Incandescent light sources in traffic signals and other transport equipment are being converted to light-emitting diode (LED) technology world-wide, mainly because of their dependability, cost-effective operation, low electric power consumption, minimal maintenance requirements, and good visibility in sunlight and adverse weather conditions. With the introduction of AlInGaP (aluminium indium gallium phosphide) LEDs, the performance of LED technology has improved in all its most important attributes. There have been considerable increases in light output for a given current, and luminous efficacy now exceeds 201m/W, about twice that of a coloured filtered incandescent lamp. LEDs emit light with pure colours, without needing filters. AlInGaP LEDs can produce colours from red to amber, and InGaN LEDs can produce colours from blue to green. The attribute ratings of the best LEDs are now: 6/6 for low cost, 5/6 for effectiveness, 5/6 for lifetime, 5/6 for reliability, 5/6 for quantity of characters and symbols that can be displayed, at least 3/6 for colour capability, 6/6 for visibility and legibility, 5/6 for power consumption, and 6/6 for free text programmability.
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