Optical films, prism optical films and light diffusion optical films, all of the foregoing for use in the manufacture of liquid crystal displays; light diffusion optical boards in the nature of plastic film for use in the manufacture of liquid crystal displays, optical reflectors for use in liquid crystal displays, back light modules each comprised of light conductive boards, each of said boards comprised of optical films, a light guiding plate, converging lens, brightness enhancement optical film and a lamp, the foregoing back light modules for use in the manufacture of liquid crystal displays