Neon signs are luminous-tube signs that contain neon or otherinert gases at a low pressure. Applying a high voltage (usually a fewthousand volts) makes the gas glow brightly. They are produced by thecraft of bending glass tubing into shapes. A worker skilled in this craft is known as a glass bender, neon or tube bender.
tubing in external diameters ranging from about 8 to 15 mm is mostcommonly used. The tube is heated in sections using several types ofburners that are selected according to the amount of glass to be heatedfor each bend. These burners include ribbon, cannon, or crossfires, aswell as a variety of torches that run on a simple combination of natural gas (butane or propane work better, however natural gas is cheapest) and air.

A section of the glass is heated until it is malleable; then it isbent into shape and aligned to a pattern containing the graphics orlettering that the final product will ultimately conform to.

An electrode is melted (or welded)to each end of the tube as it is finished. The electrodes are also leadglass and contain a small metal shell with two wires protruding throughthe glass to which the sign wiring will later be attached. All weldsand seals must be perfectly leak-proof before proceeding further.

The tube is attached to a manifold which is itself attached to a high-quality vacuum pump. The tube is then evacuated of air until it reaches near-vacuum. During evacuation, a high currentis forced through the tube via the wires protruding from each electrode(in a process known as "bombarding"). The current depends on thespecific electrodes used and the diameter of the tube, but is typicallyin the 500mA to 1000mA range, at an applied voltage usually between15,000 to 25,000V. The bombarding transformer acts as an adjustableconstant current source, and the voltage produced depends on the lengthand pressure of the tube. Typically the operator will maintain thepressure as high as the bombarder will allow to ensure maximum powerdissipation and heating. This very high power dissipation in the tubeheats the glass to a temperature of several hundred degrees Celsius,and any dirt and impurities within are drawn off in the gasified formby the vacuum pump. The current also heats the electrode metal to over600 degrees Celsius, which activates a special coating that scavengesunwanted contaminants in the tube and reduces the work functionof the electrode for cathodic emission. When completed properly, thisprocess results in a very clean interior at a high vacuum.

While still attached to the manifold, the tube is allowed to coolwhile pumping down to the lowest pressure the system can achieve. It isthen filled to a pressure of a few torr with one of the noble gases,or a mixture of them, and sometimes a small amount of mercury. Therequired pressure depends on the gas used and the diameter of the tube,with optimal values ranging from 6 torr (for a long 20mm tube filledwith argon/mercury) to 27 torr (for a short 8mm diameter tube filledwith pure neon). Neon or argon are the most common gases used; krypton, xenon, and heliumare used by artists for special purposes but are not used alone innormal signs. A premixed combination of argon and helium is often usedin lieu of pure argon when a tube is to be installed in a cold climate,since the helium increases voltage drop (and thus power dissipation),warming the tube to operating temperature faster. Neon glows bright redor reddish orange when lit. When argon or argon/helium is used, a tinydroplet of mercuryis added. Argon by itself is very dim pale lavender when lit, but thedroplet of mercury fills the tube with mercury vapor when sealed, whichthen emits ultravioletlight upon electrification. This ultraviolet emission allows finishedargon/mercury tubes to glow with a variety of bright colors when thetube has been coated on the interior with ultraviolet-sensitive phosphorsafter being bent into shape. Plain argon/mercury fill in clear glass isused for a bright but pale blue (or bluish white) color often seen insigns where cost is a major factor.

The finished glass pieces are illuminated by either a transformer or a switching power supplyrunning at voltages ranging between 3,000 and 15,000 volts and currentsbetween 20 and 60 mA. These power supplies operate as constant-currentsources (a high voltage supply with a very high internal impedance),since the tube has a negative characteristic electrical impedance.The most common current rating is 30mA for general use, with 60mA usedfor high-brightness applications like channel letters or architecturallighting. 120mA sources are occasionally seen in illuminatingapplications, but are uncommon since special electrodes are required towithstand the current, and an accidental shock from a 120mA transformeris much more likely to be fatal than from the lower current supplies.Neon signs are a type of cold cathode lighting.