1. A method of displaying a 3-dimensional (3D) image, the method comprising: alternately displaying 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 all of the plurality of segments of the backlight unit when one of the left eye images and one of the right eye images are partially simultaneously displayed on the display device.