engadget, we came across this recent press release, on how the city of Ann Arbor, Michigan plans to convert all of its more than 1,000 streetlights to LED (light-emitting-diode) lamps, at a cost of over $600,000. The city expects to save at least $100,000 a year in costs, and reduce greenhouse emissions by over 2,400 tons annually.
"The LED lights typically burn five times longer than the bulbs they replace and require less than half the energy. Each fixture draws 56 watts and is projected to last 10 years, replacing fixtures with bulbs that use more than 120 watts and last only two years."
Traditionally, LED's, while more efficient than incandescents - most everything is - have been much less efficient than alternatives such as fluorescent. The manufacturer behind the Ann Arbor process, Cree Lighting, is claiming they've created a lamp that has produced laboratory results fromm 99 lumens output per watt (warm white) to 129 lumens (cool-white), and is claiming commercial products using the technology will be available in one to two years.
The City of Chicago's Environmental Action Agenda for 2005 included a pilot project on the use of LED's for street lighting.
Because they last four or more times longer than other forms of street lighting, LED's also create labor savings by having to be changed so much less often. There are other controversies regarding the actual measurement of their efficiency, and the tonal quality of the light produced.