arcing occurs when current flows through air between two conductors that are not in direct contact. Arcing produces light as electrons move across the gap between the conductors.Because dry air is a poor conductor , the distance over which an arc will travel between conductors is small. The distance over which arcing will travel in dry air increases with an increase in voltage between the conductors. We observe arcing in the form of lightning ; we see it when a switch or other electrical contact is opened or closed; we see it in the contact between brushes and commutator in many electric motor. Arcing is a function of voltage between conductors , the conductivity of the medium between them,and the distance between conductors.