Gases
The environment inside the glass enclosure is kept at a slightly lower pressure than the atmosphere. Usually a few different gases are combined within the sphere, each creating a different color. Most are made of argon or neon, which usually create a purple color. Alternatively, Xenon provides a blue color, and helium creates a white color. Nitrogen creates an orange coloring.
Electrode
The center of the plasma sphere plays a pivotal role, as it provides the energy needed for proper functioning. The electrode in the center of the plasma ball distributes an electrical current, helping to excite gaseous molecules in the sealed atmosphere. When the gaseous molecules are excited, which occurs at different times for different gases, their energy levels rise as they absorb electrons. When the electron releases and the atom returns to its natural state, a photon is released, causing the visible light picked up by the eye.
Upwards Flow
In the earth's atmosphere, hot air constantly rises above cold air. You can see these forces in the plasma ball. As the light shines, it heats up the air in the immediate vicinity, causing the "lightning" to shoot in a general upward direction when the plasma ball is left alone.
Touching the Plasma Ball
Probably the most interesting experience of the plasma sphere takes place when you touch the glass enclosure. As atoms are constantly emitting charges, they are always searching for the path of least resistance. As humans conduct electricity well, when you touch the glass of a plasma ball, the lightning streaks will immediately flow to your finger as you become the path of least resistance. Although the energy enters your body, the charges are small enough that you won't feel them.