Diffusion plate, back light device having the same, and liquid crystal display device

A light diffusion plate, a back light device and a liquid display having the same are provided to improve optical diffusion efficiency by forming an air void with an intaglio part which is formed on a welding surface between a first base layer and a second layer. A light diffusion plate includes a first base layer(110) and a second base layer(120). The second base layer is welded on the first base layer. A plurality of intaglio parts(123) forms an air void at least one side of the first base The first base layer and the second base layer have different materials.