High-temperature properties of tungsten which influence filament temperatures, lives and thermionic-emission densities

A literature search has shown which data are most reliable for use in calculations of the lives of tungsten filaments run at very high temperatures. Some errors and their possible causes have been found in commonly-used data. Filament lives have been calculated and measured for a variety of electrical supply conditions in a range of high temperatures. The fractional thinning at burn-out can be found from a measurement of the ratio of lives under different electrical supply conditions. Hence, actual lives can be foretold accurately from measurements of heating current and initial wire diameter. Thermionic-emission measurements have confirmed that temperatures can be found from heating currents, even for short filaments where correction has to be made for the heat lost by conduction to the supports.