A bottom chassis includes a base chassis which accommodates a light source part emitting a light, a reflective film disposed on a bottom plate of the base chassis and including a reflective material to reflect the light, a cladding film disposed on the reflective film, and a light guide film disposed on the cladding film, receiving the light from the light source part through a first surface thereof, and guiding the received light to exit through a second surface thereof as a plane light, where the cladding film has a refractive index smaller than a refractive index of the light guide film.