Neon, a noble gas, is widely recognized for its association with vibrant, glowing signs. While the term “neon sign” has become a common descriptor for any brightly colored gas-filled tube, pure neon gas, when electrically stimulated, produces a specific and distinct hue.
The Distinctive Color of Pure Neon
Pure neon gas, when electrically stimulated, emits a characteristic reddish-orange glow. This color is inherent to neon, whose name comes from the Greek word “neos,” meaning new. The hue is a brilliant reddish-orange, often described as fiery or deep red-orange.
This unique color arises from neon’s atomic structure. When neon atoms are energized, their electrons absorb this energy and jump to higher energy levels. As these excited electrons return to lower energy states, they release photons. The specific wavelengths of these photons produce the reddish-orange light.
How Neon Produces Its Signature Glow
The process by which neon generates its reddish-orange light involves electrical excitation within a sealed glass tube. When a high-voltage electric current is applied across electrodes at each end of the tube, it causes electrons to flow through the low-pressure neon gas. These fast-moving electrons collide with neon atoms, transferring energy to them.
This energy transfer pushes the electrons within the neon atoms to higher, less stable energy levels. However, this excited state is temporary. The electrons quickly fall back to their original, lower energy levels, releasing the excess energy as photons of light. The specific energy differences between these levels in neon atoms result in the emission of photons primarily in the red and orange parts of the visible light spectrum, producing neon’s signature glow.
Beyond Neon: The Colors of “Neon” Signs
While pure neon gas produces a distinctive reddish-orange light, the broad spectrum of colors seen in what are commonly called “neon signs” is achieved by using different gases, gas mixtures, and internal coatings within the glass tubes. The term “neon sign” has become a general phrase, but many of these colorful displays do not contain neon at all.
Other noble gases are employed to create a diverse palette. For instance, argon gas produces a soft blue, lavender, or light purple hue when electrified. When argon is combined with a small amount of mercury vapor, it can yield more vibrant blue, green, or even white light. Mercury vapor alone emits a blue or blue-white light.
Helium gas, another noble gas, can produce orange-yellow or pinkish-red light, though its light is often fainter than neon’s. Krypton gas, when excited, emits a whitish-blue, whitish-yellow, pale white, or light purple glow. Xenon gas results in blue, bluish-white, or lavender colors.
Beyond using different gases, sign manufacturers often coat the inside of the glass tubes with phosphor powders. These coatings play a significant role in expanding the color range. When ultraviolet light strikes these phosphor coatings, they absorb the UV energy and re-emit it as visible light of various colors, allowing for greens, pinks, purples, and yellows that cannot be achieved with gases alone.