Quantitative evaluation of the discomfort glare of a tunnel pergola

The light spot on the ground at the portal of a tunnel, which is caused by the sun shining on a pergola, consists of bright areas and dark areas, and it can cause a discomfort glare for drivers. In this study, in order to evaluate the level of discomfort glare, the bright areas were compared to lamps and the dark areas were compared to the backgrounds. Using Unified Glare Rating (UGR), which is used to evaluate the glare degree in lighting places, we established a quantitative evaluation method of the discomfort glare and derived the formulas that could calculate the UGR of the pergola with equal beam spacing and unequal beam spacing. In accordance with the formulas, the UGR of the two kinds of pergolas was calculated. The results showed that the UGR of the pergola with equal beam spacing was smaller than the UGR of the pergola with unequal beam spacing, demonstrating a less level of the discomfort glare. Furthermore, the relationship between the variations of the parameters of the pergola and the UGR was analyzed, which could provide references for the design of the pergola and the improvement of driving comfort.