Last to come off of the display is the edge-lit LED backlight—a common type of backlight found in smartphones.

As mentioned earlier, the reflective mylar layer was previously one of the layers of the backlight.

In this iteration of the iPhone the mylar layer now serves two purposes; the new use, to obscure the 3D Touch sensors from view, and the traditional use, to reflect diffused light outward instead of wasting light on the internals of the iPhone.