That's actually really surprising and also sad. I understand why the efficiency and low maintenance of LED is so appealing, but you'd think in a situation like this there would be at least some thought put towards historic preservation. Don't really understand but it's just the way things are I guess.
I understand them wanting to lower carbon emissions from the lights though, but for now I’m not sure that the electric grid there is much cleaner than a gas lantern itself. Last I checked most of the electricity for Boston is generated with natural gas anyways unfortunately.
It's a lot more efficient to power an LED (or really any electric light source for that matter) with a gas fired power plant than it would be to use that same natural gas to heat up a mantle to provide incandescent light. Also, in terms of fossil fuels, natural gas is pretty much the cleanest and produces the least CO2. Still, some streetlights burning a small amount of natural gas are a literal blip on the radar compared to other sources for emissions, and it would be nice to see the uniqueness and historical value of these to at least be considered a little bit. I'd hope they plan on just replacing a certain number with LEDs while keeping some others in use.