LED Traffic Signal Luminous Intensity Degradation: A Preliminary Data Analysis

Abstract

Light emitting diodes (LEDs) have replaced a high amount of incandescent lights in the past couple decades. LEDs, when they degrade keep bright even though they fall outside of the required specification values determined by the Institute of Traffic Engineers 2005 traffic signal specification. The purpose of this research study is to take measurements of various traffic signals in both Anchorage Alaska and Fairbanks Alaska to determine the rate of decay over their years of installment. This was done by visiting 34 intersections combined and using a spectroradiometer to measure for luminance which then converted to a luminous intensity value by applying the ITE guidelines of conversion. Results confirm what was expected that traffic signals show a trend as they do degrade at an increase the longer they are out on deployment. A hypothesis testing of means was one of the methods applied to prove this theory. LEDs do degrade over time, however it is important to find the trends so that department of transportations and engineers can make the safest and cost effective decision as to when to replace a LED traffic signal.