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Abstract

A light emitting element circuit includes a light emitting element (1), a current supply path to the light emitting element (1), a constant current circuit (2) that supplies a current to the light emitting element (1) via the current supply path, and an electric discharge path that discharges an electric charge accumulated at the light emitting element (1) and at a region connected between the both electrodes when the constant current circuit (2) stops a current supply to the light emitting element (1). A light emitting element failure detector (4) that detects a short-circuit of the light emitting element (1) in a light emitting element circuit includes a current instantaneous interruption circuit (5), a voltage detector (60), and a determiner (62). The current instantaneous interruption circuit (5) is arranged on the current supply path different from the electric discharge path and instantaneously interrupts an electric current that the constant current circuit (2) supplies to the light emitting element (1). The voltage detector (60) obtains an output of a voltage Vf between the anode and cathode of the light emitting element (1) during a period of the instantaneous interruption as a measuring object. The determiner (62) determines the existence of a short-circuit from the output.

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