Mercury vapor street lamps used to give off, I think, a rather good simulation of daylight as they enabled people to see clearly into otherwise dark places, but mercury vapor street lamps have now been replaced with sodium vapor street lamps because, we are told, the sodium vapor lamps use up less electricity.
As with LED traffic lights, we see the search for energy efficiency.
Unfortunately, the yellow color of the sodium vapor lamps has been found to cause diurnal (day-night) cycle disruptions of street trees which then start to sicken. Also, the yellowish light doesn't seem to penetrate the darkness as well as the mercury vapor's white light did, so, to solve that problem, new and blindingly bright sodium vapor lights have been installed in my neighborhood, which takes us back again to using more electricity while continuing to damage the trees.
We now see in the news that some states are looking into banning the sale of incandescent lamps in favor of those spiral shaped fluorescent lamps, again for the sake of energy efficiency. After all, those new lamps not only use less energy, they last a lot longer too.
Still, they eventually wear out and while they're not recyclable, they do have to be disposed of and, oh, by the way: They contain mercury.
Am I not understanding something here?