Final answer:
Electricity ionizes the particles in the neon gas in the tubes, causing it to light up. Electrons are freed and when they return to the lower energy state, visible light is emitted, creating the characteristic neon glow.
Step-by-step explanation:
The neon in the tubes lights up because the electricity ionizes the particles (electrons) in the neon gas. When a high voltage is applied to electrodes within a gas discharge tube containing neon, the gas atoms are ionized. This means that electrons are freed from the atoms, creating ions. These energized electrons then collide with other gas atoms, causing them to emit electromagnetic radiation in the form of visible light as they return to a lower energy state. This ionization process is responsible for the characteristic glow of neon lights; however, not all gas discharge tubes actually contain neon gas, and the colors they emit can vary depending on the type of gas and the pressure within the tube.