A back-light apparatus for a display includes: a plurality of light emitting diodes attached on a substrate; a first common line mounted on the substrate to commonly connect first electrodes of the light emitting diodes; a second common line mounted on the substrate to commonly connect second electrodes of the light emitting diodes; a plurality of third lines connected to preceding second electrodes of the light emitting diodes and succeeding first electrodes of the light emitting diodes; first and second selection switches disconnecting the first common line and the second common line so that the light emitting diodes are connected in parallel; third selection switches for disconnecting the third lines so that the light emitting diodes are connected in series; a power unit to supply power to the light emitting diodes; and a control unit to control the first, second and third selection switches for the light emitting diodes.