Tungsten lamps of high efficiency — I and II

The first paper describes investigations into the cause of blackening of the bulbs of tungsten lamps and discusses methods where by this effect is avoided and the efficiency of the lamp thereby increased. The second paper describes in detail the high-efficiency tungsten lamps which have been produced by filling the bulbs with nitrogen vapor at approximately atmospheric pressure. The blackening of ordinary lamps has generally been considered due to the presence of residual gases which adhere to the surface of the glass or are occluded in the filament. These investigations show that of the residual gases, water vapor is the only one which causes perceptible blackening by means of a cyclic process in which the water oxidizes the filament, the oxide is volatilized and deposited on the bulb, where it is reduced to metallic tungsten and the water vapor again formed. This action, however, is shown to occur only in poorly exhausted lamps, and the real cause of blackening in well-exhausted lamps is due to evaporation of the filament alone. The methods of improving the efficiency of the tungsten lamp consist of the introduction of gas into the bulb at atmospheric pressure and changing the location of the deposits by means of convection currents in the gases so that the glass opposite the filament is not darkened. By making use of these principles, practical tungsten lamps have been produced having a life of over 2000 hours and an average specific consumption of one-half a watt or less per candle power. A number of different types of nitrogen-filled tungsten lamps are described in detail.