An eight-inch diameter plasma globe

Plasma lamps are novelty items which were most popular in the 1980s. They were invented by Nikola Tesla for the purpose of studying plasma. Tesla called his invention an "Inert Gas Discharge Tube".

Although there are many variations, a plasma lamp is usually a clear glass orb with a much smaller orb in its centre. Beams or snakes of "light" (actually ionized gas) move from the inner ball to the outer glass container, giving an appearance similar to multiple constant beams of coloured lightning (see electric glow discharge).

Touching the exterior orb grounds out the current, causing a single beam to snake around from the inner ball to the point of contact. The current does move into the object it makes contact with, as the glass doesn't block the flow of current when high frequencies are involved; the glass acts as the dielectric in a capacitor formed between the ionized gas and your finger.

One should be careful when placing electronic devices (such as a computer mouse) by or on the plasma lamp: not only may the glass become hot, but the high voltage may put a substantial static charge into the device, even through a plastic protective casing. Various touch-pad devices such as laptop computer trackpads and Apple computer touchpad iPods are known to not work in close proximity to these lamps.

See also: Lava lamp

External links

• POWERLABS.org - Plasma Globes (http://www.powerlabs.org/plasmaglobes.htm#%A0PROFESSIONAL%20PLASMA%20GLOBES:)
• Science Hobbyist: Plasma globes without glass or vacuum (http://amasci.com/tesla/heli1.html)