2}\big{]}} \tag{8}\]  
At this time, the expected amount of vitamin D synthesis was calculated by applying 0.003245 W/m\({}^{2}\) of EUVB irradiance, 16 h (57,600 s) of exposure time (Etimes), Skin Type 3 (Korean), and 15% of the exposed area (face, neck, hands, and arms) for the proposed lighting.