Why do aged fluorescent tubes flicker?

International audience; Common experience shows that aged and defective fluorescent tubes or bulbs may flicker and emit a clicking sound while struggling to light up. In this article, the physical mechanisms controlling the initial illumination of a functioning fluorescent tube are investigated using a simple and affordable experimental setup. Thermionic emission from the electrodes of the tube controls the startup of fluorescent tubes. The origin of the faulty startup of aged fluorescent tubes is discussed and flickering regimes using functional tubes are artificially produced when decreasing, in a controlled manner, electron emission by the thermionic effect. The physical parameters controlling the occurrence of flickering light are discussed, and their temporal statistics are reported.