Hydrogen-filled iron wire ballast lamp

An experimental and analytical study, dealing particularly with the variation of temperature along the length of the filament. As the voltage is raised there is a discontinuity in the current-voltage relation shortly after entering the ballasting range; this is accompanied by the establishment of an inflection in the temperature-length curve, there being a sudden rise near the centre. As the voltage is further increased the hot region grows in length, and the inflection disappears at the higher limit of the ballasting range. The analysis provides a qualitative explanation.