Both neon lights and fluorescent lights are long glass tubes with gas inside and an electrode on each end.
Electrical currents pass through the gas from one electrode to the other, exciting the electrons enough that they emit light energy. The only significant difference between the two types of lights is the stuff that’s inside, and the colors the gases give off.
Fluorescent lights have a dollop of mercury inside a partial vacuum. When the power goes on, the mercury vaporizes into gas and mixes with the thin air. As the electricity excites the atoms of the mercury gas, they glow with an ultraviolet color.
Unfortunately, that color is invisible to humans. To make the light visible, the light manufacturers paint a coating of phosphors on the inside of the glass tube. When excited by the ultraviolet rays, the phosphors glow white, giving visible light.
“Neon” lightsthe colorful ones in store windowsdon’t need the phosphors on the inside of the tube because they contain gases that glow visible colors. But technically, only the reddish lights actually have neon gas in them.
To get a blue color, they use a high concentration of mercury gas. For yellow, they use a sodium gas.