History :

In 1923, Georges Claude and his French company Claude Neon, introduced neon gas signs to the United States, by selling two to a Packard car dealership in Los Angeles. Earle C.Anthony purchased the two signs reading "Packard" for $1,250 apiece. Neon lighting quickly became a popular fixture in outdoor advertising. Visible even in daylight, people would stop and stare at the first neon signs for hours, dubbed "liquid fire."

While neon lighting was used around 1930 in France for general illumination, it was no more energy-efficient than conventional incandescent lighting and neon lighting came to be used primarily for eye-catching signs and advertisements.

Manufacturing Process :

Lead glass tubing in external diameters ranging from about 8 to 15 mm is most commonly used. The tube is heated in sections using several types of burners that are selected according to the amount of glass to be heated for each bend. These burners include ribbon, cannon, or crossfires, as well 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 is bent into shape and aligned to a pattern containing the graphics or lettering that the final product will ultimately conform to.

An is melted (or welded) to each end of the tube as it is finished. The electrodes are also lead glass and contain a small metal shell with two wires protruding through the glass to which the sign wiring will later be attached. All welds and 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 current is forced through the tube via the wires protruding from each electrode (in a process known as "bombarding"). The current depends on the specific electrodes used and the diameter of the tube, but is typically in the 450A to 800mA range, at an applied voltage usually between 22,000 to 26,000V. The bombarding transformer acts as an adjustable constant current source, and the voltage produced depends on the length and pressure of the tube. Typically the operator will maintain the pressure as high as the bombarder will allow to ensure maximum power dissipation and heating. This very high power dissipation in the tube heats the glass to a temperature of several hundred degrees Celsius, and any dirt and impurities within are drawn off in the gasified form by the vacuum pump. The current also heats the electrode metal to over 600 degrees Celsius, which activates a special coating that scavenges unwanted contaminants in the tube and reduces the work function of the electrode for cathodic emission. When completed properly, this process results in a very clean interior at a high vacuum.

While still attached to the manifold, the tube is allowed to cool while pumping down to the lowest pressure the system can achieve. It is then filled to a pressure of a few with one of the noble gases, or a mixture of them, and sometimes a small amount of mercury. The required pressure depends on the gas used and the diameter of the tube, with optimal values ranging from 6 torr (for a long 20 mm tube filled with argon/mercury) to 27 torr (for a short 8 mm diameter tube filled with pure neon). are the most common gases used; krypton xenon, and helium are used by artists for special purposes but are not used alone in normal signs. A premixed combination of argon and helium is often used in 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 red or reddish orange when lit. When argon or argon/helium is used, a tiny droplet of mercury is added. Argon by itself is very dim pale lavender when lit, but the droplet of mercury fills the tube with mercury vapor when sealed, which then emits ultraviolet light upon electrification. This ultraviolet emission allows finished argon/mercury tubes to glow with a variety of bright colors when the tube has been coated on the interior with ultraviolet-sensitive phosphors after being bent into shape. Plain argon/mercury fill in clear glass is used for a bright but pale blue (or bluish white) color often seen in signs where cost is a major factor.

The finished glass pieces are illuminated by either a transformer or a switching power supply running at voltages ranging between 5,000 and 15,000 volts and currents between 50 and 600 mA. These power supplies operate as constant-current sources (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 45mA for general use, with 80mA used for high-brightness applications like channel letters or architectural lighting. 120mA sources are occasionally seen in illuminating applications, but are uncommon since special electrodes are required to withstand the current, and an accidental shock from a 120mA transformer is much more likely to be fatal than from the lower current supplies. Neon signs are a type of cold cathode lighting.