Interior illumination is one of the natural ways of improving the lighting system of a building. Increasing interior illumination by natural sunlight can be affected by various factors like clouds and sun altitude which determine the sunlight intensity. Most recently, researchers have identified natural interior illumination as an opportunity to reduce electrical energy consumption in buildings. Considering that sunlight mostly illuminates areas near the windows or openings, this approach requires the development of artificial light systems capable of transmitting daylight to the deeper parts of the building. This natural lighting model will increase the system performance and reduce electric consumption by reducing the operation time of the lamps. Therefore, combining natural lighting models with different modules have attracted significant interest owing to its high potential energy saving.
In recent research, Dr. Shih-Chuan Yeh who is an associate professor at the Hungkuo Delin University of Technology in Taiwan utilized a numerical model and simulation program to investigate the characteristics of the transmitted light of symmetric prismatic sunlight collector. The proposed natural lighting system comprised of a refractive sunlight collector, guiding reflector and interior reflective emitting module. For proper analysis, the incident light beam could be divided into more than two beams due to internal reflection in the prism. The numerical model was combined with the daylight illuminances, measure during the 2016 summer, to examine the efficiency of the separate natural lighting system. Consequently, the authors also analyzed the effects of the splitting ratio of the light beam when daylight illuminates different symmetric prismatic sunlight collector apex at different times. The paper is published in the journal, Renewable Energy.
Results showed a significant increase in the average efficiency of the emerging sunlight transmitted from the underside of the sunlight collector during the day. For instance, more than 64% for symmetric prismatic sunlight collector with both 70° apex and 110° apex were reported. As a result, the degree for splitting for the incident sunlight for the sunlight collector was defined and its variation analyzed. The symmetric prismatic sunlight collector with 100° apex was observed to exhibit higher performance for incident sunlight distribution and especially in the period of the day that experienced more intense sunlight. Furthermore, the measured results indicated that during the 2016 summer, the New Taipei City experienced an average sunlight illuminance more than 80kLux under both clear and scattered sky conditions. This confirmed that the distribution of the merging sunlight is dependent on both the apex and tilt angle of the symmetric prismatic sunlight collector.
In summary, Dr. Shih-Chuan Yeh study focused on investigating the characteristics of splitting the light beam of asymmetric prismatic sunlight collector and its potential of improving the solar energy utilization efficiency, especially for lighting purposes. Because of the non-uniform collection of sunlight intensity during the day due to time and cloud factors, artificial lighting systems have been used in combination with the hybrid natural lighting systems to save energy by compensating for the insufficient indoor illumination. Therefore, as stated by Dr. Shih-Chuan Yeh in a statement to Advances in Engineering, the distribution of the incident sunlight of asymmetric prismatic sunlight collector has a great potential of improving the flexibility of utilizing solar energy in separate hybrid natural lighting systems with the main goal of enhancing energy consumption efficiency.
Yeh, S. (2019). High performance natural lighting system combined with SPSC. Renewable Energy, 143, 226-232.