A large amount of older properties built before the 1970's may not have an Earth Wire, double insulated lights have 2 layers of insulation built in.
All Class 2 Double Insulated Lighting Kensington Tiffany Collection Lights for Pubs, Clubs and Bars
Class 2, or Double Insulated lighting as they are also known as, are necessary in older properties where an Earth Wire may not be present.