Geissler tube

A Geissler tube is a glass tube filled with low-pressure gases connected to a high-voltage power source. When electricity passes through, it energizes the gas atoms, causing them to emit visible light, often in vivid colors. This glowing effect occurs because the electric current excites the gas particles, and as they return to normal, they release photons—light particles. Geissler tubes helped scientists study electricity and atomic behavior and are early precursors to modern neon signs and fluorescent lighting, illustrating how electrical energy can produce colorful light in a contained environment.