How Neon Lights Work

Simple Demonstration of Why Noble Gases Don't React

True neon lights are reddish orange. Other colors of lights are filled with different gases.
True neon lights are reddish orange. Other colors of lights are filled with different gases. Image Source, Getty Images

Neon lights are colorful, bright, and reliable, so you see them used in signs, displays, and even airport landing strips. Have you ever wondered how they work and how different colors of light are produced?

How a Neon Light Works

  • A neon light consists of a glass tube filled with a small amount (low pressure) of neon gas. Neon is used because it is one of the noble gases. One characteristic of these elements is that each atom has a filled electron shell, so the atoms don't react with other atoms and it takes a lot of energy to remove an electron.
  • There is an electrode at either end of the tube. A neon light actually works using either AC (alternating current) or DC (direct current), but if DC current is used, the glow is only seen around one electrode. AC current is used for most neon lights you see.
  • When an electric voltage is applied to the terminals (about 15,000 volts), enough energy is supplied to remove an outer electron from the neon atoms. If there is not enough voltage, there will not be enough kinetic energy for the electrons to escape their atoms and nothing will happen. The positively charged neon atoms (cations) are attracted to the negative terminal, while the free electrons are attracted to the positive terminal. These charged particles, called plasma, complete the electric circuit of the lamp.
  • So where does the light come from? Atoms in the tube are moving around, hitting each other. They transfer energy to each other, plus a lot of heat is produced. While some electrons escape their atoms, others gain enough energy to become "excited". This means they have a higher energy state. Being excited is like climbing a ladder, where an electron can be on a particular rung of the ladder, not just anywhere on its length. The electron can return to its original energy (ground state) by releasing that energy as a photon (light). The color of the light that is produced depends on how far apart the excited energy is from the original energy. Like the distance between rungs of a ladder, this is a set interval. So, each excited electron of an atom releases a characteristic wavelength of photon. In other words, each excited noble gas releases a characteristic color of light. For neon, this is a reddish-orange light.

    How Other Colors of Light Are Produced

    You see lots of different colors of signs, so you might wonder how this works. There are two main ways of producing other colors of light besides the orange-red of neon. One way is to use another gas or a mixture of gases to produce colors. As mentioned earlier, each noble gas releases a characteristic color of light.

    For example, helium glows pink, krypton is green, and argon is blue. If the gases are mixed, intermediate colors can be produced.

    The other way to produce colors is to coat the glass with a phosphor or other chemical that will glow a certain color when it is energized. Because of the range of coatings available, most modern lights no longer use neon, but are fluorescent lamps that rely on a mercury/argon discharge and a phosphor coating. If you see a clear light glowing in a color, it's a noble gas light.

    Another way to change the color of the light, although it's not used in light fixtures, is to control the energy supplied to the light. While you usually see one color per element in a light, there are actually different energy levels available to excited electrons, which correspond to a spectrum of light that element can produce.

    Brief History of the Neon Light

    Heinrich Geissler (1857)

    Geissler is considered the Father of Fluorescent Lamps. His "Geissler Tube" was a glass tube with electrodes at either end containing a gas at partial vacuum pressure. He experimented arcing current through various gases to produce light. The tube was the basis for the neon light, mercury vapor light, fluorescent light, sodium lamp, and metal halide lamp.

    William Ramsay & Morris W. Travers (1898)

    Ramsay and Travers made a neon lamp, but neon was extremely rare, so the invention was not cost-effective.

    Daniel McFarlan Moore (1904)

    Moore commercially installed the "Moore Tube", which ran an electric arc through nitrogen and carbon dioxide to produce light.

    Georges Claude (1902)

    While Claude did not invent the neon lamp, he did devise a method to isolate neon from air, making the light affordable. The neon light was demonstrated by Georges Claude in December of 1910 at the Paris Motor Show. Claude initially worked with Moore's design, but developed a reliable lamp design of his own and cornered the market for the lights until the 1930s.

    Make a Fake Neon Sign (no neon required)