Neon is a chemical element that is colorless, odorless, inert, and monatomic. However, when electricity is passed through neon gas, it emits a distinctive glow. The color that neon emits depends on the gas pressure inside the tube and the amount of electricity applied. At low pressures and voltages, neon glows a distinctive red-orange color. As the pressure and voltage increases, the color shifts to orange, yellow, green, blue, purple, pink, and eventually white. Neon has a very specific emission spectrum that lends itself to creating vibrant colors. Let’s take a closer look at what gives neon its colorful glow.
Neon’s Emission Spectrum
Neon gas consists of single neon atoms. These atoms have electrons orbiting the nucleus in different energy levels, or electron shells. The electrons tend to occupy the lowest energy levels possible. When electricity is applied to the gas, some of the electrons absorb enough energy to jump up to higher energy levels. These excited electrons are unstable and quickly fall back to lower levels, emitting photons of light in the process. The energy of the photons corresponds to the difference in energy between the two electron levels. This gives each element a distinctive set of photon energies, or emission spectrum.
Neon has electron transitions that emit red, orange, and yellow light. When neon gas absorbs less energy, the electrons jump to lower energy levels, emitting red photons around 640 nm wavelength. As more energy is applied, electrons jump to higher levels, emitting orange (610 nm) and yellow (580 nm) photons. Combinations of these red, orange, and yellow wavelengths give neon its characteristic color.
Effect of Gas Pressure
The pressure of the gas in the neon tube affects the neon’s color. At low pressures (1-5 torr), neon emits a bright red-orange color. As pressure increases up to 20 torr, the color shifts to orange. At pressures between 20-100 torr, neon glows a yellowish-orange.
The reason for this effect is that higher gas pressure increases collisions between atoms. These collisions can interrupt the excited electron transitions that produce light. Lower frequency red transitions have the longest duration and are less affected than higher frequency orange and yellow transitions. As a result, the higher pressure causes neon to shift from red to orange to yellow.
Effect of Voltage
In addition to gas pressure, the applied electrical voltage also affects the neon color. At around 5000 volts, neon glows red. As the voltage increases to 10,000-15,000 volts, the color becomes orange. From 15,000 to 30,000 volts, the color shifts to yellow or greenish-yellow. At very high voltages above 35,000 volts, neon can produce a bluish color.
Higher voltages excite the electrons to higher energy levels before they fall back down. This enables more of the higher frequency orange and yellow transitions, causing neon’s color to shift from red to orange and yellow. Extremely high voltages can sometimes excite electrons enough to emit some blue and violet light. However, this requires much higher voltages than typically found in most neon lights.
Neon Color Chart
Here is a chart summarizing the effect of gas pressure and voltage on neon’s emitted color:
|Gas Pressure (torr)||Applied Voltage (V)||Neon Color|
|20-100||>35,000||Yellow, greenish-yellow, bluish|
Other Colors of Neon
In addition to pure neon gas, some neon lights also contain other gases such as argon, helium, krypton, or xenon. Adding these gases enables more colors to be emitted beyond the red-orange-yellow of pure neon.
For example, argon emits blue light around 450 nm wavelength. Mixing argon with neon produces lights that glow purple, pink, and magenta colors. Krypton emits more yellow, green, and violet colors. Xenon adds some blue to the mix. Helium enables neon lights to reach brighter intensities.
By using various gas mixtures, neon lights can produce a rainbow of different colors beyond the red-orange-yellow of pure neon. However, pure neon is still optimal for achieving that quintessential neon glow.
Common Neon Colors
Here are some of the most common neon colors seen in signs:
– Bright red-orange: This bright glowing red-orange is the classic neon color. It’s produced by pure neon at low pressures and voltages. The red-orange hue vividly stands out at night.
– Yellow-orange: Slightly increasing the pressure shifts neon toward a yellowish-orange color. This is another very common neon sign color, though not as dramatic as the bright red.
– Pink or purple: Adding argon to the neon creates pink and purple hues popular in neon art and decor. Lower pressure neon-argon mixtures glow pink, while higher pressures shift to purple.
– Blue or green: These colors require adding xenon or krypton to the gas mixture. Blue and green neon is more expensive and less common than red/orange neon.
– White: Extremely high voltage pure neon can glow white. White neon provides bright, neutral lighting for businesses.
Factors Affecting Perceived Color
The way neon lighting appears also depends on several external factors:
– Tube size: Color seems more intense in smaller diameter tubes. Larger tubes dilute the color saturation.
– Tube length: Longer tube lengths emit more overall light, creating brighter neon colors.
– Ambient lighting: Neon appears vivid against dark backgrounds, but muted in bright daylight.
– Distance: Neon lights viewed up close seem brighter and more saturated. From a distance, the colors blend together.
– Impurities and aging: Impurities and dust can dim neon over time. Phosphor coatings also gradually lose brightness.
So the lighting conditions, viewing angle, and cleanliness all affect the perceived color of neon. But when conditions are optimal, neon’s signature glow is unmistakable.
Neon’s Unique Properties
What makes neon so suitable for lighting applications? Here are some of its useful properties:
– Inert gas: Neon does not react or combine with other elements. This prevents reactions that could dim the lights.
– Low ionization energy: Neon readily forms a glowing plasma at lower voltages than other gases. This reduces the required power.
– Lack of ultraviolet: Neon’s emission spectrum contains virtually no UV light. This makes it safe for lighting and signs.
– Vivid colors: Neon’s specific red-orange-yellow transitions create bright, vivid hues with high color saturation.
– Narrow emission bands: Emitted wavelengths are clustered in narrow peaks, giving neon’s colors high purity and intensity.
– Low power: Neon glows brightly at low wattages compared to incandescent bulbs. This improves efficiency.
Thanks to these properties, neon produces unmistakable, high-visibility lighting ideal for signs, art, and decor. The glowing reds, oranges, and yellows of neon have become iconic colors representing nightlife, theaters, and old-style urban ambience. Though other gases now produce neon-like lighting, true neon still reigns supreme for its beautiful color.
In summary, neon glows its signature red-orange color when electricity excites electrons in the gas to emit photons in the red 640 nm wavelength range. Increasing the gas pressure and applied voltage shifts the color toward orange and yellow as more higher frequency photons are emitted. Neon provides bright, efficient, high visibility lighting. Its unique emission spectrum gives neon a distinctive identity and makes it ideal for colorful signs and lighting. So next time you see a glowing neon sign, know that it’s the unique atomic structure of the neon itself that produces those beautiful, vivid colors.