The element responsible for the iconic glow of classic advertising signs is Neon. These striking displays, technically known as cold cathode gas-discharge tube lighting, rely on this noble gas to create their signature light. While the term “neon sign” is often used generically, the element Neon itself generates a specific and intense red-orange hue. The vibrant, continuous light quality of these signs makes them highly visible and attention-grabbing, especially in low-light environments. The gas’s characteristics are suited for the decades-long lifespan and consistent brilliance expected of outdoor commercial signage.
The Primary Element Neon
Neon, represented by the chemical symbol Ne and atomic number 10, is the namesake for this entire category of lighting. It belongs to the group of noble gases, meaning it is colorless, odorless, and chemically inert under most conditions. This non-reactive nature contributes to its stability, ensuring the gas does not degrade the internal electrodes or the glass tubing over many years of operation.
When pure neon gas is contained at a low pressure inside a sealed glass tube and subjected to a high-voltage electrical current, it naturally emits a brilliant reddish-orange light. This distinct color is the natural emission spectrum of the element itself, making it instantly recognizable and highly effective for advertising.
The element was discovered in 1898 by British chemists Sir William Ramsay and Morris W. Travers. French inventor Georges Claude first realized the commercial potential of the gas, displaying the first large-scale neon lamp in Paris in 1910. By 1923, neon signs were introduced to the United States, quickly becoming a defining feature of modern advertising.
How Gas Discharge Tubes Produce Light
The mechanism that causes the inert gas to glow is a phenomenon known as gas discharge or plasma generation. This process begins with a sealed glass tube that is evacuated of air and then filled with a small amount of gas, such as neon, at a very low pressure. Electrodes are sealed at each end of the tube, and a high-voltage transformer is used to apply several thousand volts across these terminals.
The application of this high voltage accelerates free electrons within the tube toward the positively charged anode. These high-speed electrons collide with the neutral gas atoms, transferring energy and knocking off an electron from the gas atom to create a positively charged ion in a process called ionization. This continuous flow of ions and free electrons creates a plasma, which is an electrically conductive gas.
The collision process also excites the electrons in the gas atoms to a higher-energy orbital shell. Because this higher energy state is unstable, the electrons quickly fall back down to their original, lower-energy ground state. As the electrons drop back down, they release the excess energy in the form of a photon, which is a particle of visible light. The specific energy difference between the orbital shells determines the precise wavelength, or color, of the emitted light.
The flashing or movement seen in many advertising signs is not a property of the gas itself, but rather a function of the electrical circuit controlling the discharge. The high-voltage transformer is wired to an electrical switching mechanism that rapidly turns the current on and off in specific sections of the sign tubing. This controlled interruption and resumption of the electrical field creates the dynamic, attention-grabbing effects required for advertising.
Achieving the Full Color Spectrum
While pure neon produces only the deep red-orange color, a full spectrum of colors is achieved by substituting or mixing other gases and introducing specialized coatings inside the glass tubes. The color of the light is fundamentally determined by the emission spectrum of the gas atoms excited within the tube. This allows technicians to utilize other noble gases to expand the palette beyond the signature neon red.
For instance, light blue and violet colors are typically produced by using Argon gas, which emits a lavender or faint blue light when energized. To intensify the blue or create a more vibrant color, a minuscule amount of liquid Mercury vapor is often added to the Argon. The Mercury vapor becomes excited along with the Argon, contributing a powerful blue component to the light output.
The Argon and Mercury combination is also the foundation for creating a wide variety of other hues through the use of phosphor coatings. The electrical discharge within the tube generates ultraviolet (UV) light. When the tube’s inner wall is coated with a phosphor powder, the UV light strikes this coating and causes it to fluoresce, emitting visible light at a different wavelength.
These phosphors allow for secondary colors that the gases alone cannot produce directly, such as pink, purple, and various shades of green and white. Some colors are also achieved by simply using colored glass tubing, which acts as a filter to change the perceived color of the light emitted by the gas inside.