plasma globe

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Plasma globe

A plasma globe

A plasma globe orplasma lamp (also called plasma ball, dome, sphere, tube or orb, depending on shape), is

(usually) a clear glass orb filled with a mixture of various noble gases with a high-voltageelectrode in the center

of the sphere. 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).

Plasma globes were most popular as novelty items 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]

Description

The effect of a conducting object (such as a hand) in close proximity with the plasma globe glass

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 othernoble gases such as argon, xenon andkrypton) at nearly

atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 25 kV,

generated by a high-voltage transformer. A much smaller orb in its center serves as
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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 dischargeand 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 electrons 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. 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.

Much of the movement of the filaments is due to heating of the gas around the filament. When gas along the

filament is heated, it becomes more buoyant and rises, carrying the filament with it. If the filament is

discharging into a fixed object (like a hand) on the side of the globe, it will begin to deform into a curved path

between the central electrode and the object. When the distance between the electrode and the object

becomes too great to maintain, the filament will break and a new filament will reform between the electrode and

the hand.

An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in

a capacitorformed 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 gases involved.

Of the noble gasses, radon is radioactive, helium escapes through the glass relatively quickly, and krypton is

quite expensive. Other gasses can be used. The heated plasma will dissociate any molecular gas into its

constituent atoms.
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Hazards

Interior of a plasma ball

Bringing conductive materials or electronic devices close to a plasma globe may cause the glass to become

hot, and the high voltage may produce a substantial static charge on the conductor, which may cause a mild

electric shock, 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 radio frequency interference (RFI) to interfere

with cordless telephones and Wi-Fi devices several feet away.

If a medium-sized fluorescent lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens

ofmilliamperes 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]

History

A plasma lamp in action
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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.

The popular product sold throughout the world today was invented by Bill Parkerin 1970 as an undergraduate

student at MIT.

The technology needed to formulate gas mixtures used in today's plasma spheres was not available to Tesla.

Modern lamps typically use combinations ofxenon, krypton and neon, although other gases can be used as

well. 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.

Applications

Plasma lamp running. Note the result when the finger touches the bulb.

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]
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