# A Simple Designed Lens for Human Centric Lighting Using LEDs
###### Abstract
Shadowless, low source brightness and highly diffuse quality made by indirect lighting provide a quiet and cool ambiance, suitable for lounges, waiting halls and areas having specular visual tasks such as workplaces with digital screens. Uplighting systems have been applied and improved over time by several methods of analyzing and simulating. [PERSON] et al. [10] and [PERSON] et al. [11] have introduced ceiling lighting fixtures combining both upward and downward directed LEDs in order to make the most of a ceiling fixture. These luminaires show high efficiency in lighting, however, the efficiency is proportional to the complexity of the fixtures. Lighting simulation and freeform lens designing are also being studied and exploited [12; 13; 14]. The available optical freeform design methods include multiparameter optimization, the Wassermann-Wolf differential equation [15; 16], tailoring method [17], point-to-point mapping [16; 18], geometric and variational method [19], and simultaneous multiple surface method [20]. The freeform design method should be selected according to the specific applications [5]. Freeform lenses have shown the difference in luminosity intensity distribution in comparison with the single typical LED, hence, the study of freeform optics has been developed for various needs on every scale. For open space lighting, like street lighting, an asymmetric freeform lens for low glared LED street light with total internal reflection [21] and microlens arrays can help in achieving the desired illuminance on the road [22]. On the microscopic scale, LED arrays have also been exploited in the study of phototherapy and many medical purposes [23; 24]. For indoor lighting, concerning the simplicity of the lighting system and also boosting up the quality of indoor uplighting, our idea is to design the form of a lens covering the LED tube and propose lighting installment for this luminaire. These free-form lenses modify the luminous intensity distribution of typical LEDs and regulate the propagation of light emitting from the light source toward the desired surfaces, particularly to the ceiling. This allows the directly illuminated area, which is the secondary light source, to be broadened, hence, increasing the diffuse quality for higher uniformity of illuminance. With the ideal room and lighting system, well-directed light by free-form lenses can result in lower light pollution since less light would be coming out of the room, meanwhile, a shadow-free and sharper image in the room is expected, giving nature-like vision and a comfortable feeling for humans when in contact. While architecture covers may need a complicated design and difficulty in installing, the ballast used in our model is simple and aims for minimalism. The setup also blocks direct viewing and eliminates direct glare caused by the contrast between the light source and the surroundings, which is superior to downlight and general fixtures. The overall size of a complete luminaire is the same as a typical fluorescent tube, making it flexible in installing in residential architecture. Despite lenses providing less glare control than lowered fixtures, we believe that the combination of our lens design and uplighting installment can provide harmony in both lighting productivity and glare control. We choose UV-stabilized acrylic plastic as the material not only for its use in delivering the light output and uniformity of all shielding media, but also for its low-cost and suitability for mass production. Clear lenses are much more efficient than common white translucent diffusers, and they result in relatively high visual comfort.