A method is provided for controlling the collimation of light from a backlight top surface. A backlight device includes a first waveguide and a transparent top film overlying the first waveguide top surface. A plurality of bubble structures is formed in the top film bottom surface, having a refractive index less than a first waveguide medium. A plurality of lenses overlies the top film top surface, where each lens is aligned overlying a corresponding gap (W) between bubble structures. The method forms a maximum angle (α) of light propagation through the first waveguide medium. In response to the values W and H (bubble structure height), light, having the maximum angle (α) of light propagation, is reflected off the bubble structure sides, through total internal reflection, into the top film. The method collimates in a vertical direction, orthogonal to the horizontal direction, light exiting the top film through the lenses.