

Well, one possibility is using something known as Fabry-Perot filter. It allows an extremely narrow frequency to pass, due to multiple reflections and interferences inside the material. Put the light source material within this filter, and you get a laser. That’s essentially the main difference between a led and a semiconductor laser. The filter makes only a narrow band of the emission be “stuck” there, creating a feedback effect that eventually tends to infinity, and a good chunk of that power passes through the filter reflectors, which are intentionally not perfect.
Other than that, I don’t think there is a filter that could be as narrow as the line emission from vapor lamps. Maybe using metamaterials, but a laser would be so much cheaper and easier. A vapor laser would certainly get the job done, but they are large and hard to maintain.
I am sorry, but it seems your Avowed is different from the one I am playing. I agree with your comment, but I am enjoying Avowed like I haven’t enjoyed any game in years! And barely any choices? Really? I just finished the first area (not the tutorial), and there were LOTS of meaningful choices! But speaking of the tutorial, there was a choice there that impacted certain future interactions. The R is definitely there in this RPG. I haven’t played a game where even the little choices matter as much as in this game!