 The streamers spread out in a fan shape, giving it the appearance of a "brush".Corona and brush discharges are sometimes called "one-electrode discharges" because they occur in the vicinity of a single electrode, and don't extend as far as the electrode carrying opposite polarity voltage in the circuit, as an electric arc (a "two-electrode discharge") does.Both brush and corona discharges represent regions next to conductors where the air has ionized and become conductive, allowing current to leak into the air.