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Light pipes are more and more used for underground lighting as a way of daylighting. The luminous environment of mine will be greatly improved if this technology can be applied in the mine underground spaces. However, the tube transmission efficiency is low in the morning, evening and the whole winter because of the low solar altitude. More sunlight was introduced into the room by adding reflectors inside the dome of light pipes. Considering the change of solar altitude angle and azimuth angle, TracePro software was used to simulate the influence of different domes and reflectors on the daylighting efficiency of light pipes under direct sunlight in sunny days. The simulation results show that after adding reflector into spherical dome, the daylighting efficiency can be improved by 13. 52% on the vernal equinox and 79. 56% on the winter solstice, while drop by 4. 11% on the summer solstice. Experimental measurements were carried out in two offices in Tongzhou, Beijing, China including clear and cloudy days. On sunny days, the average incident luminous flux could be increased by 8. 67% by adding reflectors, and the error between the simulation results and the measured results was less than 20%, which verified the reliability of the model. On cloudy days, the incident luminous flux introduced was reduced after adding reflectors, indicating that reflectors are not conducive to the collection of diffuse light. Besides weather and solar movement rules, the length of the light pipes also has a great impact on the daylighting efficiency of light pipes. How to ensure the daylighting efficiency under the condition of long-distance needs further research. [ABSTRACT FROM AUTHOR]

The vertical straight pipes are a desirable technology for delivery daylight into interior spaces because this concept benefits from luminance distribution of the whole upper hemisphere, including sunlight that is most important source of light under clear sky conditions. Vertical pipes can transport sunbeams to deep interiors independent of solar azimuth and/or room orientation. Currently, the tools for modelling different pipes are widely available, but their accuracy decreases as the aspect ratio of a light-pipe increases. In sunny environments with high solar altitudes and favorable clear skies the tubular light-guides allow to deliver daylight into deep offices, halls, or even underground spaces in building cores. The optical efficiency of such systems strongly depends on number of reflections the beams undergo on their path from the top to the bottom of a light pipe. In general, dense-grid and high CPU requirements meet when accurate numerical predictions are required. Such computations are non-attractive if intended for routine (mass) modelling. In this paper we introduce an analytical solution to the optical efficiency of straight pipes that is applicable to all aspect ratios and provides accurate predictions with very low demands on processor time. The new analytical model is validated and benchmarked against accurate HOLIGILM calculations, while showing the percent deviations are kept below 10% for most cases studied. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Theoretical and numerical analysis of the transmission function of the focusing system with high numerical aperture was conducted. The purpose of the study was to form a thin light tube in a focal area using the azimuthally polarized radiation. It was analytically shown that, due to destructive interference of two beams formed by two narrow rings, it is possible to overcome not only the full aperture diffraction limit but also the circular aperture limit. In this case, however, the intensity at the center of the focal plane is significantly reduced, which practically leads to the tube rupture. It was numerically shown that long thin one-piece tubes may be formed through the aperture apodization with diffractive axicon phase function or with complex transmission function of Laguerre-Gaussian or Airy-Gaussian beams. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents comparative monitoring of various sized commercial lightpipes at a purposely built test shed with a pitched roof. The purpose of monitoring is to simultaneously compare the performance of lightpipes of different geometries and also to provide data for establishing a formula for performance prediction. The photometric integrating box, which BRE (Building Research Establishment) has adopted as an approximation to the photometric integrating sphere, is employed to determine the lumen output of the lightpipes under real sky condition. This study presents monitoring of four sized lightpipes: straight Φ530mm, elbowed Φ530mm (with a tilted entrance), elbowed Φ450mm and elbowed Φ230mm. A mathematical model is proposed to correlate the measured lumen output, horizontal global illuminance, the diameter and length of the lightpipe, the specular reflectance, solar altitude and azimuth, and orientation of elbow if an elbowed lightpipe is tested. The coefficients in the formula are determined by regression of the monitoring data. The formula is then used to predict the lumen output of a lightpipe from the measured global illuminance for the given geometry and time. The agreement between the measured and predicted lumen output is generally satisfactory. The formula may be a useful design tool as it can predict the lumen output of a lightpipe from the global illuminance value such as those given in EnergyPlus weather data. [Copyright &y& Elsevier]