Simulation and experimental analysis of light pipes with reflector under direct sunlight

Light pipes are more and more used for underground lighting as a way of daylighting. The luminous environ- ment 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 so- lar altitude angle and azimuth angle,TracePro software was used to simulate the influence of different domes and re- flectors 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 equi- nox 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.