Experimental analysis of solar light pipes compared to direct and light-well daylight transmission methods for indoor spaces

Abstract

Effective use of natural daylight in indoor spaces contributes to reduced energy consumption in electrical systems as well as improved occupants' visual comfort. Present experiments conduct image recording of three-floor level laboratory building models designed for solar daylight transmission through four different methods (simple window, light-well, and solar light pipes using two different flooring materials) under two incident light angles. The image-based analysis of the probability density functions associated with indoor illumination quantifies the qualitative visualizations of different daylight transmission techniques. It is found that using proper diffuser material for simple windows (direct method) may sacrifice nearly 2% of the light intensity, while significantly enhancing the distribution. In addition, the use of light pipes has provided the best distribution in the environment, which, in some cases, has improved the uniformity of light up to 15.7% compared to other methods. It is shown that the visual discomfort in direct and light-well methods due to the glare formation and indoor lighting non-uniformity under inclined incident light angles can be prevented by using light transmission tubes. At the same time, the use of light tubes at vertical angles improves intensity by up to 17.5% in addition to enhanced light distribution. Present findings based on statistical analysis clearly highlight the significance of quantifying the indoor ambient light distribution in addition to the overall intensity of light. From a practical point of view, the present study suggests that the proper implementation of light transmission tubes results in enhanced uniformity and visual comfort of indoor lighting due to glare reduction while providing sufficient light intensities comparable to other daylight transmission methods. For improved solar light pipe designs, it is also suggested to consider their efficiency dependence on the tube length as well as flooring materials.