The incandescent lamps used in the green threshold lamps that form a line on the front end of an airport runway, have relatively short lives and require constant maintenance. The green filters used in front of the lamps transmit only about 20% of the light. Green light emitting diodes (LEDs) have been improved recently and are reaching brightness levels making it possible to use them in traffic lights. The red ones are already widely used in traffic lights. Our goal is to develop LED replacements for the incandescent threshold lights. Circuits that will avoid having to rewire the system will be devised. The advantage of LEDs is very long life, high reliability, freedom from sudden failur and low power consumption.
