THE APPLICATION OF LIGHT-EMITTING-DIODES TO TRAFFIC SIGNALS

Under sponsorship from the National Highway Cooperative Research Progr am, tile authors have conducted extensive research in investigating th e use of LEDs in traffic signals. The purpose was to determine whether LEDs offer advantages in such applications while maintaining the requ ired safety and performance aspects. Factors investigated were the pos sibility of reduced power, decreased maintenance costs because of very long life, and improved lumen maintenance. There were numerous safety considerations such as intensity, chromaticity, and related human fac tors. Further significant matters are environmental conditions and the ir effect on these light sources. The ultimate objective of the work h as been to demonstrate and evaluate the new technology to determine it s feasibility, and to provide recommendations for possible changes to traffic signal standards. A 2-year period of extensive testing and eva luation has been completed. This effort has included the develop ment of prototype signals of the three colors and a range of types. Extensi ve photometric design and analysis have been conducted, both under lab oratory and field conditions. Field installations have been made for h uman factors testing under controlled conditions, as well as using the devices for experimental controlled intersections. Many conclusions h ave been developed, commenting on all significant factors. The researc h work and these conclusions are summarized in the paper.