# A Simple Designed Lens for Human Centric Lighting Using LEDs
###### Abstract  
Light is generally important for human beings. Visible light supports vision and can modify circadian rhythm, and together with invisible light at longer or shorter wavelength can also make either a direct or indirect impact on human biological and mental health. For medical applications, several studies have shown success in using light to fasten the skin regeneration in burns and to cure diseases such as newborn jaundice. In daily life, an appropriate amount and time exposure to certain types of light can result in rising of alertness and mood improvement, which leads to noticeable growth in one's productivity. Therefore, human centric lighting can modify lighting factors to make the best of the natural characteristics of light. The seek an ideal indoor lighting system is widely carried out not only by scientists but also by architects. A qualified luminaire is considered by many factors, including luminous productivity, visual comfort and expenses; meanwhile, the idealization of illuminance is also constructed in many ways, such as widening the lamp's surface area, changing of luminaire's positions and applying different methods to illuminate a surface. Approaching these problems, our idea is to study the uplighting method and freeform optics using low-cost acrylic lenses. By changing lens shape and optimizing the factors which affect the illuminance such as the irradiation angle and the distance between the luminaire and the reflection surfaces, we find the most effective lens and its peaks due to each factors using the ray-tracing simulation to obtain results concerning high uniformity of illumination. refeurm optics; uplighting; ray-tracing simulation; human centric lighting +
Footnote †: journal: Medical  
brightness, etc.) and quality (glare, uniformity of illuminance, color rendition, etc. ), productivity and alertness could be boosted thanks to a boost in both visual and nonvisual factors [3; 4; 5; 6]. On the contrary, an inappropriate amount of any factor of lighting can result in discomfort, annoyance and reduced productivity. Lighting for health and wellbeing has been known as Human Centric Lighting (HCL), or circadian lighting. At present, HCL is widely being researched and invested in house and working environment design in order to maximize the benefits of proper lighting [3; 7; 8]. Up to now, downlighting and semi-direct lighting appear to be more common than other types of lumination, including uplighting. For example, recessed lighting luminaires such as LED panels are often used in a low-ceiling room for taking up small space and in showrooms and displays because downlighting provides high lighting levels over a certain area, which benefits in drawing attention to desired objects. Conversely, this characteristic of downlighting requires the whole lighting system to have a great number of luminaires to cover a large area, which is costly in indoor architecture. Luminaires recessed on one surface also cause unavoidable loss of light in the horizontal direction. This kind of problem happens less in conventional surface-mounted fixtures such as round-shaped ceiling lamps or fluorescent tubes. However, these fixtures bring up a serious contrast between luminaires and the surroundings, not to mention low uniformity of illuminance [9]. Approaching the problems, we consider an uplighting system, which has been shown to overcome several limitations of the two previous types of lumination and is successfully applied in residential architecture. In indirect or uplighting, 90-100 percent of light goes directly to the ceiling and upper walls, making use of reflection to make these surfaces secondary light sources that enlighten the space underneath. When properly designed, this system yields a considerably uniform bright ceiling and nearly uniform, glare-less illumination within the room.