Red LED traffic lights have apparently been available much longer; I don't know if they weren't used because municipalities didn't want to deal with two different technologies, or if they are being used, and they just don't look as different. Anyway, the green ones are distinctive not just because they're brighter, but because the green is much more saturated. (Apparently one of the reasons they're so bright is so they can stay in service even as some of the LEDs in the array go bad, extending the lifetime.)
Replacing a red incandescent traffic signal head with a red LED unit will cut energy use by an estimated 82 to 93 percent. The payback for the initial investment in red LED traffic lights is approximately 2.5 to 3 years through energy savings. The actual payback period depends on energy prices, the cost of the units, and any financial incentives offered by utilities or government agencies.
Also, from the same source "LED traffic signals are estimated to last 5-10 years before they must be replaced, compared with 1 to 2 years for incandescents."
At the time of that report, the green ones were not cost-effective in most places; I presume that manufacturing costs are now lower and electricity costs higher (which probably also means the payback time on the reds is now shorter.)
(no subject)
According to an January 2000 EPA Report (pdf) on LED lights:
Also, from the same source "LED traffic signals are estimated to last 5-10 years before they must be replaced, compared with 1 to 2 years for
incandescents."
At the time of that report, the green ones were not cost-effective in most places; I presume that manufacturing costs are now lower and electricity costs higher (which probably also means the payback time on the reds is now shorter.)