Many words have been written about filament saturation and filament life, not all with years of experience behind them] Sometimes when visiting laboratories one has the feeling that the life of the filament is far more important than the quality of the results, so let us try to demystify filament life?

The life of a tungsten hairpin filament very much depends upon its use and the applications present in a particular laboratory. Medturn to low magnification applications in the transmission electron microscope (TEM) may only require low emission currents (10 to 15 micro amps) with a long filament life resulting. High resolution studies require higher operating currents (20 to 45 micro amps) but, by demanding more emission current the life of the filament will suffer. Whilst a long filament life is good for the laboratory, it is not worthy of boasting, for those who have a short filament life may well be using the instrument near to the limit of its performance, a far more relevant boast!