Neon is the common term used to refer to glass tubes of ionized gas bent by glassblowers. It is very similar to fluorescent tubes used as light fixtures in principle, but is made by hand instead of by machine.
Neon's first use was in advertising signs, most memorably, beer signs. However, it isn't limited to just beer signs, or signage in general.
A neon tube is constructed out of glass tubing, bent over a variety of propane burners. The simplest tubing is just clear glass. More complex tubes are coated with up to three different chemicals and are possibly made out of colored glass. In the hands of a neon bender, glass softens to a rubbery consistency when hot and can be formed into any imaginable shape.
Once the glass is formed, electrodes are attached to the end of the tube, all of the air is pumped out of the tube, and the tube is exposed to high voltage electricity to clean it out. Most neon tubes are filled with neon, argon, krypton, or xenon at about 1% of atmospheric pressure and sometimes a blob of mercury. With these colors, you get red, sky-blue, violet, a light pink, and a light blue. All other colors are accomplished through special tubing.
A transformer is attached to the electrodes to light up the tubes. These transformers used to be large and heavy, but modern electronic transformers are compact, quiet, and safe.
Neon art can be treated as fine glassware. Neon tubes, unlike fluorescent tubes, do not burn out, so they will likely last as long as they are not broken. Sometimes, broken neon tubes can be fixed and re-pumped, but not always.
My neon uses quality components. Cheap novelty neon, as found in drugstores, generally has a transformer that is not designed to last or be replaced. Consequently, it will burn out, sometimes in a matter of months. I use higher quality transformers that can be replaced and are equipped with ground-fault detection circuits that will prevent dangerous shock in case of accidents.
Most pieces of neon art use just a few watts of power and are designed to be left on for long periods of time.