What is a Plasma Ball?

© 2025 Kieron Conway - All rights reserved.

A plasma ball is a spectacular light display created by ionised gas atoms that produce glowing filaments of coloured light. The front covers of Journey into Modern Physics (Parts 1, 2, and 3) all feature plasma balls. If you’ve never seen one in action, just search “plasma ball” on Google; there are plenty of videos showing these fascinating devices in all their glory.

There’s a lot of physics behind them, so let’s dive in.

What is Plasma?

When energy is added to a gas, its atoms heat up. If the energy is high enough, the atoms lose their outermost electrons, becoming positively charged ions. At this point, the gas transforms into plasma: often called the fourth state of matter. Plasma is a mixture of hot ions and free electrons, and it conducts electricity extremely well.

What Gases are Used in a Plasma Ball?

The globe is filled with a low-pressure mixture of noble gases (elements from Group 18 of the periodic table). These gases, such as; neon, argon, krypton, and xenon, normally have very stable electron configurations, with completely filled outer orbitals. This stability means they rarely react with other elements (as explained in Part 1 of Journey into Modern Physics).

What Produces the Vibrant Colours?

Inside the plasma ball, noble gas atoms are excited and loose electrons. When free electrons fall back into vacant orbitals, they release energy in the form of photons of light. The colour depends on the energy difference between the electron’s excited state and the orbital it falls into. Different noble gases give different characteristic colours. The following table list the common colours produced in plasma balls and also the electron orbitals that were defined in Part1 of the Journey into Modern Physics:

OUTER

GAS COLOURS ORBITS

Neon red-orange 2s, 2p

Argon blue-violet 3s, 3p

Krypton white-blue 4s, 4p

Xenon lavender-blue 5s, 5p

A plasma ball often contains a mixture of these gases, so you see multiple colours in the glowing filaments.

How is Plasma Created in the Globe?

At the centre of the globe is a small metal electrode connected to a high-voltage electronic circuit. This circuit generates alternating voltages between 2,000 and 5,000 volts, switching polarity tens of thousands of times per second. This AC voltage creates a powerful electric field that extends from the central electrode to the inner glass surface. This oscillating, electric-field excites the low-pressure gas, stripping electrons from atoms and creating plasma. The ions and electrons are constantly accelerated back and forth at high frequency, getting hotter and hotter, and as electrons recombine with ions, colourful glowing filaments called streamers extend outward from the electrode to the inner glass.

What Happens to the Plasma?

The plasma filaments form narrow pathways where alternating currents flows most easily. These resemble tiny, branching bolts of lightning. Even the gas between the bright filaments glows faintly, as weaker electron-recombination occurs throughout the contents of the globe.

What if You Touch the Globe?

Touching the outside of the glass is safe as the glass insulates you from the high voltage. However, your finger affects the electric field inside. By grounding the point of contact, you attract nearby plasma filaments, which bend toward your finger. The effect is dramatic, as demonstrated in the videos on the web, but are even more spectacular to see in real life.

More About the Streamers

Streamers constantly shift and dance around the globe. When your finger touches the glass, one streamer becomes concentrated and brighter. The plasma in that path gets hotter and denser, often glowing white as more energy is released. Once you remove your finger, the intensity drops and the streamers return to their colourful, filament-like appearance.

Is This Related to Lightning?

Yes, plasma ball streamers and lightning are based on the same principle: ionisation of gases caused by strong electric fields.

In a thunderstorm, electric charge builds up within a cloud, or between two clouds, or between the base of a thundercloud and the ground. The base of a thundercloud often becomes negatively charged, inducing a positive charge in the ground below. This creates a strong electric field between cloud and ground. Electrons are stripped from air molecules, producing glowing plasma streamers. Some fade out, but others develop into stepped leaders: branches of ionised air moving towards the ground. At the same time, positively charged streamers rise from tall objects below. When the two connect, a conductive channel forms, and a massive return stroke surges from the ground to the cloud. This discharge releases tens of thousands of amps in microseconds, heating the air to around 30,000°C: five times hotter than the surface of the Sun!

So, while the plasma globe uses oscillating high-voltage in noble gases, and lightning uses static charges in the atmosphere, both phenomena involve the same underlying physics of plasma and ionisation.

What currents are involved?

In lightening, positive charges (ions) are moving up from the earth towards the cloud while negative charges are moving downwards in the stepped leaders from the base of the thundercloud. But, when the two meet, the massive, main-current flows in the the return strike from ground to cloud, discharging the negative charge at the base of the thundercloud. This is a DC current that manifests itself as the bright lightening bolt.

In a plasma ball, the current is constantly alternating, thousands of times a second in the streamers, like a set of miniature, stepped streamers that glow as long as the power is switched on.

Plasma balls are great talking points if you have one, especially if you can explain what's going on!

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