# Designing Safe General LED Lighting that Provides the UVB Benefits of Sunlight
## 3 Methods: UVB LED General Lighting Design  
### UV Safety Evaluation  
Excessive exposure to the UV rays can cause erythema, which is a kind of skin burn [36], and UV can be harmful to the human body even if a person is exposed to the UV at a lower level continuously [7]. Therefore, the UVB-LED general lighting proposed in this paper provides a UVB intensity of light at a level that would not cause erythema, meeting the safety evaluation standard (IEC 62471) for lighting devices.  
The IEC has established the IEC 62471 standard to evaluate the photobiological safety of lighting devices using LED light sources [37]. Therein, the hazards caused to eyes and skin due to lighting are divided into the following eight categories: eye and skin photochemistry UV, eye UVA, retinal blue light, retinal blue light with a small light source, retinal heat, retinal heat caused by weak visual stimulus, eye IR, and skin heat. Each item is classified and marked by four categories, namely, the exclusion group, the low-risk group, the moderate-risk group, and the high-risk group, after analyzing spectral irradiance and radiance measured by wavelength range. IEC 62471 also classifies lighting into a general lamp service (GLS) and other lamps, and applies different test methods accordingly. In this case, GLS refers to general lighting used at homes or offices, and other lamps, excluding GLS, are those used for industrial or medical lighting devices used for suntan, water purification facilities, and medical treatments [23]. Depending on the type of lamps used, the optical characteristics of the GLS are measured with a 500-lux brightness. We further evaluated whether a hazard caused by the UVB dose existed. At this time, the hazard assessment based on the UVB light source is limited to an actinic UV hazard (AUV) and a near-UV hazard (NUV). Details of emission limits for each item are summarized in Table 2[37].  
Exempt is the safest lamp rating in Table 1, and its radiation in each item of AUV is 0.001 W/m\({}^{2}\). NUV is applied when Exempt \(\leq\) 10 W/m\({}^{2}\). AUV is calculated by integrating the AUV hazard  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Hazard Items** & **Unit** & **Exempt** & **Risk Group 1** & **Risk Group 2** \\ \hline Actinic ultraviolet hazard (AUV) & W/m\({}^{2}\) & **0.001** & 0.003 & 0.03 \\ Near-UV hazard (NUV) & W/m\({}^{2}\) & **10** & 33 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 2: IEC 62471 classification standard for ultraviolet (UV) risk items.  
weighting function (S\({}_{\text{UV}}\)) to the spectral irradiance of 200-400 nm wavelength band (Equation (4)); NUV was calculated by integrating the spectral irradiance of 315-400 nm UVA wavelength band.  
\[\text{AUV}=\int_{200}^{400}E(\lambda)S_{UV}(\lambda)\text{d}\lambda \tag{4}\]  
where \(\lambda\) = wavelength, \(E(\lambda)\) = UV spectral irradiance, and \(S_{UV}(\lambda)\) = actinic ultraviolet hazard weighting function.  
In this case, the AUV hazard weighting function (S\({}_{\text{UV}}\)) uses the weight table value by wavelength according to IEC 62471 [28]. When no reference value for the observed spectral wavelength is available, a weighted value based on each wavelength is calculated by linear interpolation, as shown by \(S^{\prime}{}_{UV}(\lambda)\) in Equation (5).  
\[S^{\prime}{}_{UV}(\lambda)=\ S_{UV}(\lambda_{l})+(\lambda-\lambda_{l})\frac{S _{UV}(\lambda_{r})-S_{UV}(\lambda_{l})}{\lambda_{r}-\lambda_{l}},\ (\lambda_{l}<\ \lambda <\ \lambda_{r}). \tag{5}\]  
Equations (6) and (7) are the final formulas of AUV and NUV, respectively.  
\[\text{AUV}=\sum_{\lambda=200}^{400}E(\lambda)S^{\prime}{}_{UV}(\lambda)\Delta\lambda \tag{6}\]  
\[\text{NUV}=\ \int_{315}^{400}E(\lambda)d\lambda=\ \int_{315}^{400}E(\lambda) \Delta\lambda. \tag{7}\]