Diffusers
For a non-ELP backlight to produce even lighting, which is critical for displays, the light is first passed through a lightguide - a specially-designed layer of plastic that diffuses the light through a series of unevenly-spaced bumps. The density of bumps increases further away from the light source according to a diffusion equation. The diffused light then travels to either side of the diffuser; the front faces the actual LCD panel, the back has a reflector to guide otherwise wasted light back toward the LCD panel. The reflector is sometimes made of aluminum foil, sometimes merely a white-pigmented surface or, as in the 3M Vikuiti ESR, consists of hundreds of polymer layers of alternating low and high refractive index. Between the lightguide and the LCD panel is usually placed a reflective polarizer film which vastly increases efficiency by repeatedly reflecting any unpolarized light back, which would otherwise be absorbed by the LCD's rear polarizer.
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