cp = 334 × 10-9 E3.68
This formula checks precisely with the one used in the engineering department of the General Electric Company at their lamp works, Harrison, N.J.
The horizontal distribution curve of a lamp with its filament mounted as is the modern tungsten is nearly a circle. This is not true, however, in the case of vertical distribution and this curve is shown, Figure [III]. As will be noted, the tip candle power is only about 23 per cent of the horizontal.
Life Tests.
The results of the life tests were very surprising. The lamps upon the test under [ideal] conditions, namely, no vibrations and constant voltage, had only an average life of 460 hours, while every one of those upon the [shock] test are still burning at the present time, having been burned 300 hours. In order to make the test still more severe, the lamps were subjected to vibrations without voltage being impressed, and as yet, not a filament has broken, the total time being 400 hours. It was impossible to give more time to these lamps as was done for those under ideal conditions, for the reason it was thought unadvisable to leave the motor, which gave the vibrations, running over night.
The curves have the same general form for the two conditions but the variations are far more great for the lamps which were upon the shock test. The reason for this is that the vibrations were so severe as to shake parts of the filament together thus giving a partial short circuit, causing great variations in candle power.
Fig I
Characteristic Curves for 15 watt tungsten lamps
Lamp of average rating used
Fig II
Characteristic Curves for 15 watt tungsten lamps
Lamp of average rating used