Analysis of the experimental performance of light pipes

•An experimental analysis of the performance of light pipes under the mediterranean climate was performed.•Exponential relation between the average and the maximum indoor illuminance with the exterior illuminance levels was found.•The Daylight Penetration Factor of the light pipe had a strong variation during the clear and low variation under cloudy sky.•The Daylight Penetration Factor depends highly on the solar position.

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.