| 摘要 |
PURPOSE:To achieve long life of a lamp without reducing the emission efficiency by properly controlling a cathode descending voltage of a pair of electrodes of a fluorescent lamp to an optimal value. CONSTITUTION:When a fluorescent lamp 2 is lighted, a lamp voltage is applied between a pair of electrodes 3a and 3b from a lighting circuit 3, and the lamp is preheated. An arc discharge is then formed, and since an ultraviolet ray is generated by exciting a quicksilver atom, a fluorescent film is excited, and a visual light is thus emitted. The cathode descending voltage of each of electrodes 3a, 3b is detected by each of cathode descending voltage detection circuits 9a, 9b through each of probes 6a, 6b, at every negative semi-cycle of the voltage to be applied at the time. The voltage is compared with a voltage set by a controller 10, and a control signal is sent to a circuit 3, and by controlling a preheating current given to the electrodes 3a, 3b, the long life of the fluorescent lamp 2 can be achieved. |
