Optical Characteristics and Applicability of a Fiber-optic Hybrid Daylighting System Exploiting Sunlight and Artificial Light

Abstract

Purpose: Using sunlight and artificial light for illuminating indoor spaces (dimlit areas) was studied by operating a fiber-optic hybrid daylighting system capable of delivering constant flux of visible light streams, which enables the implementation of constant lighting despite the variation in sunlight during daytime. Method: The system adds artificial light to a stream of sunlight when there is deficiency in sunlight to meet the target illuminance according to the feedback signal generated by the photo-sensor based control strategy developed in this work. The photometric characteristics of the mixed stream of sunlight and artificial light were analyzed and the applicability of the system was tested under actual operating conditions. Spectrum variations of light were measured and analyzed to investigate the validity of light mixing, i.e., hybrid daylighting. Besides its photometry, the control of illuminance in hybrid daylighting was explored by using a test cell on a clear and a partly cloudy day. Result: Results are presented in terms of photometric properties including spectral radiance and illuminance measured as appropriate. The mixing (adding) of artificial light to meet the target illuminance was quite successful and the illuminance remained close to the desired value within an allowable tolerance of ±3.5%.