@article{3035657,
    title = "Analysis of the experimental performance of light pipes",
    author = "Vasilakopoulou, K. and Kolokotsa, D. and Santamouris, M. and Kousis, I. and Asproulias, H. and Giannarakis, I.",
    journal = "Energy and Buildings",
    year = "2017",
    volume = "151",
    pages = "242-249",
    publisher = "Elsevier Ireland Ltd",
    issn = "0378-7788",
    doi = "10.1016/j.enbuild.2017.06.061",
    keywords = "Buildings;  Daylighting;  Energy management;  Fiber optics, Clustering techniques;  Daylight penetration factors;  Efficiency characteristic;  Experimental performance;  Experimental test cells;  Exponential relation;  Spatial and temporal variability;  Spatial in-homogeneity, Lighting",
    abstract = "Light pipes can provide daylight and improve lighting conditions in buildings. Knowledge of their optical performance is a prerequisite for their successful integration into buildings. This article presents and analyses the experimental performance and the specific efficiency characteristics of a light pipe as integrated into an experimental test-cell. Extensive measurements are performed for eight continuous months under clear, cloudy and intermediate sky conditions. The spatial and temporal variability of the indoor illuminance is analysed using clustering techniques. It is found that there is an almost exponential relation between the average and the maximum indoor illuminance with the exterior illuminance levels. In parallel, a strong spatial inhomogeneity is observed under all sky conditions. The transmissivity or Daylight Penetration Factor of the light pipe is found to present a strong daily variation during the clear days while it was almost constant under cloudy sky condtions. A clear correlation of the light pipe's Daylight Penetration Factor is found against the solar azimuh and solar altitude especially under clear sky conditions. © 2017 Elsevier B.V."
}