關鍵詞：LED 交通標誌、眩光、視覺舒適度、判別度;Traffic signs are an indispensable part of our daily lives. However, the traditional traffic signs with retroreflective sheets and external lighting are almost invisible in severe weather such as heavy rains or fogs. With the popularity of LED lighting and display applications, people start to apply LEDs in traffic signs. Due to the characteristics of small light-emitting area and high directivity, LEDs are considered more probable to induce glare that disturbs human’s visual sensation. To investigate the legibility and visual comfort of LED traffic signs, an ergonomic experiment is designed and performed.
Two factors are used in the experiments: the uminance contrast and the luminance of green background. The contrast is defined as the ratio of green-background luminance to white-text luminance. The design criterion for the luminance takes the suggestions from the Bureau of Energy, Ministry of Economic Affairs and IESNA (Illuminating Engineering Society of North America), and is set in the range of 20-500 nit. The contrast is set at 1:2 to 1:11,taken and slightly extended from the comfort region in VDT (visual display terminal) studies. Subjective ratings on legibility and visual comfort are obtained by questionnaires.
The results show that the luminance contrast is a significant factor for both the legibility and visual comfort, while the green-background luminance is not. Post hoc comparisons show that the contrast from 1:7 to 1:9 is preferable when considering the legibility and visual comfort at the same time. The contrast less than 1:5 induces relatively poor visual experiences. Finally, the experimental data are utilized to construct mathematical models of legibility and visual comfort as functions of contrast and green-background luminance. Operating suggestions for LED traffic signs are drawn from the models to provide satisfactory legibility and visual comfort.Keywords: LED traffic signs, Glare, Visual comfort, Legibility
