Diffuser sheet

A diffuser sheet is a thin, milky film in the stack of optical layers behind an LCD screen. Its job is to take light that's brighter in some places than others and spread it out, so the screen glows evenly.

It starts as a roll of clear PET film, often around a tenth of a millimeter thick. A coating is spread across one side: a liquid acrylate binder mixed with tiny round beads, often acrylic, from a few to tens of micrometers across. The coating is dried or cured with ultraviolet light, locking the beads in place. Each bead acts like a little lens. Light passing through gets bent a slightly different way at every bead, so it leaves in many directions. The back side often gets a thin anti-scratch coating, and the roll is cut to the size of the screen.

In the backlight unit, a diffuser sheet usually sits just above the diffuser plate and below the prism sheets. It softens any remaining hot spots and hides the pattern of the LEDs, so you see a smooth, even picture instead of a grid of dots. The exact stack varies by manufacturer.