When a gas is subjected to high voltage stress, the electric field is often quite non-uniform near one, or both, of the high voltage electrodes making up a spark gap. Breakdown initially begins with the formation of corona discharges near the electrode with the highest electrical stress. If the electrical field is further increased, longer length cold discharges (called streamers or burst corona) sporadically form near the stressed electrode. Streamers attract multiple electron avalanches into a single channel, propagating forward quickly via photon emission which leads to photoelectrons producing new avalanches. Streamers redistribute charge within the surrounding gas, temporarily forming regions of excess charge (space charges) in the regions surrounding the discharges.