Optical assembly includes a light emitter and a film through which light passes from the light emitter. The film has a uniform or variable pattern of individual deformities of well defined shape that are projections or depressions on or in one or more surface areas of the film. The deformities are quite small in relation to the width and length of the film. At least some of the deformities may have two or more surfaces that come together to form a ridge having a total length that is quite small in relation to the width and length of the film.