Progress towards a practical fluorine lamp

Abstract

Two major problems in the development of a lamp based on a chemical vapour deposition process involving fluorine, which will return tungsten back to the filament, are the need to protect the fused quartz envelope from attack by fluorine and the requirement of accurate and repeatable halogen dosing. The first problem has been overcome by coating the internal lamp surfaces with solution-deposited glasses based on the system Aℓ ₂O₃-TiO₂-P₂O₅. The use of a fully fluorinated grease provides a successful means of solution dosing lamps with a repeatability of ±15 per cent. A considerable gain in performance has been achieved, an average 45 per cent increase in life at the same running voltage, in comparison with bromine lamps of the same type. This improvement can only be attributed to a suppression of normal evaporation rates i.e. a truly regenerative halogen cycle has been achieved. Tungsten-fluorine lamps are limited as practical lamps only by failures caused by erosion of the filament tails.