Candescence and nigrescence curves are shown for a number of tungsten lamps, vacuum and gas-filled, ranging in size from the automobile lamps up to the 30-volt, 30-ampere lamp and the 1000-watt photoflood lamp. Data are given for similar filaments mounted in vacuum lamps and in lamps filled with argon, nitrogen, hydrogen, and helium. The filament of a vacuum lamp reaches 90 percent brightness on heating in time t=0.060I0.54; 10 percent brightness on cooling in time t=0.022I0.70; for gas-filled lamps, t=0.15I0.70 and t=0.070I0.70, respectively. (I is the normal operating current of the lamp.) The percent of total variation, P, in brightness during a cycle for a vacuum lamp on 60-cycle a.c. is P=34D−1.06, on 25-cycle a.c., P=28D−1.37; for a gas-filled lamp, P=75D−0.89 and P=63D−0.91, respectively. (D is the filament diameter in mils.)

An oscilloscope with a single-sweep circuit may be used for recording transient currents. If the current changes 1 ampere per microsecond, the oscilloscope shunt may need to have an inductance as low as .02 microhenry. An inductance tenfold lower than this can be obtained easily with a tubular resistor with a coaxial return conductor and coaxial potential leads to the oscilloscope. The resistance is provided by a layer of metal on a glass tube. Pt, Cu, and Ni have been used. Such a shunt was used to record the discharge currents of three condensers. Reasonable agreement between measured and computed currents was obtained.