Study of the Spectrumof Low-Frequency Current Fluctuations in Filaments of Electric Lamps

Abstract

We study experimentally the spectral characteristics of low-frequency current fluctuations in tungsten filaments of lighting lamps in the ranges of frequencies 2.5・10−4 – 5・10−1 Hz and temperatures 1260 – 2600 K. To decrease the influence of the edge effects and increase the measurement accuracy, we use subtraction (compensation) of the constant component of the current. Application of special schemes allowed decreasing significantly the influence of the inherent noise of power supplies which are used to feed the lamp filaments. It is found that low-frequency current fluctuations are a randomly time-interleaved aggregate of four random processes: relaxation, pulsed, stepwise, and quasi-continuous ones. We show that relative fluctuations do not exceed 3 ・ 10−4 in the entire range of the studied frequencies, and the frequency dependence of the spectral power density is well approximated by a function having the form 1/fγ and the index γ of the power spectral density within the (1.6 – 1.8) ± 0.2 limits. The dependence of the parameters of the power spectral density of low-frequency current fluctuations on the average value of the current and the volume-average temperature is studied. In our opinion, the revealed features of low-frequency fluctuations are related to the electron, atomic, and degradation processes in lamp filaments.