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 hollow center. The cavity between the inner and outer glass tubes is filled with thousands of small phosphor coated glass beads. A 5–14 kV

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' ...

produces a low power gas discharge in the bead filled cavity, producing filaments of light that simulate

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...

. Crackle tubes get their name not because of the sound they produce but rather because of the appearance of their internal behavior. The "lightning" (filaments or streamers) is forced around and in between the phosphor-coated glass beads, due to the beads'

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 ...

nature. In so doing, the phosphor is excited by the electrical energy and fluoresces producing visible light. Like

plasma globe A plasma globe or plasma lamp is a clear glass container filled with a mixture of various noble gases with a high-voltage electrode in the center of the container. When voltage is applied, a plasma is formed within the container. Plasma filam ...

s, crackle tubes respond to touch; the filaments appear to be "attracted" toward the point of contact and usually become more luminous (brighter) as the electricity is grounded. The tubes are also filled with a noble gas like neon,

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 ...

, or

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 ...

which acts as the electron transfer medium of the cavity. The gas is typically below

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...

Typically, crackle tubes are cylindrical, however, they can be made into virtually any shape, even flat plates (trademarked by the name "Luminglas" ). The filaments can also be made to any color by combining different chemicals with the base phosphor. The chemical that is used to produce blue filaments is also responsive to

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

. The filaments can change color as they progress along the length of the tube. This effect is created by using glass beads with different chemical coatings on them, and the color of the filament changes as the electrical discharge transitions from one color layer to another. Chemical coatings can also be combined onto a single coating, allowing for a crackle tube to have multiple simultaneous filaments of several different colors. Crackle tubes appear white when viewed in their off state under normal lighting conditions. Their luminosity, or light intensity, depends on several factors, but generally crackle tubes are not very bright when compared to a fluorescent light or incandescent lamp. They are best viewed in darkness. Their transformers can also be linked to an acoustic modulator, allowing the tubes to 'respond' to music or ambient noise.

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{{Artificial light sources Gas discharge lamps

See also

References