## 1 Introduction  
Since natural light contributes to the prevention of disease and the suppression of mental illness, proper exposure to daylight is an essential element for enhancing physical and mental health [1]. Natural light includes infrared and ultraviolet (UV) rays that are not provided by general lighting, and these elements have a great impact on human health [2; 3]. Particularly, UV light may cause harmful or beneficial effects depending on a person's degree of exposure; therefore, precaution is needed for appropriate exposure [4]. UV is divided into ultraviolet A (UVA) (315-400 nm) and ultraviolet B (UVB) (280-315 nm), which reach the earth surface, and ultraviolet C (UVC) (200-280 nm), which is mostly absorbed in the ozone layer and cannot reach the surface. UVA penetrates deeper into the dermal layer of the skin and produces reactive oxygen species that cause skin aging and wrinkle formation [5; 6]. Meanwhile, UVB causes skin pigmentation, weakens skin barriers, and promotes erythema and skin cancer [7; 8]. In general, UV is known to be harmful to human body, but UVB helps the body synthesize vitamin D which is an essential element for human health, benefiting health by relieving hypertension and cardiovascular disease [9; 10]. Particularly, vitamin D in the body is supplied in a very small amount through food, and most of it is known to be synthesized in the body after UVB in the sun is irradiated to the skin. Therefore, appropriate exposure to UV has recently been recommended [11; 12]. However, it is becoming difficult for modern people to be exposed to natural light due to increased indoor dwelling and UV exposure insufficiency. Kecorius has reported that people spend an average of 84% of their time indoors during the day [13], and [PERSON] has reported that exposure to UVB is limited at indoors since UVB cannot penetrate general glass [14]. As exposure to natural light and UV rays becomes difficult, various studies and efforts are being made to provide UVB indoors. In some research papers, recommended time and methods for optimum exposure to UV according to skin type, age, and current UV index (UVI, Ultraviolet index) are suggested [15], and a portable measuring device that provides information about UV during outdoor activities and consequent estimated amount of vitamin D synthesis was developed [16]. However, such methods only either suggest to the user a duration for outdoor activity or provide passive information about estimated amounts of UV and vitamin D synthesis. On the other hand, [PERSON] verified the vitamin D synthesis effect on vitamin D deficient patients by using a commercial tanning device with an artificial UV light source, and a UV special lighting device was developed that provides a UVB dose to parts of the body for skin treatment [17; 18]. Research has also been carried out on the development of UVB Light Emitting Diode (LED) indoors lighting, which provides harmless levels of UVB light [19]. However, these UV lighting technologies control the irradiation time of lighting among the users, but they fail to implement a lighting system that provides UV dose at indoors by linking to the UV exposure amount of an individual outdoors. Therefore, this paper proposes a UVB LED general lighting that provides users with a satisfactory UV dose required daily by individuals based on the calculation algorithm of UV exposure amount. The proposed system consists of an IoT (Internet of Things) UV measuring device, a smartphone, and UVB LED general lighting. The IoT UV measuring device measures the strength of UVI when the users conduct outdoor activities and sends the result to the smartphone. In the smartphone, cumulative UV doses are calculated based on the received UVI values and an output of daily optimum UV dose is given considering the skin type of the user, age of the user, and exposed area. When the cumulative UV dose of the user cannot reach the daily optimal UV dose, it compensates for the insufficient UVB dose through UVB LED general lighting.