An Embedded System for Quasi Real-time Lighting Computation based on Sky Monitoring

Abstract

Lighting simulation plays a significant role in the architectural design and evaluation of performance parameters of buildings. The general method of assuming a virtual sky in lighting simulation may lead to mismatch with the real situation, which conventionally ignores or approximates the complexity of the real sky and surrounding landscape in luminance distribution. In this paper, we propose a compact embedded system for on-board quasi realtime lighting computation based on sky monitoring and luminance mapping. The embedded system comprises a microprocessor and a calibrated low-cost image sensor with a wideangle lens. The luminance detection range of the device, by employing the high dynamic range (HDR) technique, is able to cover 7 orders of magnitude in luminance monitoring including that of the sun, sky and ambient objects during daytime. The monitored luminance can be mapped to 1.23 million sky patches, achieving high resolution of the sky and ground dome. Taking the outdoor luminance map as input, the microprocessor conducts the on-board lighting computation by RADIANCE program based on ray-tracing algorithms. This integrated embedded system is demonstrated to accomplish an intrascene lighting computation in a quasi real-time manner based on the monitored sky and ambience. Keywords: Real-time, Sky monitoring, Luminance mapping, FPGA, Embedded System