As far as guided tours of central Rome go, this one was a downer. “Look over there, at that ‘Virgin and Child,’ with that ugly lamp above it, casting such a harsh outline,” said Nathalie Naim, a municipal council member, pointing to a framed image on a wall.

Near the Colosseum, another outrage. “This used to produce a light with a golden halo, that soft and welcoming light that envelops you,” Ms. Naim lamented, nodding to one of the cast-iron lampposts that dot the city center. Alas, no more.