An example display device includes a display panel to display an image; a backlight unit to provide light to the display panel, the backlight unit including a light emitting unit to emit the light; a light guide plate to transmit the light emitted from the light emitting unit; a pair of electrodes adjacent to the light guide plate; and a polymer layer including liquid crystal molecules within the light guide plate. The liquid crystal molecules are to change orientation upon being introduced to an electric field created by the pair of electrodes to change an opacity of the light guide plate. The display device includes at least one film to collimate and direct light from the backlight unit to the display panel; and a processor to switch voltage being applied on/off to the pair of electrodes.