Fluorescent lamps with ac current generate alternating lamp power and thus the light fluctuates at twice the operating frequency. To observe the light fluctuation from a fluorescent lamp, a light detector is built by using high sensitivity phototransistors in this thesis. The test results show that the light output waveform is very similar to that of the lamp power. It is also found that the light output from the whole lamp tube is not identical because the light output fluctuation becomes significant when close to the end of the lamp. When the lamp comes to the life-end, its light output is different from those produced by lamps of good conditions. In attempts to further discuss the features of light fluctuation, an electronic ballast with balanced multi-phase outputs is designed and built to reduce the variation in the light output. With a balanced multi-phase operation, the resultant light output from lamps¡¦ multi-phase currents should be a constant. An experimental 3-phase electronic ballast circuit is built to test this theoretical prediction. Experimental tests confirm that the light fluctuation can be effectively reduced by operating lamps with balanced multi-phase currents.

Fluorescent lamps are in general driven by ac ballasting currents. The cyclic variation in arc discharging power results in light fluctuation at twice the frequency of the ac current. Light fluctuation may be intolerable when a steady light output is required in some particular applications. To eliminate light fluctuation, an electronic ballast with dc current is proposed to operate the fluorescent lamp at a constant power. The main power conversion of the electronic ballast employs the single-stage high-power-factor inverter, which is originated from a combination of the half-bridge resonant inverter and the buck-boost converter. With such a circuit configuration, the output power can be regulated by asymmetrical pulse-width-modulation. The ac output of the inverter is then rectified and filtered to provide the dc ballasting current. Driven by dc current, however, the fluorescent lamp emits electrons unilaterally from one end leading to wearing out of emission material on the cathode filament. To solve this problem, an inverter is integrated for commutation of the lamp electrodes. Furthermore, a preheating control is included to start the fluorescent lamps with zero glow-current. A prototype is designed and built for the OSRAM T5-80W fluorescent lamp. The dc operating characteristics of starting transient, light fluctuation, lighting spectra, color temperature as well as the light fluctuation are investigated from experiments. Experimental results also show that the electronic ballast is capable of high-power-factor, dimming capability and zero glow-current preheating.