| 摘要 |
<P>PROBLEM TO BE SOLVED: To effectively use a plurality of lamps while maintaining a level of illumination until the end of respective lifetime so that alignment is made for their replacement with new ones, with respect to an illuminating device that uses a plurality of discharge lamps therein. <P>SOLUTION: The illuminating device equipped with first and second discharge lamps keeps the first and second discharge lamps lighted at a constant level of illuminance over a predetermined period H<SB>11</SB>of lighting at a constant illuminance. After an elapse of the period H<SB>11</SB>, the electric power for the lamps is detected, and each lamp's remaining lighting time is predicted from the percentage of a rise in the electric power. From a difference between the predicted lamps' life times (T<SB>BF</SB>-T<SB>AF</SB>), a life time adjustment period P<SB>11</SB>is established. Over the life time adjustment period P<SB>11</SB>, a discharge lamp found to have a shorter remaining lighting time is kept lighted for a constant electric power consumption as a short lifetime discharge lamp, while a discharge lamp found to have a longer remaining lighting time is kept lighted at a constant level of illuminance, as a long lifetime discharge lamp, so that the overall illuminance can be maintained. <P>COPYRIGHT: (C)2010,JPO&INPIT |
