Glow discharge is a phenomenon that occurs in gases when they are ionized by an electric field. This process creates a plasma, which emits light, resulting in a glowing effect. The discharge typically happens at low pressures and can be observed in devices like neon signs and plasma globes. In a glow discharge, electrons are accelerated by the electric field, colliding with gas atoms and causing them to ionize. This ionization leads to the creation of positive ions and free electrons, which sustain the discharge. The emitted light can vary in color depending on the type of gas used, such as argon or krypton.