What is the gas used in light bulbs?

Answer 1

Generally, argon or krypton.
Argon , neon ,
Argon is sometimes used in incandescent lights.

Answer:

Fluorescent bulbs contain Mercury vapor so do mercury vapor lights, sodium vapor lights contain sodium vapor once they are hot, "neon" lights contain neon and a number of other gases depending on the color desired.
Argon or nitrogen
In incandescent light bulbs (the regular kind) contain an inert gas, probably Argon. Sometimes there is no gas at all and a vacuum protects the filament.

In Florescent bulbs the tubes are filled with low pressure mercury vapor along with an inert gas such as argon, xenon, neon, or krypton.
argon