Indoor daylighting using Fresnel lens solar-concentrator-based hybrid cylindrical luminaire for illumination and water heating

Abundant availability of sunlight during daytime and the broad spectrum of solar energy has attracted much attention from researchers. The photometric parameters of sunlight such as color coordinates, color rendering index, and color temperature are most appropriate for human vision as compared to artificial light sources. This is due to the fact that visible portion of sunlight is almost uniform and matches perfectly with the human eye sensitivity curve. Further, it is well known that sunlight also has great health benefits. To exploit these advantages, we have developed a solar concentrator system based on a large Fresnel lens and a light guide to transport sunlight indoors. The infrared portion of solar energy is utilized for water heating, and the visible portion of sunlight is transmitted via a plastic optical fiber (POF) bundle which guides sunlight into the rooms. One end of the POF is coupled with a light guide, and another end is coupled with a cylindrical rod-shaped luminaire made up of acrylic. POFs are low cost, flexible, and easily available compared to glass fibers, and therefore are generally used for transporting sunlight indoors. However, the spectral profile of transmitted sunlight does not remain uniform in the visible portion while propagating via long POF. To achieve optimum spectral profile, a blue LED is ingrooved into the cylindrical luminaire. The design of the system, experimental details, thermal efficiency, and photometric parameters such as color coordinates, illuminance, optical efficiency, and spectrum of indoor lighting are reported. The proposed hybrid system will reduce the requirement of electricity consumption during the daytime, improve indoor illumination quality, and be useful for sustainable development.