News Release

Green light special

Peer-Reviewed Publication

Office of Naval Research

If it seems to you that green traffic lights are getting a lot greener, you’re not imagining it. Bright new green light emitting diodes, or LEDs, are replacing incandescent bulbs in traffic lights around the country. LEDs use much less electricity and last 10 years or longer, compared with the two-year life span of incandescent lights. ONR was a pioneering supporter of the materials technology in these bright green LEDs, which are manufactured from gallium nitride. The early work was patented at the University of South Carolina. Cree Inc. of North Carolina licenses the technology and is one of two prime suppliers for the green LEDs. The Navy has long been interested in gallium nitride and related materials because they promise big improvements in the performance of ultra-wide bandwidth communications and radar systems. Gallium nitride can deliver up to 10 times as much power at microwave frequencies as the silicon and gallium-arsenide semiconductors now used in cellular telephones, military radar systems, and satellite transmitters. Most current microwave devices are made from gallium arsenide; however, there is a trade off between power and operating frequency. As frequency increases, the device’s power output drops dramatically, leaving the signal too weak to perform some communication, surveillance, or tracking tasks. Therefore, most high-power military microwave systems are still based on vacuum tubes, which have the needed power, but lack other useful properties such as lower noise. Once they are available, gallium-nitride amplifiers are expected to replace vacuum tubes in most Navy systems.

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