California Partners for Advanced Transportation Technology

New technologies have enabled the production of traffic signals that have significant advantages over standard incandescent signals, including greater energy efficiency and lower maintenance costs. Before the new signals are installed in the field, it is important to assure that they as visible as the older signals. We have developed a quality index we term the usability factor (UF) which can be used to evaluate the visibility of a new device relative to that of a standard reference lamp. We have measured UF's of a variety of new types of lamps by means of heterochromatic flicker photometry. We have found UF's ranging from 0.55 to 1.35 for centrally-viewed targets under standardized viewing conditions. We also report measurements made under conditions of reduced visibility. We attribute the wide range of UF's to spatial factors in the distribution of light among the various sources. Keywords: Traffic Signals, Energy Efficiency, Usability Factors, Flicker Photometry, LED, Human Factors