# Development and Effect Analysis of UVB-LED General Lighting to Support Vitamin D Synthesis
## 1 Introduction  
Recently, interest in the effect of natural sunlight on the human body has increased. Ultraviolet (UV) light is an electromagnetic ray that carries a wavelength shorter than visible light, and consists of 6-7% of the solar radiation that reaches the Earth's surface [1]. UV light is divided into UVA (315-400 nm), UVB (280-315 nm), and UVC (200-280 nm) [2]. Ninety-five percent of UVC and UVB is absorbed by the ozone layer present in the stratosphere. Five percent of UVB and 95% of UVA penetrate the ozone layer and reach bodies on the Earth's surface [3, 4]. Typically, UV light from sunlight is known to be harmful to the skin and eye, and overexposure should be avoided [5, 6]. Conversely, several researchers have cautioned against a deficit in UV light exposure, which may result in rickets, osteomalacia, and other musculoskeletal diseases as well as vascular diseases such as diabetes, high blood pressure,and myocardial infarction [7; 8; 9]. In addition, a certain wavelength of UV light including UVB is essential for stimulating vitamin D synthesis and is, therefore, suggested as useful in maintaining good mental health [10; 11; 12]. As awareness regarding the positive aspects of UV light from sunlight increases, appropriate exposure to sunlight is being recommended to maintain and improve health. A portable UV light-measuring device has been developed to ascertain the level of UV light exposure outdoors [13]. In addition, government agencies and meteorological agencies in some countries provide local UV intensity information [14; 15] and have suggested adequate exposure time to specific areas of concern for vitamin D deficiency [16]. Furthermore, lighting-related studies investigating the appropriate UV light dosage for people who cannot go outside due to health or work issues are being actively conducted. UV lighting devices have surpassed the existing treatment-purpose lighting to ones that can control the amount of UV light through UVB-LED, so that it can be applied to day-to-day indoor activities within the safe range of UV light exposure [17]. Moreover, the introduction of portable UV light-measuring devices and smartphone applications to UVE-LED systems support the meeting of individual UV light dosage requirements [18]. Clinical trials to test the correlation between UVB and in vivo vitamin B synthesis have been implemented [19], and an experiment related to the treatment of psoriasis using medical UV light has been reported [20]. However, the experiments thus far have only been tested on small parts of the human body or on animals (mice), and have not been able to prove that UVB-LED light exposure for a given duration supports vitamin D synthesis within a closed system lacking outside light. This study aimed to recommend UVB-LED lighting for indoor dwellers, which was supported by evidence from animal testing. Four UVB-LED light sources (UVB 100 mW, L company) were used at a distance of 1.5 m at 10.67 mW/m\({}^{2}\) to develop general indoor lighting. Photobiological safety (IEC 62471) was followed to ensure the safety of the suggested lighting. A closed system was developed where outside light was blocked from entering and the lights were installed at 1.5 m in accordance with the normal architecture of general lighting in a household. Clinical experiments were performed to measure the vitamin D levels. At this time, since the amount of vitamin D in the body was rapidly changed due to outdoor activities even after exposure to sunlight for a short time [21], there was difficulty in forcing the subjected person to stay indoors for a long duration (about three weeks) in the clinical study. Therefore, the rat was chosen as a long-term test subject. Since rats have fur covering the majority of their body, the UVB irradiance was adjusted to 26 mW/m\({}^{2}\). The experimental group (G1) and control group (G2) were observed for two weeks.