1. A method of displaying a 3-dimensional (3D) image, the method comprising: alternately scanning a left eye image and a right eye image on a display device including a plurality of image lines that are arranged sequentially; illuminating the display device by using a backlight unit including a plurality of segments that correspond to the plurality of image lines and emit light in synchronization with refresh times of the plurality of image lines; and stopping light emission of each segment of the backlight unit when one of the left eye images and one of the right eye images are partially simultaneously scanned on each of the plurality of image lines corresponding to each segment of the backlight unit, wherein delay times are between switch-on times of the plurality of segments and refresh times of the plurality of image lines.