Neon signs are distinctive visual elements, illuminating cityscapes and storefronts with their unique glow. While often broadly referred to as “neon,” these luminous tubes display an impressive array of colors far beyond the classic red-orange. The vibrant yellow-green hue, in particular, sparks curiosity about the specific elements responsible for its creation. Understanding how this color comes to life reveals an interplay of gases and specialized coatings within the glass tubing.
The Gas for Yellow-Green
Achieving a yellow-green color in a “neon” sign primarily involves the noble gas argon. While pure neon gas naturally emits a familiar red-orange light, argon alone typically produces a pale lavender or light blue glow. To create the desired yellow-green, manufacturers often combine argon gas with a small amount of mercury vapor inside the glass tube. This mixture generates significant ultraviolet (UV) light.
The UV light then interacts with a phosphor coating applied to the inner surface of the glass tube. This coating is specifically formulated to absorb the UV light and re-emit it as visible yellow-green light. Argon is chosen for its low striking voltage, which helps initiate the electrical discharge, and its versatility when combined with mercury vapor and phosphors to produce a broad spectrum of colors.
The Science of Light and Color
The production of light in these signs begins when a high-voltage electrical current is applied across the gas-filled tube. This electricity excites the gas atoms within the tube. Electrons in these atoms absorb energy and jump to higher energy levels. This elevated state is unstable, and the electrons quickly fall back to their original, lower energy levels.
When electrons return to their ground state, they release the absorbed energy as photons, which are particles of light. The specific color of the emitted light depends on the amount of energy released, which corresponds to a particular wavelength on the electromagnetic spectrum. Each type of gas has a unique atomic structure and electron configuration, leading to a distinct “emission spectrum” and a characteristic color when excited. A phosphor is a substance that absorbs energy, like UV light, and re-emits it as visible light through a process called luminescence. The specific chemical composition of the phosphor dictates which visible color it will produce.
A Spectrum of Colors
The term “neon sign” has become a general descriptor, but a wide variety of noble gases contribute to the full spectrum of colors seen in these luminous displays. Other noble gases offer different base colors when excited by electricity. Helium emits an orange-yellow or pinkish-red light, krypton produces a whitish-yellow or greenish-white hue, and xenon yields shades of blue or violet.
The extensive palette of neon sign colors is not solely dependent on the gas used. Manufacturers also employ techniques such as using tinted or colored glass tubes to modify the light’s appearance. Internal phosphor coatings play a substantial role, especially with argon-filled tubes. These coatings can convert the light emitted by the gas into nearly 100 different colors, expanding artistic possibilities beyond the natural emissions of the gases themselves. This combination of specific gases, mercury vapor, and various phosphor formulations allows for the creation of virtually any color imaginable in traditional gas-filled signs.