| 摘要 |
PROBLEM TO BE SOLVED: To perform lighting without giving the sensation incongruity in vision of a person, who is using a discharge lamp by dividing the time constant of the frequency change during the transition from the preheating frequency to the rated lighting frequency into two stages, setting the time constant of a first stage long, and making the time constant of a second stage smaller than that of the first one. SOLUTION: When a dimming switch is turned on, a first frequency shift in finished, and a transistor 19 is switched off simultaneously with the switching- off of a transistor 17, whereby a transistor 20 is switched on, the electric current flows to resistances 9a, 9b of the same time with the finish in the first frequency shift, and the frequency directly reaches the dimming lighting frequency by a second frequency shift determined by the resistances 9a, 9b. Accordingly, the frequency can be directly transferred to the dimming lighting frequency after the first frequency shift, and there is hardly time lag is hardly. That is, the frequency reaches directly the dimming lighting frequency from the frequency shift, so that the changes in frequency and luminous flux do not seem unnatural. |
