It takes a voltage of 80 volts or more across the electrodes of the neon glow tube to make it glow. When you see a neon glow tube glowing you know the voltages across it is 80 volts or more. It takes very little current to make the neon tube glow visibly, about 10 -12 ampere. When the tube glows, this small current is being conducted through the air. Even though air is a good insulator, it is not a perfect insulator.
Some electric current can travel through air.
This is the current that makes the glow tube glow. Electrons accelerate away from the terminal nearest the negatively charged object making the neon glow. These moving electrons collide with neutral neon molecules giving energy to the electrons that are in the neon atoms. When these electrons drop back to lower energy states they emit the classic, orange light of a neon tube. It takes voltages of 3000 volts to make a spark one centimeter long in air with a pressure of 1 atmosphere.