Lights may be powered either from the electric field surrounding the energized wire, or the magnetic field produced by current through the wire. The first approach takes advantage of the high electric potential gradient between conductors, but a strong enough capacitive coupling is requested to allow capacitive extraction of the power required from the warning light. This means that long conductors must be suspended parallel to the line using glass/ceramic isolators: in fact several meters of suspended conductor are generally required, total length being inversely proportional to the line voltage.