A backlight module includes at least a light guide board, a reflector film, an optic film, and a light scarce. The light guide board has a light emitting surface on which a plurality of light: converging elements is formed. The optic film has a surface on which a plurality of rib-like micro light guides is formed. Each micro light guide includes a plurality of ridges, which are of different heights and show variation of height. Either a high ridge or a low ridge of the micro light guide is made a continuous left-and-right wavy configuration and/or a continuous up-and-down height-variation configuration. Thus, light transmitting through, the optic film and converged by the micro light guides leaves the optic film in a form that is not very regular so as to facilitate subsequent use of the light in for example a liquid crystal display panel.