Plasma globe

Plasma lamps (also variously plasma globes, balls, domes, spheres, or orbs) are novelty items which were most popular in the 1980s. The plasma lamp was invented by Nikola Tesla after his experimentation with high frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena. Tesla called this invention an Inert Gas Discharge Tube.

Plasma is a highly ionized gas consisting of almost equal numbers of free electrons and positive ions.

Description

Plasma 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 (approx. 35kHz, 2-5kV), generated by a high voltage transformer. A much smaller orb in its center 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). The beams first follow the electric field lines of the dipole, but move up due to convection.

Placing a hand near the glass alters the high-frequency electric field, causing a single beam to migrate 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 touchpads used on laptop computers, digital audio players, and other similar devices. Additionally, when a metal is placed on the surface of a plasma lamp's glass, a danger of shock and burning does exist; it is very easy for electricity to be emitted from the lamp if said metal comes in contact or close proximity with certain other materials, including human tissue.

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 or metal object is placed on the glass.

History

In U.S. patent 0,514,170 ("Incandescent Electric Light", 1894 February 6), Nikola Tesla describes a plasma lamp. This patent is for one of the first high intensity discharge lamps. Tesla took an incandescent type lamp globe with the suspended conductive element and excited the element with high voltage currents from a Tesla coil, thus creating the brush discharge emanation. He gains patent protection on the particular forms of the lamp in which a light giving small body or button of refractatory material is supported by a conductor entering a very highly exhausted globe or receiver. Tesla later called this invention an "Inert Gas Discharge Tube".

The popular product sold throughout the world today was invented by the artist Bill Parker, while an undergraduate student at MIT. Later he developed it into the now ubiquitous product while he was an Artist in Residence at the Exploratorium science museum. The technology needed to carefully formulate gas mixtures used in today's plasma spheres, primarily combinations of high purity rare gases, was not available to Tesla. These gas mixtures, glass shapes and integrated circuit driven electronics used to create the vivid colors, range of motions and complex patterns seen in today's plasma spheres were all developed and patented by Bill Parker in the 1980s and 1990s. The lamps typically contain xenon, krypton and/or neon, though a number of other gases can be used as well.

Applications

Plasma lamps are mainly used as curiosities or toys for their unique lighting effects and the 'tricks' that can be performed on them by moving the hands around them. They might also form part of a school's laboratory equipment for demonstration purposes. They are not usually employed for general lighting.

Uses in popular culture

In addition, plasma balls and their variations have been employed as props and sources for special effects for science fiction television shows. Among the first appearances was a plasma ball's light output, with the glass envelope filtered out, depicting the alien Chocky in the 1984 science fiction series of the same name. In March 1985, was a plasma ball featured as the aliens "Doomsday Weapon" on the TV sci-fi series V: The Series episode "War of Illusions". A plasma ball or "gizmo" was part of the primary plot as the time- and space-warping engine of an alien spacecraft in the 1985 science fiction movie My Science Project released in August 1985. Commercially-available units (lightning plates) are prominently depicted as part of Borg technology in the series Star Trek: The Next Generation. Plasma balls also feature in the opening sequences of The X-Files. The Futurama episode Insane in the Mainframe features a robot with a plasma lamp for a head.

In the UK, the late Kenny Everett, had a plasma ball in front of him when he presented a television science quiz programme for the BBC. The programme was not particularly successful and did not last more than one series.

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