Examination of small target visibility and visibility level as road lighting design criteria

摘要

The most accepted numerical expressions of visibility in road lighting calculations are Adrian's visibility level (VL) and small target visibility (STV). Although both are referred to in recent guidelines and recommendations as design criteria, there is no agreement on their usage. They differ in their calculation method and sense and shall be interpreted in different ways. This study aims to compare and evaluate STV and VL as visibility criteria. Consequently, it is found that there can be many points with very low visibility even if the STV values are much higher than the recommendations. There is the need to define an additional criterion such as "visibility uniformity", in order to use STV in road lighting design. Or, VL values on each point shall be considered separately in design.