1. A method for operating an image display device including a plurality of backlight lamps, the method comprising: receiving a 3-Dimensional (3D) image; increasing a frame rate of the 3D image; alternately aligning, based on the increased frame rate, the first-eye image and the second-eye image of the 3D image; and alternately providing aligned first-eye and second-eye images for display; wherein (a) in a two dimensional (2D) image mode, while opening both first and second eye glasses of shutter glasses and alternatively providing aligned first and second eye images of the 3-D image, alternatively turning off the backlight lamps in synchronization with the first eye image and turning on the backlight lamps in synchronization with the second eye image, and (b) in a 3-D image mode, while maintaining the backlight lamps in an on-state, opening the first eye glass and closing the second eye glass when the first eye image is provided and closing the first eye glass and opening the second eye glass when the second eye image is provided; turning on the backlight lamps in synchronization with any one of the first-eye image and the second-eye image without separately inputting a 2D image while opening both a first-eye glass and a second-eye glass of shutter glasses when a display switching signal for viewing the 3D image as a 2-Dimensional (2D) image is input; and turning on the backlight lamps in synchronization with the alternately aligned first and second-eye image, respectively, and alternately opening the first-eye glass and the second-eye glass of shutter glasses when the display switching signal is not input.