On the Radio Noises and Oscillations Caused by Fluorescent Lamps

Abstract

The radio noises caused by fluorescent lamps were investigated in connection with high frequency oscillations in fluorescent lamps, and the mechanisms of oscillations were considered with some experimental results. Reignition oscillation, the wave form of which is irregular and consists of train of fine pulses, is sensitive to external heating of the filament and magnetic field near the cathode. Its frequency spectrum is nearly flat in broadcast band, and its noise level is 62 db (20W lamp) and 50 db (40W lamp) respectively in mean value of symetric quasi-peak voltage at 1MC, and is reduced by 30 db with 0.005 µPF capacitor conncted between lamp terminals. The twin oscillation, the waveform of which is regular and nearly sinusoidal, has the frequency spectrum which is similar to the resonance curve, and in many cases the peak of its spectrum is found in broadcast band. The high frequency oscillation is observed also in DC discharge, and its characteristics are just the same with those of the twin oscillation. The frequencies of these oscillations vary nearly in proportion to the square root of the lamp current, and are affected by interterminal capacitor. The cause of reignition oscillation is the fluctuation of ionization in increasing and decreasing period of space charge during transient time on reversing of the lamp current. The origin of twin oscillation is the oscillatory behavior of ionized medium with suitable accelerating field at the cathode surface, and for generation of the oscillation it is necessary that some conditions of the feedback from the boundary of the medium to the cathode are satisfied.