Fluorescent lamps consists of two electrodes, an inert gas filling, and a small amount of mercury. The inert gas filling is a mixture of Neon, Argon and sometimes Krypton. These gases must be inert to prevent electrode oxidation. During operation, a discharge current is fed through the tube which causes mercury atoms to release electrons into a plasma. When the electrons recombine with the Mercury ions, energy is released in the form of ultraviolet photons. These short wavelength photons are converted by a phosphor into longer wavelengths of several desired colors which combine to produce white light. The electrode filaments must be heated before ignition to prevent excessive damage. If the filament is not heated, the lamp will only survive a few thousand on/off cycles.