| 摘要 |
PURPOSE:To prevent the falling off of the light output of discharge lamp in the rated lighting, the shortening of lifetime and breakdown or the like of circuit elements constructing lighting circuits by switching forcedly lighting modes of the discharge lamp to the dimmed lighting mode when the ambient temperature of the discharge lamp becomes higher than a specified value. CONSTITUTION:When the ambient temperature TA of a discharge lamp l is lower than a specified value TAT, a switching circuit II switches the lighting mode in a lighting circuit I to either one of the rated lighting mode or the dimmed lighting mode corresponding to the operation of a dimming switching III. When the ambient temperature TA of the lamp l becomes higher than a specified value TAT, the mode is switched forcedly to the dimmed lighting mode regardless of the state of the dimmer switch III. Thus, the temperature rise of the coolest point of the discharge lamp l in the rated lighting in a high ambient temperature TA can be suppressed. Thereby the falling off of the light output of the discharge lamp l, and the shortening of lifetime and breakdown or the like of circuit elements constructing lighting circuits can be prevented. |
