1. A method for operating an image display device including a plurality of backlight lamps, the method comprising: receiving a 3-Dimensional (3D) image; alternately aligning the left-eye image and the right-eye image of the 3D image; and displaying any one of the aligned left- and right-eye images if a display switching signal for switching the 3D image to a 2-Dimensional (2D) image is input, wherein, in the displaying step, the backlight lamps are turned on in synchronization with any one of the aligned left- and right-eye images.