PURPOSE: To attain the proper fluorescent lamp filament temperature to enable the use of a fluorescent lamp over a wide range of lighting duties by varying preheating voltages for a fluorescent lamp filament according to variations in the lighting duty of any kind of fluorescent lamp.
CONSTITUTION: A lighting circuit 3 lights a fluorescent lamp 1 according to a lighting duty determined by a dimmer circuit 6. A preheating circuit 4 operates in conjunction with the lighting circuit 3 to preheat a filament during the turn- off period of the fluorescent lamp 1 under duty dimming, and preheating is not carried out while the lamp is on. The preheating circuit 4 applies either several kinds of preheating voltages in steps or a certain preheating voltage continuously to the filament according to a command to apply preheating voltages from a preheating voltage command portion 7. The fluorescent lamp 1 lighted by a fluorescent lamp drive circuit 2 emits a small amount of light at the early stage of lighting, and the amount gradually increases. In order to hold the amount of light constant, the dimmer circuit 6 varies the lighting duty according to the amount of light detected by a tight amount detecting circuit 5, and the lighting duty is fed back to the lighting circuit 3.
MIYAMOTO KAZUKI
OKI NAOYUKI
