The demand for light-emitting diode (LED) traffic signal lamps has been growing dramatically during the last four years, and it is estimated that over 300,000 have already been installed in North America, but this is still only about 3% of the total installed base of traffic signal lamps. The growth rate is accelerating, and 150,000 more LED lamps are expected to be installed during the current year. In July 1998, the Institution for Transportation Engineers (ITE) issued a standard for LED traffic signals, which assured public officials that they are a sound investment. The benefits of LED signals are well documented. In 1993, a new, more durable aluminium indium gallium phosphorus (AlInGaP) was introduced, which has become the standard for red and amber LED traffic signals and amber pedestrian signals. A more recent innovation uses a concentrated array of fewer LEDs, for example 18 rather than 300, to provide a better and more reliable lamp design. To optimise the optical and thermal design of one such signal, the recently introduced DuraLED signal, its reflector was eliminated. The light radiation pattern of this signal uniformly illuminates the interior of its Fresnel lens. High-flux LEDs, introduced by Hewlett-Packard, are even more durable and reliable, and provide more aesthetic lights at lower cost.
Abstract