High-voltage electricity and a light bulb. Footage of a high-voltage generator (right) being used to establish a circuit with a light bulb (left). The high voltage causes electrical sparks to jump across the gap between the crocodile clip and the light bulb. This display of purple electrical sparks is due to ionisation of the gas inside the bulb, forming a plasma. This is shown here with the lights on and then in close-up with the lights off.