JPS6489186A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To keep the input power to the minimum required by providing a detecting means detecting the half-wave discharge of a discharge lamp and providing a control means controlling the discharge lamp at the dim lighting state in response to this detection output. CONSTITUTION:When a discharge lamp 3 is half-wave-discharged at the terminal stage of its life, the detection current through a serial circuit 13 is increased, the detection input level of the comparator 15 of a detecting means 4 rises, and the comparator 15 generates an output. A one-shot multivibrator 16 then generates an output, thereby a transistor 19 is turned on, a relay contact is kept closed, a dimming element 2 is invariably inserted in series to the discharge lamp 3, thus the discharge lamp 3 continues the dim lighting state. The input increase is suppressed, and a lighting device is prevented from being made large-sized. An abnormality of the discharge lamp 3 is reported at the time of the dim lighting state, the room is not made dark because of the dim lighting state, and the lamp can be easily replaced.