Dusseldorf, Germany, has 17,000 gas street lamps. The city's power utility has decided to replace 10,000 of them with LED street lights, but that hasn't happened yet. So far, only about 25 of them have been installed.
Of course, LED are still kind of expensive, so there's a capital cost. But once they are in place, their operating costs are lower and they can last for a very long time. Another benefit is that you can direct light much more easily, so you can avoid sending light in all directions (people with a street light across the street from their bedroom window will understand...). The first bump in the road for LED street lights was that some people thought their white light was too cold compared to the red-ish glow of the old lamps, but that can easily be fixed by using colored LEDs. ::Replacing gas lamps with LEDs
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