Gas discharge

Electric fields cause deformations of atoms and molecules because the positively charged nucleus is attracted by the cathode, will the negative shell is attracted by the anode. Very high electric field strength may cause electrons separating from their molecule. Free electrons and positive ions are generated. As free electrons migrate to the anode and positive ions move to the cathode, an electric current starts.

neon light tube
The orange plasma inside the neon light tube is typical for a neon plasma.