SCIENCE, Class-IX.Chapter 1,
The small Tesla Coil produces an alternating high voltage potential which attracts or repels free electrons. When the electrons collide with the gaseous atoms and molecules inside the globe, the gas particles are ionized creating even more electrons, as well as, positive ions. A plasma is formed. When electrons return to the ionized gas, light is produced. Touching the globe with your finger provides a ground, an addition source or sink of electrons. You can also observe super, neat, wow effects by moving a fluorescent tube or neon light near the plasma globe. They will light up in your hands!