Simulation of Transmission of Daylight through Cylindrical Light Pipes

Abstract

This paper presents the results of modeling and simulating the transmission of beams of sunlight and diffuse skylight, separately and together, through circular light pipes with and without bends. A well-known theoretical model of the transmission of light rays through straight cylindrical light pipes was introduced by Zastrow and Wittwer in 1986 and re-examined by Swift and Smith in 1995. The present authors propose an alternative approach that differs both in terms of the procedure for the calculation of the transmission of daylight components, and in the manner with which locally measured daylight illuminance data are utilized. The authors apply raytracing principles to trace an individual ray from the entry to the exit of a pipe. Torus sections are used to model bends in cylindrical light pipes. The present method is theoretical but lends itself to practical application and can be used for the design of a particular pipe. The paper illustrates the generation of sky luminance data from locally measured diffuse horizontal daylight illuminance data using a well-known sky luminance model, and the transmission of diffuse skylight and beam sunlight though straight pipes and pipes with bends. The computational procedure was coded into a computer program. The program was used to generate some interesting results that include results from the simulation of the transmission of daylight through straight pipes and pipes with bends.