In the general public environment, ambient power-frequency electric fields are relatively small, except when near high-voltage
(HV) transmission lines. Electric fields from aerial HV transmission lines are greatest directly under the conductors and decrease with. In occupational environments, elevated electric fields also exist in HV substations/switchyards, and in particular under busbars/equipment. Other sources of power-frequency electric fields in the environment include electrical wiring, lighting and certain appliances which create small ambient electric fields (a fraction of kV/m) in the indoor environment.