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A Lichtenberg figure (German: Lichtenberg-Figur), or Lichtenberg dust figure, is a branching electric discharge that sometimes appears on the surface or in the interior of insulating materials.

Lichtenberg figures are often associated with the progressive deterioration of high-voltage components and equipment. The study of planar Lichtenberg figures along insulating surfaces and 3D electrical trees within insulating materials often provides engineers with valuable insights for improving the long-term reliability of high-voltage equipment. Lichtenberg figures are now known to occur on or within solids, liquids, and gases during electrical breakdown. Lichtenberg figures are natural phenomena that exhibit fractal properties.

Lichtenberg figures are named after the German physicist Georg Christoph Lichtenberg, who originally discovered and studied them. When they were first discovered, it was thought that their characteristic shapes might help to reveal the nature of positive and negative electric "fluids". In 1777, Lichtenberg built a large electrophorus to generate high-voltage static electricity through induction. After discharging a high-voltage point to the surface of an insulator, he recorded the resulting radial patterns by sprinkling various powdered materials onto the surface. By then pressing blank sheets of paper onto these patterns, Lichtenberg was able to transfer and record these images, thereby discovering the basic principle of modern xerography. Although Lichtenberg only studied two-dimensional (2D) figures, modern high-voltage researchers study 2D and 3D figures (electrical trees) on, and within, insulating materials.

Two-dimensional (2D) Lichtenberg figures can be produced by placing a sharp-pointed needle perpendicular to the surface of a non-conducting plate, such as of resin, ebonite, or glass. This creates a sudden, small electrical discharge along the surface of the plate. In addition to the distribution of colors thereby produced, there is also a marked difference in the form of the figure, according to the polarity of the electrical charge that was applied to the plate. If the plate receives a mixture of positive and negative charges as, for example, from an induction coil, a mixed figure results, consisting of a large red central nucleus, corresponding to the negative charge, surrounded by yellow rays, corresponding to the positive charge. It is now known that positive Lichtenberg figures have longer, branching structures because long sparks within air can more easily form and propagate from positively charged high-voltage terminals. Another type of 2D Lichtenberg figure can be created when an insulating surface becomes contaminated with semiconducting material.

The branching, self-similar patterns observed in Lichtenberg figures exhibit fractal properties. Lichtenberg figures often develop during the dielectric breakdown of solids, liquids, and even gases.

Lichtenberg figures are fern-like patterns that may appear on the skin of lightning strike victims and typically disappear in 24 hours. A lightning strike can also create a large Lichtenberg figure in grass surrounding the point struck. Following these Lichtenberg figures within the insulation during post-accident investigation of an insulation failure can be useful in finding the cause of breakdown.

Modern Lichtenberg figures can also be created within solid insulating materials, such as acrylic (polymethyl methacrylate, or PMMA) or glass by injecting them with a beam of high energy electrons from an electron beam accelerator, such as a LINAC (or Linac, a type of particle accelerator). During the discharge, the powerful electric sparks leave thousands of branching chains of fractures behind, creating a permanent Lichtenberg figure inside the specimen. Although the internal charge within the specimen is negative, the discharge is initiated from the positively charged exterior surfaces of the specimen, so that the resulting discharge creates a positive Lichtenberg figure.

Lichtenberg figures can also be produced on wood. The types of wood and grain patterns affect the shape of the Lichtenberg figure produced. What are Lichtenberg Figures and how are they created?

1927 General Electric Review Article about Lichtenberg Figures

Trap Lightning in a Block. (DIY Lichtenberg Figure at Popular Science)

Quick Facts

• Lichtenberg figures are now known to occur on or within solids, liquids, and gases during electrical breakdown.
• The study of planar Lichtenberg figures along insulating surfaces and 3D electrical trees within insulating materials often provides engineers with valuable insights for improving the long-term reliability of high-voltage equipment.
• Lichtenberg figures are natural phenomena that exhibit fractal properties.
• Lichtenberg figures are named after the German physicist Georg Christoph Lichtenberg, who originally discovered and studied them.
• Lichtenberg figures are often associated with the progressive deterioration of high-voltage components and equipment.

Source material: Wikipedia - "Lichtenberg figure". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.