Plasma globe
Plasma globes, or plasma lamps (also called plasma balls, domes, spheres, tubes or orbs, depending on shape), are novelty items that were most popular in the 1980s.[1] The plasma lamp was invented by Nikola Tesla[2] after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena, but the modern versions were first designed by Bill Parker.[1] Tesla called this invention an inert gas discharge tube.[3]
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[edit] Description
Most commonly, plasma globes are available in spheres or cylinders. Although many variations exist, a plasma lamp is usually a clear glass orb filled with a mixture of various gases (most commonly neon, sometimes with other noble gases such as argon, xenon and krypton) at nearly atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 2–5 kV, generated by a high-voltage transformer. A much smaller orb in its center serves as an electrode. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge).
Placing a hand near the glass offers an attractive place for the energy to flow. The capacity of the body to accept radio-frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. The energy is flowing through the filaments, so the filaments move too. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.[1] The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object the size of a human. The filament is thinner because the magnetic fields around it, augmented by the now-higher current flowing through it, causes a magnetohydrodynamic effect called self-focusing: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself.
An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in a capacitor formed between the ionized gas and the hand.
The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments.
The neon available for purchase for a neon-sign shop often comes in glass flasks at the pressure of a partial vacuum. These can not be used to fill a globe. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gasses involved.
Of the noble gasses, radon is radioactive, helium escapes through the glass too quickly, and krypton is quite expensive. Other gasses can be used. The plasma will take apart any molecular gas.
[edit] Potential hazards
Caution should be taken when placing electronic devices near or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge on 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, cell phones, and other similar devices.[1] Some types can radiate sufficient RFI to interfere with cordless telephones and Wi-Fi devices several feet away. If a medium-sized lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens of milliamperes to ground through the foil, enough to light a small lamp or give a small arc burn. This is possible because the glass acts as a capacitor dielectric: the inside of the lamp acts as one plate, and any conductive object on the outside acts as the other capacitor plate.[3] Ozone, which is harmful to humans, may also accumulate outside of the surface of the glass orb after a few minutes of constant operation.[1]
[edit] 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 used an incandescent-type lamp globe with a single internal conductive element and excited the element with high voltage currents from a Tesla coil, thus creating the brush discharge emanation. He gained patent protection on a particular form of the lamp in which a light-giving small body or button of refractory material is supported by a conductor entering a very highly exhausted globe or receiver. Tesla called this invention the single terminal lamp, or, later, the "Inert Gas Discharge Tube."[3]
The popular product sold throughout the world today was invented by Bill Parker in 1970 as an undergraduate student at MIT.[1]
The technology needed to formulate gas mixtures used in today's plasma spheres was not available to Tesla.[citation needed] Modern lamps typically use combinations of xenon, krypton and neon, although other gases can be used as well.[1][3] These gas mixtures, along with different glass shapes and integrated-circuit-driven electronics, create the vivid colors, range of motions and complex patterns seen in today's plasma spheres.
[edit] 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 users moving their 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. However, as of recent years, some novelty stores have begun selling a nightlight plasma lamp that can fit into a standard light socket.[4][5]
[edit] See also
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Wikimedia Commons has media related to: Plasma lamp |
- Fusor
- Lava lamp
- Vacuum arc
- Plasma (physics)
- List of light sources
- List of plasma (physics) articles
- Crackle tube
[edit] References
- ^ a b c d e f g Gache, Gabriel (January 31, 2008). "How do plasma lamps work?". Softpedia. http://news.softpedia.com/news/How-do-Plasma-Lamps-Work-77633.shtml. Retrieved Nov. 16, 2009.
- ^ Tesla, Nikola (1892). "Experiments with Alternate Currents of High Potential and High Frequency". http://www.pbs.org/tesla/res/res_art05.html. Retrieved Jul. 26, 2010.
- ^ a b c d Barros, Sam (2002). "PowerLabs Plasma Globes Page". http://www.powerlabs.org/plasmaglobes.htm#%C2%A0PRINCIPLE%20OF%20OPERATION:. Retrieved Nov. 16, 2009.
- ^ Plasma Ball Night Light Makes Us Nostalgic For Bed Wetting, gizmodo.com, 2007-11-27
- ^ Plasma Night Light, 4physics.com, 2010-02-17
