Numerical modeling of tubular daylighting devices

Tubular daylighting device (TDD) or light pipe is an effective way of energy saving and has been found increasing acceptance for indoor lighting. This article presents a new method to evaluate the TDD's optical performance by the output luminous flux. The method is using position (α, d) and angular distribution of luminous flux (φ, θ, Φ) information to describe the optical properties of the TDD's light collecting cover. With the optical information, the ray tracing simulates the output luminous flux basing on the structural and reflectivity of the light pipe. Our method makes a complete optical description of light ray passing through a top cover, thus enable the subsequent ray tracing of light pipe. As an application, lambertian beam pattern is used as light source which goes through from the cover, and then the results on various length to diameter ratios of light pipes are compared.