Patent ID: 8643307

Claim:
A lighting device comprising: a direct-current power supply device that includes a constant-current controlled power supply circuit and at least a pair of illumination lamp connection parts, wherein each of the pair of illumination lamp connection parts includes a pair of terminals to which an illumination lamp can be connected, one of the terminals of one of the illumination lamp connection parts being connected to a positive output end of the power supply circuit and the other of the terminals being connected to a non-potential connection end, one of the terminals of another of the illumination lamp connection parts being connected to the non-potential connection end and the other of the terminals being connected to a negative output end of the power supply circuit; a first voltage detection circuit to detect a voltage between the positive output end and the negative output end of the power supply circuit; a second voltage detection circuit to detect a voltage between the non-potential connection end and the positive output end or the negative output end; and a control circuit that determines a number of illumination lamps connected to the direct-current power supply device based on detection outputs of the first and second voltage detection circuits, and selects, based on the determined number, one or more voltage thresholds for causing the power supply circuit to perform a predetermined operation.