Glowing signs, with their vibrant illumination, have long been a familiar sight, transforming cityscapes. These luminous displays offer a unique visual impact. The technology behind them harnesses physics to convert electrical energy into brilliant light. This process involves specific elements, primarily noble gases, contained within sealed glass tubes.
The Role of Neon
Neon, a noble gas, is historically significant and widely recognized for its use in glowing signs. Discovered in 1898, neon was noted for its bright red light when electrically stimulated. This distinctive red-orange glow is the characteristic color of pure neon gas when an electric current passes through it. French engineer Georges Claude demonstrated the first modern neon sign in Paris in 1910, and by 1923, neon signs were introduced to the United States. Neon’s inert nature makes it suitable for prolonged use in sealed glass tubes.
How Gas-Filled Tubes Create Light
Gas-filled tubes produce light by exciting noble gases. These signs consist of sealed glass tubes containing a rarefied noble gas and electrodes at each end. When high voltage is applied, it creates an electric field that causes the gas atoms to ionize, stripping away electrons to create a plasma. Free electrons and ions accelerate through the tube, colliding with neutral gas atoms and pushing their electrons to higher energy levels. Excited electrons quickly return to lower energy levels, releasing absorbed energy as visible light, with the specific color depending on the energy differences between electron levels in the gas atoms.
Other Noble Gases and Their Colors
While neon produces a bright red-orange glow, other noble gases are used to create a wide spectrum of colors in these signs. Each noble gas emits a distinct color when electrified due to its unique atomic structure and electron energy levels. For instance, argon gas typically produces a lavender or light blue light; when combined with a small amount of mercury vapor, it can yield a deeper blue. Helium, another noble gas, emits an orange-yellow or pinkish-red glow. Krypton gas typically results in a whitish-blue or pale white light, while Xenon produces a blue or lavender hue.
To achieve an even broader range of colors, the interior of the glass tubes can be coated with phosphors. These phosphor coatings absorb ultraviolet light emitted by the excited gases (often an argon-mercury mixture) and re-emit it as different visible colors, allowing for greens, yellows, and various shades of blue.