Crackle tube
Encyclopedia
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
sends a very low power, high frequency electrostatic discharge
into the bead filled cavity, producing filaments
of light that simulate lightning
. 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
nature. In so doing, the phosphor is excited by the electrical energy and fluoresces producing visible light. Like plasma globes, 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
, or xenon
which acts as the electron transfer medium of the cavity. The gas is typically kept at only slightly above atmospheric pressure
.
Typically, crackle tubes are cylindrical in geometry, however, they can be made into virtually any solid 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. UV light may have something to do with how the phosphor is excited by the ESF (electrostatic field). The filaments themselves 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 ESD
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. Still, they are quite bright compared to similar devices. However, 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.
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
coated glass beads. A 5–14 kV transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
sends a very low power, high frequency electrostatic discharge
Electrostatic discharge
Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
into the bead filled cavity, producing filaments
Hot cathode
In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. In the accelerator community, these are referred to as thermionic cathodes. The heating element is usually an electrical filament...
of light that simulate lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
. 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
Streamers
Streamers is a play by David Rabe. After premiering at the Long Wharf Theatre in New Haven, Connecticut in 1975, the production transferred to Broadway, opening on April 21, 1976 at Lincoln Center's Mitzi E. Newhouse Theatre, where it ran for 478 performances...
) is forced around and in between the phosphor-coated glass beads, due to the beads' dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
nature. In so doing, the phosphor is excited by the electrical energy and fluoresces producing visible light. Like plasma globes, 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
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, or xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
which acts as the electron transfer medium of the cavity. The gas is typically kept at only slightly above atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
.
Typically, crackle tubes are cylindrical in geometry, however, they can be made into virtually any solid 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. UV light may have something to do with how the phosphor is excited by the ESF (electrostatic field). The filaments themselves 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 ESD
Electrostatic discharge
Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
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. Still, they are quite bright compared to similar devices. However, 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.
See also
- Plasma (physics)Plasma (physics)In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
- List of light sources
- Plasma globe