Since unveiling the Lumia 800, Nokia's touted the ClearBlack display as one of the phone's standout features. ClearBack has been the focus of more than one Nokia blog post, and with good reason: it's hard to tell where the AMOLED's blacks end and where its bezel begins. The black levels look fantastic, but more importantly Nokia's ClearBlack display includes a linear polarizer and a quarter wave retardation film to cut down on the glare from incoming light.
Nokia's blog lays out the science behind its filter system, but here's the gist: light travels through the polarizer and is re-aligned. After passing through the retardation film it bounces off a reflective layer. On its way back out, the light has become horizontally polarized and is then blocked by the polarizing layer. That stops light from reflecting back into your eyes and makes ClearBlack displays easier to see. Still confused? Here's the process in graphic form.
Wondering why the light coming from within the phone isn't affected? Simple: the light doesn't go through the initial polarization process, meaning it's unpolarized and able to pass right through the filter unchanged.