This paper discusses the technical aspects of LED (light emitting diode) traffic lights, and estimates the expected savings if all traffic lights in London were to be replaced by LEDs. LEDs have many advantages, and are now available in various colours including red, amber, green, and white. However, the move to LEDs for all three lights of a traffic signal has been slow, because it has only recently become possible to make green LEDs economically. The light of modern LEDs does not degrade with time, and tests show extremely high reliability. LED traffic lights consist of several hundred LEDs connected in series-wired chains. The annual energy savings on individual traffic signals are considerable. Traffic lights in London consist of lights for traffic signals, pedestrian signals, pedestrian crossing control wait indicator panels, regulatory box signs, and other warning and emergency signs. A table shows estimates of the economics of replacing the lights in London's 43,000 traffic signals by LEDs. For each colour, the annual savings in electricity and maintenance exceed the total installation cost. The payback period for red, amber, and green lights are 8, 28, and 18 years, respectively. A pilot site will be set up in London in early 1998, to evaluate the performance of LED traffic lights of all three colours.
Samenvatting