Plasma Tube Meets Fluorescent Light Bulb

We're all about the experiments here in the science department. Our newest science exhibit, Electricity, opened on May 14 and runs through November 6. While doing some research for the exhibit we came upon an experiment so cool that we had to immediately run downstairs and try it out.

We took a fluorescent light bulb and held it near the plasma tube. To our great delight, the bulb lit up when it was close to the tube. It didn't even have to be touching the plasma tube to spark into life! That wasn't the only interesting observation either. The light on the bulb only went as far as our hands gripping the tube. Moving our hands up and down the bulb gave the impression of pushing and pulling light. It was about as close to holding a light saber as you can get! But why was this happening? The answer is in science.

From Tesla to Today

We touched on the workings of a plasma tube in a previous blog post, but it's time to go into a little more detail. In 1894, Nikola Tesla invented the "plasma lamp," but it was different from today's plasma globes. His plasma lamp consisted of a Tesla coil emitting high voltage currents into a simple glass lamp globe. This invention was largely ignored until the a more modern form emerged in the 1970s. 

In today's plasma globes, noble gasses like xenon, krypton, and neon are contained in a glass sphere with a high-voltage electrode in the center. The energy emitted by the electrode ionizes the gasses in the lamp and creates colored streams of plasma. Different combinations of noble gasses produce different colors of plasma (pure neon creates an orange light).

When you touch a plasma lamp, the streams of plasma converge around your finger. This is because the human body is a good conductor of electricity, better than the noble gasses in the lamp. The energy "chooses" to pass through you, because you are the most efficient path for it to travel. When your finger isn't on the lamp the streams of plasma move around, discharging into the glass of the globe. Air heated by plasma will lift, bringing the plasma with it and causing the mesmerizing movement in the globe! 

The Glowing Bulb

A fluorescent bulb lights up when an electrical current ionizes mercury vapor within the bulb*. The mercury ions emit light in the ultraviolet spectrum, but humans can't see in ultraviolet. To make the light visible, the inside of fluorescent bulbs are coated with phosphor powder. The powder interacts with the UV light to produce visible light.

Normally a fluorescent bulb gains its energy when the electrodes at either end of its tube are hooked up at a source of alternating current electricity. When a fluorescent bulb is brought near a plasma tube it gains its energy from the air instead. Some of the electric field generated by the plasma tube's electrode extends past the glass and into the air. When the fluorescent tube is close enough it is able to use that energy to light up. Why does the light stop at my hand? I'm a more efficient conductor than the bulb, so the electricity runs through me into the ground. 

*Mercury is harmful to humans and the environment! Since fluorescent bulbs contain mercury, it's very important to dispose of them safely. Check websites for your local recycling organizations for more information. 

While this experiment may just seem like a cool party trick, there's more to it than that. There have been some very intriguing recent advancements involving wireless electricity. A multitude of companies are developing wireless charging devices. Most of these require direct contact between the device and the charger, but charging at a distance may soon be possible too. Researchers are developing ways to beam power to drone aircraft, or even satellites, using the powers of electromagnetism.

Want to have your own electric experience? Come by and check out our devices!

- Kate Dzikiewicz, Paul Griswold Howes Fellow