A display device with a display panel, and backlight unit including a first light guide plate (LGP) having first and second optical materials, a second LGP disposed between the first LGP and the display panel, light sources configured to provide light to the first LGP and the second LGP, and a diffuser plate in a lower portion of the second LGP. The first LGP configured such that light from a light source is guided by the second optical material and emitted towards the display panel through the first optical material; the second LGP configured to emit light towards the display panel using the diffuser plate. A controller controls the light sources to provide light to the first LGP if a three-dimensional (3D) image is displayed on the display panel, and to the second LGP if a two-dimensional (2D) image is displayed on the display panel.