The optimum operating gas pressure for incandescent tungsten filament lamps

Abstract

The life of a tungsten filament incandescent lamp may be increased by raising the gasfilling pressure. However, recent experiments have suggested that beyond a certain point the gain in life is more than offset by the consequential fall in efficacy. This aspect has been investigated theoretically and a formula developed which relates power losses (and hence efficacy) directly to a function of the gasfilling pressure. Calculations for a range of lamps relate changes in life, efficacy and overall quality to changes in gasfilling pressure. The results are supported by the experimental evidence and show that for every lamp design there exists an optimum gasfilling pressure which gives the maximum overall performance. Finally, a general equation has been derived from which the optimum gasfilling pressure can be deduced. The investigation indicates that the performance of many incandescent and tungsten halogen lamps could be improved by adjusting the gasfilling pressure to coincide with the optimum value.