What are the green lights on these houses for...?

Actually of course it isn't, being as the materials it's made of is atoms each of which contains a nucleus.

And there will be a certain amount of radioactive materials in the building materials, even if the building predates WW2.

I hope you proclaim loudly each time you go there that this nuclear-free-zone stuff is just a waste of taxpayers' money. You know you want to.

I would never proclaim anything loudly in the library. Mostly because I was properly brought up, not because I was concerned about interrupting the story time or encyclopaedia-throwing competitions or whatever it is libraries have to do nowadays to attract custom (instead of just having books on shelves).

Maybe the green lights mean "it's okay to mow the lawn, I'm not on night shift"?

Owain