# Designing Safe General LED Lighting that Provides the UVB Benefits of Sunlight
## 1 Introduction  
Ultraviolet (UV) rays are electromagnetic waves of 200-400 nm wavelength bands comprising UVA (315-400 nm), UVB (280-315 nm), and UVC (200-280 nm) [1]. Of these, the UVC and most UVB rays are absorbed into the ozone layer, and 10-30% of UVB and UVA, respectively, reach the earth's surface and affect humans [2]. Excessively exposure to UV radiation causes a harmful effect on the human body. UVA promotes aging on the skin, while UVB can cause skin cancer [3, 4]. Any wavelength lower than 315 nm has negative effects on the eyes, causing inflammation of the cornea or cataract [5]. However, adequate exposure to UVB is beneficial for human health as it assists in the synthesis of vitamin D and promotes mental health [6]. UV of sunlight can be harmful or beneficial depending on the degree of exposure [7], and issues on deterioration of health, such as vitamin D deficiency due to a lack of exposure to natural light, have been raised recently [8, 9]. Vitamin D deficiency causes rickets, osteomalacia, and hypotonia and increases the risk of developing diabetes, hypertension,and myocardial infarction [10; 11]. Therefore, vitamin D is essential for human health. Studies have introduced several ways to supplement vitamin D [12; 13; 14]. Vitamin D in the body is produced through ingestion of food and supplements, or skin exposure to UVB. However, vitamin D supplementation through diet has been reported to be limited [12; 13; 15]. Even though one steadily ingests foods beneficial to produce vitamin D, such as milk and salmon, or vitamin D supplements, vitamin D deficiency is still found [16]. Meanwhile, since sunlight can support vitamin D production even with a short exposure to it [15; 17], exposure to the UVB of the sunlight is suggested as the most effective method of meeting the vitamin D requirements [14]. However, many people stay indoors for an average of 85-90% a day [18], and some of the countries in the northern hemisphere, such as the USA and European countries, are raising the issue of a shortage of sunlight due to geographic factors. In many cases, the decrease of outdoor activities is caused by an averting behavior caused by the deterioration of air quality due to fine dust or smog. In the United States, when the air quality index (AQI) is high, the outdoor activity time is reduced by 18%--among the elderly, by 59% [19; 20]. In Korea, an alert service is operated to encourage people to refrain from outdoor activities when the concentration of fine dust is high [21]. Therefore, natural light cannot completely satisfy the required UVB dose. To address this issue, UVB irradiation devices that artificially provide adequate UVB doses have been proposed [22]. However, such UVB irradiation devices are limited by the fact that there are special lightings to which certain parts of the body must be exposed at certain distances and are used for treatments with limited uses [23]. Specialized lighting for treatment does not provide natural UVB light in daily life like sunlight because users must consciously use instruments after spending money and time. Therefore, there is a lack of research on the development of general lighting that provides UVB for human health for people who are not frequently exposed to natural light. Recently, LED light sources capable of providing various optical characteristics of UV and IR and the visible light characteristics of natural light have been developed. Although LEDs are a low-power, high-efficiency light source with a high manufacturing cost, various optical characteristics can be reproduced via output control for industrial applications [24; 25]. Several lighting devices employ LED, such as light-therapy facemasks, those found in plant factory and micro algae cultivation facilities, and lighting devices for sterilization and environmental purification using UV LEDS [26]. Owing to these devices, the concern about the harmfulness of lighting devices to the human body has increased.