Whilst they are generally very cheap to run, decorative garden lights would not be considered energy efficient if we were to refer to the standard EPC rating (which isn't really applicable). That’s because that system is designed to take into consideration the brightness of the lights, as well as the energy required to produce that light. Decorative lights, by their nature, are designed to produce ambient rather than practical light, so it isn't fair to judge them in the same way we would a lightbulb, for example.