Patent ID: 7414788

Claim:
A method for making a diffusion plate used in a direct-type backlight module, comprising the steps of: (a) providing a plastic material comprising a body material and a lower layer material, the body material having a first refractive index, the lower layer material having a third refractive index, the first refractive index being larger than the third refractive index, the body material being disposed over the lower layer material; (b) providing an upper rolling wheel and a lower wheel, wherein both wheels have repeated undulation on the surface thereof; and (c) corolling the body material and the lower layer material to form a diffusion plate, wherein the body material has a top surface, the lower layer material has a bottom surface, the bottom surface has a first microstructure, the top surface has a second microstructure, the first microstructure and the second microstructure respectively corresponding to the rolling wheels.