A plasma globe or plasma lamp is a clear glass container filled with a mixture of various

noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...

es with a

high-voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and Electrical conductor, conductors that carry high ...

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

in the center of the container. When voltage is applied, a plasma is formed within the container. 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 A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor (material), conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone e ...

and

electric glow discharge A glow discharge is a plasma formed by the passage of electric current through a gas. It is often created by applying a voltage between two electrodes in a glass tube containing a low-pressure gas. When the voltage exceeds a value called the st ...

). Plasma globes were popular as

novelty item A novelty item or simply novelty is an object which is specifically designed to serve no practical purpose, and is sold for its uniqueness, humor, or simply as something new (hence "novelty", or newness). The term also applies to practical items wi ...

s in the 1980s. The plasma lamp was invented by

Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''

currents Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

in an evacuated glass

tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...

for the purpose of studying

high voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...

phenomena. Tesla called his invention an "

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

discharge tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric ...

". The modern plasma lamp design was developed by James Falk and MIT student Bill Parker. A

crackle tube A crackle tube is a type of plasma lamp that is used most commonly in museums, night clubs, movie sets, and other applications where its appearance may be appealing for entertainment. Such a device consists of a double walled glass tube with a ...

is a related device filled with phosphor-coated beads.

Construction

Although many variations exist, a plasma globe is usually a clear glass sphere filled with a mixture of various gases (most commonly neon, sometimes with other

es such as

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...

xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

and

krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...

) at nearly atmospheric pressure. Plasma globes are driven by high-frequency (approximately )

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

at . The drive circuit is essentially a specialized

power inverter A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...

, in which current from a lower-voltage DC supply powers a high-frequency electronic oscillator circuit whose output is stepped up by a high-frequency, high-voltage

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

. The radio-frequency energy from the transformer is transmitted into the gas within the globe through an electrode at its center. Additionally, some designs utilize the globe as a resonant cavity, which provides positive feedback to the drive transistor through the transformer. A much smaller hollow glass orb can also serve as an

when it is filled with metal wool or a conducting fluid that is in communication with the transformer output. In this case, the radio-frequency energy is admitted into the larger space by capacitive coupling right through the glass. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of moving tendrils of colored light within the volume of the globe (see

and

). If a hand is placed close to the globe it produces a faint smell of

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

, as the gas is produced by high voltage interaction with atmospheric oxygen. Some globes have a control knob that varies the amount of power going to the center electrode. At the very lowest setting that will light or "strike" the globe, a single tendril is made. This single tendril's plasma channel engages enough space to transmit this lowest striking energy to the outside world through the glass of the globe. As the power is increased, this single channel's capacity is overwhelmed and a second channel forms, then a third, and so on. The tendrils each compete for a footprint on the inner orb as well. The energies flowing through these are all of the same polarity so they repel each other as like charges: a thin dark boundary surrounds each footprint on the inner electrode. 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 small amount of 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 cannot be used to fill a globe with a useful mixture. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gases involved. Of the other noble gases,

radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

escapes through the glass relatively quickly, and

is expensive. Other gases such as mercury vapor can be used. Molecular gases may be dissociated by the plasma.

Interaction

Placing a finger tip on the glass creates an attractive spot for the energy to flow because the conductive human body (having non-ohmic resistance of about 1000 ohms at room temperature) is more easily polarized than the dielectric material around the electrode (i.e. the gas within the globe) providing an alternative discharge path having less resistance. Therefore, the capacity of the large conducting 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. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner. The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized ar ...

, presented by an object, a conducting body, 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 pinch: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself. WLANL - petertf - Teslabol

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 (see also

Jacob's Ladder Jacob's Ladder ( he, סֻלָּם יַעֲקֹב ) is a ladder leading to heaven that was featured in a dream the biblical Patriarch Jacob had during his flight from his brother Esau in the Book of Genesis (chapter 28). The significance of th ...

, which exhibits a similar behavior). An electric current is produced within any conductive object near the orb. The glass acts as a

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...

in a

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

formed between the ionized gas and the hand.

History

In ("Incandescent Electric Light", 1894 February 6),

Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''

Tesla coil A Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891. It is used to produce high-voltage, low- current, high-frequency alternating-current electricity. Tesla experimented with a number of differen ...

, 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 Groundstar style of plasma globe was created by James Falk and marketed to collectors and science museums in the 1970s and 1980s.

Jerry Pournelle Jerry Eugene Pournelle (; August 7, 1933 – September 8, 2017) was an American scientist in the area of operations research and human factors research, a science fiction writer, essayist, journalist, and one of the first bloggers. In the 1960s ...

in 1984 praised Orb Corporation's Omnisphere as "the most fabulous object in the entire world" and "magnificent ... a new kind of art object", stating "you can't buy mine for any price". The technology needed to formulate gas mixtures used in today's plasma spheres was not available to Tesla. Modern lamps typically use combinations of

and neon, although other gases can be used. 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 globes 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, in recent years, some novelty stores have begun selling miniature plasma globe

nightlight A nightlight is a small light fixture, usually electrical, placed for comfort or convenience in dark areas or areas that may become dark at certain times, such as at night or during an emergency. Small long-burning candles serving a similar fun ...

s that can be mounted on a standard light socket.Plasma Night Light
, 4physics.com, 2010-02-17 Plasma globes can be used for experimenting with high voltages. If a conductive plate or wire coil is placed on the globe, capacitive coupling can transfer enough voltage to the plate or coil to produce a small arc or energize a

load. This is possible because the plasma inside the globe and the conductor outside it act as plates of a capacitor, with the glass in between as a dielectric. A step-down transformer connected between the plate and the globe's electrode can produce lower-voltage, higher-current radio frequency output. Careful earth grounding is essential to prevent injury or damage to equipment.

Hazards

Bringing conductive materials or electronic devices close to a plasma globe may cause the glass to become hot. The high voltage radio frequency energy coupled to them from within the globe may cause a mild electric shock to the person touching, even through a protective glass casing. The

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the ...

field produced by plasma globes can interfere with the operation of touchpads used on

laptop computer A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper li ...

digital audio player A portable media player (PMP) (also including the related digital audio player (DAP)) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. The data is typically stored o ...

cell phones A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...

, and other similar devices. Some types of plasma globes can radiate sufficient

radio frequency interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...

(RFI) to interfere with

cordless telephone A cordless telephone or portable telephone has a portable telephone handset that connects by radio to a base station connected to the public telephone network. The operational range is limited, usually to the same building or within some short ...

s and

Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wav ...

devices several feet or some meters away. If an electrical conductor touches the outside of the globe, capacitive coupling can induce enough potential on it to produce a small arc. This is possible because the globe's glass acts as a capacitor

: the inside of the lamp acts as one plate, and the conductive object on the outside acts as the opposite capacitor plate. This is a dangerous action that can damage the globe or other electronic devices, and presents a fire ignition hazard. Perceptible amounts of

can be formed on the surface of a plasma globe. Many people can detect ozone at concentrations of , which is right below the lowest concentration at which ozone is considered harmful to health. Exposure of produces headaches, burning eyes, and irritation to the respiratory passages.

References