Why do clear screen shields have a rainbow effect on certain angles?

This is really a physics question that I'm not fully qualified to answer, but here goes:

It depends on the thickness of the plastic sheet and the thickness of the adhesive under it, if any.

It's for the same reason that soap bubbles or liquids like oil and gasoline have a rainbow sheen when spread out on a flat surface. It happens when the light reflected from the front surface creates an interference pattern with the light reflected from the back surface of the material.

You could try a different brand of protector which might have a different adhesive or thickness in the manufacturing process. A cheap screen protector is less likely to have this issue because it won't be as smooth and flat as a good quality one. A non-reflective protector won't have the issue at all.

Regards,
-Peter

Message was edited by: LarksHead