Plasma lamp
Plasma lamps (also variously plasma globes, plasma balls, plasma domes, plasma spheres, or plasma orbs) are novelty items which were most popular in the 1980s. The technology used in the plasma sphere, high frequency currents in an evacuated glass tube, was experimented with by Nikola Tesla for the purpose of studying high voltage phenomena. Tesla called his 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 1980's and 1990's. 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 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). 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 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. Additionally, it should be noted that when a metal is placed on the surface of a plasma lamp's glass, a danger of shock 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 is placed on the glass.
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.
In addition, plasma balls and their variations have been employed as props and sources for special effects for science fiction television shows. For example, commercially-available units are prominently depicted as part of Borg technology in the series Star Trek: The Next Generation. A plasma ball's light output, with the glass envelope filtered-out, was also used to depict the alien Chocky in the science fiction series of the same name.
See also
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