Why are fairy lights called fairy lights? Iolanthe or, The Peer and the Peri, is a comic opera by Gilbert and Sullivan which opened in London on 25 November 1882, at the Savoy Theatre (the first public building in the world to be lit entirely by electricity) In Iolanthe, a story about Fairies, the Fairies wore tiaras with lights in them powered by batteries, which must have been quite large so started the Christmas fashion for decorative lights. Now you know.