LED traffic lights save electricity, but they generate less heat. That is a problem in colder climates: the cold bulbs allow snow and ice to accumulate and obscure the light. This is being blamed for a fatal accident in Oswego, Illinois. The solution being adopted is to send out road crews to clean the lights, which eliminates some or all of the cost savings. But at least they’re creating “green jobs”!
THERMODYNAMIC POSTSCRIPT: Above I said “but they generate less heat”, but I could just as well have said “because they generate less heat”. All the energy a bulb uses has to go somewhere. LED’s use less electricity precisely because they don’t generate as much waste heat. (LEDs also don’t waste energy on light invisible to the human eye, but I don’t think that’s much of a factor.)
LEDs and fluorescent bulbs are cold by design. Traffic light failures are a dramatic consequence, but there is a more commonplace one. In a home that uses electric heat, LEDs and fluorescent bulbs will save no energy during the heating months. Any heat that is not generated by lighting will be made up joule-for-joule by electric heaters, coming out precisely even. As a result, estimates of the energy saved by such lighting are substantially overstated (again, in homes with electric heat).