Products in this family include various small scale lamps or "light bulbs" in form factors typically used for indication or backlighting purposes. The incandescent types produce light by heating a thin metal filament to a high temperature, and are commonly found in legacy equipment. Neon types produce light on the basis of passing electric current through a gas such as neon at low pressure, and are not particularly efficient at production of light. They do, however, require a relatively high drive voltage compared to other common indicator lamp types, and for this reason are often used to indicate the presence of AC line voltage.