LED lighting device and illumination apparatus including same

An LED lighting device comprising:

• a power converting unit for outputting a variable output voltage, two LED lamps being connected in series between output terminal of the power converting unit through lamp sockets;
• a current detector for detecting an output current from the power converting unit;
• a first voltage detector for detecting the output voltage of the power converting unit and generating a first detection voltage corresponding to the output voltage;
• a second voltage detector for detecting an applied voltage to one of the two LED lamps and generating a second detection voltage corresponding to the applied voltage;
• and
• a control unit for controlling the power converting unit to adjust the output voltage to thereby make the output current coincide with a target value,
• wherein the control unit controls the power converting unit to decrease the output voltage if at least one of the second detection voltage and the difference voltage between the first and the second detection voltage does not fall within a predetermined voltage range, wherein the control unit counts accumulated lighting time of the LED lamps, and monotonously decreases an upper limit of the voltage range with an increase of the accumulated lighting time after the accumulated lighting time reaches a changeover time.