Development of a fiber daylighting system based on the parallel mechanism and direct focus detection

In this paper, a fiber optic daylighting system based on the parallel mechanism is designed and fabricated. This system is composed of 49 concentrating cells, which are arranged in a 7 × 7 array. The array consists of 48 sunlight-collecting cells and a sun position sensor using direct focus detection. A linear actuator, which is composed of two stepper motors and two roller screws, is used to drive the concentrating array to track the sun with the movement in a plane parallel to the plane containing the array of fiber optic collecting aperture. The solid angle of the sun tracking angle range for the concentrating cells is 4π/3 sr (covering 2/3 of the sky), satisfying the demand for 8 h of tracking. This system is suitable for building integration because it has a compact and flat shape. The sun position sensor consists of photodiodes and a fiber array in the shape of a cross. The sun position sensor can directly measure the high flux density of the focus (2500 suns). A series of tests were performed using a lux meter and spectrometer to investigate the photometric characteristics of the system for a lightless underpass of 8.6 m × 4.2 m × 2.3 m. The experiments show that the transfer efficiency of this system can reach 25% (with a 10-m long fiber). The luminous efficacy can reach 250 lum/W, which is two times than that of natural light because the fiber can filter out infrared light. The experiments also verified the feasibility of the daylighting system using the parallel mechanism and a direct detection device for highly concentrated light.