Performance evaluation of light shelves

This paper aims to objectively evaluate the potential of light shelves to improve daylighting and visual comfort. This study consists of two parts. The first part is experimental and involves measurements taken on a scaled prototype. More than one million data points were collected using illuminance sensors installed on a test chamber. The data was analyzed statistically and the performance of the light shelf was evaluated for various configurations. A horizontal light shelf is found to increase the illuminance in the interior by an average of 21%. By rotating the external light shelf to an optimal angle, up to 300% increase in illuminance can be achieved. The second part of the study consists of purely theoretical simulations. Some new metrics such as useful daylight enhancement (UDLE) were developed specifically to evaluate the daylighting performances of light shelves. A case study of a hypothetical building in Chennai is taken and simulations are performed using Radiance lighting simulation software. 1080 simulations were performed under various configurations. It is found that most of the common assumptions about the performance of light shelves are not supported by simulation results. Even though, in many cases, the horizontal light shelf is able to improve illuminance at distances greater than the height of the window, the area where there is useful daylight enhancement is low. It is commonly assumed that light shelf provides shading near the window, thus eliminating glare. However, in 30% of the simulated cases, horizontal light shelves are found to increase the illuminance near the window, thereby increasing the possibility of glare. Light shelf is also found to decrease the uniformity in illuminance. These problems can be eliminated by using a rotatable light shelf.