These are probably made for areas with SWER power lines. SWER is Single Wire, Earth Return. A single high voltage 7-20kV line would feed one side of a transformer and the other would return via a ground stake. This is a rather cheap way of electrical distribution for remote rural areas, as only one wire is used. This type of system has a lot of surges and fluctuations due to long wire runs. Thus bulbs like this are needed to take the voltage surges.