A backlight device for a display comprising (1) a side-lit light source, (2) a light guide plate and (3) a turning film comprising a light entry and a light exit surface comprising lenticular elements on the exit surface and prismatic structures on the entry surface, wherein the average values of the parameters of the features and the thickness of the film are selected to provide a peak output angle of .+-.10.degree. from normal to the light exit surface of the light guide plate and an optical gain of at least 1.25. Also disclosed are methods of making the turning film and a display incorporating the backlight.