Plasma lamp
From Freepedia
Plasma lamps (also variously plasma globes, plasma balls, plasma domes, or plasma spheres) are novelty items which were most popular in the 1980s. They were invented in 1904 by Nikola Tesla for the purpose of studying plasma, and later popularized by the Exploratorium artist Bill Parker. Tesla called his invention an Inert Gas Discharge Tube. Lamps are available in different shapes, including spheres and cylinders.
Although there are many variations, a plasma lamp is usually a clear glass orb, filled with a mixture of various gases at low pressure, and driven by high frequency alternating current at high voltage. A much smaller orb in its centre serves as an electrode. Beams or snakes of "light" (actually emergent patterns in ionized gas) extend from the inner electrode to the outer glass container, giving an appearance similar to multiple constant beams of coloured lightning (see corona discharge and electric glow discharge).
Placing a hand near the glass alters the high-frequency electric field, causing a single beam to snake around from the inner ball to the point of contact. An electric current is produced within any conductive object near the orb, 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 the hand.
One should be careful when placing electronic devices (such as a computer mouse) nearby or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge into the device, even through a protective plastic casing. The radio frequency field produced by plasma lamps can interfere with the operation of trackpads used on laptop computers, Apple iPods, and other similar devices.
Ozone may also accumulate near the surface of the glass orb after a few minutes of constant operation. It accumulates at an accelerated rate if a hand is placed on the glass.
