Neon is a colorless, odorless noble gas with the symbol Ne, discovered in 1898 by British chemists Sir William Ramsay and Morris Travers through the fractional distillation of liquefied air. As one of the six noble gases, neon is chemically inert; it does not readily form compounds with other elements, which contributes to its usefulness. Although neon is the fifth most abundant element in the universe, it is relatively rare on Earth, making up only about 0.0018% of the atmosphere by volume. Commercial neon is obtained through the complex and energy-intensive process of cryogenically separating it from air.
The Classic Glow of Neon Lighting
The most recognizable application of this element is the vibrant, luminous tubing used in decorative and commercial signage. This glow is the result of glow discharge, where a high-voltage electrical current is passed through a sealed glass tube filled with low-pressure neon gas. The electrical field accelerates free electrons, which collide with neon atoms, causing the gas to ionize. This creates a plasma, a highly ionized gas that conducts electricity and allows the current to flow continuously.
As the excited neon atoms return to their lower-energy state, they release the excess energy as light photons. Pure neon gas emits a distinctive reddish-orange light, the color most people associate with “neon” signs. However, the term “neon sign” is often used for all noble gas lighting, even when neon is not the primary gas.
Other colors are achieved by using different noble gases, such as argon, which produces a bluish-purple light, or by coating the inside of the glass tube with phosphors. The light’s color is determined by the specific energy signature, or emission spectrum, of the gas contained within the tube. The use of inert noble gases significantly extended the lifespan of these lights, making them practical for long-term use in outdoor displays.
Small-Scale Electrical Indicators
Neon gas is used in miniature components that serve functional purposes in electronics. These small devices are known as neon indicator lamps or neon glow lamps and are common in power strips, appliances, and instrument panels. The lamps consist of a small glass capsule containing low-pressure neon gas and two electrodes. A low-current glow discharge is initiated when a voltage of about 90 volts or more is applied, causing the gas to ionize and produce a glow near one or both electrodes.
This low-power operation means neon lamps require minimal current to light up, making them efficient and long-lasting indicators of current flow. When connected to an alternating current (AC) source, both electrodes glow alternately, creating a continuous light that the eye perceives as steady. This rugged technology is also incorporated into basic voltage testers used by electricians, as the lamp will only glow when a specific high voltage is present. Their long lifespan, often ranging from 20,000 to 50,000 hours, and compatibility with standard AC line voltage make them a reliable choice for power-on status lights.
Specialized Use in Extreme Cooling
Neon is used in the field of cryogenics, utilizing its physical properties at extremely low temperatures. By cooling the gas to about $-246^\circ$ Celsius, neon liquefies, becoming a powerful refrigerant. Liquid neon has a high cooling capacity, providing over 40 times the refrigerating power per unit volume compared to liquid helium. It also offers a higher boiling point than liquid helium, operating in a temperature range of roughly $24.5$ to $44.4$ Kelvin, which is suitable for many scientific and high-tech applications.
This makes liquid neon a preferred coolant in applications that require temperatures below what liquid nitrogen can achieve, but not the ultra-low range of liquid helium. It is used to cool high-temperature superconductors, which must operate below about 40 Kelvin to function efficiently. Liquid neon also plays a role in scientific research, such as cooling particle physics detectors, and in specialized medical equipment, like certain MRI cooling systems. Its inert nature ensures it will not react with the materials it is cooling, providing a safe and effective medium for maintaining constant, low temperatures.