A dimming experiment on moving striations in 50Hz AC operated fluorescent lamp

Abstract

Summary form only given. Moving striations in fluorescent lamp is a well-known phenomenon. AC operation and mixed filling-ins pose difficulties in understanding the physical reason and relative processes of moving striations. In this paper, an experiment is carried out in order to find out factors correlated to moving striations in fluorescent lamps. The basic experimental circuit consists of a 36 W T8 fluorescent lamp, a magnetic ballast and an ignitor. A photodiode is used to collect the light signal from the lamp. The circuit is supplied with 185 V 50 Hz AC and the lamp is kept on for long enough time so that temperature distribution on the tube is stable. The cold spot temperature (Tc) of the tube is about 40 centigrade. Then the lamp is quickly dimmed down (process "Dim Down") by decreasing the supply voltage until it reaches 150 V, the lowest limit for the working lamp. Immediately, the lamp is dimmed up the same way back (process "First Dim up"). Lamp current and light signals from the photodiode are taken during the process. The aim of quick dimming is that between two successive dimming, there is no enough time for total temperature relaxation on the tube. Thus, Tc and partial pressure of mercury will not change a lot. Next, we supply the circuit with 150 V 50 Hz AC for long enough time; and then quickly dim up the lamp until the supply voltage comes to 185 V (process "Second Dim up"). In this case, Tc is lower during the whole dimming process, since the lamp works under a lower voltage at first, where the correspondent Tc is about 34 centigrade. Experimental results show that amplitude of moving striations in First Dim up is much lower than that in the case of Second Dim up. Kajiwara has revealed close relationship between Tc and moving striations in a low frequency fluorescent lamp. Therefore, the big difference in relative amplitude of moving striations between First Dim up and Second Dim up can come from the difference in Tc. Compared to Second Dim up, amplitude of striations in First Dim up is much closer to that of Dim Down. That is due to the smaller difference in cold spot temperature in the two cases. In conclusion, moving striations in fluorescent lamp have close relationship with cold spot temperature of the tube. The lower Tc is, the stronger the moving striation is.