When turned on the electricity flows through the tube. The electricity charges the gas, possibly neon, and creates a plasma inside of the tube. This plasma glows a special color depending on what kind of gas is inside. You also see plasma when you look at stars. They aren't easy to find if you live in a big smoggy city, but look hard.
Stars are big balls of gases at really high temperatures.
The high temperatures charge up the atoms and create plasma. Stars are another good example of how the temperature of plasmas can be very different. Fluorescent lights are cold compared to really hot stars. But still, they are both forms of plasma. Andrew Rader Studios, All rights reserved.