On our last iPhone screen replacement job we discovered a new issue that comes with all mobile devices and is about customers that has polarised sun glasses. These customers will have problems on viewing the screen because of a new filter applied to the new mobile devices to allow the consumer to see higher brightness even under the sun light. This depend on the level of the sun glass polarization that will apply a new pattern filter on the mobile screen polarization (You can find a discussion on Apple website here).

This is not only an Apple problem, also Samsung and HTC are using the same type of screen and they will behave the same way.