Neon lighting
Created | Updated Nov 26, 2002
Introduction
Everybody has seen neon in some form or other. Its main application is as the source of light in advertising signage : from small and simple "open" signs in shops and restaurants up to the enormous signs pouring out their commercial message over the masses, screaming for your attention. This entry will try to shed some light of its own on the history, working principles and manufacturing techniques of neon lighting.
A brief history
The phenomenon of luminous tubes has been known since as early as 1675, when the French astronomer Jean Picard noticed that a mercury-filled barometer tube emitted a blueish glow when shaken. The scientific principle that was responsible was not understood at that time however. It was not until 1910, when the Frenchman Georges Claude was the first to present a commercial luminous tube using neon gas. Since then, neon lighting has become one of the most prominent forms of signage.
Working principle
So, how does it work ? Simply put, a vessel (often a glass tube) with a metal electrode at each side is filled with gas at a low pressure. Then, a high voltage is applied across the electrodes. As a result, the gas molecules* inside the tube are accelerated and travel in all directions, colliding with one another constantly. Each time a collision takes place, the molecules involved will emit light at a certain frequency of the spectrum. Since an enormous number of collisions occur each moment, we view this simply as "light".
Only two basic colors are used in modern neon signage:
- Red, where the tube is filled with neon gas, which is responsible for the light emission.
- Blue, where the tube is filled with argon gas and a drop of mercury. In this case, the evaporated mercury molecules inside are responsible for the light emission, whereas the argon gas only serves as a carrier.
So, I can hear you think, how come I see so many other colors in neon * signs ?
This is done by adding other colors to the picture by :
- Using color-glass tubes. For example : filling a yellow tube with neon (red) gas will result in an orange light.
- Coating the inside of the glass with a fluorescent powder. These are available in many variations, allowing for different colors.
- A combination of both of the above.
Using these techniques, almost any color can be made. It's even possible to make a tube that glows red using mercury/argon filling (which by itself would emit blue light).
Now that the principle behind neon lighting is somewhat clearer we can start to look at how it is manufactured.
Manufacturing
First of all, neon lighting is available in many different forms : straight tubes, curved tubes but also highly complicated bent shapes. How is this done ? By someone quite appropriately called a "neon bender" or glassblower. These people heat the glass using burners that run on a combination of gas, air and sometimes oxygen. When the glass is hot they are able to shape it to their desire by bending it and blowing into the tube. This is a difficult skill which takes many years to learn and many more to master.
Then, the electrodes are fused to the glass tube. Electrodes are small metal shells sealed inside a glass tube that's open on one end. Two metal strands run from the shell through the closed end of the glass tube. Through these the voltage can be applied. One of the electrodes also has a small diameter glass tube sealed to it called a tubulation.
Now comes the most important part in neon manufacturing : evacuating the air from the unit and filling it with gas. The glass part is connected with the tubulated electrode to a special vacuum system. Subsequently, a high voltage (between 10.000-15.000 Volts !) is applied across the electrodes. This will cause the glass to heat up very quickly, thereby releasing any impurities* that are present inside the glass itself. These are removed by the vacuum system. When the sufficient temperature has been reached (230-250ºC) the voltage is switched off and the vacuum system starts pulling the tube vacuum - i.e. sucking out the gas inside - while it cools down. When the tube has sufficiently cooled down, the rare gas (neon, argon, or a mixture of these) is added to the tube. In case of an argon filling, a minute quantity of mercury is added as well. The tube is now melted off at the tubulation and presto : a new neon tube is born !
The tube can now be installed in the sign installation. In order to light it, a high voltage (typically 1.000-15.000 Volts) transformer is connected.
