Provided is a display device. According to one embodiment, the display device includes: a backlight unit with a plurality of light emitting strings including at least one light emitting diode; and a display panel displaying an image using light outputted from the backlight unit, wherein the backlight unit includes: a light source unit including the plurality of light emitting strings and a plurality of photo transistors controlling the plurality of light emitting strings; a DC-DC converter outputting the driving voltage to the light source unit; and a driving control unit applying activated gate voltages to turn on the plurality of photo transistors and detecting driving time differences between an output time for outputting the driving voltage and applying times for applying the gate voltages.