What are Lichtenberg figures, and how do we make them?
(Last updated 06/04/24)

What are Lichtenberg figures? A bit of history...
How do we make our Acrylic Captured Lightning® sculptures?
Video clip of a huge 15 x 20 x 2 inch sculpture being discharged
Lichtenberg figures have fractal properties
Other interesting effects: fluorescence, solarization, birefringence, and discharge-free zone
"Iced 'bergs" and negative Lichtenberg figures. Do we get curved figures in a magnetic field?
Discharge speed and current measurements... and a paradox
Natural Lichtenberg figures - fulgurites, natural tattoos, and fractal lightning,
Are there practical uses for Lichtenberg figures?
Captured Lightning Sculptures are "fossilized lightning bolts"
Can I make Lichtenberg Figures?
More fun with electrons: Glowing rocks, flashing crystals, going to the dark side, and "Rad-Cams 1 and 2"
High-Beam and Glowing Air - RadCam3 
How can I get a Captured Lightning Sculpture of my very own? 
References and Further reading
Other Questions? See our Captured Lightning FAQ

Doubly-Irradiated "Windblown Lightning" Sculpture This Captured Lightning® sculpture was created by injecting trillions of electrons into a block of clear acrylic using a 5 million volt particle accelerator. Electrons were injected into one side, the specimen was rotated 180 degrees, and additional electrons were injected through the opposite side. This created two intensely-charged layers of excess electrons inside the specimen, each located about one-half inch below the surface. The charge layer on the right side was then manually discharged. The escaping electrons created a brilliant flash of miniature "lightning" that propagated upward through the nearest charge layer. Additional discharges then grew from the right layer towards the left layer, forming a complex, beautifully interconnected 3D structure. The entire discharge took place in less than 100 billionths of a second! The resulting sculpture above is illuminated from below by blue light emitting diodes (LED's). Each of our Captured Lightning sculptures contains an incredibly detailed fractal-like discharge pattern. Unlike laser art, every one of our sculptures is a one-of-a-kind treasure. As they branch, the discharge channels become increasingly thinner. The microscopic hair-like tips ultimately disappear into the acrylic. The smallest discharges are now thought to extend down to the molecular level. See our Frequently Asked Questions (FAQ) or our one-page explanation for a quick overview of how these beautiful objects are created, or you can get all the details from this web page. (Sculpture size: 3 x 3 x 2 inches or 7.6 x 7.6 x 5 cm)

What are Lichtenberg figures? A bit of history...

"Lichtenberg figures" are branching, tree-like patterns that are created by the passage of high voltage electrical discharges along the surface, or inside, electrically insulating materials (dielectrics). The first Lichtenberg figures were actually 2-dimensional "dust figures" that formed when airborne dust settled on the surface of electrically-charged plates of resin in the laboratory of their discoverer, German physicist  Georg Christoph Lichtenberg (1742-1799). Professor Lichtenberg first observed this in 1777, demonstrated the phenomenon to his physics students and peers, and reported his findings in his memoir (in Latin): De Nova Methodo Naturam Ac Motum Fluidi Electrici Investigandi (Göttinger Novi Commentarii, Göttingen, 1777). The English translation of the title is, "Concerning the New Method Of Investigating the Nature and Movement of Electric Fluid". Lichtenberg's translated paper is contained in Appendix A of a Masters thesis by Mark A Payrebrune ("Experimental Morphology of Lichtenberg Figures", McGill University, Montreal, Canada, 1979). The translated document (by Dr. J. Blain, Classics Department at McGill University) contains the following passage that describes Lichtenberg's initial discovery:

"At the beginning of spring 1777, after the completion of the new Electrophore, everything in my little room was still covered with extremely fine resinous dust that had settled, between the scraping and the shaving of the instrument's base or stand, on the walls and books. As soon as a draft in the air arose, the dust fell, much to my annoyance, on the conducting disc of the Electrophore. Often afterwards, when I held the disc suspended from the ceiling of my room, it turned out that the dust, as it settled on the base, did not cover it completely, as it previously had covered the disc, but only in certain areas. Much to my great joy, it gathered to form little stars, dim and pale at first, but as the dust was more abundantly and energetically scattered, there were very beautiful and definite figures, not unlike an engraved design. Sometimes there appeared almost innumerable stars, milky ways, and great suns. There were arcs, unclear on their concave side, but radiant on their convex side. Very glittering little twigs were formed, similar to those which frozen moisture produces on glass window panes. There were clouds of different shape and shadows that were visible in varying degrees  ...  But the most pleasing sight presented itself to me, when I saw that these figures could not be easily erased, as I tried to wipe away the dust with a feather or a rabbit foot. I could not prevent these same figures, which I had just erased, from shining forth once more, and somehow, more brightly. Therefore l placed a piece of black paper smeared with a viscous material on the figures and pressed down lightly. I was able to produce imprints of the figures, six of which the Royal Society has seen. [Note: see figures below].  This new kind of Typography has been extremely satisfying to me, hastening as I was to more remote preoccupations and having neither the time nor the inclination of  sketching the figures or destroying them all."

During his subsequent studies, Professor Lichtenberg used various high-voltage electrostatic devices to electrically charge the surfaces of various insulating materials including resin, glass, and ebonite (hard rubber). He then sprinkled mixtures of finely-powdered sulfur (yellow) and minium ("red lead", now called lead tetroxide) onto the charged surfaces. He found that powdered sulfur (which becomes negatively-charged by rubbing against its container) was more strongly attracted to the positively-charged regions on the surface. Similarly, frictionally-charged particles of red lead acquired a positive charge and were attracted to negatively-charged regions. The colored powders made previously-hidden regions of stranded surface charges, as well as their polarity, clearly visible. We now know that these charged surface regions were previously deposited by small sparks of static electricity. The sparks deposited isolated patches of electrical charge onto the surface as they flashed along the surface of the insulator. Once deposited onto the insulator surface, the charges remain stranded for a very long time since the insulator prevents them from moving and dissipating. Lichtenberg also discovered that the appearance of positive and negative dust figures was markedly different. Discharges created by a positively-charged high-voltage terminal were star-like, with long, branching paths while discharges from negatively-charged terminals were shorter, rounded, and fan-shaped or shell-shaped. By carefully pressing a piece of paper onto the dusted surface, Lichtenberg found that he could transfer the images onto a piece of paper, demonstrating what eventually became the modern processes of xerography and laser printing. The underlying physics that created Lichtenberg's dust figures evolved to become the modern-day science of plasma physics.

Positive Lichtenberg figure	Negative Lichtenberg figure

The following demonstration video is a replication of Lichtenberg's experiments using a mixture of powdered lead tetroxide and sulfur to highlight positive (yellow) and negative (red) Lichtenberg figures. In the video a Wimshurst electrostatic generator is used as the high voltage source instead of an electrophorus, as originally used by Lichtenberg, but the principles are otherwise the same. In the video, branching positive Lichtenberg figures are created first, followed by shell-shaped negative Lichtenberg figures.

Many other physicists, experimenters, and artists studied Lichtenberg figures over the next two hundred years. Notable 19th and 20th century researchers included physicists Gaston Planté and Peter T. Riess (mid-1800's). In the late 1800's, French artist and scientist Etienne Leopold Trouvelot created "Trouvelot figures" - now known to be photographic Lichtenberg figures - using a Ruhmkorff coil as a high voltage source. Other researchers included Thomas Burton Kinraide (1890's), and professors Carl Edward Magnusson, Maximilien Toepler, P. O. Pedersen, and Arthur Von Hippel (1920's-30's). Most modern researchers and artists used photographic film to directly capture the faint light emitted by the electrical discharges. A wealthy English industrialist and high voltage researcher, Lord William G. Armstrong, published two beautiful full-color books showing some of his high voltage and Lichtenberg figure research. Although these books are now quite scarce, a copy of Armstrong's first book, "Electric Movement in Air and Water, with Theoretical Inferences", was made available through the kind efforts of Jeff Behary at the Turn of the Century Electrotherapy Museum. In the mid-1920's, Von Hippel discovered that Lichtenberg figures were actually created through complex interactions between corona discharges or small electrical sparks, called streamers, and the dielectric surface below. The electrical discharges deposited matching patterns of electrical charge onto the dielectric surface below where they became temporarily stranded. Von Hippel also discovered that increasing the applied voltage, or reducing the surrounding gas pressure, caused the length and diameter of the individual paths to increase.

Riess discovered that the diameter of a positive Lichtenberg figure was about 2.8 times that of a negative figure of the same voltage. The relationships between the size of Lichtenberg figures versus voltage and polarity were utilized in early high-voltage measuring and recording instruments, such as the klydonograph, to measure both the peak voltages and polarities of high voltage impulses. A klydonograph, sometimes called "Lichtenberg's camera", could photographically record the size and shape of Lichtenberg figures that were generated by abnormal electrical surges on electrical power lines due to lightning strikes. Klydonograph measurements allowed lightning researchers and power system designers in the 1930's and 1940's to accurately measure lightning-induced voltages, thus providing critical information about the electrical characteristics of lightning strikes. This information allowed power engineers to create "man-made lightning" with similar characteristics under laboratory-controlled conditions so that they could test the effectiveness of various lightning-protection approaches. Lightning protection has since evolved to become an essential part of the design for all modern electrical transmission and distribution systems.  A schematic diagram of the active parts of a klydonograph is shown on the leftmost drawing below, along with examples of klydonograms from positive and negative high voltage transients of various amplitudes versus polarity. Notice how positive Lichtenberg figures are considerably longer than negatives figure even though the peak voltages are of equal magnitude. A more modern version of this device, called a teinograph, used a combination of delay lines and multiple klydonograph-like sensors to capture a series of time-shifted "snapshots" for a given transient, allowing engineers to capture the overall wave shape of a HV transient event. Although they were eventually replaced by modern electronic equipment, teinographs were still used through the 1960's to study the behavior of lightning and switching transients on HV transmission lines.

Schematic diagram of a klydonograph showing the position of the photographic film and high voltage electrode. Light from the high voltage discharges creates a photographic record of the event.

Comparison of photographically-captured Lichtenberg figures. Note variation in size versus peak voltage and polarity

Lichtenberg figures are now known to occur during the electrical breakdown of gases, insulating liquids, and solid dielectrics. Lichtenberg figures may be created within billionths of a second (nanoseconds) when dielectrics are subjected to very high electrical stress, or they may develop over years through a progressive series of small, low-energy, partial discharges. Countless partial discharges on the surface or the interior of solid dielectrics often create slowly-growing, partially-conductive 2D surface Lichtenberg figures or internal 3D "electrical trees". 2D electrical trees are often found along the surfaces of contaminated power line insulators. 3D trees can also form, hidden from view, inside dielectrics due to the presence of small impurities or voids, or at locations where an insulator has been physically damaged. Since these partially-conductive trees can eventually cause the complete electrical failure of the insulator, preventing their initial formation and growth is critical to the long-term reliability of all high-voltage equipment. The study of electrical trees and their prevention has been critical to the reliable design of the high-voltage power transmission systems that transfer electrical power to our homes and businesses.

3D Lichtenberg figures inside transparent plastic were first created by physicists Arno Brasch and Fritz Lange in the late 1940's. Using their newly-invented electron accelerator, they injected trillions of free electrons into plastic specimens, triggering electrical breakdown and creating carbonized internal Lichtenberg figures. Electrons are tiny, negatively charged particles that orbit the positively-charged nucleus of the atoms that make up all condensed matter. Brasch and Lange used high voltage pulses from a multi-million volt Marx Generator to drive a pulsed electron beam accelerator. An article about their research and their accelerator (which they called a "Capacitron") originally appeared in the March 10, 1947 issue of LIFE Magazine. The Capacitron could deliver a three-million volt pulse, and could generate a powerful blast of free electrons with an incredible peak current of up to 100,000 amperes. The glowing region of heavily-ionized air created by the exiting high-current beam of electrons resembled a bluish-violet rocket engine flame. A complete set of B&W pictures, including Lichtenberg figures inside a clear block of plastic, has recently become available online, as has another article with color pictures from the April, 1951 issue of Popular Mechanics. In 1944, Brasch founded the Electronized Chemicals Corporation (ECC), a pioneering researcher of using electron beams to cross-link monomers and polymers to improve their electrical and physical properties. ECC was eventually purchased by the 3M Company in 1985. 

The first formal scientific study of the injection and movement of electrical charges and charge trapping/detrapping within dielectrics was conducted by Brazilian physicist Dr. Bernhard Gross in the early 1950's. Dr. Gross confirmed that internal Lichtenberg figures could be created within a number of different polymers and glasses by injecting them with high-energy electrons from a particle accelerator. The techniques that we use to make our modern sculptures are built upon the theoretical work and experimental techniques originally developed by Brasch, Lange, and Gross. 3D acrylic Lichtenberg figures are sometimes called "electron trees" or "beam trees". We call our state-of-the-art creations Captured Lightning® sculptures.

How do we make our Acrylic Captured Lightning® sculptures?
Since 2004, we have developed and refined irradiation and fabrication techniques to create a wide variety of beautiful 2D and 3D sculptures. We begin by carefully cutting and polishing various shapes from a clear, glass-like polymer called polymethyl methacrylate (or PMMA). This material, commonly called acrylic, is sold under various trade names such as Lucite, Plexiglas, or Perspex (UK). Acrylic has a unique combination of high optical clarity and superior electrical and mechanical properties. Besides being an excellent electrical insulator, acrylic is actually clearer than glass! We have tried a number of other clear polymers, such as polycarbonate (PC), polystyrene (PS) , polyester/polyethylene terephthalate (PET), epoxy, and clear polyvinyl chloride (PVC). Lichtenberg figures can be made inside all of these polymers with varying degrees of success. However, the branches tend to be dark gray or even black instead of the sparkling white, mirror-like figures seen within acrylic. We have also experimented with making Lichtenberg figures in glass. However, since glass Lichtenberg figures often explosively shatter upon discharge or, unpredictably, days or even months later, we no longer make them. 

We inject electrons into acrylic specimens using a 5 million volt, 150 kW commercial particle accelerator called a Dynamitron. The heart of this device is the accelerator tube - a huge three-story high "vacuum tube" that operates at voltages between one and five million volts. At the top of the tube, electrons are emitted by a small, white-hot tungsten filament. The filament is connected to the negative terminal of an adjustable multi-million volt power supply. The bottom of the tube is connected to ground and the positive terminal of the high voltage supply. This configuration creates a very strong electrical field that accelerates electrons emitted from the filament. As they "fall" though the large potential difference, and they acquire a very high velocity. The bottom of the vacuum tube has very thin (only 2.3 thousandths of an inch thick!) titanium window that separates the high vacuum on the inside from atmospheric air on the outside. The high-velocity electrons pass right through the titanium window, almost as though it wasn't there! Trillions of free electrons emerge through the outside surface of the window, travel 24 inches through air then crash into our acrylic specimens on the moving carts below. Although the average lifetime of free electrons in air is only 11 billionths of a second, that's more than enough time for them to work their magic on our acrylic specimens.

The energy of the accelerated electrons is measured in millions of electron volts (or MeV). Most of our sculptures were created using electrons that had energies between 2 and 5 MeV. At these energies, electrons are traveling at relativistic velocities - between 98.5% and 99.6% of the speed of light. During irradiation, these energetic electrons burrow deep inside the acrylic before finally coming to rest. The penetration depth is a function of the energy of the electrons in the beam, the target material's dielectric properties, and its atomic density. The charging process is called "deep dielectric charging". The higher the energy of the electrons in the beam, the deeper they penetrate. For example, electrons with an energy of five MeV will penetrate about one-half inch into acrylic, but a 1/16-inch thick piece of much denser lead will completely block them.

When a thick piece of acrylic is irradiated, huge numbers of electrons accumulate inside the specimen, creating a strongly-charged cloud-like layer called a space charge. Because acrylic is an excellent electrical insulator, injected electrons become temporarily trapped inside the acrylic. By passing thick specimens through the electron beam in two or more passes, changing specimen orientation between passes, or rotating them while they're being irradiated, complex 3-dimensional space charge regions can be created inside the acrylic. As electrons accumulate during irradiation, the electrical stress (called the electric field or "E-field") inside the acrylic dramatically increases, reaching several million volts per centimeter. We normally charge our specimens to just below the point where they'll break down. We then force the charged specimens to release ("discharge") the electrons at the desired location by poking them with a heavily-insulated, pointed metal tool. This creates a small fracture that greatly concentrates the E-field at that point. The intense electrical field at the tip of the fracture overcomes the dielectric strength of the acrylic, initiating complete electrical breakdown of the specimen. During breakdown, some of the chemical bonds that held acrylic molecules together suddenly break, stripping away free electrons in a process called ionization. The newly-freed electrons become accelerated by the extreme electric field, and as they collide with other molecules, they rapidly create an ever-increasing number of new electrons in an exponentially-growing runaway process called avalanche breakdown. 

Within billionths of a second, a tree-like network of white-hot plasma channels form within the acrylic and, with a bright flash and a loud BANG, the material undergoes complete dielectric breakdown. The previously-trapped electrical charges rush out in a river-like torrent. Thousands of smaller tributaries dump their share of stored charge into larger channels that eventually merge into a single, brilliant discharge path that exits the acrylic. Although images and videos appear to suggest that we're injecting high voltage into each piece, we are actually removing the excess charges that were previously trapped inside each piece. Dielectric breakdown occurs with incredible speed - the main electrical discharge within a 4-inch square specimen lasts less than 120 billionths of a second (120 nanoseconds)! Some physicists think that dielectric breakdown within a charge-injected solid may be the most energetic (explosive) known chemical reaction.

The following image shows a 12 x 12 x 1 inch specimen being discharged. In the image, camera settings were adjusted to reduce the brilliance of the discharge so that the individual plasma channels can be seen. Note the bright descending discharge that exits from the discharge point, across the top surface of the specimen, and then to the grounded metal table below:

(Photo courtesy of Terry Blake)

As the miniature lightning bolts blast their way through the acrylic, they create millions of microscopic tubes and fractures, leaving behind a permanent "lightning fossil" deep inside the acrylic. The peak current within the electrical discharge reaches hundreds, or even thousands of amperes, depending upon the physical size of the specimen. The white-hot high-density plasma within the confined discharge channels causes the nearby acrylic to vaporize and fracture, and highest-current "roots" often char the surrounding acrylic. The exit point of the discharge creates a small crater on the surface as hot gases explosively exit the specimen.  Surprisingly, although we inject a huge amount of negative charge into our specimens, the electrical discharges originate from spark tips which are more electrically positive (versus the space charge layer), so all of our Captured Lightning® sculptures are actually "positive" Lichtenberg figures! Single-discharge branched figures continue to split as paths become finer, filling the charged area, but they never cross or form loops. The finest tips eventually disappear into the acrylic.

Some specimens self-discharge while they're being irradiated by the electron beam. This is usually caused by a small surface scratch or imperfection, left-over manufacturing or fabrication stresses, or an internal defect, such as a small bubble or inclusion, inside the acrylic. A self-discharged specimen will continue to discharge numerous times while it is being irradiated as the electron beam continues to inject new charge into the specimen. Unlike the neatly-branched structures seen in manually-triggered sculptures, self-triggered sculptures typically develop a thicker, mat-like tangle of chaotic discharges, or a complex combination of dendritic and chaotic patterns. Because of their complexity, self-discharged specimens are often among some of our most fascinating sculptures. 

Video clip of a huge 15 x 20 x 2 inch sculpture being discharged:
Following is a short video clip showing a huge 15" x 20" x 2" specimen being discharged. The specimen was first charged on one side using a 5 MeV electron beam. The electrically-charged specimen was then (very carefully!) flipped over and irradiated once more on the other side. This created two independent charge layers, each located about 1/2" below the large surfaces. Prior to discharging, the estimated potential of these internal layers was over 2.5 million volts. Because there were two very large charge layers, this specimen stored significantly more electrostatic energy than most of our other specimens - more than four kilojoules! Safety precautions were necessary to prevent the possibility of receiving a painful, and potentially dangerous, electrical shock.

Although the main discharge is quite brief (under 500 billionths of a second for this specimen), the video successfully captured the brilliance of the 4 kilojoule electrical discharge in a single video frame (shown below). Numerous secondary discharges continued to intermittently flash after the main discharge. These continued with decreasing frequency for over 30 minutes. This video is courtesy of Dr. William Hathaway, GCL Laboratories. The resulting sculpture, cradled within a custom walnut light base and illuminated by an array of white and blue LED's, is also shown below.

(Click on above image for high-resolution image)

The resulting Lichtenberg Figure is a series of branching hollow tubes surrounded by conchoidal (shell-shaped) fractures. Conchoidal fractures are characteristic of the way that glassy (amorphous) materials fracture when stressed beyond their breaking point. Since the countless fractures behave as tiny mirrors, illuminating a figure through the edges causes the entire Lichtenberg figure to glow brilliantly with the reflected colors of the external light source.

(Click for larger image) Figure 1. Dense (filiciform or fern-like) Discharges Maximum charge density Fractal dimension ~1.8 to 1.9.

(Click for larger image) Figure 2. Dendritic Discharges Moderate charge density Fractal Dimension ~1.5 to 1.8

(Click for larger image) Figure 3. Chaotic Discharges Prematurely discharged while being irradiated) Unknown fractal dimension

The self-similarity of dendritic discharges can easily be seen in the following sequence of zooms from a 12" x 12" Lichtenberg Figure. Although the branches become finer and hairlike, the overall branching structure remains similar until the finest tips ultimately disappear at the very edges of the discharge structure. Some recent research suggests that this dendritic pattern may extend to the molecular level.

View Larger Map

Other interesting properties: fluorescence, solarization, birefringence, and the discharge-free zone
When acrylic is bombarded by high-energy electrons, it glows brilliantly with a blue-white color. Radiation chemistry studies suggest that this is mainly due to luminescence that peaks at a wavelength of about 435 nm. However, acrylic also generates fainter glows from X-ray fluorescence, and Cherenkov radiation as high velocity electrons interact with acrylic molecules. The detailed light-producing mechanisms for electron-irradiated acrylic are not fully understood.

Newly-irradiated specimens develop a discolored layer in the region between the irradiated surface(s) and the discharge layer. This phenomenon, called solarization, appears to be caused by various interactions between the injected electrons and the molecular structure of the acrylic. During irradiation, electrons in the beam are initially traveling at over 99% of the speed of light. As they penetrate the specimen, they collide with acrylic molecules, rapidly coming to a stop within a fraction of an inch. Electrons in the beam have considerable kinetic energy, and as they collide with the atoms in the acrylic they release this energy as heat and x-rays. In acrylic, most solarization seems to occur in the regions directly hit by the electrons. However, regions that are intentionally covered by sheet lead (to prevent electrons from hitting some areas of the acrylic) may also exhibit solarization within deeper regions of the acrylic. As electrons crash into the lead mask, they radiate intense x-rays that apparently create a darker region of solarization in the acrylic immediately underneath the mask. Energetic collisions with electrons, x-rays, and the build-up of excess electrons stimulate chemical and physical reactions that alter the physical and optical properties of the acrylic. Deeply-trapped electrons may remain stranded within the acrylic for several years. These create color centers which also contribute to solarization. While some of these changes may last for only minutes, others persist for months or years after irradiation, and some appear to be permanent. Although all of the specific causes of solarization are not completely understood, there is evidence that irradiation creates longer-lived unstable ("metastable") compounds that preferentially absorb light at the blue end of the spectrum (wavelengths between 250 and 400 nm). Since a portion of the blue spectrum of ambient light is absorbed by the solarized region, freshly-irradiated specimens typically appear green, amber, or sometimes even rose-colored when illuminated by white light.

The solarization layer in charged acrylic specimens is most often lime-green immediately after irradiation. Within minutes of being discharged, the solarized layer changes to brownish-amber, then fades to a lighter amber color over weeks or months. The amber region usually fades away over months to several years. The fading process can usually be accelerated by heating the block in the presence of air or by leaving the specimen in bright sunlight for an extended period of time. As oxygen diffuses into the acrylic from the outside surfaces and the porous discharge layer, it slowly bleaches the solarized region, causing the solarized layer in between to gradually become thinner until it eventually disappears entirely. Most Lichtenberg figures older than 2-3 years are completely bleached. Although older specimens may no longer show any solarization, many exhibit various degrees of "fogging" from electron collisions and X-radiation damage to the acrylic's molecular structure. Some PMMA specimens exhibit comparatively little initial solarization, while a small percentage of other specimens permanently retain their amber color. Permanently-colored specimens appear to be solarized via a different, deeper penetrating mechanism, such as X-radiation, since these specimens also tend to be uniformly solarized throughout their entire thickness. These differences may be due to subtle variations in the acrylic blends and the specific catalytic agents used by acrylic manufacturers to polymerize the acrylic.

The solarized layer is often fluorescent. An amateur scientist from Australia, Daniel Rutter, discovered that monochromatic light from a green laser pointer apparently changes color when passed through the solarized layer of a Lichtenberg figure. More recently, we have discovered that the light from a near-ultraviolet source, such as a 405 nm Blu-ray laser or blue LED's, also causes the solarized region to fluoresce with a yellow-green color. Both effects appear to be due to the presence of semi-stable fluorescent components within the solarized layer. And, as the solarization fades over time, so does the fluorescence.

Most specimens also exhibit slight changes in the refractive index in the regions near the discharge layer. This may be due to residual mechanical stresses near the discharge fractures or residual electrical charges. Residual stresses near the Lichtenberg figures can sometimes be seen as multicolored regions near the discharge plane when a sculpture is illuminated by polarized light and then viewed through a second polarizing filter, a configuration called crossed polarizers. When physically stressed mechanically or by a large electrical field, acrylic exhibits a property called birefringence. When viewed through crossed polarizers, stress- or electrical-field-induced birefringence causes changes in color that are directly related to the amount and distribution of otherwise hidden mechanical and electrical stresses. The sample below clearly show internal compressive forces created by the high internal electrical field. These forces are then mostly relieved when the specimen is discharged. Following are images of the same specimen prior to charging, fully charged, and then after discharging. Little internal stress is seen in the initially uncharged specimen. The specimen was then charged by injecting electrons from the left side. The injected charge forms an intensely negative layer of charge near the center of the specimen. At the same time, positive ions (created in the air by collisions between air molecules and the high-energy electrons in the beam) are strongly attracted by the internal negative charges. The positive ions attach themselves to the external surfaces of the specimen. The outer positive "mirror" charge layer partially neutralizes the electrical field created by the internal negative charge layer, dramatically reducing the electrical field seen outside the specimen. Attraction between the internal negative layer and the positively-charged outer surfaces create intense compressive stresses within the acrylic. For the specimens below, the compressive force created between the charge layers is approximately 400 pounds per square inch (PSI). The compression can easily be seen as colored regions on either side of the center in the middle image. After the specimen is discharged, both the electrical and mechanical stresses are greatly relieved as can be seen in the rightmost image. There are still residual mechanical stresses near the discharge zone due to all the microscopic fracturing, and residual electrical stresses left over from embedded charges that were not removed by the main spark discharge. Click on any of the individual images below to see full-sized images. Further study, using a monochromatic light source, is planned for the future.

Initially uncharged specimen	Fully charged specimen (electrons were injected from left side)	Discharged specimen

Finally, all of our sculptures have a discharge-free zone along the outside boundary. Since acrylic is not a perfect insulator, some of the injected charge "leaks away" through the perimeter that separates the internal negative space charge layer and the positively-charged outer surfaces. The charge leaks away most quickly in those areas where the electrical field is greatest, such as along the perimeter. The boundary is also influenced by positive charges on surface of the specimen. As propagating streamers approach the edges of the sculpture, the electrical field "seen" by the tips of the growing discharges is dramatically reduced as they approach the positive surface charges. As the advancing streamer tips approach the outer edges, most streamers thin and die out. However, some discharge tips suddenly make an abrupt turn and then continue to grow parallel to the nearby edge.  We suspect that the positive charges on the large outer surfaces force the discharges to be confined to a thin layer, parallel to the outer surfaces of the specimen.

"Iced 'bergs" and negative Lichtenberg figures. And, do we get curved figures in a magnetic field?
From studies done by other researchers, we knew that acrylic specimens could retain their injected charge for weeks, or even months, if chilled, irradiated, and subsequently maintained at dry ice (-109F/-78.5C) temperatures. One of our team members, Todd Johnson, has christened these frozen objects as "Iced 'bergs". At room temperature, injected charge leaks away over a few minutes to a few hours for commercial acrylic. Chilling acrylic significantly reduces the speed that free charges can move inside the acrylic, and this dramatically increases the time that trapped charges can be stored. At dry ice temperatures, trapped charges can apparently be stored indefinitely. We have confirmed virtually full charge retention over several weeks, and other researchers have demonstrated charge storage for up to six months. When later discharged, these specimens behave in a fashion similar to freshly-charged specimens. The initial lime-green color of the solarized layer is also retained in chilled specimens until they are discharged. This suggests that the green color is related to the high density of electrons that remain trapped before discharging. Or perhaps this proves that electrons are green? Anyway, once discharged, chilled specimens rapidly lose their green color, changing to an amber color.

Chilled specimens develop a heavy layer of frost when exposed to humid air. When we discharge a specimen, we produce a "positive" Lichtenberg figure inside the acrylic. Photographic evidence confirms that the exiting sparks then "wrap around" the specimen. The surface sparks cover the exterior surfaces of the specimen, discharging the external layer of positive charges that have attached themselves to the specimen's surfaces. As the external surface discharges branch out, they produce a "negative" Lichtenberg figure along the large surfaces of the specimen. However, the negative surface discharges are considerably fainter than the brilliant internal discharges, so they're quite difficult to see or photograph. We accidentally discovered that, when a charged specimen is coated with frost, the negative discharges along the acrylic surface blast away the frost layer immediately above the discharges. This makes the main paths taken by the negative discharges clearly visible. The following "iced 'berg" was discharged by Todd Johnson and Dr. Timothy Koeth during our 2010 production run. As can be seen, the resulting negative Lichtenberg figures that blasted through the frost layer show considerably less branching than positive internal figures... just as professor Lichtenberg observed over 200 years ago. Other experimental evidence suggests that the "branching angle" (at the fork where a discharge path splits) for negative discharges is centered around 29 degrees, while the branching angle of positive discharges appears to be centered around 39 degrees. 

We also wondered if an externally-applied magnetic field might cause discharge paths inside the acrylic to become curved. It was known that Lichtenberg figures created within gases along dielectric surfaces become curved due to Lorentz force acting on the moving charged particles within the electrical discharges. The stronger the magnetic field, the greater the curvature:

Since we could chill charged specimens to dry ice temperatures and keep them charged indefinitely, it became possible to perform tests on charged specimens in a more controlled laboratory environment. Following our Fall, 2007 production run, Dr. Timothy Koeth placed a chilled and charged specimen within the poles of a 1.5T (15,000 Gauss) cyclotron electromagnet in his lab and then discharged it using a non-magnetic tool while it was within the magnetic field. The blue-white flash of the electrical discharge can be easily seen along the edge of the specimen in the photo below:

Image courtesy of Dr. Timothy Koeth

The above image shows the result. The pole pieces and region of maximum magnetic flux are shown by the red circle. As can be seen, the paths of the resulting Lichtenberg figure showed no evidence of any curvature. The paths look completely identical to control specimens discharged with no applied field. It's possible that the 1.5T magnetic field was simply not strong enough to show any effect. Or perhaps the net velocity of the electrons within the discharges inside acrylic is considerably slower than within gases, so the resulting Lorentz force is lower and the degree of curving is considerably smaller. A future experiment, perhaps using a stronger electromagnet, may allow us to create magnetically-curved paths.

Discharge speed and current measurements... and a paradox
During our 2007 and 2009 production runs, we measured and recorded discharge current wave forms for a number of 4" x 4" x 3/4" specimens. We designed a special holding fixture with copper foil plates that made physical contact with the large outer surfaces of a charged acrylic specimen. A heavily-insulated wire connected the pair of foil plates to a pointed discharge tool. This wire was also passed through the center of a Pearson Model 411 wideband Current Transformer (CT). When the specimen was discharged, the main current pulse flowed from the interior charge layer, through the wire (and center of the CT), to the oppositely-charged outer surfaces of the specimen. The resulting discharge current was converted to a voltage pulse via the CT - the conversion factor for this particular CT was 0.1 volt per amp. So, every 100 amps of discharge current would show up as 10 volts of output from the CT. The resulting waveform was captured and stored by a Tektronix TDS3034B 300 MHz digital storage oscilloscope (DSO). An image and schematic of the experimental configuration can be seen below:

Specimens were previously charged by injecting a cumulative charge of ~2.7 microCoulombs/cm² using an electron beam with a nominal beam energy of 4.0 MeV.  Charged specimens were then placed inside the test fixture and manually discharged. The discharge current wave forms from one of the specimens is shown below. We found that this main discharge event occurred in less than 120 billionths of a second (120 ns), the peak current reached almost 600 amperes in 45 ns, and the waveform contained four discrete current peaks. Discharges from five subsequent specimens showed similar discharge intervals, with from three to seven discrete current peaks. Overall, the peak discharge currents declined as the time between irradiation and discharge increased. This decline was expected because the injected charge slowly leaks away, reducing the amount of remaining energy and the peak discharge current. Subsequent peak current measurements on the other specimens ranged from 526 to 404 amperes.

The occurrence of multiple current peaks suggests that the electrical trees may progress via a series of larger breakdown events. Each current peak reflects a surge of newly conducting channels ("streamers" and "leaders") as newer channels blast their way into previously untapped reservoirs of charge within the acrylic, pause briefly, then surge again, etc. The average discharge velocity was between 8.5 x 10⁵ and 1.3 x 10⁶ meters/second (526 and 790 miles/second, or around 0.3% the speed of light). However, pauses between successive current surges suggest that the peak discharge velocity during the propagation phases are significantly faster. Surprisingly, the average streamer velocity within the specimen was found to be 10-100 times greater than the velocity of positive lightning leaders in air! This is thought to be due to the extreme electrical field (estimated to exceed 20 million volts/cm) at the tips of the propagating discharges.

The high streamer velocities within PMMA create a paradox, since they are over 800 times the speed of sound within PMMA. This is completely inconsistent with Griffith's theory of crack propagation within solids, which predicts that the maximum speed that cracks can propagate within a solid is limited to the speed of sound within the material (about 1.6 x 10³ meters/second for PMMA). The current waveform clearly demonstrated that the breakdown process (the complete formation of chains of cracks and gas channels across the specimen) for our Lichtenberg figures propagated at speeds that were almost 1000 times FASTER than the maximum predicted by classical fracture theory! A series of independent electro-optical measurements were taken by Dr. Timothy Koeth in his laboratory at the University of Maryland. Dr. Koeth measured the time delay between optical (light) emissions at the beginning and ends of propagating discharges within 6" x 6" x 1" specimens. His optical measurements also confirmed streamer velocities ranging between 7.4 x 10⁵ and 1.55 x 10⁶ m/s.

Some insights into this paradox may come from a Russian researcher, Yu N. Vershinin. Dr. Vershinin explored how electrostatic energy is stored and released within solid dielectrics during electrical breakdown. Specifically, he studied how energy is stored within acrylic when electrical charge is slowly injected into the material ("charge trapping"), and the effects of rapidly releasing these trapped charges ("charge detrapping") during electrical breakdown processes. Vershinin proposed that, when a dielectric contains significant trapped space charge, the stored electrostatic potential energy may be rapidly liberated, contributing to the explosive formation and growth of crack tips. As chemical bonds in the surrounding material are ruptured, some of the material breaks down into its molecular or atomic constituents, liberating high pressure gases that rapidly expand the channels behind the propagating crack tips, forcing the crack forward. Vershinin speculated (and experimentally confirmed) that for very high internal electrical fields (E-fields), the potential energy initially stored within the fields was rapidly converted into kinetic and thermal energy that drove crack propagation at hypersonic velocities. When mechanically shocked, a dielectric material that is highly stressed by an electrical field breaks down, explosively releasing energy that was previously stored within the electrical field, causing larger molecules to break into into smaller, gaseous byproducts. Breakdown occurs along rapidly propagating reaction fronts (streamers), accompanied by shock waves.

Vershinin speculated that dielectric breakdown might be closely related to the process of detonation. He found that "electronic detonation" did indeed occur within solid dielectrics, but only for propagating positive discharges within highly divergent E-fields - the very same conditions we create when making acrylic our acrylic Lichtenberg figures! An American researcher, Dr. Paul Budenstein, independently developed a theory of dielectric breakdown in solids that seems to explain many of these observations at a more fundamental level. Based upon the rate of channel expansion, Budenstein concluded that dielectric breakdown may be the fastest known chemical reaction in nature. During the breakdown process, disassociating dielectric molecules create a network of electrically-conductive plasma channels that initially have nearly the same density as the surrounding solid material. Budenstein estimated that the initial temperature of the dense plasma inside these highly-compressed channels reached 100,000 K before they supersonically expanded to create a network of hollow tubules and fractures that eventually form the resulting Lichtenberg figure. Spectral analysis shows that the initial dense plasma consists of atomic constituents of the parent dielectric, not molecular compounds. The breakdown process along each channel appears to progress in a series of discontinuous steps: gas pressure creates, and then expands, a crack into the virgin material ahead, stops temporarily, then repeats as gas expands in the newly-created crack.

Some evidence for the above theories of breakdown and discharge propagation can be seen within our Lichtenberg figures. Under a microscope, some of the discharge channels that make up the figures are found to be hollow tubes, surrounded by countless small fractures that scatter light. Some paths clearly exhibit periodic structures along the discharge channel, similar to beads along a string. These beaded structures are observed during dielectric breakdown of various polymers as well as crystalline ionic salts. The theories predict that the extreme electrical field ruptures the chemical bonds within the acrylic. The resulting electronic breakdown processes liberate gases as some of the insulating material is rapidly decomposed into its atomic constituents. Dr. Timothy Koeth has confirmed that a significant volume of gas exits from the discharge point when an acrylic specimen is discharged under water. Other researchers have determined that the evolved gases consist primarily of hydrogen, methane, carbon monoxide, and carbon dioxide. We've also observed a flame lasting for several seconds after the main discharge at the discharge point on some of our largest specimens. "Beading" appears to reflect a repetitive sequence of electronic decomposition, evolution of gases under high pressure, and formation/growth of new cracks ahead of the expanding gas zone. Following is an example of a microscopic beaded channel captured inside one of our sculptures by Dr. Bill Hathaway (GCL Laboratories). The approximate horizontal distance shown in the image below is two millimeters.

We have experimentally confirmed that "electronic detonation" during the main discharge is 10 to 100 times faster than the detonation velocity of the fastest known chemical explosives.  The stored electrostatic energy in larger specimens can exceed several kilojoules. Since this energy is typically discharged in a fraction of a microsecond, the instantaneous power liberated when creating a Captured Lightning sculpture can easily exceed a gigawatt (10⁹ watts)! Not surprisingly, the discharge creates a very loud BANG(!) as the brilliant, lightning-like spark channels wreak havoc inside the acrylic, blasting countless fractures and tubes all along the space charge layer(s). The abrupt release of previously-trapped space charge ("charge detrapping") is now known to play a major role in the degradation and breakdown of all solid dielectrics when subjected to long-term high voltage stresses, sudden voltage changes, or abrupt polarity reversals. In many respects, charge detrapping within a solid dielectric is analogous to a high-voltage capacitor discharge that occurs entirely within the insulating material. 

After the main discharge creates the Lichtenberg figure, hundreds of smaller secondary electrical discharges continue to flash throughout the specimen as pockets of residual charge redistribute themselves. Immediately after the main discharge, large sculptures sparkle and sizzle, making a sound similar to frying bacon. In large specimens, intermittent sparking has been observed over 30 minutes after the main discharge. Harmless secondary discharges often sting our fingers when we handle recently-discharged specimens. Click on the following image to see some high resolution video captured during one of our production runs that shows primary and secondary discharges.

(Photo and video courtesy of Mike Walker and Theodore Gray)
Click on the Above image to see a video clip
of many Lichtenberg figures being discharged

Occasionally, nature creates also "fossilized lightning", called fulgurites (from the Latin word "fulgur", or lightning). These are hollow, glass-lined tubes that are formed when the powerful electrical current from a lightning strike creates underground discharge channels within poorly-conducting sandy or sandy-clay soils. The intense heat from the arc-like channels melts the surrounding sand and soil particles, forming hollow glassy tubes in the soil. Larger fulgurites often exhibit fractal characteristics as they split into smaller diameter root-like branches at further distances from the site of the main strike.



Lichtenberg figures, sometimes called "lightning flowers" or "skin feathering", often form beneath the skin of unfortunate humans who have been struck by lightning. The victim often has one or more reddish radiating feathery patterns that branch outward from the entry and exit points of the strike. Here's an example of an electrical tattoo from a lucky lightning survivor:


OUCH! A temporary lightning tattoo on a "lucky" survivor
From "Lichtenberg Figures Due to a Lightning Strike" by Yves Domart, MD, and Emmanuel Garet, MD,
New England Journal of Medicine, Volume 343:1536, November 23, 2000
Medical terms for this phenomenon include arborescent lightning burn, arborescent (tree-like) erythema, keraunographic markings, or ferning patterns, and they occur on 20-30% of those struck by lightning. Although the exact causes are still subject to debate, the markings appear to be the result of physical damage to capillaries under the skin, perhaps caused by the flow of electrical current, or by shock wave bruising from external flashovers just above the skin. Skin in the affected areas is not burned. Instead, a small number of blood cells (apparently from damaged capillaries) leaks into the surrounding subcutaneous fat, causing a reddish discoloration. The marks usually fade away (on survivors!) over a period of a few hours to a few days as the body reabsorbs the loose blood cells and repairs the damaged capillaries. They are recognized by forensic pathologists as clear evidence that a victim has been struck by lightning. The patient above survived with no permanent injuries, and the lightning flowers completely faded within a few days. A small Lichtenberg figure has also been observed at the entry point where a high voltage spark penetrated the skin of an unfortunate (but surviving) local electrical experimenter who was accidentally zapped by a homemade 60,000 volt Marx Generator. No... it wasn't me!

A similar phenomenon is sometimes seen when lightning hits a grassy field, such as the following image where lightning struck a golf course flagpole, leaving this beautiful 25 foot Lichtenberg figure on the green:

(From "Lightning and Lichtenberg Figures" by Cherington, Olson and Yarnell, Injury, Volume 34, Issue 5, May 2003)

Note the similarity between the figure above and the Lichtenberg figure below (illuminated from below by blue LED's):

High voltage discharges to the surface of water can also create Lichtenberg figures. Some beautiful examples of both positive and negative Lichtenberg figures on water surfaces can be seen on Dr. Colin Pounder's Lichtenberg figures web site. Natural lightning often creates transient "Lichtenberg figures" in the sky. Air is an excellent dielectric and, although the physical breakdown mechanisms for air and Plexiglas are considerably different, the branching structure of the discharges is actually quite similar. So it should not be surprising that the branching forms of propagating lightning leaders also have fractal characteristics. This similarity can clearly be observed during so-called anvil crawler and horizontal spider lightning. Spider lightning follows a thin, positively charged cloud layer that sometimes forms within dissipating storms. These slowly propagating discharges have been known to "crawl" across the sky for up to 70 miles - literally spanning from horizon to horizon! On a much smaller scale, transient Lichtenberg figures (sometimes mistakenly called St. Elmo's Fire) sometimes appear on the outer surface of cockpit windows of airplanes as they fly through thunderstorms.

Similar branching fractal patterns also occur when thunderstorms generate electrically conductive leaders that propagate downward from a charged cloud to the ground below. When one of these leaders connects with an unfortunate object on the ground, a high current pulse (called the return stroke) surges back upward through the completed path, resulting in a Cloud-to-Ground (CG) lightning strike. The peak current is typically tens of thousands of amperes, and large positive bolts may reach several hundred thousand amperes. Exceptional examples of downward propagating positive leaders have been captured by South Dakota lightning researcher, Tom Warner. Using high speed video imaging equipment, he was able to capture the downward progression of leaders and the return strokes from a positive lightning bolt. Positive lightning is a significantly rarer, and considerably more dangerous, form of lightning than negative lightning. Tom's "slow motion" videos show the air breaking down, forming glowing conductive plasma paths (called leaders) that fan downward from a huge reservoir of excess charge within the cloud above. The brightly glowing tips of the positive leaders smoothly propagate, unlike negative leaders which propagate in a series of discrete jumps (called stepped leaders). The first descending leader to finally connect with the Earth below completes the circuit, resulting in a powerful Cloud-to-Ground (CG) lightning discharge. See Tom's web site to see his spectacular galleries of images and videos of positive and negative lightning.

Under special conditions lightning can form transient upward-growing Lichtenberg figures. This phenomenon often occurs when broadcast antennas or mountain tops generate positive leaders that propagate upward into heavily-charged negative regions above. As the ground-based positive leaders propagate into the negatively-charged regions, they form densely-branched positive Lichtenberg figures that, except for their massive scale, look quite similar to the positive Lichtenberg figures inside our Captured Lightning sculptures. This fascinating phenomenon has recently been captured in slow-motion by lightning researcher Tom Warner:
 

 

Lichtenberg figures can also be seen at some high energy pulsed power facilities, especially where deionized water is used as a dielectric to briefly store large amounts of electrical energy. The following photo is from Sandia National Laboratory's mighty ZR Machine, the world's most powerful electrical pulse generator. After the completion of a high energy experiment, the water breaks down from the huge electrical stress, becoming an electrical conductor that safely dissipates unwanted residual energy from the system. The filamentary breakdown paths form Lichtenberg figures that dance across the water's surface. If you look closely, you'll notice that many of the paths actually trace out high voltage electrical field lines along the surface of the water. Although impressive, this display is only dissipating "left over" energy after the experiment is over. The discharges below only represent ~5% of the initial energy that was actually used during the previous pulsed-power experiment.

(Click for a higher resolution image)

Are there practical uses for Lichtenberg figures?
Analysis of the form and origination points of Lichtenberg figures can be a powerful tool for diagnosing, and subsequently preventing, high voltage breakdown of solid dielectrics. By examining these figures in high voltage equipment, experts can diagnose and prevent future electrical faults within a variety of devices including high voltage power transformers, capacitors, and insulators. Historically, Lichtenberg figures (created by HV measuring equipment such as Klydonographs) were also a powerful tool for measuring the polarity and magnitude of high voltage surges on power lines caused by lightning strikes. These early measurements were critical for the development of reliable electrical power transmission and distribution systems. Lichtenberg figures are still used as a forensic clue for identifying the cause of injury or death of human and animal lightning victims. Recent studies of Lichtenberg figures and charge detrapping in polymers are revealing important details on the mechanisms that are involved in the degradation and electrical breakdown of solid insulating materials.

There may even be future medical applications as well. In 2009, a team of researchers at Texas A&M University proposed using 3D Lichtenberg figures created within various polymeric materials as "templates" for growing blood vessels (vascular tissue). There are significant similarities between branching Lichtenberg figures and animal circulatory systems - a fact not lost on many medical researchers. The hope is that, by creating branching 3D Lichtenberg figures inside a biodegradable polymer, such as polylactic acid (PLA), scientists can then use these as "molds" to support the development and growth of vascular tissue.

Vascularization is essential for growing functional replacement tissues and organs. It's possible that the 18th century technology of Lichtenberg figures may ultimately play a role in organ replacement therapy almost 240 years later!

Captured Lightning sculptures are "fossilized lightning bolts"
Captured Lightning is an accurate description for our sculptures, and holding a Captured Lightning sculpture is about the closest you can come to holding a fossilized lightning bolt. Each Lichtenberg figure is unique - a one-of-a kind treasure, sculpted in exquisite detail by the same electrical forces unleashed by natural lightning. Captured Lightning sculptures are completely safe - they are completely discharged and are not radioactive.

Two-dimensional photos cannot begin to capture the beauty and exquisite detail of 3D Captured Lightning sculptures. Following are a pair of 3D images that can be rotated 360 degrees so that you can more fully appreciate the detail within some of some doubly-irradiated sculptures. Once the images have been completely downloaded, you can drag your mouse over the image to rotate each for a full 360 degree view. 

3D Rotatable Image	3D Rotatable Image
"Heavy Weather" (Courtesy of Theodore Gray)	"Windblown Lightning" (Courtesy of Theodore Gray)

Very few people have actually seen or held one of these rare objects of scientific art. Far fewer have had the opportunity to own sculptures as beautiful and spectacular as these. Stoneridge Engineering LLC is proud to be the world's most experienced provider of these rare treasures.

Can I make my own Lichtenberg Figures?
A. Fractal wood-burning (carbonized Lichtenberg figures):
Unfortunately, since electrons must be injected deep into the acrylic, it takes a multi-million-volt electron accelerator to make 3D Captured Lightning sculptures. Even my patient, understanding spouse won't let me install one of these at home.

However, 2D Lichtenberg figures can be made by creating carbonized paths on the surfaces of some materials, such as wood or cardboard, or as "dust figures" on the surfaces of some plastics. Some artists have used this technique, sometimes called "fractal wood burning", to make 2D works of art. Please note that fractal wood burning must be done VERY carefully since it involves using dangerously high voltages and water together. We do NOT endorse fractal wood burning since it can KILL you. Because it is so dangerous in inexperienced hands, the American Association of Woodturners (AAW) has banned using this technique. 

The process requires using a high voltage (HV) source, such as a neon sign transformer (NST) or microwave oven transformer (MOT. Because the output current is limited, an NST or a solid state HV supply is much safer than using a MOT as a HV source. We strongly recommend that you DO NOT use a MOT, since these innocent looking HV transformers easily have enough power to kill you as it carbonizes parts of your body. The high current "freezes" your muscles, preventing you from letting go. It also prevents you from breathing or even screaming for help. You get NO do-overs or second chances with a MOT, and electrocution will be agonizingly painful during your last few minutes.

The experiment should be done outside since the burning material generates a large quantity of smoke, sparks, and small flames. You should always have a helper present to warn you of possibly dangerous situations and who can shut off power if you can't. Two nails or straight pins are driven into the wood with a gap of 4 - 12 inches. The surface is then lightly sprayed or brushed (with HV power OFF!) with a saltwater or baking soda solution to make it partially conductive, and the high voltage source is connected to the two nails. Once high voltage is applied to the nails, carbonized paths begin to form near the nails. Accompanied by LOTS of smoke, they begin branching as they grow towards each other. The heat from the process dries out the nearby surface, causing the branches to continuously change direction, sometimes even heading away from the opposite nail. The carbonized paths eventually grow to form Lichtenberg figures with "roots" at each nail.  A method to adjust the output voltage (such as a variable autotransformer) also helps to control the discharge process and improves the shape of the resulting figure. Finally, a pair of widely separated normally-open (NO) push buttons should be connected in series and also in series with the input power to your HV source. This safety measure requires that both buttons be pressed (one by your right hand, the other by your left) in order to power up the HV source. This insures that you won't make manual contact with the HV and it will automatically turn off power if one or the other hands are removed.

NEVER touch the HV wires, nails, alligator clips, or wood when high voltage is present. Any carelessness can be FATAL. As of mid-2023 over FORTY-FIVE people have been accidentally electrocuted by MOT power sources! Do NOT attempt to make wood Lichtenberg figures if you do not have previous experience in working with high voltage electricity or are tired or otherwise impaired. And never mix alcohol and high voltage work.  

The following video clip shows this technique being used with a safer 9,000 volt 30 mA NST as the high voltage source:

B. Acrylic Fractal Dendrites:
Following is a link to another way to make colorful patterns that look similar to Lichtenberg figures. The resulting Fractal Dendrites are created using low-cost acrylic paints and isopropyl alcohol. The colorful results are beautiful and safe to make. Be sure to check out the tutorial and video at acrylgiessen.com.
 

More fun with electrons: Glowing rocks, flashing crystals, going to the dark side, and "Rad-Cams 1 and 2"
High-energy electrons and x-rays can cause many other fascinating effects within crystalline solids. One particularly interesting phenomenon is called thermoluminescence.  In thermoluminescent materials, high-energy electromagnetic radiation, such as x-rays, may be absorbed by atoms in the crystal, causing them to rise to a higher, semi-stable energy level. When these excited atoms fall back to their normal state, they radiate electromagnetic energy, sometimes within the visible light spectrum. Thermoluminescent materials are usually triggered into releasing their stored energy by applying heat. Sensitive light detectors, such as photomultipliers, are used to detect the faint light emitted by most specimens. The light output versus temperature is called a "glow curve" and its shape tells much about the nature of the material and its cumulative radiation history. The emitted radiation is often in the infrared (IR) or ultraviolet (UV) portion of the electromagnetic spectrum, and thus not directly visible. Although many thermoluminescent materials require the application of relatively high temperatures to release their thermoluminescence, some minerals radiate visible light at room temperature. One outstanding example is the mineral Calcite (CaCO₃), which may glow brilliantly after being irradiated by a powerful electron beam or X-rays. However, the thermoluminescent glow is not from the calcite itself, but from traces of impurity elements such as manganese embedded within the crystalline structure of the calcite. Manganese is one of many known  activators, and is responsible for the characteristic yellow-orange glow seen in many calcite specimens. Other common thermoluminescent activators include lead, copper, cobalt, magnesium, iron, nickel, and silver. Very clear calcite (called "Iceland Spar) typically shows relatively little visible thermoluminescence since the purer crystals contain fewer activator atoms. 

The degree of luminescence is proportional to the amount of cumulative radiation seen by the specimen. Passing a manganese-activated calcite crystal through a high-energy electron beam several times will cause the specimen to glow brightly for many hours at room temperature. Although the glow curve for electron-irradiated calcite peaks at about 110 degrees Celsius, significant light is emitted at room temperature. The amount of light rapidly decreases as the temperature of the calcite is lowered, and virtually disappears below 0 degrees Celsius. So, if we irradiate a frozen specimen of calcite, its thermoluminescent properties will not be immediately obvious. However, if we keep it cold and then warm it up to room temperature some time later, it will then glow brightly. The following image shows Dr. Timothy Koeth admiring a spectacular glowing calcite crystal brought by Dr. David Speck during our 2010 Lichtenberg run.



Common table salt (NaCl) is also thermoluminescent. However, unlike calcite, it doesn't glow at room temperature. When irradiated with high-energy electrons, NaCl changes to a cinnamon color due to the trapping of electrons in defects in the crystal structure. Called F-Centers, these are vacancies inside the crystalline lattice of the salt crystals. Irradiated salt will remain this color as long as it is kept cool, dry, and protected from UV light. When the irradiated salt crystals are dropped onto a hotplate, each emits a brilliant green flash as it changes back to its normal (clear/white) color as can be seen in this short video clip by high school instructor Gary Bodman (Albuquerque, NM). When dropped into distilled water, the cinnamon color also disappears, and the dissolving salt emits a pale bluish-green glow (called aquoluminescence) as previously-trapped electrons liberate their energy. After exposure to light, irradiated salt changes from cinnamon to a dark blue or dark purple color. This is thought to be caused by trapped F-center electrons combining with Na+ ions, reducing them to atoms of metallic sodium. The resulting colloidal dispersion of atomic sodium throughout the crystal causes the color change. When dissolved in distilled water, the purple color also disappears. We may offer small amounts of irradiated salt ("Flashing Crystals") to interested amateur experimenters and physics instructors in the future.

Another interesting phenomenon occurs within irradiated potassium chloride (KCl). This material is normally a white crystalline solid. However, when subjected to high-energy electrons or X-radiation, it changes to a dark purple color. Applying heat or UV (sunlight) turns it back to its normal white color. This behavior is relatively rare phenomenon - KCl is a "scotophor". Unlike a phosphor, which emits light when excited by ionizing radiation, a scotophor darkens when irradiated. This process is called reversible photochromism or tenebrescence. Other example of includes photochromic eyeglass lenses that darken from UV in sunlight, and then bleach back to  normal transparency in lower light. KCl was used in some early radar cathode ray tube (CRT) displays since it could be quickly "written" by an electron beam, creating an image with very long persistence. The recorded image could then be erased by applying a bit of heat to the material. Very few minerals exhibit reversible photochromism - these include hackmanite, scapolite and tugtupite. The following image shows KCl and NaCl that have changed from being white powders (before irradiation) to dark purple and cinnamon-colored crystals after irradiation by multiple passes through a 5 MeV electron beam.



During an experimental run in June 2013, Andrew Seltzman, a guest and graduate-level physics student from the University of Wisconsin, built a protective "cave" for his Sony Cyber-Shot DSC-P72 3.2 MP camera using sheet lead topped with a one inch thick piece of high-density polyethylene (HDPE) to reduce production of X-rays. Andrew mounted his camera inside the cave and positioned it so that it could record a "cart's-eye view" of various objects being irradiated with the 3 to 5 million volt electron beam. We were thinking that the first pass through the beam might be a one-way trip, since the scattered electron and radiation levels were so intense. We were amazed to discover that the "Rad-Cam" not only survived, it faithfully recorded its journey through the beam - not just once, but for a dozen trips! The only obvious problem was that the microphone seemed to become less sensitive after every pass. However, the camera fully recovered a few days after the run.

During our Fall 2014 production run, Andrew designed a much more sophisticated radiation camera setup that used a HD GoPro Hero 3+ camera inside a 1/4" thick lead "cave". The camera "looked" through a one-inch thick leaded glass window. The new design provided significantly better radiation protection than the 2013 camera setup. You can see details of Andrew's RadCam 2 camera setup and some resulting photos and video clips captured during our 2014 run. These include a video clip with the camera looking upward (via a 45 degree stainless steel mirror) at the blue glow of electrical corona created by the high-energy electron beam as it passes though eighteen inches of air! A similar video clip also looks up at the beam through a 6" x 6" x 3/4" PMMA specimen. As it passes through the beam, it self-discharges. The brilliant glow from the specimen occurs as high-energy electrons crash into PMMA molecules, and the width of the scanning electron beam can also be estimated (approximately three inches). We suspect that the brilliant glow from the PMMA specimen is a combination of Cherenkov radiation and cathodoluminescence.  Finally, small spark-like flashes from secondary discharges can be seen after the main discharge. 

The following video clip (using the earlier RadCam 1 setup from the 2013 run) shows boxes of various minerals, and a large calcite crystal becoming energized by ionizing radiation from the beam. The crystal fluoresces a brilliant yellow-orange color while being irradiated, then continues to softly glow, looking like a hot coal. However, it remains cold to the touch. The acrylic sphere in front of the calcite fluoresces an intense blue-white as the electron beam hits it, then briefly flashes when it self-discharges. Speckles in the image and static in the audio are caused by high-energy electrons and x-rays impacting the camera's image sensor and audio electronics. The loud buzzing sound is from high-energy x-rays directly interfering with the camera's electronics as the beam is scanned across the width of the cart 100 times each second. The Sony Cyber-Shot's video and audio systems finally become overwhelmed as the camera passes directly under the electron beam. Although the radiation and ozone levels in the room would be lethal to living organisms, this tough little camera just shook off the abuse and came back for more!

High Beam and Glowing Air - RadCam3
During our 2015 production run, Andrew Seltzman brought a 3rd generation radiation-resistant HD camera. The GoPro Hero 3+ was housed within a 1/2" thick lead box with a leaded glass window. Since previous tests showed that this system could tolerate very high energy electrons and x-radiation, we decided to run the camera through the beam with it set to maximum  power (~150 kW). We also turned off the lights so that we could capture the glowing air under the accelerator's output window. As relativistic electrons collide with nitrogen molecules, they transfer some energy to the molecules, exciting them into higher rotational and vibrational states. When the excited molecules fall back to their normal state, they radiate energy at various frequencies (called spectral lines). Nitrogen's predominant spectral peak is in the near ultraviolet (337 nm or UV-A region), with 17 other peaks spanning 280 nm through 430 nm. The visible blue light is from lower frequency (400 - 430 nm) nitrogen lines, but most of the radiated light actually lies within the UV portion of the EM spectrum. In the video clip, the orange glow of the calcite specimens in the foreground intensifies just before they pass under the electron beam. We suspect that this is from increased X-radiation  as the specimens approach the beam. Speckling is from high-energy X-rays that have passed through, or have been created within, the lead shield and then struck the image sensor at various angles. Videos of other experiments done during our 2015 production run can be seen on Andrew's web site.

Frame grab from above video clip showing glow from fluorescing nitrogen molecules

Another frame grab as the cart gets closer to the electron beam.
The calcite crystals in the foreground glow brilliantly from increasing X-radiation.

 

How can I get a Captured Lightning sculpture of my very own?
We offer a wide selection of Captured Lightning sculptures that range in size from affordable 2-inch specimens through museum-quality two-inch thick blocks as large as 15  by 20 inches. Please visit Gallery 1 or Gallery 2 to select a sculpture in the right price range for you. We also offer a wide variety of lighted bases with white, blue, and multi-color color changing options. In addition to US power, many of these are also available with UK, Australian, or EC power options. Our light bases illuminate the delicate patterns within, causing the discharge channels to glow so that even the finest hair-like details become visible. We also offer a variety of attractively-priced experimental sculptures discounted from 10-40% off regular price.  Also, be sure to visit our Eye Candy page to see some of the best artistic and experimental work by Stoneridge Engineering LLC and some of our very creative friends.

Gallery 1	Gallery 2	Experimental Sculptures	"Eye Candy"

“A physical experiment which makes a bang is always worth more than a quiet one. Therefore a man cannot strongly enough ask of Heaven: if it wants to let him discover something, may it be something that makes a bang. It will resound into eternity.” – Lichtenberg, Georg Christoph, and Albert Leitzmann. 1906. "Georg Christoph Lichtenbergs Aphorismen: nach den Handschriften. Drittes Heft, 1775-1779," page 326. Originally in German, from Lichtenberg's Booklet F, Aphorism 1138, Oct 11-13, 1778.  (Thanks to Fermilab scientist and author, Bill Higgins for researching the source of the above quote!) "Thunder is good; thunder is impressive. But it is the lightning that does the work." - Mark Twain

References and Further Reading:
1. Gross, Bernard, "Irradiation Effects in Plexiglas", Journal of Polymer Science, Volume 27, 1958, Issue 115, Pages 135 - 143
2. Hashishes. Yuzo, "Two Hundred Years of Lichtenberg Figures", Journal of Electrostatics, Volume 6, Issue 1 , February 1979, Pages 1-13
3. Chadwick, K. H., "The Effect of Light Exposure on the Optical Density of Irradiated Clear Polymethylmethacrylate", 1972 Phys. Med. Biol. 17, Pages 88-93
4. Chadwick, K. H., and Leenhouts, H. P., "Fading of radiation-induced optical density in polymethylmethacrylate on oxygen diffusion", Phys. Med. Biol. 15 No 4 (October, 1970), Pages 743-744
5. L. Niemeyer, L. Pietronero*, and H. J. Wiesmann, "Fractal Dimension of Dielectric Breakdown", Phys. Rev. Lett. 52, Pages 1033–1036 (1984)
6. Gardner, Donald G., et. al., "Radiation-induced changes in the index of refraction, density, and dielectric constant of poly(methylmethacrylate)", Journal of Applied Polymer Science, Volume 11, Issue 7,July 1967, Pages 1065-1068
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39. Fractal Foundation - Learn all about fractals. A fascinating museum and web site for children and adults alike.

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