A backlight unit includes at least an optical sheet and a diffusion plate fixed to a backside of a display panel, the optical sheet and the diffusion plate forming an upper module with the display panel. The backlight unit further includes a bottom frame positioned below the upper module and a plurality of lamps positioned within the bottom frame. The backlight unit is capable of changing the lamps within the bottom frame after removal of the upper module above the bottom frame. Therefore, it is not necessary to separate the elements such as the optical film and the diffusion plate from the bottom frame individually and the device pollution or destruction can be prevented.